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

Abstract

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 Al OH 2 + , Al OH and Al O −. The Al OH 2 + and Al OH sites can adsorb the C( O)NH 2 groups through Al O H⋯O or Al O H 2 + ⋯ O hydrogen bonds. Simultaneously, the Al O − sites adsorb CH 2N +(CH 3) 3 groups by electrostatic effects or adsorb C( O)NH 2 group through the N H⋯ −O Al 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 CH 2N +(CH 3) 3 groups, which made CPAM have a insignificant effect on the adsorption of DDA on the kaolinite surface and its cation flotation.