Recovery of Cyanide from Pregnant Pulps

Cyprus Gold NZ Ltd will be recovering residual cyanide from their CIT, operation in New Zealand. The process will use air to strip the cyanide from the acidified barren pulp. DSffi. Industrial Development, who were involved in the bench and pilot studies for Cyprus, have extended the concept to pregnant pulp. The stripping of pregnant pulp eliminates the substantial loss of cyanide through carbon catalysed oxidation during the adsorption stage. A 50% increase in cyanide recovery was obtained from an extensive laboratory investigation. The presence of a cyanide recovery circuit enables leaching to be conducted, without detriment, at pHs at least as low as 9, with consequential 50% reductions in the consumption of lime and sulphuric acid. There should be a small reduction in carbon consumption, and a significant improvement in the quality of the final effiuent, at least in terms of cyanide, cyanates, copper, zinc and sulphur. A small but significant increase in gold recovery can be expected too. There is a net economic advantage of NZ$1.20/tonne of ore by stripping pregnant rather than barren pulp.