Optimisation of influential factors in electrowinning of tellurium by means of PLS modelling

Abstract: Electrowinning of tellurium is a relatively simple process that can be carried out effectively by employing the existing technology. In order to obtain tellurium with the least amount of impurities, the effects of three main factors were studied, namely current density, free concentration of caustic soda and initial concentration of tellurium. Five elements were chosen as the main impurities: Ag, Bi, Cd, Ni and Pb. A series of 17 experiments arranged in a CCF (central composite faced-centred) design has been carried out and the results were fitted using PLS (partial least squares) method. The effect of free caustic concentration was found to be the most important of the three parameters studied. Current density was also important, yielding the least amount of impurities at high current densities. Tellurium concentration had the smallest effect of the three parameters studied. From the model, current densities of 330-350 A/m2, tellurium concentrations of 90-120 g/l and free sodium hydroxide concentration of around 120 g/l are suggested as optimal conditions for obtaining the purest tellurium.