Enhancing the flotation separation of magnesite and dolomite by introducing a phosphonic acid depressant during grinding

The flotation separation of low-grade magnesite ore is hindered by its high gangue content and the similar surface properties of associated carbonate minerals. This study introduces ethylenediamine tetramethylene phosphonic acid (EDTMPA) as a novel depressant to enhance the selective separation of magnesite from dolomite in the grinding-flotation system. The separation performance was evaluated through single mineral and artificial mixed ore flotation tests, while the interaction mechanism of EDTMPA with mineral surfaces was elucidated using particle size analysis, contact angle measurement, zeta potential measurement, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermodynamic calculations. The results showed that EDTMPA, when applied during grinding, optimized the particle size distribution of magnesite and dolomite, significantly improving their flotation separation. Under optimal conditions (grinding time: 5 min; EDTMPA dosage: 20.0 mg/L; slurry pH: 10.2; Sodium oleate (NaOL) dosage: 60.0 mg/L), the artificial mixed ore flotation tests achieved the magnesite concentrate with a MgO grade of 46.47 %, a CaO grade of 2.64 %, and a MgO recovery rate of 81.67 %, yielding a separation efficiency of 84.87 %. Mechanistic studies revealed that EDTMPA selectively inhibited dolomite by strongly interacting with Ca sites on its surface, forming stable Ca-EDTMPA chelates that blocked active sites and hindered NaOL adsorption. This enhanced the hydrophobicity contrast between magnesite and dolomite, enabling efficient selective inhibition. These findings establish EDTMPA as an effective depressant for the grinding-flotation process, offering a low-carbon and efficient approach for purifying magnesite ore.