Analysis of flotation separation mechanism of magnesite and calcite and their interaction with bubbles

Herein, polyaspartic acid (PASP) was used as an environmentally friendly and efficient inhibitor to achieve the effective flotation separation of magnesite and calcite in a sodium oleate (NaOL) system. Microflotation experiments indicated that using NaOL as a collector allowed PASP to considerably reduce the flotation recovery of calcite while showing a slight impact on that of magnesite. Among them, a PASP dosage of 6 mg/L achieved a maximum flotation difference of 71.88% between magnesite and calcite. An adsorption capacity test showed that the presence of PASP significantly decreased NaOL adsorption on calcite and slightly decreased that on magnesite. Zeta potential and infrared spectroscopy analyses indicated that PASP strongly affected the surface charge of calcite and introduced corresponding characteristic functional groups on its surface; however, the effect of PASP on that of magnesite was weak. X-ray photoelectron spectroscopy indicated that PASP exhibited strong selectivity for calcite and a weak one for magnesite, which was in good agreement with the shift in the Ca and Mg peak positions and the change in their relative contents. The contact angle measurements demonstrated that PASP considerably reduced the contact angle of calcite and slightly reduced that of magnesite. Extended Derjaguin–Landau–Verwey–Overbeek theoretical calculations indicated that using NaOL alone resulted in an attraction between the magnesite/calcite particles and bubbles. After PASP addition, the attraction force was retained for magnesite, while a repulsive force was observed for calcite due to PASP selectivity, thereby hindering the adhesion between calcite particles and bubbles.