Enhanced depression of calcite via Fe(Ⅲ) preconditioning for efficient flotation separation from cassiterite: Mechanistic study

This study addresses the selectivity challenge in the flotation separation of fine cassiterite from calcium-containing gangue minerals, particularly calcite, by developing a Fe 3 + -CMC depressant system. Micro-flotation tests demonstrated that this system significantly improved separation efficiency: compared to using CMC alone, the SnO 2 recovery increased by 54.23–85.79 % (at a grade of 85.63 %), while the calcite recovery was depressed to 11.66 % (a reduction of 3.36 percentage points). The mechanism was systematically elucidated through contact angle measurements, solution chemistry calculations, surface characterization (Zeta potential, FTIR, XPS, AFM), and theoretical simulations (MD, DFT). The results indicate that Fe³ ⁺ mainly exists as Fe(OH)₃ in the pulp, which adsorbs on the cassiterite surface via hydroxyl groups and on the calcite surface through oxygen sites in CO₃²⁻. CMC consumes Fe³ ⁺ adsorbed on the cassiterite surface, while Fe³ ⁺ on the calcite surface provides additional adsorption sites for CMC, thereby enhancing its selective coverage. The stable Fe(OH)₃-CMC configuration promotes multilayer adsorption, effectively increasing cassiterite recovery while depressing calcite. This strategy, leveraging the synergistic effect of metal ion pretreatment and an organic depressant, offers a feasible approach for the efficient beneficiation of complex tin ores.