JPH1180850A - Method for recovering silver component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering a silver component with which an always high recovery rate of the silver component is obtainable by adding a specific high- polymer flocculating agent to silver halide-contg. waste water, then adding an anionic high-polymer flocculating agent thereto, thereby flocculating the waste water. SOLUTION: The N-vinyl acrylamide salt unit-contg. high-polymer flocculating agent is added to the silver halide-contg. waste water generated at the time of producing photosensitive materials, etc., and thereafter the anionic high-polymer flocculating agent is added thereto to flocculate the waste water and to separate the silver component, by which the recovery of the silver component is executed. An org. coagulating agent may be added to the waste water before or simultaneously with the addition of the N-vinyl acrylamide salt unit-contg. high-polymer flocculating agent. According to this method, the always high recovery rate of the silver component is obtd. and the efficient recovery of the silver component is made possible without receiving the influence of the density and kinds of the silver component in the waste water and the fluctuation in the characteristics, such as pH, of the waste water and without allowing the formed flocs to adhere to piping, reaction vessel, etc., as the viscosity of the flocs is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering a silver component from a silver halide-containing waste water generated during the production of a photosensitive material such as a photographic film, an X-ray film, and a photosensitive paper.

[0002]

2. Description of the Related Art Conventionally, when a silver component is separated and recovered from a silver halide-containing wastewater generated during the production of a photosensitive material such as a photographic film, an X-ray film, and a photosensitive paper, the silver halide-containing wastewater has been centrifuged. And solid-liquid separation (floating separation method), or a method of adding a foaming agent to a silver halide-containing wastewater and float-separating to separate the silver component into solid-liquid (floating separation method). .

Further, as a method using a polymer flocculant, a method of adding an inorganic flocculant such as an aluminum salt and an iron salt and an anionic polymer flocculant to a silver halide-containing wastewater,
Alternatively, the pH of the silver halide-containing wastewater is adjusted to an acidic side, and then flocculation is carried out by adding a polymerizable cationic polymer flocculant and an anionic polymer flocculant. A method has been proposed.

Further, in order to recover the silver component from the silver halide-containing wastewater at a stable and high recovery rate, a condensation type cationic polymer flocculant, a polymerization type cationic cationic polymer flocculant, A method of adding three kinds of anionic polymer flocculants (JP-A-2-159326)
No.) or a silver halide-containing wastewater, a condensation-type cationic polymer flocculant and a polymerizable cationic polymer flocculant are separately added or added simultaneously, and then an anionic polymer flocculant is added. And a method of further adding a polymerizable polymer flocculant (JP-A-5-247551).

[0005]

However, the centrifugal separation method and the flotation separation method described above are easily affected by the type and particle size of the silver component, and a stable high recovery rate of the silver component cannot be obtained. On the other hand, the method of adding an inorganic flocculant has a drawback in that the purification of silver is difficult and requires a high cost because metal components other than silver caused by the inorganic flocculant added to the floc subjected to solid-liquid separation are mixed. In addition, after adjusting the pH to the acidic side, the method of adding the polymerizable cationic polymer flocculant and the anionic polymer flocculant cannot capture fine silver components and not only has a low silver component recovery rate, but also There is a drawback that the dehydration treatment is difficult due to the poor strength and dehydration of the solid-liquid separated floc containing silver component. In addition, these methods have a disadvantage that it is difficult to cope with fluctuations in properties such as the concentration of silver component in the wastewater, the type of the silver component, and the pH of the wastewater, and a high silver component recovery rate cannot be stably obtained. was there.

As a method for remedying these drawbacks, a method disclosed in Japanese Patent Application Laid-Open No. 2-159326 has been proposed. However, it is difficult to capture fine silver component particles, and large amounts of silver halide-containing wastewater are produced. Unable to cope with property changes,
Furthermore, there is a problem that the generated floc has a high viscosity and adheres to a pipe, a reaction tank, or the like, and there is a disadvantage that the recovery rate of the silver component is reduced.

Further, in order to solve the disadvantages of the method disclosed in Japanese Patent Application Laid-Open No. 2-159326, Japanese Patent Application Laid-Open
Although the method disclosed in Japanese Patent No. 7551 is proposed,
The disadvantage of the viscosity of the formed floc was not improved, and it was not enough to stably obtain a high silver component recovery rate.

The present invention solves the above-mentioned drawbacks of the prior art, and is substantially free from the influence of changes in properties such as the concentration of silver component in the wastewater containing silver halide, the type of silver component, and the pH of the wastewater. Another object of the present invention is to provide a method for recovering silver components from silver halide-containing wastewater, which can always achieve a high silver component recovery rate without causing flocs to adhere to pipes and reaction vessels. Is what you do.

[0009]

In order to achieve this object, the present invention provides a method of adding an anionic polymer flocculant to a silver halide-containing wastewater after adding a polymer flocculant containing an N-vinylacrylamidine salt unit. It is an object of the present invention to provide a method for recovering a silver component, which comprises adding and coagulating to separate a silver component.

Hereinafter, the present invention will be described in detail. Examples of the silver halide contained in the wastewater containing silver halide to be processed in the present invention include silver chloride, silver bromide, silver iodide and the like. In general, silver halide-containing wastewater is discharged from various processes, and usually contains many chemical substances such as surfactants, emulsifiers, and bleaching agents in addition to the above silver halide. There is also a silver halide component forming a colloid, and the above-mentioned contained chemical substance component, pH of wastewater,
The properties such as the electrical conductivity are different, and it is not easy to efficiently extract the silver component from the wastewater containing silver halide.

The present inventors have developed various treatments for silver halide-containing wastewater whose components and properties are different or fluctuate as described above, including various coagulants, including their combination and order of use. As a result of examining the method, it has been found that the above-described method for recovering a silver component of the present invention can solve the disadvantages of the prior art and can always achieve a high silver component recovery rate.

The polymer flocculant containing an N-vinylacrylamidine salt unit used in the present invention will be described in more detail. The polymer coagulant containing an N-vinylacrylamidine salt unit used in the present invention is described in, for example, JP-A-5-192513, JP-A-8-155500, and JP-A-8-2.
No. 43600, JP-A-9-87323, and the like, and are polymer flocculants containing a structural unit represented by the following general formula [I]. In the following general formula [I], X ^- represents an anion, examples of which include
Examples thereof include chloride ion, bromine ion, iodine ion, nitrate ion, acetate ion, formate ion, and sulfamate ion.

[0013]

Embedded image

Although the N-vinylacrylamidine salt unit is used, in producing this polymer flocculant, the N-vinylacrylamidine salt unit is used.
It does not mean that vinylacrylamidine salt is used as a monomer, but as can be understood by referring to the above-mentioned respective patent publications, the polymer coagulant finally obtained contains an N-vinylacrylamidine salt unit. Meaning.
For example, when an N-vinylacrylamidine salt unit-containing polymer flocculant is produced by polymerizing, partially hydrolyzing, or amidinizing N-vinylformamide as a monomer (Japanese Patent Application Laid-Open No. 9-87323), -A vinylacrylamidine salt unit, an N-vinylformamide unit and a vinylamine (salt) unit,
When an acrylonitrile as a monomer and N-vinylformamide are copolymerized, (partially) hydrolyzed, and amidinated, a polymer flocculant containing an N-vinylacrylamidine salt unit is produced (JP-A-5-192513). ), N-vinylacrylamidine salt units, acrylonitrile units, N-vinylformamide units and / or
Or it contains a vinylamine (salt) unit. Further, other appropriate monomers may be used, and in addition to the above structural units, methacrylonitrile units, N-vinylacetamide units, (meth) acrylamide units, N-vinyl (meth) acrylamide units, (meth) acryl units Acid unit, methyl (meth) acrylate unit, ethyl (meth)
N containing at least one of various structural units such as an acrylate unit, a vinyl acetate unit, an N-vinylpyrrolidone unit, a styrene unit, a 2-acrylamido-2-methylpropanesulfonic acid unit, and a dimethylaminoethyl (meth) acrylate unit. -It may be a polymer flocculant containing a vinyl acrylamidine salt unit. All of the amine units may be in the form of a salt, but some may be in a free form,
In the case where an acid-based unit is contained, a salt form in which a part or all of hydrogen ions are substituted by an alkali metal ion, an ammonium ion, or the like may be used. Such various N-vinylacrylamidine salt unit-containing polymer flocculants can be used alone or in combination. Preferred examples of the N-vinylacrylamidine salt unit-containing polymer flocculant include acrylamide units, acrylonitrile units, and N-vinylacrylamidine salt units.
-A copolymer comprising vinylacrylamidine hydrochloride units, N-vinylacrylamide units, vinylamine hydrochloride units, and N-vinylformamide units.

The N-vinylacrylamidine salt unit-containing polymer flocculant can be used alone, but may also be a polymer of dimethylaminoethyl (meth) acrylate and / or a mixture of dimethylaminoethyl (meth) acrylate and acrylamide. It can also be used as a mixture with a copolymer.

The amount of the polymer coagulant containing an N-vinylacrylamidine salt unit is not particularly limited, but is preferably in the range of 1 to 1000 mg / liter (L) from the viewpoints of effect and economy.

The anionic polymer flocculant used in the present invention will be described. As the anionic polymer flocculant used in the present invention, for example, a polymer of acrylic acid or a salt thereof,
A copolymer of acrylic acid or a salt thereof and acrylamide,
Copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonate, tertiary copolymer of acrylic acid or a salt thereof and acrylamide and 2-acrylamido-2-methylpropanesulfonate, partial hydrolysis of polyacrylamide But are not particularly limited thereto. The molecular weight of the anionic polymer flocculant is not particularly limited, but is preferably in the range of 5,000,000 to 20,000,000. These anionic polymer flocculants can be used alone or as a mixture. The addition amount of the anionic polymer coagulant is not particularly limited, but is preferably in the range of 1 to 500 mg / L from the viewpoint of effect and economy.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

In the method of the present invention, before adding the polymer flocculant containing N-vinylacrylamidine salt units to the wastewater containing silver halide, or simultaneously with adding the polymer flocculant containing N-vinylacrylamidine salt units. An organic coagulant can also be added. In this case, it is preferable from the viewpoint of improving the turbidity of the treated water.

The organic coagulant that may be used in the present invention will be described. The organic coagulant that can be used in the present invention is a cationic polymer coagulant having a molecular weight of 1,000 to 1,000,000 other than the N-vinylacrylamidine salt unit-containing polymer coagulant, for example, polydimethyldiallylammonium chloride, Polyethylene imine, condensate of dialkylamine and epichlorohydrin, condensate of alkylene dichloride and polyalkylene polyamine,
Examples include a condensate of dicyandiamide and formaldehyde, but are not particularly limited thereto. These organic coagulants can be used alone or as a mixture. The amount of the organic coagulant added is not particularly limited, but is preferably in the range of 1 to 1000 mg / L from the viewpoints of effect and economy.

The order of adding each of the above-mentioned chemicals used in the present invention is as follows: a polymer coagulant containing an N-vinylacrylamidine salt unit is added first, and then an anionic polymer coagulant is added. By doing so, at least the object of the present invention can be achieved. Therefore, for example, after the step of adding the anionic polymer coagulant, the step of adding the N-vinylacrylamidine salt unit-containing polymer coagulant again, or the step other than the N-vinylacrylamidine salt unit-containing polymer coagulant May be added.

The jar test was performed by changing the type, the addition amount ratio and the stirring condition of each agent to determine the optimum type, the optimum addition amount ratio and the optimum stirring condition of each of the above-mentioned agents. Floating or sinking speed of floc, silver concentration of treated water, CST (capillary suction ti
me) It may be determined from a value or the like.

The method of the present invention can be applied at a temperature of the wastewater containing silver halide of 0 to 70 ° C.
C. is more preferred.

In the present invention, examples of means for separating flocs include, but are not limited to, flotation, sedimentation, centrifugation, and filtration separation using a vibrating sieve. For example, if the floc contains air bubbles and is light, a flotation device may be used. On the other hand, if the floc has a large density and a large particle size and has good sedimentation, a flocculation and sedimentation device may be used.

When dewatering the silver component-containing sludge obtained by concentrating the floc using a flotation device or a coagulating sedimentation device, any of dehydrators such as a screw press type dehydrator, a centrifugal dehydrator and a belt press type dehydrator can be used. These dehydrators may be used depending on the properties of the silver component-containing sludge.

By purifying the silver component-containing dehydrated cake obtained by the dehydration treatment by, for example, a heat treatment at 500 to 1000 ° C., metallic silver can be efficiently recovered.

According to the method of the present invention, it is not affected by the change in the type, concentration and properties of the silver component, and the floc is not always adhered to the pipes and the reaction tanks, so that the wastewater containing the silver halide is always high. The silver component can be recovered at a recovery rate.
The mechanism of action for obtaining the effect of the present invention is not clear, but is presumed as follows.

That is, the N-vinylacrylamidine salt unit-containing polymer flocculant used in the present invention is compared with a conventional cationic polymer flocculant such as polydimethylaminoethyl (meth) acrylate methyl chloride quaternary salt. Has a high-density cationic structure and efficiently reacts with and aggregates with a substance (dispersant such as gelatin) that disperses silver halide in silver halide-containing wastewater, thereby separating the silver component. It is considered that a high silver component recovery rate can be stably obtained. In addition, since the N-vinylacrylamidine salt unit-containing polymer flocculant has an amidine-based cyclic structure in the molecule, the generated floc has a low viscosity and adheres to the liquid-contact part of a device such as a pipe or a reaction tank. Is considered to be suppressed.

[0029]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Examples 1 to 12 and Comparative Examples 1 to 8 N-vinylacrylamidine salt unit-containing polymer flocculant (B), anionic polymer flocculant (A) and cationic polymer used in Examples and Comparative Examples The polymer flocculants (C) are shown in Table 1 together with their colloid equivalent values. Organic coagulating agent used in Examples and Comparative Examples of (Y ₁ and Y ₂₎ together with their colloid equivalent value shown in Table 2. Table 3 shows the properties of the silver halide-containing wastewater (wastewater and wastewater) used in the recovery of the silver component in Examples and Comparative Examples. Both wastewaters are wastewaters containing silver halide discharged from the step of producing a photographic photosensitive material.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

In each of the examples and comparative examples, the flocculant was added to the test silver halide-containing wastewater shown in Table 3 in the addition order and amount shown in Table 4 and stirred to remove suspended substances in the wastewater. A jar test was conducted to flocculate and separate flocs formed by flocculation precipitation. Each test was performed at room temperature under the condition of stirring at about 150 rpm for about 60 seconds after the addition of each drug. In Comparative Examples 1 and 2, the first agent was polyaluminum chloride (PAC) as an inorganic coagulant.
Was added.

[0035]

[Table 4]

Table 5 shows the processing results in the examples and comparative examples. In the column of the viscosity of the floc in Table 5, ◎ indicates that the viscosity of the floc is the lowest, and subsequently, the viscosity of the floc increases in the order of ○, Δ, and ×.

[0037]

[Table 5]

As is evident from Table 5, according to the method of the present invention, after adding a polymer flocculant containing an N-vinylacrylamidine salt unit, Examples 1 to 6 in which an anionic polymer flocculant was added and N -In Examples 7 to 12 in which an anionic polymer coagulant was added after adding a polymer coagulant containing a vinylacrylamidine salt unit and an organic coagulant,
For all of the wastewaters, a high recovery rate of the silver component was obtained, and good results were also obtained in which the generated flocs had low viscosity.

On the other hand, Comparative Examples 1-2 according to the conventional method
In comparison with the embodiment according to the method of the present invention,
The g concentration was high, and the floc produced was also viscous, and satisfactory results could not be obtained. In addition, as a method for improving the conventional method used in Comparative Examples 1 and 2, Comparative Examples 3 and 4 and Comparative Example 3 according to the processing methods proposed in JP-A-2-159326 and JP-A-5-247551, respectively. In Examples 5 to 8, better results were obtained than Comparative Examples 1 and 2 of the conventional method, but the results were inferior to those of Examples according to the method of the present invention. The recovery rate of the components was not sufficient, and the generated floc was more viscous than Comparative Examples 1 and 2 of the conventional method, and the viscosity of the floc was not improved.

According to the method of the present invention, the recovery rate of the silver component is better than any of the above-mentioned conventional methods with respect to any of the silver halide-containing effluents, and the generated floc has a low viscosity. The silver component could be efficiently recovered from the wastewater containing silver halide.

[0041]

According to the method of the present invention, there is no effect of fluctuations in properties such as the concentration of silver component in the waste water containing silver halide, the type of silver component, the pH of the waste water, and the viscosity of the floc generated. , The high silver component recovery rate is always obtained without adhering to pipes and reaction tanks, and a long-term safe operation can be expected. Thus, the silver component can be efficiently recovered.

Claims (2)

[Claims] The present invention is characterized in that a polymer flocculant containing an N-vinylacrylamidine salt unit is added to a silver halide-containing wastewater, and then an anionic polymer flocculant is added to cause coagulation to separate a silver component. Of recovering silver components. 2. An organic coagulant is added to the waste water containing silver halide before adding the polymer flocculant containing N-vinylacrylamidine salt units or simultaneously with adding the polymer flocculant containing N-vinylacrylamidine salt units. The method for recovering a silver component according to claim 1, wherein the silver component is added.