Reexamining the Adsorption of Octyl Hydroxamate on Malachite Surface: Forms of Molecules and Anions

The adsorption of chelating collector octyl hydroxamate onto malachite was studied at various pH to reveal the adsorption mechanism. Below pH 6, a substantial amount of octyl hydroxamate was consumed by copper ions in solution, leading to low malachite recovery. In the pH range from 6 to 9, octyl hydroxamate mainly existed in the molecular form. The collector reacted with the chemisorbed Cu(OH)(+) and Cu(CO3)(2)(2-) on the malachite surface. The octyl hydroxamate anion was the predominant species above pH 9. The reaction between the anion and the chemisorbed Cu(OH)(+) and Cu(CO3)(2)(2-) on the malachite surface, was responsible for flotation of malachite. At pH 9, the maximum collector adsorption and flotation recovery were achieved, presumably as a result of the coadsorption of octyl hydroxamate molecules and anions. Although Cu(OH)(+) and Cu(CO3)(2)(2-) were the predominant active species for malachite surface below and above pH 8.3, respectively, and octyl hydroxamate anion and molecule were the predominant species below and above pH 9, respectively, the same copper hydroxamate chelate was formed on the malachite surface above pH 6.