Investigation of the effect of phosphoric acid as an acidic medium in flotation separation of dolomite from magnesite

Flotation separation of carbonate minerals is difficult because of their similar surface properties. A variety of collectors and depressants have been previously used to improve their separation in acidic or alkaline media. In the present study, the flotation of dolomite and magnesite in acidic to neutral pH was investigated using oleate as collector and hydrochloric acid or phosphoric acid as pH regulator. It was found that the recovery of dolomite was high and independent of pH while that of magnesite decreased with acid addition, especially when phosphoric acid was used. Results of mineral dissolution showed a higher dissolution of dolomite than magnesite in acidic pH, which therefore provides more calcium (than magnesium) ions to interact with the oleate collector. These results are in agreement with the larger quantity of oleate adsorbed/precipitated on dolomite than on magnesite revealed by the infrared spectroscopic study. Furthermore, the new PO4 species observed in the Raman and infrared spectra of these minerals at acidic pH when phosphoric acid was used may prevent mineral dissolution and/or collector adsorption. The surface passivation of magnesite therefore explain the decrease in magnesite flotation when using phosphoric acid as pH control.