Mechanism, kinetics and thermodynamics of nickel, iron, and magnesium hydrochloric acid leaching from laterite ore

The kinetics of hydrochloric acid leaching of oxidized magnesite-iron nickel ores from the Gornostaevskoye deposit (Eastern Kazakhstan) were investigated. The ore has high contents of Mg (14.25 wt.%), Fe (10.8 wt.%) and Si (24.32 wt.%), with a Ni content of 0.87 wt.%. The optimal process parameters were determined as follows: S:L = 1:4, temperature = 85-90 °C, leaching duration = 120 min, HCl concentration = 18%, and stirring rate = 400 rpm. The extraction rates of Ni, Mg and Fe were 91.03%, 97.88% and 93.04%, respectively. The pregnant leach solution contained 1.98 g L^-1 Ni, 35.31 g L^-1 Mg and 25.12 g L^-1 Fe. Kinetic modeling indicated that the leaching of Ni, Fe, and Mg followed a mixed-control mechanism, with activation energies of 76.07 kJ mol^-1 for Ni, 125.45 kJ mol^-1 for Fe, and 119.33 kJ mol^-1 for Mg, confirming that the chemical reaction was controlled. Thermodynamic analysis revealed that pimelite, nickel silicate hydrate, and antigorite are the most reactive phases under hydrochloric acid leaching, on the basis of their highly negative ΔG values. The established mineral dissolution sequence, namely, pimelite > Ni - silicate hydrate > nepouite > antigorite > lizardite > talc > wüstite > hematite, reflects the combined influence of structural accessibility and thermodynamic favorability.