JP2000117270A - Treatment of metal-containing waste water and method for recovering valuable metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify metal-contg. waste water and to recover valuable metals simultaneously when the waste water is treated and to remarkably reduce the generation of sludge. SOLUTION: The pH of metal-contg. waste water is adjusted by an alkali agent to form a metal hydroxide, the waste water is passed through a membrane separator 2 having 1-10 μm pore diameter, the water and the metal hydroxide are efficiently separated, and the valuable metals are recovered and reutilized. The metal can be selectively separated by previously adjusting the pH of metal- contg. waste water to 3-4, separating and recovering chromium and iron hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for efficiently and stably treating metal-containing wastewater generated from a plating plant and the like, and reducing the amount of sludge generated by recovering and reusing valuable metals from the wastewater. It is about how to reduce.

[0002]

2. Description of the Related Art Metal-containing wastewater includes mine wastewater, chemical factory wastewater, smelter wastewater, steelworks wastewater, and plating factory wastewater. Above all, the plating factory wastewater has a low pH of 2-3,
Depending on the type of plating, it often contains valuable metal ions such as nickel, zinc, tin, chromium, and copper in addition to divalent iron. Since these heavy metal ions are subject to wastewater regulations as harmful metals, it is necessary to remove them from wastewater to the regulated value.

A method of treating metal-containing wastewater which has been widely used in the past is a neutralization coagulation sedimentation method. In this method, after increasing the pH of waste water with calcium hydroxide or the like to convert metal ions to hydroxide, the metal hydroxide is precipitated in a sedimentation basin or the like to remove metal from water.

Other methods of treating metal-containing wastewater include sulfide precipitation, ion exchange resin, chelate resin, membrane separation, solvent extraction, bioconcentration, and activated carbon adsorption. The features are briefly described below.

[0005] Sodium sulfide (Na ₂ S) is injected into the wastewater,
The method of precipitating heavy metals as sulfide is the sulfide precipitation method. Comparing the solubility products of hydroxide and sulfide, sulfide is much lower and a lower concentration of metal can be obtained.

[0006] The ion exchange resin method is widely used for producing pure water. When applied to wastewater treatment, metal ions are adsorbed on the cation exchange resin and / or the anion exchange resin.

The chelate resin method uses a resin having particularly high selectivity for a specific metal (a resin having a polymer having a cross-linked structure and a chelate-forming group which forms a complex with a metal ion introduced therein). Heavy metal ions can be removed to an extremely low concentration. It is used to remove mercury from waste incineration plant effluent.

The membrane separation method uses a reverse osmosis membrane (RO: Reverse).
se Osomosis) is widely used for desalination of seawater and reuse of industrial wastewater. Utilizing the osmotic pressure, only the solvent is moved through the membrane, and clear treated water can be obtained.

[0009] The bioconcentration method is a method in which a specific heavy metal ion is ingested by a microorganism and the specific heavy metal is concentrated in the body of the microorganism. However, it is in a research stage, and it is considered that there is no practical example.

In addition to these methods, methods for recovering heavy metal ions from sludge containing heavy metals include bacterial leaching and solvent extraction.

All of these methods have problems, and the neutralization coagulation sedimentation method is most widely used for treating metal-containing wastewater from the viewpoint of the stability and cost of the wastewater treatment.

[0012]

The method for treating metal-containing wastewater which has been found to date has the following problems.

First, the neutralization aggregation precipitation method has the following problems.

1) The metal hydroxide is fine, and the sedimentation and separation in the sedimentation basin is not stable. In order to prevent this, in addition to pH adjustment, it is necessary to add a polymer flocculant to increase the size of flocs and increase the sedimentation speed.

2) The pH at which metal hydroxide begins to precipitate is
In principle, it is determined by the solubility product of the metal. But,
In effect, it is affected by coexisting ions. That is, it is known that even a metal having a large solubility product co-precipitates at a relatively low pH. For example, ferrous iron has a relatively low p
H is removed as ferric hydroxide. At this time, a phenomenon in which cadmium (Cd ²⁺ ), arsenic (As), and chromium (Cr ³⁺ ) co-precipitate has been found. In addition, when halogen, cyan ion, ammonia ion, and the like coexist in the metal-containing wastewater, there is a problem in that hydroxide is hardly formed.

As a result, since the precipitate formed by the neutralization coagulation precipitation method is a mixture of various metals, it is extremely difficult to reuse the precipitate, and most of the precipitate is disposed of in a landfill or the like.

3) As a neutralizing agent for the plating wastewater,
Slaked lime (Ca (OH) ₂ ) is used. this is,
Slaked lime is considerably cheaper than sodium hydroxide, has relatively high solubility in water, and is highly reactive. However, the sediment has a high water content of 99%, and is reduced to only 70 to 80% even when subjected to a dehydrator treatment. For this reason, the volume of the sediment is large, and storage, transportation, and disposal costs increase.

Next, the sulfide precipitation method has little actual use in terms of difficulty in separating the formed precipitate (it is easy to form a colloid) and safety (generating hydrogen sulfide gas upon contact with an acidic substance). . Further, the fact that the precipitate is a mixture of various metals is the same as in the neutralization coagulation sedimentation method, and it is extremely difficult to reuse it, and it has to be disposed of by landfilling.

Next, the ion exchange resin method has been widely used for boiler water supply for thermal power generation and ultrapure water production for semiconductors. The raw water to be treated has an ion concentration of 1000 mg / l or less. This method has a problem that when the ion concentration in the wastewater is high as in wastewater treatment, inorganic ions other than metal ions are adsorbed to the resin, so that adsorption / regeneration becomes complicated. Pretreatment is also required to prevent resin contamination. Since the operation is complicated as described above, the cost increases when used for wastewater treatment. In addition, when used for a long time, the ion exchange resin is contaminated with metal hydroxides, organic substances, bacteria, and the like, and it is difficult to recover the resin by a normal operation for regenerating the resin. In addition, since it is difficult in principle to selectively separate metals other than cations and anions, the regenerating solution of the ion exchange resin is a mixture of various metal ions, and is difficult to reuse. Therefore, application to wastewater treatment with a high ion concentration is considered difficult.

Various heavy chelate resin methods have the same problems as the ion exchange resin method, and it is difficult to apply them to wastewater treatment for the purpose of recovering valuable metals.

Further, as for the membrane separation method, a reverse osmosis membrane (R
O film) has a salt concentration of 1000 to 10 such as desalination of seawater.
It is widely used for raw water of about 000 mg / l. Further, there is an example applied to reuse of plating wastewater (for example, reuse of plating wastewater by the reverse osmosis method, Yoroku Wada, PPM, 16-27, 1986). RO for wastewater treatment
By using, since not only heavy metals but also inorganic ions can be removed from raw water, there is an advantage that membrane permeated water can be reused as industrial water. However, the RO film method also has the following problems. First, a small amount of concentrated liquid is generated. However, since not only heavy metal ions but also various inorganic ions are concentrated in this concentrated liquid, it is difficult to reuse the concentrated liquid. The RO film has an extremely small film diameter and a high pressure (10 to 60).
kg / cm ² ), and there is a problem that the running cost of wastewater treatment increases. Regarding the plating wastewater treatment, an ultrafiltration membrane (UF: U
ltra Filtration), precision filtration membrane (M
F: Micron Filtration) is rarely used (for example, use of ultrafiltration membrane / microfiltration membrane in wastewater treatment. Application example to wastewater treatment-plating wastewater, Yoshimichi Kogami, water pollution research, 10, 3, 153-
154, 1987). An example of a study report combining a polymer flocculant and a UF membrane is in the United States, but has not been put to practical use (Polymer Filtration, Proc)
AESF Annu Tech Conf, VOL.
82, 607-616, 1995). This is probably because the membrane diameter is small and the amount of permeated water of the UF membrane is extremely small, and the membrane equipment is enlarged.

Finally, regarding the bioconcentration method, the rate of heavy metal uptake by living organisms is still small and unstable, and practical use is difficult at this stage. Further, there is a problem regarding a method for separating and recovering heavy metals concentrated in living organisms.

Thus, currently known methods are:
It is built from the viewpoint of removing metals from water containing metals to below the regulation value from the water or using treated water effectively. By collecting valuable metal resources from wastewater and reusing it, sludge generated There is no point of view to try to reduce.

Therefore, the present invention provides a method for purifying water and recovering valuable metals in wastewater when treating metal-containing wastewater, thereby significantly reducing the amount of sludge generated as compared with the conventional method. .

[0025]

Means for Solving the Problems The gist of the present invention is the following (1) to (8).

(1) After adjusting the pH of the metal-containing wastewater to form a metal hydroxide, water is passed through a membrane separation device having a pore size of 1 μm to 10 μm, whereby water and the metal hydroxide are separated. A method for treating metal-containing wastewater and recovering valuable metals, comprising separating the wastewater.

(2) After adjusting the pH of the metal-containing waste water to form a metal hydroxide, and also using a polymer coagulant or a liquid chelating agent in combination to form metal hydroxide flocs, A method for treating metal-containing wastewater and recovering valuable metals, comprising separating water and flocs of metal hydroxide by passing water through a membrane separation device having a pore size of 50 μm to 200 μm.

(3) Trivalent chromium From the metal-containing wastewater containing iron (II) ions, in a first step, the pH is adjusted to 3 to 4 to oxidize the iron (II) to ferric iron. After forming a hydroxide of iron and iron, water and iron and chromium hydroxide are separated by passing water through a membrane separation device having a pore size of 1 μm to 10 μm, and then, from the treated water, In the second stage, a method for treating metal-containing wastewater and recovering valuable metals, wherein the remaining metal is separated and recovered by the method (1) or (2).

(4) The method for treating metal-containing wastewater and recovering valuable metals according to (3), wherein iron oxidizing bacteria are used to oxidize ferrous iron to ferric iron.

(5) When the metal is separated and recovered from the metal-containing wastewater containing ions of nickel, zinc, trivalent chromium, and ferric iron by the method of (3) or (4), Adjusting the pH to 8 to 10 to form hydroxides of nickel and zinc, and separating water and hydroxides of nickel and zinc, and treating the metal-containing wastewater and recovering valuable metals. .

(6) The above (1) to (1), wherein a membrane made of ceramics is used as the membrane separation device.
(5) The method for treating metal-containing wastewater and recovering valuable metals according to any of (5).

(7) The metal hydroxide concentrate separated and recovered is adjusted to pH 0.5 to 3 with sulfuric acid to redissolve the metal, and the concentrated metal solution is recovered and reused. The method for treating metal-containing wastewater and recovering valuable metals according to any one of the above (1) to (6).

(8) Any one of the above (1) to (7), wherein the treated water after separating and recovering the metal hydroxide is passed through a reverse osmosis membrane to reuse the treated water. A method for treating metal-containing wastewater and a method for collecting valuable metals.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention will be described below in detail.

The present inventor recovers and reuses valuable metals from metal-containing wastewater generated from a plating plant,
From studies of treating treated water to below the effluent regulation value or reusing it in factories, it was found that the above purpose was achieved by using a membrane with a pore size much larger than before, and this membrane was used. We have succeeded in treating wastewater containing metals and developing a method for collecting valuable metals. Furthermore, by combining this method with a biological method, we succeeded in developing a method that can selectively recover valuable metals from wastewater containing many metal ions.

First, the membrane separation will be described.

The inventor of the present invention has proposed a method of cleaning plating wastewater containing nickel and zinc as main components by using NaOH to adjust the pH to 8 to 10.
After stirring for a certain period of time, the size of the generated metal hydroxide flocs was measured.
It was found that it was about 0 μm. Since this hydroxide has a very low sedimentation speed, it has been difficult to remove the hydroxide by sedimentation and separation operation using a sedimentation tank. In order to remove the floc by the sedimentation separation operation, it was considered necessary to add a polymer flocculant and the like to increase the size of the floc. When the polymer flocculant was added, the pore size of the floc increased to 50 μm or more, and the specific gravity increased.

By the way, the pore size of the RO membrane is usually from 1 mm to
100 ° (0.01 μm), the pore size of the UF membrane is 20 °
(0.002 μm) to about 2000 ° (0.2 μm), and the pore size of the MF membrane is about 0.1 μm to 10 μm. When these membranes are applied to wastewater treatment, the following 1)
Points 5) are considered to be important.

1) The membrane has a predetermined separation performance with respect to the metal hydroxide continuously.

2) The amount of permeated water of the membrane is large and the deterioration over time is small.

3) The operating pressure of the membrane is small and the deterioration over time is small.

4) The film is not easily clogged and the regeneration is easy.

5) The use pH range of the membrane is wide, and high water temperature can be used.

From these facts, it is necessary to use a membrane having a large pore diameter as a membrane used for wastewater treatment in order to secure a sufficient amount of wastewater within a range where a predetermined separation performance can be obtained. However, RO membranes and UF membranes have a small amount of permeated water, which has delayed their application to wastewater treatment.

The inventor of the present invention has estimated from the results of the measurement of the size of the metal hydroxide after the pH adjustment that separation of the metal hydroxide was possible with the MF membrane. Furthermore, it has been found that as the pore diameter of the membrane becomes smaller, the distance of the metal hydroxide particles that are going to pass through the inner wall of the pore becomes shorter, and the metal hydroxide is also removed by this interaction. From these results, in order to remove metal hydroxide by the film, 1 μm
It has been found that the above pore size is sufficient. Further, more strictly, it has been found that the maximum pore diameter should be 10 μm or less in order to prevent the metal hydroxide from leaking from the film. This makes it possible to significantly increase the amount of permeated water.

By permeating the metal-containing wastewater whose pH has been adjusted through the MF membrane, a membrane permeate and a concentrate of metal hydroxide can be obtained. For example, in the case of plating wastewater mainly containing nickel and zinc, the concentrated solution contains nickel and zinc hydroxide concentrated. When the pH of this concentrated solution is adjusted to about 0 to 3 with sulfuric acid or the like, the metal hydroxide is redissolved, and a concentrated solution of nickel ions and zinc ions is obtained. When the concentration ratio is high, this concentrated solution can be reused as a plating solution. On the other hand, since the permeated liquid contains almost no nickel ions or zinc ions, it can be discharged into public water bodies as it is. Furthermore, when the permeate is reused for factory water, etc., in order to make the water quality suitable for industrial water,
It is necessary to remove anions and cations.
This can be handled by treating with an O film.

Next, formation of flocs of nickel ions, zinc ions and the like by the polymer flocculant will be described. The polymer flocculant desirably reacts selectively with heavy metal ions in water to form a water-insoluble metal floc. Examples of the polymer flocculant for selective collection of heavy metals include polyacrylic acid, polyvinyl alcohol, and polyethylenemine. The size of the flock to be formed is 5
Since it is 0 μm or more, an MF film is sufficient for the film to be used, and it is sufficient if the pore size is 50 μm or more.
If the polymer flocculant is well selected and floc formation is sufficiently performed, a pore diameter of about 200 μm may be used. Further, instead of the polymer flocculant, a liquid chelating agent having a certain ability to selectively remove heavy metals may be used. If it is difficult to selectively adsorb and coagulate metals even when using a liquid chelating agent, when the metal is desorbed from the liquid chelating agent using sulfuric acid, etc., the pH at the time of desorption is changed to selectively select heavy metal ions. Recovery may be possible to some extent.

As the material of the membrane used in the present invention, since the pH of the wastewater is about 1 to 3, it is essential that the membrane has acid resistance. Further, since the water temperature of the waste water is 20 ° C. to 40 ° C., it is required to have heat resistance, and further, to have abrasion resistance to the generated metal hydroxide. Examples of the material of the film include stainless steel fiber as a metal material, ceramics and glass fiber as an inorganic material, and polysulfone, polyolefin, polypropylene, polyvinyl alcohol, and polyacrylonitrile as an organic polymer material. Among them, ceramics are excellent in acid resistance, abrasion resistance, and heat resistance, and are considered to be optimal as a material of a film used for plating drainage and the like. It is desirable that the ceramic material is mainly silica-alumina clay, but it is also possible to mix fly ash, which is a by-product of a power plant, and blast furnace slag and converter slag, which are by-products of a steel mill. Absent. This makes it possible to reduce the cost of ceramics.

Next, an embodiment of the present invention will be described with reference to FIG.

The apparatus for carrying out the present invention comprises a pH adjusting tank 1,
It comprises an MF membrane separation device 2 filled with a ceramic membrane or the like, a pump 3, a re-pH adjustment tank 4, an RO membrane separation device 5, and a re-dissolution tank 6. The membrane separation device 2 may be installed independently or may be installed inside the pH adjustment tank 1.

The continuous treatment of wastewater containing heavy metals is carried out as follows.

First, waste water containing heavy metals is supplied so that the residence time (HRT) in the pH adjusting tank 1 becomes 30 minutes. Subsequently, the pump 3 connected to the MF membrane separation device 2 is operated. The pump 3 for the treated water is linked with a liquid level switch installed in the pH adjusting tank 1 and is controlled by the water level in the pH adjusting tank 1. The metal hydroxide generated in the pH adjustment tank 1 is concentrated by the membrane in the MF membrane separation device 2.
The concentrated metal hydroxide is dissolved in the re-dissolution tank 6 to form a high-concentration nickel or zinc solution, which is reused in a plating bath or the like in a factory.

The MF membrane-permeated liquid was adjusted to pH =
7 to 8 and treated by the RO membrane separation device 5 to reuse as industrial water.

As a result, a small amount of the RO membrane concentrate is generated, but can be discharged into a public water area as it is because inorganic ions are mainly contained.

Next, a method of cleaning the MF membrane separation device 2 will be described. If the membrane is operated for a long period of time, the amount of permeated water gradually decreases because turbidity adheres to the membrane surface. In order to prevent this phenomenon, it is necessary to periodically clean the membrane surface to remove turbidity. Methods for cleaning the film surface are roughly classified into a physical cleaning method and a chemical cleaning method using a chemical. As a physical cleaning method, a flushing method from the inside of the film with air is effective. As a method for cleaning the inside of the membrane with air, there is a membrane surface cleaning method using a blower. The backwashing blower is operated for 30 seconds to 1 minute every hour by a timer, and continuously cleans the membrane surface from the inside of the membrane with high-pressure air. When the decrease in the amount of permeated water cannot be prevented only by the physical cleaning method, flushing is performed periodically from the outside and inside of the membrane with an acid or the like. In the case of the present invention, since the component adhering to the film is considered to be a metal hydroxide, the adhering matter can be easily dissolved by the acid. The dissolved wastewater is returned to the pH adjustment tank 1 and reprocessed.

As described above, according to the present invention, almost complete closed system of the metal-containing wastewater can be realized.

Next, a method of recovering nickel and zinc after selectively removing iron and chromium in advance from wastewater containing many metal ions such as nickel, zinc, ferrous iron and chromium will be described.

In the ordinary neutralization coagulation sedimentation method, the pH is adjusted to 8 to 1
When it is set to 0, sludge containing a mixture of nickel, zinc, ferrous iron and chromium hydroxide is generated. For this reason, it is difficult to reuse sludge. In the case of such drainage,
Separation and recovery are difficult using only the membrane method.

Therefore, the present inventor has found a method of dividing and collecting valuable metals into two groups by the following method. FIG. 2 shows this processing flow.

First, a method for removing iron and chromium in wastewater will be described. The present inventor has found that when trivalent iron precipitates as hydroxide in the pH range of 3 to 4, chromium is also removed by coprecipitation with iron. This pH
Nickel and zinc do not produce hydroxides in the area,
No coprecipitation phenomenon occurs. Therefore, iron, chromium and nickel, and zinc can be separated.

[0061] Metal-containing wastewater such as plating factory wastewater usually has a low pH of 1-2, and the wastewater contains ferrous iron. Ferric iron precipitates at very low pH, whereas ferrous iron dissolves at low pH. Therefore, for separation and recovery, it is first necessary to oxidize ferrous iron to trivalent iron in a low pH region.

The ferrous iron contained in the heavy metal-containing wastewater
As a method of oxidizing to valent iron, a method of oxidizing using agents such as sodium hypochlorite and hydrogen peroxide, ozone, and the like is widely known. However, in the method of oxidizing ferrous iron with a chemical such as sodium hypochlorite or hydrogen peroxide, it is difficult to control the amount of the oxidizing agent. Further, when the concentration of divalent iron in the wastewater is high, there is a disadvantage that the treatment cost of the oxidizing agent becomes extremely high.

In addition to these methods, there is a biological oxidation method of ferrous iron using iron oxidizing bacteria. Iron-oxidizing bacteria are roughly classified into neutral / filamentous bacteria and acidic / non-filamentous bacteria, and the bacteria used here are the latter acidic / non-filamentous bacteria. Thiobachillus ferrooxida, a chemically synthesized independent bacterium
NS is known as a representative bacterium. Such a biological method of oxidizing ferrous iron in wastewater to trivalent iron, that is, a method of oxidizing iron by a so-called iron oxidizing bacterium, is disclosed in Japanese Patent Publication No. 47-3 / 1973.
No. 8981, No. 55-18559, No. 55-
Nos. 22345 and 57-43393. When treating wastewater containing iron (II) with iron-oxidizing bacteria, iron (II) can be rapidly oxidized to iron (III) at a low pH, and the cost is lower than that of the chemical oxidation method. However, the iron oxidizing bacteria have a very low growth rate and a small ability to form flocs as compared with heterotrophic bacteria that degrade organic matter.
Therefore, measures are needed to maintain high concentrations of iron oxidizing bacteria in biological reactors. However, in a process comprising a normal biological reactor-sedimentation basin, the concentration of iron oxidizing bacteria in the biological reactor is governed by the sedimentation of the iron oxidizing bacteria in the sedimentation basin.
There is a limit to increasing the concentration of iron-oxidizing bacteria in biological reactors. Also, if the amount of aeration in the biological reaction tank is excessive, the flocs of iron oxidizing bacteria are destroyed and easily flow out of the sedimentation pond into the treated water. As a result, since the iron-oxidizing bacteria are not returned from the sedimentation tank to the biological reaction tank, the concentration of the iron-oxidizing bacteria in the biological reaction tank may decrease rapidly.

Therefore, in order to use the iron-oxidizing bacteria, the MF membrane separation device 9 for collecting the iron-oxidizing bacteria is installed inside or outside the iron-oxidizing bacteria reaction tank 8 in comparison with the ordinary biological reaction tank-sedimentation tank process. It is desirable to install and separate iron oxidizing bacteria and treated water. Size of iron oxidizing bacteria is 1μm
MF, the pore size of the MF is 1 μm or more.
A membrane is sufficient. In fact, iron oxidizing bacteria adhere to iron hydroxide
Proliferates and forms floc to some extent;
A hole diameter of about m may be used. If the membrane diameter can be increased,
There is an advantage that the amount of permeated water increases and the equipment can be downsized. Also, backwashing becomes easy. In order to promote the formation of iron-oxidizing bacterial flocs, a polymer flocculant may be added to the iron-oxidizing bacteria reaction tank 8 to such an extent that the activity of the iron-oxidizing bacteria is not inhibited. In this case, a membrane having a pore size of about 200 μm may be used for the MF membrane separator 9 for collecting iron-oxidizing bacteria.

Further, the material of the film is preferably a ceramic which is easy to clean because iron oxide easily adheres to the film.

In this example, since the MF membrane separation device 9 for collecting iron oxidizing bacteria is installed in place of the sedimentation basin, the concentration of iron oxidizing bacteria in the iron oxidizing bacterium reaction tank 8 is controlled by the precipitation of iron oxidizing bacteria. And the concentration of iron-oxidizing bacteria in the iron-oxidizing bacteria reaction tank 8 can be easily increased. As a result, in this example, the concentration of the iron-oxidizing bacteria in the iron-oxidizing bacteria reaction tank 8 was 2-3
It can be maintained twice. For this reason, the volume of the iron oxidizing bacteria reaction tank 8 can be reduced to 1/2 to 1/3 as compared with the conventional case.

According to the biological oxidation method, in the range of pH = 3-4, ferrous ions turn into trivalent iron ions and further turn into hydroxides in the iron oxidizing bacteria reaction tank 8. At this time, trivalent chromium is simultaneously precipitated by coprecipitation. The iron-chromium-based sludge thus produced can be reused as a raw material for stainless steel after drying-granulation. If chromium is not contained in the wastewater, it is easier to reuse,
It can be reused as iron sludge in the blast furnace of a steel mill.

Further, nickel ions,
Zinc ions remain. For this treatment, the pH
After adjusting the pH to 8 to 10 in the adjustment tank 1 and forming nickel and zinc hydroxides, the MF membrane separator 2 may be used to recover the nickel and zinc hydroxides. The recovered nickel and zinc hydroxides are dissolved in the re-dissolution tank 6 and reused in the plating bath at the factory.

The MF membrane permeated liquid is adjusted to pH =
7 to 8 and treated by the RO membrane separation device 5 to reuse as industrial water. A small amount of RO membrane concentrate is generated,
Since it is mainly composed of inorganic ions, it can be discharged into public water bodies as it is.

[0070]

EXAMPLE 1 The method of the present invention was applied to a plating plant rinse drainage generated from a steel mill. The applied wastewater is Ni ²⁺
Was contained at an average of 50 mg / l, Zn ²⁺ was contained at 150 mg / l, and almost no Fe ²⁺ was contained. The water temperature of the waste water was about 10 ° C to 35 ° C. Conventionally, it has been treated by the neutralization coagulation sedimentation method, and the generated sludge has been disposed of. An example in which the present method is applied to the treatment of plating wastewater generated from such a steelworks will be described with reference to FIG.

First, in the pH adjusting tank 1, the pH of the waste water was adjusted to 10 with a 1 mol NaOH solution.
The mixture was rapidly stirred for 5 minutes and slowly stirred for 20 minutes to generate a hydroxide, and the water was passed through the MF membrane separation device 2 by the pump 3. The MF membrane separation device 2 was deposited near the outlet inside the pH adjustment tank 1.

The membrane of the MF membrane separator 2 has a pore size of 1
A μm silica-alumina ceramic film was used. Backwashing of the membrane was performed by a backwashing blower for 30 seconds every hour, and the membrane surface was continuously washed from the inside of the ceramic with 1 to 5 kg / cm ² of air.

As shown in Table 1, the treated water of the continuous treatment is as follows:
Ni ²⁺ averages 0.04 mg / l, Zn ²⁺ averages 0.33
mg / l or less was good. Furthermore, when 10% sulfuric acid was added to the hydroxide concentrate to adjust the pH to 1, N
A high concentration solution of i and Zn was obtained, and reuse became possible.
Both Ni and Zn could be concentrated 76 to 77 times.

According to the present invention, it is possible to obtain treated water that complies with the regulation value, to recover valuable metals that were impossible in the past, and to reduce sludge disposal costs.

[0075]

[Table 1]

[0076]

Example 2 The method of the present invention was applied to a plating plant effluent generated from an ironworks and containing many metal ions.

The effluent has a pH of 2 to 3 and an average of 50% of Fe ^2+.
0 mg / l, Ni ²⁺ averaged 500 mg / l, Zn ²⁺ averaged 300 mg / l, and Cr ³⁺ averaged 100 mg / l. The water temperature of the waste water was about 10 ° C to 35 ° C. An example in which the present method is applied to the treatment of plating wastewater generated from such a steelworks will be described with reference to FIG.

First, activated sludge (active sludge concentration: 1000 mg / l) from a sewage treatment plant that is treating municipal sewage is put into the iron oxidizing bacteria reaction tank 8, settled, and the supernatant is discarded. Then, wastewater was charged, aeration was performed, and the growth of iron-oxidizing bacteria was attempted. The aeration was controlled by DO with the DO (dissolved oxygen) in the iron oxidizing bacteria reaction tank 8 set to 3 mg / l. PH of iron oxidizing bacteria reaction tank 8
With 10% sulfuric acid and 10% aqueous NaOH,
Controlled at 3. Nitrogen and phosphorus were added to the iron oxidizing bacteria reaction tank 8 at 10 mg / l each. Iron oxidizing bacteria reaction tank 8
About two weeks after supplying the wastewater, the ORP (redox potential) of the iron oxidizing bacteria reaction tank 8 became +550 mV or more, and the Fe ^{2+ of} the treated water became 10 mg / l or less. At this stage, the sludge in the iron oxidizing bacteria reaction tank 8 was settled, the supernatant was removed, and the same wastewater was supplied. This operation was repeated, and the iron-oxidizing bacteria multiplied, and within 24 hours, when the Fe ^{2+ of} the treated water became 10 mg / l or less, the process was shifted from batch processing to continuous operation (HRT = 3 hours).

The membrane of the MF membrane separation device 9 for collecting iron oxidizing bacteria installed inside the iron oxidizing bacterium reaction tank 8 was silica-based.
An MF film made of alumina ceramics and having a pore diameter of 10 μm was used. The blower for backwashing the MF membrane is set to 1
It runs for 1 minute every hour, with 5 kg / cm ² of air,
The film surface was continuously cleaned from the inside of the ceramic film. In the continuous operation, the aeration amount was set to +550 mV (Ag / AgCl
And the blower was controlled by the ORP.

As a result, the treated water in the continuous treatment had a good Fe ²⁺ of 0.5 mg / l or less. The concentrated solution of iron hydroxide, chromium hydroxide and iron oxidizing bacteria generated by the MF membrane
A part was returned to the iron oxidizing bacteria reaction tank 8, and a part was withdrawn, dried, granulated, and reused. Iron hydroxide, chromium hydroxide, and iron oxidizing bacteria were accumulated in the iron oxidizing bacteria reaction tank 8, and the MLSS (Mixed liquor suspended solids) concentration was controlled at 100 to 200 g / l.

Further, 1 mol of N-treated water
The pH was adjusted to 9 in the pH adjusting tank 1 with the aOH solution. The mixture was rapidly stirred for 5 minutes and slowly stirred for 20 minutes to produce a nickel and zinc hydroxide. After this, pump 3
MF membrane separation device 2 installed outside pH adjustment tank 1
Water. As the membrane of the MF membrane separation device 2, a silica-alumina-based ceramics MF membrane having a pore diameter of 1 μm was used. The backwashing of the MF film was performed by a backwashing blower for 30 seconds every hour, and the film surface was continuously washed from the inside of the ceramic with 1 to 5 kg / cm ² of air.

As shown in Table 2, the treated water of the continuous treatment is as follows:
Ni ²⁺ averages 0.04 mg / l, Zn ²⁺ averages 0.33
mg / l or less was good. In the re-dissolution tank 6, 30% sulfuric acid was added to 30-fold concentrated Ni and Zn hydroxides after the MF membrane separation, and the pH was adjusted to 0.7. As a result, both Ni and Zn could be concentrated about 27 times, and could be reused as a plating solution. The membrane permeated water was treated by the RO membrane separation device 5 and reused as industrial water.

[0083]

[Table 2]

[0084]

According to the present invention, the amount of sludge generated can be reduced by efficiently and stably treating metal-containing wastewater generated from plating plants and the like, and by collecting and reusing valuable metals from the wastewater. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a processing flow of the present invention.

FIG. 2 is a diagram showing an example of a processing flow of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 pH adjustment tank 2 MF membrane separation apparatus 3 Pump 4 Re-pH adjustment tank 5 RO membrane separation apparatus 6 Re-dissolution tank 7 Pump 8 Iron oxidizing bacteria reaction tank 9 MF membrane separation apparatus for iron oxidizing bacteria recovery 10 Pump

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 1/56 C02F 1/56 K 1/64 1/64 3/34 3/34 Z F term (reference) 4D006 GA03 GA07 HA95 KA01 KA43 KA46 KB22 KC03 KC14 KD08 KD11 KD17 KE15P KE15Q KE15R MA22 MB12 MB15 MB16 MC03 MC03X PA04 PA05 PB08 PB27 PB70 PC22 4D038 AA08 AB65 AB66 AB67 AB69 BA04 BA06 BB09 BA19 BB13 4DB06 BB13 4DB06 BB13 BB06 DB23 EA07 EA13 EA15 EA16 EA37 FA03 FA17 FA30

Claims (8)

[Claims] After the pH of a metal-containing wastewater is adjusted to form a metal hydroxide, water is passed through a membrane separation device having a pore size of 1 μm to 10 μm to separate water and the metal hydroxide. A method for treating metal-containing wastewater and recovering valuable metals. 2. After adjusting the pH of the metal-containing wastewater to form a metal hydroxide, and also using a polymer coagulant or a liquid chelating agent in combination to form a metal hydroxide floc, A method for treating metal-containing wastewater and recovering valuable metals, wherein water and flocs of metal hydroxide are separated by passing water through a membrane separation device having a pore size of 50 μm to 200 μm. 3. In a first step, the pH is adjusted to 3 to 4 from metal-containing wastewater containing ions of trivalent chromium and iron (II) to oxidize iron (II) to iron (III) to form chromium. After the iron hydroxide is formed, water and iron and chromium hydroxide are separated by passing water through a membrane separation device having a pore size of 1 μm to 10 μm. A method for treating metal-containing wastewater and recovering valuable metals, comprising separating and recovering the remaining metal by the method according to claim 1 or 2 in two stages. 4. The method for treating metal-containing wastewater and recovering valuable metals according to claim 3, wherein iron oxidizing bacteria are used when oxidizing ferrous iron to ferric iron. 5. A metal-containing wastewater containing ions of nickel, zinc, trivalent chromium and divalent iron, wherein the wastewater contains metal ions.
In the second step, the pH is adjusted to 8 to 10 to form hydroxides of nickel and zinc, and the water is separated from the hydroxides of nickel and zinc. A method for treating metal-containing wastewater and recovering valuable metals. 6. The method for treating metal-containing wastewater and recovering valuable metals according to claim 1, wherein a membrane made of ceramics is used as the membrane separation device. 7. The concentrate of a metal hydroxide separated and recovered,
The treatment of metal-containing wastewater according to any one of claims 1 to 6, wherein the metal is redissolved by adjusting the pH to 0.5 to 3 with sulfuric acid, and a concentrated solution of the metal is collected and reused. And how to collect valuable metals. 8. The metal-containing material according to claim 1, wherein the treated water after separating and recovering the metal hydroxide is passed through a reverse osmosis membrane to reuse the treated water. Wastewater treatment method and valuable metal recovery method.