The preg-robbing of gold and silver by clays during cyanidation under agitation and heap leaching conditions

Laboratory scale leaching tests were carried out in different experimental conditions, with monitoring of gold and silver recovery, the concentration of cyanide used in leaching, solution pH, and precious metal adsorption onto clay. Evidence for the adsorption or re-precipitation of gold from cyanide solutions onto clay minerals is conclusive and indicates that adsorption contributes to the total gold loss from conventional cyanidation. The loss is related to the type of clay, and appears to be affected by the extent of time cyanidation. It was observed that silver adsorption capacity was above 80% and that the degree of adsorption for gold oscillated between 1.68% and 7.49%, depending on the type and characteristics of the evaluated clay.