Selective Collection Mechanism of a Novel Phosphonic Acid Collector in Reverse Flotation Separation of Magnesite and Dolomite

As a key mineral resource in China, magnesite is crucial for the country’s economic and industrial development. This mineral often coexists with dolomite, making their flotation separation crucial for efficient magnesite recovery. In this study, dodecylamine dimethylenephosphonic acid (DNBP), a newly synthesized phosphonic acid collector, was applied to the flotation separation of magnesite and dolomite. Single mineral flotation tests showed that when the concentration of DNBP was 50 mg/L, the concentration of ethylenediaminetetraacetic acid (EDTA) was 40 mg/L and the pH value was 9, the recovery of magnesite and dolomite were 16.47% and 52.18%, respectively. Artificial mixed ore tests demonstrated that the reverse flotation separation of magnesite and dolomite could be achieved using DNBP as the collector and EDTA as the depressant. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the adsorption of DNBP on both magnesite and dolomite surfaces, while the adsorption characteristics were more pronounced on dolomite. Complementary computational simulations incorporating implicit aqueous solvation and TS dispersion correction further showed that both the −3 and −4 valent DNBP species exhibited more favorable interaction energies on dolomite than on magnesite, supporting the preferential collection of dolomite by DNBP. Actual ore flotation tests further reduced the CaO grade from 1.34% in the feed to 0.58% in the concentrate at a concentrate yield of 65.49%, supporting the applicability of the EDTA–DNBP reagent system to low-grade magnesite ore.