Sulphuric acid pressure leaching of laterites - speciation and prediction of metal solubilities "at temperature"

Sulphuric acid pressure leaching of nickeliferous laterites has attracted c onsiderable attention from the nickel industry during the past 5 years. The process is especially advantageous for limonitic laterites that mostly con tain goethite, because iron precipitates releasing acid and thus rendering low acid consumption. It is also applicable to mixtures of limonites and sa prolites, although at a higher acid consumption due to magnesium. Effective process design requires the solubility of metals that precipitate during t he process to be known. In the present work, determination of metal solubil ities is based on a simple speciation program that assumes the presence of only one dominant complex for each metal. The thermodynamic data for the pr ecipitation reactions are extracted from high-temperature experiments with monometallic systems published previously. The validity of the approach is then tested against mixed bimetallic systems, and finally applied to calcul ate the solubility of aluminium, iron and magnesium in laterite leaching ef fluents "at temperature". In both cases of limonitic feed and limonitic/sap rolitic blends, the prediction closely follows metal solubilities measured experimentally at temperatures from 230 to 270 degrees C and at terminal-fr ee acidities ranging from 10 to 75 g/l. (C) 2000 Elsevier Science B.V. All rights reserved.