Abstract
Valuable minerals can be extracted from different sources, such as the run-of-mine and tailings. It has been observed that due to the ineffectiveness of several metallurgical processes, the generated tailings carry significant values. The beneficiation of valuable minerals using the current optimized process plant could not be efficient. This situation forces several companies to dispose of their tailing in well-secured dams to develop suitable techniques after a deep understanding of the mineralogy of the disposed material for further processing. Most South African companies operating in the Bushveld Igneous Complex (BIC) face such challenges. Due to the volume of tailing generated yearly (1 095 000 metric Tons) and the overall grade of Cu (0.071%) and Ni (0.228%) on one side and the other, the environmental risk which can be due to the presence of the dams, the current research project was initiated to propose an efficient and cost-effective process route for their beneficiation. This study investigated the impact of pulp chemistry during flotation on the generated PGMs tailings from the BIC to recover Cu and Ni. The effects of critical variables such as pulp density, pH, and reagent dosages (collectors, activators, and depressants) were investigated on Cu and Ni recoveries using Response Surface Methodology (RSM) to determine the correlation between dependent and independent variables. Further investigations were performed to examine the flotation kinetics and understand the behavior of different compounds in the sample during the flotation process. The classical first-order and modified Kelsall models were applied to account for the entrainment effect of non-valuable and fast and slow-floating minerals, respectively. Before experimentation, an extensive characterization of the tested tailings material was performed using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and Fire assay to analyze the chemical and mineralogical composition of mining tailings. After characterization, it was noticed that 80% passed 150 μm. At the same time, the sample contained base metals in the form of chalcopyrite and pentlandite, occurring together with pyrrhotite in a gangue material dominated by enstatite, anorthite, and chromites.
The optimization through the RSM-CCD revealed that optimal floating conditions of pH 9 with 124.2, 100.6, 75.7, and 54.1 g/ ton of Sodium isobutyl xanthate (SIBX), Copper sulfate (CuSO4), Starch, and SenDep, and results reveal that 74% and 27.5% of Cu and Ni are recovered, respectively. The grades of Cu and Ni improved to 2.75%
and 0.51%, respectively. Flotation kinetics analysis confirmed that the modified Kelsall model fits the flotation process under optimized conditions.