WO2010143623A1

WO2010143623A1 - Method for recovering water and metals from plating wastewater resulting from washing

Info

Publication number: WO2010143623A1
Application number: PCT/JP2010/059680
Authority: WO
Inventors: 一郎住田; 勇一村松; 孝之篠崎
Original assignee: 栗田工業株式会社; 新日本製鐵株式会社
Priority date: 2009-06-11
Filing date: 2010-06-08
Publication date: 2010-12-16
Also published as: CN102459096B; JP5471054B2; JP2010284593A; CN102459096A

Abstract

A method for water and metal recovery from a plating wastewater resulting from washing is disclosed with which water and metals are efficiently recovered from the plating wastewater, the method comprising an iron insolubilization step in which the pH of the plating wastewater is regulated to 3-6 in the presence of an oxidizing agent to oxidize divalent iron ions contained in the liquid to trivalent iron ions and precipitate an iron hydroxide, a solid-liquid separation step in which the water treated in the iron insolubilization step is subjected to solid-liquid separation by means of a microfiltration membrane, an ultrafiltration membrane, or a filter, a reverse osmosis membrane separation step in which the water separated in the solid-liquid separation step is treated with a reverse osmosis membrane and the filtrate water is taken as treated water out of the system, and a crystallization step in which an alkali is added to the high-concentration water resulting from the reverse osmosis membrane separation step and the metals contained in the liquid are precipitated as carbonates by a crystallization method in which acid-insoluble particles are used as seed crystals.

Description

Methods for recovering water and metals from plating cleaning wastewater

The present invention relates to a method for efficiently recovering water and valuable metals from plating washing wastewater, and in particular, efficiently recovers both water and valuable metals such as nickel and zinc from washing wastewater in the electroplating process. The present invention relates to a method for reducing the amount of sludge generated by wastewater treatment.

The plating washing wastewater discharged from the plating factory generally has a pH of 2 to 3, and in many cases contains valuable metals such as nickel, zinc, chromium and copper in addition to divalent iron. It is desirable to reuse.

As described in Patent Document 1, conventionally, a neutralization coagulation precipitation method (hydroxide precipitation method) has been adopted as a method for treating plating washing wastewater. In this method, the pH of the waste water is made alkaline, and metal ions are precipitated as hydroxides and separated and removed. When recovering valuable metals such as nickel and zinc by this method, in order to separate these metals from iron and recover them, a method of coagulating and precipitating under different pH conditions is employed. That is, this is a method in which Fe ²⁺ is oxidized to Fe ³⁺ in the presence of an oxidizing agent or the like at pH 3 to 6, and then precipitated and removed as a hydroxide, and then nickel and zinc are precipitated and separated at pH 7 to 10. When water is further collected, nickel and zinc are precipitated and separated, and then solid-liquid separation such as sand filtration and ultrafiltration, or reverse osmosis (RO) membrane treatment is performed according to the required water quality of the collected water. .

Other treatment methods for metal-containing wastewater include the sulfide precipitation method, ion exchange method, chelate resin method, and membrane separation method.

The sulfide precipitation method is a method in which a metal is precipitated as a sulfide by adding sodium sulfide. In this method, since the solubility product of the metal sulfide is lower than that of the hydroxide precipitation method, metals can be treated at a lower concentration from the viewpoint of wastewater treatment.

As described in Patent Document 2, the ion exchange method is to remove the metal ions in the waste water by adsorbing to the ion exchange resin, and if used within the range of the adsorption capacity of the ion exchange resin, the ion exchange method is reliable. It is possible to remove metal ions.

The chelate resin method uses a chelate resin having selectivity for a specific metal to adsorb and remove the metal. As with the ion exchange resin, it is possible to reliably remove metal ions, but the chelate resin has selectivity for the metal, and a metal that can be adsorbed and removed is specified.

The membrane separation method uses a RO membrane to remove metal ions, and provides a good treated water quality.

However, each method has the following problems when recovering both water and valuable metals from the metal-containing wastewater.

i) Neutralization coagulation sedimentation method Hydroxides have fine flocs and are unstable in the sedimentation basin, so a precipitation aid such as a polymer coagulant is required for stable operation. Further, the hydroxide sludge has a water content of about 70 to 80%, and the treatment of a large amount of generated sludge becomes a problem.
Moreover, in order to separate and recover iron, nickel, and zinc by this method, it is necessary to set the pH at the time of neutralization to two stages, so the sedimentation basin is provided in two stages, and a large installation space is required. It is.
Furthermore, when RO (reverse osmosis) membrane treatment is performed at a later stage for water recovery, ions are increased by the neutralization treatment, which increases the ion load on the RO membrane.

ii) Sulfide precipitation method Sulfide has a low solubility product and can reduce the metal ion concentration. However, since the sulfide precipitate is fine, precipitation separation is poor. Further, since sulfides generate hydrogen sulfide under acidic conditions, there is a safety problem.

iii) Ion exchange method Since the ion exchange resin adsorbs almost all ions, the amount of adsorbed ions other than metal ions is large in the wastewater treatment, and the efficiency is poor for the purpose of removing metal ions. In addition, a large amount of regenerative medicine is required, and the regenerated liquid contains these ions in a mixed state, so that it is difficult to recover valuable metals.

iv) Chelate resin method Although the selectivity for metal ions is higher than that of ion exchange resins, attention must be paid to the behavior of coexisting ions. In addition, sulfuric acid or hydrochloric acid is usually used for regeneration, but a large amount of acid remains in the regeneration solution, and the concentration of metal ions in the recovered solution is at most about 2 to 3% by weight, and the concentration is low for reuse.

v) Membrane separation method The use of RO membrane can provide good treated water quality. However, the metal ion concentrated on the RO concentrated water side is only about 10 times that in the wastewater, so RO membrane alone can recover metal. Not suitable.

JP 2002-192168 A JP 2004-107780 A

The object of the present invention is to solve the above-mentioned conventional problems and to provide a method for efficiently recovering water and metal from plating washing waste water.

The method for recovering water and metal from the plating cleaning wastewater according to the first aspect is a method of recovering water and metal from the plating cleaning wastewater, adjusting the plating cleaning wastewater to pH 3 to 6 in the presence of an oxidizing agent, The iron insolubilization step of oxidizing the divalent iron ions into trivalent iron ions and precipitating iron hydroxide, and the treated water in the iron insolubilization step are separated into solid and liquid using a microfiltration membrane, ultrafiltration membrane or filter A solid-liquid separation step, a reverse osmosis membrane separation process in which the separated water separated in the solid-liquid separation step is subjected to a reverse osmosis membrane separation process, and the permeate is taken out of the system as treated water; And a crystallization step of depositing a metal in the liquid as a carbonate by a crystallization method in which an alkali is added to water and acid-insoluble particles are used as seed crystals.

The method for recovering water and metal from the plating washing waste water according to the second aspect is the metal recovery according to the first aspect, wherein, in the crystallization step, the metal carbonate precipitated on the seed crystal is dissolved in an acid to obtain a metal salt solution. It has the process.

In the second aspect, the third aspect of the method for recovering water and metal from the plating washing wastewater is characterized in that the metal salt solution obtained in the metal recovery step is reused as a plating solution.

The fourth aspect of the method for recovering water and metal from the plating washing wastewater is characterized in that, in any one of the first to third aspects, the treated water of the crystallization step is returned to the iron insolubilization step for treatment. To do.

According to the present invention, water and metal can be efficiently recovered from the plating washing waste water.

That is, first, iron is precipitated as iron hydroxide (Fe (OH) ₃ ) in the iron insolubilization step, and this is separated and removed in the solid-liquid separation step. Since this solid-liquid separation is performed with a microfiltration (MF) membrane, an ultrafiltration (UF) membrane, or a filter, the solid-liquid separation is excellent. Since the pH is adjusted to 3 to 6 in the iron precipitation step, iron hydroxide is precipitated, but metal ions such as nickel and zinc are dissolved. Therefore, the separated water containing the dissolved metal ions is obtained from the solid-liquid separation step.

In the present invention, this solid-liquid separated water is first concentrated by RO membrane separation treatment. RO membrane permeated water has a water quality as good as pure water, and can be taken out of the system as treated water and reused as plating cleaning water, or used at other points of use.

Metal ions such as nickel and zinc concentrated in the RO-concentrated water are precipitated as metal carbonates on the seed crystal by the subsequent crystallization treatment. According to the crystallization method, the metal can be recovered as metal carbonate particles having good dehydration properties. In addition, the crystallization method does not require a sedimentation basin or dehydration equipment as in the neutralization precipitation method.
Nickel and zinc can also be insolubilized as hydroxides, but hydroxides are not suitable for crystallization because they generate flocs with high moisture content including moisture.

In the second aspect, since acid-insoluble particles are used as seed crystals of this crystallization method, the metal carbonate precipitated on the seed crystals can be dissolved in an acid and easily recovered as a metal salt solution. According to the third aspect, this metal salt solution can be reused as a plating solution, and the recovered seed crystals can be reused in the crystallization step.

In the treated water of the crystallization process, metal ions for recovery purposes and fine metals that have not been captured on the seed crystals even when insolubilized remain. In the fourth aspect, since this crystallization treated water is returned to the iron insolubilization step and treated again, the metal recovery rate and water recovery rate can be increased.

As described above, according to the present invention, water and valuable metals can be efficiently recovered from the plating washing waste water. In addition, a series of combinations of iron precipitation process, solid-liquid separation process, RO membrane separation process, and crystallization process can reduce the amount of treated wastewater and the amount of discharged metal, greatly reducing the final sludge generation amount. be able to.

It is a systematic diagram which shows embodiment of the recovery method of the water and metal from the plating washing | cleaning waste_water | drain of this invention. It is a systematic diagram which shows the structure of a crystallizer. It is a systematic diagram which shows the structure of an acid contact apparatus.

Hereinafter, embodiments of a method for recovering water and metal from plating washing wastewater of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a method for recovering water and metal from plating washing waste water according to the present invention, FIG. 2 is a system diagram showing the structure of a crystallizer, and FIG. 3 is the structure of an acid contact device. FIG.

In the present invention, first, the plating cleaning waste water as raw water is introduced into the agglomeration / oxidation tank 1, and an oxidizing agent (sodium hypochlorite (NaClO) in FIG. 1) and a pH adjusting agent (in FIG. 1, as an alkaline agent). Caustic soda (NaOH)) and a flocculant (ferric chloride (FeCl ₃ ) in FIG. 1) are added, and divalent iron (Fe ²⁺ ) in the liquid is converted to trivalent iron (Fe ³⁺ ) at pH 3-6. To precipitate iron hydroxide (Fe (OH) ₃ ).

In this iron insolubilization step, as the oxidizing agent, hydrogen peroxide, potassium permanganate, chlorine, ozone, or the like can be used in addition to NaClO. The addition amount of the oxidizing agent may be equal to or more than the equivalent for oxidizing Fe ²⁺ in the liquid to Fe ³⁺ .

Although the plating washing wastewater is usually acidic at a pH of less than 3, for example, about pH 2, it needs to be at least pH 3 for precipitation of Fe (OH) ₃ , so that NaOH, Ca (OH) are used as pH adjusters. _The pH is adjusted by adding alkali such as ₂ . However, depending on the concentration in the waste water, the pH is adjusted to 3 to 7, particularly 5 to 6, since nickel and zinc in the liquid are precipitated when the pH exceeds 7.

In this iron insolubilization step, addition of a flocculant is not essential, but a flocculant such as FeCl ₃ may be added in order to improve the sedimentation of Fe (OH) ₃ floc. By adding a flocculant such as FeCl _3, the sedimentation property of the insolubilized particles is improved, the sedimentation efficiency in the subsequent sedimentation tank 2 is increased, and the floc diameter is increased so that the downstream UF membrane device 3 The filterability of can also be improved. The addition of a flocculant is also preferable in order to agglomerate organic substances in the plating washing waste water to reduce the load on the subsequent RO membrane device 6 and to prevent contamination of the RO membrane. Amount of FeCl ₃ is generally 10 ~ 200mg / L, preferably about 100 ~ 150mg / L.

The liquid in which the floc of Fe (OH) ₃ is precipitated in the coagulation / oxidation tank 1 is then solid-liquid separated by an MF membrane, a UF membrane or a filter (for example, a sand filter). In the method of FIG. After solid-liquid separation in the precipitation tank 2, membrane filtration is performed with an MF membrane device (MF membrane separation device) 3. Although this sedimentation tank 2 is not essential, by precipitating and separating the coarse floc of Fe (OH) _{3 in} the sedimentation tank 2 in advance, the load on the UF membrane device 3 in the subsequent stage is reduced, and the frequency of backwashing is reduced. A flux can be aimed at.

Separating the sludge settling tank 2 is discharged out of the system, the separation liquid pump P _A, is introduced into the UF membrane device 3, is a membrane filtration. The UF membrane device 3 is regularly backwashed, and the collected Fe (OH) ₃ sludge is discharged out of the system together with the backwash drainage.

The filtered water of the UF membrane device 3 is introduced into the adjustment tank 5 through the UF treatment water tank 4 and the water quality is adjusted in the adjustment tank 5. That is, prior to processing the filtered water of the UF membrane device 3 by the RO membrane device (RO membrane separation device) 6, sodium bisulfite (NaHSO ₃ ) and sodium sulfite (Na ₂ ) are added to the UF membrane filtered water to protect the RO membrane. It is necessary to add a reducing agent such as SO ₄ ) or contact with activated carbon to remove the remaining oxidizing agent, and to prevent precipitation of metal hydroxides such as nickel and zinc by concentration in the RO membrane device 6. Accordingly, a pH adjusting agent is added to adjust the pH of the water (RO feed water) supplied to the RO membrane device 6 to 4 to 6, preferably 4 to 5.

The amount of the reducing agent added to the UF membrane filtered water is usually 5 to 20 mg / L, preferably 10 to 15 mg / L in excess of the equivalent of the remaining oxidizing agent.

The water whose water quality has been adjusted in the adjustment tank 5 is introduced into the RO membrane device 6 by the pump P _B and subjected to membrane separation treatment into permeated water (RO permeated water) and concentrated water (RO concentrated water). A part of the concentrated water is supplied to the RO concentrated water tank 7, and the remaining part is circulated.

The treatment with the RO membrane device 6 is performed at a concentration factor of 5 to 10 times and a water recovery rate of 80 to 90%, so that metal ions can be highly concentrated and the water recovery rate can be increased without causing operational troubles. It is preferable in terms of enhancement.

Since the RO permeated water obtained by the RO membrane device 6 has the same good water quality as pure water, it can be reused as plating cleaning water. Moreover, this RO permeated water can also be used at other use points.

The metal ions in the RO concentrated water are concentrated to 5 to 10 times the metal ion concentration in the plating washing wastewater. This RO concentrated water is introduced into the crystallizer 8 through the RO concentrated water tank 7 and crystallized. Is done.

The crystallization apparatus 8 is not particularly limited as long as it can promote the precipitation of metal carbonate. For example, a seed crystal is packed in the crystallization reaction tower 10 as shown in FIG. A tower reactor in which RO concentrated water is passed from the bottom of the tower to form a fluidized bed of seed crystals in the tower can be suitably used.

In the apparatus of FIG. 2, the raw crystallization water is passed from the lower part of the reaction tower 10 through the pipe 11 by the pump P ₁ , and the treated water flows out from the pipe 12 and is introduced into the treated water tank 9. From the tower top part of the treated water is processed is circulated to the bottom of the column by the circulation pipe 14 and a circulation pump P _2.

Alkali carbonate such as sodium carbonate (Na ₂ CO ₃ ) or a mixed solution of sodium bicarbonate (NaHCO ₃ ) and caustic soda (NaOH) is injected from the upper part of the crystallization reaction tower 13. A metal carbonate precipitates on the seed crystal flowing in the tower in accordance with a reaction between sodium carbonate and metal ions, for example, according to the following reaction.
Ni ²⁺ + Na ₂ CO ₃ → NiCO ₃ (precipitation) + 2Na ⁺
Zn ²⁺ + Na ₂ CO ₃ → ZnCO ₃ (precipitation) + 2Na ⁺

The metal carbonate needs to be precipitated by raising the pH of the crystallization raw water to 7 to 10, preferably 8 to 9. Therefore, the alkali carbonate injected into the crystallization tower reaction tower 10 is an amount necessary for forming the metal carbonate, and the liquid pH in the crystallization tower is such an amount. When the pH is less than 7, carbonate is not precipitated, and when it exceeds 10, zinc carbonate is easily dissolved again.

Thus, in the crystallization process, it is necessary to increase the pH, but in the present invention, prior to the crystallization process, it is necessary for pH adjustment in order to reduce the amount of water to be crystallized by performing RO membrane separation treatment and concentrating. The amount of chemicals can be reduced.

In the present invention, acid-insoluble particles that are not dissolved by acid treatment in the subsequent metal recovery step are used as seed crystals. As the acid-insoluble particles, sand (silica sand), anthracite and the like can be used. The seed crystal grain size is suitably about 0.1 to 1 mm, particularly about 0.2 to 0.4 mm.

Through the crystallization treatment, metal ions in the crystallization raw water are insolubilized as metal carbonates and precipitate on the seed crystal surface. The seed crystal particles grow by precipitation of the metal carbonate and increase to a particle size of 0.3 to 1.5 mm. The increased particles are extracted from the crystallizer and fed to the metal recovery process.

The treated water of the crystallizer 8 is introduced into the crystallized water tank 9.

In the crystallization method, although depending on the operating conditions, the recovery rate of metal ions is often 70 to 90%, generally about 80%. For this reason, it is preferable to return a part of this crystallization treatment water to the iron insolubilization step and to circulate it together with the raw water plating washing waste water. Thereby, the metal ions which could not be recovered by one crystallization process can be repeatedly crystallized, and the overall metal recovery rate can be increased.

In the present invention, the ratio of the crystallized water to be circulated is 10 to 80% of the water introduced into the crystallized water tank 9, the total water recovery rate is 70 to 90%, and the metal recovery rate is 80%. It is preferable to perform the treatment under the condition of about 95%.

In the crystallizer 8, when an acid such as sulfuric acid or hydrochloric acid is brought into contact with particles having a metal carbonate such as nickel or zinc attached using an acid-insoluble seed crystal as a nucleus, the metal carbonate such as nickel or zinc is redissolved. Thus, a highly concentrated solution of metal sulfate or chloride is obtained. In the treatment of the electroplating washing waste water, the high-concentration metal sulfate aqueous solution thus obtained can be reused as it is in the plating bath. In addition, after the recovered particles are brought into contact with an acid to dissolve the metal carbonate, acid-insoluble seed crystal particles remain, but these seed crystal particles should be used again as seed crystals in a crystallizer. Can do. By reusing seed crystal particles in this way, particle size management in the crystallizer becomes easy.

Therefore, it is preferable to periodically extract seed crystal particles having a metal carbonate precipitated on the surface from the crystallizer 8 and treat them with an acid to recover the metal salt solution and the seed crystal, respectively.

The device for bringing the particles extracted from the crystallizer 8 (particles having a metal carbonate deposited on the surface of the seed crystal) into contact with the acid is not particularly limited as long as it can efficiently bring both into contact with each other. However, for example, an acid contact device as shown in FIG. 3 can be used.

This acid contact device has an acid contact tower 20 into which the drawn particles from the crystallizer 8 are charged, and a water collecting plate (porous) through which only water can pass without passing through the particles in the lower part of the tower. Plate or mesh). In processing the extracted particles from the crystallizer 8, the valves V ₁ and V ₂ are opened, the other valves are closed, the extracted particles are put into the acid contact tower 20 from the pipe 21, and moisture is supplied to the pipe 23, Extract from 24. This water is returned to the crystallization water tank 9. Next, the valves V ₃ and V ₄ are opened, the other valves are closed, and an acid such as sulfuric acid is passed through the

pipes

25 and 23 from the lower part of the acid contact tower 20 by the pump P ₃ to contact the acid and the particles. To dissolve the metal carbonate on the surface of the seed crystal. A solution containing metal ions in which the metal carbonate is dissolved is taken out via the pipe 26. As this metal salt solution, since a high concentration solution of about 5 to 15% by weight of metal ions is usually obtained, this metal salt solution can be suitably reused as a plating solution.

After dissolving the metal carbonate on the surface of the seed crystal, the valves V ₂ and V ₅ are opened, the other valves are closed, and the water is acidified at a high flow rate through the

pipes

24 and 23 by a pump (not shown). and passed through from the bottom of the contact tower 20, the seed crystals through the valve V ₅ to return to reuse the crystallizer 8.

The acid used for dissolving the metal carbonate on the seed crystal is preferably a high concentration sulfuric acid aqueous solution of about 50 to 98% by weight or a 20 to 35% by weight hydrochloric acid aqueous solution.

In the conventional hydroxide precipitation method, it is possible to insolubilize metal ions, re-dissolve them with an acid, and reuse them in a plating bath, but by performing a crystallization treatment as in the present invention. , No sedimentation tank or dehydrator is required. Moreover, since it is possible to obtain particles having a relatively large particle size and good drainage properties, it is possible to use an acid contact device as shown in FIG. The metal salt solution can be recovered.

As described above, according to the present invention, the amount of waste water and the amount of discharged metal are reduced, the amount of sludge generated in the entire system is greatly reduced, and water and valuable metals are efficiently recovered from the plating washing waste water. can do.

Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
Water and metal were recovered from the plating washing waste water by the method shown in FIG.

First, 5 mg / L of sodium hypochlorite is added to the plating washing wastewater in the coagulation / oxidation tank 1 to oxidize Fe ²⁺ contained in the waste liquid to Fe ³⁺ , and the pH is adjusted to 5 using caustic soda. , Fe ³⁺ is insolubilized as iron hydroxide Fe (OH) ₃ and 100 mg / L of ferric chloride (FeCl ₃ ) is added to increase the particle size of the insolubilized Fe (OH) _3. did.

The treatment liquid in the flocculation / oxidation tank 1 was introduced into the precipitation tank 2 and most of the generated floc was settled and separated, and then the separation liquid in the precipitation tank 2 was subjected to membrane filtration with the UF membrane device 3. This UF membrane device 3 was regularly backwashed.

The filtered water of the UF membrane device 3 is introduced into the adjustment tank 5 through the UF treatment water tank 4, and after adding residual sodium bisulfite 15mg / L to remove residual chlorine, it is supplied to the RO membrane apparatus 6 (RO supply water) ), RO permeated water was recovered, and RO concentrated water was supplied to the crystallizer 8 through the RO concentrated water tank 7 for crystallization treatment. The water recovery rate of this RO membrane device 6 was 80%.

The crystallization apparatus 8 is a crystallization reaction tower 10 as shown in FIG. 2 filled with sand having a particle size of about 0.2 mm. RO concentrated water is passed from the lower part of the crystallization reaction tower 10 to sand. In addition, the pH in the fluidized bed was adjusted to 9 by adding sodium carbonate (Na ₂ CO ₃ ) to the fluidized bed. Crystallized water from the crystallizer 8 was received in a crystallized water tank 9.

Table 1 shows the water quality for each process in this treatment.

From Table 1, the following is clear.

Iron was insolubilized by the iron insolubilization treatment, and was removed to a level that was not detected at the stage of RO supply water. Nickel and zinc were hardly insolubilized up to the RO membrane device 6 and were in a dissolved state. About 80% of nickel and zinc concentrated in a dissolved state on the RO concentrated water side were removed by crystallization treatment (metal recovery rate 80%). At this time, nickel and zinc were deposited on the surface of sand introduced as seed crystals, and an increase in seed crystal particle diameter was observed.

UF backwash wastewater and crystallization treated water are discharged as wastewater, so the overall water recovery rate is 75%.

[Example 2]
In Example 1, the seed crystal having a particle size increased to about 0.3 to 0.4 mm by the crystallization treatment is guided to the acid contact tower 20 shown in FIG. A weight% aqueous sulfuric acid solution was injected. The water content of the particles after draining was 10% by weight. By injecting sulfuric acid from the lower part of the tower, nickel and zinc adhering to the seed crystal surface were dissolved, and a sulfate solution of nickel and zinc was obtained from the upper part of the tower. The nickel and zinc concentrations of this solution were 1.5 wt% and 17 wt%, respectively. As a result, nickel and zinc in plating washing wastewater in the raw water are concentrated 600 times and 577 times, respectively.

[Example 3]
In Example 1, 90% of the crystallization treated water was returned to the inlet side of the flocculation / oxidation tank 1 and treated in the same manner as in the treatment with the plating washing waste water. In this example, the one-pass metal recovery rate in the crystallization treatment is not changed to 80%, but by returning the crystallization treatment water and treating it again, the crystallization treatment is repeated and the entire metal is recovered. The recovery increased to 98%. The water recovery rate was improved to 92%.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application (Japanese Patent Application No. 2009-140335) filed on June 11, 2009, which is incorporated by reference in its entirety.

Claims

In the method of recovering water and metal from plating washing wastewater,
An iron insolubilization step in which the plating washing wastewater is adjusted to pH 3 to 6 in the presence of an oxidizing agent to oxidize divalent iron ions in the solution to trivalent iron ions and precipitate iron hydroxide;
A solid-liquid separation step of solid-liquid separation of the treated water of the iron insolubilization step with a microfiltration membrane, an ultrafiltration membrane or a filter;
Reverse osmosis membrane separation treatment of the separated water separated in the solid-liquid separation step, and removing the permeated water out of the system as treated water;
And a crystallization step of precipitating the metal in the liquid as a carbonate by a crystallization method in which an alkali is added to the concentrated water in the reverse osmosis membrane separation step, and acid-insoluble particles are used as seed crystals. To recover water and metal from plating cleaning wastewater.
In Claim 1, the said crystallization process has a metal collection | recovery process which dissolves the metal carbonate deposited on the seed crystal in an acid, and obtains a metal salt solution. Collection method.
3. The method for recovering water and metal from plating washing drainage according to claim 2, wherein the metal salt solution obtained in the metal recovery step is reused as a plating solution.
3. The method for recovering water and metal from plating washing waste water according to claim 2, wherein seed crystals from the metal recovery step are recovered and reused in the crystallization step.
3. The method for recovering water and metal from plating cleaning waste water according to claim 2, wherein the acid is a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution.
6. The method for recovering water and metal from plating washing wastewater according to any one of claims 1 to 5, wherein a part of the treated water in the crystallization step is returned to the iron insolubilization step for treatment.