Quantitative Analysis of Dolomite and Limestone by Pressed powder Method with Supermini200

Application Note WDXRF1058

Introduction 

Both dolomite and limestone are important mineral resources used in various industries such as cement, electronics, iron manufacturing, glass, paper and pulp, agriculture. Each industry has particular interests in contents and components. For example in the cement industry, dolomite and limestone are sources of Ca. In iron manufacturing, Ca acts as an absorber of impurities like Si, S and P, and Mg protects the furnace walls from corrosive elements like S and P. In the glass industry, low content of Fe is preferred because Fe can color glass.   

X-ray fluorescence (XRF) analysis quickly and easily offers precise elemental analysis results allowing control of the components in the product during the manufacturing process.

This application note demonstrates the excellent performance of Supermini200 for the analysis of dolomite and limestone.

Instrument 

The Supermini200 is a benchtop sequential wavelength dispersive XRF (WDXRF) spectrometer designed specifically to deliver excellent performance while eliminating conventional installation requirements such as cooling water, special power supply and large floor space. By selecting the optional sealed proportional counter instead of the gas flow proportional counter, requirement of P10 gas can be eliminated as well, realizing a truly utility free WDXRF instrument. Featuring a unique air-cooled 200W X-ray tube, two detectors, three analyzing crystals with selectable vacuum or helium environment, the Supermini200 can analyze elements from oxygen to uranium. 

The Windows®-based software used to operate the Supermini200 shares the same platform running Rigaku’s popular high-power WDXRF ZSX family instruments. This means that it has the same advanced algorithms, multiple language support and an intuitive user-friendly interface. 

Sample Preparation 

The samples were ground in a tungsten carbide container for two minutes. The sample to binder ratio is 4.2 g to 0.42 g. Each ground sample mixed with binder (Chemplex Spectro Blend® No.660) was pelletized using an aluminum ring (inner diameter : 32 mm) under the pressure of 150 kN. 

Measurement and calibration 

Measurements were performed on the Supermini200 for SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO, SO₃, Na₂O, K2O, TiO₂, P₂O₅ and MnO. Measurement conditions are shown in Table 1. 

Table 1:  Measurement conditions

Element Si Al Fe Ca
Line
kV-mA 50-4.00 50-4.00 50-4.00 50-4.00
Primary Filter OUT OUT OUT OUT
Slit Std Std Std Std
Crystal PET PET LiF(200) PET
Detector PC PC SC PC
Time Peak (s) 20 20 40 10
BG (s) 10x2 10x2 20 4x2
         
Element Mg S Na K
Line
kV-mA 50-4.00 50-4.00 50-4.00 50-4.00
Primary Filter OUT OUT OUT Al40
Slit Std Std Std Std
Crystal RX25 PET RX25 PET
Detector PC PC PC PC
Time Peak (s) 40 40 40 40
BG (s) 10x2 20 20x2 20
       
Element Ti P Mn  
Line
kV-mA 50-4.00 50-4.00 50-4.00
Primary Filter OUT OUT OUT
Slit Std Std Std
Crystal LiF(200) PET PET
Detector SC PC PC
Time Peak (s) 40 40 200
BG (s) 10x2 10x2 100x2

The calibration curves were generated using dolomite and limestone standards shown below:  

  • National Institute of Standards and Technology (NIST) standards SRM1c and 88b 
  • Geological Survey of Japan, AIST (GSJ) standards JDo-1 and JLs-1
  • Bureau of Analysed Samples Ltd. (BAS) standards BCS-CRM368 and 393. 
  • European Committee for Iron and Steel Standardization (ECISS) CRM782-1

In order to extend the calibration range, NIST cement standards SRM1881a, 1884a, 1885a, 1886a, 1887a, 1888a and 1889a were added for Na2O and SO3. Ma-trix correction was applied to the components except for SO3 and Na2O. The correction coefficients were calculated theoretically by the fundamental parameter (FP) method. The calibration curves are shown in Figure 1 and the calibration results are listed in Table 2.


XRF1058 Figure 1a Calibration curves for dolomite and limestoneXRF1058 Figure 1b Calibration curves for dolomite and limestone

Figure 1: Calibration curves for dolomite and limestone


Table 2:  Calibration results (unit : mass%)

Component Calibration range Accuracy
SiO₂ 0.12 - 6.84 0.18
Al₂O₃ 0.0174 - 1.3 0.038
Fe₂O₃ 0.0178 - 0.55 0.028
CaO 29.95 - 55.4 0.2
MgO 0.15 - 21.29 0.42
SO₃ 0.0397 - 4.622 0.12
Na₂O 0.00194 - 1.068 0.013
K₂O 0.00232 - 0.28 0.002
TiO₂ 0.00133 - 0.07 0.0036
P₂O₅ 0.0044 - 0.04 0.0016
MnO 0.00209 - 0.081 0.0019

The accuracy of the linear calibration curves are calculated by the following formula:

$Accuracy = \sqrt{ \frac{\sum_i{(C_i-\hat{C}_i)^2}}{n-2} }$

$C_i$: calculated value of standard sample
$\hat{C}_i$: reference value of standard sample
n : number of standard samples. 

Analysis Results 

Table 3:  Repeatability test results for dolomite (unit : mass%)

  SiO₂ Al₂O₃ Fe₂O₃ CaO MgO SO₃ Na₂O K₂O TiO₂ P₂O₅ MnO
Chemical value 0.266 0.104 0.450 30.34 21.29 0.0397 - 0.0260 0.0042 0.0128 0.081
N=1 0.2725 0.1153 0.4502 29.80 20.91 0.0395 0.034 0.0261 0.0043 0.0131 0.0793
2 0.2677 0.1155 0.4523 29.87 20.95 0.0390 0.048 0.0269 0.0037 0.0132 0.0788
3 0.2679 0.1202 0.4502 29.85 20.96 0.0403 0.046 0.0263 0.0041 0.0151 0.0793
4 0.2711 0.1190 0.4496 29.84 20.89 0.0404 0.036 0.0261 0.0038 0.0142 0.0793
5 0.2709 0.1161 0.4502 29.89 20.97 0.0403 0.033 0.0259 0.0044 0.0138 0.0795
6 0.2714 0.1214 0.4517 29.86 20.86 0.0397 0.047 0.0289 0.0043 0.0144 0.0796
7 0.2664 0.1175 0.4494 29.75 20.91 0.0406 0.043 0.0249 0.0041 0.0137 0.0788
8 0.2691 0.1182 0.4504 29.84 20.93 0.0408 0.034 0.0246 0.0041 0.0141 0.0794
9 0.2688 0.1161 0.4499 29.80 20.89 0.0410 0.048 0.0270 0.0040 0.0147 0.0795
10 0.2699 0.1175 0.4474 29.80 20.97 0.0410 0.039 0.0249 0.0045 0.0147 0.0794
Avg. 0.2696 0.1177 0.4501 29.83 20.92 0.0403 0.041 0.0262 0.0041 0.0141 0.0793
Max. 0.2725 0.1214 0.4523 29.89 20.97 0.0410 0.048 0.0289 0.0045 0.0151 0.0796
Min. 0.2664 0.1153 0.4474 29.75 20.86 0.0390 0.033 0.0246 0.0037 0.0131 0.0788
Range 0.0061 0.0061 0.0049 0.14 0.11 0.0020 0.015 0.0043 0.0008 0.0020 0.0008
Std. dev. 0.0019 0.0020 0.0013 0.04 0.04 0.0007 0.006 0.0013 0.0003 0.0007 0.0003
RSD % 0.71 1.74 0.29 0.14 0.17 1.66 15.15 4.85 6.15 4.66 0.35

Table 4:  Repeatability test results for limestone (unit : mass%)

  SiO₂ Al₂O Fe₂O₃ CaO MgO SO₃ Na₂O K₂O TiO₂ P₂O₅ MnO
Chemical value 0.12 0.0207 0.0178 55.09 0.606 0.0307 0.00194 0.00297 0.002 0.0295 0.00209
N=1 0.1222 0.0249 0.0165 54.23 0.51 0.0288 N.D. 0.0034 0.0024 0.0298 0.0025
2 0.1217 0.0238 0.0173 54.18 0.51 0.0300 N.D. 0.0027 0.0024 0.0297 0.0023
3 0.1236 0.0226 0.0174 54.32 0.52 0.0281 N.D. 0.0027 0.0026 0.0313 0.0023
4 0.1219 0.0255 0.0178 54.42 0.52 0.0299 N.D. 0.0034 0.0025 0.0307 0.0028
5 0.1205 0.0240 0.0167 54.28 0.51 0.0289 N.D. 0.0043 0.0026 0.0295 0.0024
6 0.1184 0.0257 0.0167 54.34 0.53 0.0288 N.D. 0.0038 0.0021 0.0288 0.0027
7 0.1218 0.0234 0.0165 54.32 0.51 0.0295 N.D. 0.0026 0.0022 0.0307 0.0026
8 0.1219 0.0242 0.0171 54.33 0.52 0.0290 N.D. 0.0035 0.0024 0.0298 0.0023
9 0.1202 0.0244 0.0164 54.18 0.53 0.0287 N.D. 0.0034 0.0021 0.0317 0.0027
10 0.1193 0.0234 0.0175 54.29 0.52 0.0281 N.D. 0.0031 0.0025 0.0310 0.0025
Avg. 0.1212 0.0242 0.0170 54.29 0.52 0.0290 - 0.0033 0.0024 0.0303 0.0025
Max. 0.1236 0.0257 0.0178 54.42 0.53 0.0300 - 0.0043 0.0026 0.0317 0.0028
Min. 0.1184 0.0226 0.0164 54.18 0.51 0.0281 - 0.0026 0.0021 0.0288 0.0023
Range 0.0052 0.0031 0.0014 0.25 0.02 0.0019 - 0.0017 0.0005 0.0029 0.0006
Std. dev. 0.0016 0.0010 0.0005 0.08 0.01 0.0007 - 0.0005 0.0002 0.0009 0.0002
RSD % 1.28 4.00 2.82 0.14 1.16 2.27 - 15.90 7.71 3.01 8.07
N.D. : Not Detected (below the Lower Limit of Detection, LLD)

Repeatability tests for dolomite and limestone were carried out and the results are shown in Table 3 and 4. The standard deviations for both major and minor components are very small. 

Conclusions

The results show that high precision analysis of elements in dolomite and limestone can be performed using the benchtop WDXRF spectrometer Supermini200. The calibration curves obtained using the theoretical alpha corrections show good linearity by pressed powder method for both major and trace components.  

Supermini200 is a benchtop spectrometer with a small footprint and is able to be operated with only a wall power outlet. Since Supermini200 is not site-specific, it has the great advantage that it can be installed any-where, and is therefore particularly suited for mining sites or small laboratories. 

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