Flotation of Quartz from Gypsum Using a Single Collector 1-Hexadecyl-3-methylimidazolium Chloride: Experimental and Molecular Dynamics Simulation Insights

Quartz is the primary solid impurity in phosphogypsum (PG), which severely degrades the purity and industrial value of PG. To address this critical issue, we explored the feasibility of using the ionic liquid 1-hexadecyl-3-methylimidazolium chloride ([HMIM]Cl) as a single reagent for the flotation of quartz from gypsum, and the separation mechanism of [HMIM]Cl was explained by a combination of experiments and molecular dynamics simulation (MDS). The flotation tests clearly demonstrate that [HMIM]Cl exhibits an outstanding selectivity with quartz recovery exceeding 93% and gypsum recovery below 13% in a wide pH range of 2-11. The floatability difference between quartz and gypsum in the presence of [HMIM]Cl is significantly enlarged; therefore, the selective separation of quartz from gypsum can be realized using [HMIM]Cl alone without the assistance of any other reagents. Flotation of PG showed that the purity of PG increased from 90.78% to 96.03%, while the SiO₂ content decreased from 6.65% to 2.26% at 180 g/t [HMIM]Cl. This is ascribed to the fact that [HMIM]Cl can selectively adsorb on the surface of quartz by strong electrostatic attraction and hydrogen bonding, whereas the interaction between [HMIM]Cl and the gypsum surface is limited to a weak electrostatic attraction. The adsorption density of [HMIM]Cl on the quartz surface is dramatically higher than that on the gypsum surface, which enhanced the hydrophobicity of quartz. Consequently, [HMIM]Cl is a promising collector for the selective flotation separation of quartz from gypsum.