The cation effect on adsorption of surfactant in the froth flotation of low-grade diasporic bauxite

Froth flotation has been proved to be the economic way to upgrade the low-grade diasporic bauxites by desilication of kaolinite. However, the recovery rate of diaspore varied significantly in industry due to water quality (cations) and the mechanism remains unknown. This report investigates the effect of common water hardness cations (Ca2+ and Mg2+ ) on the recovery of diaspore and kaolinite using micro-flotation at various pH values. The results show that adding Ca2+ significantly enhanced the diaspore recovery rate even under acidic conditions (pH = 4-7). In contrast, adding Mg2+ reduced the diaspore recovery rate to below 50% when the pH value was between 8 and 9 while adding Ca2+ increase the recovery rate to above 95%. In addition, adding either cation shows minimal change to the recovery of kaolinite. The mechanism has been revealed by thermodynamics speciation, zeta potential and synchrotron-based near edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The change of both dipole-dipole interaction and hydrogen bonding plays a vital role on this cation effect.