SOLUTION PURIFICATION OF COPPER ELECTROREFINING ELECTROLYTE - A NOVEL WAY TO RECOVER PRECIOUS METALS

Typical copper electrorefining electrolyte contains tens of grams of copper, some nickel and a wide variety of impurities. Some of these impurities comprise trace amounts of dissolved precious metals like Ag, Pd and Pt that currently are not fully exploited. This study presents an electrochemical method to recover precious metals via a combined electrodeposition-redox replacement (EDRR) process, where energy is used only to deposit copper during the ED-step, while the RR-step relies on the spontaneous replacement of copper by the precious metals (i.e. cementation). In order to conduct the recovery successfully, process parameters such as deposition potential (EDE), deposition time (tDE), redox replacement time (tRR) and the number of cycles (n) was adjusted. Investigations performed in synthetic electrolyte (40 g/L Cu, Ag = 10 ppm) proved the possibility to recover a high purity silver. Short deposition times (tDE) were found to result in small Cu particles that provided a suitably high surface area for silver cementation. In addition, experiments performed in real industrial electrolytes containing 44 g/L Cu and 54 ppb Ag (Boliden Harjavalta, Pori), demonstrated that EDRR could attain Ag recoveries of between 46–67% in an energy efficient, additive-free manner.
The authors want to acknowledge NoWaste project, grant number: 297962 (VB, PH and KY) funded by Academy of Finland as well as GoldTail, grant number: 297962 (BW, ML). D.J thanks the National Centre for Research and Development, Poland (under the Lider program, Grant agreement LIDER/001/L-8/NCBR/2017). V.B would like to thank the Intramural CSIC incorporation project as well as research group of Hydrometallurgy and Corrosion in School of Chemical Technology of Aalto University. Academy of Finland funded “RawMatTERS Finland Infrastructure” (RAMI) based at Aalto University is greatly acknowledged.