JP2013112881A - Method of recovering silver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of efficiently recovering silver of high purity from a silver solution of low concentration by a simple device.SOLUTION: The method of recovering silver includes: extracting silver in a solvent from an acid aqueous solution whose silver concentration is equal to or lower than 100 mg/L with tributyl phosphate as an extraction agent; and then recovering the silver in the solvent, wherein it is preferable that the silver quality of the recovered object of the silver is equal to or higher than 50%. Further, the extraction pH in the solvent extraction of silver is controlled to be equal to or below 1.0. The process of recovering the silver in the solvent includes a step of back-extracting the silver from the solvent containing the silver and a step of recovering the silver by cementation from a silver solution obtained by back extraction. When cementation is performed using copper components, the liquid from which the silver is separated after the cementation is supplied to a back extraction agent and repeatedly used. As the back extraction agent, a sodium thiosulfate solution, hydrochloric acid, a saline solution or nitric acid whose silver concentration is equal to or higher than 0.5 g/L is used.

Description

  The present invention relates to a method for efficiently recovering silver from an aqueous solution containing silver at a low concentration.

  Silver is used in a wide range of fields such as photographic materials and electronic component materials. On the other hand, most of the silver mined in the mine is produced in association with ores such as copper and zinc and contains a very small amount compared to copper and zinc. For this reason, recovery of silver from each waste product, waste liquid, or ore is desired, and various methods are being studied.

  As a typical method for separating and collecting silver in an aqueous solution by a wet method, for example, there is a method in which it is precipitated and recovered after being converted into a hardly soluble silver halide such as silver chloride.

  This method utilizes the fact that silver halide is hardly soluble and has low solubility in aqueous solutions. However, the solubility does not become zero, and silver halide dissolves slightly.

  As an example of the solubility of silver halide, for example, when silver chloride is dissolved in a hydrochloric acid solution, the calculated value indicates that the solubility of silver is about 75 mg / L. However, it is known that the solubility of silver varies depending on conditions such as the coexistence of acid and the temperature at which silver halide is dissolved, and the silver concentration in the liquid varies depending on the operating conditions. For this reason, it is difficult to show a clear solubility of silver, but it is considered to be approximately 100 ppm or less.

  Therefore, the precipitation recovery method using silver halide is effective for a solution containing silver having a solubility higher than that of silver halide, but cannot be applied to a silver-containing solution having a solubility lower than that. For this reason, there are currently very few examples relating to silver recovery from dilute silver solutions of below solubility.

  Patent Document 1 describes an example in which silver is recovered from a dilute silver solution using cementation.

JP2008-115429A

  However, according to the example of Patent Document 1, the silver quality of the recovered product obtained by cementation is as low as about 1.4% at maximum, and the concentrated silver cannot be recovered. Therefore, it is considered that another process is required to increase the purity of silver.

  Then, this invention makes it a subject to provide the method of collect | recovering highly pure silver efficiently from a low concentration silver solution with a simple apparatus.

  As a result of intensive studies to solve the above problems, the present inventors prepared a low-concentration silver acidic aqueous solution, extracted silver using tributyl phosphate as an extractant, and then recovered silver. It was found that high-purity silver can be efficiently recovered from a low-concentration silver solution with a simple apparatus.

  The present invention completed on the basis of the above knowledge, in one aspect, after extracting silver from an acidic aqueous solution having a silver concentration of 100 mg / L or less using tributyl phosphoric acid as an extractant, recovers silver in the solvent. This is a recovery method.

  In one embodiment of the silver recovery method according to the present invention, the silver recovery product has a silver quality of 50% or more.

  In still another embodiment of the silver recovery method according to the present invention, the extraction pH in the silver solvent extraction is controlled to 1.0 or less.

  In still another embodiment of the silver recovery method according to the present invention, the step of recovering silver in the solvent includes a step of back extracting silver from a solvent containing silver, and a silver solution obtained by back extraction. Recovering silver by cementation.

  In still another embodiment of the silver recovery method according to the present invention, the step of recovering silver in the solvent back-extracts silver from the solvent from which the silver has been extracted using a sodium thiosulfate solution as a back extractant. Process.

  In still another embodiment of the silver recovery method according to the present invention, the concentration of silver in the sodium thiosulfate solution obtained by back extracting the silver is controlled to 0.5 g / L or more.

  In yet another embodiment of the method for recovering silver according to the present invention, the step of recovering silver in the solvent includes using thiosulfuric acid, hydrochloric acid, saline solution or nitric acid as a back extractant from the solvent from which the silver has been extracted. Back-extracting silver.

  In another embodiment of the silver recovery method according to the present invention, when cementation is performed using a copper component, a solution obtained by separating the silver after the cementation is supplied to the back extractant and repeatedly used. .

  In still another embodiment of the silver recovery method according to the present invention, the acidic aqueous solution is based on a post-leaching solution obtained by leaching ore or concentrate containing copper sulfide.

  According to the present invention, a metal having high silver quality can be recovered in a high yield from a dilute silver aqueous solution that is difficult to recover by the conventional method. Moreover, since pH adjustment and heating are unnecessary, it leads to an improvement in safety and cost reduction. Thus, according to the present invention, it is possible to provide a method for efficiently recovering high-purity silver from a low-concentration silver solution with a simple apparatus.

It is a flowchart of the collection | recovery method of the silver which concerns on embodiment of this invention. It is a graph which shows the relationship between the extraction rate of silver obtained in Example 3, and pH. It is a graph which shows the relationship between the reaction time obtained in Example 5, and the silver concentration in a liquid.

  Below, embodiment of the collection | recovery method of the silver which concerns on this invention is described. FIG. 1 shows a flow chart of a silver recovery method according to an embodiment of the present invention.

  In the silver recovery method according to the embodiment of the present invention, an acidic aqueous solution having a silver concentration of 100 mg / L or less is used as a solution to be treated, and after extracting silver from the acidic aqueous solution with tributyl phosphate as an extractant, the solvent Collect the silver inside.

(Processing solution)
In the present invention, an aqueous solution having a silver concentration of 100 mg / L or less is to be treated. In one embodiment, the aqueous solution targeted for silver recovery is a post-leaching solution of copper concentrate and is based on an ore or concentrate containing copper sulfide, typically copper sulfide. It is a solution after leaching having a silver concentration of 100 mg / L or less, obtained by leaching ore or concentrate. As the leaching solution, any known one can be used, and there is no particular limitation, and an acidic aqueous solution of a mineral acid such as sulfuric acid or hydrochloric acid is usually used. Therefore, the silver-containing aqueous solution (hereinafter also referred to as “pre-extraction solution”) to be treated according to the present invention is generally acidic, for example, at a pH of 2.5 or less, typically at a pH of 0 to 1.5. is there. The silver concentration in the aqueous solution targeted by the present invention is 100 mg / L or less, and typically 10 to 50 mg / L. Moreover, the copper concentration in the liquid after leaching is typically 0.1 to 30 g / L, and further contains 10 to 200 g / L of chlorine and 10 to 120 g / L of bromine. In addition, when the acidic aqueous solution contains impurities such as iron and zinc, it is preferable to remove them as much as possible because high-purity silver can be recovered.

(Solvent extraction)
From an acidic aqueous solution having a silver concentration of 100 mg / L or less, silver is solvent-extracted using TBP as an extractant. Solvent extraction operation itself may follow a conventional method. For example, a silver-containing aqueous solution (aqueous phase) and an extractant (organic phase) are brought into contact with each other, and these are typically stirred and mixed with a mixer to react silver with the extractant. The reaction can be carried out at room temperature (10 to 30 ° C.) to 60 ° C. under atmospheric pressure. The O / A ratio, which is the volume ratio of the extractant (O) and the aqueous solution (A), is not particularly limited, and solvent extraction can be performed at an arbitrary volume ratio. In the solvent extraction of silver, the extraction rate of silver increases as the extraction pH decreases. Thus, the lower the extraction pH, the more efficiently silver is extracted, and the extraction effect becomes very good when the pH is controlled to be 1.0 or less, more preferably 0.5 or less.

(Tributyl phosphate)
In the present invention, tributyl phosphate is used as an extractant. Tributyl phosphate is a common drug and is a type of extractant called a neutral extractant. Neutral extractant is said to extract a non-electrostatic complex. For example, the extraction reaction of silver chloride is expressed by the following formula (1), and is extracted by solvating tributyl phosphate with a metal complex. Is different. Metals such as silver are present as ions or complexes in the liquid, and the complex species changes depending on the anion concentration in the liquid. Taking a silver chloride complex as an example, the complex species changes depending on the chlorine concentration and exists in a form such as AgCl ₂ ^- or AgCl.
TBP + AgCl ₂ ⁻ = AgCl · TBP + Cl ⁻ (1)
The metal extracted with TBP exists as a complex in the solvent, and the metal extracted into TBP can be back-extracted by mixing TBP with an aqueous solution in which the metal complex can be dissolved. For example, silver chloride has almost no solubility in pure water and cannot be back-extracted with water. On the other hand, since iron chloride, zinc chloride, and the like have solubility in water, they can be back-extracted from TBP with water, and silver and other metals can be easily separated.
Further, when the silver remaining in the solvent is back-extracted, the back-extraction is performed by using a solution in which silver chloride can be dissolved, for example, hydrochloric acid, nitric acid, saline, thiosulfuric acid solution or the like.
Examples of tributyl phosphoric acid include TBP manufactured by Daihachi Chemical Co., Ltd., which can be used by mixing with any diluent. Tributyl phosphoric acid is a chemically stable substance, and is known to have low volatility and explosiveness and little influence on the human body.

(Back extraction)
After solvent extraction of silver with tributyl phosphate, silver can be back extracted from the silver-containing solvent using sodium thiosulfate solution as a back extractant. For back extraction conditions, the concentration of the sodium thiosulfate solution is preferably 0.1 to 2.0 mol / L, more preferably 0.5 to 1.0 mol / L, and the pH is preferably 4 to 7, more preferably. Is 5-7. Moreover, the O / A ratio which is a volume ratio of the extractant (O) and the aqueous solution (A), the reaction time, the reaction temperature, and the number of back extraction stages can be arbitrarily adopted. When a sodium thiosulfate solution is used, the silver in the solvent can be easily dissolved even in the form of a hardly soluble silver halide such as silver chloride, and silver is precipitated in the thiosulfate solution. This can be suppressed satisfactorily.
At this time, the concentration of silver in the sodium thiosulfate solution obtained by back extracting silver is preferably controlled to 0.5 g / L or more, more preferably 1.0 g / L or more. preferable. By controlling in this way, the total amount of the solution to be handled can be reduced, so that the cementation can be efficiently and industrially collected in the subsequent cementation process. Control of the concentration of silver in the sodium thiosulfate solution from which silver is back-extracted to 0.5 g / L or more is not particularly limited, but can be performed by adjusting the O / A ratio, for example.
As the back extractant, in addition to sodium thiosulfate, thiosulfuric acid, hydrochloric acid, saline solution, nitric acid, or the like can be used.

(Silver cementation)
Subsequently, high purity silver can be precipitated by cementation with respect to the solution obtained by back extracting the silver. Silver cementation can be performed by a known method, and can be performed by immersing metallic copper or metallic iron in a silver solution. At this time, the shape of metallic copper or metallic iron can be any shape such as a plate or powder. Moreover, the post-cementation solution obtained at this time can be supplied to the above-mentioned back extractant and used repeatedly. Reusing the post-cementation solution in this way is advantageous in terms of cost. Moreover, when supplying the liquid after cementation to the above-mentioned back extractant and reusing, it is preferable that the metal used for cementation is not extracted to tributyl phosphate. In this respect, since copper is difficult to be extracted into tributyl phosphate, it is preferable to use a copper component such as copper scrap.

  The silver recovery method according to the present invention efficiently recovers high-purity silver (silver quality of recovered silver is 50% or more) from a low-concentration silver solution with a simple apparatus by the above-described configuration. A method can be provided.

  Next, examples of the present invention will be described. In addition, a present Example is an example to the last, and is not restrict | limited to this example. That is, all aspects or modifications other than the embodiments are included within the scope of the technical idea of the present invention.

(Example 1: Silver extraction)
Extracted with 100 vol% TBP (manufactured by Daihachi Chemical Co., Ltd.) against an aqueous solution (Cu: 20 g / L, Ag: 30 mg / L, Cl: 130 g / L, Br: 13 g / L) simulating a pre-silver extraction solution And how much silver can be extracted and recovered. Table 1 shows the concentration of silver and copper in the solvent before and after extraction when the two-stage extraction was performed at an O / A ratio of 1/1 and after extraction. From Table 1, the silver concentration in the solution was changed from 30 mg / L to less than 1 mg / L, and almost the entire amount could be extracted. On the other hand, the concentration of copper did not change before and after extraction, and was hardly extracted. This confirmed that silver can be selectively extracted.

(Example 2: repeated extraction using TBP after back extraction)
In the present invention, TBP from which silver is back-extracted can be used for repeated extraction. Therefore, a test was conducted to confirm whether or not silver extraction could be repeated. Extraction was performed in two stages using the same simulated solution as that used in Example 1 and under the same conditions. The test results are shown in Table 2. From Table 2, it was confirmed that even when TBP was repeatedly used, the extraction effect was not changed and almost all silver could be selectively extracted. This confirmed that TBP could be used repeatedly.

(Example 3: Effect of pH in back extraction of silver)
Extraction was carried out by adjusting the pH to 0-2 using 50 vol% TBP, the same simulated solution used in Example 1, and the effect of pH in silver extraction was confirmed. Extraction was performed using O / A = 1/1, room temperature for 15 minutes, and pH adjustment using hydrochloric acid. FIG. 2 shows the relationship between extraction rate and pH. As the pH decreased, the silver extraction rate increased, and the lower the pH, the more efficient the silver extraction, and it was confirmed that the pH of 1.0 or less was particularly effective.

(Example 4: Back extraction of silver)
Silver was extracted, and back extraction was performed in one stage using a 1.0 mol / L sodium thiosulfate solution on TBP containing 25 mg / L of silver. The extraction conditions were O / A = 1/1, room temperature, and the reaction time was 15 minutes. The back extraction results are shown in Table 3. As shown in Table 3, the silver concentration in TBP after back extraction was less than 0.1 mg / L, and it was confirmed that almost all silver in TBP could be back extracted.

(Example 5: Silver cementation)
Cementation was performed using a copper plate while blowing nitrogen gas into an aqueous solution containing 1.0 g / L silver and 1.0 mol / L sodium thiosulfate as a solution after back extraction of silver. The test conditions were a silver solution of 1 L, a nitrogen gas flow rate of 0.5 L / min, a deposition area of 40 cm ² , a reaction temperature of 40 ° C., and a reaction time of 3 hours.
As a test result, the relationship between the reaction time and the silver concentration in the liquid is shown in FIG. From the test results, good precipitation of silver was confirmed, and the silver concentration in the liquid decreased from 1.0 g / L to less than about 50 mg / L, and 0.9 g of crude silver could be recovered. The silver quality of the obtained crude silver was 80% or more. From this result, it was confirmed that high-purity silver can be easily precipitated and recovered by cementation from the silver solution obtained by back extraction.

(Example 6: repeated back extraction with post-cementation solution)
In the present invention, the post-silver cementation solution can be subjected to back extraction again. Therefore, a repeated test was performed to confirm whether or not the solution after cementation can be used repeatedly.
As the back extract, a post-silver cementation solution containing 1.0 mol / L sodium thiosulfate, 350 mg / L silver and 1100 mg / L copper was used, and TBP containing 25 mg / L silver was used as the solvent. . Using these, back extraction was performed under the conditions of O / A = 2/1, room temperature, and reaction time of 15 minutes. The test results are shown in Table 4. From the test results, even when a post-cementation solution containing copper was used, almost all of the silver in the TBP could be back-extracted, which was inferior to the case of no silver or copper described in Example 2. It was confirmed that no results were obtained. Moreover, it was confirmed that copper was not mixed into the solvent after back extraction, and the post-cementation solution could be used repeatedly.

Claims (9)

  A silver recovery method for recovering silver in the solvent after extracting silver from an acidic aqueous solution having a silver concentration of 100 mg / L or less using tributyl phosphate as an extractant.   The silver recovery method according to claim 1, wherein the silver recovery product has a silver quality of 50% or more.   The method for recovering silver according to claim 1 or 2, wherein an extraction pH in the silver solvent extraction is controlled to 1.0 or less.   The step of recovering silver in the solvent includes a step of back extracting silver from a solvent containing silver and a step of recovering silver by cementation from a silver solution obtained by back extraction. The method for recovering silver according to any one of the above.   The step of recovering silver in the solvent includes the step of back extracting silver from the solvent from which the silver has been extracted using a sodium thiosulfate solution as a back extractant. Method.   The silver recovery method according to claim 5, wherein the concentration of silver in the sodium thiosulfate solution obtained by back-extracting silver is controlled to 0.5 g / L or more.   The step of recovering silver in the solvent includes a step of back extracting silver from the solvent from which the silver has been extracted using thiosulfuric acid, hydrochloric acid, saline solution or nitric acid as a back extractant. The recovery method of silver as described.   The method for recovering silver according to any one of claims 4 to 7, wherein when cementation is performed using a copper component, a solution obtained by separating the silver after cementation is supplied to the back extractant and repeatedly used.   The method for recovering silver according to any one of claims 1 to 8, wherein the acidic aqueous solution is based on a post-leaching solution obtained by leaching ore or concentrate containing copper sulfide.

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