JP4657680B2 - Recovery method of phosphorus component - Google Patents

Description

  The present invention relates to a method useful for recovering phosphorus components that cause eutrophication of various water bodies.

  Phosphorus phosphorus in treated water such as sewage treatment plants, merged septic tanks and industrial wastewater treatment facilities, and treated water such as domestic wastewater causes eutrophication and causes pollution of rivers, lakes and seawater. In particular, it is necessary to suppress eutrophication in closed water areas (for example, closed lakes or bays or sea areas where there is little flow) due to phosphorus components. Moreover, in the fear of depletion of phosphorus resources, recovery of phosphorus from the treated water is also called out.

Known methods for removing or recovering the phosphorus component include removing phosphate ions by adsorbing phosphate ions in an aqueous solution to an adsorbent, or desorbing phosphate ions adsorbed on an adsorbent with an alkali. . For example, Japanese Patent Application Laid-Open No. 54-146455 (Patent Document 1) discloses a method of bringing a phosphate ion-containing aqueous solution adjusted to a pH of about 1.5 to 5.5 into contact with zirconium oxide hydrate, the phosphate ion A method is disclosed in which a zirconium oxide hydrate is brought into contact with an alkaline aqueous solution by contacting with a containing aqueous solution and phosphate ions are eliminated. This document also describes that adsorbed phosphate ions were desorbed by passing a 2% aqueous sodium hydroxide solution. Japanese Patent Laid-Open No. 54-149261 (Patent Document 2) discloses a method using titanium oxide hydrate instead of zirconium oxide hydrate of Patent Document 1. JP-A-56-28638 (Patent Document 3) and JP-A-56-53742 (Patent Document 4) include a hydrate of titanium oxide, zirconium oxide or tin oxide or a mixture thereof and a resin. An adsorbent obtained by curing the mixture is disclosed. Japanese Patent Application Laid-Open No. 56-118734 (Patent Document 5) and Japanese Patent Application Laid-Open No. 57-50543 (Patent Document 6) describe a mixture of a hydrous ferrite of titanium, zirconium or tin or a mixture thereof and a resin. An adsorbent obtained by curing is disclosed. These Patent Documents 5 and 6 also describe that the adsorbed phosphate ions were desorbed by passing a 15% aqueous sodium hydroxide solution. In JP-A-10-296077 (Patent Document 7), at least one kind of a hydrous ferrite of titanium, zirconium or tin and a polymer having a dichloroethylene structure derived from a vinylidene chloride monomer in the molecule are disclosed. An ion adsorbent obtained by curing a composition containing it is disclosed. This document also discloses a method for regenerating an ion adsorbent in which an ion adsorbent having adsorbed ions is treated with an alkaline aqueous solution and then with an acidic aqueous solution. In this document, a liquid to be treated having a phosphate ion concentration of 500 mg / L (pH = 3) is passed through a packed bed of ion adsorbent at a space velocity of SV = 10 hr ⁻¹ , and the adsorbent is then subjected to 7 wt% hydroxylation. It describes that the adsorbent was regenerated by treating with an aqueous sodium solution to desorb phosphate ions, washing the adsorbent with distilled water, and immersing it in a 2 wt% aqueous sulfuric acid solution.

  In these methods, in order to recover the phosphoric acid component from the desorbed liquid, it is necessary to precipitate the phosphate and to separate and remove the precipitate. However, the concentration of the phosphoric acid component in the desorbed solution is too low to precipitate the phosphate. Therefore, in Japanese Patent Laid-Open No. 11-92122 (Patent Document 8), phosphorus is extracted from an acid solution from a phosphorus-containing solid material such as sewage sludge incineration ash, and an insoluble matter is separated. The metal hydrated oxide having exchangeability is brought into contact with the metal hydrated oxide so that phosphorus contained as phosphate ions in the acid solution is adsorbed to the metal hydrated oxide, and then the alkali solution is brought into contact with the metal hydrated oxide. A method is disclosed in which phosphate ions are transferred to the alkali solution side from the metal hydrated oxide, and the alkali solution to which the phosphate ions have transferred is recovered. This document also describes adjusting the pH of the acid solution to 1.5-2. However, in this method, since it is necessary to desorb phosphate ions from the metal hydrated oxide in addition to neutralizing the acid solution with an alkali solution, a large amount of alkali is required.

In Patent Document 8, the alkaline solution brought into contact with the metal hydrated oxide is adjusted to a temperature at which the salt of phosphoric acid and alkali is not precipitated, and the recovered alkaline solution is adjusted to a temperature at which the phosphate is precipitated. It is also disclosed to separate and recover the precipitated phosphate by lowering. Specifically, the column is filled with an adsorbent, and phosphoric acid-containing sulfuric acid having a pH of 2.0 is passed at a space velocity of 0.7 / hr to remove 99% phosphoric acid, and then 1% water at 35 ° C. Sodium oxide solution is passed through at a space velocity of 6 / hr to recover phosphorus at a recovery rate of 95%, and the recovered sodium hydroxide solution is cooled to 15 ° C. to precipitate trisodium phosphate hydrate crystals. It has been described that. However, since the phosphate concentration in the alkaline solution is low, it is difficult to increase the phosphate recovery even if the alkaline solution is cooled. In addition, a large amount of energy is required to cool a large amount of the alkaline solution. Patent Document 8 further describes that a metal hydroxide that generates an insoluble phosphate is added to the recovered alkaline solution to precipitate the phosphate, and the precipitated phosphate is separated and recovered. Yes. However, the use of insoluble phosphate is limited, and the phosphorus component cannot be effectively reused.
JP 54-146455 A (claims, page 3, lower left column, Example 2) JP 54-149261 A (Claims) JP-A-56-28638 (Claims) JP-A-56-53742 (Claims) JP-A-56-118734 (claims, Example 8) JP-A-57-50543 (Claims, Example 9) JP-A-10-296077 (Claims, Test Example 2) JP-A-11-92122 (Claims, paragraph numbers [0026] to [0028])

  Accordingly, an object of the present invention is to provide a useful method for efficiently recovering a phosphorus component even in water to be treated having a low concentration of the phosphorus component.

  Another object of the present invention is to provide a method capable of reducing the amount of alkali used and recovering the phosphorus component efficiently in energy while suppressing corrosion of the apparatus.

  Still another object of the present invention is to provide a method for recovering a phosphoric acid component for effectively using a phosphorus component without producing an insoluble phosphate.

  In the present inventors, the solubility of soluble phosphates such as sodium phosphate is highly dependent on the alkali concentration, whereas relatively high amounts of phosphate are soluble in water at low alkali concentrations. Focusing on the fact that the solubility of phosphate drops to about 1% by weight or less at a temperature of 25 ° C. when the alkali concentration exceeds 15% by weight, intensive studies were conducted in order to achieve the above problems. As a result, the liquid to be treated containing phosphate ions at a low concentration was adsorbed with an adsorbent, and the adsorbent was treated with a low-concentration alkaline aqueous solution (such as an aqueous sodium hydroxide solution) to desorb phosphate ions. Later, when the aqueous solution containing the generated soluble phosphate is concentrated at a low temperature under reduced pressure until a specific alkali concentration is reached, highly pure phosphate is efficiently precipitated while suppressing corrosion of the concentrator. And the present invention was completed.

  That is, in the phosphorus component recovery method of the present invention, an aqueous solution containing a phosphate is concentrated under reduced pressure to precipitate the phosphate, and solid-liquid separation is performed to recover the phosphate. In this method, an aqueous solution containing a phosphate (for example, 0.1 to 20% by weight alkaline aqueous solution) is concentrated until the alkali concentration becomes 8 to 30% by weight (for example, 10 to 30% by weight). Good. The phosphate may be a salt of phosphoric acid and an alkali metal, and an aqueous solution having a phosphorus conversion concentration of 100 to 5000 mg / L may be concentrated at a concentration factor of 1.5 to 100 times. Concentration may be performed at a temperature of 20 to 70 ° C. (for example, 30 to 60 ° C.) and a pressure of 1 to 25 kPa. The precipitation of phosphate may be performed by adjusting the alkali concentration accompanying the concentration, or by adjusting the temperature of the concentrated solution together with the adjustment of the concentration or independently of the adjustment of the concentration. For example, the phosphate may be precipitated by lowering the temperature of the concentrate.

  When the phosphorus component is recovered from the water to be treated containing phosphate ions at a low concentration, it is usually carried out as follows. That is, by subjecting the liquid to be treated containing phosphate ions to an adsorption treatment with an adsorbent, desorbing the adsorbent to which phosphate ions have been adsorbed with an alkaline aqueous solution, and concentrating the alkaline aqueous solution containing the produced phosphate Phosphate may be precipitated. Examples of the adsorbent include various adsorbents capable of adsorbing a phosphorus component, for example, an adsorbent composed of at least one hydrated ferrite salt selected from titanium, zirconium, and tin (zirconium water). An adsorbent composed of a mixture of a hydrated ferrite or a hydrated ferrite of zirconium and at least one selected from hydrated zirconium oxide and hydrated iron oxide may also be used. Moreover, you may use sodium hydroxide aqueous solution as alkaline aqueous solution. Note that the separated liquid separated from the phosphate by solid-liquid separation may be reused for desorption of phosphoric acid from the adsorbent.

  More specifically, the phosphate component in the liquid to be treated is adsorbed with an adsorbent, and the adsorbed phosphate component is an alkali metal having a concentration of 0.1 to 20% by weight (for example, 0.1 to 10% by weight). Desorption with an aqueous solution of hydroxide, and an aqueous solution containing an alkali metal phosphate produced by desorption under reduced pressure, the concentration of alkali metal hydroxide is 8 to 30% by weight (for example, 10 to 30% by weight) Then, the concentration of the phosphoric acid component in the liquid to be treated is separated by separating the precipitated alkali metal phosphate by solid-liquid separation. It can be recovered efficiently.

  In the present invention, since the aqueous solution containing a phosphate is concentrated under reduced pressure, the phosphorus component can be efficiently recovered even if the water to be treated has a low concentration of the phosphorus component. Moreover, since it carries out under pressure reduction, it can concentrate at low temperature and can also suppress the corrosion of an apparatus (for example, apparatus which can contact the said concentrate, especially concentration apparatus). Also, phosphate ions can be desorbed from the adsorbent with a low-concentration alkaline aqueous solution and concentrated to a specific alkali concentration, so that the amount of alkali used can be reduced and the phosphorus component can be recovered efficiently and efficiently. it can. Furthermore, since alkali metals can be used instead of alkaline earth metals that generate insoluble phosphates as alkalis, phosphates (phosphorus components) can be recovered without generating insoluble phosphates, which are soluble Therefore, it can be effectively reused as a phosphorus component.

  In the present invention, even when the concentration of phosphate is low, phosphate can be efficiently recovered from an aqueous solution containing phosphate (or an aqueous solution in which phosphate is dissolved) at a high recovery rate. Therefore, the origin of the aqueous solution is not particularly limited, and may be wastewater containing phosphate, and the aqueous solution containing phosphate may be acidic or alkaline. In the case where the pH of the aqueous solution is alkaline, the amount of phosphorus adsorbed may be increased by adding an acid to make it neutral to acidic and then adsorbing with an adsorbent. In a preferred embodiment, the liquid to be treated (phosphate solution) containing phosphoric acid (phosphate ions) is adsorbed with an adsorbent, the adsorbent that adsorbs phosphate ions is desorbed with an aqueous alkaline solution, and the phosphate ions are phosphorylated. In many cases, an aqueous solution containing an acid salt is concentrated. In this method, phosphoric acid can be efficiently recovered in the form of a phosphate from an aqueous solution containing an extremely low concentration of phosphate ions.

[Processed liquid and adsorption treatment]
In the adsorption treatment step, a liquid to be treated containing a phosphate component (particularly, phosphate ions present in the form of ions) is adsorbed with an adsorbent, and the phosphate component is held in a form concentrated in the adsorbent. The phosphoric acid component may be a variety of ionically dissociated phosphoric acid (phosphate phosphorous), such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, and the like.

  The treated liquid is not particularly limited as long as it is treated water containing a phosphoric acid component (phosphate phosphorus such as phosphate ion). For example, a sewage treatment plant, a sewerage treatment plant, a septic tank (a combined septic tank is used). In many cases, treated water in facilities such as factory wastewater treatment facilities and domestic wastewater are used.

  The concentration of the phosphoric acid component (phosphate ion) in the liquid to be treated may be, for example, about 0.1 to 100 mg / L in terms of phosphorus on a weight basis, and usually 0.1 to 50 mg / L, preferably Is about 0.5 to 30 mg / L, more preferably about 1 to 20 mg / L. Note that the liquid to be treated may be filtered prior to the adsorption treatment in order to remove impurities and impurities.

As the adsorbent, various adsorbents capable of adsorbing a phosphate component (phosphate ion), such as activated carbon, alumina, clay mineral, titanium oxide, zirconium oxide, tin oxide, ion exchange resin (carboxyl group, sulfonic acid group) And anion exchange resins and cation exchange resins having a fluoroalkylsulfonic acid group. In order to increase the adsorption efficiency (or recovery efficiency) of the phosphate component, the adsorbent is at least a hydrated oxide of a specific metal [at least one component selected from tetravalent metals such as titanium, zirconium and tin. It is advantageous that it is composed of at least a hydrated ferrite (such as a double salt) of the specific metal. This adsorbent may be composed of (a) the hydrated ferrite of the specific metal alone, (b) the hydrated ferrite of the specific metal (such as a double salt) and the specific metal ( A mixture with a hydrated oxide of at least one metal selected from titanium, zirconium, tin) and iron, (c) a hydrated ferrite (such as a double salt) of the specific metal, and hydration of iron It is advantageously composed of a mixture with oxides. Further, the adsorbent may be an adsorbent containing at least zirconium (such as hydrated zirconium oxide) as a main component. Among the adsorbents, zirconium ferrite adsorbent, for example, zirconium hydrated ferrite, or a mixture of zirconium hydrated ferrite and at least one selected from hydrated zirconium oxide and hydrated iron oxide Has a high adsorption capacity for the phosphate component. Such an adsorbent can be obtained as “Seven Tol ^™ -P” from Nippon Enviro Chemicals.

  For the method for producing these adsorbents, the above-mentioned Patent Documents 2 to 7 can be referred to. For example, (a) the hydrated ferrite of the specific metal (hereinafter sometimes simply referred to as a double salt), or (b) the hydrated ferrite of the specific metal (double salt) and the specific metal The mixture with the hydrated oxide of at least one metal selected from (titanium, zirconium, tin) and iron can be produced, for example, by the following method.

  First, a ferrous salt corresponding to about 0.2 to 11 times moles of a specific metal ion in a solution (solution containing a specific metal ion) in which at least one specific metal salt is dissolved. After the addition, alkali is added to maintain the pH of the solution at about 6 or higher (preferably about 7-12). Thereafter, if necessary, the temperature of the solution is adjusted to about 30 to 100 ° C., and then an oxidizing component is introduced to form a hydrous ferrite precipitate. For example, by introducing an oxidizing gas (air, oxygen gas, ozone, etc.) or adding an oxidizing agent (hydrogen peroxide, sodium hypochlorite, potassium hypochlorite, etc.) It can be carried out.

  The resulting precipitate is filtered off, washed with water and dried to obtain the double salt or mixture. Drying can be performed by air drying or heating, and the moisture content after drying is preferably about 6 to 30% by weight.

  More specifically, (c) a mixture of the hydrated ferrite (such as a double salt) of the specific metal and the hydrated oxide of iron in the above method is at least one specific metal salt. Can be prepared in the same manner as in the above method, except that a ferrous salt corresponding to about 2 to 11 times mol of the specific metal ion in the solution is added to the solution containing the specific metal ion. .

Examples of the hydrated oxide of iron include hydrates of iron oxides such as FeO, Fe ₂ O ₃ and Fe ₃ O ₄ (monohydrate, dihydrate, trihydrate, tetrahydrate, etc.) Say. In the mixture (c) composed of hydrous ferrite (double salt) and iron hydrated oxide, the content of hydrous ferrite (double salt) is 24 to 100% by weight, preferably 50 to 99%. It is about wt%.

  (B1) The mixture of at least one of the hydrated ferrites of the specific metal and at least one of the hydrated oxides of the specific metal is a solution in which at least one specific metal salt is dissolved (specific A solution containing metal ions) can be prepared in the same manner as described above except that the ferrous salt is added in a range of about 0.2 times mol or more and less than about 2 times mol to the specific metal ions in the solution. . In the mixture (b1), the content of hydrous ferrite is 20 to 100% by weight, preferably about 50 to 99% by weight.

  Examples of the specific metal salt include titanium tetrachloride, titanium sulfate, titanyl sulfate, zirconium oxychloride, zirconium tetrachloride, zirconium nitrate, zirconium sulfate, zirconium acetate, tin tetrachloride, tin nitrate, and tin sulfate. These metal salts may be hydrated salts. These metal salts are usually used in the form of a solution of about 0.05 to 2 mol per liter.

  Examples of the ferrous salt include ferrous sulfate, ferrous nitrate, and ferrous chloride. These iron salts may also be hydrated salts. These ferrous salts are usually added in the form of a solid, but may be added in the form of a solution.

  Examples of the alkali include alkali metal compounds (alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate), alkaline earth metal compounds (such as calcium hydroxide), and ammonia. Is mentioned. These alkalis are usually used in the form of an aqueous solution of about 5 to 20% by weight.

  The blowing time of the oxidizing gas can be selected according to the kind of the oxidizing gas, and is usually about 1 to 3 hours.

The hydrated ferrite (double salt) of the specific metal can be represented by, for example, the formula MFe ₂ (OH) ₃ (wherein M represents titanium, zirconium or tin). The hydrated oxide of the specific metal M is represented by the formula MO ₂ · nH ₂ O (wherein M represents titanium, zirconium or tin, and n is 0.5 to 2), specifically, For example, MO ₂ · H ₂ O (MO (OH) ₂ ), MO ₂ · 2H ₂ O (M (OH) ₄ ), MO ₂ · nH ₂ O (wherein n is 1.5 to 2). ) And the like.

The shape of the hydrated ferrite of the specific metal or the mixture of this ferrite and the metal hydrated oxide is not particularly limited, but from the viewpoint of the mixing operation with the resin for granulation and the adsorption performance, Usually, it is a granular material. The average particle size of the powder is usually 1 to 500 μm, preferably 2 to 250 μm, and more preferably about 3 to 100 μm. The hydrated ferrite of the specific metal or a mixture of this ferrite and a metal hydrated oxide may be used as an adsorbent as it is, and is molded or granulated using a binder resin, and the molded adsorbent May be used as As binder resin, thermoplastic resin (vinyl chloride resin, vinylidene chloride resin, fluorine resin, acrylic resin, styrene resin, polyester resin, polyamide resin, polyethersulfone resin, etc.), thermosetting resin (Epoxy resin, vinyl ester resin, urethane resin, phenol resin, etc.) can be used. Preferred binder resins include polymers having a dichloroethylene structure derived from vinylidene chloride monomers in the molecule, such as vinylidene chloride homopolymers and copolymers of vinylidene chloride and other polymerizable monomers. It is done. The content of the dichloroethylene structure [—C (Cl) ₂ —CH ₂ —] derived from vinylidene chloride constituting the vinylidene chloride copolymer is usually 30 to 99% by weight, preferably 50 to 98% by weight in terms of monomer. %, More preferably 60 to 95% by weight.

  The ratio of the binder resin is 5 to 50 parts by weight, preferably 7 to 45 parts by weight, and more preferably about 10 to 30 parts by weight with respect to 100 parts by weight of the adsorbent. The binder resin may contain additives such as stabilizers (antioxidants, ultraviolet absorbers, etc.), auxiliary agents for improving moldability, plasticizers, antistatic agents and the like. The polymer may be used in the form of a solution or solid, and may be used in the form of a dispersion or suspension (emulsion, suspension, slurry, etc.).

  Molding or granulation is performed by a conventional method using a hydrated ferrite of a specific metal or a mixture of this ferrite and a metal hydrated oxide, and a binder resin, for example, a mixture of both. A method of crushing and sizing, a method of extruding a mixture of both into a cylindrical shape, cutting the cured cylindrical adsorbent to an appropriate length to obtain a pellet-shaped adsorbent, and further using this columnar molded product as a malmerizer Using a granulated machine (such as a rotary tumbling granulator or a centrifugal fluidized coating granulator) with a granulated or spherical molding method, etc. A mixture with a metal hydrated oxide can be coated and granulated with a binder resin to obtain a molded adsorbent (such as a spherical adsorbent). The average particle size of the pulverized product is, for example, about 0.1 to 15 mm, preferably about 0.2 to 10 mm, and more preferably about 0.3 to 5 mm.

  In the coating granulation, a hydrated ferrite of a specific metal, a small particle of this ferrite and a metal hydrated oxide, or other small particles may be used as a nucleus. The material used as the core is not particularly limited, but water-insoluble materials such as clay minerals, metal oxides such as zeolite, silica, and alumina, silicates, carbon materials (activated carbon, graphite, carbon black, etc.), resin moldings, etc. Is mentioned. In particular, when regenerating repeatedly, a substance having high chemical resistance such as alumina, zirconium oxide, zirconium silicate, iron oxide and activated carbon is preferable. The particle size of the nuclear material is usually 0.1 to 0.9 times, preferably 0.2 to 0.8 times, and most preferably 0.3 to 0.7 times the particle size of the shaped adsorbent. Degree. The nucleus is not necessarily spherical, and may be cylindrical, cubic, or crushed.

  The molded adsorbent prepared in this way (for example, a spherical ion adsorbent) has a high packing property in a column or the like, is less likely to be clogged, and can be easily washed with water. The average particle diameter of the shaped adsorbent is usually 0.1 to 15 mm, preferably 0.2 to 10 mm, and more preferably 0.3 to 5 mm.

  Such an adsorbent has a high ion exchange capacity due to a large number of hydroxyl groups present on the surface, and acts as an anion exchanger in an acidic solution and as a cation exchanger in an alkaline solution. That is, the phosphate component (phosphate ion) in the liquid to be treated is selectively adsorbed in the acidic region, and the phosphate component is efficiently desorbed in the alkaline region. In addition, the adsorption | suction order with respect to the anion of the adsorption agent (the said zirconium ferrite adsorption agent etc.) comprised with the said hydrated zirconium oxide is as follows, and has a high adsorption capacity with respect to phosphate ion.

PO ₄ ³⁻ > F ⁻ > SO ₄ ²⁻ > Br ⁻ > NO ₂ ⁻ > Cl ⁻ > NO ₃ ⁻
In order to efficiently adsorb phosphoric acid components (phosphate ions) using an adsorbent having such characteristics, it is advantageous to adsorb an acidic liquid to be treated. The pH of the liquid to be treated is in an acidic region, for example, 1 to 7, preferably 1.5 to 5, and more preferably about 2 to 5 (for example, 2 to 4). In addition, pH adjustment of a to-be-processed liquid can be performed using an inorganic acid (hydrochloric acid, a sulfuric acid, nitric acid etc.) or an organic acid, and an inorganic acid is usually used in many cases.

The adsorption of the phosphoric acid component may be performed by bringing the liquid to be treated into contact with the adsorbent. For example, (1) a method of adding an adsorbent to the liquid to be treated, (2) a packed bed filled with the adsorbent (3) Moving bed method in which the adsorbent and the liquid to be treated are brought into countercurrent contact in the tower filled with the adsorbent, and the treated water is discharged from the upper part of the tower. (4) The adsorbent The liquid to be treated is supplied to the packed bed filled with, and the liquid to be treated is adsorbed by a method such as a fluidized bed method in which both are brought into contact with each other while forming a fluidized bed and the treated water flows out in an overflow format. Also good. Moreover, any of a batch type, a semibatch type, and a continuous type can be adopted for the adsorption treatment. Usually, the liquid to be treated is often passed through a packed bed filled with an adsorbent. The space velocity SV of the liquid to be treated with respect to the adsorbent layer may be about ^{1 to} 50 hr ⁻¹ , preferably 1.5 to 30 hr ⁻¹ and 2 to 20 hr ⁻¹ (for example, 2 to 15 hr ⁻¹ ).

  By such adsorption treatment, the concentration of the phosphoric acid component in the treatment liquid can be greatly reduced. For example, a phosphoric acid component can be adsorbed with a high removal rate or adsorption rate (for example, a removal rate of about 70 to 100%, particularly about 75 to 95%), and the concentration of the phosphoric acid component in the treatment liquid is reduced to 1 mg / L or less. it can.

  Note that the adsorbent subjected to the adsorption treatment may be washed with water or acidic water (such as dilute sulfuric acid water), if necessary, and used for the desorption step.

[Desorption treatment]
In order to desorb or elute the phosphoric acid component from the adsorbent, an alkaline aqueous solution (desorbed solution) is used. Examples of the alkali include inorganic bases (alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkali metal carbonates such as potassium carbonate, sodium carbonate and sodium bicarbonate, alkalis such as calcium hydroxide and magnesium hydroxide). Examples thereof include earth metal hydroxides, alkaline earth metal carbonates such as calcium carbonate and calcium hydrogen carbonate, ammonia or aqueous ammonia, and organic bases (eg, aliphatic amines such as triethylamine). These alkalis can be used alone or in combination of two or more. A preferable aqueous alkali solution is an aqueous solution of an alkali metal hydroxide (for example, an aqueous sodium hydroxide solution).

  The alkali concentration in the aqueous alkali solution is, for example, 0.1 to 20% by weight (for example, 0.2 to 15% by weight) as long as the desorption efficiency of the phosphoric acid component and the precipitation efficiency after concentration are not impaired. Preferably, it can be selected from the range of about 0.5 to 10% by weight. The alkali concentration is usually 0.1 to 10% by weight (for example, 0.5 to 8% by weight), preferably 0.5 to 7% by weight (for example, 1 to 6% by weight), and more preferably 0.5%. It is about -6 wt% (for example, 2-5 wt%). When an alkaline solution having such a concentration is used, the phosphoric acid component adsorbed on the adsorbent can be desorbed with a high desorption rate (for example, a desorption rate of about 90 to 100%).

  The amount of the desorbing solution (alkaline aqueous solution) used is not particularly limited as long as it does not impair the concentrating property. For example, it is selected from a range of about 1 to 20 times the volume of the adsorbent with respect to 1 It is usually 1 to 15 times (for example, 1 to 10 times), preferably 1.5 to 7 times, and more preferably about 2 to 5 times. In order to desorb the adsorbed component from the adsorbent, various methods that allow the desorbed liquid (alkaline aqueous solution) and the adsorbent to come into contact with each other, for example, (1) Adsorbed to the liquid to be treated in the same manner as the adsorption process. Methods such as (2) fixed bed method, (3) moving bed method, and (4) fluidized bed method can be employed. The desorption treatment may be any of batch, semi-batch and continuous methods. When desorbing adsorbed components from the adsorbent by batch operation, adsorbent and desorbed liquid (alkaline aqueous solution) are mixed for an appropriate period of time (for example, 10 minutes to 24 hours) and brought into contact with each other. Alternatively, the adsorbent and the aqueous solution containing the phosphate may be separated by solid-liquid separation.

In many cases, an alkaline aqueous solution is passed through a packed bed (packed tower) filled with an adsorbent adsorbing a phosphoric acid component. The space velocity SV of the alkaline aqueous solution with respect to the adsorbent layer may be about ^{1 to} 50 hr ⁻¹ , preferably 1.5 to 30 hr ⁻¹ , 2 to 20 hr ⁻¹ (for example, 2 to 15 hr ⁻¹ ). The alkaline aqueous solution may be passed through the packed tower in one pass or may be circulated. In the case of circulating liquid, the processing time can be shortened by flowing at a high flow rate (for example, SV = about 5 to 50 hr ⁻¹ ).

  In this desorption operation, the desorption process can usually be sufficiently desorbed by a single desorption process, but the desorption process may be performed multiple times with an alkaline solution. Alkaline aqueous solutions having different alkali concentrations may be used. For example, an aqueous solution with a high alkali concentration may be used in the early stage of the desorption treatment, and the adsorbent may be desorbed by using an aqueous solution with a low alkali concentration in the later stage. An aqueous solution having a low alkali concentration may be used, and an aqueous solution having a high alkali concentration may be used later in the desorption treatment. Further, the desorption treatment may be performed under heating or heating. For example, a heated alkaline solution may be brought into contact with the adsorbent.

  The adsorbent can be regenerated by such desorption treatment. In the regeneration of the adsorbent, if necessary, the adsorbent may be washed and the adsorbent may be acid-treated. As the acid, for example, an inorganic acid (hydrochloric acid, sulfuric acid, etc.) or an organic acid can be used, and the concentration of the aqueous solution of the acid is, for example, about 0.1 to 5% by weight (for example, 0.1 to 2.5% by weight). It may be.

[Concentration treatment]
Efficient precipitation of phosphate by evaporating water and concentrating an aqueous solution (for example, an alkaline aqueous solution) containing a phosphate (for example, an alkali metal phosphate produced by the elimination) under reduced pressure. Can do. The concentration of the phosphate in the aqueous solution subjected to the concentration treatment is 100 to 5000 mg / L, preferably 200 to 4000 mg / L, more preferably 300 to 3000 mg / L (for example, 500 to 3000 mg / L) in terms of phosphorus. L) degree may be sufficient. When the adsorption and desorption of the phosphoric acid component by the adsorbent is used, phosphoric acid at a concentration of about 500 to 5000 mg / L, particularly 1000 to 4000 mg / L (for example, 1500 to 3000 mg / L) in terms of phosphorus. An aqueous solution containing a salt can be easily obtained.

  Concentration of the aqueous solution may be carried out by removing water under normal pressure. However, if it is concentrated under normal pressure using a normal evaporator, it takes a long time or the aqueous solution is heated to a high temperature (for example, 80 to 100 ° C.). Needs to be heated and requires a lot of energy. Further, when concentrated by heating to a high temperature, as the alkali concentration increases, the devices that come into contact with the concentrated liquid (concentrators, solid-liquid separators, lines and units associated with these devices, etc.) are likely to be corroded. Moreover, in order to prevent corrosion, it is necessary to make the said apparatus with an expensive material with high corrosion resistance. Therefore, the concentration of the aqueous solution is preferably performed under reduced pressure in order to remove moisture. In particular, it is preferable to concentrate at a low temperature. When such a concentration method is used, corrosion can be prevented even if the device is made of inexpensive stainless steel (SUS).

  Concentration is, for example, at a pressure of 1 to 25 kPa (eg 1 to 23 kPa), preferably 2 to 22 kPa (eg 2 to 20 kPa), more preferably 3 to 18 kPa (eg 3 to 15 kPa). The concentration temperature can be selected from a temperature at which corrosion can be suppressed according to the material of the apparatus, for example, a temperature of about 20 to 70 ° C., and is usually 25 to 65 ° C., preferably 30 to 60 ° C., more preferably 35 to 58 ° C. It may be about 40 ° C to 55 ° C.

  The concentration ratio (the amount of liquid before concentration / the amount of liquid after concentration) can be selected from a range of about 1.5 to 100 times (for example, 2 to 90 times) depending on the phosphate concentration. It may be about 20 times, preferably about 2 to 10 times (for example, 2 to 5 times).

  The concentration of the phosphate in the concentrate is, for example, about 1000 to 20000 mg / L, preferably 2000 to 17000 mg / L, more preferably 3000 to 15000 mg / L (for example, 5000 to 12000 mg / L) in terms of phosphorus. May be.

  In concentration of such an aqueous solution, it is advantageous to concentrate until the alkali concentration (for example, the concentration of alkali metal hydroxide) reaches a specific concentration. FIG. 1 is a graph showing the relationship between the sodium phosphate concentration and the sodium hydroxide concentration in an aqueous solution at a temperature of 25 ° C. As is apparent from this graph, when the sodium hydroxide concentration is 5% by weight, the solubility of sodium phosphate is about 6% by weight, and when the sodium hydroxide concentration is concentrated to 10% by weight, Solubility is about 3% by weight, when sodium hydroxide concentration is concentrated to 15% by weight, sodium phosphate solubility is 1% by weight or less, and when sodium hydroxide concentration is concentrated to 17-18% by weight, Sodium phosphate is almost precipitated. Therefore, the precipitation amount of phosphate can be easily controlled by concentrating the aqueous solution and adjusting the degree of concentration (alkali concentration in the concentrated solution).

  As is clear from the relationship shown in FIG. 1 above, in the concentration of the aqueous solution, the alkali concentration (for example, the concentration of alkali metal hydroxide) is 8 to 30 wt% (for example, 10 to 30 wt%), preferably 10 to 10 wt%. It is advantageous to concentrate to 28% by weight (for example 10 to 25% by weight), more preferably 10 to 20% by weight (for example 12 to 18% by weight), especially 13 to 17% by weight. In general, the larger the difference in alkali concentration before and after the concentration, the better. However, when the alkali is sodium hydroxide, a large phosphate solubility difference does not occur even if the alkali concentration exceeds 16% by weight. Therefore, the difference in alkali concentration before and after concentration is about 1 to 20% by weight, preferably about 2 to 17% by weight, more preferably about 3 to 15% by weight (for example, 5 to 12% by weight). It may be about 10% by weight.

  The concentrator is usually connected to a depressurization or vacuum apparatus (or unit) or provided with a depressurization or vacuum unit in order to evaporate the water of the desorbed liquid by depressurization. The concentration apparatus may be a batch apparatus, a semi-batch apparatus, or a continuous apparatus (for example, a flash distillation apparatus). The concentrator may be heated if necessary, and water may be removed under reduced pressure while stirring. In order to efficiently concentrate the desorbed liquid while preventing local heating, it is advantageous to use a rotatable hollow heat transfer coil (double tubular coil). That is, as a concentrating device, a container body that is connected to a decompression means and can be decompressed and can be heated, and is rotatably disposed in the container body, and the heating medium supply pipe and the heating medium supply pipe are the same. An apparatus including a double tubular rotary shaft provided with a drain discharge pipe arranged in a core shape, and heating means capable of heating the heating container as needed can be used. Using such a device, when the heat transfer coil is rotated in the desorbed liquid and concentrated under reduced pressure through a heat medium (steam, etc.) into the hollow portion of the heat transfer coil, the liquid boundary film on the coil surface is accompanied by rotation. Therefore, there is no adhesion of scale to the coil surface, and local heating and phosphate modification can be prevented. Moreover, concentration at a low temperature (for example, about 35 to 55 ° C.) is possible. Such a device is disclosed in Japanese Patent Publication No. 6-47041, and is commercially available as “Dynamic Conductor Vacuum Concentrator” from G-Tech Co., Ltd.

  By such concentration, phosphate can be efficiently precipitated or crystallized even at room temperature (for example, about 15 to 25 ° C.). Therefore, the precipitation of phosphate may be performed at the concentration temperature, or the phosphate (such as alkali metal phosphate) may be precipitated or crystallized by lowering the temperature to a temperature lower than the concentration temperature (concentration operation temperature). Good. When the temperature of the concentrate is lowered (or the concentrate is cooled), the phosphate can be precipitated efficiently without increasing the concentration factor, and the crystal form of the phosphate can be controlled according to the precipitation temperature conditions. Precipitates (crystals) with high properties (or filterability) can be generated. Moreover, in order to control the crystal shape of the phosphate, the concentrated solution may be kept warm at a predetermined temperature if necessary. For example, a phosphate (such as sodium phosphate) may be precipitated as a sherbet, a needle, or a mixture thereof depending on the crystallization conditions. More specifically, when the precipitation temperature from the concentration temperature is low, the phosphate precipitates as a fine sherbet, and when the precipitation temperature is room temperature (for example, about 15 to 25 ° C.), the phosphate is a sherbet. When the shape and needle crystals are mixed and precipitated, and the precipitation temperature is high, the phosphate may be precipitated as needle crystals. In addition, compared with a sherbet-like crystal, the needle-like crystal has good liquid drainage and is easy to separate into solid and liquid. Therefore, when the crystallization temperature is increased and the temperature is maintained (for example, the temperature is maintained at about 25 to 35 ° C.), acicular crystals can be efficiently precipitated.

  The precipitation temperature is, for example, about 0 to 60 ° C., preferably about 5 to 50 ° C., more preferably about 10 to 40 ° C. (for example, 15 to 30 ° C.), and usually about room temperature (15 to 25 ° C.). There are many.

  In order to increase the precipitation efficiency of phosphate, both the concentration ratio and the temperature (or cooling temperature) of the concentrate may be controlled. For example, it may be concentrated at a relatively high temperature (for example, 40 to 50 ° C.) to increase the concentration factor, and the concentrate may be held at a relatively high temperature (for example, 25 to 35 ° C.) to precipitate phosphate. It is also possible to cool the concentrated liquid with an increased concentration ratio to a low temperature (for example, about 10 to 20 ° C.) to precipitate the phosphate.

  Concentration and precipitation may be performed in the same apparatus, or may be performed in different apparatuses. For example, the concentration rate may be increased, and phosphate may be precipitated in the concentrator, or the concentrated solution may be transferred to another tank (precipitation tank), and phosphate may be precipitated in the precipitation tank.

  By such a concentration treatment, the phosphoric acid component contained in the concentrated liquid can be recovered at a recovery rate of about 60% or more (60 to 100%), particularly about 80 to 98% (for example, 85 to 95%) as a phosphate. .

[Solid-liquid separation and phosphate recovery]
The precipitated phosphate (such as an alkali metal phosphate) can be recovered by separation by a conventional solid-liquid separation, for example, filtration or centrifugation. By this solid-liquid separation, the phosphoric acid component in the liquid to be treated is separated at a high rate (for example, 80% or more) as a phosphate crystallized product (for example, a high-purity phosphate crystal having a purity of 90% or more). Can be recovered. For example, when the alkali is sodium, the phosphate deposit may be in the form of either sodium hydrogen phosphate or sodium phosphate, and can usually be recovered in the form of sodium phosphate Na ₃ PO ₄ . Further, phosphate is often recovered as a hydrate, for example, trisodium phosphate dodecahydrate.

  The separated and recovered phosphate deposits may be washed with a washing liquid (water, aqueous alkali solution, etc.) or dried as necessary.

  The liquid phase (separated liquid or alkaline solution) produced by solid-liquid separation of the concentrated liquid has a high alkali concentration. Therefore, this separation liquid can be reused as an alkaline aqueous solution for desorbing the phosphoric acid component from the adsorbent that has adsorbed the phosphoric acid component. In many cases, the separation liquid is diluted to an appropriate concentration and used for desorption. The separation liquid may contain a small amount (for example, about 2 to 600 mg / L, particularly about 10 to 500 mg / L) of phosphate ions. When such a separation liquid is used for desorption of the phosphoric acid component from the adsorbent, the desorption efficiency of the phosphoric acid component may decrease. Therefore, after the phosphoric acid component is desorbed from the adsorbent using the separation liquid (or diluted separation liquid), it is further removed from the adsorbent using a fresh alkaline aqueous solution (an aqueous solution substantially free of phosphoric acid). When the phosphoric acid component is eliminated, the elimination efficiency of the phosphoric acid component can be improved.

  The present invention removes phosphorous components from various treated water containing phosphoric acid components, for example, sewage treatment plants, treated septic tanks, treated water from factory wastewater treatment facilities, and domestic wastewater, and can be recovered at a high recovery rate. Therefore, it is useful for suppressing eutrophication of rivers, lakes and seawater (especially closed water areas), and is useful for recycling phosphorus. For example, the recovered phosphate can be used not only as a fertilizer but also widely reused as a raw material for the production of phosphorus compounds.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[Example 1]
The reagent sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd., first grade) was dissolved in tap water to prepare a 5 wt% sodium hydroxide solution. To this solution, sodium dihydrogen phosphate dihydrate (manufactured by Wako Pure Chemical Industries, Ltd., first grade) is added, and phosphate ions are contained at a concentration of 3,000 mg-P / L in terms of phosphorus. A sodium solution was prepared.

  10 L of this sodium hydroxide aqueous solution (total phosphorus amount is 30 g) was concentrated with a vacuum low-temperature concentrator (manufactured by G-Tech Co., Ltd .: heat transfer tube rotating dynamic conductor). This concentrator supplies heated steam to a heat transfer coil immersed in the liquid to be concentrated and heats the liquid to be concentrated while rotating the heat transfer coil, so that the surface of the heat transfer coil (heat transfer tube) is centrifuged. When the force acts and the liquid boundary film on the heat transfer surface is peeled and updated, the maturation coefficient is remarkably improved, the temperature of the film is lowered, and scale adhesion can be prevented. The material of the container body of the concentrator is made of stainless steel.

  The inside of this apparatus is depressurized to 10 kPa, and then 10 L of the sodium hydroxide aqueous solution (containing 30 g of total phosphorus) is charged into the apparatus, and heated by flowing steam into the heat transfer coil at a temperature of about 45 ° C. The water started to evaporate. While maintaining the pressure constant at around 10 kPa, the evaporation operation is continued at a water evaporation rate of 0.5 L / min, and the solution is concentrated until the sodium hydroxide concentration reaches 15% by weight, that is, until the liquid volume in the apparatus becomes 3.3 L. (3-fold concentration). The liquid temperature of the concentrate was about 50 ° C. The evaporated water was cooled by a condenser and recovered as condensed water (first liquid).

  The introduction of steam was stopped, the pressure of the apparatus was returned to atmospheric pressure, and the concentrated liquid (concentrated liquid) was extracted to the outside. There was no scale adhesion on the surface of the heat transfer tube of the device or the inner wall of the tank.

  When the concentrate was kept at room temperature (25 ° C.), phosphate crystals were precipitated. The phosphate crystals and the liquid phase (separated liquid, second liquid) were separated using a filter. The phosphorus concentration in the first liquid and the second liquid was measured by ion chromatography. As a result, the first liquid was only 0.1 mg-P / L, and the second liquid was 510 mg-P / L. The total amount of phosphorus in this second liquid was 1.5 g, and 28.5 g of phosphorus could be recovered as phosphate crystals (recovery rate 95%).

[Example 2]
Phosphate crystals were obtained in the same manner as in Example 1 except that the concentration ratio was doubled (sodium hydroxide concentration: 10% by weight). The recovery rate of phosphorus was 93%.

[Example 3]
In the same manner as in Example 1, phosphate crystals were obtained in the same manner as in Example 1, except that the concentration ratio was 4 times (sodium hydroxide concentration: 20% by weight). The recovery rate of phosphorus was 97%. Although precipitation of phosphate crystals was observed during the concentration operation, the concentration operation could be completed without any trouble even if the concentration was continued as it was, and a concentrated solution could be obtained.

[Example 4]
(1) Preparation of phosphate-containing solution Waste water from a septic tank installed in a general household is packed with a zirconium ferrite-based phosphorus adsorbent ("Seventor ^TM- P" manufactured by Nippon Envirochemicals Co., Ltd.) And phosphate ions were adsorbed. It was subjected to adsorption treatment in 10 septic tanks, and the phosphorus adsorbent that adsorbed phosphate ions was extracted from the adsorption tower and collected, and packed in the regeneration tower. On this phosphorus adsorbent, phosphate ions of 8 g-P / kg-adsorbent were adsorbed in terms of phosphorus.

  The phosphorus adsorbent adsorbing phosphate ions was back-washed with 3 times the amount of water relative to the adsorbent capacity, and the washing water was discharged. Next, a 7% by weight sodium hydroxide solution, which is 3 times the amount of the adsorbent in the regeneration tower, is passed through to desorb phosphate ions from the adsorbent and contain 2500 mg-P / L of phosphorus. A weight% sodium hydroxide solution (leaving solution) was obtained. In this desorbed liquid, 95% by weight of adsorbed phosphorus was desorbed. The regeneration tower was washed with 5 times the amount of water with respect to the adsorbent volume, and 7 times the 1 wt% sulfuric acid solution was passed through to activate and regenerate the adsorbent.

(2) Concentration of phosphate-containing solution The desorbed solution was concentrated with a vacuum low-temperature concentrator (manufactured by G-Tech Co., Ltd .: heat transfer tube rotating dynamic conductor). That is, the inside of the concentrator is depressurized to 10 kPa, then 10 L of desorbing liquid (including 25 g of total phosphorus) is charged into the apparatus and heated by flowing steam into the heat transfer coil at a temperature of about 45 ° C. The water started to evaporate. While maintaining the pressure constant at around 10 kPa, the evaporation operation is continued at an evaporation amount of water of 0.5 L / min, and the desorbed liquid is supplied into the apparatus in an amount that decreases with evaporation, while the sodium hydroxide concentration is 21 It concentrated until it became weight%, ie, 30L of stock solutions became 10L (3 times concentration). The liquid temperature of the concentrate was about 50 ° C. The evaporated water was cooled by a condenser and recovered as condensed water (first liquid).

  The introduction of steam was stopped, the pressure of the apparatus was returned to atmospheric pressure, and the concentrated liquid (concentrated liquid) was extracted to the outside. There was no scale adhesion on the surface of the heat transfer tube of the device or the inner wall of the tank.

(3) Crystallization / recovery of phosphate Phosphate was crystallized from the concentrated solution thus obtained by the following method.

a) Leave in a constant temperature bath at 40 ° C. for 1 day for crystallization b) Leave in a constant temperature bath at 30 ° C. for 1 day to crystallize c) Leave in a constant temperature bath at 5 ° C. for 1 day D) Let stand at room temperature (25 ° C.) for 1 day to crystallize e) Let stand in a constant temperature bath at 40 ° C. for 3 hours, and then let it stand at room temperature for 1 day for crystallization.

  In either method, phosphate crystals were obtained, but when the precipitation temperature was increased, the proportion of needle crystals increased, and when the precipitation temperature was lower than room temperature, the crystals became finer and became sherbet-like.

  After the precipitation of the phosphate, the concentrated liquid in a solid-liquid mixed state is filtered, the phosphate crystal is taken out, and the phosphorus content in the phosphate is measured. The crystal from the concentrated liquid (phosphate) The phosphorus recovery rate of each was 90% by weight or more, and phosphorus could be efficiently recovered as phosphate crystals. Note that the phosphorus recovery rate R in the concentrated liquid is expressed by the formula R (%) = (Pp / Pc) based on the phosphorus content Pc in the concentrated liquid and the phosphorus content Pp of the precipitated phosphate. ) × 100.

(4) Result of analysis of recovered phosphate The component analysis of the obtained phosphate crystals was performed. The result is shown.

(4-1) Elemental analysis Elemental analysis was performed using an organic elemental analyzer ("MT-700HCN" manufactured by Yanaco), and the following results were obtained. Sodium was quantified by ICP emission analysis using an ICP emission analyzer (“OPTIMA-3300DV” manufactured by Perkin Elmer).

C <0.1%, H = 0.81%, N <0.1%, P = 8.0%, Na = 20%
(4-2) Loss on ignition Perform thermal analysis (TG-DTA) using a differential heat and thermogravimetric simultaneous measurement device (“DTG-60” manufactured by Shimadzu Corp.) to measure temperature change and weight loss up to 1050 ° C. Upon examination, the following results were obtained.

Loss on drying (110 ° C.) = 51.7%
Ash content (1050 ° C.) = 44.6%
(4-3) Anion analysis Using an ion chromatograph ("HIC-10A" manufactured by Shimadzu Corporation), anions were quantified by ion chromatography, and the following results were obtained.

PO ₄ = 25%, PO ₃ <0.01%, PO ₂ <0.01%, Cl = 3.0 ppm
(4-4) Sodium hydroxide When sodium hydroxide was quantified according to JIS K 9012 6.1 “Trisodium phosphate · 12 water (reagent): Sodium hydroxide quantitative test method”, the following results were obtained.

NaOH = 3.1%
(4-5) Crystal purity The main component of the needle-like crystal is presumed to be Na ₃ PO ₄ · 12H ₂ O or Na ₃ PO ₄ · 12H ₂ O · 1/4 NaOH. The results of calculating the purity of these crystals based on the analytical data are shown in the table below. The purity of the crystal is calculated based on (a) PO ₄ ion concentration (= 24.5%) quantified by ion chromatography and (b) sodium concentration (= 20.1%) quantified by ICP method. And (c) the weight loss at 250 ° C. (= 52.8%) is calculated assuming that it corresponds to the hydrated water of phosphate (12H ₂ O), and (d) the ash content at 1050 ° C. (= 44.6%) was calculated by assuming that all correspond to Na ₃ PO ₄ or Na ₃ PO ₄ · 1/4 NaOH.

  From these results, it was confirmed that the recovered phosphate was a highly pure sodium phosphate salt. As described above, it was confirmed that phosphorus discharged from the septic tank was adsorbed with a phosphorus adsorbent and the phosphorus could be efficiently recovered as phosphate crystals.

FIG. 1 is a graph showing the relationship between the sodium phosphate concentration and the sodium hydroxide concentration in an aqueous solution at a temperature of 25 ° C.

Claims (9)

A 0.1 to 20% by weight alkaline aqueous solution containing a phosphate in a concentration of 100 to 5000 mg / L in terms of phosphorus, at a temperature of 35 to 58 ° C. and a pressure of 2 to 20 kPa until the alkali concentration becomes 8 to 30% by weight . A method in which phosphate is precipitated by concentration under reduced pressure, and the phosphate is recovered by solid-liquid separation. The phosphate is a salt of phosphoric acid and an alkali metal, and an aqueous solution having a phosphate concentration of 500 to 3000 mg / L in terms of phosphorus is concentrated at a concentration ratio of 1.5 to 100 times. the method of. The method according to claim 1, wherein the concentration is carried out under reduced pressure at a temperature of 40 to 55 ° C and a pressure of 3 to 15 kPa.   The method according to claim 1, wherein the phosphate is precipitated by lowering the temperature of the concentrate.   The treatment liquid containing phosphate ions is adsorbed with an adsorbent, the adsorbent adsorbed with phosphate ions is desorbed with an aqueous alkaline solution, and the aqueous alkali solution containing the generated phosphate is concentrated. the method of.   The adsorbent is composed of hydrated ferrite of zirconium, or a mixture of hydrated ferrite of zirconium and at least one selected from hydrated zirconium oxide and hydrated iron oxide. 5. The method according to 5.   The method according to claim 5, wherein the aqueous alkaline solution is an aqueous sodium hydroxide solution.   The method according to claim 5, wherein the separation liquid separated from the phosphate by solid-liquid separation is reused for desorption of phosphoric acid from the adsorbent. An adsorbent composed of at least one hydrated ferrite selected from titanium, zirconium, and tin is used to adsorb the phosphoric acid component in the liquid to be treated, and the adsorbed phosphoric acid component has a concentration of 0. Desorbed with an aqueous solution of 1 to 20% by weight alkali metal hydroxide, and an aqueous solution containing an alkali metal phosphate produced by the desorption at a concentration of 100 to 5000 mg / L in terms of phosphorus , temperature 35 to 58 ° C., pressure After concentration under reduced pressure of 2 to 20 kPa until the concentration of alkali metal hydroxide is 8 to 30% by weight, the temperature of the concentrate is lowered to precipitate an alkali metal phosphate, and the precipitated alkali phosphate A method of separating a metal salt by solid-liquid separation and recovering a phosphoric acid component in a liquid to be treated.

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