Enhanced fluorite-calcite separation through selective hydroximic acid adsorption driven by cationic-π interactions

• Cation-π interactions between phenyl and fluorite/calcite were investigated. • Interactions between alkyl/aryl hydroxamate and fluorite/calcite were characterized. • The effect of cation-π interactions on selective adsorption was explored. • Flotation separation of fluorite and calcite was achieved via cation-π interactions. • Integrating chemical interactions with cation-π interactions is beneficial. Cation-π interactions are important non-covalent forces that significantly enhance the selective adsorption of surfactants on particle surfaces, thereby improving separation processes. However, studies on these interactions and the development of related chemicals remain limited due to the challenges in accurately measuring cation-π interactions in the coexistence of multiple interactions. To address this limited understanding, this work investigates the mechanism of cation-π interactions in the separation of fluorite and calcite particles using two hydroxamic acids, i.e., benzohydroxamic acid (BHA) and octyl hydroxamic acid (OHA). Flotation tests revealed that BHA, which contains phenyl groups, effectively separates fluorite from calcite, whereas OHA, lacking phenyl groups, does not achieve this separation. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and first-principles calculations confirmed the formation of hydroxamate-Ca 2+ chemical bonds and cation-π bonds between adsorbed BHA and both mineral surfaces. Surface force measurements via atomic force microscope demonstrated that phenyl-containing hydroxamate groups exhibit stronger attraction with fluorite than with calcite, agreeing with its better flotation performance. This enhanced interaction is attributed to the higher positive charge and greater number density of calcium ions on the fluorite surface, which enhance cation-π interactions. These findings highlight the importance of modulating cation-π interactions in particle separation processes and provide valuable insights for developing more efficient chemical separation technologies.