Effect of sulfuric acid pretreatment on flotation performance of calcite and fluorite

Abstract

Difficulty in separating calcite and fluorite owing to their similar surface properties is the focus of research in the field of mineral processing. To increase the selectivity difference between these two minerals, sulfuric acid was introduced as a surface pretreatmentand, and aluminium sulfate was used as the flotation depressant. The effects of H2SO4 pretreatment on calcite and fluorite flotation performance and the mechanisms thereof were studied by combining microflotation experiments, solution chemical calculations, scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FT-IR) spectroscopy, and density functional theory (DFT). Microflotation experiments showed that sulfuric acid pretreatment significantly reduced the flotation recovery of calcite to less than 10%, while it had little effect on fluorite, where the recovery reached greater than 80%. SEM-EDS and FT-IR analyses showed that, after sulfuric acid treatment, the surface composition of calcite was converted from CaCO3 to CaSO4, while the fluorite surface remained almost unchanged. DFT calculations showed that CaSO4 was more hydrophilic than CaCO3; therefore, it was more likely to interact with water molecules. The presence of water molecules affected the adsorption of the sodium oleate (NaOL) collector on the mineral surface. Therefore, the calcite surface adsorption ability of NaOL after sulfuric acid pretreatment was weakened, resulting in a significant decrease in flotation recovery.