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.
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.
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
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
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.
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
Figure 2. Calibration graph for Al2O3 in bauxite
Table 2. Calibration results
Figure 3. Calibration graph for Fe2O3 in bauxite
Table 3. Results of the repeatability test
Figure 4. Calibration graph for TiO2 in bauxite
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.