Public defence in Processing of Materials, MSc Mika Sahlman

Title of the thesis: Effects of nickel in copper production: implications for high-purity copper electrorefining

Thesis defender: Mika Sahlman
Opponent: Prof. Jan Cilliers, Imperial College London, United Kingdom
Custos: Prof. Mari Lundström, Aalto University School of Chemical Engineering

The majority of the world’s high-purity copper is produced electrolytically by refining impure copper anodes from smelters into copper cathodes, which are then manufactured into various copper products. Nickel is a common additive in various copper products, as it improves the corrosion resistance of copper. However, once the copper-containing products are recycled, nickel ends up in the electrorefining process, where it can cause problems. This issue is further complicated by the integration of industrial base metal processes, which share their material streams.

This thesis studied the effects of nickel in copper electrorefining. Various electrolysis experiments were designed to study the contamination of the copper cathodes, the growth of copper cathodes, and to track the movement of impurity particles in the electrorefining cell. Both synthetic and industrial solutions and samples were used in the investigation.

It was found that nickel mainly contaminates the cathodes via particle entrapment of so-called anode slimes. Electrolyte inclusions were found to be plausible but unlikely to cause major contamination in industrial operations. Nickel may also contribute to the formation of rougher cathodes, but this effect can be mitigated with the use of electrolyte additives such as bone glue, thiourea, and chloride. The video recording of the impurity particles in electrorefining revealed that the particles detaching from the anodes are significantly larger than previously thought. Increasing the nickel concentration of the anodes and electrolyte can also cause larger portions of the impurities to flow upwards instead of settling down during passivation, which increases the risk of cathode contamination.

Based on the results, industrial electrorefineries can – on average – increase their nickel concentrations in the electrolyte without having major detrimental effects on cathode production. This thesis also introduces to academia a novel and low-cost research method for the study of cathode growth.

Keywords: copper, nickel, electrorefining, cathode contamination, industrial electrochemistry

Thesis available for public display 10 days prior to the defence at Aaltodoc. 

Contact information: 
mika.sahlman@aalto.fi