Pressure acid leaching of laterites at 250 °C:: A solution chemical model and its applications

Laterite leach solutions were simplified to a ternary electrolyte system by lumping all divalent metal sulfates into one with the chemical and thermodynamic properties of MgSO(4). The simplified leach solution was assumed to contain H(2)SO(4), Al(2)(SO(4))(3), and pseudo-MgSO(4). The ion-association-interaction approach, as developed previously, along with previously identified species and interaction parameters for this ternary electrolyte system, was implemented to develop a chemical model for the laterite leach solutions at 250 degrees C. The model was tested against experimental solubility data for aluminum, and a very good match was obtained for pseudo-MgSO(4) concentrations less than 0.25 molal. The model was also implemented to calculate true acidities "at temperature." The need to maintain higher H(2)SO(4) concentrations in solution during processing of high-magnesium ores was explained. Finally, a new rate equation for nickel extraction was developed. It is based on true acidity at temperature and is applicable to both limonites and limonite-saprolite blends.