Statistical analysis of the distribution of impurities during copper electrorefining

Abstract

Electrolytic copper refining makes it possible to obtain high purity metal, so the analysis of the main ways of impurity transition into electrolysis products is an actual problem. If it is solved, the process can be controlled when changing the composition of raw materials and, as a result, the content of impurities in the anodes. This paper uses the comprehensive analysis and synchronization of a large array of data on impurities concentrations in various process media (anodes, electrolyte, slime, and cathode metal) obtained on the series of commercial cells to identify the directions of impurity flows and relationship between their content in these media. It is shown that the transition of impurities from one process medium (source) to another (receiver) is implemented according to four main patterns: linear increase, no visible dependence, the presence of a limit concentration in the receiver and the presence of a threshold concentration in the source. The paper provides the results obtained in the statistical analysis of the distribution of six impurities (bismuth, arsenic, lead, sulfur, nickel and silver) belonging to different groups in four main pairs of the impurity source – receiver: anode – solution, anode – slime, slime – cathode, solution – cathode. The coefficients of linear regression equations are determined and their significance is estimated for all dependencies of the impurity concentration in the source on the content in the receiver. The coefficients obtained make it possible to explain the impurity transition paths observed in the commercial cells and predict the quality of cathode copper and the composition of slimes when the anode composition changes. The calculations showed that impurities are accumulated in cathodes due to the occlusion of slime particles and incomplete solution removal from the surface of commercial cathodes rather than due to electrochemical reactions. The copper electrorefining technology should be improved and developed so as to find surface-active additives that would prevent the adsorption of suspended slime particles on the cathode surface, as well as better wash them from the electrolyte.