Optimisation of the selective flotation of galena and sphalerite at Rosh Pinah Mine

Abstract

A study was carried out to improve the flotation selectivity between galena and sphalerite during the flotation of a Cu-Pb-Zn sulphide composite ore from the Rosh Pinah Mine (Namibia). Xanthate collectors were found to be unselective for the flotation of the Rosh Pinah composite sample. It was observed that the recovery of sphalerite increased with both the recovery of galena and the concentrate mass pull. In addition, the recovery of sphalerite increased after activation with Cu(II) ions while that of galena decreased when the composite was dry ground in a mild steel mill with mild steel grinding media. However, the recovery of galena was not affected after wet milling in a stainless steel mill. The recovery of Cu(II)-activated sphalerite was independent of the milling environment (wet or dry) and grinding media. The activation of sphalerite by cuprous cyanide complexes, which are present in the recycled water, was clearly shown in this study. Both batch flotation tests and XPS analysis have confirmed that sphalerite was activated by copper(I) from the cuprous cyanide complexes. The recovery of copper(I)-activated sphalerite increased further when the composite was dry milled as compared to wet milling. Batch flotation tests have shown that the use of cyanide alone is not efficient for the depression of sphalerite due to the mineralogical texture of the Rosh Pinah ore. A large quantity of galena locked and/or attached to sphalerite was observed in the lead concentrate. Their prevalence increased with increasing particle size. The use of both cyanide and zinc sulphate improved the depression of sphalerite much better than cyanide alone. A flowsheet has been proposed to improve selectivity between galena and sphalerite in the lead flotation circuit. It includes the regrinding of the lead rougher concentrate prior to the cleaning stage due to poor liberation between galena and sphalerite.