Garnierite characterisation for open data bases for nickel laterite exploration
Résumé
The nickel laterite mining industry faces lower recovery rates related to low ore grades, multiple nickel carrying minerals, as well as lateral and vertical heterogeneities at ore deposit scale. Garnierite, a complex mixture of nickel-bearing phyllosilicates, occurs at the base of nickel laterite profiles. Samples of Ni-rich and Ni-poor phyllosilicates from garnierite and host saprolite, from New Caledonia and the Dominican Republic, were analyzed by laboratory X-ray diffractometry (XRD), Fourier Transform Infrared (FTIR) and Raman spectroscopies. These phyllosilicates are mainly composed of serpentine-, talc- and/or sepiolite-like phases. XRD allows clearly distinguishing the different phyllosilicate phases. Moreover, it shows a difference between Ni-rich and Ni-poor phases after refinement of the diffractograms, in particular the (060) reflection, little exploited at present. When Ni is present, the peaks are broader and the spacing corresponding to the (060) reflection tends to be less than 1.534 Å. Mg substitution by Ni also cause shifts of hydroxyl bands in FTIR (3500–3800 cm−1 and 500–800 cm−1 spectral range), and Raman spectra (3500–3700 cm−1 spectral range). Moreover, the intensities of the bands can be correlated with the Ni content. Both are reliable indicators to define the nature of garnierite. In Raman spectroscopy, the substitution of Mg by Ni generates shifts on most bands, and there is a variation in intensity ratios between several bands which are correlated with Ni content.
Our results can be applied to spectra obtained by online and handheld analytical devices, in-field core scanners or XRD/X-Ray fluorescence (XRF) combined expert systems.
