Selective adsorption of a high-performance depressant onto dolomite causing effective flotation separation of magnesite from dolomite

This research focused on the adsorption features and depression mechanism of 1-hydroxyethylene-1,1-diphosphonic acid (HEDP) used as a novel dolomite depressant on dolomite and magnesite surfaces, to extend the application of HEDP for the selective flotation of magnesite from dolomite. The depression impacts of HEDP on the flotation behaviors of the two minerals were investigated through micro-flotation tests. The flotation results indicated that, when sodium oleate (NaOl) was used as the collector, HEDP displayed an outstanding depression effect on the dolomite flotation, whereas it had only a slight influence on the magnesite flotation. Dolomite and magnesite could be efficiently separated at approximately pH 10 with a reagent scheme of 200 mg/L HEDP and 120 mg/L NaOl. The selective depression mechanism of HEDP for dolomite was revealed using contact angle, X-ray photoelectron spectroscopy (XPS), zeta potential, and infrared spectrum (IR) analyses. The results from the contact angle tests indicated that HEDP selectively reduced the surface hydrophobicity of dolomite in the NaOl system. Besides, zeta-potential measurements and IR analyses revealed that the addition of HEDP prior to NaOl had no significant impact on the adsorption of NaOl onto magnesite; however, this addition strongly prevented NaOl from being adsorbed onto dolomite, resulting in a significant difference in the flotation performances of the two minerals. Furthermore, crystal chemistry calculations and XPS analyses confirmed that the strong adsorption of HEDP on the dolomite surface could be attributed to the interaction between the HEDP electron-rich groups and the calcium species exposed to dolomite. Thus, HEDP could be used as a high-performance depressant for the dolomite flotation to realize the decalcification of the magnesite flotation.