Optimisation of fast quantification of fluorine content using handheld LIBS

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Fluorine quantification is difficult using conventional techniques since it usually includes heavy sample preparation such as dissolution.  Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-element detection that has been successfully used to quantify fluorine using either elementary or CaF molecular bands. The developed models demonstrated that a precise and accurate quantification of fluorine is possible using a calibrated handheld LIBS, providing an on-line estimation of the processes efficiency and a real-time adaptation.

Highlights

• Samples with fluorine content from 1.48% to 40.73% were analyzed with handheld LIBS.
• Peak areas of two CaF molecular bands were correlated with real fluorine contents.
• A non-linear correlation was exhibited between CaF intensity areas and fluorine contents.
• Quantification accuracy was improved using multivariate models.
• Precise and accurate quantification of fluorine is possible using a calibrated handheld LIBS, providing an on-line estimation of the processes efficiency and a real-time adaptation.

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Optimisation of fast quantification of fluorine content using handheld laser induced breakdown spectroscopy

Y.Foucaud, C.Fabre, B.Demeusy, I.V.Filippova, L.O.Filippov


Spectrochimica Acta Part B: Atomic Spectroscopy

First Published Volume 158, August 2019, 105628

Abstract
Hydrofluoric acid represents the majority of the industrial applications of fluorine in the world. It is synthetized from fluorite, which is commonly purified by the froth flotation process to attain the high-grades required for hydrofluoric acid production. Besides, in metallic ores such as tungsten and phosphate ores, fluorite does not represent any added value compared to the extracted metals and is, therefore, considered as a gangue mineral that has to be rejected. In both cases, the fluorine content has to be known precisely in the flotation process as well as in all the industrial applications involving fluorine, to estimate the process efficiency and to optimise the operations. Nevertheless, fluorine quantification is difficult using conventional techniques since it usually includes heavy sample preparation such as dissolution. Though, Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-element detection that has been successfully used to quantify fluorine using either elementary or CaF molecular bands. Here, rock samples exhibiting a wide range of fluorine contents (from 1.48% to 40.73%) were analysed,the fluorine being mainly comprised in fluorite. These samples corresponded to the products of different flotation tests conducted on the same tungsten-skarn ore. The experimental conditions were optimised to study the two CaF molecular bands, located between 529 and 543 nm, and between 590 and 606 nm, respectively. Systematically, the LIBS emission intensities of the two studied bands were evaluated using the peak areas, which were normalised, averaged over several ablated zones, and correlated with the fluorine content determined by the fluoride-ion sensitive electrode method. The particle size played a key role as significant differences in the LIBS intensities were exhibited between the 10–150 μm and the <20 μm powders, with no discernible correlation between the size ranges and signal magnitude. Furthermore, the matrix effects strongly impacted the LIBS intensities, which displayed a non-linear relationship with the fluorine contents: this induced the development of non-linear univariate models that were calculated on 27 training samples and validated on nine testing samples (3:1 ratio). Although non-linear models fitted adequately the experimental data, a multivariate approach considering the two studied CaF bands was adopted to overcome the matrix effects. A formula with linear, quadratic, and interaction terms was generated from the multivariate regression, predicting fluorine contents with R2 = 0.94 and a mean average error of 2.18%F. The developed models demonstrated that a precise and accurate quantification of fluorine is possible using a calibrated handheld LIBS, providing an on-line estimation of the processes efficiency and a real-time adaptation.

Keywords: LIBS, CaF, Particle size, Molecular bands, Normalisation with total light, Non-linear models, Multivariate modelling

Access Full Article:
https://www.sciencedirect.com/science/article/abs/pii/S0584854719300527

About this publication: Spectrochimica Acta Part B: Atomic Spectroscopy is intended for the rapid publication of both original work and reviews of papers having a relationship to spectrochemical analysis.


Another breakthrough from SciAps

SciAps provides the only handheld LIBS that can do geochemical applications.
No other company is even trying it. 

The SciAps Z features the most advanced LIBS technology of any handheld and your only choice for applications outside of the world of metal alloys including geological materials, ceramics, liquids and more. The Z utilizes the most powerful laser, operating at 5-6 mJ/pulse, up to 50 Hz rep rate, Class 3B 1064nm wavelength. The spectrometer range of 190 nm out to 950 nm delivers full periodic table coverage and the widest spectrometer range available in a handheld LIBS. The patented OPTi-purgeTM integrated argon gas purge (optional) yields better limits of detection for many elements compared to air-based analysis. Internal 3D stage raster the laser allowing for surgical analysis of inclusions or veins if desired, all easily viewed through the integrated camera and laser targeting. Full customization of raster settings allows you the most flexibility in testing and the ProfileBuilder PC software gives you the power to do spectral analysis and build your own calibrations. No X-rays means no travel restrictions or licensing headaches.

There are now dozens of SciAps Z-300 analyzers being used globally for geochemical exploration projects. Discover in-field analysis of Li, Be, B, C, Na, F; lithium in hard rocks and brines; and high sensitivity to other major elements Mg, Si, Al, Ca, K.

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We can run samples in our materials laboratory, or visit you with an analyzer for a brief feasibility study. 

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Check out our Academic LIBS Advancement Program…

We frequently loan out HH LIBS units for a few weeks or a month to academic researchers, so that they can perform a study or field analysis. LIBS is often a preferred technique, especially for students, since operators do not have to deal with the regulatory complexities of X-ray fluorescence analyzers. SciAps Z-300 will measure every element in the periodic table – yes even hydrogen! And our accompanying ProfileBuilder software provides operators complete freedom to modify laser and spectrometer parameters and generate their own calibrations. You’re not limited to factory-imposed calibrations or unchangeable multi-variant techniques.

How does it work?

Easy. Contact us (academic@sciaps.com) with a brief description of what you want to measure. As your work progresses, we’d appreciate continued updates. Don’t worry, we understand that you can’t compromise a future publication. We’ll get you the analyzer, train you at a regularly scheduled time (often via GoTo Meeting or Skype but in-person works too). The goal is to raise awareness of the amazing world of applications available to handheld LIBS.

Please note at this time we must limit the loaner program to researchers working at U.S. and Canadian institutions. However, researchers from these countries may travel globally with the analyzer.


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