A COMPARISON OF THE REDUCTION OF MILLER CHLORIDES WITH SODIUM-CARBONATE AND SODIUM-SILICATE

The conventional gold refining process involves injecting gaseous chlo rine into the molten gold to remove the metallic impurities. Silver an d the base metals are collected in a molten chloride mixture that form s on the surface of the molten gold. This mixture, which is known as M iller chlorides, mainly consists of silver and copper chlorides. In th e present work, the reduction of the Miller chlorides with either sodi um carbonate (Na2CO3) or sodium silicate (Na2O.SiO2) and carbon was in vestigated. The effects of smelting temperature, sodium carbonate or s odium silicate additions and carbon on the metal recovery and purity w ere determined. With sodium carbonate, metal recoveries approaching 10 0% could be;achieved. With sodium silicate, slightly lower metal recov eries were obtained and borax (Na2B2O4) was required as a flux. Also, higher temperatures were necessary. A comparison is made between the u se of either sodium silicate or sodium carbonate for the reduction of the Miller chlorides. Some results on the air refining of the smelt pr oduct under a borosilicate slag are presented. Copyright (C) 1996 Cana dian Institute of Mining and Metallurgy.