An introductory electrochemical approach to studying hydrometallurgical reactions
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I. INTRODUCTION
THAT many hydrometallurgical processes are electrochemical in nature is well established. Examples include the self-evident processes such as electrowinning/refining and electroplating, to the less obvious such as flotation, hydrogen reduction of metals, bacterial leaching of sulfide minerals, cementation, and leaching of ores.[1] Examination of the literature shows a broad range of electrochemical techniques employed by researchers to study hydrometallurgical processes. Polarization plots, chronopotentiometry, chronoamperometry, frequency response analysis, capacitance measurements, and cyclic voltammetry are to name a few. Further information on these electrochemical methods can be found in texts such as those by Sawyer et al.[2] and Bard and Faulkner.[3] The usefulness of these techniques is undisputable, but for the uninitiated, the choice can be daunting. To further the confusion, some techniques are more appropriate than others for an individual system. Where does the researcher wishing to venture into using electrochemical methods begin? It has been the authors’ experience that electrochemistry is frequently under-utilized in hydrometallurgical research. In a few extreme instances, the authors have encountered active avoidance of electrochemistry because of these issues. The aim of the current article is therefore to present a simple electrochemical method that can be applied to a range of hydrometallurgical problems. It is hoped that researchers adopting this approach will further their investigations employing whatever specialized electrochemical techniques their research dictates. A. A Brief History of Electrochemistry in Hydrometallurgy One of the earliest examples of studies employing electrochemistry to investigate a hydrometallurgical process is
SHERRYL ROBERTSON, Senior Technical Officer, is with the Chemistry Department, James Cook University, Townsville, Qld 4811, Australia. MATTHEW JEFFREY, Senior Lecturer, is with the Chemical Engineering Department, Monash University, Vic, 3800, Australia. HONGGUANG ZHANG, Research Fellow, is with the A.J. Parker CRC for Hydrometallurgy, Murdoch University, WA, 6150, Australia. ELIZABETH HO, Research Scientist, is with the Minerals Division, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 Australia. Manuscript submitted January 19, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
the pioneering work of Kudryk and Kellogg who, in 1954, studied the mechanism of gold leaching in cyanide solutions.[4] They showed that the leaching reaction can be represented by two half reactions: the oxidation of gold to form the gold cyanide complex; and the reduction of oxygen to form hydroxide ions. Using plots of current vs potential, they showed that under typical cyanidation conditions, the leaching reaction is limited by the diffusion of oxygen to the gold surface. Around the same time, the electrochemical study of cementation reactions had commenced. In 1956, Sedzimir showed that the mechanism of the lead-zinc cementation reaction
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