Technical evaluation of converting starter-sheet copper electrowinning to permanent cathode technology at Anglo American Platinum's Rustenburg base metals refinery

Abstract

Developments in copper electrowinning technology in recent decades have shown significant advantages of permanent cathode technology and the use of edge strips on cathode blanks. The existing starter-sheet operation at Rustenburg Base Metals Refinery is labour-intensive. The performance and operability of the tankhouse are highly dependent on structural integrity, equipment reliability, and overall operational excellence. The aim of this research was to determine the viability of sustainably and cost-effectively converting an existing low current density starter-sheet copper electrowinning operation to use of permanent cathodes. An eighteen-harvest cycle permanent cathode pilot trial was carried out in the starter-sheet tankhouse under existing plant operating conditions, to assess the ability to consistently produce good quality copper. SS316L cathode blanks were used for plating. New V-notch busbars and vinyl ester capping boards with electrode chairs were designed and fitted to the cells during the test campaign. This thesis describes the rigorous test work and results, including the installation of new cell-top furniture and busbars. In addition, the process design considerations for the conversion are summarized. The evaluation of current plant performance has shown significant improvements in the starter-sheet operation from all aspects, notably producing a historic record monthly scrap rate of 2.06 %. A total of 137.17 t of copper was produced from permanent cathode technology. Good quality copper was produced from standard current density (< 150 A/m2) cycles; unfavourable results were observed during higher current density cycles (< 290 A/m2). Industry-standard current efficiencies with minimal scrap production were achieved: the highest cycle current efficiency was 92.51%. For the existing electrolyte composition, the operational current density, size of Pb–Sb (6%) anodes, type of cathode edge strips, effect of over-plating, and the use of fibreglass electrode-stabilizing plates installed at the base of the electrowinning cells proved to be important conversion considerations. The installation of the new cell-top furniture proved seamless with easy integration into the existing electrical reticulation network. Good copper cathode quality and efficiency were produced using new V-notch busbars and subsequent symmetrical arrangement of electrodes. The future of the tankhouse aims to increase capacity from 20.6 kt/a to 24.5 kt/a with the commissioning of permanent cathode cells on the East and Centre bays of the tankhouse and incorporating automated cathode stripping. Constraining the implementation to minimize capital expenditure is possible in a bid to improve safety, operability, and to remove man-equipment interactions from the process. The key is to maximize the re-use of existing equipment, leverage synergies within the refinery, and consider the implementation of the conversion in a phased approach in line with the natural replacement cycle of current cell-top furniture. Ultimately, moving away from the labour-intense, double product handling starter-sheet operation to the latest permanent cathode technology will improve the operability and re-imagine mining to improve people’s lives.