The QTM* process for the recovery of silver from Miller chlorides

CIM Bulletin, Vol. 88, No. 993, 1995

C.A. Pickles, Department of Materials and Metallurgical Engineering, Queen's University, Kingston, Ontario J.M. Toguri and R.A. Bergman, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, and J. Clark and H. Truong, Royal Canadian Mint, Ottawa, Ontario

Miller chlorides, which are a mixture of silver and copper chlorides, are produced when impure molten gold is refined with chlorine. Usually the copper and silver are recovered from the chlorides by a hydrometallurgical cementation process. However, this process is slow, requires considerable floor space, and generates waste water solutions which are not environmentally acceptable. In the present work, the pyrometallurgical reduction of the Miller chlorides was investigated according to the following reactions: 2AgCl + Na2O.SiO2 + C = 2Ag + 2NaCl + SiO2 + CO 2CuCl + Na2O.SiO2 + C = 2Cu + 2NaCl + SiO2 + CO Sodium hexaborate (borax) was added as a flux. Pilot plant tests were performed at the Royal Canadian Mint in Ottawa, Ontario. The effects of charcoal additions and smelting temperature on the metal recovery and composition were determined. With carbon additions, silver recoveries of almost 100% were achieved. Without carbon, the silver recoveries were lower but some separation of the copper from the silver was possible. Oxygen refining of the silver-copper alloy under a borosilicate slag was also investigated. The process was implemented at the Royal Canadian Mint in Ottawa, Ontario, Canada.  

Keywords: Metallurgy, Miller chlorides, Pyrometallurgy, Metal recovery processes