EDXRF Analysis of Iron Ores as Fused Beads

Iron ore is a key mineral present on Earth. Due to the increasing demand in the steel industry for this mineral, the fact that the production process, or the final product, is negatively affected by interference of the components present in the iron ore, is a significant issue.

This necessitates monitoring the chemical composition of iron ores in order to control the mining process (Figure 1) and improve the feeding process of melting furnaces during the manufacture of steels.

Open pit mining of iron ore

Figure 1. Open pit mining of iron ore

In iron ore samples, it is necessary to monitor a number of elements such as P, S, K, Mn, Mg, Ca, Ti, Al, Si, in addition to the major element Fe. Albeit the concentration of some of these elements is very low, they have a significant influence on the steel production process and the final product quality.

The S2 RANGER is an energy dispersive X-ray fluorescence (EDXRF) spectrometer that can analyze all of these major and minor elements directly, providing an accurate means of controlling the mining process as well as any subsequent production processes. This article demonstrates the analytical performance of the S2 RANGER to analyze iron ore samples prepared as fused beads.

Instrumentation

S2 RANGER is an all-in-one, benchtop spectrometer featuring a user-friendly TouchControl™ interface, an XFlash® silicon drift detector (SDD) and a Pd target X-ray tube. The ability of the XFlash detector to handle high count rates enables very accurate and precise results by reducing the statistical errors.

Additionally, the outstanding energy resolution of the XFlash detector allows distinguishing different elements and ensures detecting even elements of small concentrations alongside the main elements. A characteristic spectrum of an iron ore sample is shown in Figure 2, clearly resolving all of the elements present in the sample.

Spectrum of an iron ore sample in the energy range of 1.2 to 2.7keV

Figure 2. Spectrum of an iron ore sample in the energy range of 1.2 to 2.7keV

Experimental Procedure

Sample Preparation

The samples were prepared as fused beads so that iron ores obtained from different mining sites can be measured due to the elimination of their mineralogical effects. A drying oven was used to dry the standards at 110°C for 1h.

After mixing 1g standard material with 10g flux (Lithium Tetraborate 66 % + Lithium Metaboarate 34 % + LiBr 0.2 %), the fusion machine TheOx® from Claisse®, Quebec, Canada, was employed to prepare the fused beads, using the pre-installed 'Iron Ore' method.

Measurement Parameters

After defining two measurement regions, the optimization of the tube current was performed. The tube current was then fixed to obtain maximum count rate for the different elements. The detailed measurement parameters are summarized in Table 1. All measurements were carried out under vacuum.

Table 1. Measurement parameters for the different elements

Elements Tube voltage [kV] Tube current [µA] Filter Measurement time [s]
Mg, Al, Si, P, S 10 1350 None 100
K, Ca, Ti, Mn, Fe 40 275 500 µm Al 100

Calibration

The calibration for the elements was performed using a set of 15 international certified reference materials (CRMs). The concentration ranges of the different iron ore CRMs utilized to perform the calibration are presented in Table 2. The standard deviation (SD) for the calibration curves of the various elements present in the iron ore is also given in Table 2, showing the accuracy of the calibration.

Table 2. Concentration ranges used for the iron ore calibration

Element Minimum Concentration [%] Maximum Concentration [%] Standard deviation of calibration curve [%]
Fe2O3 39.4 95.6 0.27
SiO2 1.40 25.5 0.07
TiO2 0.022 10.2 0.03
Al2O3 0.13 10.3 0.08
CaO 0.015 9.51 0.04
MgO 0.017 6.17 0.08
P2O5 0.009 2.63 0.01
SO3 0.005 2.27 0.02
Mn3O4 0.022 1.94 0.01
K2O 0.003 1.83 0.03

The low SD values obtained illustrate the high performance that can be delivered by the system. The calibration curves for the major oxides such as Fe2O3 and SiO2 are shown in Figures 3 and 4, respectively. The calibration curve for the P2O5 in the lower concentration range is depicted in Figure 5.

Calibration curve for Fe2O3

Figure 3. Calibration curve for Fe2O3

Calibration curve for SiO2

Figure 4. Calibration curve for SiO2

Calibration curve for P2O5

Figure 5. Calibration curve for P2O5

Experimental Results

Several certified reference materials were measured and evaluated in order to demonstrate the accuracy of the calibration for iron ore samples. Table 3 compares the measured and certified concentrations for CRM SX11-36 and NCS 19003b from this accuracy test.

Table 3. Accuracy test of iron ore calibration with two different CRMs

Element Certified conc. [%] Measured conc. [%] Certified conc. [%] Measured conc. [%]
Fe2O3 93.99 94.15 85.09 85.19
SiO2 3.35 3.30 1.4 1.31
TiO2 0.023 0.041 10.21 10.14
Al2O3 0.345 0.337 3.36 3.40
CaO 0.37 0.33 0.055 0.089
MgO n.a. < 0.01 1.34 1.28
P2O5 0.017 0.023 0.02 0.023
SO3 0.005 0.004 0.032 0.032
Mn3O4 1.68 1.70 0.462 0.452
K2O 0.03 0.09 n.a. 0.017

The standard reference material CRM SX56-16 was measured for 10 times to prove the precision of the system. Unloading and reloading of the sample into the measurement chamber was done for each measurement. The comparison of the results obtained for these 10 measurements against the certified values of the CRM is shown in Table 4.

Table 4. Precision test of ten repetitive measurements of CRM SX56-16

CRM SX56-16 Fe2O3 [%] SiO2 [%] CaO [%] Mn3O4 [%] Al2O3 [%] TiO2 [%] MgO [%] P2O5 [%] SO3 [%] K2O [%]
17.07.13 09:51 81.88 5.07 9.55 0.679 1.35 0.090 1.48 0.164 0.047 0.034
17.07.13 10:08 81.80 5.11 9.55 0.662 1.33 0.105 1.49 0.151 0.037 0.035
17.07.13 10:26 81.81 5.12 9.55 0.650 1.31 0.090 1.48 0.142 0.038 0.037
17.07.13 10:44 81.91 5.09 9.56 0.664 1.35 0.099 1.50 0.152 0.043 0.031
17.07.13 11:01 81.92 5.10 9.57 0.665 1.34 0.115 1.53 0.145 0.040 0.037
17.07.13 11:19 81.91 5.09 9.54 0.662 1.32 0.084 1.48 0.133 0.040 0.039
17.07.13 11:36 81.81 5.07 9.56 0.662 1.30 0.094 1.50 0.147 0.041 0.038
17.07.13 11:54 81.86 5.05 9.56 0.662 1.31 0.095 1.50 0.144 0.043 0.030
17.07.13 12:12 81.84 5.10 9.55 0.644 1.33 0.097 1.52 0.142 0.040 0.035
17.07.13 12:29 81.91 5.10 9.55 0.660 1.29 0.104 1.46 0.131 0.047 0.037
Mean value 81.87 5.09 9.55 0.661 1.32 0.097 1.495 0.140 0.042 0.035
Abs. std. dev. 0.047 0.021 0.006 0.009 0.021 0.009 0.020 0.009 0.003 0.003
Rel. std. dev. 0.06 0.41 0.07 1.39 1.59 9.19 1.36 6.53 8.19 8.35
Certified value 81.91 5.18 9.51 0.662 1.331 0.101 1.491 0.14 T 0.045

Conclusion

The results clearly demonstrate the superior analytical performance of the EDXRF spectrometer S2 RANGER equipped with XFlash® detector. Here, the 10 most important elements present in iron ores were measured in the required concentration range for major and minor elements, using a set of 15 standard reference materials.

The preparation of samples as fused beads eliminated the mineralogical effects caused by varying mineral compositions between the samples obtained from different mining sites. In addition, the sample preparation process for this method is not time-intensive and requires no chemical sample digestion steps.

The high degree of accuracy and precision proves the applicability of the EDXRF spectrometer S2 RANGER equipped with XFlash® detector to monitor the chemical composition of iron ores. It is also possible to use this method to 'certify' secondary (mine specific) standards for pressed pellets calibrations.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

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