Recovery of silver from low-silver leaching solution

Used in this test lean liquid containing silver chloride leaching, FeCl 2 -O 2 respectively from leaching of copper sulphide concentrate leaching solution Cl 2 -O 2, and concentrate leaching sphalerite FeCl 3 leaching of galena concentrate. In this chlorinated leachate, silver is present in the form of complex ions [(AgCl 4 ) 3 - ), and NaI is added to cause AgI precipitation. After filtration and decantation washing, Na 2 S was added to convert the AgI to an Ag 2 S precipitate, and the expensive NaI was regenerated for recycling. Its response is;

(AgCl 4 ) 3 - +NaI AgI+NaCl+3Cl -

2AgI+Na 2 S Ag 2 S+2NaI

A total of five batches were carried out in the experiment, and each of the above three infusions containing silver of 0.05 to 0.07 g of ∕L was treated with 8 L of each. The results showed that, when these three are contained immersion (g / L) Cu 10, and the zinc and lead 5 200, no significant effect on the recovery of silver, but the pH of the solution, temperature, and amount of sodium iodide The job has a significant impact.

pH: The pH of the solution should be kept below 2.0 to avoid Fe(OH) 3 coprecipitation and contaminate AgI when AgI precipitates. By using only 5% of the stoichiometric amount of Na 2 S, 95% of AgI can be converted to Ag 2 S in 10 minutes. That is, the end point of Na 2 S addition is pH 10.5, and it should not be excessive, so as not to affect the returning use of the NaI regeneration liquid. If necessary, the excess FeCl 2 can be added to the Ag 2 S filtration solution to remove the excess Na 2 S S 2 to form FeS. This reaction should be controlled at pH ≤ 7.0.

Liquid temperature: The AgI precipitate formed by the above reaction is easy to flocculate only at a liquid temperature of 21 ° C, which is convenient for washing and filtration. When the temperature rises to 34 ° C, only slight flocculation occurs, and at 49 ° C, no flocculation occurs at all. Since the AgI particle size is extremely fine, AgI can be effectively flocculated by slowly stirring at a liquid temperature of 21 ° C, and then allowed to stand for 60 min and then decanted to recover 95% of AgI.

When the amount of sodium iodide is added, the iodine is added in a stoichiometric amount, and the precipitation rate of AgI by silver can reach 92%; when the amount of iodine added is 1.2 times the stoichiometric amount, the precipitation rate of AgI can reach 99%. From the precipitation of silver to the regeneration of sodium iodide, the iodine loss rate during the operation was 4.8%.

This method is commonly used to recover silver from oxygen-containing chlorinated leach solution. The Ag 2 S produced contains Ag85.0%, S12.6%, Fe, Cu, Pb, Bi and other impurities less than 2.5%. Placed in an alkaline solution containing NaOH, adding aluminum powder so that the silver is reduced to metallic:

2Al+2NaOH+2H 2 O Na 2 Al 2 O 4 +6H +

6H + +3Ag 2 S+6NaOH 3Na 2 S+6H 2 O+6Ag↓

The precipitated crude silver is reduced and purified by fire refining.

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