Reagent trends in the gold extraction industry

Abstract

In this paper modern collectors for gold flotation and alternative lixiviants to cyanide are discussed. In flotation the trend is for a combination of canthates and of xanthate and dithiophosphate to be used with additions of varying amounts of copper sulphate when the ores are highly sulphidic. Despite the very impressive safety record of cyanide to date it is conceivable that environmental concerns could fuel trends to alternative lixiviants such as halogen based systems, nitric acid systems or thiourea for leaching. A detailed account of recent adsorption and desorption studies using thiourea and activated carbon carried out at the Precious Metals Research Centre is presented. In this it is established that adsorption of the gold thiourea complex is favoured at pH values below 3 and that this phenomenon can be used to strip gold from loaded carbon under highly alkaline conditions at considerably faster rates than from cyanide based elution systems. It is shown that minor additions of sodium cyanide suppress precipitation reactions from the pregnant thiourea solutions without greatly affecting the kinetics of elution. © 1992.