A study of the gold colloid dissolution kinetics in oxygenated ammoniacal thiosulfate solutions
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Colloidal gold has a characteristic absorption peak at 530 nm that can be used to monitor the extent of gold dissolution in different lixiviant systems using an ultraviolet-visible spectrophotometer. This paper reports the kinetics of the dissolution of gold colloid in ammoniacal thiosulfate solutions using oxygen as a oxidant at pH 9.3-9.5 and temperature 25-48 °C. The relative rates of gold dissolution in different lixiviant systems are in descending order: oxygen-cyanide > copper(II)-ammonia-thiosulfate > oxygen-ammonia-thiosulfate > oxygen-ammonia > copper(II)-ammonia. The predominant gold(I) species in oxygenated thiosulfate solution based on the measured potentials on gold electrode is gold-thiosulfate complex (Au(S 2O3)23-). However, the measured potentials in the absence of thiosulfate are close to the reported values for the Au(NH3)43+/Au(NH3) 2+ couple, which indicates that disproportionation or oxidation of Au(NH3)2+ occurs. The initial rates of gold dissolution show reaction orders of ≈ 0.3 with respect to oxygen and ammonia, and are independent of the concentration of thiosulfate and chloride. The dissolution kinetics follow a shrinking core model with an activation energy of 25-37 kJ mol-1, indicating a mixed chemical-diffusion-controlled reaction.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions|
|Copyright:||© 2004 Elsevier B.V|
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