Selective adsorption mechanism of a novel hydroxamic acid containing a thioether group collector for flotation separation of bastnaesite from calcite

Abstract

Multifunctional collectors have been widely used in mineral flotation processing to improve the recovery and grade. However, the synergistic effect of the functional groups in multifunctional collector adsorption on mineral surfaces during flotation separation remains elusive. In this study, a novel hydroxamic acid containing a thioether group collector, 2-(benzylthio)-acetohydroxamic acid (BTHA), was synthesized to separate bastnaesite and calcite. Compared to traditional hydroxamic acid collectors, BTHA exhibited superior selectivity and collecting ability for bastnaesite-calcite flotation separation systems. In the presence of BTHA, the flotation behavior of bastnaesite and calcite was significantly different at pH 8.0 (recovery gap ΔR ∼ 72 %). This indicated that BTHA could selectively separate bastnaesite from calcite. Moreover, BTHA exhibited faster adsorption kinetics on bastnaesite compared to conventional collectors, resulting in stronger adsorption on the bastnaesite surface. Based on spectroscopic analysis and Density Functional Theory (DFT) calculations, BTHA can form five-membered ring complexes on both bastnaesite and calcite surfaces, but BTHA exhibited a larger interaction energy and stronger electron transfer capacity with bastnaesite surface action sites (e.g., Ce(OH)²⁺) compared to calcite surface action sites (e.g., Ca²⁺). Moreover, the superior flotation separation performance of BTHA could have stemmed from the formation of additional Ce-S bonds between the thioether group in BTHA and the bastnaesite surface, which further stabilized the adsorption structure of BTHA on the bastnaesite surface. This work provides valuable insights for the development of new collectors and exploration of their interaction mechanisms with mineral surfaces.