Selective adsorption of 1-hydroxyethylidene-1,1-diphosphonic acid on calcite surface in smithsonite flotation system

Removing calcite is a tricky problem in smithsonite flotation because of its better floatability. 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP), a scale inhibitor in water treatment industry, was chosen as a calcite depressant. This study validated the effectiveness of HEDP in separating smithsonite from calcite by flotation using sodium oleate (NaOL) as the collector, and obtained a 70% recovery difference in a single mineral flotation. Artificial mixed mineral flotation obtained a concentrate with a grade of 44% and a recovery of more than 80%. Zeta potential, Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) tests were conducted to obtained some crucial information on the adsorption of NaOL and HEDP, demonstrating that the adsorption of HEDP on calcite surfaces was stronger than smithsonite. The intense adsorption of HEDP on calcite surfaces was attributed to chelation with surface calcium sites. Quantum chemical calculations suggested that the selectivity of HEDP was closely related to the phosphate groups. HEDP was chemically adsorbed on calcite surface by complexing with calcium sites to form six-membered ring chelate. Partial oxygen atoms of phosphate groups dominated in the reaction with calcium sites, and the deprotonation of phosphate groups enhanced the reactivity.