Insights into the selective adsorption mechanism of a multifunctional thioether-containing hydroxamic acid on separation of wolframite from fluorite

Both thioether and hydroxamate groups are excellent iron ligands. Herein, to improve the properties of hydroxamic acid and the recovery of tungsten-minerals, a surfactant containing thioether and hydroxamate groups, 2-(benzylthio)-acetohydroxamic acid (BTHA), was introduced to separate wolframite from fluorite. The properties, predicted by Density Functional Theory (DFT) calculations and Molecular Dynamics (MD), indicated that BTHA, as a multifunctional surfactant (i.e., thioether and hydroxamate groups), could enhance its hydrophobicity and selectively adsorb on the desired mineral surfaces. The experimental results of micro-flotation and contact angles confirmed BTHA had a strong collecting ability and good selectivity toward wolframite versus fluorite. The adsorption mechanism, surveyed through zeta potential, solution chemical analysis and XPS, demonstrated only electrostatic adsorption on fluorite surfaces, while chemisorption and hydrogen bonding would be produced on wolframite surfaces. The thioether and hydroxamate groups could co-absorb onto wolframite's surfaces to form Fe S bonds and five-membered hydroxamate-(O, O)-Fe rings.