Pulp chemistry in calcite flotation. Modelling of oleate adsorption using theoretical equilibrium calculations

Abstract

The usual method of obtaining calcite concentrates is reverse flotation, i.e. removal of impurities by flotation. This paper considers the conditions required for direct flotation of calcite. The reason is that calcite often occurs as an impurity in apatite and scheelite flotation, where it floats together with the principal mineral. In this context it is relevant to understand the mechanisms that control the flotation of calcite. Flotation experiments have been performed with oleate as the collector reagent and water glass as the dispersant and modifier. To be able to explain what happens in the flotation, solubility and adsorption experiments have been conducted parallel to, and under the same conditions as, the flotation experiments. Theoretical equilibrium calculations have been made with the help of data from the practical experiments for the purpose of modelling the adsorption experiments. The calculations point to the existence of a surface complex, CaOHO1, which is important at pH>10 and low oleate concentrations. Ca(O1) 2 is formed at lower pH. Water glass has a negative effect on oleate adsorption and if the water glass concentration is high enough, >200 g/t, calcite is totally depressed. With theoretical equilibrium calculations it is possible to predict that silicate ions will form complexes with calcium ions at the mineral surface.