Effect of metal ions on the flotation separation of biotite from quartz using mixed anionic/cationic collectors

Metal cations have great effects on the flotation of silicate minerals whereas the interaction mechanism is unclear. Single mineral flotation demonstrated that the recovery of biotite rose to 94.69% and 96.41%, and that of quartz declined to 1.21% and 2.01% after introducing small amounts of Ca2+ and Mg2+, respectively. Artificial mixed mineral tests indicated that Ca2+ and Mg2+ could increase the Gaudin's selectivity index by 11.98 and 11.37, respectively, compared with 11.53 without metal ions. QCM-D measurements revealed that sodium oleate (NaOL) and dodecylamine (DDA) could co-absorb on the biotite surface, and a rigid DDA layer formed on these surfaces with/without metal ions. Moreover, the adsorption of NaOL on the biotite surface could be enhanced by Mg2+, from dissipated to rigid adsorption, while that on the quartz surface was barely influenced. Surface chemistry analysis confirmed that metal ions acted as adsorption bridges between mineral surfaces and carboxylate, thereby enhancing the adsorption of collectors.