A comparison of the reduction of miller chlorides with sodium carbonate and sodium silicate

Abstract

The conventional gold refining process involves injecting gaseous chlorine into the molten gold to remove the metallic impurities. Silver and the base metals are collected in a molten chloride mixture that forms on the surface of the molten gold. This mixture, which is known as Miller chlorides, mainly consists of silver and copper chlorides. In the present work, the reduction of the Miller chlorides with either sodium carbonate (Na 2CO 3) or sodium silicate (Na 2O.SiO 2) and carbon was investigated. The effects of smelting temperature, sodium carbonate or sodium silicate additions and carbon on the metal recovery and purity were determined. With sodium carbonate, metal recoveries approaching 100% could be achieved. With sodium silicate, slightly lower metal recoveries were obtained and borax (Na 2B 2O 4) was required as a flux. Also, higher temperatures were necessary. A comparison is made between the use of either sodium silicate or sodium carbonate for the reduction of the Miller chlorides. Some results on the air refining of the smelt product under a borosilicate slag are presented