Recovery of tellurium from sodium carbonate slag

Abstract

This study is devoted to tellurium recovery from sodium carbonate slag, formed in the fire refining process of crude silver. The slag was modified by silica additions and then reduced by carbon oxide. The degree of the slag modification was defined by the parameter kw: (Equation presented) where: n i - the mole numbers of silica, sodium carbonate and sodium oxide. The compositions of the investigated slag determined by the parameter kw and the mole fraction of the tellurium oxide (xTeO2) are given in the following Table. (Table presented) The reduction of tellurium was very fast for all the investigated slags, which was manifested by an almost complete conversion of CO into CO2. Unfortunately, at the same time, a side reaction took place, and as a results sodium telluride was formed, which reported to the slag: (Equation presented) The tellurium content in the reduced slag decreases as the parameter kw increases, and only the slag with the kw equal unity was suitable for the tellurium recovery in form of dusts, containing more than 76 wt-% tellurium.