Existence of Maghemite and Trevorite in Nickel Laterites

A lateritic nickel ore (-3.36mm fraction) and a fraction obtained from the cyclosizer overflow (-8 mu m fraction) were investigated with the aim to identify the nickel-bearing phases. Both samples were subjected to selective leaching with hydrogen peroxide, ammonium oxalate, and finally with the dithionite-citrate-bicarbonate system. Dissolution in warm concentrated HCl was also performed. Mossbauer spectroscopy, X-ray diffraction, and chemical analysis were performed to fully characterize all materials. It was found that part of the nickel is associated with goethite, whereas trevorite could account for the remaining nickel. However, due to the presence of large amounts of maghemite in the samples, it was found not possible to unambiguously identify trevorite. Chromium and aluminum spinels were found not to contain any nickel.