Investigating the Role of Ferrous Ions in Depressing Calcite to Achieve Selective Rhodochrosite Flotation: Surface Chemistry and Experimental Insights

Modulating surface characteristics via metal ions has proven to be a successful approach to enhance the flotation efficiency of carbonates. Consequently, this research thoroughly examines how ferrous ions (Fe²⁺) influence the selective separation of rhodochrosite from calcite. Flotation experiments revealed that at pH 9.0, Fe²⁺ strongly depressed calcite flotation (recovery < 20%) while exerting a negligible influence on the floatability of rhodochrosite (recovery > 75%), enabling effective selective separation. To elucidate the underlying mechanism, contact angle measurements, zeta potential analysis, ToF-SIMS, SEM-EDS, XPS and Visual MINTEQ solution chemistry calculations were employed to characterize mineral surface properties. The results demonstrate that Fe²⁺ undergoes chemisorption onto the calcite surface, inducing the formation of a dense, uniform iron hydroxide layer. This layer creates a stable hydrophilic barrier that inhibits collector adsorption. In contrast, only a thin, discontinuous layer forms on the rhodochrosite surface, which is insufficient to hinder collector interaction. These findings reveal the intrinsic mechanism of selective interfacial regulation by ferrous ions, providing a new theoretical basis for the flotation separation of refractory carbonate minerals.