Utilization of sodium carbonate to eliminate the adverse effect of Ca2+ on smithsonite sulphidisation flotation

Sulphidisation xanthate flotation is a common process in dealing with zinc oxide minerals and sulphidisation is the key procedure in the zinc mineral recovery. In this study, the effect of Ca2+ on the sulphidisation flotation of smithsonite was investigated by flotation tests. The results show that the presence of Ca2+ impairs the sulphidisation flotation of smithsonite. Adsorption studies and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) analysis illustrate that at pH 9.5, where the sulphidisation process is routinely performed, the positively charged Ca(OH)(2(s)), Ca(OH)(2(s)), and CaOH+ produced due to hydrolysis and precipitation of Ca2+ will preferentially adsorb onto smithsonite surface, preventing the adsorption of sulfur ions. Thus, the insufficient sulphidisation on smithsonite surface cannot promote the mineral flotation performance. Interestingly, sodium carbonate can eliminate adverse effect of Ca2+ by charge reversal. For its reactivity with Ca2+ the formation of negatively charged calcium carbonate ceases the adsorption of calcium onto smithsonite surface as a consequence of electrostatic repulsion. As thus, the sulphidisation flotation of smithsonite is regained.