X-ray fluorescence spectroscopy (XRF) is an established analytical technique in the building materials industry for monitoring and controlling the chemical composition of the raw materials used in the production of clinkers and, ultimately, cements. Continuous analysis of the raw mix allows process adjustments, ensuring product quality and consistency, while maximizing kiln efficiency and minimizing CO2 emissions. XRF is a safe, cost-effective and highly reliable method and does not require daily re-calibration.
This application note demonstrates that the Epsilon 4, a benchtop energy dispersive X-ray fluorescence spectrometer, is more than capable of analyzing MgO, Al2O3, SiO2, SO3, Cl, K2O, CaO, TiO2 and Fe2O3 in raw mix, without the need for helium in 5 minutes.
Measurements were performed using a Malvern Panalytical Epsilon 4 EDXRF spectrometer, equipped with a 10 W, 50 kV silver (Ag) anode X-ray tube, 6 software-selectable filters, a helium purge facility (included in the system but not used in this study), a
high-resolution SDD silicon drift detector, a sample spinner, and a 10-position removable sample tray for batch analysis.
The raw mix reference standards were analyzed as pressed powder pellets. The sample preparation technique is easily mastered, safe and relatively inexpensive. Five grams of raw mix sample was mixed with 0.5 gram of binder (wax) and pressed to pellets of 30 mm in diameter at 20 ton and 30 s dwell time.
Eleven commercially available Chinese raw mix reference standards were used to set up the calibrations. Two different measurement conditions were used, each optimizing the excitation of a group of elements (see Table 1). The total measurement time per standard was five minutes.
Table 1. Measurement conditions
Figures 1, 2 and 3 show the resulting calibration graphs for MgO, Al2O3 and CaO in raw mix samples, respectively. The graphs show good correlation between the certified concentrations and the measured intensities. Detailed calibration results for all analyzed elements in the raw mix standards are listed in Table 2. The RMS (root mean square) value is equivalent to 1 sigma standard deviation.
Table 2. Calibration details
Figure 1. Calibration graph for MgO in raw mix
Accuracy, precision and LSF
To test the instrument accuracy and precision, one pressed pellet standard was measured 20 times consecutively. The certified concentrations, average concentrations and RMS values for all elements are presented in Table 3, demonstrating excellent accuracy and precision.
In cement manufacturing, the lime saturation factor (LSF) is used to control the composition of the raw mix. Using this economical method, the absolute uncertainty on the LSF value is 0.05. The formula used is the following:
LSF = 100*CaO / (2.8*SiO2 + 1.18*Al2O3 + 0.65*Fe2O3)
Figure 2. Calibration graph for Al2O3 in raw mix
Table 3. Repeatability results.
Figure 3. Calibration graph for CaO in raw mix
The results clearly demonstrate the capability of Epsilon 4 for the analysis of raw mix in only 5 minutes in an economical way. The high resolution and outstanding sensitivity of the SDD silicon drift detector combined with powerful software deconvolution algorithms make it possible to quantify 9 compounds in raw mix without the need for helium. Excellent results have been obtained for the calibrations and repeatability test. Furthermore, the low uncertainty on the LSF value demonstrates that the Epsilon 4 is an ideal instrument for the analysis of raw mix.