Analysis of major and minor elements in bauxite samples prepared as fused beads

This data sheet describes the analysis of major and minor elements present in bauxite prepared as fused beads, using the Epsilon 4 energy dispersive X-ray fluorescence (EDXRF) spectrometer together with the Eagon 2 fusion machine.

In order to perform the right quality control of bauxite raw material, not only the aluminum concentration is monitored, but also concentrations of other elements like silicon (Si), iron (Fe) and titanium (Ti), which are of vital importance.

Introduction

In order to perform the right quality control of bauxite raw material, not only the aluminium concentration is monitored, but also concentrations of other elements like silicon (Si), iron (Fe) and titanium (Ti), which are of vital importance. This application note describes the analysis of major and minor elements  present  in  bauxite  prepared  as   fused   beads,   using the Epsilon 4 energy dispersive X-ray fluorescence (EDXRF) spectrometer together with the Claisse Eagon 2 fusion machine.

Sample preparation

Calibrations were set up using seven certified reference materials (CRM) prepared in duplicates as fused beads. The CRMs include NIST (696b, 600, 696, 697) and GBW (07177, 07181, 07182). The fused beads were prepared using a 1/10 flux (50% Li2B4O7/50% LiBO2) to sample ratio. The fusions were performed at 1150°C using a Claisse Eagon 2 automatic fusion machine.

Instrumentation

Measurements were performed using the Epsilon 4 EDXRF spectrometer, equipped with a 10 W, 50 kV silver anode X-ray tube, 6 filters, a helium purge facility, a high-resolution silicon drift detector (SDD), a sample spinner and a 10-position removable sample tray

Measurement conditions

The measurement conditions for measuring Al2O3, CaO, Cr2O3, Fe2O3, K2O, MgO, MnO, P2O5, SO3, SiO2, TiO2, ZnO and ZrO2 present in the prepared samples are given in Table 1. The total measurement time per sample was 4 minutes. Figure 1 shows the spectra for Al2O3 and SiO2 of a NIST bauxite standard.

Table 1. Measurement conditions 

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Accurate calibration results

The calibration graphs  for  Al2O3,  Fe2O3  and  TiO2  in  fused  bauxite are shown in Figures 2, 3 and 4,  respectively,  demonstrating  the good correlation between the certified concentrations and the measured intensities. Table 2 lists the root mean square (RMS) of the individual compound calibrations. The LLD values are calculated using the measurement times documented in Table 1.

Precise results

A repeatability test was performed by measuring NIST 698 standard twenty times, to test the precision of the Epsilon 4. The results are given in Table 3. The results show a good agreement between certified and average measured concentrations. The low RMS values for the repeatability measurements show  the  good  stability  of  the  system  as a whole.

Figure 1. The spectrum of standard NIST 696B, obtained with 5 kV under helium; showing the excellent resolution and the high sensitivity of the detector 

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Figure 2. Calibration graph for Al2O3 in bauxite 

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Table 2. Calibration results 

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Figure 3. Calibration graph for Fe2O3 in bauxite 

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Table 3. Results of the repeatability test 

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Figure 4. Calibration graph for TiO2 in bauxite 

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Conclusion

This work clearly demonstrates the suitability of the Epsilon 4 EDXRF spectrometer for the quantitative analysis of Al2O3, CaO, Cr2O3, Fe2O3, K2O, MgO, MnO, P2O5, SO3, SiO2, TiO2, ZnO and ZrO2 in bauxite prepared as fused beads. Accurate and precise results can be obtained in just 4 minutes.

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