PROCEDE DE LIXIVIATION DE L'OR

Leaching of gold-bearing solids, such as crushed lean ores or material recovered from very old waste tips can be carried out with a dilute aqueous alkali cyanide solution, but the extent and/or rate of recovery of gold is impaired by the anaerobic or reducing conditions that can exist in such heaps, and especially towards their base and or by poor supply of oxygen in agitation leaching. The rate and/or extent of gold recovery in heap leaching can be increased and the supply of oxygen simply controlled by slow release in agitation leaching, using otherwise identical conditions by employing an effective amount of a slow dissolving poorly soluble solid metal peroxide, either by incorporating it within the heap or in the mixture of gold-bearing solids and lixiviant. The peroxide is advantageously calcium peroxide because it is not only very effective but also is environmentally suitable. The amount employed is preferably from 1 to 10 parts w/w per 1000 parts of gold-bearing solids for the low grade material, usually containing from 1 to 10 g gold per tonne solids.