Novel dual-functional depressant for the selective depression behavior and mechanism of fluorite and calcite in bastnaesite flotation

Abstract

The efficient separation of bastnaesite from calcium-bearing gangue minerals remains a formidable challenge in the rare earth industry due to their similar active sites. In this work, dimethylphosphinic acid aminoethyl sulfonate (NCCS) was rationally designed and synthesized as a novel dual-functional depressant to achieve this selective separation. Micro-flotation results demonstrated that at a dosage of 20 mg/L, NCCS exhibited superior selective depression toward fluorite and calcite across a wide pH range, while maintaining bastnaesite recovery above 80%. In ternary mixed mineral systems, NCCS enabled the production of a high-quality concentrate with a Ce grade of approximately 18% and a recovery exceeding 80%, highlighting its industrial potential. Bubble particle wrap angle, FTIR, zeta potential, and XPS analyses revealed that NCCS chemisorbed on fluorite and calcite via stable trinuclear and dinuclear chelation, respectively, which enhanced surface hydrophilicity and blocked collector (H205) adsorption. Conversely, NCCS only weakly physisorbed on bastnaesite through sulfonic groups due to structural mismatch and electrostatic repulsion, allowing its ready displacement by H205. This study demonstrates that NCCS is a highly selective depressant, offering a promising strategy for the efficient purification of rare earth minerals.