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

•Ca2+ ions and sodium silicate have co-depression effect on bastnaesite flotation.•EDTA can be used to eliminate the co-depression effect on bastnaesite flotation.•Ca2+ ions adsorbed on bastnaesite could be dissolved and removed by EDTA.•The rare earth flotation can be improved by combination of EDTA and sodium silicate. Bastnaesite is an important strategic resource. Since the calcium-bearing gangue minerals in the pulp can dissolve and release Ca2+ ions, Ca2+ 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 Ca2+ 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 Ca2+ ions and EDTA than with Ca2+ ions alone, the surface potential of bastnaesite was significantly negative. XPS shows that EDTA prevented Ca-SiO3 precipitation between Ca2+ ions and sodium silicate by complexing Ca2+ ions, which hindered the adsorption of sodium silicate to bastnaesite. SEM-EDS show that the addition of EDTA between Ca2+ ions and sodium silicate, Ca2+ ions had desorbed from the bastnaesite surface. Density functional theory (DFT) calculation showed that the adsorption energy of EDTA and Ca2+ ions was much smaller than that of sodium silicate and Ca2+ ions and Ca2+ ions and mineral surface.