Effect of various factors on the physicochemical properties of cathodes during copper electrorefining

Abstract

The copper electrorefining process adopted by Nornickel’s Polar Division is based on the use of various surface active agents (or, surfactants), such as hide glue used as a colloid that helps smoothen the cathode surface and prevent dendrite formation and thiourea that helps with the generation of ductile cathode deposits. The study was based on the surfactant consumption rates adopted by the Copper Electrowinning Section of the Copper Plant. Pursuant to the London Metal Exchange standards, the testing of specimens is based on the Spiral Elongation Number (SEN) indicative of the physical properties of copper cathodes – i.e. ductility and recrystallization ability during heat treatment. It is a fact that the ductility of electrolytic deposit is dictated by the crystal size and the concentration of impurities. This paper describes a laboratory study that shows that the average size of crystals in the copper electrolytic deposit tends to decrease as the concentration of thiourea in the nickel-bearing copper electrolyte rises. A relationship was established between the average size of crystals in the copper cathode deposit and the duration of its growth. The study helped determine how fast the concentration of thiourea tends to rise in commercial electrolyte depending on the copper cathode build-up duration. A direct relationship was established between the concentration of sulphur and other impurities in copper cathodes and the concentration of thiourea in copper electrolyte. The conducted study helped determine the relationships between the concentration of thiourea in the copper electrorefining electrolyte, the crystal size in the cathode deposit, impurities and the physico-mechanical properties of copper cathodes.