Selective depression of phenoxyacetyl chloride on magnesite: Implications for effective flotation separation of magnesite from dolomite

In order to improve the flotation separation of magnesite from dolomite effectively, the organic regulator, phenoxyacetyl chloride (POC), was first introduced as a selective depressant of magnesite, with dodecylamine (DDA) as the collector. The results of single mineral flotation showed that POC could selectively inhibit magnesite but hardly affect dolomite. The results of reverse flotation of a synthetic mixture of magnesite and dolomite were basically consistent with those of single mineral flotation. With DDA as the collector and POC as the depressant, dolomite floated selectively against magnesite. Magnesite and dolomite could be efficiently separated at pH 8.00 with a reagent scheme of 0.50 mg/mL POC and 30.00 mg/L DDA. When the mixed ore for the synthetic mineral, grading 42.60 % MgO and 2.84 % CaO, a magnesite concentrate with 46.85 % MgO and 0.45 % CaO was achieved. Contact angle, Zeta potential, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and DFT analyses showed that POC selectively adsorbed on the surface of magnesite, by chelating Mg on the surface of magnesite. The results from the contact angle tests indicated that POC selectively reduced the surface hydrophobicity of magnesite in the DDA system. Besides, Zeta-potential measurements and FTIR analyses revealed that the addition of POC prior to DDA had no significant impact on the adsorption of DDA onto dolomite; the addition of POC strongly prevented DDA from being adsorbed onto magnesite, resulting in a significant difference in the flotation performances of the two minerals. Furthermore, XPS analyses and DFT calculations confirmed that the adsorption of POC on the magnesite surface could be attributed to the interaction between the POC electron-rich groups and the Mg exposed to magnesite, POC could be used as a high-performance inhibitor for the magnesite flotation to realize the decalcificationic. Based on these experimental results, a possible model for the flotation separation process of magnesite has been proposed.