The Behaviour of Silver During the Roasting of Zinc Concentrates

Abstract

AbstractThermodynamic analysis of the behaviour of silver during the roasting of zinc concentrates indicates that silver will ultimately report as Ag, Ag2SO4 or AgCl. Of these silver phases, Only AgCl is appreciably volatile at the roasting temperatures used, and, AgCl volatility is significantly enhanced by the presence of other chlorides such-as NaC. Silver from Ag2SO4 is also volatilized when chloride is present. The presence of SO2 in the gas suppresses silver vapourization from NaCl-bearing systems and this seems to be due to the sulphation of the NaCl. A large portion of the silver contained in a commercial zinc concentrate was volatilized in the presence of NaCl; the extent of Ag vapourization increases with increasing chloride levels to about 1% NaCl, but is insensitive to higher concentrations. Silver vapourization increases with prolonged roasting times and higher temperatures. Silver added to the commercial concentrate as the chloride, sulphate or sulphide is also appreciably volatilized, and t...