Why is Near-Infrared Spectroscopy Important to Mining?

By Isabelle Robinson, M.Sc.Mar 5 2019

As material research escalates, the need for increasingly complex ore deposits is increasing. Consequently, the mining industry has put more effort into refining its methods of extraction. It is essential to understand the detailed characteristics of the mined material, while also maintaining the rate of extraction. Due to this, there has been increased use of near-infrared spectroscopy for analyzing minerals, as it can provide a quick and comprehensive analysis of the ore, both before and during mining operations.

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The term near-infrared spectroscopy refers to the method of light reflectance measurement used to identify compounds and materials. It is appealing as a procedure as it is both efficient and non-destructive, and has a wide range of applications. These include measuring food quality, pharmaceutical constituent validation, climate change research, counterfeit product identification, crop monitoring for agricultural purposes, and the quantification of mined minerals.

It has been found that the use of near-infrared spectroscopy as a mineral analyzer can produce a clean, high-quality spectrum. It uses a short-wave infrared camera to increase the spectrum clarity. This means that it provides light in the region of 1001-2500 nanometers, allowing it to more precisely identify the minerals in the material and its metallurgic properties. In addition to this, this technique can identify critical material indicators and problem gangue minerals, such as swelling clays.

Near-infrared spectroscopy is particularly sensitive to the characteristics of C-H minerals, which are part of the methylene, methoxy, carboxyl, and aryl groups. The technique is also sensitive to hydroxy O-H, mercapto S-H, and amino N-H. In simple terms, this means that the camera can differentiate the crystallinity of single minerals containing hydroxy silicate minerals, sulfate minerals, and carbonate minerals in layered silicate.

Single minerals include clay and chlorite, while hydroxy-silicates are minerals such as epidote. Sulfate and carbonate minerals are very popular and include the likes of calcite and gypsum (which is used to make concrete). In addition to this, near-infrared spectroscopy provides a higher resolution identification of darker mineral samples than conventional methods, which have struggled with this aspect due to their reflectance-based measurement systems.

Another reason why this technology is becoming popular with the mining industry is the fact that it can be miniaturized into a small, portable machine which is able to identify rock samples with high accuracy quickly. In the mining industry, exploration geologists carry the portable NIR technology in a backpack which can be easily transported around the site. The mineral spectra are collected by applying a probe to the surface of the rock in question. The probe is connected to the spectrometer via an optical fiber wire, and all the data is stored in spectral files on a computer. The identification process is completed by comparing the collected spectra to a known mineral spectra library.

Historically, near-infrared spectroscopy has been a slow and cumbersome process. However, with the development of new, smaller technologies, it has quickly become an invaluable piece of mining equipment. Specific NIR technology, such as the ASD TerraSpec Halo, are sold globally. This device weighs as little as 2.5 kilograms and can analyze the rock on site in 20 seconds or less. This has the additional benefit of gaining detailed knowledge in real-time, allowing exploration geologists the power to make faster decisions.

References

• Kenaston, B. (2018, March 27). NIR FOR THE MINING INDUSTRY. Retrieved from Malvern Panalytical: https://www.materials-talks.com/blog/2018/03/27/nir-for-the-mining-industry/
• Kirby, J. (2018). Near-infrared technology essential for rapid and accurate mineral sampling. Retrieved from Canadian Mining and Energy: https://www.miningandenergy.ca/technology/article/near_infrared_technology/
• Liancun, X. (2017). Mineral identification and geological mapping using near-infrared spectroscopy analysis. IEEE

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