CN117735773A - Treatment method of high-salt high-fluorine sulfur-containing wastewater - Google Patents
Treatment method of high-salt high-fluorine sulfur-containing wastewater Download PDFInfo
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- CN117735773A CN117735773A CN202311860537.0A CN202311860537A CN117735773A CN 117735773 A CN117735773 A CN 117735773A CN 202311860537 A CN202311860537 A CN 202311860537A CN 117735773 A CN117735773 A CN 117735773A
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- wastewater
- calcium
- ions
- sulfate
- solid
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- 238000000034 method Methods 0.000 title claims abstract description 52
- 238000011282 treatment Methods 0.000 title description 30
- 229910052731 fluorine Inorganic materials 0.000 title description 19
- 239000011737 fluorine Substances 0.000 title description 19
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 title description 9
- 229910052717 sulfur Inorganic materials 0.000 title description 9
- 239000011593 sulfur Substances 0.000 title description 9
- -1 fluoride ions Chemical class 0.000 claims abstract description 49
- 238000001704 evaporation Methods 0.000 claims abstract description 47
- 230000008020 evaporation Effects 0.000 claims abstract description 47
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- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims abstract description 33
- 239000011575 calcium Substances 0.000 claims abstract description 33
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Abstract
The application provides a wastewater treatment method, wherein the wastewater contains fluoride ions, sulfate radicals and one or more cations, and the method sequentially comprises the following steps: regulating the pH value of the wastewater; defluorination of the wastewater to at least partially remove fluoride ions from the wastewater; first solid-liquid separation; calcium removal is carried out on the wastewater; a second solid-liquid separation; the pH of the wastewater is regulated back; the wastewater is subjected to an evaporation operation to at least partially remove cations and sulfate from the wastewater. The method can remove water-soluble salts, fluoride ions and sulfate radicals in the wastewater conveniently and efficiently with low cost, and realize very efficient separation, recovery and reutilization of water and various salt components in the wastewater.
Description
Technical Field
The application relates to the field of environmental protection, in particular to a method for treating high-salt high-fluorine sulfur-containing wastewater, which can effectively remove salt, fluoride ions and sulfate radicals (such as sulfate radical or sulfite radical) in the wastewater, effectively separate various impurities or components contained in the wastewater, and recycle water or other components according to requirements.
Background
The treatment of high-salt and high-fluoride wastewater with very high salt and fluoride contents has been an environmental challenge of serious domestic concern, and in order to effectively remove salt components and fluoride ions from such wastewater, complex treatment steps, extremely high operating costs, and extremely high losses and high failure rates to wastewater treatment equipment are often required. When such high-salt high-fluorine wastewater contains a large amount of sulfate radicals and sulfite radicals at the same time, the treatment of the wastewater becomes particularly complicated and difficult.
Heretofore, various techniques have been considered for treating fluorine-containing wastewater by a fluorine removal method such as a chemical precipitation method, a coagulation precipitation method, an adsorption method, an ion exchange method, a membrane filtration method, an electrochemical method, an induced crystallization method and the like. However, these prior art methods all use a number of problems that have not been addressed.
For example, when chemical precipitation and coagulation precipitation are used, it is often necessary to add calcium to the wastewater to effect precipitation removal of fluoride ions from the wastewater. However, because calcium fluoride has certain solubility in water, the wastewater after the treatment still has the fluoride ion concentration of about 20mg/L, and the wastewater still does not accord with the discharge concentration of industrial wastewater. And at this point further reduction of the fluoride ion content of the wastewater often requires relatively complex treatments, it is difficult to further reduce the fluoride concentration of the wastewater to a level that meets emission standards in a simple and efficient manner. The complexity and difficulty of the above-mentioned defluorination process are further increased when the fluorine-containing wastewater contains a large amount of sulfate radicals (e.g., sulfate radicals, sulfite radicals, etc.). Specifically, sulfate radicals such as sulfate radicals and sulfite radicals rob calcium ions with fluorine ions to generate calcium sulfate and calcium sulfite precipitates, so that the added calcium ions cannot effectively remove fluorine ions and are wasted, and the concentration of fluorine ions in wastewater subjected to the defluorination operation is greatly fluctuated, so that the wastewater treatment process cannot be controlled.
Secondly, after fluoride ions and sulfate radicals are removed from the wastewater by precipitation, the obtained high-salt wastewater often needs to enter an evaporation section such as multi-effect evaporation or MVR evaporation for desalination treatment, and as the solubility of calcium salts containing sulfuric acid (such as calcium sulfate and calcium sulfite) in brine is far higher than the solubility of the calcium salts containing sulfuric acid in clear water, a large amount of calcium salts containing sulfuric acid (such as calcium sulfate and calcium sulfite) enter evaporation equipment, and as evaporation progresses, the wastewater begins to concentrate, and calcium sulfate and calcium sulfite are separated out, so that a heat exchanger is blocked. In addition, the dissolution of the calcium salts containing sulfuric acid (for example, calcium sulfate and calcium sulfite) itself changes with a change in temperature, and even if the wastewater to be treated is not concentrated during heating, the wastewater is likely to be precipitated due to a change in temperature in the equipment, thereby causing clogging of the evaporator or the heat exchanger. To clear these blockages, a great deal of manpower and financial resources are often required to shut down, replace and maintain the equipment, and thus delay in shut down of the wastewater treatment equipment and the need to additionally invest in built back-up facilities can also severely affect the cost, applicability and operating efficiency of the associated equipment.
In order to solve the above problems, various enterprises and scientific institutions have invested a lot of manpower and material costs and have conducted a lot of researches, but a technology has not been successfully developed so far, and all the above problems have been effectively solved. A spot is visible on the difficulty of treating wastewater with three characteristics of high fluorine, high salt and sulfur. There remains a need in the art to provide a wastewater treatment technique that overcomes the above-described difficulties.
Disclosure of Invention
The inventors of the present application have made extensive and intensive studies with a view to solving the problems as described above, and have succeeded in developing a wastewater treatment method by performing design of a wastewater treatment process, and have succeeded in solving the problems as described above, which have been urgently solved in the prior art.
The application discloses a wastewater treatment method, wherein the wastewater contains fluoride ions, sulfate radicals and one or more cations, and the method sequentially comprises the following steps:
step A: regulating the pH value of the wastewater;
and (B) step (B): defluorination of the wastewater to at least partially remove fluoride ions from the wastewater;
step C: performing first solid-liquid separation;
step D: calcium removal is carried out on the wastewater;
step E: performing second solid-liquid separation;
step F: the pH of the wastewater is regulated back;
Step G: the wastewater is subjected to an evaporation operation to at least partially remove cations and sulfate from the wastewater.
According to one embodiment of the present application, the sulfate-containing group comprises at least one of the following: sulfite, bisulfite, sulfate, bisulfate, thiosulfate.
According to another embodiment of the present application, the cation comprises at least one of the following: sodium ion, potassium ion, lithium ion, ammonium ion.
According to another embodiment of the present application, in step a, the pH of the wastewater is adjusted to 8-9.
According to another embodiment of the present application, in step B, fluoride ions in the wastewater are at least partially removed by adding a soluble calcium salt to the wastewater, the molar ratio of calcium ions in the soluble calcium salt to fluoride ions in the wastewater being from 3:4 to 1:1.
According to another embodiment of the present application, the soluble calcium salt is selected from at least one of the following: calcium hydroxide, calcium chloride, calcium nitrate, calcium hypochlorite, calcium formate, and calcium acetate.
According to another embodiment of the present application, a flocculant is added to the wastewater between said step B and step C. According to another embodiment of the present application, the flocculant is selected from at least one of the following: polyacrylamide (PAM), gelatin, starch, polyvinyl alcohol, sodium polyacrylate, poly (sulfonated styrene-maleic acid), chitosan, cationic melamine polymer, tannin, cationic starch, cationic dicyandiamide polymer, polyamine, polydimethyldiallylammonium chloride, polyaluminum chloride (PAC), ferrous sulfate, alum. According to another embodiment of the present application, the flocculant is added in an amount of 1-10% by weight of the wastewater treated in step C, based on the weight of the wastewater.
According to another embodiment of the present application, in said step D, the waste water is decalcified by raising the pH of the waste water to a value of > 12 and introducing carbonate into the waste water.
According to another embodiment of the present application, in said step D, the molar ratio of the introduced carbonate to the soluble calcium ions contained in the wastewater is comprised between 1:1 and 1.5:1.
According to another embodiment of the present application, in the step E, the second solid-liquid separation is performed by a press filtration method.
According to another embodiment of the present application, a carbonate solution is formulated in said step E using a portion of the separated liquid phase and the sodium carbonate solution is transported to step D.
According to another embodiment of the present application, in said step F, the pH of the wastewater is adjusted to 6-9.
According to another embodiment of the present application, in the step G, the wastewater is subjected to an evaporation operation to obtain evaporated water vapor and a concentrated mother liquor, and the water vapor is condensed to obtain purified water.
According to another embodiment of the present application, the concentrated mother liquor is optionally at least partially refluxed to step C.
In the following detailed description, methods, apparatus and devices of the present application are further described with reference to the accompanying drawings.
Drawings
FIG. 1 shows a flow chart of a wastewater treatment process according to one embodiment of the present application.
Detailed Description
"Range" is disclosed herein in the form of lower and upper limits. There may be one or more lower limits and one or more upper limits, respectively. The given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular ranges. All ranges that can be defined in this way are inclusive and combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for specific parameters, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.
In this application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values.
In this application, all embodiments and preferred embodiments mentioned herein can be combined with each other to form new solutions, unless specifically stated otherwise.
In the present application, all technical features mentioned herein as well as preferred features may be combined with each other to form new solutions, if not specifically stated.
In the present application, the term "comprising" as referred to herein means open or closed, unless otherwise specified. For example, the term "comprising" may mean that other components not listed may also be included, or that only listed components may be included.
The wastewater to be treated by the method developed in the present application is wastewater containing fluoride, sulfate and one or more cations, and is also referred to as "high-salt high-fluorine sulfur-containing wastewater" in the present application.
The wastewater may be from various sources such as paper, printing, leather, metal processing, chemical fiber, acid, electroplating, oil refining, pesticides, pharmaceuticals, organic synthesis, oil exploitation, oil refining, textile, food processing, wood processing, machinery manufacturing, etc., and may be from specific contaminated waters, domestic sewage or landscape waters, etc. So long as it is "high salt, high fluorine and sulfur containing" can be treated by the methods described herein.
In the present application, "high fluorine" means that the fluoride ion in the wastewater exceeds the regulations of the relevant laws and regulations, for example, the content may be 30mg/L or more, or 50-500000mg/L, or 60-400000mg/L, or 80-300000mg/L, or 100-200000mg/L, or 120-100000mg/L, or 150-80000mg/L, or 200-60000mg/L, or 250-50000mg/L, or 300-20000mg/L, or 400-10000mg/L, or 500-8000mg/L, or 600-7000mg/L, or 1000-6000mg/L, or 2000-5500mg/L, or 3000-5000mg/L, or a range of values obtained by combining any two of the above-mentioned end values with each other.
In this application, when describing wastewater as "sulfur-containing" or having "sulfate-containing," it is meant that the wastewater contains sulfur-containing anions that may include at least one of the following: sulfite, hydrogen sulfite, sulfate, hydrogen sulfate, thiosulfate; including, for example, sulfite, sulfate, or a combination thereof. According to one embodiment of the present application, the total concentration of sulfate-containing groups in the wastewater may be 20-500000mg/L, or 40-400000mg/L, or 50-300000mg/L, or 80-200000mg/L, or 100-100000mg/L, or 150-80000mg/L, or 200-60000mg/L, or 250-50000mg/L, or 300-20000mg/L, or 400-10000mg/L, or 500-8000mg/L, or 600-7000mg/L, or 1000-6000mg/L, or 2000-5500mg/L, or 3000-5000mg/L, or within a numerical range obtained by combining any two of the above-mentioned end values with each other.
In this application, "high salt" means that the wastewater may contain a large amount of various salts, and the type and concentration of salts contained in the wastewater are determined by the specific source and process from which the wastewater is generated. Note that the "salt" ranges described herein do not include "fluoride" and "sulfate" as described above, but that at least a portion of these "fluoride" and "sulfate" containing counter cations may be included in the "salt" ranges described herein for treatment, separation, and recycling as part of the "salt". According to one embodiment of the present application, the salts may comprise various inorganic salts or inorganic salts of various cations, examples of which include, for example, at least one of the following: sodium ion, potassium ion, lithium ion, ammonium ion, various other inorganic cations and organic cations that do not form a precipitate with fluoride ion, and the like. Anions included in the salts can include nitrate, chloride, bromide, iodide, phosphate, phosphite, hypophosphite, hydroxide, carbonate, silicate, bicarbonate, phosphate, dihydrogen phosphate, chlorate, bromate, iodate, and various organic anions such as formate, acetate, benzoate, and the like.
Examples of organic compounds that may also be contained in the wastewater include organic matter, microorganisms, and suspended matter, for example: humic acid, proteins, aliphatic compounds, aromatic compounds, esters, saccharides, amino acids, organic chlorides, organic phosphorus compounds, organic heavy metal compounds, urea, muramic acid, fatty amines, uric acid, organic bases, pectins, chitin, quaternary amine compounds, and the like; examples of microorganisms include various bacteria, fungi, algae, protozoa, and metazoan; examples of suspensions include various small organic or inorganic particles and droplets.
In this application, TDS is used primarily to characterize the amount of "salts" contained in wastewater. TDS is an acronym for english for total dissolved solid matter (Total Dissolved Solids) and theoretically includes the total amount of inorganic salts, organic matter, microorganisms, suspended matter, etc. dissolved in water. However, the total amount of inorganic salts (i.e., the "salts" described above) in the wastewater treated by the method of the present invention tends to be much larger than the other components (organics, microorganisms, suspended matters, etc.), so that the amount of "salts" contained in the wastewater can be substantially reflected in the TDS in the present application. According to one embodiment of the present application, TDS in a water sample may be detected by methods known in the art, for example, using a commercially available TDS tester.
In the present application, COD or COD may also be used Cr To characterize the total amount of impurities (including organic contaminants, as well as some inorganic impurities that may be oxidized) contained in the wastewater. COD (chemical oxygen demand) Cr Refers to the chemical oxygen demand of wastewater measured in a strongly acidic solution using potassium dichromate as the oxidizing agent, as can be measured by standard method GB11892-89, for example.
The wastewater treatment method sequentially comprises the following steps:
step A: regulating the pH value of the wastewater;
and (B) step (B): defluorination of the wastewater to at least partially remove fluoride ions from the wastewater;
step C: performing first solid-liquid separation;
step D: calcium removal is carried out on the wastewater;
step E: performing second solid-liquid separation;
step F: the pH of the wastewater is regulated back;
step G: the wastewater is subjected to an evaporation operation to at least partially remove cations and sulfate from the wastewater.
A flowchart of a method according to one embodiment of the present application is shown in fig. 1, and a method of the present application will be described in detail below in conjunction with the flowchart.
As shown in fig. 1, the wastewater to be treated is first collected in any suitable container, apparatus or facility, which may be a wastewater collection tank, or the like. The wastewater collection tank or the wastewater collection tank can play a role in water storage at the same time, and temporarily contains wastewater when the wastewater treatment system is shut down; in addition, the pretreatment device can also function as a pretreatment device, for example, for preliminary sedimentation and other operations.
As shown in fig. 1, step a is performed after the wastewater is transferred from the wastewater collection tank or wastewater collection tank into the pH adjusting apparatus: and adjusting the pH value of the wastewater. According to one embodiment of the present application, the pH of the wastewater is adjusted in this step to a value in the range of 8-9, such as 8.1-8.9, or 8.2-8.8, or 8.3-8.7, or 8.4-8.6, or 8.4-8.5, or a combination of any two of the above endpoints. The pH adjustment may be performed using conventional acids and bases, examples of useful acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, and the like, and examples of useful bases include sodium hydroxide, potassium hydroxide, aqueous ammonia, and the like. Depending on the particular pH of the wastewater, the acids and bases may be added as solids or as aqueous solutions to treat the wastewater to the desired pH range. The step of adjusting the pH of the wastewater may be performed in any suitable vessel, such as in a separate pond or tank, or may be performed in the same vessel as the subsequent step or steps, such as pH adjustment and subsequent defluorination and/or precipitation steps may be performed in the same vessel. Through the research of the inventor of the application, the optimal fluoride ion removal effect can be achieved by adjusting the pH value of the wastewater to the range.
The wastewater after the pH adjustment is then subjected to a defluorination operation. Specifically, in the defluorination step, a soluble calcium salt is added to the wastewater such that calcium ions and fluoride ions form CaF 2 And precipitating to at least partially remove fluoride ions from the wastewater. Examples of the soluble calcium salt may include one or more of the following: calcium chloride, calcium hydroxide, calcium nitrate, calcium hypochlorite, calcium formate, and calcium acetate. In this step, the fluoride ion content of the wastewater is first detected, and then the concentration and flow/volume/weight of the soluble calcium salt added are selected so that the molar amount of soluble calcium salt is in stoichiometric excess with respect to the molar amount of fluoride ions in the wastewater, i.e., the molar ratio of calcium ions added to fluoride ions in the wastewater in this step>1:2, in particular 3:4 to 1:1, for example 1:1.3 to 1:1.05, or 1:1.2 to 1:1.1, or within the numerical range obtained by combining any two of the above endpoints with each other. The soluble calcium salt may be added in the form of a solution, e.gThe concentration of the solution may be 0.001 to 4mol/L, for example 0.01 to 2mol/L, or 0.05 to 1.5mol/L, or 0.1 to 1.2mol/L, or 0.2 to 1.0mol/L, or 0.5 to 0.8mol/L, or within a numerical range obtained by combining any two of the above-mentioned end values with each other. In this step B, fluoride ions in the wastewater are caused to be at least partially removed, for example at least 80%, or at least 85%, or at least 90%, or at least 92%, or at least 95%, or at least 98%, or at least 99%, or at least 99.5%, or at least 99.9%, or about 100%. According to one embodiment of the present application, at least a substantial portion of the fluoride ions in the wastewater solution phase form precipitates (e.g., caF after the treatment of step B 2 Precipitation).
After said step B, step C is performed: and carrying out first solid-liquid separation on the wastewater. According to one embodiment of the application, the first solid-liquid separation is performed by precipitation, filtration, centrifugal separation and the like to separate and remove solid CaF from the wastewater 2 Microparticles, and any other solid particles that may be present. According to one embodiment of the present application, the first solid-liquid separation step is performed by a precipitation method, for example, it may be performed in a precipitation tank.
According to one embodiment of the present application, a flocculant is added to the wastewater in step C, and the addition of the flocculant promotes the formation of solid particulate matter and liquid droplets (e.g., caF formed in step B) in the wastewater 2 Small particles, small droplets of organic contaminants contained in wastewater, etc.). Examples of the flocculant include at least one of: polyacrylamide (PAM), gelatin, starch, polyvinyl alcohol, sodium polyacrylate, poly (sulfonated styrene-maleic acid), chitosan, cationic melamine polymer, tannin, cationic starch, cationic dicyandiamide polymer, polyamine, polydimethyldiallylammonium chloride, polyaluminum chloride (PAC), ferrous sulfate, alum. According to a specific embodiment, the flocculant is PAM. The flocculant may be in solid form, liquid form, solution form (e.g. water Solutions) or dispersions (suspensions, colloids or emulsions). According to one embodiment, the flocculant is added in an amount of 1 to 10 wt%, such as 2 to 9 wt%, or 3 to 8 wt%, or 4 to 7 wt%, or 5 to 6 wt%, or within the range of values obtained by combining any two of the above endpoints with each other, based on the weight of the wastewater treated in step C.
According to one embodiment of the present application, in the above step B and step C, the pH of the wastewater is kept always in the range of 8-9, for example 8.1-8.9, or 8.2-8.8, or 8.3-8.7, or 8.4-8.6, or 8.4-8.5, or in the range obtained by combining any two of the above endpoints with each other.
After the first solid-liquid separation step C, the wastewater is subjected to a decalcifying step D to remove and recover as much as possible an excessive portion of calcium ions added for removing fluorine ions in step B. Specifically, in said step D, the pH of the wastewater is further raised by the addition of a base, whereby carbonate is introduced into the wastewater so that, under the raised pH conditions, the residual calcium ions of the wastewater form calcium carbonate to precipitate out. According to one embodiment of the present application, in step D, the pH of the wastewater is raised to a value of 12 or more, or 12-14, or 12.2-13.8, or 12.5-13.5, or 12.8-13.2, or 12.9-13.0, or within a range of values obtained by combining any two of the above endpoints with each other. The alkaline agent used to raise the pH may include at least one of the following: sodium hydroxide, potassium hydroxide, ammonia water. According to one embodiment, naOH is used here to carry out the increase of the pH of the wastewater. The alkaline agent may be added in the form of a solid or an aqueous solution, and in the case of using an aqueous solution, the concentration of the aqueous solution may be 0.001 to 5mol/L, for example, 0.005 to 4mol/L, or 0.01 to 3mol/L, or 0.02 to 2mol/L, or 0.05 to 1.5mol/L, or 0.1 to 1.2mol/L, or 0.2 to 1.0mol/L, or 0.3 to 0.9mol/L, or 0.4 to 0.8mol/L, or 0.6 to 0.7mol/L, or within a numerical range obtained by combining any two of the above-mentioned end values with each other. The carbonate may be from potassium carbonate, sodium bicarbonate, potassium bicarbonate, or a combination of two or more of the foregoing. According to one embodiment of the present application, sodium carbonate (e.g., in the form of a sodium carbonate solution) may be used to introduce carbonate into the wastewater to promote precipitation of calcium ions in the wastewater as calcium carbonate. According to one embodiment of the present application, the concentration of the sodium carbonate solution is 0.1-30 wt%, such as 0.5-25 wt%, or 1-20 wt%, or 2-18 wt%, or 5-15 wt%, or 8-12 wt%, or 9-10 wt%, or within the numerical range obtained by combining any two of the above endpoints with each other. According to one embodiment of the present application, in said step D, the calcium ion concentration in the supernatant of the wastewater obtained after the first solid-liquid separation of step C is first characterized and the amount of sodium carbonate solution to be added is determined from the measured calcium ion concentration in the supernatant. For example, the molar ratio of carbonate in the added sodium carbonate solution to calcium ions in the supernatant obtained in step C (calcium ions in the solution phase) may be in the range of 1:1 to 1.5:1, for example 1.1:1 to 1.4:1, or 1:2 to 1.3:1, or in the range of values obtained by combining any two of the above endpoints with each other.
According to one embodiment of the present application, in this step D, calcium ions in the wastewater are at least partially removed, for example at least 80%, or at least 85%, or at least 90%, or at least 92%, or at least 95%, or at least 98%, or at least 99%, or at least 99.5%, or at least 99.9%, or about 100%. According to one embodiment of the present application, at least a substantial portion of the calcium ions in the wastewater form precipitates (e.g., caCO) 3 Precipitation).
Next, in step E, a second solid-liquid separation is performed to separate the solid precipitate (e.g., calcium carbonate) generated in the above step from the liquid phase to effect removal of calcium ions from the wastewater. According to one embodiment of the application, the second solid-liquid separation is performed by precipitation, filtration, centrifugal separation and the like to separate and remove solid CaCO from wastewater 3 Microparticles, and any other solid particles that may be present. According to the applicationIn one embodiment, the second solid-liquid separation step is performed by filtration, for example, in a filter press.
The filter press is a known filtering device in the art, and the principle is that a water body containing solid particles flows through the filtering mechanism under the action of a compressing force applied by a compressing mechanism driven by manpower, mechanical force or hydraulic force, so that the solid particles can be effectively connected to the intelligence quotient of the filtering mechanism, and the filter cake can be dried to different degrees by adopting air flows such as compressed air or steam. Types of filter presses include plate and frame filter presses, chamber filter presses, vertical filter presses, and belt filter presses.
After the second solid-liquid phase separation in step E, the separated solid phase (mainly calcium carbonate) may be discarded as waste, for example, provided to a third party for waste treatment or recycled according to the actual situation. The liquid phase obtained by the second solid-liquid phase separation may be subjected to subsequent further steps (e.g., pH-adjusting step F and evaporation step G) and discharged after reaching the discharge standard. In addition, the liquid phase can be at least partially recycled. For example, according to one embodiment of the present application, the higher pH in the liquid phase, containing substantial amounts of NaOH and carbonate, may be recycled appropriately, for example, to step C or step D, for calcium ion removal from the wastewater, to reduce the overall sodium carbonate and bicarbonate dosage in the process of the present invention. According to one embodiment of the present application, recycling and reuse of calcium ions (calcium chloride) and carbonate (sodium carbonate) is achieved in the manner described above, with additional water, calcium ions, hydroxyl and carbonate being replenished as needed.
According to one embodiment of the present application, an acid is added to the wastewater obtained by the treatment in step E, and the pH of the wastewater is adjusted back to 6-9, this step being referred to herein as pH adjustment step F. Examples of acids that may be used with the acids according to one embodiment of the present application include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, and the like, and various concentrations of the above acids may be used. In said step F, the target pH may be 6-9, for example 6.2-8.8, or 6.4-8.6, or 6.5-8.5, or 6.8-8.3, or 6.9-8.0, or 7.0-7.9, or 7.2-7.7, or 7.4-7.5, or within the range of values obtained by combining any two of the above endpoints with each other. The acid may be added in the form of an aqueous solution and the concentration of the acid may be 0.001 to 5mol/L, for example 0.005 to 4mol/L, or 0.01 to 3mol/L, or 0.02 to 2mol/L, or 0.05 to 1.5mol/L, or 0.1 to 1.2mol/L, or 0.2 to 1.0mol/L, or 0.3 to 0.9mol/L, or 0.4 to 0.8mol/L, or 0.6 to 0.7mol/L, or within a numerical range obtained by combining any two of the above end values with each other.
After said step F, the wastewater is subjected to an evaporation operation to at least partially remove cations and sulphate contained in the wastewater. This step also removes residual calcium ions, fluoride ions, and other anions from the wastewater, non-limiting examples of which include, for example, nitrate, chloride, bromide, iodide, phosphate, phosphite, hypophosphite, hydroxide, carbonate, silicate, bicarbonate, phosphate, dihydrogen phosphate, chlorate, bromate, iodate, and various organic anions such as formate, acetate, benzoate, and the like. The cations represent various cations contained in the wastewater in addition to calcium ions, such as at least one of the following: sodium ions, potassium ions, lithium ions, ammonium ions, and small amounts of other ions that may be contained in the wastewater, such as various inorganic or organic cations that do not form a precipitate with fluoride ions.
Specifically, in this step G, the wastewater, which has been brought back to pH in said step F, is subjected to an evaporation treatment in an evaporator, so that a portion of the water is heated to boiling and forms steam, which is clean, substantially free of various acid anions and metal cations, and after condensation forms purified water, which is optionally discharged as purified wastewater after heat recovery or recycled as purified water; the concentrated mother liquor contains the other salts and a small amount of residual F and calcium ions. The waste water staying in the evaporator system is continuously concentrated, after the density is detected to meet the salt discharging requirement specified by the system, the waste water is pumped into a cooling tank and then enters a centrifugal machine to remove the separated solids, the remained liquid is called mother liquid, and the mother liquid and the separated solids are concentrated and enriched with a plurality of factors affecting the normal operation, such as calcium ion fluoride ions, organic matters and the like. According to one embodiment of the present application, some salts in solid state, such as sodium chloride, sodium sulphate, sodium sulphite etc. may be recovered from the concentrated mother liquor, and at least a part of the concentrated mother liquor and/or at least a part of the precipitated solid phase may optionally be recycled back to step C or step D, e.g. for the purpose of adjusting the waste water concentration, promoting precipitation of calcium ions by means of carbonate remaining in the concentrated mother liquor, etc. according to specific needs.
The evaporation step G may be performed using a suitable evaporation treatment apparatus, and for example, a multistage evaporation, a rising film evaporator, a falling film evaporator, a wiped film evaporator, an MVR evaporator, a dividing wall evaporator, a circulation evaporator, a once-through evaporator, a central circulation tube evaporator, a suspended frame evaporator, a column evaporator, or the like may be used. According to one embodiment of the present application, an MVR evaporator may be used. According to an exemplary embodiment of the present application, the components of the evaporator that are in contact with the wastewater are made of a corrosion-resistant material, which may include stainless steel, brass, titanium alloy, polyethylene, polytetrafluoroethylene, etc., and most preferably a titanium alloy (e.g., TA10 titanium alloy) material, to prevent corrosion or damage to the components by the wastewater. The evaporation step may be carried out under conventional operating conditions (including temperature, pressure, flow, etc.) of the evaporator described hereinabove.
Without wishing to be bound by any particular theory, by using the method of the present application, contaminant components such as fluoride, calcium, TDS, etc. in the wastewater can be removed very efficiently and with high stability from the wastewater without interference from other ions (e.g., sulfate, sulfite, etc.) present in the wastewater during the various operating steps, without undesirable precipitation during the process, section or step where precipitation is not desired (particularly in the evaporator), thereby avoiding the need for equipment components (e.g., gauntlets, valves, etc. in the evaporator) ) Clogging and corrosion, etc. The method of the invention can stably output high-quality purified wastewater, wherein the fluorine content and TDS and COD in the purified wastewater Cr The level accords with the relevant regulations of environmental protection laws and regulations in various countries worldwide, and the water body and the salt can be conveniently recycled, so that the cost and the complexity of the wastewater treatment process are obviously reduced.
The present application is described below in terms of specific embodiments for the purpose of better understanding the contents of the present application. It should be understood that these embodiments are merely illustrative and not limiting. The reagents used in the examples were commercially available as usual unless otherwise indicated. The methods and conditions used in the examples are conventional methods and conditions unless otherwise specified.
Examples
In the examples below, the methods of the present application were performed using different formulations and process conditions and characterized for the treatment of wastewater.
In the following examples, the pH of wastewater was measured using a pH meter; measuring the content of calcium ions in the wastewater by using an EDTA titration method; measuring the fluoride ion content in the wastewater by using thorium nitrate titration technology; COD of wastewater was tested according to the standard method described in GB11892-89 Cr The method comprises the steps of carrying out a first treatment on the surface of the Total salt content in the wastewater was measured using a TDS tester.
In the following examples, the wastewater to be treated was wastewater produced by the difluoromethane F22 process, which had an initial pH of about 7.5, a fluoride ion concentration of about 4500mg/L, an initial salt content (TDS) of about 11w mg/L, and an initial TOC Cr About 1300mg/L, sulfate concentration about 23000mg/L, sulfite concentration about 12000mg/L.
Example 1
In this example 1, wastewater was treated according to the procedure described in fig. 1. The pH of the wastewater was first adjusted in the raw water tank with a 20 wt% NaOH aqueous solution (supplemented with 2M hydrochloric acid if necessary), monitored with a pH meter, adjusted to 9 and kept at this level using. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 270 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 3:4. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 1710mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type container device with stirring, the wastewater from the sedimentation tank overflows from the upper end of a calcium removing kettle, 32wt% sodium hydroxide aqueous solution is added from the top of the reaction kettle in the calcium removing section to control the pH value of the water phase to be 12-13, and 10wt% sodium carbonate aqueous solution is also added from the top of the reaction kettle at the flow rate of 90L/h, so that the molar ratio of carbonate ions to calcium ions is about 1.2:1.
And then using a plate-and-frame filter press to filter the wastewater, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter pressing treatment, adjusting the pH value to about 7.5, and then conveying the wastewater into an MVR evaporation system for evaporation treatment under the conditions that the temperature is 72-78 ℃ and the pressure is-65 to-75 KPa.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Example 2
In this example 2, wastewater was treated according to the procedure described in fig. 1. The pH of the wastewater was first adjusted in the raw water tank with a 32wt% aqueous NaOH solution (supplemented with 30wt% hydrochloric acid, if necessary), monitored with a pH meter, adjusted to 9 and kept at this level using. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 360 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 1:1. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 6340mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type vessel apparatus with stirring, to which an aqueous sodium hydroxide solution having a concentration of 32% by weight is added at a calcium removal section to control the pH of the aqueous phase to 12-13, and an aqueous sodium carbonate solution having a concentration of 10% by weight is added thereto at a flow rate of 340L/hr so that the molar ratio of carbonate ions to calcium ions is about 1.2:1.
And then using a plate-and-frame filter press to filter the wastewater, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter pressing treatment, adjusting the pH value to about 7.5, then conveying the wastewater into an MVR evaporation system, and performing evaporation treatment under the conditions of the temperature of 72-78 ℃ and the pressure of-65 to-75 KPa.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Example 3
In this example 3, wastewater was treated according to the procedure described in fig. 1. The pH of the wastewater was first adjusted in the raw water tank with a 20 wt% NaOH aqueous solution (supplemented with 2M hydrochloric acid if necessary), monitored with a pH meter, adjusted to 9 and kept at this level using. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 360 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 1:1. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 6340mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type vessel apparatus with stirring, to which an aqueous sodium hydroxide solution having a concentration of 32% by weight is added at a calcium removal section to control the pH of the aqueous phase to 12 to 13, and an aqueous sodium carbonate solution having a concentration of 10% by weight is added thereto at a flow rate of 425L/hr so that the molar ratio of carbonate ions to calcium ions is about 1.5:1.
And then using a plate-and-frame filter press to filter the wastewater, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter pressing treatment, adjusting the pH value to about 7.5, then conveying the wastewater into an MVR evaporation system, and performing evaporation treatment under the conditions of the temperature of 72-78 ℃ and the pressure of-65 to-75 KPa.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Example 4
In this example 4, wastewater was treated according to the procedure described in fig. 1. The pH of the wastewater was first adjusted in the raw water tank with a 20 wt% NaOH aqueous solution (supplemented with 2M hydrochloric acid if necessary), monitored with a pH meter, adjusted to 9 and kept at this level using. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added to the defluorination section with the calcium chloride addition amount controlled at 360 kg/hr (in terms ofThe solid weight of calcium chloride) such that the molar ratio of calcium ions to fluoride ions is maintained at about 1:1. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 6340mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type vessel apparatus with stirring, to which an aqueous sodium hydroxide solution having a concentration of 32% by weight is added at a calcium removal section to control the pH of the aqueous phase to 13 to 14, and an aqueous sodium carbonate solution having a concentration of 10% by weight is added thereto at a flow rate of 425L/hr so that the molar ratio of carbonate ions to calcium ions is about 1.5:1.
The wastewater was then press-filtered using a plate and frame filter press, a 30wt% hydrochloric acid solution was added to the press-filtered wastewater, the pH was adjusted back to about 7.5, and then evaporated in example 5.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Example 5
In this example, the wastewater treated by the procedure of example 4 was fed into an MVR evaporator, and the evaporation treatment was performed in an MVR evaporation system at a temperature of 72 to 78℃and a pressure of-65 to-75 KPa.
The mother liquor was refluxed into the system and run for 24 hours, and the results are shown in table 2.
Specifically, in the evaporation process in the MVR evaporator, the wastewater is boiled and evaporated to form relatively clean water vapor, the relatively clean water vapor is condensed into condensed water (or called purified water) after heat is recycled, the recycled or discharged wastewater stays in the system and is continuously concentrated, after the detected density reaches the salt discharging requirement specified by the system, the wastewater is pumped into a cooling tank (crystal slurry tank) for cooling so as to reduce the salt solubility, then the material enters a centrifugal machine, the separated solid is removed, the remained liquid is called mother liquor, and many factors affecting the normal operation such as calcium ion fluoride ions and organic matters are concentrated and enriched.
At this time, mother liquor is discharged into a sedimentation tank used for the first solid-liquid separation, the mother liquor is discharged irregularly, the reflux is not in a fixed proportion, the operation is determined according to the change of the current of the compressor, the temperature difference of an inlet and an outlet of the compressor is observed to determine whether the boiling point is reduced or not after the discharge, if the boiling point is not reduced obviously, the pollution factors in the possibly enriched mother liquor are too high, the mother liquor still needs to be discharged, and if the pollution factors are reduced obviously, the mother liquor is not discharged any more in a short period.
In the prior art, a separate dryer is needed for drying mother liquor of the MVR evaporation system, a large amount of steam or electricity is generally consumed, anions contained in the mother liquor are conveyed to an upstream sedimentation tank, such as a sedimentation tank used for first solid-liquid separation, are combined with calcium ions in wastewater for sedimentation, excessive calcium ions are removed in a softening stage, and a large amount of organic matters are carried out by calcium fluoride sediment and calcium carbonate sediment, and are discharged along with sludge in a filter press, so that pollution factors enriched in the mother liquor are removed. Thereby avoiding significant waste of steam, electrical energy, equipment life and manpower in the prior art.
Comparative example 1
In this comparative example 1, the pH of the wastewater was first adjusted with a 20 wt% NaOH aqueous solution (supplemented with 2M hydrochloric acid if necessary) in a raw water tank, the pH of the wastewater was monitored with a pH meter, the pH was adjusted to 7 and the use was kept at this level. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 270 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 3:4. While continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying supernatant separated by the sedimentation tank to downstream calcium removal A working section. The calcium ion concentration in the supernatant was measured to be about 1800mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type vessel apparatus with stirring, to which an aqueous sodium hydroxide solution having a concentration of 32wt% is added at a calcium removal section to control the pH of the aqueous phase to be higher than 12, and an aqueous sodium carbonate solution having a concentration of 10wt% is added thereto at a flow rate of 95L/hr so that the molar ratio of carbonate ions to calcium ions is about 1.2:1.
And then, using a plate-and-frame filter press to filter-press the wastewater, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter-pressing treatment, and adjusting the pH value to about 7.5. The fluorine ion content of the comparative example exceeds the standard, and the requirement of the evaporator on the fluorine ion content in the wastewater cannot be met.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Comparative example 2
In this comparative example 2, the pH of the wastewater was first adjusted with a 20 wt% NaOH aqueous solution (if necessary supplemented with 2M hydrochloric acid) in the raw water tank, the pH of the wastewater was monitored with a pH meter, the pH was adjusted to 9 and the use was kept at this level. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 225 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 2.5:4. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 630mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open-mouth kettle type container equipment with stirring, and the concentration is added into the equipment in a calcium removal sectionIs a 32wt% aqueous sodium hydroxide solution to control the pH of the aqueous phase to above 12 and an aqueous sodium carbonate solution having a concentration of 10wt% is added thereto at a flow rate of 35L/hr such that the molar ratio of carbonate ions to calcium ions is about 1.2:1.
And then, using a plate-and-frame filter press to filter-press the wastewater, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter-pressing treatment, and adjusting the pH value to about 7.5. The fluorine ion content of the comparative example exceeds the standard, and the requirement of the evaporator on the fluorine ion content in the wastewater cannot be met.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Comparative example 3
In this comparative example 3, the pH of the wastewater was first adjusted with a 20 wt% NaOH aqueous solution (if necessary supplemented with 2M hydrochloric acid) in the raw water tank, the pH of the wastewater was monitored with a pH meter, the pH was adjusted to 9 and the use was kept at this level. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 360 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 1:1. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 6340mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type vessel apparatus with stirring, to which an aqueous sodium hydroxide solution having a concentration of 32wt% is added at a calcium removal section to control the pH of the aqueous phase to be higher than 12, and an aqueous sodium carbonate solution having a concentration of 10wt% is added thereto at a flow rate of 315L/hr so that the molar ratio of carbonate ions to calcium ions is about 1.1:1.
And then, carrying out filter pressing on the wastewater by using a plate-and-frame filter press, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter pressing treatment, adjusting the pH value to about 7.5, and then conveying the wastewater to an MVR evaporation system. The comparative example has a calcium ion content exceeding the standard, and cannot meet the requirements of the evaporator on the fluorine ion content in the wastewater.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Comparative example 4
In this comparative example 4, the pH of the wastewater was first adjusted with a 20 wt% NaOH aqueous solution (if necessary supplemented with 2M hydrochloric acid) in the raw water tank, the pH of the wastewater was monitored with a pH meter, the pH was adjusted to 9 and the use was kept at this level. As described above, the initial fluoride ion concentration of the wastewater in the raw water tank was found to be 4500mg/L.
The wastewater is treated by 4m 3 The flow rate/h is continuously pumped to a defluorination section, the defluorination section is a section with a volume of 20m 3 Is provided with an open kettle type container for stirring. An aqueous solution of calcium chloride having a concentration of 30wt% was added at the defluorination section, the calcium chloride addition being controlled at 360 kg/h (based on the solid weight of calcium chloride) so that the molar ratio of calcium ions to fluoride ions was maintained at about 1:1. And (3) continuously and fully stirring the wastewater, conveying the suspension generated in the defluorination working section to a sedimentation tank, carrying out first solid-liquid separation, and conveying the supernatant separated out of the sedimentation tank to a downstream calcium removal working section. The calcium ion concentration in the supernatant was measured to be about 6340mg/L.
The calcium removal section is arranged at a section of 20m 3 Is carried out in an open kettle type vessel apparatus with stirring, to which an aqueous sodium hydroxide solution having a concentration of 32% by weight is added at a calcium removal section to control the pH of the aqueous phase to 11, and an aqueous sodium carbonate solution having a concentration of 10% by weight is added thereto at a flow rate of 425L/hr so that the molar ratio of carbonate ions to calcium ions is about 1.5:1.
And then, using a plate-and-frame filter press to filter-press the wastewater, adding a hydrochloric acid solution with the concentration of 30wt% into the wastewater subjected to the filter-pressing treatment, and adjusting the pH value to about 7.5. The comparative example has a calcium ion content exceeding the standard, and cannot meet the requirements of the evaporator on the fluorine ion content in the wastewater.
The various indices of the wastewater before delivery to the evaporation section are shown in table 1.
Comparative example 5
In this comparative example 5, the wastewater treated by the procedure of comparative example 4 was fed into an MVR evaporation system, and the evaporation treatment was performed at a temperature of 72 to 78℃and a pressure of-65 to-75 KPa. The results are shown in Table 2.
TABLE 1 fluoride ion and calcium ion concentration variation for examples 1-4 and comparative examples 1-4
Since fluoride ions are highly corrosive, considering the service life of the evaporation equipment, even though a TA10 heat exchanger is used, the fluoride ion concentration in the wastewater fed to the evaporator must be controlled to 30ppm or less, and thus neither comparative example 1 nor comparative example 2 can satisfy the requirements of evaporation operation.
Since the high concentration of calcium ions causes clogging, the frequency of shutdown maintenance is reduced in consideration of stabilization of the evaporation equipment, and the calcium ions should be controlled to 200ppm or less, so that neither comparative example 3 nor comparative example 4 can satisfy the requirements.
As can be seen from the examples and comparative examples data shown in table 1, very desirable fluoride and calcium ion removal effects can be achieved by the process parameters specifically designed according to the present invention, such as pH range and actual ratio; however, in the comparative example, since at least one of the above-mentioned process parameters does not satisfy the range defined in the present application, satisfactory removal effects of fluorine ions and calcium ions cannot be achieved.
TABLE 2 boiling point increase and clogging conditions for wastewater of example 5 and comparative example 5
From the experimental data of invention example 5 and comparative example 5 shown in table 2, it can be seen that the concentration of calcium ions in the wastewater fed to the evaporator for evaporation treatment must be lower than a specific level, otherwise, too high calcium content causes an excessively large increase in boiling point of the wastewater during evaporation treatment and forms precipitated substances, which cause the evaporator to be blocked, which may lead to the evaporator having to be shut down and maintained, and may lead to serious problems such as uneven local heating and flying temperature, which may cause significant damage and malfunction of the apparatus. In addition, it can be seen from the experimental data shown in table 2 that the amplitude of boiling point increase of the wastewater during evaporation in the evaporation apparatus can be very effectively reduced by performing a specially designed reflux of the mother liquor.
The condensate water obtained by condensing the steam generated during the evaporation of the wastewater of example 5 was characterized, and the characterization results are summarized in the following table 3.
TABLE 3 example 5 and comparative example 5
| Index (I) | Salt content | CODcr | Fluoride ions | Sulfate ion | Sulfite ion |
| Concentration (mg/L) | ＜80 | ＜100 | ＜1 | No detection of | No detection of |
From the experimental data in table 3, it can be seen that in example 5, the content of various impurities or pollutants in the wastewater treated by the method of the present invention is far lower than the standards of the related laws and regulations, and the quality of water body is even higher than that of general industrial water.
Summary
In summary, the invention successfully develops a method suitable for treating high-salt high-fluorine sulfur-containing wastewater, which can efficiently and stably remove fluorine ions, TDS, sulfate radicals and sulfite ions in the wastewater, can be used for large-scale wastewater treatment, has stable operation, low maintenance frequency, high quality of discharged wastewater and no worry about blockage of a heat exchanger and the like.
Claims (10)
1. A method for treating wastewater, wherein the wastewater contains fluoride ions, sulfate radicals and one or more cations, the method sequentially comprises the following steps:
step A: regulating the pH value of the wastewater;
and (B) step (B): defluorination of the wastewater to at least partially remove fluoride ions from the wastewater;
Step C: performing first solid-liquid separation;
step D: calcium removal is carried out on the wastewater;
step E: performing second solid-liquid separation;
step F: the pH of the wastewater is regulated back;
step G: performing an evaporation operation on the wastewater to at least partially remove cations and sulfate groups from the wastewater;
the sulfate-containing group includes at least one of: sulfite, hydrogen sulfite, sulfate, hydrogen sulfate, thiosulfate;
the cations include at least one of: sodium ion, potassium ion, lithium ion, ammonium ion.
2. The wastewater treatment method according to claim 1, wherein in step a, the pH of the wastewater is adjusted to 8 to 9.
3. The wastewater treatment method according to claim 1, wherein in step B, fluoride ions in the wastewater are at least partially removed by adding a soluble calcium salt to the wastewater, the molar ratio of calcium ions in the soluble calcium salt to fluoride ions in the wastewater being 3:4 to 1:1;
the soluble calcium salt is selected from at least one of the following: calcium chloride, calcium hydroxide, calcium nitrate, calcium hypochlorite, calcium formate, and calcium acetate.
4. The wastewater treatment method according to claim 1, wherein a flocculant is added to the wastewater in the step C;
The flocculant is selected from at least one of the following: polyacrylamide (PAM), gelatin, starch, polyvinyl alcohol, sodium polyacrylate, poly (sulfonated styrene-maleic acid), chitosan, cationic melamine polymer, tannin, cationic starch, cationic dicyandiamide polymer, polyamine, polydimethyldiallylammonium chloride, polyaluminum chloride (PAC), ferrous sulfate, alum;
and C, taking the weight of the wastewater treated in the step C as a reference, wherein the addition amount of the flocculant is 1-10% of the weight of the wastewater.
5. The method of wastewater treatment according to claim 1, wherein in the step D, calcium is removed from the wastewater by raising the pH of the wastewater to 12 or more and introducing carbonate into the wastewater.
6. The wastewater treatment method according to claim 5, wherein in the step D, a molar ratio of the introduced carbonate to soluble calcium ions contained in the wastewater is 1:1 to 1.5:1.
7. The wastewater treatment method according to claim 1, wherein in the step E, the second solid-liquid separation is performed by a press filtration method.
8. The wastewater treatment method according to claim 1, wherein a carbonate solution is prepared using a part of the separated liquid phase in the step E, and the sodium carbonate solution is transferred to the step D.
9. The wastewater treatment method according to claim 1, wherein in the step F, the pH of the wastewater is adjusted to 6 to 9.
10. The wastewater treatment method according to claim 1, wherein in the step G, the wastewater is subjected to an evaporation operation to obtain evaporated water vapor and a concentrated mother liquor, and the water vapor is condensed to obtain purified water;
optionally refluxing the concentrated mother liquor at least partially to step C.
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