JPS59451B2 - Silver recovery method from silver-containing aqueous solution - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for recovering high-grade silver from an aqueous solution in which silver and base metals such as copper and nickel are dissolved. This invention relates to a purification method that involves separation and removal by extraction.

Silver rarely exists alone in nature; it often coexists with base metals such as copper, nickel, zinc, and cobalt.

For example, about two-thirds of the silver collected each year in Japan is said to be a by-product of copper.

Therefore, in hydrometallurgy of silver, a mixed solution of silver and base metals is often used.

Silver smelting generally utilizes insoluble residue (anode slime) produced by electrolytic smelting of base metals.

That is, since silver exists in a concentrated form in this insoluble residue, this residue is subjected to a melting treatment to obtain crude silver, which is then used as an anode for electrolytic refining.

The electrolyte is a silver nitrate solution, and the cathode is made of stainless steel or other material.

However, if the base metal content of the crude silver accumulates excessively in the electrolyte, the quality of the electrolytic silver deposited on the cathode will be impaired, so after a certain period of time, at least a portion of the electrolyte should be transferred to another system. It must be extracted and processed.

However, expensive silver,
There are problems with high costs, such as the complicated process required to recover copper and harmful free nitric acid, and the need to replenish nitric acid and silver when building a new bath.

In addition, silver is often used in combination with base metals such as copper in electrical products and other processed products, so the slag and used scraps produced during processing are as important as silver resources as naturally produced silver. It is.

This silver resource is also input as an auxiliary material in the base metal smelting process mentioned above, and silver is finally recovered through a long process consisting of dry smelting and hydrorefining.

However, when recovering silver, it is economically desirable to recover silver more directly from silver resources, in contrast to the above method, from the standpoint of improving the recovery rate and reducing the interest burden required for collection days. .

In particular, the rapid recovery of silver is attracting attention as a major attraction for the smelting industry, as silver is a precious metal whose price is subject to fluctuations on an international basis.

As a method to meet this demand, a method can be considered in which the silver raw material is wet-dissolved and then recovered.

Silver thread compounds are generally chemically stable, so in order to practically dissolve them, it is possible to use strong acids such as nitric acid or complex salt solutions such as ammonia or cyanide, but these methods do not dissolve silver. As the base metals melt, many of the base metals also melt at the same time.

Therefore, in order to recover high-grade silver with high efficiency,
Purification of the silver solution is important.

For example, when recovering electrolytic silver using the electrolytic method, the copper concentration in the silver solution must be controlled to 109/11 or less, but as we saw earlier, problems remain in terms of efficiency and cost. .

On the other hand, the economic evaluation of base metals is by no means low, and easy dumping is not considered environmentally friendly, so all of these metals must be recovered as valuable metals.

However, in the past, there have been few attempts to purify and recover impure silver solutions; rather, the method has generally been to separate crude silver or crude silver compounds and then re-purify them using melting or electrolytic methods. .

For example, there are substitution methods that use active metals such as copper, zinc, aluminum, and iron, which have a greater ionization tendency than silver, electrowinning methods that use insoluble anodes such as carbon, and reducing agents such as sulfur dioxide gas and hydrazine. Examples include a chemical reduction method used, a halide precipitation method that takes advantage of the fact that silver halide is sparingly soluble, and the like.

However, in order to speed up recovery and reduce costs, it is desired to establish a practical recovery method that can directly purify base metals from impure silver solutions.

This invention was made in view of the above circumstances, and provides a purification method that directly recovers high-grade silver from a solution in which silver and base metals are dissolved, and also directly recovers base metal components.

This invention provides an aqueous solution in which at least one base metal among copper, nickel, cobalt, and zinc and silver are dissolved at pH 0,
The base metal is extracted and separated into the organic solvent phase by mixing with a water-immiscible organic solvent containing an extractant having selective exchange properties for cations in the range of 2 to 13.0. It is characterized by supplying a base metal recovery process and also supplying an aqueous solution containing silver to the silver recovery process.

This will be explained in detail below.

The aqueous solution selected for solvent extraction in this invention contains at least one base metal among copper, nickel, cobalt, and zinc.
It is an aqueous solution in which silver coexists, and specifically refers to an aqueous solution obtained by dissolving silver resources in nitric acid, other mineral acids, or alkalis such as ammonia.

In such an aqueous solution, silver and base metals coordinate with water and ammonia molecules and are dissolved as cations.

When this aqueous solution is extracted with an extractant that selectively exchanges cations while maintaining the pH in the range of 0.2 to 13, base metal components such as copper and nickel react with the extractant and are dissolved in water. Forms a complex compound that is insoluble but soluble in organic solvents, and is extracted into organic solvents.

However, since silver is not extracted into the organic solvent and substantially remains in the aqueous solution, the purpose of separating and purifying silver is achieved here.

The pH conditions during solvent extraction are limited to a range of 0.2 to 13, but when it is desired to extract copper among base metals, the pH condition is
The preferred pH range is 0.5 or higher, pH 2.5 or higher if you want to extract nickel or cobalt, and pH 3 or higher if you want to extract zinc.

If the pH is less than 0.2, the extraction operation will be impossible, and if the pH exceeds 13, the extraction rate of base metals will decrease, and a small amount of silver components will be extracted, causing problems. .

In the extractable complex compound produced by solvent extraction, there is a certain stoichiometric relationship between the extractant and the metal ion, and there is a maximum saturation capacity of the metal ion that can be extracted.

When the pH is low, the reaction equilibrium of complex formation is biased toward decomposition (reverse reaction) of the complex, and the equilibrium extraction capacity is generally smaller than the maximum saturation capacity mentioned above, and the alkalinity becomes significantly excessive. Eventually, extraction will virtually no longer occur.

However, if the pH is in the range of 0.2 to 13, a certain pH
Since there is a metal-specific equilibrium capacity for each value, therefore, if the equilibrium capacity is known in advance, it is possible to determine the necessary extraction amount to extract the desired amount of base metal.

The extractant with selective exchange properties for cations used in this invention refers to substances that can form stable and water-insoluble complexes with base metal ions. There are hydroxyquinolines and hydroxyquinolines.

All of them have the ability to selectively extract base metals within the above-mentioned pH range, but when considering other properties, price, etc., hydroxy hydroxymes are often superior for practical use.

These hydroxy hydroxymes are organic compounds that share a hydroxyl group and a hydroxyme group in their molecules and are substantially insoluble in water, especially when both groups are arranged adjacent to each other at the α or β position. Valid if applicable.

First, α-hydroxy hydroxime has the following general structural formula, where R1 and R2 are hydrocarbon groups having 6 to 20 carbon atoms, R3 is a hydrocarbon group or a hydrogen atom, and these hydrocarbon groups may be the same or different.

In addition, β-hydroxy hydroxyme is a hydroxy group with a hydroxyl group attached to an aromatic ring, as shown in the general structural formula below.
A benzophenone type is preferred; in the formula, R4 represents hydrogen or a hydrocarbon group having 6 to 20 carbon atoms, R5 represents 1 to 4 hydrocarbon groups, and the number of carbon atoms is limited to 1 to 20.

However, a part of R5 may be substituted with a substituent other than a hydrocarbon, and in particular, an electron-withdrawing group such as a halogen promotes chelate formation with a metal ion.

Specifically, representative examples of hydroxy hydroxymes are shown, and 5,8-diethyl-7-hydroxytodecane-6-
Oxime, 19-hydroxy-hexatruffle-9,
27-renine-18-oxime, 5.10-diethyl-
8-hydroxytetradecane = 7-oxime, 2-hydroxy-37-methyl-5-ethylbenzophenone oxime, 2-hydroxy-5-(1,1-dimethyl-propyl)-benzophenone oxime, 2-hydroxy-3
, 5-dioctylbenzophenone oxime, 2-hydroxy-5-phenylbenzophenone oxime, 4-ethoxy-2-hydroxy-phenone capryloxime, 4
-butyl-2-hydroxy-phenosteryl oxime, and the like.

Next, what is one of the extractants, hydroxyquinori?
It refers to an 8-hydroxyquinoline derivative, and its general structural formula is as shown below.

In the formula, R represents 1 to 6 hydrocarbon groups, and when the total number of carbon atoms is in the range of 8 to 30, the hydroxyquinolines exhibit practical solubility in organic solvents.

The main concrete examples are, for example, 7- (3
-(5,5,7,7,)tetramethyl-1-octyl)
]-]8-hydroxyquinoline 7-(3-(5,5-dimethyl-1-hexyl))]-]]]8-hydroxyquinoline 7-todecyl-8-droxyquinoline, and the like.

Now, when performing solvent extraction using an extractant that has selective exchange properties for the above-mentioned cations, 1. This extractant is used after being dissolved and diluted in a water-insoluble organic solvent.

For example, hydroxy hydroxymes usually have 1 to 50
%, preferably at a concentration of 1 to 25%, kerosene (soluble oil)
It is used by dissolving and diluting it in any hydrocarbon solvent that is insoluble in water, such as xylene or xylene.

Here, hydrocarbon solvents include olethane, isooctane,
Aliphatic carbon elements such as decane, pentane or mixtures thereof; aromatic hydrocarbons such as benzene, xylene, toluene and mixtures thereof; alicyclic hydrocarbons such as cyclohexane, cyclopenkune, cyclooctane or mixtures thereof; Furthermore, there are mixtures of the above, kerosene, gasoline, benzene, light oil, etc.

Hydroxyquinolines can also be used diluted in the same way, and a preferred organic solvent for dilution is a mixture of a hydrocarbon solvent such as xylene and a small amount of higher alcohol.

Extraction conditions for base metals vary somewhat depending on the type of extractant with selective exchange for cations, but the most basic
The H conditions are as described above.

Regarding the relationship between the type of base metal and extraction ability, both hydroxy hydroxymes and hydroxyquinolines can extract copper best.

Among hydroxy hydroxymes, nickel and cobalt can be extracted next to copper, but the extraction power of zinc is inferior.

Hydroxyquinolines have superior extraction power for zinc.

In addition to the above-mentioned extractants that have selective exchange properties for cations, higher organic acids such as quaternary carboxylic acids and acidic alkyl phosphates are known, but they have poor extraction properties. In many cases, it is not always appropriate.

For example, in the case of copper extraction, quaternary carboxylic acid has p
H about 3.5 or higher, pH for acidic alkyl phosphate esters
The extraction of copper begins at about 3 or more.

The organic solvent from which base metals have been extracted by solvent extraction is subjected to a base metal recovery step according to a conventional method.

Back extraction and other methods are applied to recover the base metal.

For example, when an acidic aqueous solution of sulfuric acid or the like is mixed with the organic solvent containing a base metal, back extraction can be carried out from the organic solvent side to the base metal aqueous solution side.

Since back extraction is a reverse reaction of extraction, it requires acidic water solubility that is outside the above extraction pH conditions.

Note that when back-extracting, it is also possible to perform back-extraction fractionally by utilizing the fact that pH conditions differ depending on the metal species.

However, since cobalt is difficult to back-extract, it is considered practically preferable to treat an organic solvent with hydrogen sulfide gas and recover it as a sulfide when recovering this base metal.

On the other hand, for the final recovery of silver, conventional methods such as electrolysis may be applied to the silver-containing aqueous solution purified by the solvent extraction described above, but the method of this invention is particularly applicable to the electrolytic crude production of crude silver anodes. Then, as described below, it becomes possible to quickly recover high-grade silver under a closed recovery process.

That is, in electrolytic refining in which pure silver is deposited on the cathode using crude silver as an anode and a silver nitrate solution as an electrolyte, at least a portion of the electrolyte is continuously or intermittently extracted from the electrolytic cell, and the electrolyte is injected into the electrolyte. The above-mentioned solvent extraction is performed to separate and remove base metals such as copper, and the purified electrolyte is recycled to the above-mentioned electrolytic cell.

In this way, the copper concentration during electrolysis can be maintained below a predetermined value, so high-grade silver can be recovered in a short period of time in a closed process, and unlike conventional methods, costs are reduced. Significant savings are possible.

Next, an example will be explained.

Example 1 0 Sample silver-containing aqueous solution: A crude silver anode electrolyte was used.

This electrolyte contained free nitric acid 4 g/l, copper content 609/l,
It is an aqueous solution with a pH of 1.2, and the copper concentration has increased to 25 g/l by purifying the crude silver anode.

Of the impurities in the crude silver anode, the main soluble one is copper, and according to JIS, the copper content in the electrical chain is 30
pI) m or less.

For this reason, most silver electrolytic factories carry out electrolysis in a vacuum manner, analyze the liquid composition in advance before electrolysis, and ensure that the copper content does not exceed the limit concentration (30 to 20 Vl) until the anode is completely electrolyzed. Renew some of the electrolyte and reduce the copper concentration (
It is held at 1 (around 1, #).

○Extraction performance test of cation-exchangeable extractants by shaker test: The following three types of extractants were each diluted and dissolved in an organic solvent, and 100 cc of the solution and 5 Q cc of the above solution were placed in a sealed flask and shaken for 15 minutes. After standing for a while, the upper organic phase was analyzed.

The results are shown below.

(b) When LIX65N (trade name of General Mills Chemicals Co., Ltd., whose main component is 4-nonyl-β-hydroxybenzophenone oxime) is selected as the extractant and a 38% kerosene solution is used, copper in the separated organic phase Minutes are 4.
The copper content was 7 g/l, and the copper content was 0.05 g/l.

(b) When SME 529 (trade name, Shell Chemicals Co., Ltd., whose main component is 5-nonyl-2-hydroxyphenol methyl ketoxime) is selected as the extractant and a 25% kerosene solution is used, the separated organic The copper content in the phase was 3.7 g/l, and the silver content was less than 0.05 g/13.

(/ra) When 7-dodecyl-8-hydroxyquinoline is selected as the extractant and a 15% isodecanol-xylene mixed solution (indecanol 7.5%) is used, the copper content in the separated organic phase is 2. 7 El/IJ, copper content is 0.
It was below 059/13.

○Solvent extraction and metal recovery: The above-mentioned supplied silver-containing aqueous solution was supplied to the first stage of a three-stage countercurrent mixer-settler using a metering pump at a flow rate of 3 Q CC/min.

In addition, 35% of the extractant LIM64N (trade name of General Mills Chemical Company, main component is benzophenone oxime)
The kerosene solution was supplied to the third stage of the mixer settler described above at a rate of 30 CC/min using a metering pump.

The residence times were 2 minutes and 15 minutes, respectively.

Analysis of the aqueous solution obtained from the third stage settler revealed that
The copper content is the same as before extraction, but the copper content is 1g, 8g/
It dropped to 11.

This is a concentration that can be returned directly to the silver electrolyzer.

On the other hand, the kerosene solution from which the copper content has been extracted is introduced into a two-stage mixer settler and subjected to back extraction.

The acid solution for back extraction was an electrolytic solution (H2804215!/Lcu45.F/d) from a copper electrolytic factory adjacent to the copper electrolytic factory.
), and the same amount as the above kerosene solution was supplied to the two-stage mixer settler.

As a result, most of the copper content in the kerosene solution was back-extracted to the acid solution side, and the copper content in the kerosene solution was reduced to 1 νl or less, so this kerosene solution was supplied to the three-stage mixer settler and used for extraction. It was used repeatedly.

Note that the acid solution after back extraction has only a slight increase in copper content and can be returned to the copper electrolysis factory.

Example 2 0 The sludge obtained by neutralizing the wastewater from a silver-containing aqueous solution Niprint circuit manufacturing factory with caustic soda has a water content of 85%, but on a dry ore basis, the copper content is 22%. 1.8%, Zenro 0.05%
Contains.

This sludge was added to an aqueous solution with a total ammonia content of 65 J9/11 adjusted with ammonium carbonate and aqueous ammonia so that the pulp concentration was approximately 8% (based on dry ore).
After stirring for an hour, it was filtered.

In this way, the copper and silver in the sludge will dissolve, but
The gold remains in the insoluble residue.

The composition of this solution was copper 17.29/11, silver 1.4νl,
The pH was 11.5.

○Solvent extraction and metal recovery: The above filtrate was fed at a rate of 20 CC/min to the same three-stage countercurrent mixer settler as in Example 1, and the above 35% kerosene solution of extractant LIX64N was added to the same three-stage countercurrent mixer settler as in Example 1.
The solvent was extracted at CC/min.

Since the copper content was removed from the ammoniacal aqueous solution by this extraction operation, this aqueous solution was used again to dissolve the sludge, and thereafter used in the same solvent extraction.

Repeat this operation several times, and after extracting the solution, the copper concentration in the solution is 77! When the temperature rose to 1/1 or more, hydrazine was added to this ammoniacal aqueous solution for reduction treatment to obtain silver powder.

The copper concentration in the above ammoniacal aqueous solution is 20ppII
The copper contamination of the above silver powder is 1119m or less (
(undetectable), demonstrating high quality.

On the other hand, the kerosene solution from which the copper content was extracted by the solvent extraction was supplied to the same two-stage mixer settler as in Example 1,
At the same time, add 2 Q CC of sulfuric acid aqueous solution with a concentration of 150 i/l.
Back extraction was performed by supplying at a rate of /min.

The kerosene solution that had lost its copper content through this back extraction was recycled and used in the solvent extraction step.

In addition, the sulfuric acid aqueous solution from which the copper was extracted is reused, and the copper concentration is 4.09/L! When the temperature rises to
The electrolyte was supplied as an electrolytic solution to an electrolytic cell with a copper plate as a cathode, electrolysis was performed, and high-grade electrodeposited copper was recovered.

As is clear from the above, the present invention includes at least one base metal selected from copper, nickel, cobalt, and zinc;
This method provides a method for purifying a silver-containing aqueous solution by performing solvent extraction on an aqueous solution in which silver coexists using an extractant that selectively exchanges cations. Since silver can be recovered more directly from the silver aqueous solution and the base metal can also be recovered more directly, it can contribute to improving recovery efficiency and reducing recovery costs.

In particular, if this invention is applied to the electrolytic refining of crude silver anodes, high-grade silver can be recovered in a short period of time through a short process, reducing interest costs and making it easier to cope with unstable silver market conditions. It can be dealt with flexibly, and the economic benefits are immeasurable.

Claims (1)

[Claims] 1 An aqueous solution in which at least one base metal among copper, nickel, cobalt, and zinc and silver are dissolved is heated to a pH of 0.2 to 1.
3.0 with a water-immiscible organic solvent containing an extractant having selective exchange properties for cations, the base metal is extracted and separated into the organic solvent phase, and then the base metal-containing organic solvent is 1. A method for recovering silver from a silver-containing aqueous solution, which comprises supplying a silver-containing aqueous solution to a base metal recovery step and supplying an aqueous solution containing silver to a silver recovery step.