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

Abstract

Partial neutralization is typically used to remove Fe3+ ions from the acid leach solution of laterite. However, during this process, significant amounts of Mg2+, Ni2+, Co2+, and SO2–4 are lost. With increasing initial Fe3+ concentration and solution pH, the severity of loss increases, with the precipitation of Fe3+. 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 [Fe4(OH−)2(SO2–4)4]•[2SO2–4•yH2O]•[M2+] 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 M2+ and SO2–4 could be destroyed via intense agitation, releasing approximately 100% of Mg2+, Ni2+, and Co2+ 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 Mg2+, Ni2+, and Co2+ 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 Mg2+, Ni2+, and Co2+ 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.