Feasibility of bench-scale selective bioflotation of copper oxide minerals using Rhodococcus opacus

Abstract

Bench-scale selective bioflotation tests were carried out in a 1 L Denver cell using Rhodococcus opacus (R. opacus) cells as a collector in malachite-silica binary mixture and copper (Cu) oxide ore systems. Through the first set of tests carried out on the binary mixture, cell concentration and malachite fraction in the feed were optimized, and further the role of shear force by varying impeller speed (800,1000, and 1200 rpm) and adhesive force by varying pH (7 and 11) and ionic strength (1, 100, and 300 mM) were examined. Overall, high malachite selectivity was observed under optimized conditions (both recovery and grade > 90%). In addition, the recovery and grade of malachite were very sensitive to pH changes, with greater values being obtained at pH 7, whereas the impeller speed and the ionic strength did not seem to play a big role over the range tested. The trend was in qualitative agreement with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profiles, which show the relative magnitudes of the adhesive forces between the mineral and the attached cell under equal hydrodynamic conditions. The second set of tests was conducted using Cu oxide ores with two different particle sizes (74-150 pm and - 74 mu m) under the optimized conditions determined from the first set of tests. The recovery and grade of malachite were found to be much greater for finer ores (recovery = 29.15% and grade = 5.17%) than those for coarser ones (recovery = 1.34% and grade = 3.06%), which is likely due to differences in malachite liberation. Further comparison of the finer ore result with that obtained from the conventional process (i.e., sulfidization followed by xanthate adsorption) indicated that the malachite selectivity of bioflotation is much higher than that of the conventional process (grade = 1.43%).