Selective depression of calcium-bearing gangue minerals in bastnaesite flotation by a multi-group synergistic depressant: experiments and DFT calculations

The efficient flotation separation of bastnaesite from chemically similar calcium-bearing gangue minerals, such as fluorite and calcite, remains a formidable challenge. In this study, N-phosphonomethyl-N-carboxymethyl sulfamic acid (CPMS), a multi-group synergistic depressant, was designed and synthesized for selective bastnaesite flotation. Single mineral flotation tests showed that CPMS strongly depressed fluorite and calcite over pH 7–11 while maintaining bastnaesite recovery above 90%. In the artificial ternary system, a concentrate containing 23.21% Ce was obtained at pH 9.12 with a Ce recovery of 91.25%. Contact angle and zeta potential analyses revealed that CPMS preferentially altered the wettability and electrokinetic response of fluorite and calcite. XPS results supported the involvement of phosphonate and carboxylate groups in interactions with surface Ca sites, whereas the sulfonate group was inferred to contribute mainly to interfacial hydration. DFT calculations predicted much more negative adsorption energies for CPMS on fluorite and calcite than on bastnaesite. Electronic structure analysis further indicated predominantly covalent P-O-Ca interactions and mainly electrostatic C-O-Ca interactions. These results support CPMS as a selective depressant for bastnaesite systems and provide a functional-group design strategy for calcium-bearing gangue depression. Download: Download high-res image (225KB) Download: Download full-size image