Abstract
The high-temperature acid pressure leaching of nickeliferous laterites has attracted considerable attention from the nickel industry during the recent years. The process is especially advantageous for low-grade limonitic laterites. It is also applicable to mixtures of limonites and high-grade saprolites, although at higher acid consumption due to magnesium. It is advantageous, therefore, to derive a universal kinetic equation of Ni dissolution that is equally applicable to both types of feed. In the present work, a kinetic equation was derived using the concentration of hydrogen ion “at temperature” calculated from a solution speciation approach, and the assumption that nickel associated with magnesium dissolves instantaneously. This universal kinetic equation was successfully tested against various feeds that contained from 1.2% to 1.9% of Ni and up to 3.85% of Mg at temperatures from 230°C to 270°C, acid/ore ratios from 0.15 to 0.5, and concentrations of solids in the feed (pulp density) of up to 30%. The use of acidity “at temperature” made it possible to explain an apparent dependence of the ultimate Ni extraction on the acid/ore ratio, and on the terminal stoichiometric acid concentration during leaching.
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