THE REDUCTION OF MILLER CHLORIDES WITH SODIUM-SILICATE AND CARBON

In the refining of molten gold, the silver and the copper impurities a re chlorinated and form a molten chloride mixture on the surface of th e gold. This silver chloride-copper chloride salt is known as Miller c hlorides. In the present work, the reduction of this chloride with sod ium silicate and carbon was studied. A silver-copper alloy, a silica-b ased slag and a sodium chloride salt were produced. The overall reacti ons were as follows: 2AgCl + Na2O.SiO2 + C = 2Ag + 2NaCl + SiO2 + CO a nd 2CuCl + Na2O.SiO2 + C = 2Cu + 2NaCl + SiO2 + CO The effects of char coal, sodium silicate, borax additions and crucible type on the metal recovery and composition were determined. Experiments were performed i n resistance, gas-fired and induction furnaces. The results show that even at relatively high temperatures, such as 1400 degrees C, sodium s ilicate additions considerably in excess of the stoichiometric are req uired to achieve silver recoveries approaching 100 percent. For a give n sodium silicate addition, borax additions improved the silver recove ry. Mechanical mixing of the solid reagents followed by smelting in a clay graphite crucible in an induction furnace resulted in the highest metal recoveries and rapid material throughput.