Anode effects in electrowinning

In traditional electrowinning operations, metal particles from commercial i nsoluble anodes flake off the immersed surfaces under high current densitie s and thus become occluded on the adjacent cathode surface thereby impairin g the cathode product quality and market grade. This results in an undesira ble physical appearance of the cathode due to irregular protrusions which i mpede subsequent material handling operations such as packaging, weighing a nd shipping. The paper serves to highlight the existing problems inherent w ith permanent anodes and suggests possible areas for further research and d evelopment studies. At present, permanent anodes are employed in the worldwide electrolytic ind ustry for the recovery of bare metals such as copper, nickel, cobalt, and z inc while smaller scale operations exist to recover precious metals such as gold and silver from leach solutions. The coupling of solvent extraction w ith electrowinning technology (SX-EW) is now a widespread practice. Unfortu nately, the usage of permanent anodes has the disadvantages of ongoing main tenance costs to clean the anode surfaces and refurbish the wetted area, re sults in lower anode useful life, the expense of anode replacement, lower c urrent efficiency, higher power consumption as compared to electrorefining, and inferior cathode quality which becomes contaminated due to deteriorati on of the metal or metal alloy used to fabricate the insoluble anodes. Apart from improvements in productivity and cathode product quality, and lo wer labour requirements, the driving force to remedy present electrowinning performance is mainly a reduction in energy. Another associated problem ar ea is the usage of mother blanks fabricated from either aluminum, copper ti tanium, or stainless steel as employed to enable full deposit stripping. It is recognized that the construction of the different hanger bars used to s upport both permanent anodes and mother blanks presents another problem are a for study which is addressed within the paper. The writers advocate inves tigations to improve non-ferrous metal stripping practice, increase current efficiency and extend the useful life of permanent electrodes. The anticip ated improvement in full plate cathode chemical and physical quality will b enefit downstream operations such as copper wirerod production and subseque nt fine wire drawing. (C) 1998 Elsevier Science Ltd. All rights reserved.