Mechanisms of Ligand Structures of Fe-Salicylic Acid and Fe-Gallic Acid Colloidal Complexes Regulating the Flotation Behavior of Scheelite with Calcite

The similarity in surface properties between scheelite and calcite makes their flotation separation particularly challenging, thereby severely limiting the efficient utilization of tungsten resources. In this paper, Fe-SYA and Fe-GA colloidal complexes were synthesized via a metal-organic coordination strategy using Fe³⁺ with salicylic acid (SYA) and gallic acid (GA), respectively, and their structure-dependent flotation regulation mechanisms were systematically investigated. The structural stability, interfacial adsorption behavior, and their relationship with flotation selectivity were elucidated through contact angle measurements, zeta potential analysis, XPS, TEM and DFT calculations. The results showed that Fe-SYA and Fe-GA preferentially adsorbed on the calcite surface at pH=4 and a ratio of 1:1/2, significantly reducing calcite hydrophobicity and collector adsorption, while exerting only a minor effect on scheelite, thereby enabling selective separation. Owing to its abundant phenolic hydroxyl groups, Fe-GA formed a stable reticulated polydentate coordination structure with enhanced electronegativity and spatial stability, facilitating the formation of a dense inhibition film on calcite and yielding superior flotation performance, with a WO₃ concentrate grade of 71.03% and a recovery of 86.54%. In contrast, Fe-SYA exhibited lower structural stability and was prone to hydrolysis into Fe(OH)₃ colloids under alkaline conditions, resulting in non-selective inhibition. This work elucidates the structure–selectivity relationship of metal-organic colloidal complexes and provides a green and efficient strategy for the flotation separation of calcium-bearing minerals.