Assessment of water quality effects on flotation of copper–cobalt oxide ore

•The variation in flotation process water quality reflects on metallurgical results.•Recycling process water induces negative impact on flotation of Cu–Co oxide ore.•The chemical species in recycled water interfere with reagents efficiency.•Excess thiosulphate ions presence alters mineral surfaces and creates reducing conditions in the pulp.•Thiosulphate presence depending on concentration promotes or hinders cobalt and copper flotation.

Results from lab scale flotation show that when process water was re-used copper and cobalt recovery from an oxidized ore decreased respectively with 25% and 30% at the rougher stage bringing lower grade concentrate as well. The presence of thiosulphate ions contributed to slow down of NaHS consumption during sulphidisation of pure malachite and hindered collector adsorption. Elevated concentration of thiosulphate ions affected malachite surface properties and induced dissolution effects. DRIFT spectroscopy on activated malachite enabled to reveal the effects of thiosulphate ions presence with hydrophilic species being identified.