Surface chemistry insights into chlorite–specularite separation by phosphonic acid pre-adsorption

Achieving selective flotation separation between chlorite and specularite is inherently difficult, primarily because of their overlapping surface characteristics and analogous reactivity toward commonly used depressants. In this work, we propose a novel pre-adsorption strategy using two phosphonic acid reagents—bisphosphonomethyl glycine (BPMG) and aminotrimethylene phosphonic acid (ATMP)—to selectively modify chlorite surfaces. Systematic flotation experiments, combined with contact angle and zeta potential analyses, FTIR and XPS spectroscopy, and density functional theory (DFT) simulations, revealed that both reagents strongly chelate with Al³ ⁺ and Mg²⁺ sites on chlorite. Such targeted surface modification impedes the subsequent adsorption of depressants while promoting collector interaction, thereby creating a more pronounced difference in flotation behavior between the two minerals. ATMP demonstrated enhanced efficacy compared to BPMG, a consequence of its structurally enriched phosphonate functionalities and more stable complexation with Mg²⁺ and Ca²⁺. Under optimized conditions, the recovery difference between chlorite and specularite exceeded 70 %, and artificial mixed mineral tests confirmed enhanced Fe grade and recovery. This study introduces phosphonic acid pre-adsorption as an innovative route to overcome the limitations of traditional depressants and provides new surface chemistry insights for designing selective reagents in complex iron ore flotation.