Understanding the crystal chemistry of Nickel (Ni), in particular how the element is bonded to its surrounding elements, can improve its extraction process, making it greener and increasing the yield. Scientists from Diamond (the UK’s national synchrotron facility), in collaboration with mineralogists from the University of Barcelona, Spain, have combined measurements on the Microfocus Spectroscopy beamline (I18) and Raman spectroscopy to elucidate the chemistry and local environment of Ni in a Mn-oxyhydroxyde aggregate.
Nickel is of great interest, particularly because it can be used in batteries potentially suitable to power electric cars. However, although this metal is relatively abundant on earth, it is only in very specific geographical areas that its extraction can be carried out at an acceptable economic cost.
The Caribbean Basin holds some of the world’s major deposits of nickel in the form of laterite, a soil type formed by weathering of the Earth’s crust. But the mechanisms by which Ni is retained by and liberated from the laterite minerals are still not well understood. EXAFS (Extended X-ray Abosrption Fine Structure) spectroscopy is a technique of choice to investigate the coordination environment of Ni, but the usual high heterogeneity of natural samples means that conventional bulk characterisation is difficult and that a microfocused beam is needed to perform the analysis.
Diamond scientists studied Ni lateritic deposits from Moa Bay, eastern Cuba, in order to determine why Ni accumulates in the Mn-oxyhydroxyde rather than anywhere else in the matrix and how it behaves in it. They took a multi-scale approach by first using a combination of techniques (micro X-ray diffraction, electron probe micro-analysis and micro X-ray fluorescence) to define the region of interest on a representative Mn-oxyhydroxyde aggregate. Microfocus Raman spectroscopy and synchrotron radiation microfocus X-ray absorption spectroscopy (μXAS) then helped them to elucidate the chemistry and local environment of Ni in the aggregate with a 5μm resolution. The data obtained from the experimental maps showed the distribution of Ni and established its relationships with the other major elements, in particular aluminium. The scientists concluded that the main determinant of Ni concentration is the association of this element with Mn and that, according to the amount of Ni and Al present, two differentiated regions could be identified with different structural and chemical features.
Dr Josep Roque-Rosell, lead author of the publication (doi: 10.1016/j.chemgeo.2010.04.006), said: “This is a preliminary study on natural samples that has given us some trends and insights on how Ni behaves in lateritic soils, which was not fully understood before. We now plan to carry out more in depth research. This study also illustrates how μXAS can complement Microfocus Raman spectroscopy.”