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LIBS, XRF and Raman sensors for optimal bauxite sorting
Abstract
Bauxite, bauxite residues (BR) and Bayer Liquor are important resources for Al, Sc, V and Ga. Bauxite is currently the solely source for primary aluminium. At global scale about 80 plants produce alumina. From these resources, about 1 to 1.4 tonnes of bauxite residues are generated per tonne of alumina (Ujaczko et al. 2018). Bauxites present heterogeneous grades at lateral and vertical scale, variable mineralogy, and chemistry. Therefore, it is important to localize most precisely minerals hosting valuable metals for Al, Sc, V and Ga, but also hazardous minerals/metals for processing such as reactive silica (aluminosilicates), TiO2 (rutile, anatase), and minerals generating moisture (phyllosilicates). This must be done at the beginning of the value chain on mine sites to reduce transport and processing costs, and BR volumes. In this study, different types of sensors were applied to major lithologies of the karst bauxite deposits of SODICAPEI (Villeveyrac, Southern France), for optimal bauxite sorting. Therefore, the applicability of Laser-Induced Breakdown Spectroscopy (LIBS) was investigated with an industrial LIBS system and a LIBS core scanning system. Furthermore, first time-gated Raman and XRF spectroscopic analyses were performed with the multi-sensor ANCORELOG system.Our results, obtained in the frame of the EIT ANCORELOG and T-REX projects, show that LIBS is powerful to precisely define the bottom and top layer of bauxite ores and define the bauxite types by measurement of major and trace elements (Al, Mg, K, Na, Ca, C, Si, Ti, Fe, S). Furthermore, LIBS can access the critical parameters crucial for bauxite processing. XRF gives semiquantitative data for Mn, Fe, Cr, Ti, V, Ca, K while time-gated Raman spectroscopy allows deciphering clay minerals, Ti-minerals, boehmite and carbonates, all allowing defining bauxite on and offset.
... The ANCORELOG sensors and scanner are currently tested on VMS-type deposits and materials in southern Spain. Further materials such as bauxites (Meima et al, 2021;Orberger et al, 2022) and process materials from TiO2 pigment production and Al-production will be tested. ...
Copper porphyries represent complex alteration zones, hosting variable grades of Cu- (Au-Mo), but also Pb, Zn, Te, Bi and Ag. Moreover, environmental harmful elements, such as As or Cd are present. It is therefore crucial that mining companies get reliable chemical and mineralogical drill core data from the earliest exploration state on to avoid project failure and to obtain threedimensional models for mine and processing planning. Systematic sensor-based drill core logging and material sorting coupled with smart data evaluation is the ideal solution for accurate in-field and in-plant real time decision-making to reduce waste and anticipate dysfunction during metal production. Risks and operational costs can be reduced while increasing resource efficiency. In this paper, as an example, specific alteration zones of the Niaz porphyry copper (Mo)-deposit in north-western Iran were investigated by laser-induced breakdown spectroscopy (LIBS), X-ray Fluorescence (XRF), time-gated Raman spectroscopy, dual energy X-ray transmission (DE-XRT), multi energy X-ray transmission (ME-XRT) and X-ray computed tomography (CT). Most of these instruments were combined in the European Institute of Innovation and Technology (EIT) RawMaterials project ANCORELOG. The sensor results were compared and evaluated against laboratory results obtained by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), and optical microscopy for calibration. Fast LIBS, Raman and XRF core-scanner instruments clearly allow to distinguish the alteration zones: The potassic-phyllic alteration zone is characterised by two differently mineralised rock types: (i) the Cu-mineralised quartz diorite where the key minerals are chlorite and barite, quartz, albite/oligoclase, muscovite and the major ore mineral is chalcopyrite; (ii) the Cu-Mo-mineralised monzonite, where carbonates, orthoclase and albite/oligoclase are the key minerals. Ore minerals are molybdenite and chalcopyrite. The propylitic alteration zone is characterised by a coarse-grained diorite. Key minerals are orthoclase, epidote, sphene and apatite. Molybdenite is the major ore mineral. The phyllic-argillic mineralised zone is represented by a microgranular quartz-diorite. Key minerals are kaolinite-dickite, quartz, albite, muscovite-sericite and apatite. The major ore mineral is chalcopyrite. The peripheral part of the porphyry is a coarse-grained skarn with andradite, calcite, tremolite and epidote as key minerals. The major ore mineral is chalcopyrite. LIBS elemental mapping clearly reflects the ore mineralogy and texture. Analysis of reconstructed three-dimensional CT volume data revealed structural information as well as two to three different groups of grey values. After calibration, eg by SEM or LIBS, mine-geologists can assign these grey values to minerals or elements with low (eg Al, Si), medium (eg Fe, Cu), and high (eg Mo) effective atomic numbers. Our study shows that sensor-based characterisation of successive alteration zones and Cu-Mo mineralised zones is possible for unknown samples. XRF, Raman spectroscopy, LIBS and XRT can be used and adapted in-field on mine and exploration sites as well as in plants. Selected samples of drill cores can then be sent for CT analysis and detailed LIBS imaging.
Copper porphyries represent complex alteration zones, hosting variable grades of Cu- (Au-Mo), but also Pb, Zn, Te, Bi and Ag. Moreover, environmental harmful elements, such as As or Cd are present. It is therefore crucial that mining companies get reliable chemical and mineralogical drill core data from the earliest exploration state on to avoid project failure and to obtain threedimensional models for mine and processing planning. Systematic sensor-based drill core logging and material sorting coupled with smart data evaluation is the ideal solution for accurate in-field and in-plant real time decision-making to reduce waste and anticipate dysfunction during metal production. Risks and operational costs can be reduced while increasing resource efficiency. In this paper, as an example, specific alteration zones of the Niaz porphyry copper (Mo)-deposit in north-western Iran were investigated by laser-induced breakdown spectroscopy (LIBS), X-ray Fluorescence (XRF), time-gated Raman spectroscopy, dual energy X-ray transmission (DE-XRT), multi energy X-ray transmission (ME-XRT) and X-ray computed tomography (CT). Most of these instruments were combined in the European Institute of Innovation and Technology (EIT) RawMaterials project ANCORELOG. The sensor results were compared and evaluated against laboratory results obtained by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), and optical microscopy for calibration. Fast LIBS, Raman and XRF core-scanner instruments clearly allow to distinguish the alteration zones: The potassic-phyllic alteration zone is characterised by two differently mineralised rock types: (i) the Cu-mineralised quartz diorite where the key minerals are chlorite and barite, quartz, albite/oligoclase, muscovite and the major ore mineral is chalcopyrite; (ii) the Cu-Mo-mineralised monzonite, where carbonates, orthoclase and albite/oligoclase are the key minerals. Ore minerals are molybdenite and chalcopyrite. The propylitic alteration zone is characterised by a coarse-grained diorite. Key minerals are orthoclase, epidote, sphene and apatite. Molybdenite is the major ore mineral. The phyllic-argillic mineralised zone is represented by a microgranular quartz-diorite. Key minerals are kaolinite-dickite, quartz, albite, muscovite-sericite and apatite. The major ore mineral is chalcopyrite. The peripheral part of the porphyry is a coarse-grained skarn with andradite, calcite, tremolite and epidote as key minerals. The major ore mineral is chalcopyrite. LIBS elemental mapping clearly reflects the ore mineralogy and texture. Analysis of reconstructed three-dimensional CT volume data revealed structural information as well as two to three different groups of grey values. After calibration, eg by SEM or LIBS, mine-geologists can assign these grey values to minerals or elements with low (eg Al, Si), medium (eg Fe, Cu), and high (eg Mo) effective atomic numbers. Our study shows that sensor-based characterisation of successive alteration zones and Cu-Mo mineralised zones is possible for unknown samples. XRF, Raman spectroscopy, LIBS and XRT can be used and adapted in-field on mine and exploration sites as well as in plants. Selected samples of drill cores can then be sent for CT analysis and detailed LIBS imaging.
The EU aluminium production from, e.g., bauxite is one of the backbones to support Europe’s green and digital transition. In support of sustainable bauxite exploration and mining, Laser Induced Breakdown Spectroscopy (LIBS) was used on the major facies of the karst bauxite deposits of SODICAPEI (Southern France). Our results showed that LIBS is a very promising technology to define the bottom and top layer of bauxite ores and to access critical parameters crucial for bauxite mining and processing. First LIBS tests were made on scandium standards to find appropriate Sc emission lines for future applications.
Laser‐induced breakdown spectroscopy (LIBS) is a rapidly developing technique for
chemical materials analysis. LIBS is applied for fundamental investigations, e.g., the laser plasma matter interaction, for element, molecule, and isotope analysis, and for various technical applications, e.g., minimal destructive materials inspection, the monitoring of production processes, and remote analysis of materials in hostile environment. In this review, we focus on the element analysis of industrial materials and the in‐line chemical sensing in industrial production. After a brief introduction we discuss the optical emission of chemical elements in laser‐induced plasma and the capability of LIBS for multi‐element detection. An overview of the various classes of industrial materials analyzed by LIBS is given. This includes so‐called Technology materials that are essential for the functionality of modern high‐tech devices (smartphones, computers, cars, etc.). The LIBS technique enables unique applications for rapid element analysis under harsh conditions where
other techniques are not available. We present several examples of LIBS‐based sensors that are applied in‐line and at‐line of industrial production processes.
This work presents the latest chemometric tools developed by the RLS science team to optimize the scientific outcome of the Raman system onboard the ExoMars 2022 rover. Feldspar, pyroxene and olivine samples were first analyzed through the RLS ExoMars Simulator to determine the spectroscopic indicators to be used for a proper discrimination of mineral phases on Mars. Being the main components of Martian basaltic rocks, lepidocrocite, augite and forsterite were then used as mineral proxies to prepare binary mixtures. By emulating the operational constraints of the RLS, Raman datasets gathered from laboratory mixtures were used to build external calibration curves. Providing excellent coefficients of determination (R² 0.9942÷0.9997), binary curves were finally used to semi-quantify ternary mixtures of feldspar, pyroxene and olivine minerals. As Raman results are in good agreement with real concentration values, this work suggests the RLS could be effectively used to perform semi-quantitative mineralogical studies of the basaltic geological units found at Oxia Planum. As such, crucial information about the geological evolution of Martian Crust could be extrapolated. In light of the outstanding scientific impact this analytical method could have for the ExoMars mission, further methodological improvements to be discussed in a dedicated work are finally proposed.
Portable X-ray fluorescence spectroscopy is now widely used in almost any field of geoscience. Handheld XRF analysers are easy to use, and results are available in almost real time anywhere. However, the results do not always match laboratory analyses, and this may deter users. Rather than analytical issues, the bias often results from sample preparation differences. Instrument setup and analysis conditions need to be fully understood to avoid reporting erroneous results. The technique’s limitations must be kept in mind. We describe a number of issues and potential pitfalls observed from our experience and described in the literature. This includes the analytical mode and parameters; protective films; sample geometry and density, especially for light elements; analytical interferences between elements; physical effects of the matrix and sample condition, and more. Nevertheless, portable X-ray fluorescence spectroscopy (pXRF) results gathered with sufficient care by experienced users are both precise and reliable, if not fully accurate, and they can constitute robust data sets. Rather than being a substitute for laboratory analyses, pXRF measurements are a valuable complement to those. pXRF improves the quality and relevance of laboratory data sets.
Geochemical and mineralogical characterization studies play an important role in the definition of mineral deposits. Each mineral system has a unique set of minerals with different chemical makeup and physical properties. Platinum-group elements (PGEs), for example, are scarce resources with many applications. The optimization of extraction process efficiency is therefore crucial to prevent resource shortage and increased bulk prices. To improve the mineral liberation process, high throughput sensors must be added alongside the production line as part of fast process analysis implementation. Current analytical methods are either ineffective to assess PGE content, or unusable in the conditions of the processing facilities. This article shows how Laser-induced breakdown spectroscopy (LIBS) technology, developed by ELEMISSION Inc, can circumvent these drawbacks by enabling automated, ultra-fast, and precise quantitative mineral analyses in any working environment. The drill core samples that were used in this study were collected at the Stillwater platinum group element mine in the United States. The data used for the mineralogical database was validated using the TESCAN Integrated Mineral Analyzer (TIMA) instrument
Time-gated (TG) Raman spectroscopy (RS) has been shown to be an effective technical solution for the major problem whereby sample-induced fluorescence masks the Raman signal during spectral detection. Technical methods of fluorescence rejection have come a long way since the early implementations of large and expensive laboratory equipment, such as the optical Kerr gate. Today, more affordable small sized options are available. These improvements are largely due to advances in the production of spectroscopic and electronic components, leading to the reduction of device complexity and costs. An integral part of TG Raman spectroscopy is the temporally precise synchronization (picosecond range) between the pulsed laser excitation source and the sensitive and fast detector. The detector is able to collect the Raman signal during the short laser pulses, while fluorescence emission, which has a longer delay, is rejected during the detector dead-time. TG Raman is also resistant against ambient light as well as thermal emissions, due to its short measurement duty cycle.
In recent years, the focus in the study of ultra-sensitive and fast detectors has been on gated and intensified charge coupled devices (ICCDs), or on CMOS single-photon avalanche diode (SPAD) arrays, which are also suitable for performing TG RS. SPAD arrays have the advantage of being even more sensitive, with better temporal resolution compared to gated CCDs, and without the requirement for excessive detector cooling. This review aims to provide an overview of TG Raman from early to recent developments, its applications and extensions.
On-line, real-time chemical and mineralogical analyses on drill cores are highly demanded by mining companies. However, they are a challenge because of drill core surface state and sample heterogeneities. We selected four rock samples: highly porous, siliceous breccia and serpentinized harzburgite coming from the base of a nickel laterite profile in New Caledonia which were sonic drilled, and fine grained, homogeneous sandstone and coarse grained granite which were diamond drilled and provided by Eijkelkamp Sonic Drill with unknown origin. The samples were analysed at five surface states (diamond or sonic drilled, cut as squares, polished at 6 and 0.25 μm, powdered <80 μm) by portable XRF spectroscopy (pXRF) in mining and soil modes and portable infrared spectroscopy (pIR, Visible and Near Infrared-Short Wave Infrared range (VNIR-SWIR)). A total of 52 pXRF and 200 pIR analyses were performed per sample at each surface state. This study shows that the surface state has minor influence on the results of the portable instruments. By comparing pIR and pXRF results with laboratory devices (Raman spectroscopy, XRD with Rietveld refinement, XRF spectroscopy and ICP-AES), we evidence the lower and less accurate information obtained from handheld instruments in terms of chemistry and mineralogy. The porosity and grain size effect on the measurement need to be taken into consideration for on-line drill core analyses. We show that the combination of complementary analytical techniques helps to overcome the drawbacks of the core texture and of the precision of portable instruments in order to define the regions of interest (ROI) for mining companies. We also demonstrate that a precise pXRF calibration is mandatory and that the concentration of light elements (Si, Mg), even if not accurate, shows sufficient contrast along the lateritic profile for ROI definition.
Measuring distances in the range between a few centimetres and a few metres are of special interest for automated industrial LIBS applications. They allow for a reliable optical access to measuring objects in a process line under harsh industrial environments. In that range a compromise can be found between the conflicting requirements with respect to the protection of the optics facing the measuring object on one side, and sufficiently high laser irradiance and high receiving solid angle of the measuring radiation on the other side. A concise overview about LIBS studies published in the last four years focusing on industrial applications or perspectives therefore is given. Recent R&D activities in the field of automated LIBS for industrial applications are presented focusing on the following application cases: (a) combined use of inline measured 3D geometry information and LIBS analyses for high-speed sorting tasks of piece goods; (b) sorting of refractories; (c) identification of steel blooms in a rolling mill; (d) inverse production scenario for the recovery of valuable materials from end-of-life electronic equipment. For measuring distances of only a few centimetres the size of a LIBS instrument can be downscaled significantly allowing to set up handheld LIBS analysers. Whereas the precursors of such concepts were studied already more than fifteen years ago, quite recently a competitive market arose where various models of handheld LIBS systems are offered. Industrial application fields are mainly positive material identification of metals and sorting of light metal scraps for recycling purposes. A comparative synopsis of features of these LIBS systems will be presented and arising research themes in this context are outlined.
Since the world economy has been confronted with an increasing supply risk of critical raw materials (CRMs), there is a major interest in identifying alternative secondary sources of CRMs. Bauxite residues from alumina production are available at a multi‐million ton scale worldwide. So far, attempts have been made to find alternative re‐use applications for bauxite residues, for instance in cement / pig iron production. However, bauxite residues can also be an untapped secondary source for CRMs. Depending on their geologic origin and processing, bauxite residues can contain considerable amounts of valuable elements. The obvious primary consideration for CRM recovery is the economic value of the materials contained. However, there are further benefits from re‐use of bauxite residues in general, and from CRM recovery in particular. These go beyond monetary values (e.g. reduced investment / operational costs by savings in disposal). For instance, benefits for the environment and health can be achieved by abatement of tailing storage as well as by reduction of emissions from conventional primary mining. Whereas certain tools (e.g. life‐cycle analysis) can be used to quantify the latter, other benefits (in particular sustained social and technological development) are harder to quantify. This review evaluates strategies of bauxite residue re‐use/re‐cycle and identifies associated benefits beyond elemental recovery. Further, methodologies to translate risks and benefits into quantifiable data are discussed. Ultimately, such quantitative data are a prerequisite for facilitating decision making regarding bauxite residue re‐use/re‐cycle and a stepping stone towards developing a zero waste technology.
The identification of mineralogical phases in drill cores is one of the most challenging tasks in the mining activity in view of an efficient metal extraction. This process requires the analytical characterization of large volumes of material to obtain a complete set of data in a minimum of time. None of the commonly used methods in mineralogical analyses, such as IR‐based techniques, X‐rays fluorescence, and hyperspectral imaging, is capable to provide a fully satisfactory response for several reasons, the main one being the complexity of the ores. Moreover, the characterization is often conducted in remote laboratories and only on selected samples to limit the time waste. A possible alternative solution requires a multianalytical approach exploiting on‐field techniques. This strategy is currently being developed within SOLSA, a joint EU H2020 project, and consists of an automatic expert system coupling sonic drilling, imaging, profilometer, hyperspectral cameras, and a combination of Raman spectroscopy, X‐rays fluorescence, and X‐rays diffraction. In this work, the principles on which this cooperative approach is based are discussed, with application to two specific test samples, showing the potential and novelty of the method. In particular, a case is considered in which the sample characterization by the separate use of a single technique fails, whereas the combination of the three analyses (Raman spectroscopy, X‐rays fluorescence, and X‐rays diffraction) works even if the system is very complex.
Four different spectrometer types were used to measure spectra in the library: (1) Beckman™ 5270 covering the spectral range 0.2 to 3 μm, (2) standard, high resolution (hi-res), and high-resolution Next Generation (hi-resNG) models of Analytical Spectral Devices (ASD) field portable spectrometers covering the range from 0.35 to 2.5 μm, (3) Nicolet™ Fourier Transform Infra-Red (FTIR) interferometer spectrometers covering the range from about 1.12 to 216 μm, and (4) the NASA Airborne Visible/Infra-Red Imaging Spectrometer AVIRIS, covering the range 0.37 to 2.5 μm. Measurements of rocks, soils, and natural mixtures of minerals were made in laboratory and field settings. Spectra of plant components and vegetation plots, comprising many plant types and species with varying backgrounds, are also in this library. Measurements by airborne spectrometers are included for forested vegetation plots, in which the trees are too tall for measurement by a field spectrometer. This report describes the instruments used, the organization of materials into chapters, metadata descriptions of spectra and samples, and possible artifacts in the spectral measurements. To facilitate greater application of the spectra, the library has also been convolved to selected spectrometer and imaging spectrometers sampling and bandpasses, and resampled to selected broadband multispectral sensors. The native file format of the library is the SPECtrum Processing Routines (SPECPR) data format. This report describes how to access freely available software to read the SPECPR format. To facilitate broader access to the library, we produced generic formats of the spectra and metadata in text files. The library is provided on digital media and online at https://speclab.cr.usgs.gov/spectral-lib.html. A long-term archive of these data are stored on the USGS ScienceBase data server (https://dx.doi.org/10.5066/F7RR1WDJ).
The suggested citation for the USGS Spectral Library version 7 is:
Kokaly, R.F., Clark, R.N., Swayze, G.A., Livo, K.E., Hoefen, T.M., Pearson, N.C., Wise, R.A., Benzel, W.M., Lowers, H.A., Driscoll, R.L., and Klein, A.J., 2017, USGS Spectral Library Version 7: U.S. Geological Survey Data Series 1035, 61 p., https://doi.org/10.3133/ds1035.
In the last thirty years, portable X-ray fluorescence (pXRF) has grown from prototypes to being a key technique for field geochemical analyses, especially for mining and environmental applications. This technology provides real-time or near real-time decision support for operational field decisions (exploration, mining, site remediation or waste management), provides a cost-saving alternative to classical laboratory analysis programs, and deals efficiently with remote or harsh field conditions. The ability to rapidly collect a large number of samples and replicate analyses facilitates acquisition of higher data density compatible with geostatistics.
pXRF can be used profitably for sample screening and selection tasks, dynamic sampling plans based on field observations and measurements, grid mapping of a site and determining relative element abundance. In waste management and remediation, pXRF is used to identify unknown waste composition, and verify waste loads before disposal or treatment.
In all applications, having robust QA/QC plans and systematic laboratory controls on selected samples are essential for ensuring reliable measurements. The best overall results are usually achieved through a clever combination of field (pXRF) and lab data, with pXRF providing the bulk of the data at low cost, on larger data sets and potentially with better reliability than lab-based campaigns based on a limited number of samples.
Bauxite samples collected with permission from currently active mining areas in the Parnassos-Ghiona Mts district were studied using both conventional (optical microscopy and powder XRD) and, for the first time in the literature, micro-scale advanced non-destructive spectroscopic techniques, in particular Laser μ-Raman. The results showed that the different bauxite types (diasporic or boehmitic) can easily be identified regardless of sample type (porous white-grey or massive red brown) by recording spectra in the low-wavenumber region (250 1/cm – 600 1/cm) where distinct bands of the natural AlOOH polymorphs are easily discernible (448 1/cm for diaspore and 362 1/cm for boehmite). The method described herein could equally be applied in the laboratory as well as in-situ at the mines for quick and accurate phase determination, in order to bypass the laborious and time-consuming indirect bulk techniques (such as XRD) routinely used to this date.
CRC LEME, in collaboration with Genalysis Laboratory Services, has investigated the effects of some of the routine laboratory treatments on spectral mineralogy, such as drying, crushing and pulping (particle size). In one specific study, regolith materials from a diamond drill intersection taken from the Jaguar Cu-Zn-Ag deposit, 4 km south of Teutonic Bore in the Eastern Goldfields Province of the Yilgarn Craton, were used. The main ore body is approximately 250 m below surface. The regolith materials, spanning a depth of 130 m, comprise colluvium-alluvium overlying saprolite, saprock and bedrock (basaltic composition). All of the samples were dried at 121 ° C before crushing and pulverising due to the presence of moist clay in the regolith samples that cause problems during preparation. The regolith materials were crushed to approximately 2 mm, to simulate chips, using a Boyd crusher and rotary sample splitter. One half of each sample was left as chips while the other half was pulverised to
The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications
of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS,
providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches
(e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing
and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical
field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.
Laser-induced breakdown spectroscopy (LIBS) is a simple, straightforward, and versatile form of atomic emission spectroscopy that focuses a rapidly-pulsed laser beam onto a sample to form a plasma containing its constituent elements and then uses spectral analysis of the emitted light to detect the elements present. In theory, LIBS is capable of qualitative, semi-quantitative, and quantitative analysis of all elements in the periodic table. LIBS can be performed in the laboratory or outside in the ambient environment for on-site analysis in situ; LIBS can also be used for rapid microscale compositional imaging. This review first presents a description of the LIBS technique and then discusses and illustrates through a historic literature review how LIBS has been used to analyze gases, natural waters, minerals, rocks, sediments, and soils. Given the persistent need of analytical instrumentation for the rapid chemical analysis of geologic materials in the field, and the capability of LIBS to analyze any type of sample in real time with little to no preparation, there is a vast potential for the routine application of LIBS across a broad spectrum of the geosciences that is as yet only minimally realized.
This article reviews nonconventional Raman spectroscopy techniques and discusses present and future applications of these techniques in the Earth and planetary sciences. Time-resolved spectroscopy opens new ways to limit or exploit luminescence effects, whereas techniques based on coherent anti-Stokes Raman scattering (CARS) or surface-enhanced Raman spectroscopy (SERS) allow the Raman signal to be considerably enhanced even down to very high spatial resolutions. In addition, compact portable Raman spectrometers are now routinely used out of the laboratory and are even integrated to two rovers going to Mars in the near future.
During recent years, important developments have been achieved in the application of laser induced breakdown spectroscopy (LIBS) for elemental imaging. The aim of this review is to report recent instrumental configurations, data processing methodologies and applications related to LIBS-based imaging. In the first section, different instrumental alternatives of LIBS for qualitative or quantitative imaging measurements are presented, including the scanning configuration, focusing systems, laser properties, and spectral detection tools. The second section reviews the different LIBS imaging data processing methodologies that have been proposed. Finally, the last section of this review reports the wide variety of laboratory applications that have benefited from LIBS mapping techniques, such as those in the biomedical, geological and industrial fields.
Mineral flotation processes are controlled by monitoring the grade of the present minerals. The performance of flotation can be greatly optimized by online assaying of the minerals in the slurry flows. However, online and quantitative mineral identification of the slurries is challenging. The major focus of this research is about measuring mineral contents from the elemental concentrations acquired by an on-stream slurry analyzer operating based on laser-induced breakdown spectroscopy (LIBS). A multivariate statistical method called partial least squares regression is employed to perform the elemental to mineral conversion. In this work, the samples under study come from an iron concentrator where knowledge about the grade of silicates and iron oxides are important for controlling the flotation plant. In total, the concentrations of six out of ten minerals were successfully estimated. This accomplishment provides quantitative knowledge about mineral contents from the nearly real-time assay data without any modification on the measurement setup or further instrumentation. This can lead to many benefits such as rapid control of concentrate quality, enhanced recovery and savings in money, time, energy and manpower. The proposed technique is applicable to all types of slurry samples.
Resource estimation for metals in mine tailings and ore deposits requires many samples, usually in the form of drill cores. In order to detect zones of metal enrichment or depletion as well as different lithological zones in such cores, two different core scanning methods were tested on three drill core metres from tailings of a former Pb-Zn mine to obtain chemical information. The results provide an objective basis for further sub-sampling of the taken drill cores and help reduce the amount of samples and therefore the costs for further investigations.For the determination of element concentrations a prototype of a core scanner working with laser-induced breakdown spectroscopy (LIBS) was tested and the results were compared to data from a commercially available ITRAX core scanner, working with energy-dispersive X-ray fluorescence (EDXRF). Apart from a smooth surface, no complex sample preparation was necessary. Peak intensities of selected elements determined by the two scanners were calibrated by means of linear regression (LR) and partial least squares (PLS) regression with respect to bulk geochemical wavelength-dispersive XRF (WDXRF) analysis results of representative core samples. The application of PLS compensates for matrix effects in LIBS and EDXRF and improves prediction accuracy for most elements, compared to LR. In general, prediction ability of PLS models is slightly higher for EDXRF results than for LIBS. The advantage of the LIBS core scanner is the high spatial resolution and the ability to create two-dimensional (2D) element distribution images as well as phase or mineral distribution maps of the drill core at larger scales. Within the analysed tailing cores metal-rich layers with concentrations up to a maximum of 2.2% Pb + Zn + Cu, could be detected by both core scanning methods. Since these layers are not visible by the human eye, the used core scanning methods are appropriate methods for mineral exploration.
After a brief introduction to laser induced breakdown spectroscopy (LIBS), this chapter outlines the historical development of the technique. From the early founders to the current contributors, their significant advances are acknowledged, described, and referenced. Knowing this history helps researchers to avoid duplication of something already discovered, and provides leads to the original literature. Laser plasmas initiated on a variety of media are illustrated, and generic LIBS spectra are introduced. The chapter concludes with pertinent facts, such as the volume of publications per year, publication density for applications, significant recent reviews, and the spectral regions in which LIBS has been utilized.
Laser-induced breakdown spectroscopy (LIBS) has become an established analytical atomic spectrometry technique and is valued for its very compelling set of advantageous analytical and technical characteristics. It is a rapid, versatile, non-contact technique, which is capable of providing qualitative and quantitative analytical information for practically any sample, in a virtually non-destructive way, without any substantial sample preparation. The instrumentation is simple, robust, compact, and even enables remote analysis. This review attempts to give a critical overview of the diverse progress of the field, focusing on the results of the last five years. The advancement of LIBS instrumentation and data evaluation is discussed in detail and selected results of some prominent applications are also described.
In this investigation, Raman spectroscopy with 1064 and 632.8 nm excitation was used to investigate real mineral samples of bauxite ore from mines of Northern Brazil, together with Raman mapping and X-rays diffraction. The obtained results show clearly that the use of microRaman spectroscopy is a powerful tool for the identification of all the minerals usually found in bauxites: gibbsite, kaolinite, goethite, hematite, anatase and quartz. Bulk samples can also be analysed, and FT-Raman is more adequate due to better signal-to-noise ratio and representativity, although not efficient for kaolinite. The identification of fingerprinting vibrations for all the minerals allows the acquisition of Raman-based chemical maps, potentially powerful tools for process mineralogy applied to bauxite ores.
Building a Hyperspectral library and its incorporation into sparse unmixing for mineral identification
- T Bui
- B Orberger
- S Blancher
- A Mohamed-Djafari
- H Pillière
- A Salaün
- X Bourrat
- N Maubec
- T Lefevre
- C Rodriguez
- S Grazulis
- C Duée
- D Harang
- T Wallmach
- D Chateigner
- Le Guen
Bui, T, Orberger, B, Blancher, S, Mohamed-Djafari, A, Pillière, H, Salaün, A, Bourrat, X, Maubec, N, Lefevre, T, Rodriguez,
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