Solvoleaching process of metal oxides using acidic organic extractants
Abstract
The applicability of solvoleaching process for treating various metal oxides (MOs) using acidic extractant, di-(2-ethylhexyl) phosphoric acid/D2EHPA or neodecanoic acid/Versatic 10, was investigated. Solvoleaching of MOs was found to be in accordance with the values of standard Gibbs energy of reaction between H + and MOs (ΔG 0 298K ), standard Gibbs energy of formation (ΔG f 0 ) and lattice energy (U). Exceptions happened to MOs like Cu 2 O, iron oxides (FeO, Fe 3 O 4 , Fe 2 O 3 ), Co 3 O 4 , MnO 2 , V 2 O 5 and NiO, which could be explained by the proposed solvoleaching mechanism using D2EHPA. Addition of a small amount of water could substantially increase solvoleaching yields and kinetics. Metallic copper could serve as a reducing agent (creating coupled reduction-oxidation/redox reactions with the MOs) to improve the metal solvoleaching and prevent oxidation of D2EHPA molecules, whilst graphite acted as a catalyst for the redox reactions. Versatic-10 showed similar solvoleaching behavior, albeit with a lower solvoleaching capacity than D2EHPA. Recovery of metals from loaded D2EHPA was accomplished by stripping with a pH-controlled aqueous solution or by precipitation-stripping with oxalic acid to produce final products. In particular, Fe stripping could only occur using HCl, necessitating a selective stripping procedure. Recyclability of D2EHPA was evaluated by performing five solvoleaching-stripping cycles.