ISO Simplified Borate Fusion / WDXRF Analytical Method for Iron Ore Including Total Iron Analysis: Part 2

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1 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN ISO Simplified Borate Fusion / WDXRF Analytical Method for Iron Ore Including Total Iron Analysis: Part 2 Mathieu Bouchard, Alex Milliard, and Sebastien Rivard Corporation Scientifique Claisse, Québec, QC, Canada S. Ness Intertek Genalysis, Perth, Australia ABSTRACT A very efficient analytical method using an automated fusion machine as sample preparation tool and a Wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometer for the determination of all the elements of interest for the iron ore industry has been optimized from the ISO standard method. This updated method allows for the simplification of both laboratory and spectrometry processes and so, in comparison with the original ISO method, becomes less restrictive in practice. This method was used to prepare a large variety of iron ores and exploration samples from all over the world. Results of the prevailing XRF application based on pure oxide standards as described in the ISO standard method are compared to the results of a unique XRF calibration application based on Certified Reference Materials (CRMs) for iron ores and iron ores exploration materials. The universal sample preparation fusion method for iron ores and exploration samples developed during the first phase of this project was used to select and evaluate a set of CRMs. Selected throughout the world from well recognized sources, the chosen set of CRMs allows a wide coverage for all the elements of interest of the iron ore industry, excluding tin oxide. This fusion method allows a matrix match for materials from different origins. A critical evaluation of precision and accuracy has been performed against the ISO standard method. Reference materials not included in the calibration (Control samples) was also investigated for accuracy evaluation. Furthermore, comparisons will be made between the data collected from this fusion method implemented in combination with a Bruker S4 Explorer WDXRF Spectrometer, and the analytical requirements of ISO. All deviations from the prevailing standard method parameters (calibration, standards, flux, Fluxer, etc.) will also be pointed out and discussed.

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN INTRODUCTION Whether it is dealing with high-grade hematite, low-grade hematite or magnetite, assays performed on exploration sample, concentrate, internal standard and/or reference material, will always be of paramount financial importance when it comes to the survival of a mining company. In this regard, the existence of a small bias associated with the total iron analysis process could result in millions of dollars in revenue losses for mining companies given the fact that their products are sold in millions of tons. The current International Standard Method, which remains widely accepted among peers, is the one entitled: Iron ores -- Determination of Various Elements by X-ray Fluorescence Spectrometry -- Part 1: Comprehensive Procedure (ISO :2003). However, there are a number of unveiled and corroborated limitations to the predominant version of this standard; it lacks adaptability when coping with recent advances in the fields of sample preparation by fusion and Wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometry. The preparation of standards made of pure oxides is a complex and time consuming task and the calibration ranges do not cover for the exploration samples. The industry needs a single calibration for both the iron ore products and the exploration samples and forced us to rethink the calibration methodology that is described in the standard method. Good Certified Reference Materials (CRMs) from this industry are readily available and allow the evaluation of a simplified calibration strategy to the usual mixes of pure oxides. Using CRMs from worldwide sources that cover both the iron ores and the exploration samples as required by the industry, makes the matrix covered by this application much more complex. It also makes using pressed powder much more challenging due to the difficulties of matrix matching the calibration standards and the samples from the ores and exploration samples. Taking this information into account, using the borate fusion preparation allows for a more accurate analysis and requires less calibration curves because the technique removes particle size and mineralogy effects [1, 2]. For these reasons, and also to facilitate the lab work needed for the calibration, it is desirable to use a single fusion method, for the preparation of all the iron ore types and most of the common exploration sample types, combined with WDXRF, to comply with the ISO analytical performance requirements. To reach these objectives, a robust analytical method using an automated fusion machine as sample preparation tool and a WDXRF spectrometer has been optimized from the methodology described in the ISO standard method for the quantification of all elements of interest in the iron ore industry. This single method was used to prepare fused disks from more than 150 types of materials (CRMs and various samples) covering a very vast range of compositions. A set of CRMs from more than 10 suppliers of different origins were selected as calibration standards and allowed a matrix match for worldwide origin iron ores. The performance evaluation was completed using the new calibration approach and according to the instructions provided by the International Organization for Standardization (ISO), through the standard method for analysis of iron ores by X-ray fluorescence: ISO [3]. To better evaluate the accuracy of the CRM based calibration, a pure oxide calibration was prepared according to the ISO guidelines and served as a reference.

4 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN EXPERIMENTAL -Apparatus and instrumental conditions A Claisse M4 TM propane fired automatic Fluxer was used to generate all calibration standard fusion glass disks, but sample preparation for the precision evaluation were run using both the M4 TM and the TheOx Fluxers; The M4 TM auto-regulating gas system fluxer and the TheOx electric fluxer have both been designed with pre-set fusion programs allowing for the most repeatable and reproducible fusion conditions as well as the capability to retain the volatile elements.. A Fisher Scientific drying oven was used for moisture determinations. This method was used for all the samples and consisted in drying at 105 C in a clean ceramic/porcelain crucible for 120 minutes. A Fisher Scientific Isotemp programmable muffle furnace was used for the Loss On Ignition (LOI) determinations. The LOI method used for all the samples was an ignition at 1000 C in a clean ceramic/porcelain crucible for 60 minutes. This method was completed after the moisture determination, using the same crucible and dried sample. Table 1. Spectrometer Operation Parameters Element / Line kv ma Crystal Collimator Detector a Peak ( 2 ) Time (s) Bkd 1 b ( 2 ) Bkd 2 b ( 2 ) Time bkd (s) Fe K LiF 220 Fine SC Si K PET Fine FC Ca K LiF 200 Coarse FC Mn K LiF 200 Coarse SC Al K PET Coarse FC Ti K LiF 200 Coarse FC Mg K XS-55 Coarse FC P K Ge Coarse FC S K Ge Coarse FC K K LiF 200 Coarse FC Sn L LiF 200 Fine FC V K LiF 200 Coarse FC Cr K LiF 200 Coarse SC Co K LiF 200 Coarse SC Ni K LiF 200 Coarse SC Cu K LiF 200 Coarse SC Zn K LiF 200 Coarse SC As K LiF 200 Coarse SC Pb L LiF 200 Coarse SC Ba L LiF 200 Coarse FC Na K XS-55 Coarse FC Sr K LiF 200 Fine SC Zr K LiF 200 Coarse SC a FC = gas flow proportional counter; SC = Scintillation Counter b Bkd 1 and Bkd 2 = position value for the needed background when used

5 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN A Bruker-AXS S4 Explorer sequential WDXRF spectrometer with a rhodium endwindow X-ray tube was used for data generation. A 34 mm collimator mask and vacuum were used for all the measurements. Spectrometer analytical conditions, peak-line, background measurements, background position, pulse-height, counting time and others were selected and optimized following the guidelines of ISO and by wavelength step-scanning of selected standard disks. The spectrometer set-up and performance evaluation guide also included in the ISO were used to verify proper spectrometer operation. The optimal spectrometer analytical conditions for the measurement of all elements are listed in Table 1. -Sample preparation method The optimization of the sample preparation was performed on both the iron ore and the exploration samples using a majority of parameters described in ISO , still some parameters had to be modified to achieve such a wide calibration. The platinum ware used for this project was made from 95% platinum and 5% gold. This alloy is accepted by the ISO standard and for decades, it has been the most commonly used material for this purpose. As described in the ISO test method, it was proven that our optimized fusion method can be used to prepare glass disks with a diameter ranging between 32 to 40 mm. Nevertheless, all glass disks produced for this application had a 40 mm diameter. The sample-to-flux ratio was as described in the ISO standard and kept at 1: Sample can be fused on an original basis or on a dry basis. The "Catch Weight" correction used for weighing was applied as described in the standard method. The standard method recommends using one of the three following fluxes: Pure sodium tetraborate, pure lithium tetraborate (LiT) or a mix of 35% lithium tetraborate with 65% of lithium metaborate (LiM). The flux used for this study was 50% lithium tetraborate with 50% of lithium metaborate which made the preparation of exploration samples easier without decreasing the success rate of the iron ore preparation. The oxidizer recommended by the standard method is Sodium Nitrate (NaNO 3 ), but after evaluating three different oxidizers (NaNO 3, LiNO 3 and NH 4 NO 3 ), ammonium nitrate (NH 4 NO 3 ) was selected for this project since it allowed analyzing Sodium (Na) on top of obtaining very precise results. This substitution was made because Na is now considered as an element of interest in the iron ore related materials. The ammonium iodine can be used as a Non-Wetting Agent (NWA) when needed, as stated in the standard method. However, the methodology described in this paper does not recommend using NWA. It has also been determined that using a VortexMixer TM to mix the sample and flux homogeneously prior to the fusion is more advantageous than using a glass rod, as it minimizes the possibility of material loss. The VortexMixer TM speed was controlled to avoid any loss of material because variance from the ratio of flux to sample weight causes error in the results [4]. The temperature range of the fusion process was kept between 1000 and 1050 C. It is well known that over the critical temperature of 1050 C, flux [5] and other compounds like SO 3 [2] begin to volatilize without consistency and can change the sample-to-flux ratio. Finally, the fusion process had pre-programmed steps with fixed times in order to obtain the highest level of precision and accuracy. The study presented in the following paper proves that a high level of precision is attainable for this sample preparation using both gas powered and electric powered fully automatic fusion instruments.

6 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN Global sample preparation method A 40 mm diameter, 1 mm thick shallow mold 1 was used to eliminate the curvature effect, which can occur after multiple heating cycles. Pure grade pre-fused flux * composition of 50.0% lithium tetraborate, 50.0% lithium metaborate was selected to increase the homogeneity and make stable glass disks. The maximum fusion temperature used for this fusion is 1050 C for both gas and electric Fluxers. The cooling process was achieved with forced air for 5 minutes. -Step by step procedure It is important to understand that this method can fuse "as received" basis samples or dried basis samples. If the disks are made using dried samples, the LOI determination must be established in parallel to the fusion process for spectrometry correction. If the "as received" basis samples are preferred over the dry basis samples, a weigh factor will have to be calculated from the moisture determination in parallel to establishing the LOI determination for spectrometry correction. For a 40 mm glass preparation, weigh 0.66 g of sample in a clean and dry Pt/Au crucible. Report the value of the weighed sample portion with ± g tolerance before any further calculations. Tare the analytical scale. Add 0.40 g of NH 4 NO 3 with a tolerance of ± 0.01 g on top of the sample portion. Tare the scale again. Then add 6.80 g of Claisse LiT/LiM: 50.0/50.0, Pure Grade Flux on top of the sample/oxidizer portion. Report the value of the weighed flux portion with ± g tolerance before any further calculations. Use a VortexMixer TM to mix the sample/oxidizer with the flux. The VortexMixer TM speed must be controlled to avoid any material loss, because variance from the ratio of flux to sample weight causes error in the results [4]. Place the crucible with its preparation on the selected fusion equipment. Utilize the appropriate optimize fusion program for the selected fusion equipment. Analyze the glass preparation as soon as possible and/or protect the obtained glass disk in a safety container on a vacuumed desiccator. -Robustness of the fusion method More than 160 different samples from 12 renowned mining companies and reference materials from more than 10 recognized reference material manufacturers were fused using the global project. This analytical method for iron ore products and exploration samples revealed good efficiency to prepare homogenous and stable lithium borate glass disks with all of the materials; it had limitations only for the preparation of iron ore related materials that contained relatively high level of Copper (Cu). When the content of this element was higher than 500 to 700 ppm, the glass disk had a tendency to stick to the mold and often lead to disk cracking. For this reason, it was determined that high Copper 1 Available at Corporation Scientifique Claisse

7 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN iron ores needed a different sample preparation fusion methodology that includes a NWA to avoid having the disk to stick to the mold. -Preparation for calibration, selection of control samples Pure Oxide Calibration: For this part of the work, we referred directly to the ISO standard method [3]. Only a few modifications were brought to the described procedure. First, we added a binary standard made of 30% Al 2 O 3 and 70% of Fe 2 O 3 to cover a wider range of exploration sample. We then prepared the synthetic calibration standard to add low concentration sodium points on the calibration curve. Finally, two binary overlap calibration standards were modified from 10% Cr 2 O 3 : 90% SiO 2 and 10% ZnO: 90% SiO 2 to 2% Cr 2 O 3 : 98% SiO 2 and 2% ZnO: 98% SiO 2, because they were impossible to fuse with the optimized automated fusion sample preparation. The only way to prepare these two calibration standards in their original composition was by increasing the fusion time and/or by increasing the temperature of the method. It was preferred to modify the calibration standard compositions instead of modifying the sample preparation method in a way which would of decreased the productivity and/or the precision of the sample preparation method. Certified Reference Materials Calibration: As previously mentioned, more than 80 CRM glass preparations were produced and evaluated only to select the best set of standards for the calibration of the borate fusion and XRF analytical application for iron ores and the related exploration samples. Out of all the evaluated CRMs, 16 were selected as iron ore calibration standards and 12 were selected as exploration calibration standards. Table 2 shows the compound concentrations for the two separate CRM sets as well as for the global application. The concentrations of the compounds of interest are presented in element form or oxide form depending on the market requirements. Table 2 also presents the composition of the selected control samples. The selected CRMs originated from the following list of producers: - Bureau of Analysed Samples Ltd (BAS) - CCRMP, CANMET Mining and Mineral Sciences Laboratories - China National Analysis Center for Iron and Steel - Dillinger Hütte Laboratory - European Committee for Iron and Steel Standardization (ECISS) - European Coal and Steel Community (ECSC) - Geological Institute for Chemical Minerals - Geostats Pty Ltd - Institut de Recherche de la Sidérurgie (IRSID) - Institute for Geology Ore Deposits, Petrography, Mineralogy and Geochemistry (IGEM) - National Institute of Standards & Technology (NIST) - Swedish Institute for Metals Research

8 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN Table 2. CRM sets compound concentration and control samples composition Iron Ore Exploration Global Control a Control a Control a Control a Compound Min. Max. Min. Max. Min. Max Fe (%) SiO 2 (%) Al 2 O 3 (%) TiO 2 (%) Mn (%) CaO (%) P (%) S (%) MgO (%) K 2 O (%) Na 2 O (%) V (%) N/A N/A Cr (%) N/A Co (%) N/A Ni (%) N/A Cu (%) N/A Zn (%) N/A As (%) N/A N/A N/A Sr (%) N/A N/A Zr (%) N/A N/A Ba (%) N/A N/A Pb (%) N/A N/A N/A a Control sample: One or more certified RM, not used in the calibration and having a composition within the calibration range for each element to be analyzed. When using only one validation certified RM, select a sample in the middle of the concentration ranges. When several validation CRMs are used, select samples covering high and low values.

9 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN RESULTS AND DISCUSSION -Calibration For the calibration of the WDXRF instrument and further evaluation of precision and accuracy of this borate fusion and XRF analytical method, selected CRMs were prepared in duplicates using an M4 TM gas Fluxer to verify the precision of the sample preparation over the wide range of composition that was covered. -Precision and accuracy For the precision evaluation, 12 glass disks were produced using both the M4 TM gas Fluxer and the TheOx electric Fluxer. All fusion positions of both instruments were used to produce the complete set of glass disks of the precision evaluation. The sample selected for the precision evaluation was a high iron magnetite known to be relatively difficult to prepare using fusion. The accuracy evaluation was conducted using four control samples which were CRMs that were not included in the calibration. Table 3. ISO precision test results Compound Concentration ISO d Limit XRF M4 TM TheOx (%) Fe SiO Al 2 O TiO Mn CaO P S <LLD N/A N/A N/A N/A MgO K 2 O Na 2 O N/A V Cr Co Ni Cu Zn As <LLD N/A N/A N/A N/A Sr N/A 0, Zr N/A 0, Ba Pb

10 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN It is important to note that the ISO limits for precision are not fixed. The ISO limits are variable as a function of the concentration of the element in the sample analyzed. The ISO precision test was applied as described in the method [3]. The standard deviation limit calculated for all the elements is shown in Table 3. The precision results of the spectrometer are presented as well as the precision of the M4 TM gas Fluxer and the TheOx electric Fluxer. These results were compared to the ISO precision limits. The values obtained for all the compounds met the specified limits. The ISO method refers to a trueness test for the accuracy evaluation. This test is complex even for experienced analysts. For this reason the accuracy results are presented in the following tables as the maximum deviation between certified values and results. Accuracy validation was examined on the 2 different calibration curves: a first calibration based on pure oxides fused into calibration glass disks acting as the reference methodology as described in the ISO test method and a second calibration based on CRMs fused into glass disks. This allowed evaluating the performance of the CRM based calibration against the reference methodology. The maximum deviation was calculated using two different preparations for the four control samples. Table 4. Control sample 1 accuracy evaluation JK 42 Certified Max. Dev. Max. Dev. Compound Values (%) (%) (%) Pure oxides CRMs Fe SiO Al 2 O TiO Mn CaO P S MgO K 2 O Na 2 O V Cr Co Ni Cu Zn As N/A N/A N/A Sr N/A N/A N/A Zr N/A N/A N/A Ba N/A N/A N/A Pb N/A N/A N/A LOI N/A N/A N/A Table 5. Control sample 2 accuracy evaluation GIOP-37 Certified Max. Dev. Max. Dev. Compound Values (%) (%) (%) Pure oxides CRMs Fe SiO Al 2 O TiO Mn CaO P S MgO K 2 O Na 2 O V Cr <LLD <LLD Co Ni Cu Zn As Sr N/A Zr N/A Ba Pb LOI

11 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN Table 6. Control sample 3 accuracy evaluation NIST SRM 692 Certified Max. Dev. Max. Dev. Compound Values (%) (%) (%) Pure oxides CRMs Fe SiO Al 2 O TiO Mn CaO P S MgO K 2 O Na 2 O V N/A N/A N/A Cr N/A N/A N/A Co N/A N/A N/A Ni N/A N/A N/A Cu N/A N/A N/A Zn N/A N/A N/A As N/A N/A N/A Sr N/A N/A N/A Zr N/A N/A N/A Ba N/A N/A N/A Pb N/A N/A N/A LOI N/A N/A N/A Table 7. Control sample 4 accuracy evaluation FER-2 Certified Max. Dev. Max. Dev. Compound Values (%) (%) (%) Pure oxides CRMs Fe SiO Al 2 O TiO Mn CaO P S MgO K 2 O Na 2 O V N/A N/A N/A Cr Co <LLD <LLD Ni Cu Zn As N/A N/A N/A Sr N/A Zr N/A Ba Pb N/A N/A N/A LOI N/A N/A N/A The accuracy results presented in the four previous tables demonstrate that both calibration strategies allow for similar accuracy levels for all the evaluated elements and over the different types of iron ore related material. The great benefit of using a CRM based calibration is the simplified calibration work as the CRMs are fused into glass disks in parallel of two simple operations: drying and ignition. The pure oxide calibration strategy as described in the ISO test method necessitates many steps in order to prepare all the mixes of the different oxide powders to produce the various calibration points (drying of all powders, ignition of some powders, weighing of all powders to produce all the mixes in the exact ratio, etc.). It is time consuming as well as expensive to buy all the oxide powders in analytical grade. It also opens the door to many manipulation errors that can bring bias in the analysis.

12 Copyright JCPDS-International Centre for Diffraction Data 2014 ISSN CONCLUSIONS To match the actual needs and expectations of the iron ore industry regarding the elemental characterization of iron ore materials and exploration minerals, a new borate fusion and XRF application was evaluated through this study. Consisting in a single method of preparation by fusion, it allows fusing the various iron ore types and the exploration samples normally found in this industry in a lithium borate glass disk. A CRM based calibration proved to provide the same level of precision and accuracy for iron ore samples when compared to the traditional pure oxide calibration as recommended in the ISO international test method. In addition to providing high analytical performance in line with the ISO analytical targets, the CRM based calibration allows for extended calibration ranges that cover both the iron ores and the exploration samples and also makes the analysis of Sodium (Na) possible and easier. Finally, this alternative CRM based application significantly simplifies the preparation of the calibration standard fused disks which allows saving time and minimize the work needed to prepare the application. It was also proven that both the M4 TM gas Fluxer and the TheOx electric Fluxer offer the same versatility and ability to fuse the full range of samples all while offering similar analytical performances. References 1. ANZELMO, J. A., The Role of XRF, Inter-Element Corrections, and Sample Preparation Effects in the 100-Year Evolution of ASTM Standard Test Method C114, Journal of ASTM International, Vol. 6, No. 2, Paper ID JAI101730, available online at , pp SPANGENBERG, J. and FONTBOTÉ, L., X-Ray Fluorescence Analysis of Base Metal Sulphide and Iron-Manganese Oxide Ore Samples in Fused Glass Disk, X-Ray Spectrometry, Vol. 23, 1994, pp ISO :2003 (First edition, ), Iron ores Determination of various elements by X-ray fluorescence spectrometry Part 1: Comprehensive procedure (ISO :2003), 72 pp. 4. BÉRUBÉ, L., RIVARD, S., ANZELMO, J. A., XRF Fusion Precision with TheAnt, International Cement Review, March, 2008, 4 pp. 5. LOUBSER, M., STRYDOM, C., and POTGIETER, H., A Thermogravimetric Analysis Study of Volatilization of Flux Mixtures Used in XRF Sample Preparation, X-Ray Spectrom. 2004; 33: , Published online January 29 th 2004 in Wiley InterScience ( DOI: /xrs.700