Process Mineralogy of Lateritic Nickel Ore

This chapter presents a methodology for studying low-grade lateritic nickel ore, which usually presents complex mineralogy, with widespread nickel in several mineral phases. The study is focused on determining the mineralogy and the distribution of nickel in the bearing minerals. Laboratory assays comprise homogenization, sampling, and particle size analysis. Chemical analyses by X-ray fluorescence are performed in all fraction sizes, while mineralogical assessments by X-ray diffraction are carried out for the head samples. The mineralogical composition of the samples and the partition of main elements in the bearing minerals are assayed by size fraction through automated image analysis software (MLA) coupled with a scanning electron microscope (SEM). The chemical compositions of the several minerals identified in MLA are determined during systematic observations on SEM with energy-dispersive spectrometer (EDS).

Two samples of lateritic nickel ore have been characterized, one silicate and other oxidized, with nickel grades of 0.60 and 0.28 wt%, respectively. The nickel grades in the oxidized ore vary from 0.16 to 0.26 wt% above 0.037 mm, increasing to 0.41–0.42 wt% below this fraction, where 79 wt% of total nickel is contained. In the silicate ore, the nickel grades vary from 0.42 to 0.47 wt% above 0.15 mm, where 36 wt% of the total nickel are present, while the nickel grades below this fraction increase, varying from 0.60 to 0.68 wt%; the fraction −0.020 mm is responsible for 38 % of total nickel present in the sample.

The silicate ore mineralogy consists mainly of clay minerals with nickel (67 wt%; vermiculite/smectite group) and pyroxene (22 wt%), besides minor phases like goethite, kaolinite, quartz, Cr-spinel, and other minerals. The oxidized ore is composed essentially of goethite (49 wt%) and Cr-spinel (41 wt%), besides quartz, kaolinite, Ni clay minerals, hematite, and other minor phases. Considering the interval −0.30 +0.020 mm, in the silicate ore, the clay minerals are responsible for 93 wt% of total nickel contained, while goethite responds for 93 wt% of total nickel present in the oxidized ore.