Dissolution behavior of elemental tellurium and tellurium dioxide in alkaline cyanide solutions

Elemental tellurium and tellurium dioxide are related to the hydrometallurgy of precious metal tellurides in two ways: (1) both species are products of precious metals tellurides cyanidation; and (2) tellurium dioxide is a by-product of the roasting of tellurides to produce metallic gold/silver prior to cyanidation. An investigation to elucidate the dissolution behavior of elemental tellurium and tellurium dioxide at 1250 mg/L CN−, pH 10.9, and 25 °C was carried out. For this purpose, batch test, thermodynamic simulation, and voltametric techniques were employed. The results showed that 8% of elemental tellurium was dissolved due to the inability of dissolved atmospheric oxygen to oxidize it. However, according to the potential-pH diagram, tellurium dissolution should continue to produce TeO2(OH)22−. Cyclic voltammetry for tellurium showed an oxidation pathway to form TeO32− and TeO42− at 240 and 982 mV, although an oxidation process indicating the slight dissolution of elemental tellurium was observed at −75 mV. Tellurium dissolution form tellurium dioxide reached 82% but it could be enhanced by increasing the pH beyond 11.5. The tellurium dioxide hydrolysis in alkaline media produced TeO2(OH)22− but the pH of the system tends to decrease; if pH in not adjusted, H2TeO3 will form, hindering the tellurium dissolution.