Efficient removal of iron during partial neutralization of nickel laterite acid leach solution: DFT calculation and experimental verification of mechanism

Partial neutralization is typically used to remove Fe 3+ ions from the acid leach solution of laterite. However, during this process, significant amounts of Mg 2+ , Ni 2+ , Co 2+ , and SO 2– 4 are lost. With increasing initial Fe 3+ concentration and solution pH, the severity of loss increases, with the precipitation of Fe 3+ . In this study, the mechanisms of ion co-precipitation during partial neutralization were investigated. Based on density functional theory calculations, a precipitation pathway through the formation of [Fe 4 (OH − ) 2 (SO 2– 4) 4 ]•[2SO 2 – 4 •yH 2 O]•[M 2+ ] was proposed. The differential charge density diagram indicated that the O atoms acted as the charge acceptors and maintained the precipitate structure. The coordination between M 2+ and SO 2– 4 could be destroyed via intense agitation, releasing approximately 100% of Mg 2+ , Ni 2+ , and Co 2+ ions from the precipitates to the solution. Furthermore, the addition of cationic or anionic surfactants limited the formation of these coordination bonds. The highest retention percentages of Mg 2+ , Ni 2+ , and Co 2+ in solution were 99.4, 99.6, and 99.9%, respectively, after adding 2 × 10 −5  mol/L of sodium dodecylbenzenesulfonate (CTAB). In addition, a high temperature could break these coordination bonds. The retention percentages of Mg 2+ , Ni 2+ , and Co 2+ increased from 82.6, 85.2, and 86.5% to 99.9, 99.6, and 99.8%, respectively, as the temperature increased from 25 to 65 °C. These results confirmed the rationality of the proposed structure of the precipitate.