Recovery of chromite fines from wastewater streams by column flotation

In the Western Chrome Mine in South Africa, the process water stream contains approximately 3% chromite fines (<100 μm), which report to the tailings dam. This results in resource loss and water contamination. Consequently, in this paper, the effects of pH, as well as the influence of anionic and cationic collectors on the floatability of chromite fines in columns, were investigated. Electrokinetic studies were used to elucidate the mechanism of collector adsorption and the findings were correlated with the optimal flotation conditions. The presence of the aqueous metal species Al3+, Cr3+, Fe2+ and Mg2+ resulting from the dissolution of chromite appeared to have a significant influence on the flotation of chromite fines. These species were found to adsorb on chromite surfaces and shift the point of zero charge (PZC) of the chromite. The optimal recovery of chromite fines was observed at a pH of approximately 4 for anionic flotation and 11 for cationic flotation. In column flotation tests for the fresh wastewater stream containing 3% chromite fines, a recovery and grade of approximately 40% and 43.5%, respectively were obtained with sodium dodecyl sulphate (SDS) flotation. A recovery and grade of approximately 32% and 45%, respectively were obtained with cetyl trimethyl ammonium bromide (CTMAB) flotation. Both cationic and anionic flotation deteriorated with an increase in aging of the chromite.