A kinetic and thermodynamic study of the removal of calcium and magnesium from aqueous solutions similar to those of complex sulphide flotation by the addition of sodium carbonate

Abstract

ABSTRACT The use of recycled water in flotation has a negative impact on flotation of sulphide mineral species because these waters contain chemical species that affect the recovery and selectivity of the process. This study aims to study the reaction mechanism between aqueous calcium and magnesium sulphate contained in the water released by complex sulphide flotation process, and the carbonate ions added to the water as sodium carbonate (Na2CO3). The addition of Na2CO3 has been shown to have a positive effect on the recovery and grade of the final Pb-Cu concentrate obtained, but the reasons of this are not yet fully understood. The present study was conducted by adding Na2CO3 to a saturated gypsum solution containing Mg(II). Analytical techniques such as XRD, TGA and zeta potential measurements were used to characterise the obtained solids. It was observed that the addition of Na2CO3 favoured the precipitation of the Ca(II) as calcite and vaterite. The reaction kinetics was found to be of second-order. In the case of magnesium alone, the precipitates are amorphous. This study provides new information on the reaction mechanism between metal ions and carbonates. The information collected can help design processes for the removal of ions from flotation water.