Eliminating the co-depression effect of Ca2+ ions and sodium silicate on bastnaesite flotation by using EDTA

Bastnaesite is an important strategic resource. Since the calcium-bearing gangue minerals in the pulp can dissolve and release Ca 2+ ions, Ca 2+ ions and sodium silicate have a co-depression effect on bastnaesite flotation, which will affect the separation and purification of bastnaesite. In this study, the mechanism of eliminating the co-depression effect using ethylene diamine tetraacetic acid (EDTA) was studied by micro-flotation, bench-scale flotation, zeta potential, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM)–energy spectrometry (EDS), contact angle and DFT calculations measurements. Micro-flotation results show that the addition of EDTA can effectively eliminated the co-depresses effect of Ca 2+ ions and sodium silicate. Bench-scale flotation tests showed that a high-quality rare earth (REE) ore concentrate with higher grade and recovery (62.35 % and 62.08 %, respectively) could be enriched by adding EDTA. Zeta potential results show that the combination of Ca 2+ ions and EDTA than with Ca 2+ ions alone, the surface potential of bastnaesite was significantly negative. XPS shows that EDTA prevented Ca-SiO 3 precipitation between Ca 2+ ions and sodium silicate by complexing Ca 2+ ions, which hindered the adsorption of sodium silicate to bastnaesite. SEM-EDS show that the addition of EDTA between Ca 2+ ions and sodium silicate, Ca 2+ ions had desorbed from the bastnaesite surface. Density functional theory (DFT) calculation showed that the adsorption energy of EDTA and Ca 2+ ions was much smaller than that of sodium silicate and Ca 2+ ions and Ca 2+ ions and mineral surface.