Characterization of Weda Bay nickel laterite ore from Indonesia

Abstract

International audienceThe association of fine grained MgeNi silicates with oxy-hydroxides in laterites and saprolites representschallenges for ore processing, in particular, in nickel enrichment. The Weda Bay nickel deposit in Indonesia is atypical example of these complex ores, where clays such as nontronites develop on polyphase serpentinite asprotolith. Thus, ores at Weda Bay have a very fine textured and complex mineralogy, which requires a comprehensivemineralogical identification through the use of a series of different types of analytical approaches (i.e.macroscopic and microscopic methods including SEM equipped with energy dispersive X-ray spectrometry(EDS), Raman spectroscopy, Infrared and X-ray fluorescence spectroscopy, and QEMSCAN® mapping). Nickelrich saprolites were found to be principally composed of several types of MgeNi serpentines, quartz, clays(nontronite in particular) and little amounts of iron hydroxides. Besides, some parts of the deposit were characterizedby the development of nontronites at the interface between the saprolite and the limonite zone. Abovethis zone, the limonite zone is dominated by iron hydroxides as expected, which replace all earlier silicatesincluding serpentine, and contains a significant amount of nickel. The representative composite ore samplecontains several nickel bearers with variable nickel grade of 2 to 3%. Exceptionally richer phases such aspolygonal Fe (Ni)-rich serpentine were also found with nickel grade of 5 to 10%. Serpentine types as well asother newly formed silicates such as Fe-Mg-(Ni) smectites, are intimately mixed, preventing any mineral separation.Therefore, the only phases which can be separated are quartz and magnetite. This complicates theupgrading of nickel in Weda Bay laterite ore