The efficiency of processes and the quality of products have both been improved in many industries through the use of near-infrared (NIR) reflectance spectroscopy. Expanded application of NIR could be beneficial for mining and ore processing, but the technology is currently being under-utilized. Mineral ores are now being quantitatively analysed through a combination of NIR spectroscopy and chemometric predictive models to provide real-time information needed for ore processing.
NIR is most frequently applied to the analysis of organic materials. However, variations in the composition of many inorganic minerals mean that they too have significant NIR features, meaning that the opportunity is there to create predictive models for these minerals.
For decades, it has been known that certain minerals produce unique spectra. Spectral measurements of reflected sunlight are relied upon for remote sensing of the Earth for geologic and environmental mapping (Goetz and Rowan, 1981).
A wide range of geologic problems have successfully applied NIR spectroscopy, including mineral exploration (Goetz et al 1983); airborne and space-borne mapping of hydrothermal alteration (Kruse et al 2003); mineralogical analysis of drill cores (Kruse 1996); field mapping of expansive soils (Chabrillat et al 2002); and field mapping of mineral assemblages for gold deposit exploration (Bierwirth 2002).
NIR spectroscopy can now be used for a wider range of applications thanks to the use of chemometrics to quantitatively relate measured NIR spectra to properties of interest. Two examples of these are field determination of soil swell potential (Goetz et al 2001) and gangue mineral measurement of mineral ore moving on a conveyor (Goetz et al 2009).
Electronic and vibrational processes in mineral lattices determine the shape of the spectra and the positions of absorption features. These are also a function of particle size (Hunt, 1977; Pieters and Englert, 1997). The NIR spectrum produced by a specific mineral is a result of several kinds of electronic processes. This was revealed through NIR spectroscopic evaluation of minerals. The mineral spectrum is made up of crystal field effects, charge transfer, color centers and conduction band transitions.
This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.
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