Application of fluoride to enhance aluminum cementation of gold from acidic thiocyanate solution

The cementation of gold from acidic thiocyanate solution was studied using aluminum powder. The related parameters such as pH, thiocyanate concentration, gold concentration, temperature, stirring speed, aluminum/gold mass ratio, presence of iron (III) and gas atmosphere were systematically investigated. The results show that temperature and deoxygenation were determined to positively affect the gold recovery. Conversely, the presence of iron (III) inhibits significantly the cementation reaction. The addition of fluoride into leach solution could overcome the inhibitory effect of iron (III) and enhance the gold cementation rate. It was established that the rate of the reaction was first-order with respect to the gold concentration. The activation energy was found to be 41.9kJ/mol and the cementation process was considered to be chemically controlled without the presence of ferric ion and the addition of fluoride ion in solution. A possible cementation mechanism was proposed.