New flowsheet for processing chromite fines by column flotation and the collector adsorption mechanism

Tailings produced from Uckopru Chromite Concentrator are composed of fines mostly below 1 mm of which 52.3 wt. % is below 0.1 mm. A new flow sheet involving shaking table for processing -1+0.1 mm size fraction, and High Intensity Wet Magnetic Separator (HIWMS) and column flotation for treating -0.1 mm size fraction was put forward. According to the new flowsheet, the Uckopru Concentrator tailings assaying 13.99 wt. % Cr₂O₃ was upgraded to 47.4 percent Cr₂O₃ at a recovery of 66.4 wt. % using shaking table followed by a combination of magnetic separation and column flotation with a mixture of anionic collectors at pH 11. The success of such high pH with anionic surfactants is indeed intriguing. Electrokinetic methods were used to elucidate the mechanism of collector adsorption and correlate the findings with the optimum flotation conditions. Multivalent constituent ions such as Cr³⁺, Al³⁺, Fe²⁺ and Mg²⁺ were found to adsorb on chromite surface and shift the iep of chromite in the direction of oxide form of the mineral. The anionic collectors also imparted a negative charge to chromite in the entire pH region. The positive sites on the chromite surface, onto which anionic collectors adsorb, are generated through the formation of significant amounts of hydroxy complexes of magnesium ion at pH 11. Complementary infrared data reveals the absence of a shift in the spectra indicating the possibility of physical adsorption in the system.