Compound analysis of
limestone prepared as
pressed powder pellets
Epsilon 3X
Introduction
This data sheet investigates the capability of the Epsilon 3X, 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.
Application background
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 3X was used for a full
and accurate analysis of limestone.
Instrumentation
Measurements were performed using a PANalytical Epsilon 3X
EDXRF spectrometer, equipped with a 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.
Sample preparation
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.
Measurement procedure
Three measurement conditions were used to optimize the
excitation of a group of elements (see Table 1). The total
measurement time per sample was 10 minutes. Figure 1 shows
an example of an XRF spectrum of a limestone standard.
Table 1. Three measurement conditions
Compounds
kV
μA
Medium
Filter
Meas. time
(s)
Figure 1. A XRF spectrum of a limestone standard, obtained using the first
measurement condition
Calibration results
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 (* RMS: The more accurate calibrations have the
smaller RMS values.)
Compounds
Contration range
(wt %)
Correlation
coefficient
RMS*
(wt %)
CaO
29.95 -55.59
0.9998
0.226
Al2O3
0.021 - 3.200
0.9977
0.081
Fe2O3
0.018 - 1.250
0.9986
0.026
MgO
0.110 -17.500
0.9996
0.270
SiO2
0.120 - 9.500
0.9930
0.430
SrO
0.008 - 0.280
0.9999
0.002
K 2O
0.003 - 0.960
0.9998
0.008
MnO
0.0021 - 0.0420
0.9967
0.001
Na2O, MgO,
Al2O3, SiO2,
P2O5, SO3
4.5
1000
Helium
None
420
Na2O
0.002 - 0.130
0.9002
0.023
P2O5
0.001 - 0.048
0.9405
0.007
CaO, K2O, MnO,
TiO2
14
250
Helium
Al-Thin
120
SO3
0.0170 - 0.1970
0.9854
0.009
TiO2
0.002 - 0.150
0.9991
0.002
SrO, Pb, Fe2O3
50
180
Air
Ag
60
Pb (ppm)
0.9405
1.7
0.7 -15
CaO concentration (wt %)
27.0
30.0
36.0
33.0
39.0
CaO concentration (wt %)
51.5
51
50.5
Precision and accuracy
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 and 5 minutes as total measurements times, 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 10 minutes. The results are summarized in Table 4, and a graphical representation of the 10 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.
5
10
Table 3. Overview of the time used per condition, when the total
measurement was shortened in the precision measurements.
Total measurement time
Compound
10 min
5 min
2 min
Na2O, MgO,
Al2O3, SiO2,
P2O5, SO3
7 min
3 min
1 min
CaO, K2O,
MnO, TiO2
2 min
1 min
30 sec
SrO, Pb,
Fe2O3
1 min
1 min
30 sec
15
20
Measurement point
Figure 3. The precision study of the CaO concentration in the SX35-14
standard performed with 10 and 2 min. measurement times. The dashed
lines illustrate 2 times RMS (2σ, 95% probability) of each measurement
time (10 min bleu, 2 min red).
Table 4. Summary of the results of the repeatability measurements,
obtained for 3 different measurement times. The certified values of the
limestone standard SX35-14 are included.
Certified
Compound
Conc.
(wt %)
RMS
(wt %)
10 min
Avg.
(wt %)
51.29
RMS
(wt %)
5 min
2 min
RMS
(wt %)
RMS
(wt %)
CaO
51.49
0.09
0.02
0.04
0.06
Al2O3
0.483
0.006
0.443
0.002
0.002
0.005
Fe2O3
0.422
0.004
0.428
0.003
0.003
0.005
MgO
2.161
0.008
2.233
0.010
0.011
0.020
SiO2
2.533
0.011
2.339
0.006
0.008
0.014
SrO
0.030
0.001
0.028
0.0001
0.0001
0.0002
K2O
0.075
0.003
0.074
0.0015
0.0026
0.0029
MnO
0.020
<0.001
0.020
0.0004
0.0006
0.0010
NaO2
0.042
0.003
0.048
0.001
0.002
0.004
P2O5
0.034
0.001
0.037
0.001
0.001
0.001
SO3
0.197
0.005
0.207
0.001
0.002
0.004
TiO2
0.023
0.001
0.023
0.002
0.002
0.002
7.2
0.4
0.6
0.8
Pb (ppm)
Global and near
0
42.0
Figure 2. Calibration graph for CaO in limestone standards prepared as
pressed powder pellets
2 min
-
-
Conclusions
The results clearly demonstrate the excellent capability
of the Epsilon 3X for the full analysis of the mineral
content of limestone.
The high performance of the silicon drift detector in the
Epsilon 3X makes it possible to get accurate and fast
results.
The Epsilon 3X 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.
PANalytical B.V.
Lelyweg 1, 7602 EA Almelo
P.O. Box 13, 7600 AA Almelo
The Netherlands
T+31 (0) 546 534 444
F+31 (0) 546 534 598
[email protected]
www.panalytical.com
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Although diligent care has been used to ensure that the information herein is accurate, nothing contained herein can be construed to imply any representation or warranty as to the accuracy, currency or completeness
of this information. The content hereof is subject to change without further notice. Please contact us for the latest version of this document or further information. © PANalytical B.V. 2009. 9498 707 58211 PN10765
Corrected intensity
24.0
10 min
52