Efficient magnesium removal by reverse flotation of apatite using cyclic modified fatty acid soaps: Experiment and DFT calculation

A self–made cyclic modified fatty acid soaps (CMFAS) was used as a collector for the reverse flotation of phosphate rock for the first time. Pure mineral tests indicate that at a CMFAS dosage of 800 g/t, the phosphorus concentrate achieved a P 2 O 5 grade of 25.43 %, a recovery of 90.83 %, an MgO grade of 0.42 %, and a recovery of 13.52 %, demonstrating relatively good performance. When 1200 g/t NaOL was used, the phosphorus concentrate had a P 2 O 5 grade of 25.18 %, a recovery of 52.07 %, an MgO grade of 1.68 %, and a recovery of 30.56 %. Fourier transform infrared spectroscopy (FT–IR) analysis revealed the formation of a new complex when dolomite reacted with CMFAS, accompanied by a new absorption peak in the infrared spectrum. Conversely, no new absorption peaks were observed for CMFAS and apatite. Zeta potential test results showed that the collector addition shifted the isoelectric points of both dolomite and apatite in a negative direction, with the most pronounced shift observed in the dolomite–CMFAS system at 53.88 mV. Density functional theory (DFT) calculations showed that the sulfonic acid group of CMFAS preferentially adsorbs onto dolomite, with an adsorption energy of 85.37 kJ·mol −1 , significantly higher than the 31.32 kJ·mol −1 observed for apatite. Although NaOL also reacts with dolomite, its interaction with apatite is more pronounced. The adsorption energy between NaOL and dolomite (73.91 kJ·mol −1 ) exceeds that of apatite (35.67 kJ·mol −1 ). Therefore, CMFAS is a promising reverse flotation collector for apatite, ensuring phosphate recovery while effectively removing magnesium minerals.