Flotation separation of homogenized fluorite and calcite using sodium silicate and AlCl3 as a combined depressant

Abstract

Effective flotation separation of fluorite and calcite is a critical challenge due to their comparable physicochemical characteristics and surface iso-transformation. The effects of sodium silicate (SS) and Al³⁺ on the flotation separation of homogenized fluorite and calcite were investigated based on flotation experiments and various measurements such as Zeta potential, scanning electron microscopy (SEM), solution chemistry, X-ray photoelectron spectroscopy (XPS), microcalorimetry. The results showed that the combination of SS and Al³⁺ significantly depressed calcite flotation, but only slightly affecting fluorite flotation. The surface potential of calcite was found to be increased in the presence of Al³⁺, enhancing the adsorption of SS. A higher affinity for the formation and adsorption of aluminum oxide on the surface of calcite compared to fluorite was indicated by SEM results, increasing the selective depression of SS on calcite. The DFT findings verified the formation of Al − O bonds upon the interaction between Al³⁺ and calcite. However, no Al − O bonds occurred on fluorite surface. The distinct adsorption energies were attributed to variations in the surface bonding characteristics of Al³⁺ with O on the calcite and F⁻ on the fluorite. The microcalorimetry analyses revealed that the adsorption of Al³⁺ on calcite surface exhibited more negative adsorption enthalpy and faster adsorption kinetics, improving the adsorption of SS species on calcite surface, ultimately reducing the floatability of calcite.