Selective Recovery Of Gold And Silver From Scrap Gold And Silver Plating

Gold,silver as a precious metal,which is an important raw material for making jewelry and coins,but also an important reserve for a country.With the rapid development of science and economy,gold and silver are widely used in the aerospace,electronics,medical and other industrial sectors due to their unique properties.The wide application and consumption of gold and silver will gradually produce a large amount of waste containing gold and silver.Scrap gold and silver plating is an important product in the wastes with high recovery value,the content of gold and silver is much higher than that in natural minerals.At present,the main method of recovering gold and silver is cyanidation,chlorination,thiosulfate,iodination etc.However,the cyanide method is no longer in line with the requirements of the times because it will cause serious pollution to the environment.Thiosulfate leaching technology of greens environmental protection is one of the effective ways to replace cyanidation with the advantages of fast leaching rate,low toxicity and simple operation.In this paper,a company's scrap gold and silver plating are taken as the research object.In order to achieve the selective extraction of gold and silver,under the premise of complete extraction of gold and silver,requires plating substrate material insoluble or less dissolved at the same time.First,the thiosulfate method is selected as the extraction technology to separate gold and silver from the waste gold and silver plating parts.Then use ultrasonic assisted leaching to improve the leaching rate,while studying the kinetics of the leaching process,the conclusions are as follows:First of all,through scanning electron microscopy and quantitative analysis:the scrap gold plating is based on a copper zinc alloy,the surface is plated with nickel,and the gold layer is plated on the convex surface of the strip.In the scrap gold plating,the content of gold is about 97.80 g/t,the content of copper is 62.30%,the content of zinc is 35.80%,the content of nickel is 1.26%;The scrap silver plating is based on copper zinc alloy,the surface is all covered with silver coating.In the scrap silver plating,the content of silver is about 0.16%,the content of copper is 62.30%,the content of zinc is 37.54%.Second,in the leaching experiment,orthogonal experiments and conditional experiments were designed to determine the optimal leaching conditions for scrap gold plating:The concentration of sodium thiosulfate is 0.1 mol/L,the concentration of copper sulfate is 0.036 mol/L,the concentration of ammonia is 0.5 mol/L,the concentration of ammonium sulfate is 0.1 mol/L,and the leaching time is 50 min.The best conditions for the leaching of waste silver plating:The concentration of sodium thiosulfate is 0.1 mol/L,the concentration of copper sulfate is 0.012 mol/L,the concentration of ammonia is 0.5 mol/L,the concentration of ammonium sulfate is 0.1 mol/L,and the leaching time is 50 min.At the same time,the ultrasonic assisted leaching experiment shows that the appropriate ultrasonic power and time can effectively improve the leaching rate and separation efficiency of gold and silver.Through the study of thiosulfate leaching mechanism have shown that,the appropriate dosage of other agents is very important for prevent over-consumption of thiosulfate leaching reagents in leaching process.The kinetic analysis is confirm that the leaching kinetic models of gold and silver are the reaction nuclear reduction model.The activation energy of gold leaching reaction was 24.96 kJ·mol-1 and is mixed control;the activation energy of silver leaching reaction was 6.82 kJ·mol-1 and is boundary layer control.At the same time,the influence of leaching reagent on leaching kinetics of scrap and silver plating was obtained.