Maximise pyrite depression in copper ore flotation using high salinity water

Abstract

Numerous copper flotation plants have to use high salinity water, but high salinity water is detrimental to copper flotation by promoting copper activation on pyrite. Despite the effective depression of pyrite by the combined use of sodium metabisulfite (MBS, Na2S2O5) and Hi-Cr steel grinding media in high salinity water, many copper processing plants still desalinate saline water with a considerably high cost, which motivated this study to identify the best chemical solution to maximise the depression of pyrite in copper flotation using high salinity water. Flotation tests and pulp chemistry measurements indicated that the combination of high chromium (Hi-Cr) steel and MBS completely depressed pyrite flotation in high salinity water as achieved by Hi-Cr steel alone in fresh water, but this combination did depress chalcopyrite flotation to some extent. This is because the decomposition of MBS, induced by copper ions, formed strongly oxidising radical species which oxidised both copper-activated pyrite and chalcopyrite. To overcome the drawback of MBS, potassium peroxymonosulfate (PMS, KHSO5) was chosen to depress pyrite in high salinity water in conjunction with forged steel grinding media. This combination also completely depressed pyrite flotation but did not depress chalcopyrite flotation in high salinity water, equivalent to the results achieved by Hi-Cr steel alone in fresh water. This was attributed to the decomposition of PMS predominately induced by iron ions, forming the strongly oxidising radical species which selectively oxidised copper-activated pyrite rather than chalcopyrite.