Adsorption mechanism of a novel collector (2-ethylhexyl) phosphonic acid mono-2-ethylhexyl ester for selective flotation separation of ilmenite from titanaugite

To address the challenge of separating ilmenite from titanaugite, the feasibility of a novel collector (2-ethylhexyl) phosphonic acid mono-2-ethylhexyl ester (HEHEHP) was firstly investigated in this work. The flotation results indicated that HEHEHP possessed superior collecting performance over a broader pH range for ilmenite compared to benzohydroxamic acid and sodium oleate. Under conditions with a pH of 8.0±0.2, a high-quality concentrate with a TiO₂ grade of 40.74% and a recovery of 87.66% was achieved. Adsorption studies and AFM analysis implied that the adsorption density of HEHEHP on ilmenite was significantly higher than that on titanaugite. Zeta potential analysis implied that the negatively charged HEHEHP anion primarily acted on ilmenite through chemisorption. ToF-SIMS, XPS, and FTIR further corroborated that HEHEHP interacted with the Fe and Ti sites on the ilmenite surface primarily through the P=O and P-OH functional groups in the adsorption process, leading to the formation of PO-Fe or PO-Ti bonds, thereby chemically adsorbing onto the ilmenite. DFT calculations proved that the two O atoms in the PO(OH) group exhibited significant reactivity, serving as the main active sites during the adsorption of HEHEHP. In summary, the chemical interactions between the PO(OH) group in HEHEHP and the active Fe and Ti sites on the ilmenite surface are responsible for the primary mechanism for the selective adsorption of HEHEHP.