WDXRF Pressed Powder Analysis of Copper Concentrate

Copper, one of the key base metals, is utilized in the form of copper alloys and electric cables in a myriad of applications, including automobile, machinery, electronics, construction, and much more. Copper ore mined predominantly as sulfide ore is processed and supplied as concentrate of 20-40% in copper content. Copper concentrate carries many different impurities, which are either valuable elements or detrimental to quality in copper metal products and harmful to the human health and environment.

The amount of ore grade copper in modern copper deposits is in decreasing trend with increased impurities. Hence, the demand for analyzing copper ore and concentrate in order to accurately and rapidly determine major and trace amounts of different metal impurities is increasing. X-ray fluorescence spectrometry is the ideal solution to accurately and rapidly analyze ore grade of copper. This article demonstrates the ability of the Supermini200 benchtop wavelength dispersive X-ray fluorescence (WDXRF) spectrometer from Rigaku to perform the traditional calibration method of copper ore concentrate analysis as well as standardless analysis through the use of the fundamental parameter method.

Supermini200 WDXRF Spectrometer

The Supermini200 WDXRF system exhibits high sensitivity and high resolution for light elements. High spectral resolution is critical for copper concentrate analysis as the material contains several heavy elements with overlapping and close spectral lines. The unique benchtop system is designed to reduce installation prerequisites, including installation space, power supply and cooling water. With an air-cooled 200W X-ray tube and three analyzing crystals, the system is capable of analyzing elements from oxygen to uranium.

The Supermini200 WDXRF System

Figure 1. The Supermini200 WDXRF System

The operation software facilitates operators to use the system for different applications. Standardless analysis program, ‘SQX,’ can rapidly determine the presence and approximate concentrations of different elements in the unknown sample without the need for selecting and preparing any suitable reference materials.

Reference Samples and Sample Preparation

For calibration, 15 copper concentrate samples were utilized as references. The pressed powder technique was used to prepare these powder samples. It is the most commonly used method for powder samples in XRF spectrometry analysis as it is simple, economical, consumes less time, and requires low skill level. The samples were dried for 2 hours at 105 °C, and then the binder was added at 10% by mass. The resultant mixture was pulverized in a steel container, followed by pressing into aluminum support ring under 200 kN pressure.

Calibration and Results

The Supermini200 with Pd target X-ray tube was used to perform the calibration for the elements of Cu, Cd, As, Ag, Bi, Pb, and Zn. Tube condition was 4 mA and 50 kV and path atmosphere was in vacuum. The Cd-Kα line was measured using the primary beam filter of Zr in order to avoid interference from Pd target lines.

The scattered tube target X-rays reflected from the sample was used as an internal standard to correct the matrix effects in the calibration of Cd, Ag, Bi and Pb. In this analysis, the copper concentrates utilized for calibration have relatively high concentrations of molybdenum. The overlapping of the molybdenum line with Pd-Kα Compton line does not allow the line to be utilized as the internal standard, as shown in Figure 2. Hence, the correction was made through the application of a scattered X-rays from the X-ray continuum.

Spectral chart adjacent to scattering X-rays of target element for sample including molybdenum

Figure 2. Spectral chart adjacent to scattering X-rays of target element for sample including molybdenum

Calibration curves of the measured elements are demonstrated in Figure 3 and 4. The accuracy of calibration of corrected calibration curves was better than the calibration without correction. The accuracies without any matrix correction were 0.0091 mass% (Pb), 43 ppm (Bi), 15 ppm (Ag) and 6 ppm (Cd), respectively.

Calibration curves of copper concentrate

Figure 3. Calibration curves of copper concentrate

Calibration curves corrected by scattering X-ray as internal standard

Figure 4. Calibration curves corrected by scattering X-ray as internal standard

The accuracy is estimated using the following formula:

where,

Ci : calculated value of standard sample
Ci : reference value of standard sample
n : number of standard samples.
m : degree of freedom (linear 2, quad. 3)

Ten repeat analyses were performed in order to assess the repeatability or precision of the copper concentrate analysis. The results are listed in Table 1.

Table 1. 10 time repeat measurement

Component / Element Chemical Value XRF
Average Std.dev. RSD%
Cu 28.3 28.4 0.016 0.056
Zn 3.75 3.80 0.013 0.34
Pb 0.31 0.30 0.003 1.1
Bi* 1180 1211 9.5 0.78
Ag* 253 266 12.9 4.8
As* 1300 1349 30.7 2.3
Cd* 110 120 6.2 5.2

unit : mass%, * ppm,

SQX Analysis

SQX is a semi-quantitative analysis program that can present the concentrations through theoretical calculation by utilizing fundamental parameter and internal sensitivity library without any standards. The results of sequential scan measurement from fluorine to uranium were used to perform the calculation. The theoretical line overlap correction function is integrated with the program, thus optimizing the SQX analysis for screening analysis of unknown ore samples containing multiple heavy elements. The results of the SQX analysis for a representative sample are listed in Table 3. The results were in line with chemical values.

Table 2. Result of SQX analysis

Component / Element SQX result Chemical value
MgO 0.50 -
A2O3 1.5 -
SiO2 6.5 -
S 29.6 -
K2O 0.34 -
CaO 1.6 -
Mn 0.069 -
Fe 28.3 -
Cu 29.3 28.8
Zn 1.6 1.56
As 0.24 0.21
Mo 0.25 -
Ag 0.016 0.017
Pb 0.20 0.21
Bi 0.027 0.026

unit : mass%

Conclusion

The results clearly demonstrate the ability of the Supermini200 WDXRF spectrometer to perform the traditional calibration method of copper ore concentrate analysis as well as standardless analysis through the use of the fundamental parameter method. The benchtop spectrometer is a robust instrument to analyze the ore and concentrate for both process control and screening.

This information has been sourced, reviewed and adapted from materials provided by Rigaku.

For more information on this source, please visit Rigaku.

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