The role of cationic polyacrylamide in the reverse flotation of diasporic bauxite

The reverse flotation separation of kaolinite and diaspore has been achieved by using the collector dodecylamine (DDA) and depressant cationic polyacrylamide (CPAM) at pH 5.5–8.5. The flotation results have been explained by adsorption measurement, solution chemistry and density functional theory (DFT) calculations. At pH 5.5–8.5, the main components at the diaspore/water interface are AlOH2+, AlOH and AlO−. The AlOH2+ and AlOH sites can adsorb the C(O)NH2 groups through AlOH⋯O or AlOH2+⋯O hydrogen bonds. Simultaneously, the AlO− sites adsorb CH2N+(CH3)3 groups by electrostatic effects or adsorb C(O)NH2 group through the NH⋯−OAl hydrogen bond. The absorption of CPAM on all the crystal planes of diaspore prevented the majority of DDA cationic species from adsorbing on the diaspore surface, and thus, depressed diaspore flotation. The adsorption ability of the CPAM cation group on the negatively charged sites on the kaolinite surface was weakened by the inductive and steric effect of methyl in CH2N+(CH3)3 groups, which made CPAM have a insignificant effect on the adsorption of DDA on the kaolinite surface and its cation flotation.