JP2008285691A - Method for recovering silver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method where, from a silver-containing aqueous solution in which silver and the other metal are coexistent, silver is efficiently and selectively separated and recovered by an extraction process. <P>SOLUTION: A silver-containing aqueous solution is admixed with inorganic acid at a concentration of 0.5 to 2 mol/l, the aqueous solution and a crown ether-containing organic solvent are contacted, so as to extract silver into the organic solvent, and thereafter, the silver is stripped from the organic solvent, so as to be recovered. As the crown ether, the one having a group comprising 6 pieces of oxygen such as dicyclohexano-18C6-crown ether and benzo-18C6-crown ether is preferable. Further, as the inorganic acid, nitric acid, perchloric acid or the like can be suitably used. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for selectively separating and recovering silver from an aqueous solution containing silver by an extraction method.

  Cleaning drainage from the plating process, photographic developer drainage, copper electrolytic drainage, etc. contain silver, but recovery of silver from these silver-containing aqueous solutions is an effective use of valuable metals. Is important. Moreover, since several ppm of silver is contained in the copper electrolyte, the quality of electrolytic copper can be improved by collecting only silver in advance.

  Conventionally, as a method for recovering silver from an aqueous solution containing silver, an electrolysis method, a precipitation method, an ion exchange method, an extraction method, and the like are known. Among these, according to the extraction method, silver can be selectively separated and recovered from an aqueous solution in which other metal ions coexist by using a collector having high selectivity to silver.

  For example, Japanese Patent Application Laid-Open No. 60-228626 describes a method of solvent extraction of silver by bringing a nitrate solution containing silver into contact with a mixed extractant composed of dialkyl phosphoric acid and oxime. However, there is no description about selectivity when other metals coexist, and its influence is unknown.

  Further, according to Japanese Patent Application Laid-Open No. 08-169714, a silver-containing aqueous solution containing manganese, nickel, zinc, iron, cadmium and copper is supported by a porous material carrying O, O-bis (2-ethylhexyl) hydrogenthiophosphate. A method is described in which silver is adsorbed on a resin and then eluted with an organic solvent, and the silver is recovered from the organic solvent containing silver. However, if the hydrochloric acid in the aqueous phase is not present at about 5 mol / liter, a large amount of copper is extracted together with silver ions, so that a large amount of acid is required. Furthermore, since a solution containing thiouric acid and hydrochloric acid is used as a back extractant, there is a problem that handling is difficult.

  In addition, crown ether is known as an extractant with high silver selectivity. Since the ligand of the crown ether forms a cyclic structure, high selectivity can be expected due to the size effect and the like. For example, JP-A-2002-97183 discloses alkanoyl monoaza crown ether as a selective extraction reagent for silver. However, this publication does not describe specific extraction conditions.

JP 60-228626 A Japanese Patent Laid-Open No. 08-169714 JP 2002-97183 A

  In view of the above-described conventional circumstances, an object of the present invention is to provide a method for selectively and efficiently separating and recovering silver by an extraction method from a silver-containing aqueous solution in which silver and other metals coexist. .

  To achieve the above object, the silver recovery method provided by the present invention comprises adding an inorganic acid to an aqueous solution containing silver at a concentration of 0.5 to 2 mol / liter, and an organic solvent containing the aqueous solution and crown ether. And silver is extracted into the organic solvent, and then silver is back-extracted from the organic solvent.

  According to the present invention, only silver can be selectively and efficiently recovered by an extraction method from a silver-containing aqueous solution in which silver and other metals coexist. Therefore, valuable silver can be recovered from the washing waste water from the plating process, the photographic developing waste water, the electrolytic copper waste water, and the like. Moreover, if it applies to the electrolytic solution of copper, it can contribute not only to the recovery of silver but also to the production of higher purity electrolytic copper.

  In the silver recovery method according to the present invention, when extracting silver from a silver-containing aqueous solution into an organic solvent using an organic solvent containing crown ether, an inorganic acid is added to the silver-containing aqueous solution, and the concentration of the inorganic acid Is prepared in the range of 0.5 to 2 mol / liter. By bringing an organic solvent in which crown ether is dissolved into contact with the aqueous solution prepared with the inorganic acid concentration, silver can be selectively and efficiently extracted from the silver-containing aqueous solution and transferred into the organic solvent.

  The reason why the coexistence of the inorganic acid is effective in the extraction of silver with crown ether is as follows. When the silver-containing aqueous solution and the organic solvent containing crown ether are contacted in the extraction step, a part of the crown ether is distributed in the aqueous solution, and the crown ether and silver form a cation complex, and then the complex Forms an ion pair with the anion and moves into the organic solvent. Therefore, the greater the concentration of anions that form ion pairs with the complex, the more the equilibrium tends to form ion pairs, that is, the silver in the aqueous solution is more likely to be extracted into the organic solvent.

  As anions that form ion pairs with the above complexes, organic anions are generally better than inorganic anions because they have a large molecular volume and are less hydrated and have better extractability. In view of ease and post-treatment such as disposal, inorganic anions can be used preferably. As the inorganic anion source, inorganic acids, potassium salts, sodium salts and the like can be considered. However, since potassium and sodium have an ionic radius close to that of silver and interfere with silver extraction, inorganic acids are desirable. Furthermore, nitric acid or perchloric acid can be suitably used as the inorganic acid.

The concentration of the inorganic acid in the silver-containing aqueous solution needs to be in the range of 0.5 to 2 mol / liter. When the concentration of the inorganic acid in the aqueous solution exceeds 2 mol / liter, the oxonium ion (chemical formula: H ₃ O +) generated from the inorganic acid hinders the extraction of silver, and the extraction efficiency decreases. If the concentration of the inorganic acid in the aqueous solution is less than 0.5 mol / liter, a selective silver extraction effect cannot be expected. The density | concentration of the inorganic acid in a preferable silver containing aqueous solution is 1-2 mol / l.

  The crown ether used for silver extraction has a ligand such as an oxygen atom or a nitrogen atom forming a cyclic structure, and has a high affinity for ions having a radius close to the pore diameter. Therefore, by using crown ether, copper, cadmium, iron, zinc, etc. have an ionic radius that is too large or too small, so the mutual affinity becomes small, so they are not extracted and only silver with the same ionic radius is used. Can be selectively extracted.

  Furthermore, since the ionic radius of silver is about 1.3 angstroms, a crown ether having six ligands and having a pore radius of about 1.3 to 1.4 angstroms is preferable. Further, the affinity between a general ligand and silver is highest in the sulfur atom, followed by the nitrogen atom and the oxygen atom. However, a crown ether containing a sulfur atom cannot obtain a sufficient concentration because of poor solubility in an organic solvent. Moreover, since the nitrogen atom has high affinity with protons in an acidic solution, the reactivity with silver decreases.

  For these reasons, it is particularly desirable that the crown ether used in the present invention has a group containing 6 oxygens. Specific examples of such crown ethers include dicyclohexano 18C6 crown ether and benzo 18C6 crown ether.

  The organic solvent for dissolving the crown ether is not particularly limited as long as the solubility of the crown ether is high and the solubility in water is low. For example, alcohols such as octanol, alkanes such as octane, and organic chlorines such as toluene and chloroform. A compound etc. can be used conveniently.

  In the method of the present invention, the silver-containing aqueous solution and the organic solvent containing crown ether are contacted in the extraction step to extract silver into the organic solvent, and then the organic phase and the aqueous phase are separated, and the separated organic phase (organic solvent) The silver is back-extracted into the back extract by contacting the back extract with As the back extraction liquid, an easy-to-handle aqueous solution such as pure water or a thin mineral acid can be used. Since there are almost no metal ions other than silver in this back-extracted solution, the silver in the solution can be recovered as high-purity metallic silver by subsequent electrolysis or the like.

[Example 1]
Nitric acid was added to each aqueous solution containing 0.04 mol / liter or 0.1 mol / liter of silver to change the concentration of nitric acid in the range of 0.0001 to 5 mol / liter. To 10 ml of each silver-containing aqueous solution having a changed concentration of nitric acid, 10 ml of a chloroform solution in which 1.5 times the silver concentration of dicyclohexano 18C6 crown ether was dissolved was added, and the mixture was brought into contact with stirring for 10 minutes while stirring. Extracted.

  Next, the organic phase and the aqueous phase were separated, the concentration of silver remaining in each aqueous solution was measured, the silver distribution ratio was determined, and the results are shown in FIG. The silver distribution ratio = the silver concentration transferred to the organic phase / the silver concentration remaining in the aqueous solution, and the larger the distribution ratio, the higher the silver extraction rate. From the results shown in FIG. 1, the distribution ratio of silver increases as the concentration of nitric acid in the aqueous solution increases from around 0.5 mol / liter, but when the concentration of nitric acid exceeds 2 mol / liter, the distribution ratio decreases conversely. I know what to do.

[Comparative Example 1]
Silver was extracted in the same manner as in Example 1 except that potassium nitrate solution or sodium nitrate was added to an aqueous solution containing 0.04 mol / liter of silver. The concentration of silver remaining in each aqueous solution was measured, the silver distribution ratio was determined in the same manner as in Example 1, and the results are shown in FIG. 1 together with the results of Example 1.

  As can be seen from FIG. 1, in the case of potassium nitrate, the silver distribution ratio decreased with increasing concentration. Further, in the case of sodium nitrate, the silver distribution ratio increases with an increase in the concentration thereof, but the distribution ratio is much lower than that in the case of adding nitric acid of Example 1 above.

[Example 2]
In addition to 0.001 mol / liter of silver, an aqueous solution containing the same concentration of copper, cadmium, nickel, zinc and magnesium was prepared. To this silver-containing aqueous solution, nitric acid or perchloric acid was added to a concentration of 1.5 mol / liter. To 10 ml of each silver-containing aqueous solution, 10 ml of a chloroform solution in which dicyclohexano 18C6 crown ether was dissolved in 1.5 times mole of silver concentration was added and contacted for 10 minutes with stirring and shaking to extract silver.

  Next, the organic phase and the aqueous phase were separated, 10 ml of pure water was added to the separated chloroform solution, and contacted for 10 minutes with stirring and shaking, so that the components extracted into the chloroform solution were back extracted into the aqueous phase. Thereafter, the organic phase and the aqueous phase were separated, and the concentration of each metal remaining in the aqueous solution and the concentration of back-extracted silver were measured.

  As a result, the silver extraction rate was 98% when nitric acid was added to the silver-containing aqueous solution, and 99% when perchloric acid was added. In either case, no other metal component was extracted. Further, the sum of the amount of silver remaining in the silver-containing aqueous solution after extraction and the amount of back-extracted silver was substantially the same as 0.001 mol / liter that was initially present in the silver-containing aqueous solution, It was confirmed that silver could be back extracted with water.

It is a graph which shows the relationship between the nitric acid compound density | concentration and Ag distribution ratio of silver containing aqueous solution.

Claims (2)

  A method for selectively extracting and recovering silver from an aqueous solution containing silver, wherein an inorganic acid is added to the aqueous solution containing silver at a concentration of 0.5 to 2 mol / liter, and the aqueous solution and crown ether are added. A method for recovering silver, comprising: extracting silver from an organic solvent by contacting with an organic solvent, and then back-extracting silver from the organic solvent.   The method for recovering silver according to claim 1, wherein the crown ether has a group containing six oxygens.

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