JP5573763B2 - High purity silver production waste liquid treatment method - Google Patents

Description

  The present invention relates to a method for treating a waste liquid generated in a high purity silver production process.

  Conventionally, silver is used to produce anode slime generated in the electrolytic refining process in the refining of copper, lead, etc., intermediates generated in the processing process of silver-containing liquids such as plating solutions and photographic developers, and refining processes for precious metals. Recovered from smelting intermediate. As a method for recovering silver from these smelting intermediates, for example, silver is leached from the smelting intermediate using an aqueous sulfite solution, the resulting leachate is acidified to precipitate silver chloride, and the precipitated chloride A method is known in which silver is purified by oxidation treatment in an acidic aqueous solution, and the purified silver chloride is reduced in an alkaline aqueous solution to obtain silver (see Patent Document 1). According to this method, high-purity silver can be efficiently obtained without performing dry refining that remains problematic in terms of environment and work.

Japanese Patent No. 4207959

However, in the method described in Patent Document 1, a waste liquid containing impurities such as Se and Te and a large amount of sulfite ion (SO ₃ ²⁻ ) is generated in the step of precipitating silver chloride and the step of purifying silver chloride. Therefore, in the wastewater treatment process of the waste liquid, it is necessary to remove impurities such as Se and Te by reduction treatment and to neutralize SO ₃ ²⁻ , which requires a large amount of chemicals, and wastewater treatment is expensive. There was a problem of becoming.

  This invention is made | formed in view of the said situation, The place made into the objective is to aim at reduction of the wastewater treatment load of the waste liquid generated in the manufacturing process of high purity silver.

  The inventors of the present invention have made extensive studies to solve the above problems, and found that the above problems can be solved by effectively using the generated waste liquid as a chemical for the process, thereby completing the present invention. It came. Specifically, the present invention provides the following.

(1) A silver leaching step of leaching silver from a smelting intermediate containing silver with a sulfite aqueous solution, a silver chloride precipitation step of neutralizing the leached liquor to precipitate silver chloride, and the precipitated silver chloride as an acidic aqueous solution A method for producing high purity silver comprising a silver chloride refining step, wherein the sulfuric acid and / or hydrochloric acid are added to the waste liquid generated in the silver chloride precipitation step and / or the silver chloride refining step. The SO ₃ ^2- step for removing SO ₃ ^2- from the waste liquid and the SO ₂ gas generated in the de-SO ₃ ^2- step are absorbed in an aqueous solution of alkali metal hydroxide and / or alkali metal carbonate. A sulfite aqueous solution generation step for obtaining a sulfite aqueous solution, and using the sulfite aqueous solution obtained in the sulfite aqueous solution generation step as a sulfite aqueous solution used in the silver leaching step. A method for treating a high-purity silver production waste liquid.

(2) In the de-SO ₃ ^2- step, sulfuric acid and / or hydrochloric acid is added so that the pH of the waste liquid after addition of sulfuric acid and / or hydrochloric acid is 0 to 4.5. Manufacturing waste liquid treatment method.

  (3) After adjusting the sulfite concentration of the sulfite aqueous solution obtained in the sulfite aqueous solution generation step to 150 to 250 g / L, the adjusted sulfite aqueous solution is used in the silver leaching step. The processing method of the high purity silver manufacture waste liquid as described in (1) or (2) utilized as above.

(4) The method for treating a high-purity silver production waste liquid according to (3), wherein the sulfite concentration is adjusted using the waste liquid after removing SO ₃ ^2- in the de-SO ₃ ^2- step.

  According to the present invention, waste liquid that requires wastewater treatment can be effectively used as a process chemical, so that the amount of chemical required for wastewater wastewater treatment such as impurity removal and neutralization can be reduced. The wastewater treatment load can be reduced. In addition, the cost of chemicals for process can be reduced.

It is process drawing which shows an example of the manufacturing method of the high purity silver to which the processing method of the waste liquid concerning one Embodiment of this invention is applied. It is process drawing which shows an example of the manufacturing method of the conventional high purity silver.

  Hereinafter, the waste liquid treatment method of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing a method for producing high purity silver to which a waste liquid processing method according to an embodiment of the present invention is applied, and FIG. 2 is a diagram showing high purity silver to which the waste liquid processing method of the present invention is applied. It is process drawing which shows an example of this manufacturing method, ie, the conventional manufacturing method of high purity silver. First, a conventional method for producing high-purity silver will be briefly described with reference to FIG. 2, and then the waste liquid treatment method of the present invention will be described in detail with reference to FIG.

[Production method of high purity silver]
The method for producing high purity silver to which the waste liquid treatment method of the present invention is applied has a pretreatment step, a silver leaching step, a silver chloride precipitation step, a silver chloride purification step, and a silver powder recovery step (FIG. 2). ). In the manufacturing method of high purity silver which has this process, the smelting intermediate containing silver is used as a raw material. The smelting intermediate is not particularly limited. For example, an anode slime generated in an electrolytic purification process in the refining of copper, lead, etc., which is a smelting intermediate containing a sparingly soluble silver compound and an impurity element, Intermediates generated in the processing step of a silver-containing solution such as a plating solution and a photographic developer, the refining step of a noble metal, and the like. Here, as impurity elements contained in the smelting intermediate, for example, copper, nickel, lead, iron, cobalt, manganese, sulfur, zinc, cadmium, tin, gold, group V such as arsenic, antimony, bismuth, etc. Elements, group VI elements such as selenium and tellurium, and platinum group elements. When an anode slime containing a large amount of noble metal is used as a raw material, gold or palladium is first leached by leaching with chlorine gas in order to preferentially collect more expensive noble metals such as gold and palladium. The leachate is processed in a separate process to recover gold and palladium. The leaching residue produced simultaneously with leaching with chlorine gas usually contains about 15 to 30% by mass of silver in the form of silver chloride. In addition, the smelting intermediate of the present invention includes a leaching residue with chlorine gas as described above and a smelting intermediate that has undergone a pretreatment process described later.

<Pretreatment process>
The pretreatment step is a step of adding water to the smelting intermediate and washing the smelting intermediate with repulp. The repulp washing is performed for the purpose of removing impurities adhering to the leaching residue and anions in the leaching residue, particularly Cl ⁻ . The pretreatment step is not an essential step, but is preferably performed from the viewpoint of reducing the amount of impurities mixed. Further, if Cl ⁻ remains in the leaching residue, the pH is lowered at the time of leaching, and thus pH adjustment is necessary. However, it is also preferable from the viewpoint that this pH adjustment becomes unnecessary.

<Silver leaching process>
The silver leaching step is a step of leaching silver from a smelting intermediate with a sulfite aqueous solution. By adding a sulfite aqueous solution to the smelting intermediate, a silver leaching solution dissolved as complex ions can be obtained. The reaction formula in the case where the sulfite is sodium sulfite (Na ₂ SO ₃ ) and the hardly soluble silver compound is silver chloride is shown below.
(Formula) AgCl + Na ₂ SO ₃ → Na [Ag (SO ₃ )] + NaCl

In the above formula, silver chloride reacts with sodium sulfite to form a stable silver sulfite complex (Na [Ag (SO ₃ )]). At this time, part of the impurity element is also dissolved and mixed in the leachate.

  The sulfite is not particularly limited as long as it is a water-soluble sulfite, and examples thereof include sodium sulfite, potassium sulfite, calcium sulfite, ammonium sulfite, cesium sulfite, and rubidium sulfite. Sodium sulfite is preferable from the viewpoint of ease and economy. The waste liquid treatment method of the present invention is characterized in that the sulfite is obtained from the waste liquid, and the details will be described later.

  The sulfite concentration of the aqueous sulfite solution is not particularly limited, but is preferably 150 to 250 g / L, and more preferably 200 to 250 g / L. In addition, since the solubility of the silver compound with respect to sulfite aqueous solution will fall if it is less than 150 g / L, a large capacity | capacitance installation may be needed in order to obtain a desired amount. On the other hand, when the sulfite concentration exceeds 250 g / L, the sulfite is difficult to dissolve.

The pH in the silver leaching step is preferably 8 to 12, and more preferably 10 to 11. If the pH is less than 8, sulfite begins to rapidly change to bisulfite, and the silver compound may be insufficiently dissolved. When the pH exceeds 12, metallic silver is precipitated from silver sulfite complex (when sodium sulfite is sodium sulfite, Na [Ag (SO ₃ )]), and the apparent leaching rate of silver may decrease. is there.

It is preferable that the temperature in a silver leaching process is 20-80 degreeC, and it is preferable that it is 30-60 degreeC. If the temperature is less than 20 ° C., the solubility of sulfite is lowered, and it may be difficult to make the sulfite concentration of the sulfite aqueous solution a desired concentration (for example, 150 g / L). When the temperature exceeds 80 ° C., metallic silver precipitates from silver sulfite complex (when sodium sulfite is sodium sulfite, Na [Ag (SO ₃ )]), and the apparent leaching rate of silver decreases. There is.

  The silver leaching rate in the silver leaching step is preferably 95% or more. If the silver leaching rate is 95% or more in the silver leaching step, the finally obtained silver recovery rate can be 96% or more.

<Silver chloride precipitation process>
The silver leaching step is a step of precipitating silver chloride by neutralizing the leaching solution obtained in the silver leaching step. When the leaching solution is neutralized, it cannot be present as complex ions, and chloride ions in the leaching solution And silver chloride combined with it. When the smelting intermediate used as a raw material contains a hardly soluble silver compound other than chloride, a predetermined amount of chloride ion is added to precipitate as silver chloride. As a supply source of chloride ions, water-soluble chlorides such as hydrochloric acid and sodium chloride are preferably used.

The neutralizing agent for neutralizing the leachate is not particularly limited, and examples thereof include sulfuric acid and hydrochloric acid, and sulfuric acid is preferable from the viewpoint of corrosion resistance of the pipe and cost. The pH at the neutralization point is preferably from 0 to 4.5, more preferably from 1 to 2. When the pH of the neutralization point of the leachate obtained in the above silver leaching process is adjusted to be in the acidic range, sulfite ions are sequentially converted into hydrogen sulfite ions, sulfurous acid, sulfur dioxide, and the ability to form complex with silver is lost. Is called. By adjusting the pH of the neutralization point to be 4.5 or less, almost the entire amount of silver can be recovered as silver chloride. In the neutralization reaction of the leachate, SO ₂ gas is generated by decomposition of sulfite. The generated SO ₂ gas may be effectively used as the leaching step chemical by, for example, blowing it into a sodium hydroxide aqueous solution and collecting it as a sodium sulfite aqueous solution in a sulfite aqueous solution generation step described later.

  Although the temperature in a silver chloride precipitation process is not specifically limited, It is preferable that it is 20-100 degreeC. At this time, since some of impurity elements such as gold, selenium, tellurium and lead are precipitated as chloride, the purity of silver chloride is not so high at this point. Therefore, the precipitate is solid-liquid separated and then purified in the next step.

The filtrate after solid-liquid separation of the precipitate contains impurity elements such as selenium and tellurium, and a large amount of H ₂ SO ₃ , Na ₂ SO _{4 and the} like. Therefore, usually, the filtrate is discharged after being subjected to wastewater treatment as a waste liquid together with the filtrate generated in the silver chloride purification process which is the next process. In contrast, the waste liquid treatment method of the present invention is characterized in that a part or all of the filtrate is effectively used as the leaching step chemical, and details will be described later.

<Silver chloride purification process>
The silver chloride refining step is a step of purifying the silver chloride in the precipitate obtained in the silver chloride precipitation step by oxidizing it in an acidic aqueous solution. When the precipitate is oxidized with an oxidizing agent, it precipitates as a chloride. Impurity elements such as selenium and tellurium are dissolved in the acidic aqueous solution. As a result, the remaining precipitate is substantially converted to silver chloride, so that high-purity silver chloride can be obtained by subsequent solid-liquid separation and washing.

  The method of oxidation treatment is not particularly limited, but hydrogen peroxide, chlorine gas, and chloric acid are less contaminated with silver chloride while suspending the precipitate in an acidic aqueous solution and adjusting the oxidation-reduction potential. An oxidizing agent such as salt may be added. The acidic aqueous solution is not particularly limited, and for example, hydrochloric acid, hydrobromic acid, hydroiodic acid and the like can be suitably used. Among these, hydrochloric acid is particularly preferable in that it generates chlorine by an oxidizing agent and easily dissolves an impurity element present in the form of a metal, and has a large solubility in a chloride of an assumed impurity element.

  The oxidation-reduction potential (silver / silver chloride electrode standard) is not particularly limited, but is preferably adjusted to 800 to 1200 mV, more preferably 900 to 1000 mV. When the oxidation-reduction potential is 800 mV or more, an element that exists as a metal or an intermetallic compound and becomes soluble in an acidic aqueous solution by oxidation, for example, an impurity element such as selenium or tellurium can be dissolved. Although the temperature in this process is not specifically limited, It is preferable that it is 40-80 degreeC. If the temperature is lower than 40 ° C., the impurity dissolution reaction may be slow. When the temperature exceeds 80 ° C., when hydrogen peroxide or chlorate is used as an oxidant, the self-decomposition thereof is also promoted, so that the amount of the oxidant used increases.

The filtrate after solid-liquid separation of the precipitates remaining after the oxidation treatment is acidic and contains impurity elements such as selenium and tellurium, H ₂ SO ₃ , HCl, and the like. Therefore, usually, the filtrate is discharged after being subjected to wastewater treatment as a waste liquid together with the filtrate generated in the silver chloride precipitation step. In contrast, the waste liquid treatment method of the present invention is characterized in that a part or all of the filtrate is effectively used as the leaching step chemical, and details will be described later.

<Silver powder recovery process>
The silver powder recovery step is a step of obtaining silver metal powder by reducing the high-purity silver chloride obtained in the silver chloride purification step with a reducing agent in an alkaline aqueous solution. The silver powder that has undergone this step is in the form of a powder having an average particle diameter of several hundreds of μm and has a high purity of 99.99% by mass or more.

  The method of the reduction treatment is not particularly limited, but the high-purity silver chloride obtained in the silver chloride purification step is suspended in an alkaline aqueous solution, and the oxidation-reduction potential is adjusted, and the contamination to silver is small. It is preferable to add a reducing agent such as hydrazine, saccharide, or formalin. The aqueous alkali solution is not particularly limited, but is preferably prepared using 1 to 5 equivalents of alkali hydroxide and / or alkali carbonate with respect to silver. If it is less than 1 equivalent, unreduced silver chloride may remain and contaminate the resulting metallic silver. If it exceeds 5 equivalents, the cost may increase due to an excessive effect. The alkali hydroxide and / or alkali carbonate is not particularly limited, but it is preferable to use sodium hydroxide that is less burdensome in wastewater treatment and inexpensive. The alkali hydroxide and / or alkali carbonate is preferably added so that the pH of the aqueous alkali solution is 13 or more. The end point is when the oxidation-reduction potential (silver / silver chloride electrode standard) is stable at −700 mV or less.

[Waste liquid treatment method]
Next, the waste liquid treatment method of the present invention will be described. Method of processing waste liquid of the present invention, de-SO ₃ to remove the SO ₃ ^2-from the effluent by adding waste liquid of sulfuric acid and / or hydrochloric acid generated in the silver chloride precipitation step and / or the silver chloride purification step ^{2 A} sulfite aqueous solution generation step of absorbing a SO ₂ gas generated in the de-SO ₃ ^2- step in an aqueous solution of an alkali metal hydroxide and / or an alkali metal carbonate to obtain an aqueous sulfite solution, The sulfite aqueous solution obtained in the sulfite aqueous solution generation step is used as the sulfite aqueous solution used in the silver leaching step. A waste liquid treatment method according to an embodiment of the present invention in which the sulfite aqueous solution used in the silver leaching step is a sodium sulfite aqueous solution will be described with reference to the process diagram of the method for producing high-purity silver shown in FIG.

<De-SO ₃ ^2- step>
In the waste liquid treatment method according to an embodiment of the present invention, as shown in FIG. 1, not all of the filtrate generated in the silver chloride precipitation step and the silver chloride purification step is treated as a waste liquid, but one of them. Sulfuric acid is added to the part, and a SO ₃ ^2- step for removing SO ₃ ^2- from the waste liquid is performed. In addition to impurity elements such as selenium and tellurium, the filtrate obtained by solid-liquid separation of the precipitate obtained in the silver chloride precipitation step contains silver sulfite complex salt (Na [Ag (SO ₃ )]) to silver chloride. A large amount of SO ₃ ²⁻ decomposed when changed to. In addition to impurity elements such as selenium and tellurium, the filtrate remaining after the oxidation treatment in the silver chloride refining step is separated from silver sulfite complex salt (Na [Ag (SO ₃ )]). SO ₃ ^2- decomposed when converted to silver chloride is contained. When sulfuric acid is added to the waste liquid as the filtrate, SO ₃ ²⁻ dissolved in the waste liquid becomes SO ₂ gas, and SO ₂ gas is released from the waste liquid.

The amount of sulfuric acid to be added is not particularly limited, and the amount by which sulfuric acid is added is such that the pH of the waste liquid is 0 to 4.5, and more preferably 0.8 to 1.0. If the pH of the waste liquid after addition of sulfuric acid is less than 0, the amount of neutralizing agent used increases in the process after recycling as the leaching process chemical or as a diluent for adjusting the concentration of the chemical. There is a case. When the pH of the waste liquid after addition of sulfuric acid exceeds 4.5, only sodium bisulfite (NaHSO ₃ ) may be decomposed. Although the temperature in this process is not specifically limited, It is preferable that it is 20-40 degreeC. If the temperature is lower than 20 ° C., Na ₂ SO ₃ may precipitate. If the temperature exceeds 40 ° C., the effect may be small and energy costs may be wasted.

The waste liquid after releasing SO ₂ gas (hereinafter referred to as post-treatment water) is used as an alternative to the chemical in the silver leaching process, that is, a diluting liquid for adjusting the sulfite ion concentration of the sulfite aqueous solution. Also good. The treated water contains impurity elements such as selenium and tellurium, but these are extremely small amounts, and there is no problem as industrial water used in the process. If the treated water is effectively used as described above, the amount of industrial water used can be reduced. In addition, use of the water after a process can obtain a high-purity silver ingot having a good surface state by limiting 30% of the total volume of the diluted solution.

<Sulphite aqueous solution production process>
In the sulfite aqueous solution generation step in the waste liquid treatment method according to an embodiment of the present invention, the SO ₂ gas generated in the de-SO ₃ ^2- step is recovered and absorbed in the sodium hydroxide aqueous solution to thereby form the sodium sulfite aqueous solution. obtain. Although the density | concentration of sodium hydroxide aqueous solution is not specifically limited, Preferably it is 10-24 mass%. When the concentration of the sodium hydroxide aqueous solution is less than 10% by mass, the concentration of sodium sulfite may not reach the purpose. If the concentration of the aqueous sodium hydroxide exceeds 24% by mass, it may solidify during winter operations. The temperature in this step is not particularly limited, but is preferably 5 to 30 ° C. When the temperature is lower than 5 ° C., the solubility of sodium sulfite is lowered and crystals may be precipitated. When the temperature exceeds 30 ° C., humidification may be required.

  The sodium sulfite aqueous solution obtained in the sulfite aqueous solution generation step preferably adjusts the sodium sulfite concentration to 150 to 250 g / L, more preferably 200 to 250 g / L, and then uses the sulfite used in the silver leaching step. Used as part of the aqueous sodium solution. When the sodium sulfite concentration is less than 150 g / L, the solubility of silver chloride in the aqueous sodium sulfite solution decreases, so a large capacity of equipment may be required to obtain the desired amount. When the sodium sulfite concentration exceeds 250 g / L, sodium sulfite is difficult to dissolve.

According to the waste liquid treatment method according to an embodiment of the present invention, the waste liquid containing impurities such as Se and Te and a large amount of SO ₃ ²⁻ generated in the silver chloride precipitation step and the silver chloride purification step is treated with the silver. It can be effectively used as an aqueous solution of sodium sulfite which is a chemical for the precipitation process. Therefore, by reducing the amount of chemicals required for wastewater wastewater treatment, not only the wastewater treatment load is reduced, but also the amount of chemicals used for the silver deposition step can be reduced. The cost required for the production process of pure silver can also be reduced. Further, the treated water, which is a waste liquid after releasing SO ₂ gas, can be used as a substitute for the chemical in the silver leaching step, that is, a diluting liquid for adjusting the sodium sulfite concentration of the sodium sulfite aqueous solution. it can. If the treated water is effectively used as a diluent, the amount of industrial water used can be reduced.

  The present invention is not limited to the above-described embodiment, and modifications, improvements, and the like are included in the present invention as long as the object of the present invention can be achieved.

For example, in the waste liquid treatment method according to the above-described embodiment, a case has been described in which, in the sulfite aqueous solution generation step, SO ₂ gas is absorbed into a sodium hydroxide aqueous solution to obtain a sulfite aqueous solution, but the present invention is not limited thereto. For example, it may be absorbed in an aqueous solution of an alkali metal hydroxide such as KOH, RbOH, CsOH, LiOH and / or an alkali metal carbonate such as K ₂ CO ₃ , Rb ₂ CO ₃ , or CsCO ₃ .

For example, in the waste liquid treatment method according to the above embodiment, the case where sulfuric acid is used when removing SO ₃ ²⁻ from the waste liquid has been described, but the present invention is not limited to this. For example, a mixed solution of hydrochloric acid, sulfuric acid, and hydrochloric acid may be used, and the amount by which the pH of the waste liquid becomes 0 to 4.5 by addition is preferable, and the amount that becomes 0.8 to 1.0 is more preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention does not receive a restriction | limiting at all by these description.

<Test Example 1>
A chlorine leaching residue obtained by leaching the anode slime produced in the copper electrolysis process with chlorine gas was used as a test raw material. The chlorine leaching residue was analyzed by ICP emission spectroscopy (ICP-AES), and the composition shown in Table 1 was obtained.

(1) Pretreatment process A
45 g (wet weight) of the chlorine leaching residue was placed in a 1 L beaker, and water was added so that the total amount would be 400 ml, followed by repulping. The residue after repulping was 47 g in wet weight, and the filtrate was approximately 400 ml.
(2) Silver leaching process A
A sodium sulfite aqueous solution (230 g / L) prepared using commercially available sodium sulfite was added to 47 g of the residue after the repulping in the pretreatment step A, and silver was leached by stirring for 1 hour. The pH at the time of leaching was approximately 10.5. Next, filtration and washing were performed to obtain 400 ml of a leachate and 23 g (wet weight) of a residue.

(3) Silver chloride precipitation step A
A thin sulfuric acid aqueous solution was added to the leachate obtained in the silver leaching step A, the pH was adjusted to 4.9, and the mixture was stirred for 1 hour while maintaining the pH to obtain a slurry. The resulting slurry was filtered and washed, and the precipitate was collected. During the reaction, SO ₂ gas was generated due to decomposition of sodium sulfite, and thus the reaction was performed in a fume hood. Thin sulfuric acid was added to the generated filtrate, and the pH was adjusted to 0.9, followed by stirring for 1 hour while maintaining the pH as it was, and the generated SO ₂ gas was recovered (de-SO ₃ ^2- step). Next, the SO ₂ gas was blown into a sodium hydroxide aqueous solution and absorbed to obtain a sodium sulfite aqueous solution (sulfite aqueous solution generation step). Incidentally, filtrate after SO ₂ gas recovery as processed water was separately recovered.

(4) Pretreatment process B
45 g (wet weight) of the chlorine leaching residue was placed in a 1 L beaker, and water was added so that the total amount would be 400 ml, followed by repulping. The residue after repulping was 47 g in wet weight, and the filtrate was approximately 400 ml.

(5) Silver leaching process B
A sodium sulfite aqueous solution prepared using the filtrate generated in the silver chloride precipitation step A was added to 47 g of the residue after the repulping in the pretreatment step B, and the mixture was stirred for 1 hour to leach silver. In addition, the sodium sulfite aqueous solution added was adjusted to a sodium sulfite concentration of 230 g / L using a diluted solution obtained by mixing water after treatment and water collected in the silver chloride precipitation step A at a volume ratio of 30/70. . In addition, it was about 10.5 when pH at the time of leaching was measured. Thereafter, filtration and washing were performed to obtain 400 ml of a leachate and 23 g (wet weight) of a residue. The silver concentration of the leachate is 20 g / L, the silver quality of the residue is 0.2% (based on the dry amount), and the silver leach rate calculated from the ratio of the amount of silver contained in the leachate and the residue is approximately 99.1%. Met.

(6) Silver chloride precipitation process B
A thin sulfuric acid aqueous solution was added to the leachate obtained in the silver leaching step B, and the pH was adjusted to 4.9, followed by stirring for 1 hour while maintaining the pH as it was to obtain a slurry. The resulting slurry was filtered and washed, and the precipitate was collected. The generated filtrate was used for preparing an aqueous sodium sulfite solution used in the next silver leaching step, and the filtrate after the SO ₂ gas recovery was also recovered as post-treatment water.

(7) Silver chloride refining step Pretreatment step B, silver leaching step using sodium sulfite aqueous solution prepared using the filtrate generated in the silver chloride precipitation step and post-treatment water after SO ₂ gas recovery B and silver chloride precipitation step B were repeated a plurality of times. The resulting 250 g (wet weight) silver chloride precipitate was suspended in 500 ml of a 6 mol / L hydrochloric acid aqueous solution, and this slurry was heated to 60 ° C. Then, 50 ml of a hydrogen peroxide solution having a concentration of 35% by mass was added dropwise over about 1 hour so as to add the whole amount, and oxidation treatment was performed. The oxidation-reduction potential (silver / silver chloride electrode standard) of this slurry was 1000 mV or more. After cooling, the slurry was filtered and washed thoroughly with water to obtain 240 g (wet weight) of purified silver chloride.

(8) Silver powder recovery step 240 g (wet weight) of the purified silver chloride obtained in the silver chloride purification step is suspended in 1000 ml of a sodium hydroxide aqueous solution having a concentration of 8.6% by mass and heated to 70 ° C. Further, hydrazine having a concentration of 60% by mass was further reduced by addition until the oxidation-reduction potential was stabilized at −700 mV or less, and silver powder was recovered. The silver powder was dissolved in an aqueous nitric acid solution and analyzed by ICP emission spectroscopy (ICP-AES) and ICP mass spectrometry (ICP-MS). The results are shown in Table 2.

As shown in Table 2, an aqueous sodium sulfite solution prepared using the filtrate generated in the silver chloride precipitation step was used as a chemical in the silver leaching step, and SO ₂ gas was recovered from the filtrate generated in the silver chloride precipitation step. It was confirmed that silver powder having a purity of 99.99% by mass or more was obtained even when post-treatment water was used as a drug diluent in the silver leaching process (Table 2). Moreover, the recovery rate of silver calculated through the whole process was 96%, and it was also confirmed that it can be recovered in a high yield. From this, it became clear that the filtrate generated in the silver chloride precipitation process can be effectively used as a chemical for silver leaching process.

<Test Example 2>
When the filtrate generated in the silver chloride precipitation step was used as it is for the repulp water (suspension) of the silver leaching step B without passing through the SO ₃ ^2- step, the sodium sulfite concentration was 100 to 200 g / L. The result was not stable, and was insufficient for the required amount. As a result, the silver quality of the residue obtained in the silver leaching step B is 5.5% (dry basis), and the silver leaching rate calculated from the ratio of the amount of silver contained in the leaching solution and the residue is 76 % Was a low value. From this, it was clarified that the filtrate generated in the silver chloride precipitation step is not suitable for use in the silver leaching step unless it passes through the de-SO ₃ ^2- step.

<Test Example 3>
Thin sulfuric acid was added to the filtrate generated in the silver chloride precipitation step, and the pH was adjusted to 0.9, followed by stirring for 1 hour while maintaining the pH as it was to release SO ₂ gas, and SO ₃ ^{2− in the} filtrate. Was removed. Then, by mixing the water filtrate after the SO ₃ ^2-removing ratio by volume 50/50, the resulting solution was used as Reparupu cleaning solution in the pretreatment step (1). And when the said silver leaching process B was performed about the obtained residue after a repulp by the method similar to Test Example 1, the silver leaching rate in this leaching stage was as low as 85%. This revealed that the filtrate after removal of SO ₃ ²⁻ was not suitable for use as a repulp washing liquid in the pretreatment step.

Claims (3)

A silver leaching step of leaching silver from a smelting intermediate containing silver with a sulfite aqueous solution;
A silver chloride precipitation step of neutralizing the leached liquor to precipitate silver chloride;
In the method for producing high-purity silver, the silver chloride purification step of oxidizing and purifying the precipitated silver chloride in an acidic aqueous solution,
A de-SO ₃ ^2- step for removing SO ₃ ^2- from the waste solution by adding sulfuric acid and / or hydrochloric acid to the waste solution generated in the silver chloride precipitation step and / or the silver chloride purification step;
A sulfite aqueous solution generating step of absorbing the SO ₂ gas generated in the de-SO ₃ ^2- step into an aqueous solution of alkali metal hydroxide and / or alkali metal carbonate to obtain an aqueous sulfite solution, and
The sulfite concentration of the sulfite aqueous solution obtained in the sulfite aqueous solution generation step is adjusted using the waste liquid after removing SO ₃ ^2- in the de-SO ₃ ^2- step , and then the sulfite after the adjustment A method for treating a high-purity silver production waste liquid, wherein an aqueous salt solution is used as an aqueous sulfite solution used in the silver leaching step. 2. The high-purity silver production waste liquid according to claim 1, wherein in the de-SO ₃ ^2- step, sulfuric acid and / or hydrochloric acid is added so that the pH of the waste liquid after addition of sulfuric acid and / or hydrochloric acid is 0 to 4.5. Processing method. After adjusting the sulfite concentration of the sulfite aqueous solution obtained in the sulfite aqueous solution generation step to 150 to 250 g / L, the adjusted sulfite aqueous solution is used as the sulfite aqueous solution used in the silver leaching step. The processing method of the high purity silver manufacture waste liquid of Claim 1 or 2.

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