Particulates in hydrometallurgy: Part III. Dewatering behavior of flocculated laterite acid leach residues

Three polyacrylamide-based polymers of different chemical properties (polymer A, 34 pct anionic, 11×10⁶ mol wt; polymer B, 7 pct anionic, 7.5×10⁶ mol wt; polymer C, nonionic, 13.5×10⁶ mol wt) were used to evaluate the flocculation behavior of laterite acid leach residues. The solid-liquid separation characteristics of the leach residues were investigated with the aid of settling rate, supernatant turbidity, and slurry filtrability measurements. The polymeric flocculants were found to be effective in improving the dewatering properties of the acid leach residues. Polymer effectiveness increased with increasing polymer dosage for all the polymers, but an optimum polymer dose was only found for polymer A (34 pct anionic, 11×10⁶ mol wt) in the studied range of polymer addition. Similarly, the dewatering behavior was improved at higher polymer molecular weight. In addition, it was found that the flocculation performance was adversely affected by an increase in the degree of polymer hydrolysis which, in turn, increases the ratio of carboxylic to amide functional groups in the polymer chain. Polymer C (nonionic ∼0 pct hydrolysis, 13.5×10⁶ mol wt) was found to be the most efficient flocculant in terms of all the performance criteria investigated. The preceding results were rationalized in terms of bridging flocculation, the ionization and molecular configuration of the polymers, hydrogen bonding, and the solid/aqueous interfacial charge.