Reduction Mechanism of Tellurium Species from Copper Electrowinning Solutions

The presence of tellurium in copper-nickel sulfide ores results in downstream contamination of leach solutions and electrolytes. Tellurium must be removed from leach solutions before electrowinning to prevent contamination of copper cathodes. Cuprous ion is industrially used as a reductant to remove tellurium ions. However, the reduction kinetics of tellurium ions with cuprous is not well known. In this study, the slow Te-VI reduction step with cuprous was identified and a plausible Te-VI reduction mechanism was suggested. The rate-determining step was investigated by studying the kinetics of the coupled reaction of Te-VI and Te-IV with cuprous. The rate law suggested for the reduction of Te-IV with cuprous and the coupled kinetics equation for consecutive reduction reactions of Te-IV and Te-VI were derived. It was shown that the rate constant of the coupled reaction is very close to the rate constant calculated based on the assumption that Te-VI reduction is a rate-determining step.