Study On Extraction Of Gold And Silver From Copper Anode

Copper anode slime contains a large number of precious metals and rare elements, which is an important raw material to extract precious metals. Copper anode slime treatment is to recover precious metals and valuable elements. The process of copper anode slime treatment are divided into four types of technology: pyrometallurgy process, flotation-metallurgy process, hydrometallurgy process and half hydrometallurgy process. At present, half hydrometallurgy process were used by most domestic factory. In this thesis, using thiourea solution to extract gold and silver selectively from copper anode slime was studied through experiments.In this thesis, copper anode slime was pretreated to remove copper at first, and gold and silver were leached from removal copper anode slime with acidic thiourea solution. The central composite design of response surface method and single factor experiment were used to study the gold and silver leaching process from removal copper anode slime, and the optimum process conditions are:leaching time24h, liquid-solid ratio20:1thiourea concentration50g/L, leaching temperature40℃, and stirring speed400rpm, in this conditions after three periods leaching, gold and silver leaching rates reached96.15%and99.36%respectively, and the valuable elements such as Se, Te, getted enrichment. The study of the gold and silver leaching kinetics found that thiourea leaching silver from removal copper anode slime is mainly controlled by the solid membrane diffusion, the diffusion apparent activation energy of the leaching process is12.28kJ/mol, and gold leaching process from removal copper anode slime is mainly controlled by chemical reaction in less than12h leaching time.Distribution of silver thiourea complexes in acidic thiourea leaching solution were analysed, the results show that the main thiourea complexes of silver in the copper anode slime leaching solution were in the forms of [Ag(TU)4]+and [Ag(TU)3]+,and the [Ag(TU)4]+concentration is the largest. The electrochemical process of silver electrodeposition from the acidic thiourea leaching solution has been studied utilizing cyclic voltammetry. The order that each species are electrochemical reduced in succession was Fe3、RSSR、H+、[Au(TU)2]+、[Ag(TU)4]+and [Ag(TU)3]+Gold priority in silver is electrochemical reduced precipitation, then reduced with silver together, and in company with Fe3+H2, RSSR and other metallic impurities are reduced. However the cathode hydrogen evolution is the main reason for reducing the current efficiency.The research results of electrodepositing gold and silver from thiourea leaching liquid containing gold and silver showed that, when the initial concentration of silver in the leaching liquid is1g/L, as the current density increased from10A/m-2to25A/m-2, current efficiency gradually increased to27.09%, the residue silver concentration gradually increased to0.7092g/L, silver deposition rate rapidly reduced from81.66%to29.11%; When the initial concentration of silver in the leaching liquid is6.8731g/L, current density is20A/m-2, As the extension of electrodeposition time, the deposition rate increased to86.65%, and the current efficiency gradually reduced from75.64%to67.40%; High concentration of silver in the leaching liquid can significantly improve the current efficiency, when the silver concentration is8.7921g/L, the current efficiency could reach99.06%in2h; when electrodepositing gold and silver from leaching liquid in different period of time with high and low current density, electrodepositing6h at current density of20A/m-2,10h at current density of10A/m-2, Ag deposition rate reached97.26%, Au deposition rate approximated100%and the deposition contains Ag91.63%, Aul.05%.