Study of Fe²⁺ removal from laterite nickel-ore leaching pregnant solutions: optimization and kinetics

This research offers substantial insights into improving the hydrometallurgical processing of nickel ores, with a particular emphasis on minimizing impurities to meet the demands of modern industries, such as electric vehicle battery manufacturing. The study focuses on optimizing iron (Fe) removal from nickel laterite ore pregnant leach solution (PLS) using Response Surface Methodology (RSM), examining key variables including agitation speed, precipitation temperature, and precipitation duration. Employing a two-stage precipitation process with calcium carbonate (CaCO₃), this research concentrates specifically on second-stage Fe removal. This stage aimed to maximize Fe²⁺ removal efficiency while minimizing losses of valuable metals. Experimental results indicated an optimal Fe removal efficiency of 10.93% during the second stage and achieved under conditions of 450 rpm agitation, 90 min of precipitation, and a temperature of 90 °C, yielding a total Fe removal rate of 98.74%. Kinetic analysis across first-, second-, and third-order models suggests that the third-order model exhibits the highest R²; however, similar R² values across models prevented conclusive determination of the reaction order. The activation energy (Ea) derived from this study is 12.99 kJ/mol, indicating energy-efficient Fe precipitation. Characterization of the precipitate via X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirmed hematite (Fe₂O₃) and goethite (FeOOH) as primary Fe compounds, along with calcium sulfate (CaSO₄), which may hydrate to form gypsum. These findings provide valuable insights into optimizing Fe removal in nickel laterite ore processing, demonstrating high Fe removal efficiency under controlled operational parameters.