Geochemical Fingerprinting of Coltan Minerals Using LIBS
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Geochemical Fingerprinting of Coltan Minerals Using LIBS www.AppliedSpectra.com Introduction Conflict minerals are minerals mined in areas of armed conflict or human rights abuses. The United States' Dodd- Frank Wall Street Reform and Consumer Protection Act, signed into law in July 2010, requires manufacturers to disclose whether conflict minerals from the Democratic Republic of Congo (DRC) are used in their products [1- 3]. Conflict Minerals are used in a wide variety of products, such as mobile phones, laptops, medical devices, and jewelry. All companies that manufacture goods containing gold, tin, tungsten and tantalum are affected. These so-called “conflict minerals” are used in a wide variety of products, such as mobile phones, laptops, medical devices and jewelry. The rules require “reasonable inquiries” into the country of origin of these rare earth metals and minerals. Four most commonly mined conflict minerals are cassiterite (for tin), wolframite (for tungsten), coltan (for tantalum), and gold ore. The electronic device manufacturers, whose products use elements from these minerals, may be required to supply the country of origin information for source minerals. In many cases, tracing the supply chain back to the smelter facility can be extremely difficult and time-consuming. LIBS (Laser Induced Breakdown Spectroscopy) has previously been used to determine chemical composition in a number of geological materials, including silicates, carbonates and lithium [4-7]. Columbite-tantalite mineral ores, also known as coltan, contain significant quantities of tantalum and niobium. This application note describes a rapid and environmentally friendly method for classifying the geographical source of coltan mineral ores using Applied Spectra's J200 LIBS Instrument.
Transcript of Geochemical Fingerprinting of Coltan Minerals Using LIBS
Geochemical Fingerprinting of Coltan Minerals Using LIBS
www.AppliedSpectra.com
IntroductionConflict minerals are minerals mined in areas of armed conflict or human rights abuses. The United States' Dodd-Frank Wall Street Reform and Consumer Protection Act, signed into law in July 2010, requires manufacturers to disclose whether conflict minerals from the Democratic Republic of Congo (DRC) are used in their products [1-3].
Conflict Minerals are used in a wide variety of products, such as mobile phones, laptops, medical devices, and jewelry.
All companies that manufacture goods containing gold, tin, tungsten and tantalum are affected. These so-called “conflict minerals” are used in a wide variety of products, such as mobile phones, laptops, medical devices and jewelry.
The rules require “reasonable inquiries” into the country of origin of these rare earth metals and minerals. Four most commonly mined conflict minerals are cassiterite (for tin), wolframite (for tungsten), coltan (for tantalum), and gold ore. The electronic device manufacturers, whose products use elements from these minerals, may be required to supply the country of origin information for
source minerals. In many cases, tracing the supply chain back to the smelter facility can be extremely difficult and time-consuming.
LIBS (Laser Induced Breakdown Spectroscopy) has previously been used to determine chemical composition in a number of geological materials, including silicates, carbonates and lithium [4-7]. Columbite-tantalite mineral ores, also known as coltan, contain significant quantities of tantalum and niobium.
This application note describes a rapid and environmentally friendly method for classifying the geographical source of coltan mineral ores using Applied Spectra's J200 LIBS Instrument.
Applied Spectra, Inc.46665 Fremont Blvd.Fremont, CA 94538
Telephone: + 1 510.657.7679 [email protected]
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Geochemical Fingerprinting of Conflict Minerals Using LIBS
Operating Parameters
Applied Spectra Inc.’s J200 LIBS Instrument
• 266 nm Nd:YAG laser (ns) and an ICCD detector (HP model) detector
• Applied Spectra Axiom Software
• FlexTM sample chamber
• Coltan samples collected from three granite pegmatite fields in North America:
Set 1 - Starret pegmatite in central Maine, U.S.Set 2 - Pack Rat and Beebe Hole pegmatite fields of San Diego Count, CA, U.S.Set 3 - Moose pegmatite in Northwest Territories, Canada.
Sample Analysis
The characteristic LIBS spectra for the coltan ore was obtained using the J200 LIBS Instrument (HP model) with a 2 x 2 sampling grid pattern. The spacing between each sampling location was 0.5 mm (Figure 1).
Forty laser pulses were applied at each location on the sample. The first fifteen laser pulses at each location were used to self-clean the surface of the ore. The spectra from the remaining 25 laser shots were averaged for analysis.
Figure 1. J200 LIBS Instrument Axiom Software GUI showing high resolution sample image and measured LIBS spectrum. Green dots indicate the locations of laser sampling.
Applied Spectra, Inc.46665 Fremont Blvd.Fremont, CA 94538
Telephone: + 1 510.657.7679 [email protected]
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Geochemical Fingerprinting of Conflict Minerals Using LIBS
Data were taken in the spectral range from 250 to 490 nm (Figure 3) to include LIBS emission lines associated with signature elements associated with coltan minerals. Emission wavelengths of these elements are shown in Table 1.
Table 1. Key elements for coltan minerals and their emission lines.
Figure 2. Identification of tantalum (Ta) peak ID is performed by TruLIBSTM database.
Chemometric analysis was performed on the LIBS spectra to produce the cluster plot and sample classification result. Partial Least Square Discriminant Analysis (PLSDA) was the statistical method used to discriminate among coltan ores of different geographic origins. Figure 4 shows the PCA plot. An individual point in the figure is the projection of each of 100 LIBS spectra collected per sample. The 2D PCA plot shows that most of the within-class spectra cluster together, with only a single substantial outlier for the Pack Rat/Beebe samples.
The classification study used a leave-one-sample-out (LOSO) cross-validation approach. The spectra from the ith sample are held out of the training data for the classification sample library. This ith sample was then used as the test data. Only four PLSDA components were needed to achieve near perfect classification of tested coltan samples into the correct group.
Figure 3. Representative LIBS spectra in the spectral range from 250 to 490 nm for coltan samples from three locations.
Applied Spectra, Inc.46665 Fremont Blvd.Fremont, CA 94538
Telephone: + 1 510.657.7679 [email protected]
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Geochemical Fingerprinting of Conflict Minerals Using LIBS
ConclusionThe Applied Spectra J200 LIBS Instrument was effectively used to distinguish and identify the geographical origin of coltan ores collected from different regions of North America. Successful classification
results for these coltan samples were possible by developing an effective PLSDA model based on LIBS emission lines of signature elements such as Fe, Mn, Nb, Ta, W, Ti, and Zr. With on-board statistical algorithms for effective material classification, the J200 LIBS Instrument provides a powerful platform to determine source or origin for many geological samples.
References1. "Conflict Minerals, Proposed Rule" Federal Register 75 (23 December 2010): 80948- 80975.
2. “SEC’s Proposed Rules on Conflict Minerals Disclosure Could Have Broad Impact”, January 2011, Cooley Alert, 2011 Cooley, LLP 3000 El Camino Real, Palo Alto, CA 94306.
3. Hayes, K. and Burge, R. (2003) Coltan Mining in the Democratic Republic of Congo: How tantalum-using industries can commit to the reconstruction of the DRC: Fauna and Flora International (Cambridge, UK), 60p.
4. Fabre, C., Boiron, M.-C., Dubessy, J., Chabiron, A., Charoy, B., and Crespo, T.M., (2002), Advances in lithium analysis in solids by means of laser-induced breakdown spectroscopy: an exploratory study, Geochimica et CosmochimicaActa, 66: 1401-1407.
5. L. Brostoff, J. Gonzalez, P. Jett and R. E. Russo, (2009), Trace Element Fingerprinting of Ancient Chinese Gold with Femtosecond Laser Ablation-Inductively Coupled Mass Spectrometry, Journal of Archaeological Science, 36, 2, 461-466).
6. Harmon, R.S., Remus, J.J., McManus, C., DeLucia, F.C., Gottfried, J., and Miziolek, A.W. (2009), LIBS Analysis of Geomaterials: Geochemical Fingerprinting for the Rapid Analysis and Discrimination of Minerals: Applied Geochemistry, 24:1125-1141.
7. Harmon, RS, Shughrue, KM, Remus,JJ. ,Wise, MA, Hark, RR, and East, L, Can the Provenance of the Conflict Minerals Columbite and Tantalite be Ascertained by Laser-Induced Breakdown Spectroscopy?, Analytical and Bioanalytical Chemistry (in press).
Figure 4. PCA Analysis. PCA plot of LIBS spectra for coltan ores.
Table 2. Coltan mineral classification results. Percentage of LIBS data from each sample assigned to a particular geographical location. indicates 75-100% correct classification; indicates 50-74% correct classification.
Table 2 lists the percentage of LIBS measurements for each coltan mineral that was assigned to a specific geographical origin. The PLSDA model produced excellent results for identifying coltan minerals to their correct geographical source.
