Influence of cations Ca2 +, Mg2 + and Zn2 + on the flotation and surface charge of smithsonite and dolomite with sodium oleate and sodium silicate

Abstract

This study aimed to determine the conditions required for selective flotation between smithsonite and dolomite using sodium oleate and sodium silicate. Microflotation test results demonstrated recoveries of 95% and 5% for smithsonite and dolomite, respectively, from 2.5 × 10^− 5 M sodium oleate and 50 mg/L sodium silicate at pH 9.5. The smithsonite was depressed by the cations Ca^2 + and Mg^2 + and, the dolomite was depressed by Zn^2 + cations, which was probably caused by the reaction of these cations with the oleate anions in the solution, decreasing the concentration of collector available for adsorption onto the minerals. The powerful depression of smithsonite caused by Ca^2 + cations compared with that caused by Mg^2 + cations can be considered to have occurred because of the higher concentration of Ca^2 + in the solution. From the zeta potential measurements at pH 9.5, we concluded that the predominant species of oleate and of sodium silicate were adsorbed onto both minerals, and the silicate species prevented the adsorption of oleate anions onto dolomite. The decrease in the negative zeta potential of both minerals after cation conditioning can be related to the electrostatic attraction between the cations and the negative sites on their surfaces. The negative zeta potential of smithsonite increased at a concentration of 1 × 10^− 6 M Ca^2 + and Mg^2 +, whereas the potential decreases at a concentration of 1 × 10^− 3 M, which can be related to a lower concentration of oleate anions being available for adsorption.