Novel hydrometallurgical process for recovering and preparing high purity silver from copper anode slime
Aiming at the problems of long process flow,precious metal backlog and environmental pollution in the traditional electrolytic refining silver process of copper anode slime. Thus,a novel hydrometallurgical process for recovering silver with ammonia leaching solution as raw material in the study,through a shortened process,acidification precipitation AgCl,H2O2 leaching purification,and efficient reduction with formaldehyde,based on the precipitation characteristics of AgCl and the AgCl-NH3-H2O phase-pH diagram. The effects of acidification precipitation AgCl and leaching impurity under different conditions were studied systematically. The experimental results indicates that,through concentrated HCl to adjust acidity of ammonia leaching solution less than 7.5,[Ag(NH3)2]+can be transformed into AgCl precipitation,the reaction was carried out at 40 ℃ for 1.5 h at pH=5 under the optimal conditions,and the precipitation rate of AgCl reach 99.94％,and the synergistic precipitation rates of Cu,Bi and Pb are 3.46％,94.01％ and 87.05％,respectively. Under the optimized conditions of liquid-solid ratio of 5∶1,HCl concentration of 3.5 mol/L,H2O2 concentration of 3 mol/L,reaction temperature of 85 ℃ and reaction time of 2 h,the crude AgCl is purified by acidic chlorination oxidation,the removal rates of Cu,Bi and Pb are 98.75％,97.5％ and 99.12％,respectively. Refined AgCl is reduced by formaldehyde to obtain black granular silver powder,which meets the requirements of GB/T 4135―20161# standard silver ingot according to TS/Y 958-2014 standard testing.
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