Effect of Chloride Electrolyte Additive on the Quality of Electrorefined Copper Cathode

Sodium chloride (NaCl) is used in electrorefining as an electrolyte additive for refinement of copper grains and reduction of cathode impurities such as Ag and Sb. This is done by precipitating them out of solution as metallic chloride crystals. In this study a laboratory scale electrorefining circuit was used for the electrodeposition of copper in the presence of Bone glue, thiourea, Avitone and NaCl as electrolyte additives. The effect of NaCl on physical and chemical quality of cathode deposits was studied to achieve the optimum chloride concentration in the electrolyte. Cathode chemical composition was analysed using Spark Analysis for Traces (SAFT) machine and cathode morphology analysed using Optical Microscope (OM). Anode slime elemental composition was analysed by Inductively Coupled Plasma Mass Spectroscope (ICP-MS). It was found that chloride concentration in electrolyte affect the cathode deposit physical appearance and chemical quality and also plays a major role in making the composition of anode slime. Ag in cathode was found to be lower between chloride concentrations of 0.02g/l and 0.025g/l whereas Sb in cathode was lower at concentrations lower than 0.025g/l. Chloride concentration of 0.02g/l produced smoother and compact cathode deposits which were free from pits and nodules. At higher chloride concentration cathode deposits developed a pit-like appearance on the surface and grew nodules next to the pits.