A novel depressant N,N-bis(phosphonomethyl)glycine for magnesite-dolomite separation and its mechanism

Abstract

In this study a novel depressant, N,N-bis(phosphonomethyl)glycine (BPMG), is proposed for the beneficiation of magnesite from dolomite using sodium oleate (NaOL) as the collector. Laboratory flotation results show that BPMG selectively depresses the flotation of dolomite but has almost no effect on magnesite at an approximate pH of 10.0. In addition, wettability analysis reveals that differences in the NaOL adsorption characteristics due to BPMG pre-adsorption are responsible for the different flotation characteristics of the two minerals. According to the zeta potential and Fourier transform infrared spectra analysis, BPMG is adsorbed onto both magnesite and dolomite surfaces, with dolomite adsorbing strength considerably more than magnesite. Moreover, X-ray photoelectron spectroscopy results confirm that BPMG is adsorbed onto the dolomite surface by chelation between the calcium sites and the phosphonyl structure of BPMG, and on the magnesite surface by weak adsorption. As a result, BPMG is preferentially adsorbed firmly onto the dolomite surface rather than the magnesite surface. BPMG dominates the selective depression of dolomite when NaOL is used as the collector.