Behaviour of selenium and tellurium in copper electrowinning process

Abstract

The revamping project to be implemented at Norilsk Nickel’s refining facilities includes commissioning of a nickel plant and increasing the output of copper obtained by electrowinning from liquors produced in matte leach processes. At the revamped facility, a major portion of selenium and a considerable share of tellurium will be transferred with calciner gases to a sulphuric acid facility. The microimpurities that remain after calcination get distributed between the leachates. Considering that semiproducts keep circulating between the nickel and copper plants, selenium and tellurium can accumulate in the product solutions and thus affect the quality of finished metals. This paper examines the behaviour of selenium and tellurium in copper electrowinning process and formulates certain requirements for copper electrolyte that will ensure production of high-purity copper cathodes for commercial application. It is shown that, at low concentrations of selenium (IV) and tellurium (IV) in the copper electrolyte, their discharge follows the laws of diffusion kinetics, i.e. occurs at maximum current, together with cathode reduction of copper, and the concentrations of selenium and tellurium in copper change in correlation with the concentration of chalcogenides in the solution. Simultaneously with cathode reduction on a lead anode, selenium (IV) and tellurium (IV) get oxidized to selenium (VI) and tellurium (VI) that are not precipitable with copper and get accumulated in circulating solutions. It is shown that the concentration of chalcogenides has a negative first order from the removal of copper per unit volume of electrolyte. That’s why the contamination of cathode copper with selenium and tellurium rapidly decreases with an increase in copper removal. The paper provides data that can be used to estimate the allowable concentration of toxic microimpurities in the feed electrolyte that would not affect the desired copper purity level.