Electrowinning of gold from cyanide leach liquor

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Date
2019-05
Authors
Kavipriya Arumugam
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The electrowinning of gold from cyanide leach liquor was investigated at various experimental conditions. The experimental study consisted of designing an electrowinning cell and selectivity of different types of electrode material for the electrowinning of gold. The electrowinning cell was used to investigate the effect of pH, temperature and the morphology of gold deposited on two different types of electrode which are stainless steel plate and steel wool. The recovery of gold from the electrowinning of cyanide leach liquor increased from 36.3% at 25 °C to 41.3% at 40 °C. The increase in temperature, increases the diffusion coefficient of AuCN thus increasing the deposition rate. However, the recovery decreased to 11.85% at 60 °C because cyanide destruction occurs at an elevated temperature. The effect of pH on the recovery of gold depends on the composition of the electrolyte. For aurochloride the recovery is high at pH 2 as shown in Au-Cl pourbaix diagram where the [AuCl4]¯ is stable at the pH range of 0-8. Whereas, for aurocyanide the recovery is high at pH 11 because CN¯ predominates at pH >9 and prevents the evolution of HCN gas. There is a slight increase in the pH of the electrolyte solution at the end of each electrowinning experiment. This increase in pH in the electrolyte solution was due to the side reactions such as cyanide oxidation and water reduction. The deposition of gold on steel wool electrode has a higher weight percent at 43.48% compared to weight percent deposition on stainless steel plate, which is at 14.26%. Steel wool electrode has its inherent properties; its high surface area to volume ratio and porosity allow the metal ions to be distributed throughout the electrode during electrowinning process.
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