Behaviour of Silica during Metal Recovery from Bauxite Residue by Acidic Leaching

Bauxite residue represents an interesting source for not only major elements such as aluminium, iron and titanium, but also for rare earths (REEs), while the residue after metal recovery can be used for low-carbon building materials and cementitious binders. Several methods based on direct acidic leaching for recovering metals from bauxite residue have been reported. The co-dissolution of iron represents a significant drawback for REEs recovery upon silica polymerization. The behaviour of silica has been studied during acidic leaching with concentrated mineral acid (H2SO4). The extraction of aluminium, iron and titanium is limited due to an insufficient amount of acidic solution for leaching caused by the polymerization of silica. Kinetic studies have demonstrated that at constant temperatures, silica dissolution increases with increasing acid concentration, but it decreases when the temperature is increased and the acid concentration is reduced. This is due to an enhancement in the solubility of monomeric silicic acid formed during acidic leaching. The control mechanisms of silica dissolution have been described according to the shrinking core model by a chemical reaction stage, i.e. silica polymerization, followed by a diffusion stage, because of the silica gel adsorbed on the surface of the particles that limits the metal extraction.

Publication year:2017

Accessibility:Open