Interaction Mechanism of Sulfated Castor Oil in Flotation of Fluorite: Experimental Investigation and DFT Calculations

Fluorite (CaF2) is a strategically important non-metallic mineral resource worldwide, and flotation remains the predominant technology for its separation from associated gangue minerals. However, conventional fatty acid-based collectors often suffered from limitations such as unsatisfactory separation performance, poor water dispersibility, and unstable flotation performance under complex pulp conditions, necessitating structural modification to improve their collecting capability. Herein, sulfated castor oil (TRO) was proposed as an efficient collector for fluorite flotation, and its flotation performance and interfacial adsorption mechanism were systematically investigated through micro-flotation experiments, zeta potential measurements, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Micro-flotation tests revealed TRO’s excellent collecting ability for fluorite under weakly acidic conditions. At a TRO concentration of 4 × 10−4 mol·L−1, the fluorite recovery exceeded 98%, which was significantly higher than that achieved with sodium oleate (NaOl) under comparable single-mineral conditions. Zeta potential measurements indicated that TRO adsorption on fluorite involved both electrostatic interactions and chemical interactions, with the dominant contribution depending on the solution pH. XPS analyses further confirmed the occurrence of chemical adsorption between TRO and fluorite surfaces. DFT calculations revealed that TRO adsorption on the fluorite (111) surface was thermodynamically favorable, with both carboxylate and sulfate ester functional groups participating in coordination with surface calcium sites. Moreover, electronic structure analyses suggested that carboxylate groups exhibited a relatively higher degree of covalent character during coordination, while sulfate ester groups afforded supplementary anchoring effects. This study provides molecular-level insights into the adsorption mechanism of sulfated collectors on fluorite surfaces and offers valuable guidance for the rational design of high-performance collectors for mineral flotation.