The flotation behaviour of chromite with respect to the beneficiation of UG2 ore

The UG2 reef of the Bushveld Igneous Complex in South Africa is a valuable source of platinum group metals (PGMs) that is beneficiated by flotation. C hromite is one of the main gangue constituents of UG2 ore and it is essenti al that the amount of chromite reporting to the concentrate during flotatio n be minimised since it is detrimental to the subsequent smelting operation s. It is generally considered that chromite is naturally hydrophilic and on ly reports to the concentrate by entrainment. However, it is possible that, under certain conditions, the chromite can be activated by the typical rea gent suite used in the flotation of UG2 ore, rendering it hydrophobic and a menable to true flotation. The aim of this work was to investigate the effe ct of copper sulphate and the collectors, sodium isobutyl xanthate and dith iophosphate on the flotability of chromite in a microflotation cell. The ef fect of copper sulphate on the zeta potential of chromite was also determin ed. It was found that collectors alone have an insignificant effect on the flotation of chromite whereas, in the presence of copper sulphate recoverie s of above 60% were observed in mildly acid to mildly alkaline solutions de creasing to 20% at a pH value of 10. The extent of activation depended on t he copper sulphate dosage. Zeta potential measurements showed that, above p H 4 copper species were adsorbed on the chromite and between pH 5 and 9 the adsorption bead to charge reversal of the chromite particles to positive v alues. The speciation programme, MINTEQA2, was used to predict the copper s pecies present over the pH range used. It was postulated that the activatio n is due to the adsorption of copper hydroxide species at the chromite surf ace, which then act as sites for collector adsorption. (C) 1999 Published b y Elsevier Science Ltd. All rights reserved.