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Study of the electrochemistry of gold telluride in acid and alkaline solutions

Jayasekera, Sunil (1989) Study of the electrochemistry of gold telluride in acid and alkaline solutions. PhD thesis, Murdoch University.

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Abstract

The work described in this thesis was undertaken to obtain a better understanding of the dissolution behaviour of gold tellurides which comprise a significant proportion of the gold found at Kalgoorlie, Western Australia and at other localities such as Fiji and Colorado. It deals mainly with a fundamental electrochemical study of synthetic calaverite (AuTe2). The electrochemical techniques of linear potential sweep voltammetry, cyclic voltammetry, controlled potential coulometry, controlled potential electrolysis and potentiometry were employed. To support and confirm the electrochemical results. the surface products formed during the reaction of AuTe2 were examined and identified using optical and scanning electron microscopy. In order to identify the features observed on the AuTe2 voltammograms resulting from electrochemically active tellurium species, the electrochemical behaviour of elemental tellurium was also investigated under similar experimental conditions as an integral part of this study.

The anodic decomposition potentials of AuTe2 were determined as a function of pH and the results compared with potential-pH diagrams constructed using thermodynamic data. The initial oxidation products of AuTe2 in relatively strong acid perchlorate solutions have been shown to be metallic gold and soluble HTeO2+. This is in accord with the thermodynamic predictions, but the situation is complicated at higher anodic potentials due to the accumulation of sparingly soluble tellurous acid (H2TeO3). This species is also responsible for the passivation of the reacting surface at pH values above 2. The rate of dissolution of AuTe2 in chloride media is enhanced at higher chloride concentrations and lower pH. At low acid concentrations, the surface is passivated by the formation of a film of H2TeO3.

The initial oxidation of AuTe2 in alkaline perchlorate solutions proceeds via formation of metallic gold and H2TeO3. Since H2TeO3 is readily dissolved in alkaline solutions the reacting surface remains active. The rate of dissolution increases with increasing pH.

The rate of dissolution of AuTe2 in alkaline cyanide media increases with both cyanide concentration and pH. Using the appropriate Evans' diagrams, it was shown that under conventional cyanidation conditions the rate of dissolution is extremely slow. Ways of improving the dissolution rate are suggested. Alternatively, the feasibility of leaching AuTe2 in acid chloride media using oxidants such as Fe3+ was also demonstrated. The implications of the results obtained on likely hydroraetallurgical routes for the direct leaching of AuTe2 are discussed.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Mathematical and Physical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Ritchie, Ian and Avraamides, James
URI: http://researchrepository.murdoch.edu.au/id/eprint/51563
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