Flotation Investigations on Ni-Cu Sulphide Ores With Pyrrhotite, Talc and Pre-Oxidation Issues

Abstract

Canadian Ni-Cu sulphide ores vary in complexities from location to location posing serious processing issues. This thesis represents an experimental investigation of the fundamental characteristics and flotation of two Ni-Cu sulphide samples, namely, an oxidized ore blend and a fresh ore blend. Bench-scale flotation tests were conducted to better understand the effects of complexity associated with gangue mineralogy involving talc, chlorite and pyrrhotite (Po) in the behaviour of low-grade blends assaying 0.4-0.5% Ni & 0.5-0.7% Cu. Po content at 5.8-7.5% was much higher than the pentlandite (Pn) and chalcopyrite (Cp) combined. The reagents included a collector (PIBX) and depressants (CMC, DETA, SMBS, YTD & FTD). The colour of the oxidized ore blend was yellowish brown due to the formation of iron oxide species compared to the dark greyish colour of the fresh ore blend. The ionic conductivities of the oxidized ore blend slurry were much higher than those with the fresh-ore blend, which were, in turn, higher than the case with the tap water used. The pH value of the oxidized ore blend slurry was lower than the fresh-ore blend case due to acid-producing reactions, requiring about 2.2 more lime in batch tests. As part of characterization, extraction tests were conducted using toluene and EDTA/DETA to quantify elemental sulphur and metal ions suspected of causing inadvertent activation of Po. Through flotation investigations, CMC, YTD & FTD for depression of talc/chlorite and DETA & SMBS for Po depression were demonstrated to be effective when used in selected combinations. Flotation selectivity was assessed using plots of concentrate grade/recovery and relative recoveries of Po vs Pn and Cp. The relation between extracted sulphur and the mineralogical composition of the concentrates investigated using multivariable regression indicated strong correlations for collectorless flotation of the oxidized ore blend, indicating elemental sulphur is associated primarily with Pn and secondarily with Cp. Flotation kinetics involving the reagent systems and particle size effects were analyzed using the first-order models. Overall, the most effective reagent formulation for Po depression was SMBS/DETA combination, but YTD was also highly effective. Particle size distribution was found to be a significant factor, with finer particle sizes resulting in increased recovery of Pn and Cp but decreased recovery of Po.