Hydroxamic acid interactions with solvated cerium hydroxides in the flotation of monazite and bastnasite-Experiments and DFT study

Density functional theory (DFT) simulations and experiments were performed to clarify the interaction mechanisms between hydroxamic acid collectors and cerium hydroxides during the flotation of bastnasite and monazite minerals. These minerals showed considerable floatability at moderately alkaline pH which was related to the adsorption of hydroxamic acids on their surfaces as confirmed by vibrational spectroscopic and zeta potential measurements. DFT simulations showed that at moderately alkaline pH, the interactions between solvated Ce(OH)(2+) and Ce(OH)(2)(+) and heptyl-hydroxamic acid (HHA) anions resulted in the formation of, respectively, [ Ce(OH)(HHA)(x)(H2O)(y])(2-x) (x[y = ] = 1[6],2[3],3[1]) and [Ce(OH)(2)(HHA)(x)(H2O)y](1-x) (x[y = ] = 1[5],2[1],3[0]) complexes. The collector anions were found to interact directly through formation of two covalent bonds between their two polar-head oxygen atoms and cerium in the hydroxide complexes. However, formation of such new bonds resulted in breakage of a few covalent/electrostatic bonds between cerium and water molecules initially present in the first hydration shell of the rare-earth metal cation. Building up in the electric double layer of the semi-soluble minerals, these complexes, and by extension, those from other rare-earth elements belonging to monazite and bastnasite, are speculated to play a role in the interactions between rare-earth minerals and hydroxamic acid collectors. (C) 2016 Elsevier B.V. All rights reserved.