This data sheet investigates the capability of the Epsilon 4, a benchtop energy dispersive X-ray fluorescence spectrometer (EDXRF), as an analytical tool for a complete analysis of the quality and composition of limestone.
Limestone is the principal source of CaCO3, which is used as raw material in a wide range of applications. It is used as an additive in steel making, as main component for cement and, when purified, it even can be used as supplement for calciumrich animal feed or pharmaceutical fillers. Al2O3, SiO2, MgO and Fe2O3 are further considered as the main compounds of limestone, and are important in the use of limestone. The grade and application of the raw material is determined by the ratio between these main compounds, as well as the presence of other minor and trace compounds, like MnO, P2O5 and Pb. In this data sheet, the Epsilon 4 was used for a full and accurate analysis of limestone.
This application note investigates the capability of the Epsilon 4, a bench top energy dispersive X-ray fluorescence spectrometer (EDXRF), as an analytical tool for a complete analysis of the quality and composition of limestone.
Limestone is the principal source of CaCO3, which is used as raw material in a wide range of applications. It is used as an additive in steel making, as main component for cement and, when purified, it even can be used as supplement for calcium-rich animal feed or pharmaceutical fillers. Al2O3, SiO2, MgO and Fe2O3 are further considered as the main compounds of limestone, and are important in the use of limestone. The grade and application of the raw material is determined by the ratio between these main compounds, as well as the presence of other minor and trace compounds, like MnO, P2O5 and Pb. In this application note, the Epsilon 4 was used for a full and accurate analysis of limestone.
Measurements were performed using a Malvern Panalytical Epsilon 4 EDXRF spectrometer, equipped with a 10 W, 50 kV silver anode X-ray tube, 6 beam filters, a helium purge facility, a high-resolution silicon drift detector, a sample spinner and a 10-position removable sample changer.
Pressed pellets were made from 11 commercially available limestone standards. The pellets were made by mixing 12 g of limestone powder with 3 g of Ultrawax binder.
Three measurement conditions were used to optimize the excitation of a group of elements (see Table 1). The total measurement time per sample was 6 minutes. Figure 1 shows an example of an XRF spectrum of a limestone standard.
Table 1. Three measurement conditions
Figure 1. An XRF spectrum of a limestone standard, obtained using the first measurement condition
The calibration was set up using 10 certified reference materials (CRM) and 1 standard kept aside for the precision measurements. Figure 2 shows a calibration graph acquired for CaO, using the conditions listed in Table 1. In Table 2 the calibration results are summarized for all compounds, with the corresponding correlation coefficients and RMS values (1 sigma). The calibrations show high correlations for all compounds of limestone. Also a calibration for traces of lead (Pb) was obtained but with limited quality because only three standards contain certified concentrations of Pb.
Table 2. Calibration details
Figure 2. Calibration graph for CaO in limestone standards prepared as pressed powder pellets
To test the precision and accuracy of the method, the certified reference standard SX35-14 (Dillinger Hütte Laboratory) was measured 20 consecutive times. The measurement was repeated using 2 minutes as total measurement time, to analyze the influence of time on the precision. The total time for each measurement was divided over the three conditions according to Table 3, but all measurements were done using the calibration setup for 6 minutes. The results are summarized in Table 4, and a graphical representation of the 6 and 2 minute measurements for the CaO concentration is illustrated in Figure 3. The measured averages are close to the certified values, which show the accuracy of the method. The RMS values for shorter measurement times are slightly increased; however in all cases the repeatability is still acceptable. This is illustrated in Figure 3 with the dashed lines, showing 2 times RMS (2σ, 95% probability) for the different measurement times.
Table 3. Overview of the time used per condition, when the total measurement was shortened in the precision measurements.
Figure 3. The precision study of the CaO concentration in the SX35-14 standard performed with 6 and 2 min. measurement times. The dashed lines illustrate 2 times RMS (2σ, 95% probability) of each measurement time (6 min bleu, 2 min red).
Table 4. Summary of the results of the repeatability measurements, obtained for different measurement times. The certified values of the limestone standard SX35-14 are included.
The results clearly demonstrate the excellent capability of the Epsilon 4 for the full analysis of the mineral content of limestone. The high performance of the silicon drift detector in the Epsilon 4 makes it possible to get accurate and fast results. The Epsilon 4 will give the user the opportunity to control the production process close to their production facilities, and analyze the grade of the excavated limestone. The required precision will determine the required measurement time of the application.
