The development of a caustic pre-leaching step for the recovery of Au from a refractory ore tailings heap

Abstract

The re-treatment of gold tailing heaps is a potentially significant revenue stream for both larger and smaller scale gold companies. Limited access to capital and lack of skilled labour remain restrictive especially when dealing with a refractory ore and/or where limited amount of material are available. Alternative techniques such as low temperature pre-leaching options to unlock value are therefore in demand.Several low temperature pre-leaching experiments in acidic and alkaline solutions, followed by cyanidation were performed which ultimately led to the further investigation of a caustic pre-leaching step. The Au recovery were found to be a balance between the Au being released for cyanidation through gangue mineral dissolution and the Au being leached/lost in the pre-leaching step. Depending on the NaOH concentration, the major elements (excluding Na) in the pre-leach solution were found to be Si (500–8500 mg/L), S (2400–1800 mg/L), Al (350–50 mg/L), Zn (10–100 mg/L), Fe (60–75 mg/L) and As (20–55 mg/L). Au recovery in the subsequent cyanide and elution step increased with pre-treatment temperature and NaOH concentration, reaching a peak before either stabilising or decreasing. Longer pre-leaching residence time and a lower solids percentage resulted in less Au being recovered.