Exploring Dextrin as an Eco-Friendly Depressant for Selective Flotation Separation of Scheelite and Calcite Minerals

Depressants are essential additives in the flotation separation of scheelite-calcite minerals. However, traditional inorganic depressants such as sodium silicate have the disadvantages of high dosage, environmental pollution, and being non-efficient, which leads to a growing interest in eco-friendly and effective organic alternatives. In this study, a polysaccharide, dextrin, was used as a green depressant for the flotation separation of scheelite from calcite. Micro-flotation experiments indicated that dextrin selectively depressed calcite at natural pH yet scheelite remained floatable using sodium oleate (NaOL) as a collector. Adsorption density and zeta potential results indicated that dextrin was preferentially adsorbed on the calcite surface and prevented the subsequent NaOL from adsorption. By contrast, dextrin had a weak interaction with scheelite, allowing NaOL to be adsorbed on the scheelite surface. Fourier transform infrared spectroscopy (FTIR) analysis and density functional theory (DFT) calculations suggested that the Ca2+ active sites on the calcite surface interacted with -OH groups on the carbon ring of dextrin. X-ray photoelectron spectroscopy (XPS) tests confirmed the chemical interaction between -OH groups in dextrin and Ca2+ active sites on the mineral surfaces, and importantly, the interaction was much stronger for calcite than for scheelite.