The crude silver chloride produced in the chlorine refining of gold is sent to the silver refining process. In this section the silver chloride is leached of its impurities, then reduced to metal that is cast into anodes and electrolyzed. The silver chloride cake is reduced to 100% passing 20 mm and charged into a rotating rubber lined barrel that rotates at 4-6 rpm and leaching is performed by a hot solution of 4-7% sodium chloride and 1.0-1.5 % HCl. During the leaching process, the supernatant liquor is decanted and further leaching solution added. Approximately a total of sixteen such changes are needed to get a silver chloride 99.8% pure during a period of five days. Reduction to metal is performing by layering the silver chloride with iron plates in hot diluted sulphuric acid over a period of two days. Normally, the final and eight is taken up with washing the silver sponge produced over 99.8% pure.
An updated process considers additions of sodium chlorate and hydrochloric acid for leaching and zinc powder for precipitation. The chlorides are reduced to a granular powder of minus 2 mm by quenching in water and then both the leaching and precipitation reactions performed in a conical tank. The resultant silver sponge is collected in a pan filter located under the tank. The leaching and reduction processes need two days to complete the reactions and the silver produced is 99.8% pure and is refined by a electrolytic process.
Silver Chloride Treatment Flowsheet