The Influence of Grinding Media on the Pulp Chemical Conditions and Flotation Performance of Nchanga Underground Copper Ore

Nchanga copper ore is a complex mixture of sulphide and oxide minerals and processing consists of sulphide flotation followed by sulphidisation and an oxide flotation step. The copper oxides have proved difficult to recover. The reason for poor recovery has been attributed to complex mineralogical characteristics of the ore. Previous laboratory test work carried out on the ore showed an improvement in the flotation recovery of oxide minerals after regrinding the sulphide rougher tails with mild steel media. However, further investigation showed that the increase in recovery was not due to increased liberation. This indicated that the increase was due to some other factors resulting from the regrind, such as change in the chemical environment. The influence of grinding media on the pulp chemical conditions and the resulting flotation performance of Nchanga underground copper ore has been studied to understand how grinding media affect the chemical conditions of the pulp. The media employed were stainless steel and mild steel, which created different chemical conditions in the pulp as measured by dissolved oxygen (DO), oxidation-reduction potential (ORP) and pH. Better overall flotation performance was obtained in pulp ground by stainless steel media than by mild steel media. There was an improvement in the recovery of both sulphide and oxide minerals in the oxide flotation stage after regrinding by mild steel media. Stainless steel regrind did not increase the recovery but improved the grade of the oxide minerals in the oxide flotation stage. However, the flotation recovery of copper obtained after regrind by mild steel media was almost the same as that obtained without regrind by stainless steel media again indicating that the increased recovery obtained was not due to increased liberation. Several interesting observations concerning pulp chemistry measurements are discussed. Keywords: Pulp chemistry; grinding media; dissolved oxygen; pulp potential; copper flotation (Af. J. of Science and Technology: 2002 3(2): 1-8