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Laser-induced breakdown spectroscopy (LIBS) is a rapid, minimally destructive chemical analysis technique that takes operational principles from atomic emission spectroscopy (AES). LIBS is a technique that can be used on a range of material forms and has been used throughout the industrial and food processing industries as a quality control method. Now, LIBS is being utilized as a tool for the real-time monitoring of mineralogical samples across all stages of the mining production cycle.
What is LIBS?
As mentioned, LIBS is a variation of AES. In LIBS, a high energy laser is focused in short pulses towards a sample so that a small part of the sample atomizes, turns into a plasma, and is excited, but only in the sections where the laser is focused. When the material starts to form, a plasma is dependent on many factors, including the optical breakdown threshold, the analysis environment, and the materials being analyzed.
When the plasma starts to cool, each element gives off a characteristic emission—a light wavelength emission with a spectral peak that is characteristic of that element. These emissions are then picked up by a detector and spectrally analyzed to determine the composition of the sample, enabling it to be identified. Because the sample forms a plasma and is subsequently cooled while only removing a small amount of sample mass, the technique is generally characterized as either a minimally destructive or a non-destructive technique.
The technique is fast and can be prepared without the need for sample preparation, so raw minerals and mining ores can be used without needing to do anything to them. Additionally, the detection can be done from a remote location, which is why it is used for continuous monitoring applications and is therefore applicable to the mining sector. LIBS can also theoretically detect every element in the sample. However, the real-world analyses can be limited by the wavelength range of the spectrograph and the sensitivity of the detector.
Bringing LIBS to Mining Sites
After successful use as a monitoring and quality control technique in food and other industrial sectors, companies and research councils have started to use LIBS at mining sites, as well as throughout the whole processing life cycle that the minerals undergo. The remote detection capabilities mean that LIBS can be brought to mining sites via portable handheld instruments, while the quick analysis time can be utilized in various processing lines, and in the conveyor belts that are used to remove the mined material. LIBS can also be used with materials in a solid, liquid, or gaseous state, meaning a range of materials arising from the mine can be analyzed, as can any effluent produced.
There are many different aspects of mineralogical analyses where LIBS can be used, besides its use in different mining sectors. LIBS is being trialed as a method for scanning coarse rock streams, and other areas use it for analyzing the mining waste. LIBS is also being used to analyze grades of gold ores directly in the field to analyze whether it is worth mining the ore from a value perspective, as well being used in oil sands to determine the relative amount of bitumen compared to the concentration of mineral solids and water.
From a general monitoring and quality control perspective, LIBS is also used for analyzing phosphate deposits, iron sintering processes, magnesite crushed ore compositions, potash, copper ores, and nickel ores, to name a few examples where LIBS has already been introduced.
LIBS can also be used to detect whether any of the mineralogical samples being mined contain toxic substances within them and enables the necessary precautions to be undertaken if a positive result is found. LIBS instruments have also been sent on spacecraft to collect geological samples on other celestial bodies, so the mining potential for LIBS is not strictly limited to mining sites on Earth.
Advantages of LIBS
Aside from being a rapid, real-time, and portable analysis technique, the operational principles of LIBS have some inherent benefits, as well as there being some specific areas where it excels over other mineral analysis methods. LIBS, as a general technique, can measure a large number of elements simultaneously and can also detect some of the lighter elements that are beyond the capabilities of other techniques. This is important for mineralogical studies, as the minerals, will often contain hydrogen, beryllium, magnesium, sodium, lithium, carbon, nitrogen and oxygen elements (with some in high abundancies in some minerals), and being able to identify these elements makes it easier to identify and distinguish between different minerals.
As with any LIBS application, there is no need to treat the minerals specially, so they can stay in their native environments for analysis. Even in their natural environments, the LIBS analyses do not suffer from any substrate interference and can profile both the mineralogical sample at its surface and its depth. Moreover, the LIBS analyses can be performed in a wide range of material matrices and often has a detection limit in the low parts per million (ppm) range, but, as mentioned above, this does vary depending on the detector. One other aspect that makes LIBS ideal for mine sites is that it can be used in almost all environments, including vacuum environments.
Some of the other analysis techniques that are commonly used include X-ray fluorescence (XRF) and prompt gamma neutron activation analysis (PGNAA). Compared to XRF, LIBS has a much higher sensitivity, and it does not suffer from analysis interferences from some metals like XRF does, and it does not have any restrictions on detecting elements based on their atomic weight. While PGNAA is an effective technique, it can be limited in use around radiation protection areas, while LIBS analyses do not give off any radiation to the surrounding analysis environment. Moreover, LIBS analyses do not expose workers to excessive amounts of radiation, nor does it damage any of the processing equipment after long periods. Because LIBS is a laser-based technique, it also has a distinct advantage over both XRF and PGNAA in that it can be combined with other laser spectroscopy techniques such as Raman to perform more in-depth analyses.
References and Further Reading
“Laser-Induced Breakdown Spectroscopy: Fundamentals, Applications, and Challenges”- Anabitarte F. et al., International Scholarly Research Notices, 2012, DOI: 10.5402/2012/285240
“Industrial Online Raw Materials Analyzer Based on Laser-Induced Breakdown Spectroscopy”- Gaft M. et al., Applied Spectroscopy, 2014, DOI: 10.1366/13-07382
Applied Spectra: https://appliedspectra.com/technology/libs.html
Mining Technology: https://www.mining-technology.com/news/crc-ore-nrc-canada-libs-minerology/
Spectroscopy Online: http://www.spectroscopyonline.com/libs-advantage-mining-and-energy-applications
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