Selective flotation of scheelite from calcite using Al-Na2SiO3 polymer as depressant and Pb-BHA complexes as collector

In previous studies, by regulating the Pb/BHA ratio and pH, lead complexes of benzohydroxamic acid (Pb-BHA) have been proven to be selective for the separation of scheelite from calcium minerals. In this study, sodium silicate (Na2SiO3) and Al-Na2SiO3 polymer were used as depressants for the further separation of scheelite from calcite. Flotation results indicated that both scheelite and calcite were depressed by Na2SiO3, while Al-Na2SiO3 polymer gave good selectivity. The depressing ability of Na2SiO3 for calcite was significantly improved due to the formation of some Al-Na2SiO3 species with aluminum ions, while the reverse was true for scheelite. Zeta potential results indicated that both colloidal Na2SiO3 and Al-Na2SiO3 particles were negatively charged and difficult to adsorb on the negative scheelite surface through electrostatic attraction, especially for Al-Na2SiO3. Xray photoelectron spectroscopy analysis results showed that the Al-Na2SiO3 adsorbed amount on the scheelite surface was less than the Na2SiO3 adsorbed amount, while the reverse was true on the calcite surface. Binding energy analysis results indicated that calcium cations of scheelite and calcite surfaces could bond to oxygen atoms of Na2SiO3/Al-Na2SiO3 through chemisorption. However, compared with Na2SiO3, Al-Na2SiO3 showed weaker chemisorption on the scheelite surface, but adsorbed more powerfully onto the calcite surface. Therefore, Al-Na2SiO3 showed excellent selectivity for scheelite and calcite, which has been successfully applied at the Shizhuyuan mine.