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Previous work has shown that addition of sodium salts can increase the extraction of nickel from laterite ores subjected to pressure acid leaching. This paper uses quantitative X-ray diffraction and electron microprobe analysis to characterise two residues that form in the absence and the presence of sodium sulfate and identify the mineralogical factors associated with the increase in nickel extraction.

The nickel containing phases in both residues include amorphous silica, hematite, alunite/jarosite and chromite. Comparing the amount of nickel associated with each phase highlights the difference that sodium sulfate additive has on the amounts of nickel associated with hematite, but especially silica. It appears that the reduction in nickel associated with these two phases is responsible for the majority of the observed increase in nickel extraction. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved.