Using the S2 RANGER EDXRF Spectrometer to Analyze Gypsum and Carbonate Rocks

Dolomite and limestone are two major types of carbonate rocks. Dolomite is predominately used as concrete aggregate, ornamental stone, and for magnesium production, whereas limestone is used as raw material in the glass and cement industries, and as a building material.

Another sedimentary rock is gypsum, mainly used as a fertilizer and a building material. Grade control of these industrial minerals can be effectively carried out with X-ray fluorescence analysis (XRF).

Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF)

EDXRF is widely used for controlling mining operations and identifying the grade of final products. It is user friendly, and modern EDXRF instruments deliver advanced analytical performance. Typically, EDXRF instruments have a smaller benchtop footprint and a low cost of ownership, rendering them appealing for dedicated analytical tasks.

Conventional EDXRF spectrometers do however, have very limited performance for light elements such as magnesium and sodium due to the use of a thick detector window, which virtually absorbs all radiation of light elements.

Conversely, the EDXRF spectrometer S2 RANGER (Figure 1) equipped with the XFlash LE detector has far superior capabilities due to the unique combination of advanced detector technology, a thin stabilized entrance window, and high power direct excitation. This article discusses the advantages of using the S2 RANGER equipped with XFlash LE to analyze gypsum and carbonate rocks with the GEO-QUANT M solution.

The S2 RANGER EDXRF spectrometer

Figure 1. The S2 RANGER EDXRF spectrometer

Advantages of the S2 RANGER EDXRF Spectrometer

EDXRF spectrometers have become an essential instrument for elemental analysis in research and for process or quality control. The following advantages make the S2 RANGER equipped with XFlash LE an attractive instrument for a variety of industrial applications:

  • Analytical flexibility
  • Low operating costs
  • Smaller footprint
  • Easy operation with TouchControl

The elements in the samples are excited directly with 50W. The XFlash silicon drift detector is operable at very high count rates, helping achieve excellent standard deviation. The XFlash LE detector is able to effectively detect light elements such as magnesium and sodium because of the thin stabilized entrance window.

Carbonates can be effectively analyzed without using a helium purge, thanks to the use of the integrated vacuum pump. This optimized analytical performance in particular, for light elements enables the fusion method to be applied for sample preparation, which further improves the accuracy and precision of results.

GEO-QUANT M is used to calibrate the S2 RANGER with XFlash LE. It is the Bruker solution to rapidly analyze major elements in geological samples, including Fe, Mn, Ti, Ca, K, S, P, Si, Al, Mg, and Na.

GEO-QUANT M is supplied with 20 certified reference materials to encompass a broad concentration range as well as with three validation standards for checking the calibration quality. The standards are supplied as powders and are prepared in accordance with the sample preparation manual using the installed fusion equipment.

Experimental Procedure

Calibration standards were prepared as fused beads using 0.8g samples with 8.0 g flux (lithiumborate mix for gypsum and lithium tetraborate for other standards). Using the same method, eight certified reference materials carbonate rocks (GBW 07127, GBW 07128, GBW 07130, GBW 07134), limestone (IPT 44, GBW 7120), and gypsum standards (GYP-C, GYP-D) were also prepared.

The S2 RANGER was used to perform the measurements. The total measurement time was 10min. Optimized measurement parameters can be obtained with GEO-QUANT M. Table 1 provides the comparison of the accuracy test results of the validation samples against the certified concentrations.

Table 1. Accuracy test of GEO-QUANT M with certified materials (carbonate rocks and gypsum) standards

  Carbonate rock
GBW 07127 GBW 07128 GBW 07134 GBW 07130
Cert. Meas. Cert. Meas. Cert. Meas. Cert. Meas.
Na2O 0,022 0.07 0.029 0.04 0.03 0.02 0.015 0.08
MgO 6.76 6.73 11.62 11.51 14.96 14.91 1.42 1.42
Al2O3 0.17 0.18 0.22 0.24 0.18 0.18 0.18 0.19
SiO2 0.55 0.53 0.72 0.71 1.17 1.14 1.08 1.19
P2O5 0.008 0.10 0.014 0.08 0.009 0.06 0.005 0.13
SO3 0.017 0.08 0.013 0.09 0.041 0.02 0.014 0.09
K2O 0.043 0.03 0.05 0.04 0.03 0.03 0.043 0.05
CaO 47.89 47.83 41.95 41.91 38.08 38.26 54.08 54.14
TiO2 0.01 0.01 0.02 0.02 0.01 0.01 0.007 0.00
Mn2O3 0.01 0.01 0.01 0.01 0.024 0.03 0.004 0.01
Fe2O3 0.19 0.19 0.21 0.20 0.45 0.43 0.222 0.22

 

  Limestone Gypsum
GBW 07120 IPT 44 GYP-C GYP-D
Cert. Meas. Cert. Meas. Cert. Meas. Cert. Meas.
Na2O 0.03 0.07 0.002 0.06 0.02 0.00 0.07 0.00
MgO 0.71 0.71 2.93 2.92 5.35 5.11 1.73 1.60
Al2O3 0.68 0.66 0.33 0.37 0.79 0.84 2.03 2.04
SiO2 6.65 6.60 2.69 2.67 3.50 3.69 8.70 8.93
P2O5 0.012 0.13 0.013 0.21 0.02 < LLD 0.03 0.00
SO3 0.009 0.03 n.d. 0.20 32.97 32.82 36.72 36.53
K2O 0.15 0.14 n.d. 0.10 0.36 0.32 0.54 0.51
CaO 51.1 51.20 50.5 50.66 30.38 30.51 28.21 28.61
TiO2 0.038 0.03 0.019 0.01 Trace 0.04 Trace 0.08
Mn2O3 0.004 0.01 0.015 0.02 Trace 0.01 Trace 0.02
Fe2O3 0.21 0.20 0.3 0.29 0.40 0.40 1.08 1.06

Experimental Results

The certified reference material GBW07127 was measured 44 times for one week in order to illustrate the long time stability of the S2 RANGER in conjunction with GEO-QUANT M. Table 2 shows the repeatability and reproducibility of the method and the long time stability of the S2 RANGER.

The stability results of MgO and CaO measurement in GBW07127 for a period of one week are depicted in Figure 2. The correlation of measured versus certified concentrations for Al2O3 and Cao is illustrated in Figure 3.

Table 2. Analytical precision of carbonate rock GBW 07127 Accuracy test of GEO-QUANT M with carbonate rocks and gypsum standards Precision test 44 times alternated measurement

  Na2O MgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 Mn2O3 Fe2O3
Certified Concentration [%] 0.022 6.76 0.17 0.55 0.008 0.017 0.043 47.89 0.011 0.008 0.193
Average [%] 0.05 6.76 0.07 0.53 0.10 0.09 0.04 47.87 0.01 0.01 0.18
Min. [%] 0.02 6.71 0.06 0.52 0.09 0.08 0.03 47.70 0.00 0.01 0.18
Max. [%] 0.08 6.81 0.07 0.53 0.12 0.10 0.06 48.03 0.02 0.01 0.19
Abs. Std. Dev. [%] 0.02 0.02 0.00 0.00 0.01 0.00 0.01 0.08 0.01 0.00 0.00
Rel. Std. Dev. 36.84 0.34 5.05 0.69 5.30 2.31 15.79 0.16 86.12 22.73 0.80

The stability test of MgO and CaO in GBW07127 dashed lines show the three times of standard deviation of the measurement.

Figure 2. The stability test of MgO and CaO in GBW07127 dashed lines show the three times of standard deviation of the measurement.

Correlation of measured versus certified concentrations for Al2O3 and CaO for GEO-QUANT M standards ( red) and certified reference materials (blue).

Figure 3. Correlation of measured versus certified concentrations for Al2O3 and CaO for GEO-QUANT M standards ( red) and certified reference materials (blue).

Conclusions

From the stability test results, the S2 RANGER with XFlash LE in conjunction with GEO-QUANT M based on fused beads delivers high analytical precision and outstanding accuracy. The selected measurement parameters facilitated the optimum performance of the spectrometer.

The results of repeated measurements for a period of one week demonstrated the long-term stability of the S2 RANGER LE. The achieved precision of the wide range oxide calibration of GEO-QUANT M satisfies both research and industry requirements. Hence, the S2 RANGER with XFlash LE is a useful instrument for grade control in mining sites for gypsum, dolomite, and limestone.

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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