Steric Hindrance-Controlled Selective Adsorption of Amine Surfactants: The Crucial Role of Cation Vacancies on Aluminosilicate Mineral Surface

Abstract Selectively regulating feldspar surface hydrophobicity remains a key challenge for the flotation separation of quartz from feldspar. This challenge is closely related to its heterogeneous surface chemistry and the limited understanding of how cation leaching affects collector adsorption. To address this gap, this work elucidates a previously overlooked cation-vacancy-mediated adsorption mechanism of amine surfactants on the feldspar surface, and proposes a steric hindrance-regulation strategy to selectively weaken feldspar flotation. A series of fatty amines with different substitution patterns (primary, secondary, and tertiary) was investigated. The results reveal that amines promote cation leaching from the feldspar surface, and preferentially adsorb at the resulting cation-vacancy-associated sites. Increasing N-methyl substitution hinders the approach of amino groups to these vacancies, and weakens the hydrogen bonding with surrounding oxygen atoms, reducing adsorption-layer stability on feldspar. In contrast, adsorption on quartz is primarily driven by electrostatic attraction and is less affected by steric hindrance. Consequently, flotation selectivity is positively correlated with steric hindrance. An optimal flotation concentrate with 94.39% SiO2 grade and 76.90% recovery was obtained using 10–5 mol/L DMDDA (tertiary amine) and 5 × 10–5 mol/L sodium oleate as collectors at pH 7. This insight provides a valuable reference for flotation separation systems involving aluminosilicate minerals.