WO2007131278A1

WO2007131278A1 - Process for treatment of water to reduce fluoride levels

Info

Publication number: WO2007131278A1
Application number: PCT/AU2007/000642
Authority: WO
Inventors: Samuel Robert Haycraft; Dennis Ray Jones; Ellen Gaby
Original assignee: Orica Australia Pty Ltd
Priority date: 2006-05-15
Filing date: 2007-05-14
Publication date: 2007-11-22
Also published as: TW200812916A

Abstract

Improved methods for removal of fluoride from waste water, particularly from waste water generated through semiconductor manufacture. In one aspect, an improved fluoride precipitation method is provided in which fluoride is immobilized in the solid generated. In this method the precipitated fluoride is adsorbed or complexed into a cation exchange resin. In another aspect, waste water containing fluoride is treated with a macroporous anion exchange resin to improve the efficiency of fluoride removal by the improved fluoride precipitation method. After treatment with macroporous anion exchange resin waste water is subjected to fluoride precipitation employing cation exchange resin alone or in combination with addition of a water-soluble calcium salt. The methods herein can be applied to mixed acid waste water containing various species including mixed acid etchant, dissolved silica species and buffered oxide etchant and having fluoride levels up to 40,000 ppm. The methods of this invention are optionally combined with reverse osmosis to provided additional reductions in fluoride. Fluoride levels below 10 ppm or preferably 1-3 ppm or less can be obtained employing these methods.

Description

PROCESS FOR TREATMENT OF WATER TO REDUCE FLUORIDE LEVELS

BACKGROUND OF THE INVENTION

[0001] Fluoride in the form of hydrofluoric acid or fluoride salts is widely used in various industrial applications. The semiconductor industry, for example, utilizes large amounts of fluoride compounds in etching and cleaning processes and as a consequence generates large quantities of fluoride-containing waste water, which represents a major disposal problem. Current municipal discharge limits of fluoride are low, usually 1-3 ppm, and in addition many municipalities have also imposed total pound/day limits on fluoride discharge. Fluoride levels in waste water from such industries must be significantly reduced before the water can be released into municipal waste treatment systems. [0002] Precipitation methods largely based on addition of calcium chloride or other calcium species to generate calcium fluoride, accompanied by flocculation and/or settling steps to precipitate the calcium fluoride, are currently employed for fluoride reduction in such industrial waste water. However, fluoride-containing waste water is often a complex mixtures of components containing mixed acids, such as sulfuric, nitric and acetic acid (e.g., mixed acid etch, MEA), and soluble and colloidal silica, as well as buffers, such as buffered oxide etch (BOE), containing components such as ammonium fluoride, buffers and surfactants, which can inhibit or prevent the effective use of normal waste water treatment steps, such as adjusting pH. Large amounts of calcium chloride and/or ferric chloride, sodium hydroxide and other chemicals may be consumed in precipitation methods. Addition of the large amounts of chloride and other salts needed to reduce fluoride to acceptable levels may also result in unacceptable levels of chloride or other regulated species too high for municipal discharge. Currently- employed methods for fluoride reduction generally are inefficient, time intensive, expensive, may not sufficiently lower fluoride levels and can generate large amounts of residual sludge containing fluoride and other unacceptable chemical species, rendering the sludge a hazardous waste material, which represent a costly problem for off-site disposal. [0003] The present invention provides improved methods for fluoride reduction in waste water that ameliorate one or more of these difficulties. [0004] Various methods for the treatment of water to reduce fluoride levels have been reported employing precipitation, ion-exchange, membrane separation or various combinations of such steps: Precipitation

[0005] U.S. patent 6,436,297 relates to a method of defluoridation of waste water including a step of acid neutralization between a basic neutralization step and a decanting step. More specifically, the pH of the waste water is initially adjusted to pH 6.5 employing dead lime (Ca (OH)2), then in a second step the pH is adjusted to 8.2 by addition of dead lime. The basic solution is then adjusted to a pH between 5.5 and 7 by addition of an acid other than hydrofluoric acid (e.g., sulfuric acid). Liquid is then decanted from the solids formed. Flocculants may be added to the treated water prior to decantation. Steps of continuous extraction of the solid are also mentioned. Levels of fluoride ranging from 8-11 ppm are reported to be achievable in water treated by this process. [0006] U.S. patent 6,355,221 relates to a method of removing soluble fluoride from waste water which involves addition of a calcium-containing reagent to the waste water to form calcium fluoride. Prior to addition of the calcium, seed particles of calcium fluoride are added to the waste water to facilitate calcium fluoride formation and precipitation. The patent also reports passing waste water containing added calcium reagent and seed particles through a tubular reactor at a velocity sufficient to allow soluble fluoride to react with the calcium reagent and seed particles to form enhanced particles which can be removed from the water. [0007] U.S. patent 6,267,892 reports a method for processing fluoride waste water to reduce fluoride levels that includes a step of adding a calcium compound to the waste water to generate calcium fluoride and employs a device including a reaction vessel and a sedimentation vessel. A polymer solution described as a high molecular weight coagulant can be added to the reaction vessel. [0008] U.S. patent 5,403, 495 relates to a multiple stage process for removing dissolved fluoride from waste water involving the formation of a so-called "enhanced calcium or magnesium fluoride precipitate" by formation of a first calcium or magnesium fluoride precipitate followed by repeated cycles of sequentially contacting this precipitate with a calcium or magnesium ion source and fluoride ion (i.e., in waste water). This recycling of the enhanced precipitate in contact with additional calcium or magnesium ions and in contact with the fluoride- containing waste water is reported to remove fluoride from waste water and to increase the particle size of the enhanced precipitate. The enhanced precipitate is ultimately separated from treated water by settling or filtering. [0009] U.S. patent 5,215,632 relates to a two-step precipitation method for removing fluoride and sulfate ion impurities from aqueous sodium chlorate solutions during manufacture of sodium chlorate crystals. The method involves a first addition of calcium chloride and a source of phosphate to form a first precipitate which is removed. Carbonate ion is then added to the solution to form a second precipitate. Removal of the second precipitate is said to remove 99% of the fluoride and sulfate ion impurities.

[00010] U.S. patent 4,808,316 relates to a method for treating waste water containing both uranium and fluorine in which slaked lime is first added to the waste water and precipitate is then removed (a neutralizing precipitation step). The supernatant from the neutralizing precipitation step is then contacted with a first chelating resin which selectively adsorbs fluorine ions and a second chelating resin which selectively adsorbs uranyl ions to adsorb and remove ions remaining in the supernatant. The resins are washed and regenerated and the liquid used for washing and regeneration of the resins is returned to the neutralizing precipitation step. A phenol-formalin chelating resin of zirconium hydroxide type is described for use as the chelating resin that adsorbs fluoride. Fluoride is reported to be eluted from this resin by washing with aqueous sodium hydroxide. A decarbonation step may be provided for decomposing carbonate ions prior to the neutralization precipitation step. [00011] U.S. patent 4,028,237 relates to a method for removing fluorine from fluorine-containing waste water, in which aluminum ions are first added to the waste water reportedly to convert fluorine to low solubility hydroxyfluoride complexes. Phosphoric acid or phosphate and a calcium compound are then added to form fluoride apatite. Solids formed are removed, leaving residual fluoride in the water. More specifically, the method involves separating waste water into concentrated and dilute fluoride-containing waste water portions, adding calcium compound to the concentrated fluoride-containing waste water to form calcium fluoride, and adding aluminum ions to the dilute fluoride waste water to convert fluoride to low solubility complexes. The separated treated waste waters are then mixed and calcium ions are added to the mixture to form fluoride apatite and solids are removed. Ion-exchange

[00012] U.S. published patent application 2005/0145572 (published July 7, 2005), now U.S. patent 6,998,054, reports two processes for fluoride removal from industrial waste water. The first method employs a series of four ion-exchange steps in which waste water is passed sequentially through (1) a strong acid cation resin (to exchange cations for hydrogen ions); (2) a strong base anion resin in sulfate form (to remove hexafluorosilicates), (3) a weak base anion exchange resin having tertiary amine groups in the free base form (to remove acids) and (4) a weak base anion exchange resin in the free base form (to remove hydrofluoric acid). [00013] The second method reported in the published application requires initial treatment of a strong acid cation exchange resin containing hydrogen ions with a solution of an aluminum salt to exchange the hydrogen ions for aluminum ions, and thereafter removing fluoride ions from waste water by passing the waste water through a column of the aluminum-exchanged strong acid cation exchange resin. The cation exchange resin employed is described as having all available cation capacity filled by aluminum ions. The resin is reported to facilitate the complexation reaction of aluminum ions with fluoride ions within the reactive matrix of the ion exchange resin. The level of fluoride that can be successfully removed is not reported, however, the method is said to be suitable for use in neutral or slightly alkaline pH waste water, such as that discharged from a conventional fluoride precipitation system. [00014] U.S. patent 5,876,685 reports a method for purifying fluoride ion from fluoride containing waste and recycling hydrofluoric acid. In the method "substantially all of the fluoride ion" is reported to be removed from a solution containing greater than 10 ppm of fluoride ion and a mixture of other anions and silicon in several forms. In this method, the pH of the solution containing fluoride ion is adjusted to alkaline pH (pH 8-9) to hydrolyze fluorosilicic acid and any complex metal fluorides, after which the alkaline solution is passed through a column of Type 2 strong base anion exchange resin, in the hydroxide (OH-) form. Fluoride and other anions (nitrate) are reported to be adsorbed, while dissolved and colloidal silica tend to pass through the column. Fluoride is then released from the column and on application of several additional steps purified hydrofluoric acid is produced. In tests of simulated waste water containing fluoride, nitric acid and fluorosilicic acid, fluoride levels of less than 5 ppm in the column effluent are reported. [00015] U.S. patents 5,707,514 and 5,772,891 relate to a multi-step process for treating waste water from semiconductor manufacture including precipitation and ion exchange steps and a water treatment apparatus for carrying out the process. The patents note that acidic waste water from semiconductor plants is treated by addition of large amounts of chemicals (e.g., slaked lime, caustic soda, polyaluminium chloride, polymer coagulants, etc.) to effect removal of fluoride and sulfate by precipitation. The residual water after such precipitation steps has relatively high electrical conductivity and as such is not readily recyclable. In the process reported in the patents, water treated by several steps of precipitation and solid-liquid separation is passed through a cation exchange resin to remove calcium ions (among others) and decrease conductivity. The used cation exchange resin is regenerated by contacting it with the acidic waste water entering the treatment apparatus which releases calcium ions into the waste water. The regenerated cation exchange resin is then separated from the waste water and reused. The released calcium ions are said to react with fluoride in the acidic waste water to form some CaF₂ , but after contact with the cation exchange resin, the waste water is subjected to the several steps of precipitation and separation noted above and the resulting water with decreased fluoride and sulfate is passed through the regenerated cation exchange resin. In this cycle, the cation exchange resin is used to reduce conductivity of treated water and does not appear to remove any substantial amount of fluoride or sulfate. [00016] U.S. patent 4,734,200 reports a process for treating acid waste water generated in wet process phosphoric acid plants to remove fluoride and/or phosphorous-type contaminants. The water treated is reported to contain SiF62- which on passage through a strong base anion exchange column is said to be loaded onto the resin removing it from the waste water. This step is conducted at the pH of the waste water said to be between 1.5 and 2. It is reported that fluoride can be released from the anion exchange material to prepare useful materials. Phosphate ions are reported to be removed by raising the pH to between 5 and 7 and contacting the pH-adjusted waste water with strong base anion exchange resin to load phosphate ions onto the resin removing them from the waste water. In a related process, U.S. patent 4,965,061 reports a process for recovery of fluoride from waste fluorosilicic acid solution and converting the waste fluorosilicic acid into hydrofluoric acid. The process releases SiF62- from the strong base anion exchange material which was used to treat the waste water, precipitates SiF62- as (NH4)2SiF6 and generates hydrofluoric acid from the precipitated salt.

[00017] U.S. patent 4,952,386 relates to a method for purification of hydrofluoric acid by passing the acid through a cation exchange material and an anion exchange material to remove ions from the hydrofluoric acid. Membrane Separation [00018] U.S. patent 5,043,072 relates to a method of treating fluoride- containing water which employs a reaction step to form a suspension, a membrane separation step to form a concentrated suspension and a permeate with reduced fluoride and a circulation step, in which at least a portion of the membrane-separated concentrated suspension is introduced into the reaction step to function as seed crystal for precipitation of fluoride and the remaining concentrated suspension is introduced into a circulation tank. A calcium and/or aluminum compound is added to the water along with a portion of concentrated suspension, while the pH of the liquid suspension is adjusted to 6-8. The resulting suspension is introduced into the circulation tank where it is mixed with the remaining concentrated suspension. The suspension from the circulation tank is treated by membrane separation (microfiltration membrane or ultrafiltration membrane) to separate it into the permeate solution and the concentrated suspension. Solids which precipitate and build up in the circulation tank are removed. In a specifically exemplified process, raw water containing 370 mg/L fluoride is treated to generate a permeate containing from 17-25 mg/L of fluoride. The permeate is optionally further treated by passing it through a fluoride ion- adsorbing material. Fluoride ion-adsorbing materials are said to be tritium, zirconium, titanium or hafnium-type cation-exchange resins, strong or weak acidic cation-exchange resins, haloalkyl-silane-type adsorbent resins, weak basic anion- exchange resins, rare earth metal oxide hydrate-type chelate resins, aluminium salt-type chelate resins and like adsorbent resins, as well as, active alumina or magnesia- type adsorbents. The permeate may also optionally be treated by passing through COD-adsorbing materials which are said to include gel-type or MR(macro reticular)- type weak, medium or strong basic anion-exchange resins as well as active charcoal. COD (chemical Oxygen demand) refers to the amount of dissolved oxygen required for full chemical oxidation of organic and inorganic matter in the water, expressed in mg/L.

[00019] U. S. patent 6,338,803 reports a process for treating waste water containing hydrogen fluoride, mixed acid etchant waste, dissolved silica and solid particles using reverse osmosis. The pH of the waste water is adjusted to about 7 or above, solid materials are removed by filtration and the filtered waste water is then fed through a reverse osmosis membrane to generate a permeate stream of treated water having reduced fluoride levels. Anti-sealant can be added prior to application of reverse osmosis to prevent fouling of the membrane. The patent is reported to be best applied to waste water containing 2000 ppm or less of fluoride, 250 ppm or less of calcium, 10 ppm or less of magnesium, 200 ppm or less of silica, 10 ppm or less of iron or aluminum, 7500 ppm or less of combined nitrate and nitrite, and 5000 ppm or less of acetate.

[00020] Despite the methods that have been reported, there remains a need in the art for a method for reduction of fluoride in waste water that provides efficient reduction with a minimum of process steps, with decreased levels of contaminated solid waste which must in turn be properly handled and disposed of as hazardous waste and at reduced cost. The present invention relates to improved methods for reduction of fluoride levels in waste water which provide one or more of these benefits.

SUMMARY OF THE INVENTION

[00021] This invention relates to methods for the reduction of fluoride levels in liquid waste streams, particularly in industrial waste water and more particularly in waste water that contains hydrofluoric acid (HF), mixed acid etch (MAE, a mixture of HF, nitric acid and acetic acid), and dissolved silica as generated by silicon wafer manufacturer. The waste water treated by the methods herein may also contain buffered oxide etch (BOE) components and further may contain colloidal silica. The methods of this invention are useful to reduce fluoride levels in the presence of mixed acids, including for example sulfuric acid, nitric acid, and optionally acetic acid, dissolved silica, peroxide, and/or BOE chemicals, including for example ammonium fluoride, ammonium hydroxide and ammonia. [00022] The methods herein can be employed to reduce fluoride levels in waste water and are particularly useful for waste water containing fluoride levels greater than 100 ppm. The method can also be employed to reduce fluoride levels in waste water containing fluoride levels greater than 1000 ppm. The method can also be employed to reduce fluoride levels in waste water containing fluoride levels greater than 3000 ppm.

[00023] In certain embodiments, the methods herein can be applied to reduce fluoride levels in such waste water by 50% or more, 75% or more, 90% or more, 99% or more, or 99.99% or more. In certain embodiments, the methods herein can be used to reduce fluoride levels from 40-40,000 ppm to levels of 10 ppm or below and preferably are applied to reduce fluoride levels to 1-3 ppm or less to meet municipal discharge limits. It will be understood that methods of this invention can be repeated more than once on a given batch of waste water to achieved desired reduction in fluoride levels.

[00024] Methods of this invention can provide efficient fluoride reduction in shorter process times and at lower cost compared to current fluoride removal methods employing precipitation, flocculation and settling, and do not require that the pH of the waste water be controlled throughout the process. Methods herein can minimize addition of ionic species, such as chloride. In specific embodiments, methods herein can significantly reduce the amount of residual sludge created compared to methods currently employed (reductions of residual solid waste of 50% over traditional phys/chemical methods can be obtained). Further, in preferred embodiments, the solid fluoride-containing waste generated in the processes herein is predominantly a low-water content solid, rather than the gel- like sludge that is typically generated through conventional precipitation methods. [00025] In one aspect, the invention provides a method for immobilizing fluoride removed from waste water in a solid from which only relatively low levels of fluoride are leachable. In specific embodiments, the solid fluoride-containing waste generated by methods herein leaches less than about 3500 ppm as measured by the TCLP (Toxicity Characteristic Leaching Procedure) method. In specific embodiments, the solid waste generated in processes herein exhibits sufficiently low leachable fluoride levels that it can meet local and/or federal regulatory requirements for disposal in a non-hazardous landfill. [00026] In specific embodiments, the invention provides an improved precipitation method for reduction of fluoride levels in waste water which results in a relatively low water content fluoride-containing solid (residual waste solid) , e.g., where the percent moisture in the solid is 50% by weight or less, i.e., in a compact solid form which reduces disposal costs. In specific embodiments, the volume of residual waste solid is 10% or less or preferably 5% or less of the total treated liquid waste volume. In specific embodiments, the waste solid produced is a low- water content solid that does not leach substantial amounts of fluoride, e.g., not greater than 3500 ppm as measured by the TCLP method. [00027] In one embodiment of this improved precipitation method, a water- soluble calcium salt, such as calcium chloride, is added to the waste water and the waste water is contacted with a cation exchange resin, particularly a cation exchange resin in the sodium or calcium form (chemical form), to reduce fluoride levels and generate a solid from which only relatively low levels of fluoride are leachable. Most generally, the water-soluble calcium salt and the cation exchange resin are added to the waste water and the added components are mixed until a desired level of fluoride is achieved or the until the fluoride level stabilizes. In a preferred embodiment, the water-soluble calcium salt is added to the waste water, the treated water is mixed sufficiently to allow the components therein to react and thereafter the cation exchange resin is added. Once fluoride reduction is achieved, the solid is separated from the treated water. Addition of calcium ion is believed to remove fluoride, at least in part, by the generation of low solubility calcium fluoride (CaF₂). The calcium-treated waste water is mixed sufficiently to allow the components to react. Reaction is complete when the measured fluoride level in the mixture stabilizes. Typically the treated waste water is mixed for 15- 30 minutes or more. In general, an amount of calcium ion sufficient to reduce fluoride levels in the waste water by a desired amount is added. In general, the amount of cation exchange resin added is sufficient to achieve the desired levels of residual fluoride. Cation exchange resin can, for example, be incrementally added to the calcium-treated waste water while periodically monitoring fluoride concentration to achieve the desired fluoride level.

[00028] In a specific embodiment, the waste water is contacted with cation exchange resin after addition of calcium ion, and before removal of any solids which might have been formed. The solid that precipitates and/or forms on addition of calcium ion and the cation exchange resin can be separated from the waste water by conventional methods to generate a low water-content solid. In specific embodiments, this solid exhibits low levels of fluoride leaching as noted above. [00029] In a specific embodiment, a stoichiometric amount of Ca²⁺ (i.e., one equivalent) with respect to the fluoride present, assuming formation of CaF₂, (where one equivalent of Ca²⁺is 50% of the molar amount of fluoride present or expected to be present in the waste water) is added. In other embodiments, a sub-stoichiometric amount of Ca²⁺ is added. More specifically, a sub- stoichiometric amount of Ca²⁺ ranging from 5% to less than 50% of the molar amount of fluoride present in the waste water is added. In other specific embodiments, the calcium level in the waste water can range from 10% to less than 50% of the molar amount of fluoride present in the waste water. In a preferred embodiment, a sub-stoichiometric amount of Ca²⁺ ranging from 10% to 25% of the molar amount of fluoride present is added. [00030] The water-soluble salt may be added to the waste water as a solid or more typically as an aqueous solution. This soluble salt solution is preferably relatively concentrated, e.g., containing 20% or more by weight or the salt. In a specific embodiment, a 30% by weight aqueous calcium chloride solution is employed. [00031] The cation exchange resin is preferably a strong acid cation exchange resin in the sodium or calcium form. In specific embodiments, the cation exchange resin is a cation exchange resin, other than one that is in the proton (acid) form or in the aluminum form (i. e., where the predominate cation in the resin is Al⁺³). The cation exchange resin can be in the physical form of whole beads or in powdered form. The amount of cation exchange resin added generally depends upon the amount of soluble calcium salt added, which in turn depends upon the amount of fluoride in the waste water. In a specific embodiment, the volume of cation exchange resin added ranges from 0.05% up to 10% of the volume of waste water treated. . In a specific embodiment, the volume of cation exchange resin added ranges from 0.25% up to 10% of the volume of waste water treated. In a specific embodiment, a volume of cation exchange resin equal to 10% or less of the total volume of the waste water and additives is added. In a more specific embodiment, a volume of whole bead cation exchange resin equal to 5% or less of the volume of waste water treated is added. In other specific embodiments, a volume of cation exchange resin ranging from 0.4% to 5% of the volume of waste water treated is added. In a specific embodiment, cation exchange resin can be incrementally added. In this embodiment, an initial addition of cation exchange resin ranging from 0.25% to 5% of the volume of waste water treated is added and thereafter additional cation exchange resin can be added, if necessary, to minimize fluoride levels in the treated waste water and optionally to decrease treatment time. Addition of levels of cation exchange resin less thani 0% of the volume of waste water treated is preferred to minimize the amount of solid waste generated. In another specific embodiment, a volume of powdered cation exchange resin equal to 2-2.5% of the total volume is added. [00032] In a specific embodiment, the cation exchange resin has a mean particle size between 30 -1 ,000 microns. In a specific embodiment, the cation exchange resin has a mean particle size between 30 and 300 microns. In a specific embodiment, the cation exchange resin is powdered and has a mean particle size between 30 and 300 microns. Powdered cation exchange resin is generally preferred for more rapid water treatment. [00033] The waste water and combined additives including cation exchange resin are mixed for a sufficient time to obtain a stable reduced level of fluoride. The water and combined additives are contacted and mixed in a vessel of appropriate size which is equipped with a means for agitation or stirring to facilitate interaction of the additives and resin and the waste water components. The vessel employed is preferably an open-topped vessel. Typically, the combined materials are mixed for 15-30 minutes or more. After sufficient mixing, the supernatant, treated water is separated from the solids (any precipitate and resin) to provide treated water with reduced fluoride levels. Fluoride levels in the treated water can be measured using any appropriate art-known method. Treated water is separated from the solids. In a specific embodiment, the treated water is separated from the solids by filtering. In a specific embodiment, the separated solids containing cation exchange resin and any precipitated salts do not leach high levels of fluoride ion (i.e., do not leach greater than about 3500 ppm as measured by the TCLP method) and in specific embodiments the solid does not leach levels of fluoride that would require the solid to be categorized as hazardous waste. [00034] The improved precipitation method employing addition of cation exchange resin, as described above, alone can provide a significant reduction in fluoride levels in the treated waste water. This method can, for example, be employed to reduce fluoride levels in semiconductor waste water from greater than 20,000 ppm to 2,000 ppm or less. The improved precipitation method can be combined with other methods of fluoride removal, such as reverse osmosis, where the supernatant of the improved precipitation method is subjected to reverse osmosis to provide significant additional fluoride removal and provide treated water with fluoride levels below 10 ppm and preferably fluoride levels of 1-3 ppm of less. The improved precipitation method can also be combined with other steps as described herein to provide treated water with such desirable low levels of fluoride.

[00035] Treatment of waste water with the improved precipitation method is optionally preceded by a step of pH adjustment to a pH of 4 or above, a pH between 5 and 6, a pH of 8 or above or a pH of 10 or above.

[00036] In another aspect of the invention, fluoride-containing waste water is contacted with cation exchange resin in the calcium form which functions to remove significant levels of fluoride from the waste water and results in a solid (resin containing fluoride) which is a low-water content solid (i.e., not a gel or slurry) and in specific embodiments which is a fluoride-containing solid which exhibits relatively low levels of fluoride leaching (i.e., less than 3500 ppm). In this aspect, prior addition of a soluble calcium salt is not required to facilitate fluoride removal. The cation exchange resin is preferably a strong acid cation exchange resin in the calcium form. The cation exchange resin can be in the physical form of whole beads or in powdered form. The amount of cation exchange resin added generally depends upon the amount of fluoride in the waste water. Most generally, the amount of cation exchange resin added ranges from 0.25% to 10% by volume of the waste water treated. More specifically, the amount of cation exchange resin added ranges from 0.5% to 5% by volume of the waste water treated. In a specific embodiment, a volume of cation exchange resin equal to 10% or less of the volume of waste water. In a more specific embodiment, a volume of whole bead cation exchange resin equal to 5% or less of the volume of waste water is added. As noted above, cation exchange resin in the calcium form can be incrementally added to the waste water while monitoring fluoride levels until a desired reduced level of fluoride is obtained. After an initial addition, additional cation exchange resin in the calcium form can be added, if necessary, to minimize fluoride levels in the treated waste water and optionally to decrease treatment time. In another specific embodiment, a volume of powdered cation exchange resin equal to 2-2.5% of the volume of waste water is added. In a specific embodiment, the cation exchange resin has a mean particle size between 30 - 1 ,000 microns. In a specific embodiment, the cation exchange resin has a mean particle size between 30 and 300 microns. In a specific embodiment, the cation exchange resin is powdered and has a mean particle size between 30 and 300 microns. Powdered cation exchange resin is generally preferred for more rapid water treatment. The waste water and cation exchange resin are mixed for a sufficient time to obtain a stable reduced level of fluoride. The water and resin are contacted and mixed in a vessel of appropriate size which is equipped with a means for agitation or stirring to facilitate interaction of the additives and resin and the waste water components. The vessel employed is preferably an open-topped vessel. Typically, the combined additives are mixed for 15-30 minutes or more. After sufficient mixing, the supernatant, treated water is separated from the solid (resin) to provide treated water with reduced fluoride levels. Fluoride levels in the treated water can be measured. Treated water is separated from the solid. In a specific embodiment, the treated water is separated from the solid by filtering. The residual solid is preferably a low-water content solid (less than 50% by weight water). In specific embodiments, the volume of residual waste solid generated is 10% or less or more preferably 5% or less of the total volume of treated liquid. In a specific embodiment, the separated solids containing fluoride and cation exchange resin do not leach high levels of fluoride ion (i.e., do not leach greater than about 3500 ppm as measured by the TCLP method) and in specific embodiments, the solid does not leach levels of fluoride that would require the solid to be categorized as hazardous waste. Contact of fluoride-containing waste water with cation exchange resin in the calcium form without prior addition of a soluble calcium salt can provide a significant reduction in fluoride levels in the treated waste water. This method can be combined with other methods of fluoride removal, such as reverse osmosis where the supernatant separated from the resin is subjected to reverse osmosis to provide significant additional fluoride removal and provide treated water with fluoride levels below 10 ppm and preferably fluoride levels of 1-3 ppm or less.

[00037] Treatment of waste water with cation exchange resin in the calcium form is optionally preceded by a step of pH adjustment to a pH of 4 or above, a pH between 5 and 6, a pH of 8 or above or a pH of 10 or above.

[00038] In another aspect of the invention, mixed acid waste water containing fluoride, mixed acids, and/or dissolved silica and/or BOE is contacted with a macroporous anion exchange resin which increases the efficiency of removal of fluoride and which is at least in part believed to remove one or more chemical species (other than fluoride itself) which interfere (one or more interferants) with efficient removal of fluoride. In one embodiment, the fluoride-containing waste water is contacted with anion exchange resin and subjected to calcium addition, calcium addition and contact with cation exchange resin, or contact with cation exchange resin in the calcium form, as described above. In specific embodiments, a volume of macroporous anion exchange resin ranging from 0.5% to 5% of the volume of the waste water is added to and mixed with the waste water. Preferably, the volume of macroporous anion exchange resin added is less than 2% of the volume of waste water to be treated. In specific embodiments, the volume of macroporous anion exchange resin added is between 1% and 2% of the volume of waste water to be treated. In this aspect of the invention, a step of pH adjustment to a pH of 4 or above, a pH between 5 and 6, a pH of 8 or above or a pH of 10 or above is optionally performed prior to or after treatment with the anion exchange resin. Preferably the macroporous anion exchange resin comprises iron. Preferably the macroporous anion exchange resin is a magnetic resin. In a preferred embodiment, the pH of the waste water is adjusted to a pH between 5 and 6. [00039] In a specific embodiment, fluoride-containing waste water is first contacted with the macroporous anion exchange resin and thereafter a water- soluble calcium salt or aqueous solution containing the salt is added to the waste water. This embodiment is preferred for application to the treatment of fluoride - containing waste water that also contains BOE. The waste water is thereafter contacted with cation exchange resin as described above. In alternative embodiments, calcium is added to the waste water at the same time as or prior to contacting the waste water with the macroporous anion exchange resin. The level of calcium added to the waste water in these embodiments is such that the level of calcium in the waste water is equal to or less than 50% of the molar amount of fluoride in the waste water (stoichiometric or sub-stoichiometric as described above). In specific embodiments, the level of calcium in the waste water is adjusted to be between 5% to 50% of the molar amount of fluoride present in the waste water. In additional embodiments, the level of calcium in the waste water is adjusted to be between 10% to 25% of the molar amount of fluoride present in the waste water. In these embodiments, the pH of the waste water is optionally adjusted to a pH of 4 or above, a pH between 5 and 6, a pH of 8 or above or a pH of 10 prior to treatment. In a preferred embodiment the pH of the waste water is adjusted to be between 5 and 6. [00040] In more preferred embodiments, the macroporous anion exchange resin is a strong base anion exchange resin in the chloride form and more preferably it is a Type 1 strong base anion exchange resin. Preferably the anion exchange resin is formed from a hydrophilic polymer. In a particular embodiment, the anion exchange resin has a mean particle size between 30 and 1000 microns and more specifically has a mean particle size between 30 and 300 micron. In other specific embodiments, the macroporous anion exchange resin comprises iron (III) oxide dispersed in the resin. In additional specific embodiments, the macroporous anion exchange resin is a magnetic resin. In yet other specific embodiments, the anion exchange resin is a macroporous strong base anion exchange resin with iron (III) oxide dispersed in the resin and which has a mean particle size between 30 and 300 micron. Treatment with this anion exchange resin is believed at least in part to remove or decrease the level of one or more chemical species in the waste water, other than the fluoride ion itself, which interfere with removal of fluoride in subsequent process steps. [00041] The waste water is contacted with the macroporous anion exchange resin and other treatment components in a vessel of appropriate size which is equipped with a means for agitation or stirring to facilitate interaction of the anion exchange resin with the waste water. When the waste water initially treated with the macroporous anion exchange resin, the mixture is stirred or agitated for a time sufficient to effect the removal of interfering species. Typically, the combined additives are mixed for 15-30 minutes or more. The anion exchange resin is optionally separated from the water prior to further processing (i.e., prior to addition of calcium and contact with cation exchange resin) and can be reused for further treatment. When the anion exchange resin is a magnetic resin, a magnetic device can be employed for such separation. In a preferred embodiment, however, the anion exchange resin is not separated from the water prior to further processing.

[00042] In this embodiment of the invention, after initial treatment with macroporous anion exchange resin, the improved precipitation method can be applied as described above by adding the water-soluble calcium salt, such as calcium chloride, to the waste water to facilitate precipitation of fluoride as calcium fluoride. Typically, the soluble calcium salt is added such that the molar calcium ion level in the waste water is equal to or less than 50% of the molar amount of fluoride present in the waste water. Again the addition of soluble calcium salt is performed in an appropriate vessel equipped with means for stirring or agitation. If the anion exchange resin is not separated from the water, the calcium salt is simply added to the same vessel employed for contacting the anion exchange resin with the waste water. After addition of calcium ion, the waste water mixture is contacted with cation exchange resin in the sodium or calcium form (chemical form) as described above. The cation exchange resin can again simply be added to the vessel in which the preceding steps were conducted. The water and combined additives including cation exchange resin are mixed for a sufficient time to obtain a stable reduced level of fluoride. Typically, the combined additives are mixed for 15-30 minutes or more. After sufficient mixing, the supernatant, treated water is separated from the solids (any precipitate and resin(s)) to provide treated water with reduced fluoride levels. Fluoride levels in the treated water can be measured. In preferred embodiments, fluoride levels can be reduced to 10 ppm or more preferably to 1-3 ppm or less. Treated water is separated from the solids. In a specific embodiment, the treated water is separated from the solids by filtering. In a specific embodiment, the separated fluoride-containing solids containing anion exchange resin, cation exchange resin and any precipitated salts do not leach high levels of fluoride ion and in preferred embodiments leach levels of fluoride ion that are sufficiently low that the solid is not categorized as hazardous waste. [00043] It is generally the case that lower fluoride levels can be achieved by increasing the contact time of the waste water treatment mixture with cation exchange resin or by increasing the amount of cation exchange resin added. Powdered cation exchange resin is generally preferred for more rapid water treatment. When whole bead cation exchange resin is employed higher volumes of resin or increased contact times can be required to achieve the same reduction in fluoride compared to powdered resin. The volume of cation exchange resin selected for addition can be added in one or more addition steps followed by mixing. Dependent upon the particle size of the cation exchange resin employed and the amount of cation exchange resin added, fluoride levels of 10 ppm or less or 1-3 ppm or less can be achieved in one or two cation exchange treatment steps. The use of lower volumes of cation exchange resin results in lower amounts of solid waste produced and is thus generally preferred. [00044] In an alternate embodiment of this aspect of the invention, after contacting with macroporous anion exchange treatment, the waste water can be directly contacted with cation exchange resin in the calcium form, without prior addition of a water-soluble calcium salt, as described above. The cation exchange resin in the calcium form is contacted with the pretreated waste water in an appropriate vessel equipped with means for stirring or agitation. If the anion exchange resin is not separated from the water in the first step, the cation exchange resin in the calcium form is simply added to the same vessel employed for contacting the anion exchange resin with the waste water. The water and combined additives including the cation exchange resin are mixed for a sufficient time to obtain a stable reduced level of fluoride. Typically, the combined additives are mixed for 15-30 minutes or more. After sufficient mixing, the supernatant treated water is separated from the solids (any precipitate and resin(s)) to provide treated water with reduced fluoride levels. Fluoride levels in the treated water can be measured. In preferred embodiments, fluoride levels can be reduced to 10 ppm or more preferably to 1-3 ppm or less. Treated water is separated from the solids. In a specific embodiment, the treated water is separated from the solids by filtering. In a specific embodiment, the separated fluoride-containing solids containing anion exchange resin, the cation exchange resin and any precipitated salts do not leach high levels of fluoride ion and in preferred embodiments leach levels of fluoride ion that are sufficiently low that the solid is not categorized as hazardous waste.

[00045] The mixed acid, fluoride-containing waste water is typically very acidic with pH below 4 and often with pH below 1. The processes of this invention have been found to function for removal of fluoride without adjustment of the initial pH of the waste water. However, the processes can be conducted at pH of 1.75 or above, at pH of 4 or above, at basic pH of 8 or above and at very basic pH between 10-12.

[00046] Thus, in related embodiments, waste water containing fluoride, mixed acids, soluble silica and/or BOE is initially treated by adjusting the pH, if necessary, to a pH of 4 or more, by addition of base, such as a hydroxide. The pH may be adjusted by addition of a solid basic salt, such as NaOH, to the waste water. The pH may also be adjusted by addition of a concentrated base solution. The pH can alternatively be adjusted to a more basic pH of 8 or higher. As another alternative, the pH of the waste water can be initially adjusted to high pH of 10-12 prior to further processing. After initial pH adjustment it is not necessary to further adjust or control the pH of the water as treatment continues. The pH- adjusted waste water is subjected to improved precipitation as described above or contacted with the cation exchange resin in the calcium form as described above. The pH-adjusted waste water can also be contacted with anion exchange resin as described above followed by improved precipitation or contact with cation exchange resin in the calcium form. [00047] In other related embodiments, waste water containing fluoride, mixed acids, soluble silica and/or BOE is first treated by contact with anion exchange resin as described above. Thereafter, the pH is adjusted, to a pH of 4 or more, by addition of base, such as a hydroxide. The pH may be adjusted by addition of a solid basic salt, such as NaOH, to the waste water. The pH may also be adjusted by addition of a concentrated base solution. The pH can alternatively be adjusted to a more basic pH of 8 or higher. As another alternative, the pH of the waste water can be initially adjusted to high pH of 10-12 prior to further processing. After initial pH adjustment it is not necessary to further adjust or control the pH of the water as treatment continues. The pH-adjusted waste water is then subjected to improved precipitation as described above or contacted with the cation exchange resin in the calcium form as described above and the further process steps are conducted as described above.

[00048] If the waste water containing fluoride also contains or is suspected to contain peroxide or other volatile compounds, it is optionally aerated prior to treatment by the foregoing method steps to remove peroxide or other volatile compounds that may be present. If the waste water containing fluoride is know to also contain ammonium ion, the pH is optionally initially adjusted to a pH between 10-12 to off-gas ammonia. The presence of ammonium ion can interfere with the measurement of fluoride by certain methods, thus it may be desirable to decrease the level of or remove ammonium prior to further processing of the waste.

[00049] The waste water may initially contain particulate matter. The methods of this invention do not require removal of such particulates. However, particulates can optionally be removed by filtration prior to treatment by the method of this invention. Colloidal silica present, for example, is optionally removed by filtration methods, particularly membrane filtration, prior to further treatment. After treatment to reduce fluoride levels, the treated water may, dependent upon local regulations or the intended use of the water, be subjected to additional purification steps including membrane filtration, reverse osmosis, and/or pH adjustment.

BRIEF DESCRIPTION OF THE FIGURES [00050] Figure 1 is a schematic illustration of a process system for removing fluoride and/or interferants from waste water.

DETAILED DESCRIPTION OF THE INVENTION

[00051] The present invention relates to the reduction of fluoride levels in waste water generated in industrial processes where the waste water can contain other anions, particularly nitrate, sulfate and other anions of acidic species, e.g., acetate and other carboxylate anions, dissolved silica, including silicates, fluorosilicates, and other fluorinated silica species, and/or may contain ammonia, ammonium fluoride or ammonium ion. [00052] Most generally the methods herein can be applied to any water stream from which it is desired to remove or decrease the levels of fluoride. The methods herein are particularly beneficial for applications in which the initial levels of fluoride are greater than 100 ppm, greater than 1000 ppm, greater than 10,000 ppm or greater than 30,000 ppm. [00053] In particular embodiments, the invention relates to reduction of fluoride levels in waste water generated in semiconductor manufacture, for example, from cleaning and etching processes. These waste waters are complex mixtures and can contain mixed acid etch components, such as nitrates, sulfates and/or acetates and other organic anions, dissolved and/or colloidal silica, various metal ions, metal oxides, various volatile organic species, various dissolved organic species, as well as buffered oxide etch species, such as ammonium hydroxide, ammonia, and ammonium fluoride and surfactants. It is believed that one or more components in such waste waters interfere with fluoride removal by conventional precipitation methods, such as those employing addition of water soluble calcium salts to form low solubility calcium fluoride. Typically, waste water streams from several different semiconductor manufacturing or cleaning steps or processes may be combined for treatment to remove fluoride and, as a consequence, the waste water generated is typically a complex mixture of species which can include one or more of such interferants.

[00054] Additionally, because a given manufacturing facility may conduct different processes at different times, the components present in fluoride- containing waste water and the fluoride level itself may vary significantly with time. The fluoride level in a given batch of waste water can be measured prior to treatment to minimize additive additions. However, because it may be difficult in any practical way to track levels of all components that may be present and which may interfere with fluoride removal, the use of a single treatment method that can be adjusted for fluoride level present, but that can also sufficiently reduce or remove interferants when present to obtain fluoride levels below 10 ppm can provide significant benefit. [00055] The waste water is typically acidic with initial pH less than 4, and more typically the waste water has initial pH less than 3 and in many cases has initial pH less than 1. However, the fluoride-containing waste water generated may also be basic, for example, through mixing of a mixed acid waste stream with a waste stream containing base. The methods of this invention can be applied to fluoride- containing waste streams of different initial pH. [00056] Fluoride levels in such waste water can typically range from tens of ppms up to tens of thousands of ppms of fluoride. Fluoride can be present in the free ionic form, in more complex species, e.g., SiF₄ or SiFβ^", or associated in some way with organic or inorganic species (such as dissolved organics or dissolved inorganic species, or polymeric silica-containing species). [00057] The term fluoride refers generally to fluoride ion (F^"), hydrofluoric acid (HF) or any other chemical species which contains fluorine and which can generate or release fluoride in the waste water stream, including fluoride salts and more complex fluoride-containing anions, such as fluorosilicates, hydroxyfluorides, and silica fluorides. [00058] The methods herein are particularly useful in mixed acid fluoride containing waste waters. This waste water has acidic pH, typically lower than pH 4, and contains at least one anion in addition to fluoride and chloride, and more typically contains two or more anions other than fluoride and chloride. The mixed acid waste water can contain one or more or two or more of nitrate (nitric acid), sulfate (sulfuric acid), phosphate (phosphoric acid), acetate (acetic acid) or other carboxylates (carboxylic acids). The waste water treatable by the methods herein can contain dissolved silica species which can be in the form, among others, of SiO₂, Si(OH)₄, SiF(OH)₃, SiF₂(OH)₂₁Si F₃(OH) and SiF₄ which may be present as neutral or anionic species as well as SiF₆ ^" and soluble polymeric silicates and fluorosilicates e.g., species containing more than one silicon atom). Waste water can also contain components of buffered oxide etch, such as ammonium fluoride, ammonium hydroxide and ammonia, as well as surfactants, dispersants and the like. Waste water can also contain various organic species (e.g., solvents), metal ions and various other complex anions containing fluorine. [00059] The term "stoichiometric" is used herein consistent with its use in the art to refer to relative number of atoms or ions in a given chemical species. The term is used to refer to the relative number of moles of given atoms or ions that are combined to form a chemical species having a given chemical formula. For example, one mole of Ca²⁺ combines with 2 moles of F^~ to form the salt CaF₂, thus the stoichiometric amount of Ca²⁺ to combine with F^" to form CaF₂ is Vz mole of calcium ion for each mole of fluoride ion. The term is used herein to refer to the amount of calcium ion added to waste water with the assumption that CaF₂ is formed. The term "sub-stoichiometric" is used herein to refer to molar amounts of an atom or ion that are less than stoichiometric with respect to a reference atom or ion for formation of a given chemical species. Thus, molar amounts of calcium ion less than Vz of the molar amount of fluoride are sub-stoichiometric assuming formation of CaF₂.

[00060] In one aspect, the invention provides an improved fluoride precipitation method in which precipitated fluoride is substantially immobilized in the residual solid which is separated from treated water. Fluoride is substantially immobilized if less than 3500mg/L fluoride can be leached from the solid employing TCLP methods. [00061] In this improved precipitation method, a soluble calcium salt is added to the waste water to introduce calcium ions into the water. The amount of calcium ion added is typically about 50% of the molar amount of fluoride (i.e., one equivalent relative to fluoride) that is in the waste water (one mole of calcium should react with two moles of fluoride to form CaFa). Dependent upon the presence and amounts of interferants that may be present in the water, additional calcium ion may be required to obtain a desired level of fluoride reduction. However, it is generally preferred that amounts of calcium ion in excess of the amount needed to obtain a desired reduction in fluoride are avoided. Addition of excess calcium (as water-soluble calcium salt) can result in the generation of solid that retains liquid or that is in a gel form which is more difficult and expensive to handle and properly dispose of. After calcium salt addition, the mixture is mixed or agitated to facilitate interaction of the combined additives and to obtain a stable measured fluoride ion level. It has been found that addition of calcium salt to the fluoride-containing waste water, results in initial wide fluctuations of the nominal measured fluoride ion level in the water as measured using a fluoride-selective ion probe. These fluctuations may be the result of interference in the fluoride ion measurement from added ions and incomplete mixing. Mixing is continued until the nominal measured fluoride level stabilizes which is believed to be indicative of completed reaction of additives and/or uniform mixing. The combination is mixed for a time which can range from 1-30 minutes, or longer if needed. More typically a mixing time of 15-30 minutes or longer is employed. It is however also generally the case that process time (i.e., mixing time) can be decreased by addition of higher amounts of calcium ion. Thus, the amount of calcium ion added can be adjusted to meet the needs of a given application to obtain a desired reduction in fluoride employing a convenient processing time at an acceptable processing cost. [00062] Although, calcium fluoride has low solubility in water, it is not found to readily precipitate in the treated waste water. In the process of this invention, fluoride-containing waste water, to which calcium has been added, is contacted with a cation exchange resin, in the sodium or calcium form, which facilitates adsorption and/or precipitation of calcium fluoride and functions to reduce fluoride levels in the treated waste water. The amount of cation exchange resin added preferably ranges from about 0.05% by total volume of water being treated to about 10% by volume of the water treated dependent upon the level of fluoride present and/or the amount of soluble calcium salt added. More preferably the amount of cation exchange resin added ranges from about 1 % to about 5% of the volume of water treated.

[00063] Reduction of 50% or more, 75% or more, 90% or more, 99% or more, 99.99% or more of fluoride in waste water can be achieved employing this improved precipitation method. This improved precipitation method is particularly useful for reducing fluoride levels in waste water that contains fluoride levels higher than 100 ppm, in waste water that contains fluoride levels higher than 1000 ppm and in waste water that contains fluoride levels higher than 10,000 ppm. [00064] In a specific embodiment, when calcium chloride is added as a 30% by weight aqueous solution, the volume of cation exchange resin added is equal to the volume of calcium chloride solution added. The combined additives are mixed or agitated until a stable reduced fluoride level is obtained, for 1-30 minutes or more. Additional steps of calcium salt addition followed by cation exchange resin addition can be performed, if necessary or desirable, to provide reduced levels of fluoride or to decrease processing time. Thereafter, treated water exhibiting reduced fluoride levels is separated from the solids.

[00065] The precipitated material formed in this method is a low-water content solid rather than a gel-like sludge. The level of fluoride that can be leached from the solid after separation from treated water can be measured employing the TCLP (Toxicity Characteristic Leaching Procedure) method. A benefit of certain embodiments of the methods herein is that residual solids formed during this treatment method do not leach unacceptable levels of fluoride and can as a result be classified as non-hazardous waste with respect to fluoride levels. Residual fluoride-containing solids generated in exemplary applications of processes herein have been shown to meet the requirements for non-hazardous waste disposal (Subtitle Class D landfill) based on the TCLP method. [00066] The TCLP testing procedures are described in US EPA publication SW- 856 entitled "Test Methods for Evaluating Solid Waste, Physical / Chemical Methods" and use TCLP leachate which has been solvent extracted with methylene chloride at a pH > 11 and at a pH < 2 by either Method 2510 or 3520. [00067] While not wishing to be bound by any particular theory, it is believed that the fluoride removed from the waste water is predominantly complexed on or within the cation exchange resin, likely associated with calcium or sodium ions in the resin, and is immobilized in the solid and cannot be readily leached out of the resin. Fluoride may also be precipitated as calcium or possibly sodium fluoride intermingled with resin or possibly precipitate in or on the resin.

[00068] The amount of water-soluble calcium salt added to the waste water in the methods of this invention is generally based on the amount of fluoride that is in the waste water or that is estimated to be in the waste water. The amount of fluoride in the waste water can be measured or estimated by any art known means prior to application of the method steps herein in order to select the amount of water soluble calcium salt to be added. A particularly useful method for rapid fluoride measurement is the SPADNS ion-specific electrode colorimetric method (Hach, Loveland CO). Fluoride-ion measurements may be made directly on waste water or treated waste water. Improved accuracy in such direct fluoride measurements on waste water has been obtained by adjusting the pH of the sample tested to pH between 5 and 6. It may be appropriate when higher fluoride levels are present to dilute the waste water sample prior to measurement. It is preferred, however, to prepare waste water samples in TISAB buffer (total ionic strength adjustment buffer) for fluoride ion probe measurement. The use of this buffer is known in the art (M.S. Frant and J.W. Ross, Jr. (1968) "Use of Total Ionic Strength Adjustment Buffer (TISAB) for Electrode Determination of Fluoride in Water Supplies" Orion Research, Vol. 40, NO. 7). Dependent upon the other components present in the waste water, fluoride ion measurements in which the TISAB buffer is not used may give "false high" readings of fluoride ion concentration. [00069] If the amount of fluoride in the waste water generated remains relatively constant with time (or for each batch of waste water that is to be treated), the amount of fluoride in a given batch can be estimated based on the known range of fluoride that is found in the waste water. Thus, if the fluoride concentration is known from prior measurement or can be estimated based on prior measurement it is not necessary to measure fluoride immediately prior to performing the methods herein. Alternatively, the amount of soluble calcium salt added can be based on a known or estimated maximum amount of fluoride in the waste water to be treated from a given source. Because a large excess of calcium is not required to effect fluoride removal as CaF₂, it is likely in most cases that addition of calcium to a level that is 50% of such a maximum molar amount of fluoride (the stoichiometric amount of calcium ion need relative to fluoride to form CaF₂) that may be present will not result in unnecessary addition of unacceptable amounts of other anions, such as chloride, into the waste water or solid waste. It is most preferred to minimize addition of the water-soluble calcium salt, to that level that provides the desired level of fluoride reduction, however, processing time may be reduced by addition of excess calcium salt. Thus, it is generally preferred to limit any excess addition of the calcium salt up to a 3-fold excess over stoichiometric. In specific embodiments of the methods herein addition of sub-stoichiometric amounts of calcium ion have been found to result in effective removal of fluoride ion from waste water. In these specific embodiments, addition of excesses of water-soluble calcium salts is avoided.

[00070] In another aspect of the invention, it has been demonstrated that fluoride levels in waste water can be reduced by directly contacting the fluoride- containing waste water with cation exchange resin in the calcium form. This method does not require addition of any water soluble calcium salt to the waste water. After separation from the treated water, the residual fluoride-containing resin generated in this treatment step can substantially immobilize fluoride as described above in the improved precipitation process. The amount of cation exchange resin in the calcium form that is added can generally range from about 0.05% by total volume of water being treated to about 10% by volume of the water treated dependent upon the level of fluoride present in the water. More preferably, the amount of cation exchange resin added ranges from about 1 % to about 5% of the volume of water treated. Cation exchange resin can be added in a series of aliquots with stirring to obtain a desired reduction in fluoride level. Reduction of 50% or more, 75% or more, 90% or more or 99% or more of fluoride can be achieved employing this method. This method is particularly useful for reducing fluoride levels in waste water that contains fluoride levels higher than 100 ppm, in waste water that contains fluoride levels higher than 1000 ppm and in waste water that contains fluoride levels higher than 10,000 ppm. [00071] In general any type of cation exchange resin in the calcium form can be employed. It is preferred that the cation exchange resin is a strong acid cation exchange resin. As is known in the art, cation exchange resins in the calcium form can be prepared from cation exchange resins in the acid form or sodium form by contacting the cation exchange resin with a solution containing calcium ions. [00072] While not wishing to be bound by any particular theory, it is believed that the fluoride removed from the waste water by direct contact with cation exchange resin in the calcium form is predominantly complexed within or on the cation exchange resin, likely associated with the calcium ions in the resin, and is immobilized in the resin and cannot be readily leached out of the resin. It may also be the case that when sodium ions are present in the waste water that a portion of the calcium ions in the cation exchange resin in the calcium form are replaced with sodium ions and/or that some level of sodium fluoride is also precipitated in or on the resin. [00073] The improved precipitation method herein can be combined with art- known methods for removal of fluoride ion. Reduction of fluoride levels by directly contacting waste water with cation exchange resin in the calcium form can also be combined with art-known methods for removal of fluoride ions, such as reverse osmosis. For example, treatment of the waste water by the improved precipitation methods herein or by contact with cation exchange resin in the calcium form can be followed by one or more steps of reverse osmosis. [00074] In additional methods provided herein mixed acid waste water containing fluoride is pretreated prior to substantial fluoride removal to remove or reduce the level of one or more interferant species and thereafter treated by precipitation and/or cation-exchange steps to reduce the fluoride level in the waste water. The interferants may in general be organic or inorganic species and they may be ionic or neutral species. Without wishing to be bound by any particular theory of operation, it is believed that the interferants include anions other than fluorine, such as sulfate and/or phosphate, and/or are dissolved silica containing species, such as silicates, fluorosilicates, silicon fluorides and soluble or dispersed polymeric silica containing species which may in addition contain fluorine. Additionally, interferants can include organic species. The one or more interferants prevent efficient reaction of fluoride with calcium to complex fluoride and remove it from the waste water down to levels below 10 ppm and preferably down to levels of 1-3 ppm or less. The interferant(s) may detrimentally affect ionization of fluoride (i.e., the dissociation of fluoride-containing species to form fluoride), may in addition detrimentally affect ionization of chloride and/or may inhibit the formation of insoluble fluoride salts, particularly calcium fluoride. It is believed that decreasing the levels of such interferant(s) functions to facilitate improved reduction of fluoride levels in the waste water. [00075] In a specific embodiment, the waste water is pretreated by contact with anion exchange resin to remove or reduce the levels of one or more such interferants. Preferably, the anion exchange resin is a macroporous anion exchange resin. More preferably, the anion exchange resin is in the chloride ion form. Preferably, the anion exchange resin comprises a polymer which has a hydrophilic backbone. In specific embodiments, the macroporous anion exchange resin is a macroporous anion exchange resin formed from a hydrophilic polymer and containing dispersed species, including a Fe (III) oxide, such as gamma- Fe2O3 (maghemite), such as those resins described in U.S. patents 5,900,146 and 6,171 ,489 which are magnetic ion exchange resins. The macroporous anion exchange resin can be a strong base anion exchange resin having dispersed therein from about 10% to about 50% of iron(lll) oxide by total weight of resin. The iron oxide may be gamma-Fe₂θ₃ which is dispersed during resin preparation with a solid dispersant, such as a pigment dispersant.

[00076] Without wishing to be bound by any particular theory, it is currently believed that the anion exchange resin, and particularly the macroporous anion exchange resin, removes or reduced the level of one or more interferants, as described above, by anion exchange, adsorption or a combination of these processes. In specific embodiments, where the anion exchange resin is formed from a hydrophilic polymer, adsorption of organic or inorganic hydrophilic species may contribute to the function of the resin. In other embodiments, where the anion exchange resin comprises disperse Fe(III) oxide, complexation of organic or inorganic species with Fe(III) and/or adsorption to Fe(III) oxide may contribute to the function of the resin.

[00077] In a specific embodiment, a macroporous anion exchange resin is a copolymer of glycidyl methacrylate and divinyl benzene (also called diethenylbenzene) and optional other monomers and which is functionalized with trimethylamine-quatemized chlorides, as described in U.S. patents 5,900,146 and 6,171 ,489. In a more specific embodiment, the anion exchange resin is a copolymer of glycidyl methacrylate, divinyl benzene and ethenylethylbenzene (also called ethyl vinyl benzene) which is functionalized with trimethylamine-quatemized chlorides. In a yet more specific embodiment, the anion exchange resin is a copolymer of glycidyl methacrylate, divinyl benzene and ethenylethylbenzene, which is functionalized with trimethylamine-quatemized chlorides and wherein 50% or more of the monomers incorporated into the copolymer are glycidyl methacrylate. In another more specific embodiment, the anion exchange resin is a copolymer of glycidyl methacrylate, divinyl benzene and ethenylethylbenzene, which is functionalized with trimethylamine-quatemized chlorides, and wherein between 50% to 80% of the monomers incorporated into the copolymer are glycidyl methacrylate. A macroporous magnetic anion exchange resin prepared essentially as described in U.S. patents 5,900,146 and 6,171,489 which can be employed in the methods of this invention is currently commercially available under the Trade Name MIEX® HW1201 (Orica Australia Pty, Ltd., Australia). [00078] Preferably the macroporous anion exchange resin has mean particle size between 30 and 1 ,000 microns and more preferably has mean particle size of 300 micron or less. In a more specific embodiment, the anion exchange resin is a macroporous magnetic strong base anion exchange resin in the chloride form containing gamma Fe₂O₃.

[00079] After reduction or removal of interferants, e.g., after contact with the anion exchange resin, fluoride is precipitated employing a soluble calcium salt and cation exchange resin as described above. The amount of calcium ion added is typically about 50% of the molar amount of fluoride that is in the waste water (one mole of calcium should react with two moles of fluoride to form CaF₂). It has been found, in contrast to prior art precipitation methods, that it is not necessary in the process herein to add excess soluble calcium salt. Addition of excess calcium ion, however, may decrease the processing time required to achieve a desired reduced level of fluoride. [00080] As noted above, but without wishing to be bound by any theory, it is believed that removal of interferants facilitates the use of less calcium. After calcium salt addition, the mixture is mixed or agitated to facilitate interaction of the combined additives. The calcium-containing waste water is then contacted with cation exchange resin, particularly in the sodium or calcium form which facilitates adsorption and/or precipitation of calcium fluoride and functions to reduce fluoride levels in the treated waste water to 10 ppm or less. The amount of cation exchange resin added ranges from about 0.05% by total volume of water being treated to about 10% by volume of the water treated, dependent upon the level of fluoride present, the amount of soluble calcium salt added, and the processing time. Dependent upon the amount of resin added and more importantly on the particle size of the cation exchange resin employed, fluoride levels of 1-3 ppm can be achieved in this method. The combined additives are mixed or agitated until a stable reduced fluoride level is obtained, 1-30 minutes or more. Thereafter, treated water exhibiting reduced fluoride levels is separated from the solids. [00081] The term cation exchange resin is used as broadly herein as it is understood and used in the art to refer to a resin which functions for exchange of cations in a solution. In general, any cation exchange resin, other than a resin in the hydrogen form, can function in the methods herein. More specifically, cation exchange resins in the sodium ion form or the calcium ion form can be employed in the method of this invention. Both gel-based and macroporous resins can be employed. Whole bead resins or crushed resins can be employed. Strong acid cation exchange resins are preferred to weak acid cation exchange resins. In one embodiment, a gel-based, strong acid cation exchange resin in the sodium form, such as IR-120 (Rohm and Haas) with a minimum capacity 2.0 eq/L can be employed. In another embodiment, a powdered strong acid cation exchange resin in the sodium form ground to a nominal mean particle size of 300 micron can be used. In particular, a powdered Styrene DVB gel-based cation resin with SOS- functionality and in the sodium form having mean particle size of 200 microns which is currently available under the Trade Name MIEX® HW3251 (Orica Australia Pty. Ltd, Australia) can be used. [00082] As noted above, in the improved precipitation method cation exchange resin is added after calcium has been added to the waste water and its addition facilitates reduction of fluoride levels in the water and immobilization of fluoride in the solids. The efficiency and level of fluoride reduction in the waste water depends at least in part on the particle size of the resin, the amount of resin added and the contact time. In the presently preferred method of the invention, the cation exchange resin and adsorbed or precipitated salts that are separated from the treated water having reduced fluoride content are not regenerated. The solid material is collected and disposed of under appropriate conditions. The separated solids contain the solid used to remove interferant (if not separated from the water after initial treatment), cation exchange resin and any precipitated fluoride salts (e.g., CaF₂ and possibly NaF).

[00083] It has been found that cation exchange resin in the calcium form can be employed in methods herein. The term "in the calcium form" refers to a cation exchange resin in which calcium is at least the predominant cation in the resin. Preferred cation exchange resins in the calcium ion form are those in which excess calcium ions have been contacted with the resin to remove any measurable level of other cations. Art-known methods can be employed to prepare cation exchange resins in the calcium ion form. In a specific embodiment, cation exchange resins in the calcium form can be prepared by contacting a cation exchange resin in the proton or Na form with a saturated calcium chloride solution. More specifically, a cation exchange resin in the calcium form was prepared by contacting 300 mL of IR-120 Na form (Rohm & Haas) with an excess of saturated calcium chloride solution (250 ml of 100% calcium chloride dissolved into 400 ml of Dl water) for two days followed by rinsing with Dl water. [00084] Mixed acid fluoride-containing waste water may contain ammonium ions, peroxide or other volatile compounds. These species may be reduced or removed from the waste water prior to treatment by the methods herein. Ammonium can be removed from the waste water, for example, by adjusting the pH of the waste water to pH 10-12 (by addition of base as described below) and allowing ammonia to off-gas. Peroxide and other volatiles can be removed by aerating the waste water for a sufficient time prior to application of treatment steps herein. Other methods known in the art for removal of ammonium ion and/or removal of peroxide or other volatiles can be employed in this invention that are not incompatible with the later ion exchange steps and removal of fluoride. [00085] Mixed acid fluoride-containing waste water will typically have a pH of less than 4, although waste water of higher pH may be generated during mixing of waste streams prior to treatment. In specific embodiments, the pH of the waste water is initially adjusted to be 4 or greater. Adjustment of the pH is not necessary, but may be beneficial in a given water treatment system design. The processes herein function for reduction of fluoride in waste water having initial pH ranging from below 1 to over 10. However, as noted above, initial adjustment of the waste water to pH 10-12 can be used to reduce or remove ammonium ion as ammonia. Further, initial adjustment of pH of the waste water to basic pH, e.g., pH 8 or more, has been found to facilitate removal of fluoride by the processes herein, at least in part because, floe that is formed during the process is generally larger when the initial pH of the waste water is basic. [00086] The pH of the fluorine-containing waste water can be adjusted to pH 4 or greater by addition of base which can be by addition of a basic salts (e.g., NaOH is preferred, but KOH can also be employed) to the waste water or by addition of an aqueous solution of a basic salt. It is preferable not to significantly increase the volume of the water to be treated, so it is preferred to adjust the pH of the waste water by adding a selected amount of a solid basic salt or by addition of a relatively concentrated aqueous solution of the basic salt (e.g., 20% by weight or more). It is preferred to employ a basic salt other than a basic calcium salt. It is preferred not to introduce calcium ions into the waste water prior to the anion exchange step of this process. For example, the use of calcium hydroxide (which may be provided in various forms of lime) is not preferred. [00087] Contact of the waste water in the first step with anion exchange resin used to remove interferants is not believed to substantially remove fluoride directly. In waste water as described herein, at most, minor amounts of fluoride are removed by exchange or adsorption in the first treatment step. After contact of waste water as described herein with the anion exchange resin, no significant reduction in fluoride ion as measured using a fluoride ion selective electrode (Hach) is observed. [00088] The methods herein are particularly applicable to waste water containing moderate (40 ppm to 1 ,000 ppm), moderately high (1 ,000 to 5,000), high (5,000 to 10,000 ppm) or very high fluoride (10, 000 ppm or more) concentrations. [00089] The methods herein can optionally be combined with a reverse osmosis process to further reduce the level of fluoride in the water separated from the precipitated solid. U.S. patent 6,338,803 described a reverse osmosis process that can be used in combination with methods of this invention. Multiple-pass reverse osmosis processes can, for example, be employed. The reject stream from the reverse osmosis membrane containing fluoride can be recycled back and mixed in with the incoming fluoride-containing waste water to be reprocessed for fluoride removal. In general, any known reverse osmosis method for reducing fluoride levels an be employed. [00090] A polishing step of reverse osmosis can be applied to treated water containing 1-3 ppm to further reduce fluoride levels to less than 1 ppm. If this step is employed the concentrate from the reverse osmosis unit can be cycled back to the initial waste water stream for continued treatment, since it will be quite more dilute in fluoride than the primary waste water stream.

[00091] After treatment to reduce fluoride levels the treated water may, dependent upon local regulations or the intended use of the water, be subjected to additional purification steps including membrane filtration, reverse osmosis, and/or pH adjustment. For example, if chloride reduction is desired, the treated water can be contacted with an anion exchange resin (e.g., macroporous anion exchange resin MIEX® HW1201 (Trademark, Orica Australia, Pty., Australia)) in the CO₃ ^" form. The resin used to reduce chloride will be in the chloride form and can be recycled, if desired, for use in initial pretreatment of the waste water as described herein below. [00092] In certain embodiments, the waste water is initially treated with anion exchange resin which is preferably a macroporous anion exchange resin. The term anion exchange resin is used as broadly herein as it is understood and used in the art to refer to a resin which functions for exchange of anions in a solution. In general, any anion exchange resin (other than those which contain fluoride ion) can function in the methods herein. More specifically, anion exchange resins in the chloride ion form and particularly those which can remove potentially interfering sulfate and/or phosphate ions, are useful in the methods herein. Strong base anion exchange resins in the chloride ion form are preferred. Both Type 1 and Type 2 strongly basic and weakly basic anionic ion exchange resins can be employed.

[00093] The anion exchange resin is preferably a macroporous resin. The term "macroporous" is used herein as broadly as it is used in the art and generally is used to refer to solids or polymers which comprise a large number of macropores which range in size from about 50 nm - 1 μm in diameter. A macroporous resin has a generally increased total surface area for contact with liquid (e.g., waste water) compared to non-macroporous resins. Preferably, the anion-exchange resin has mean particle size of 300 micron or less. The resin may be employed in the physical form of whole beads or in the form of crushed beads or powder. Various Type 1 and Type 2 macroporous strong base anion-exchange resins in the chloride form can be used with effectiveness related at least in part to resin particle size with smaller particle size resulting in faster reaction rate (exchange rates). Less preferred anion-exchange resin beads include Type 2 weakly basic anion-exchange resins and non-macroporous resins, such as gel based resins. In a specific embodiment, the anion-exchange resin is a magnetic macroporous Type 1 strong base anion-exchange resin in the chloride form which has a mean particle size of 300 microns or less. The terms Type I and Type 2 anion exchange resins refer respectively to resins containing trimethylammonium groups and dimethylethanolamino groups, respectively, on the resin. [00094] It is preferred that the anion exchange resin comprises a hydrophilic polymer. The term "hydrophilic" as used herein with respect to polymers refers to polymers in which at least portions of the polymers are hydrophilic. The term hydrophilic generally relates to molecular species, or parts thereof, that exhibit an affinity for water, often because of the formation of hydrogen bonds. Hydrophilic species are polar or contain polar portions and tend to exhibit an affinity for other polar species. For example, a polymer that is hydrophilic can associate with other hydrophilic species or polar species. Hydrophilic polymers may, for example, adsorb hydrophilic or polar species. Preferably the polymers of the resins herein are more hydrophilic than conventional acrylic and styrenic anion exchange resins. [00095] Polymers employed in anion exchange resins can be generally described as having a polymer backbone comprising one or more side groups attached to the backbone which function for crosslinking and one or more side groups attached to the polymer backbone which carry spacer groups that are (or can be ) functionalized with anion exchange sites, e.g., quaternary ammonium groups. Additionally, these polymers may further comprise backbone monomers which do not function for crosslinking and do not carry functional groups. In specific embodiments herein, the spacer groups between the polymer backbone and the anion exchange site of functionalized monomers are hydrophilic and preferably are more hydrophilic than is typically found in acrylic or styrenic polymers. Additionally, hydrophilic side groups can be incorporated into polymer backbone monomers that are hydrophilic or carry one or more hydrophilic groups. Thus, in specific embodiments, hydrophilic polymers include polymers carrying side groups that are hydrophilic. Examples of hydrophilic monomers some of which can be functionalized with anion exchange sites, include among others, glycidal methacrylate, dialkylaminoalkylmethacrylate, dimethylaminoethylmethylacrylate, 2-vinyl-4,4-dialkyl-5-oxazolone, 2-vinyl-4,4- dimethyl-5-oxazolone, diacetone acrylaminde, vinyl benzoates, vinyl benzoate halides, and vinyl benzoate chloride. Hydrophilic spacers, side groups and monomers include, among others, those that contain one or more ester linkages, one or more hydroxide groups, one or more amide groups, one or more carbonyl groups, one or more amine or imine groups or combinations of such groups. [00096] In specific embodiments herein, macroporous anion exchange resins useful in this invention include those comprising a copolymer of glycidal methacrylate with a crosslinking polymer and those comprising a copolymer of glycidal methacrylate with a crosslinking polymer and a backbone polymer. In specific embodiments, macroporous anion exchange resins useful in this invention include those wherein the glycidal methacrylate monomer comprises 50% or more of the monomers of the copolymer. In other specific embodiments, macroporous anion exchange resins useful in this invention include those wherein the glycidal methacrylate monomer comprises 75% or more of the monomers of the copolymer. In other specific embodiments, macroporous anion exchange resins useful in this invention include those wherein the glycidal methacrylate monomer comprises between 50% and 80% of the monomers of the copolymer.

[00097] As described in U.S. patents 5,900,146 and 6,171 ,489, the crosslinking monomer may be selected from a wide range of monomers, including divinyl monomers such as divinyl benezene, ethyleneglycol dimethacrylate or poly(ethyleneglycol) dimethacrylate or methylene bisacrylamide, ethyleneglycol divinylether and polyvinyl ester compounds having two or more double bonds. A wide range of functional monomers may also be used including, among many others, glycidyl methacrylate, vinyl benzyl chloride, dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl acrylamide, as well as methacrylamide, vinyl pyridine, diallylamine, and their quaternized derivatives, as well as N-vinyl formamide and its hydrolyzed derivative, and methyl acrylate and its derivatives. The backbone monomers include any monomer polymerizable by free radicals such as styrene, vinyl toluene, methylmethacrylate and other acrylates and methacrylates, particularly those that are substituted and carry one or more hydrophilic groups. [00098] In a specific embodiment, the macroporous anion exchange resin is a magnetic anion-exchange resin comprising dispersed iron oxide. The use of magnetic anion-exchange resin results in assisted agglomeration of the resin for rapid settling or the resin can be removed or separated from the liquid phase by magnetic removal. Resins incorporating magnetic particles (magnetic resins) rapidly agglomerate and settle due to magnetic attraction. Magnetic polymer beads, in particular, magnetic polymer beads which are Type I, strong base anion- exchange resins in the chloride form are described in U.S. patent 6,171 ,489, which is incorporated by reference herein for its description of such beads. [00099] The term "contact" or "contacting" as used in the description of the methods herein is used broadly to refer to any means for bringing a liquid waste stream (e.g., waste water stream) into contact with a solid such as an ion exchange resin. The solid or resin may be added to a volume of waste water in an appropriate container. Alternatively, the waste water may be added to the solid or resin. The waste water may be passed through a container holding the solid or resin. Any means known in the art for contacting a solid herein with a liquid, such as the waste water herein, can be employed in the "contacting" steps of this invention. Dependent upon the means used for achieving contact, a means for mixing the combined solid and liquid components may be employed to ensure sufficient contact of liquid with particles of solid. In one embodiment, the solid, resins and other additives are added to the waste water essentially in a batch process from which treated water is removed by separating the water from the solid, for example by some means of filtration. In this embodiment, the any resins, solids and other additives are contacted with the waste water in an open topped container. In this embodiment, the macroporous anion exchange resin is optionally separated from the water before addition of the calcium salt and cation exchange resin. [000100] It will be appreciated by one of ordinary skill in the art that the step of contacting may result in the release of heat or gas which would need to be accommodated by the vessels and other equipment employed in carrying out the process. The process of this invention is conducted at any convenient temperature and does not require heating or cooling of waste water. The process will typically be carried out at ambient temperature which may range from 5-4O⁰C, but will more typically be carried out at temperatures from 20 to 25⁰C. The process is most conveniently practiced at ambient pressure in an open-topped container, tank or column to avoid pressure build-up from gases that may be released during treatment. The processes herein can be conducted without application of external cooling, however, dependent upon components present in the waste water and the amount of heat that may be released during treatment, the process container or tank may be cooled to maintain desired temperatures in the container or tank. [000101] In specific embodiments, anion and cation exchange resin used in treatment are combined during treatment with any precipitates and the combined solids are separated from treated waste water. The solid residue is optionally dried and disposed of properly. In an alternative embodiment, the anion exchange resin used in the pre-treatment step to remove interferants, is separated from the waste water prior to precipitation and/or contact with cation exchange resin. When magnetic anion exchange resin is employed, magnetic separation can be employed to separate the resin from the treated water. Separated anion exchange, resin can be reused for more than one batch of waste water. Alternatively, separated anion exchange resin can be regenerated by treatment with brine and reused for additional treatment. In this case, eluant from anion exchange resin regeneration must be disposed of properly. In a preferred embodiment, anion exchange resin is not regenerated. [000102] In specific embodiments, steps in which the waste water is contacted with resins or other solids may be conducted in one or more open-top columns, where the resin or solid is packed into the columns and the waste water is contacted with the resin or solid by passing the waste water through the columns. The waste water may be recycled through a single column or through a series of columns, as necessary, to ultimately achieve the desired reduced fluoride level. In such an embodiment, the resin containing columns are used until their capacity for removal of interferant or fluoride is exhausted. In a specific embodiment, continuous waste water processing can be conducted employing a series of such columns in which exhausted resin-containing columns can be switched out for new columns, without significantly disrupting the treatment process. Exhausted resin columns can, for example, be capped and disposed of properly. [000103] The method of this invention optionally includes a step of adjusting pH, for example as a pretreatment step prior to contact of the waste water with anion exchange resin or during or after anion exchange treatment. The term adjusting is employed to emphasize that a single step of addition of base (or acid) can be used to select (i.e., adjust) the pH of the waste water. In embodiment, pH is optionally adjusted prior to contact with the anion exchange resin at the start of the fluoride removal process. In another embodiment, pH is optionally adjusted during or after anion exchange treatment. In yet another embodiment, a step of adjusting pH is optionally employed prior to adding soluble calcium salt and subsequent addition of cation exchange resin. In a further embodiment, a step of adjusting pH is optionally employed prior to contacting waste water with cation exchange resin in the calcium form. [000104] In optional embodiments of the invention, when fluoride levels in waste water exceed about 20,000 ppm fluoride, the waste water can be diluted with water or more preferably with waste water containing lower fluoride levels prior to treatment as described herein above. [000105] In specific embodiments, the methods of this invention, unless otherwise specified, individually can exclude the following: multiple steps (two or more) of pH adjustment during treatment of waste water; continuous extraction of solid precipitate; addition of seed particles of calcium fluoride to facilitate formation and precipitation of calcium fluoride; addition of coagulants, particularly those that are polymer solutions; recycling of precipitate in contact with additional calcium or magnesium ions and fluoride containing waste water; addition of phosphate; addition of carbonate; addition of a phenol-formalin chelating resin of zirconium hydroxide type; addition of aluminium ion; use of cation exchange resin in the aluminum form; use of tritium, zirconium, titanium or hafnium-type cation-exchange resins, use of haloalkyl-silane-type adsorbent resins, use of rare earth metal oxide hydrate-type chelate resins, use of aluminium salt-type chelate resins; use of multiple steps of contacting the waste water sequentially with more than one cation exchange resin and more than one cation exchange resin; use of sequential steps of contacting the waste water with a strong acid cation resin (to exchange cations for hydrogen ions); a strong base anion resin in sulfate form (to remove hexafluorosilicates), a weak base anion exchange resin having tertiary amine groups in the free base form (to remove acids) and a weak base anion exchange resin in the free base form (to remove hydrofluoric acid); use of aluminum-exchanged strong acid cation exchange resin; or adjustment of waste water to alkaline pH (pH 8-9) to hydrolyze fluorosilicic acid and complex metal fluorides, followed by passage through a column of Type 2 strong base anion exchange resin, in the hydroxide (OH^") form.

In specific embodiments of the methods of this invention can further comprise one or more of the following; application of one or more steps of reverse osmosis to reduced-fluoride level waste water treated by methods herein to further reduce fluoride levels or to remove or reduce the level of other undesirable components; or a step of contacting reduced-fluoride level waste water resulting form treatment by methods herein and separated from added resin and solids added or formed during with a macroporous anion exchange resin or with a cation ion exchange resin.

[000106] Figure 1 schematically illustrates a treatment system for carrying out the methods of this invention. The system is illustrated for batch treatments. An open-topped container or tank (10) of appropriate size is equipped with some means for agitating or mixing. The container is illustrated as having a mechanical stirrer (12), but can alternatively be provided with a gas (e.g., air) supply for mixing. In general, any means for mixing or agitating can be employed. A fluid connection to the waste water stream (14) is provided to the tank. Means for introducing a selected volume of anion exchange resin (16) is provided. Means for introducing a selected volume of a solution of soluble calcium salt (e.g., CaCI₂, 18) is also provided. Alternatively, a means for adding the soluble salt in solid form is provided. Further, means for introducing a selected volume or amount of cation exchange resin (20) is provided. Any means for introducing a solid or liquid into the container can be employed. In the illustrated system, all components are added to and mixed in a single container or tank. After addition and mixing as described herein above, the combined solids and water are pumped (22) through a liquid-solid separator (24) to provide treated water (25) separated from solid. Any means for separating the treated water from the solid can be used, including various types of filtering devices, including a filter press, and a centrifuge.

Alternatively, the bulk of the solids may be allowed to settle in the tank, the shape of which may be selected to provide a settling region for the solid, and the treated water may then be pumped from the tank leaving the settled solid behind. The illustrated system can further be provided with a means for introducing base (or acid) to adjust the pH of the waste water prior to or during treatment. [000107] In an alternative embodiment, the anion-exchange resin used to remove interferants can be separated from the treated water before addition of calcium and cation exchange resin. Various alternative system configurations can be employed to remove this resin or solid. In particular, when the resin or solid employed is magnetic, it will agglomerate when agitation is stopped. Treated water can be separated from agglomerated solid and transferred to a second tank for subsequent treatment steps. In this embodiment, the resin or other solid can be reused to treat additional waste water. Alternatively magnetic separators or filters can be used to remove the magnetic resin or solid. To avoid potential release of hazardous materials, the resin or other solid is preferably not regenerated. Ultimately, the used resin or solid is preferably combined with the solids formed on precipitation for proper disposal.

[000108] The system illustrated in Figure 1 can also be employed for carrying out the improved precipitation method without a pre-treatment step. In this case, means for introducing the anion exchange resin is not required. Further, water separated from the solids can optionally be directed to a reverse osmosis membrane wherein the permeate provides treated water and the rejected stream is recycled for mixing with the incoming waste water stream. [000109] The system illustrated in Figure 1 can alternatively be employed for carrying out waste water treatment by contact with cation exchange resin in the calcium form. In this case, means for introducing the anion exchange resin and the calcium salt is not required. Further, water separated from the solids can optionally be directed to a reverse osmosis membrane wherein the permeate provides treated water and the rejected stream is recycled for mixing with the incoming waste water stream. When the system of Figure 1 is employed for initial treatment employing anion exchange resin followed by treatment with cation exchange resin in the calcium form, means for introducing the soluble calcium salt is not needed. [000110] Treated water with reduced fluoride levels (25) separated from resins and other solids can be subjected to further purification dependent upon local regulation and the intended use or destination of the water. If, for example, it is desired to decrease the level of chloride in the water, it may be contacted with an anion exchange resin in the bicarbonate form. In this case, the used anion exchange resin which is now in the chloride form may be recycled for use to remove interferants from the fluoride-containing waste water. In a specific embodiment, a macroporous anion exchange resin, such as macroporous anion exchange resin MIEX® HW1201 in the HCO3- form can be used for chloride removal and recycled for pretreatment of fluoride-containing waste water. [000111] Any means for mixing or agitation of the solid and liquid components may be employed that does not detrimentally affect the process steps and which provides for adequate dispersion of the resin or other additive in the waste water. Exemplary means for mixing and agitation include mechanical stirrers of various designs, aeration or gas sparging, and cyclones among many others. When magnetic ion exchange beads are employed in the methods herein, the beads are combined with waste water containing fluoride and agitation (or mixing) is applied which is of sufficient intensity that the magnetic agglomeration of the resin beads is disrupted to disperse the beads in the waste water. Removal of agitation or mixing results in rapid agglomeration and settling of magnetic beads. [000112] When a Markush group or other grouping is used herein, all individual members of the group and all combinations and possible subcombinations of the group are intended to be individually included in the disclosure. Every formulation or combination of reagents or components described or exemplified herein can be used to practice the invention, unless otherwise stated. One of ordinary skill in the art will appreciate that methods, device elements, and materials other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such methods, device elements, and materials are intended to be included in this invention. Whenever a range is given in the specification, for example, a temperature range, a frequency range, a time range, or a composition range, all intermediate ranges and all subranges, as well as, all individual values included in the ranges given are intended to be included in the disclosure. Any one or more individual members of a range or group disclosed herein can be excluded from a claim of this invention. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[000113] As used herein, "comprising" is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term "comprising", particularly in a description of components of a composition or in a description of elements of a device, can be exchanged with "consisting essentially of or "consisting of. [000114] Although the description herein contains many specificities, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the embodiments of the invention. Each reference cited herein is hereby incorporated by reference in its entirety. However, if any inconsistency arises between a cited reference and the present disclosure, the present disclosure takes precedent. Some references provided herein are incorporated by reference herein to provide details concerning the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art. Other references may be cited to provide additional or alternative device elements, additional or alternative materials, additional or alternative methods of analysis or application of the invention. United States provisional application 60/747,266, filed May 15, 2006 is incorporated by reference in its entirety herein. THE EXAMPLES

Example 1 : Fluoride Removal from Semiconductor Plant Waste Water (Sample I) [000115] The waste water treated in this example contained:

Component Concentration

Fluoride 2,900 ppm Sulfate 4,500 ppm Chloride 1 ,800 ppm Ammonia 0.28 ppm

Al 25 ppm Cr 1.5 ppm

Low VOC This is a partial listing of the components of the waste water measured using standard analytical techniques. Dissolved silica was not measured, but was known to be present because of the source of the waste water.

[000116] Sample 1 was treated as follows: The pH was not adjusted prior to treatment and was less than pH 2. About

1.2% by volume (to total water volume) of a macroporous Type 1 strong base anion exchange magnetic resin formed from a hydrophilic polymer (MIEX® HW1201 , Orica Australia Pty, Ltd., Australia) was added to the waste water and the mixture was mixed for 15 minutes to allow reaction of the resin with components in the waste water.

[000117] Calcium chloride, as a 30% aqueous solution, was then added to the water-anion exchange resin combination (0.6 gallons/125 gallons waste). The volume of 30% calcium chloride added was about 0.5% by volume of the total volume of water treated. [000118] The combined calcium chloride, anion-exchange resin and water was mixed until the nominal fluoride level as measure by a fluoride-selective probe (Hach, Loveland, CO) stabilized, i.e., for about 15 minutes. A gel-based strong acid cation exchange resin in the sodium form having sulfonic acid functionality (IR-120, Rohm & Haas) was then added to the water treatment mixture. The volume of cation exchange resin added was equal to the volume of 30% calcium chloride solution added. The treatment mixture was then mixed for 30 minutes. The combined solids were then separated from the water through a filter press to provide treated water and solid waste. [000119] The treated water had the following levels of measured components:

Component Concentration

Fluoride 3.7 ppm

Sulfate 2,500 ppm

Chloride 14,000 ppm

Ammonia 7.7 ppm

Aluminium <200 ug/L

Chromium 710 ug/L

[000120] The solid waste collected was determined to contain:

Component Concentration

Fluoride (soluble) 2700 mg/Kg

Sulfate (soluble) 2600 mg/Kg

Chloride (soluble) 4900 mg/Kg

Sulfide, reactive <50 mg/Kg

Al not determined

Cr <0.20 mg/L pH 10.8

%Moisture 46%

Example 2: Fluoride Removal from Semiconductor Plant Waste Water (Sample II)

[000121] The Sample Il waste water contained:

Component Concentration

Fluoride 11 ,000 ppm

Sulfate 14 ppm Chloride 52 ppm

Ammonia 1600 ppm

Al 5.8 ppm

Cr 0.13 ppm higher VOC 280 ug/L acetone + 4.4 ug/L toluene

This is a partial listing of the components of the waste water measured using standard analytical techniques. Dissolved silica was not measured, but was known to be present because of the source of the waste water.

[000122] Sample Il was treated as follows: The pH was not adjusted and was believed to be less than pH 2.0;

MIEX® HW1201 (Orica Australia Pty, Ltd., Australia) was added to the waste water (1.2% by volume of the total water volume). The combined anion-exchange resin and water was mixed for 15 minutes to allow reaction of the resin with components in the water. Calcium chloride, as a 30% aqueous solution, was then added to the water-anion exchange resin combination (2gal/ 125 gal of waste water). The combined calcium chloride, anion-exchange resin and water was mixed until the measured fluoride level stabilized (about 15 minutes). A gel-based strong acid cation exchange resin in the sodium form having sulfonic acid functionality (IR-120 Rohm & Haas) was then added to the water treatment mixture. The volume of cation exchange resin added was equal to the volume of 30% calcium chloride solution added. The treatment mixture was then mixed for 30 minutes. The combined solids were then separated from the water through a filter press to provide treated water and solid waste. [000123] The treated water had the following levels of measured components:

Component Concentration

Fluoride 8.6 ppm

Sulfate 580 ppm Chloride 25,000 ppm

Ammonia 2100 ppm Aluminium 710 ug/L

Chromium <10 ug/L

VOC acetone 31 ug/L + toluene 9.5 ug/L

[000124] The solid waste collected was determined to contain:

Component Concentration

Fluoride (soluble) 3100 mg/Kg Sulfate(soluble) 160 mg/Kg Chloride (soluble) 6800 mg/Kg Sulfide, reactive <50 mg/Kg

Al not determined Cr <0.20 mg/L

PH 8.93

%Moisture 48%

Example 3: Use of Alternative Cation Exchanαe Resins [000125] Fluoride-containing waste water analogous to that treated in Examples 1 and 2 was contacted with a powdered cation exchange resin. The resin was a powdered Strong Acid Cation Resin, a styrene DVB Gel based resin with sulfate functionality in the sodium form and ground to nominal 200 micron particle size with 4.8 meq/dry gram, 40-60% moisture content and 95% ionic conversion (currently available under the Trade Name MIEX® HW3251 (Orica Australia Pty. Ltd, Australia).

[000126] The volume of powdered cation exchange resin added was 50% the volume of aqueous 30% calcium chloride solution that had been added. The water was mixed with the powdered cation exchange resins for 30 minutes. With this treatment, an acceptably low fluoride ion concentration down to 3 ppm or less can be achieved. Example 4: Exemplary Jar Tests

[000127] A series of jar tests (200 ml_ of waste water) were performed on mixed acid waste containing 30,000 ppm fluoride and moderate levels of BOE.

[000128] In Test 1 , the pH of the sample was adjusted from pH 1.75 to pH 12.1 by addition of base. The pH adjusted sample was stirred for 45 minutes after which 3 ml. of solid CaCI₂ (anhydrous) was added and the sample was mixed for another 15 minutes. MIEX® HW3251 (Trademark, Orica Australia Pty, Ltd., Australia) powdered cation exchange resin (6 mL) was then added and the mixture was stirred again for 30 minutes. The solids were then allowed to settle (2-3 min) before fluoride levels were measured using the SPANDS fluoride ion-selective probe method (Hach, Loveland, CO). This treatment decreased fluoride levels in the waste water to 300 ppm (a 100-fold decrease).

[000129] In Test 2, MIEX® HW1201 (Orica Australia Pty, Ltd., Australia) macroporous anion exchange resin (6 mL) was added to the sample and the sample was stirred for 15 minutes. The pH of the sample was then adjusted from pH 1.75 to 11.8 and stirred for another 30 minutes. Solid CaCI₂ (anhydrous, 3 mL) was added and the sample was mixed for another 15 minutes. MIEX® HW3251 (Trademark, Orica Australia Pty, Ltd., Australia) powdered cation exchange resin was then added (3 mL) and the sample was stirred for another 30 minutes. After 2-3 minutes of settling, the fluoride level was measured to be below the detection limit (less than 1 ppm). [000130] Test 3 was conducted as Test 2 using 50% of the volume of powdered cation exchange resin (1.5 mL) used in Test 2. Again the fluoride level was reduced to below 1 ppm.

[000131] Test 4 was conducted as Tests 2 and 3 with the exception that the powdered cation exchange resin was replaced with 6 mL of gel-based cation exchange resin (IR-120, Rohm & Haas). Again the fluoride level was reduced to below 1 ppm. [000132] Test 5 was conducted as Test 2 with no pH adjustment and with 30 minutes of stirring after addition of macroporous anion exchange resin. The fluoride level was reduced to 800 ppm.

[000133] Test 6 was conducted as Test 2 with addition of 6 mL of a different macroporous anion exchange resin. ResinTech SBMP1 , a strong base Type 1 macroporous anion resin in the chloride form with particle size between 420 and 1200 microns and capacity of 1.15 meq/ml was used. The fluoride level was reduced to 200 ppm.

[000134] Test 7 was conducted as Test 6 replacing the macroporous anion exchange resin with a gel-based resin RTI-1245. The fluoride level was reduced to 300 ppm.

[000135] The forgoing examples are illustrative and are not intended to limit the scope of the invention.

Claims

THE CLAIMS:

1. A method for treating waste water containing fluoride to reduce the levels of fluoride in the waste water and form a solid containing immobilized fluoride which comprises the steps of

(a) adding a water-soluble calcium salt to the waste water in an amount such that the added calcium is 50% or less of the molar amount of fluoride in the waste water;

(b) adding a cation exchange resin in the sodium or calcium form to the waste water; and thereafter

(c) separating the solids added, formed or both from the treated water.

2. The method of claim 1 wherein the cation exchange resin is added after addition of the water-soluble calcium salt.

3. The method of claim 1 wherein the cation exchange resin is in the sodium form.

4. The method of any one of claims 1-3 further comprising the step of contacting the waste water containing fluoride with a macroporous anion exchange resin prior to adding the water-soluble calcium salt.

5. The method of any one of claims 1-3 further comprising the step of contacting the waste water containing fluoride with a macroporous anion exchange resin after adding the water-soluble calcium salt, but after contacting the waste water with cation exchange resin.

6. A method for treating waste water containing fluoride to reduce the levels of fluoride in the waste water and form a solid containing immobilized fluoride which comprises the steps of:

(a) contacting the waste water with a cation exchange resin in the calcium form; and thereafter

(b) separating the resin and any solids formed from the treated water.

7. The method of claim 6 further comprising the step of contacting the waste water containing fluoride with a macroporous anion exchange resin prior to contacting the waste water with cation exchange resin in the calcium form.

8. The method of claim 6 further comprising the step of contacting the waste water with a macroporous anion exchange resin after contacting the waste water with cation exchange resin.

9. The method of any one of claims 1-10 wherein the pH of the waste water is adjusted to pH 5 or higher prior to treatment.

10. The method of any one of claims 1-10 wherein the pH of the waste water is adjusted to pH 8 or higher prior to treatment.

11. The method of any one of claims 1-10 wherein the pH of the waste water is adjusted to at least pH 10 prior to treatment.

12. The method of any one of claims 4, 5, 7, or 8 wherein the pH of the waste water is adjusted to pH 5 or higher after first contacting the waste water with macroporous anion exchange resin.

13. The method of any one of claims 4, 5, 7, or 8 wherein the pH of the waste water is adjusted to pH 8 or higher after first contacting the waste water with macroporous anion exchange resin.

14. The method of any one of claims 1-13 further comprising a step of subjecting treated water to reverse osmosis.

15. The method of any one of claims 1-14 further comprising contacting the treated water separated from the resin and solids with macroporous anion exchange resin.

16. The method of any one of claims 1-5 or 9-15 wherein the water-soluble calcium salt is calcium chloride.

17. The method of any one of claims 1-5 or 9-16 wherein the amount of the water-soluble calcium salt added is such that the amount of calcium in the treated waste water is sub-stoichiometric with respect to the amount of fluoride in the waste water.

18. The method of any one of claims 1-5 or 9-16 wherein amount of the water- soluble calcium salt added is such that the amount of calcium in the treated waste water is between 5% and 50% of the molar amount of fluoride in the waste water.

19. The method of any one of 1-5 or 9-16 wherein the water-soluble calcium salt is added such that the amount of calcium in the treated waste water is between 5% and 25% of the molar amount of fluoride in the waste water.

20. The method of any one of claims 1-5 or 9-16 wherein the water-soluble calcium salt is added such that the amount of calcium in the treated waste water between 10% and 25% of the molar amount of fluoride in the waste water.

21. The method of any one of claims 1-5 or 9-16 wherein the water-soluble calcium salt is added to the waste water as an aqueous solution containing 20% or more by weight of the salt.

22. The method of claim 21 wherein the water-soluble calcium salt is added to the waste water as an aqueous solution containing 30% by weight of the salt.

23. The method of any one of claims 1-5 or 9-16 wherein the water-soluble calcium salt is added to the waste water as a solid.

24. The method of any one of claims 1-23 wherein the volume of cation exchange resin added to the treated waste water between 0.05% and 10% of the volume of the waste water treated.

25. The method of any one of claims 1-23 wherein the volume of cation exchange resin added to the treated waste water between 0.5% and 5% of the volume of the waste water treated.

26. The method of any one of claims 1-23 wherein the volume of cation exchange resin added to the treated waste water between 0.5% and 2.5% of the volume of the waste water treated.

27. The method of any one of claims 1-26 wherein the cation exchange resin is a strong acid cation exchange resin.

28. The method of any one of claims 1-27 wherein the cation exchange resin is powdered.

29. The method of any one of claims 1-28 wherein the cation exchange resin is macroporous.

30. The method of any one of claims 1-29 wherein the cation exchange resin has mean particle size of 300 micron or less.

31. The method of any one of claims 1-27 wherein the cation exchange resin is a gel-based resin.

32. The method of any one of claims 4, 5, 7, or 8-31 wherein the macroporous anion exchange resin comprises iron.

33. The method of any one of claims 4, 5, 7, or 8-32 wherein the macroporous anion exchange resin is magnetic.

34. The method of any one of claims 4, 5, 7, or 8-33 wherein the macroporous anion exchange resin is a strong base anion exchange resin.

35. The method of any one of claims 4, 5, 7, or 8-33 wherein the macroporous anion exchange resin is a strong base anion exchange resin in the chloride form.

36. The method of any one of claims 4, 5, 7, or 8-35 wherein the macroporous anion exchange resin is a Type 1 strong base anion exchange resin.

37. The method of any one of claims 4, 5, 7, or 8-36 wherein the macroporous anion exchange resin is formed from a hydrophilic polymer

38. The method of any one of claims 4, 5, 7, or 8-36 wherein the macroporous anion exchange resin is a copolymer of oxiranylmethyl ester and divinyl benzene.

39. The method of any one of claims 4, 5, 7, or 8-36 wherein the macroporous anion exchange resin is a copolymer of oxiranylmethyl ester, divinyl benzene and ethyl vinyl benzene.

40. The method of any one of claims 4, 5, 7, or 8-39 wherein the macroporous anion exchange resin has a mean particle size between 30 and 1000 microns.

41. The method of any one of claims 4, 5, 7, or 8-39 wherein the macroporous anion exchange resin has a mean particle size between 30 and 300 micron.

42. The method of any one of claims 4, 5, 7, or 8-41 wherein the macroporous anion exchange resin comprises iron (III) oxide dispersed in the resin.

43. The method of any one of claims 4, 5, 7, or 8-42 wherein a volume of macroporous anion exchange resin is added to the waste water ranging from 0.5 to 5% of the volume of the waste water treated.

44. The method of claim 43 wherein the volume of macroporous anion exchange resin added to the waste water is less than 2% of the volume of the waste water treated.

45. The method of claim 43 wherein the volume of macroporous anion exchange resin added to the waste water is between 1 % and 2% of the volume of the waste water treated.

46. The method of any one of claims 1-45 wherein the initial level of fluoride in the waste water is 100 ppm or more.

47. The method of any of claims 1-45 wherein the initial level of fluoride in the waste water is 1000 ppm or more.

48. The method of any one of claims 1-45 wherein the initial level of fluoride in the waste water is 10,000 ppm or more.

49. The method of any one of claims 1-48 further comprising a step of measuring the initial molar amount of fluoride present in the waste water.

50. The method of any one of claim 1-49 further comprising a step of contacting the treated water with an anion exchange resin in the CU₃ ^~ form to reduce chloride levels.