Methodology to Control and Prevent AG Precipitation in Cyanidation Circuit Using UV Spectrophotometry

"Silver and gold leaching by cyanidation is a well-known process used around the world. This reaction is often accompanied by the leaching of other species throughtout the cyanidation circuit that causes the diversion of cyanide towards non valuable by-products (SCN-, Cu(CN)x, Fe(CN)x, etc.). One of the detrimental impacts of the formation of these by-products is the precipitation of silver-cyanide complexes that occurs when cyanide concentration is too low. Without any extra-addition of free cyanide, the precipitated silver is lost and cannot be recovered causing an important economic loss. To overcome silver precipitation, cyanidation circuits are often operated at higher cyanide concentrations. Recently, COREM’s research team has been working on a technology to measure and control silver precipitation during the cyanidation process. Moreover, a methodology has been elaborated in order to evaluate threshold cyanide level which corresponds to the cyanide concentration at which silver starts to precipitate. This technology has been tested on site on a real cyanidation circuit at Agnico Eagle’s LaRonde mine."