XRF Analysis of Iron Ore with the ARL OPTIM’X Spectrometer

Commercial iron is produced through the refinement of iron ore, which is a massive global undertaking. In 2021, 2.6 billion metric tons of iron ore were mined, resulting in 1.6 billion metric tons of iron content. A total of 90% of extracted iron ore is used to make steel, with the remainder being used for various applications.

The applications include various battery materials in which iron is used due to its ease of oxidation and ready accessibility. Iron is essential in battery manufacturing and research, whether in traditional nickel-iron batteries or emerging technologies, such as iron-air batteries and lithium iron phosphate (LFP) cathodes.

Understanding the actual composition of iron ore can help with refinement and eventual purity determination of the final iron metal, which is essential for highly technical applications, such as batteries, where purity could significantly impact performance. This article describes a wavelength-dispersive X-Ray fluorescence (WDXRF) spectroscopy technique for iron ore analysis that reduces analysis time.

Given the massive amounts of ore extracted and processed each year, it is important that characterization techniques are as effective as possible, as even a minute of extra time can amplify the quantities under consideration tremendously.

Figure 1. Thermo Scientific ARL OPTIM’X XRF Spectrometer with its 13-position sample loader. Image Credit: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Instrumentation

The Thermo Scientific^™ ARL OPTIM’X^™ XRF Spectrometer is a WDXRF instrument with low operation and maintenance costs. The ARL OPTIM’X Spectrometer is equipped with the innovative Thermo Scientific^™ SmartGonio^™ Goniometer, which enables it to encompass the elemental range from fluorine (₉F) to americium (₉₅Am).

The spectrometer has two power levels: 50 W and 200 W. The 200 W version typically acquires data 2.5× faster than the 50 W version. The 50 W version was used for this article.

The ARL OPTIM’X Spectrometer requires no external or internal water cooling and has a 10× higher spectral resolution than traditional energy dispersive XRF (EDXRF) instruments, and also superior precision and stability. It performs consistently for critical elements, such as sodium (₁₁Na), magnesium (₁₂Mg), and even fluorine (₉F).

Analytical Conditions

Data for 12 elements (Al, Cr, Ca, K, Fe, Mn, Mg, Si, Ti, S, P, and V) were collected from each iron ore sample using the 50 W ARL OPTIM’X Spectrometer at 30 kV and 1.67 mA for a total analysis time of 7.6 minutes (Mg required 60 seconds). The measurement time can be adjusted further based on the application.

With the 200 W instrument, total counting time can be reduced by a factor of 2.5 while maintaining accuracy and precision. The total analysis time is reduced to three minutes if the 200 W ARL OPTIM’X Spectrometer is used.

Figure 2. Seven fused beads are used for the calibration. Image Credit: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Sample Preparation

Calibration was carried out with the help of seven iron ore-certified reference materials (CRMs). With a sample-to-flux ratio of 1:10, samples were fused into beads without ignition. The fusion mix was given an ammonium nitrate oxidizer. The concentration ranges of the various oxides covered by the calibration are shown in Table 1. R2 and standard error of estimates (SEE) values were calculated for each compound.

The sample preparation as fused beads eliminates any grain size or mineralogical effects that could interfere with the X-Ray fluorescence analysis. As a result, excellent analysis accuracy is obtained, particularly for major and minor elements/oxides.

Trace element determination is trickier due to sample dilution, as trace levels in the actual fused bead are 10 times lower than in the original sample. As a result, longer counting times may be used for trace element determination when necessary. When the best trace element determination is required, samples are prepared as pressed pellets.

Table 1. Concentration ranges and calibration parameter values for iron ore components. N = number of CRMs; R² = coefficient of determination; SEE = standard error of estimate. Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Calibration

Calibration curves were plotted to connect elemental X-Ray intensities to oxide concentrations (Figure 3). When only one form of each oxide is present in the sample, X-Ray fluorescence can quantify individual elements, and the results can be directly related to the oxide forms.

Figure 3. Calibration curves for a selection of oxides found in iron ore. Image Credit: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Validation

To validate the calibration, an iron ore reference material (405) was used (Table 2). CRM reference values are compared to the results of the first 10 replicate analyses. Table 3 displays the repeatability of the CRM’s 10 replicates.

Table 2. Reference iron ore (405) analysis with the ARL OPTIM’X Spectrometer. Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Table 3. Repeatability of reference iron ore (405) analysis using the ARL OPTIM’X Spectrometer. Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Conclusion

This article demonstrated the ARL OPTIM’X Spectrometer’s appropriateness for analyzing iron ore samples. This compact instrument enables fast and reliable analysis as well as outstanding repeatability. The 50 W ARL OPTIM’X Spectrometer required a total analysis time of 7.6 minutes.

The sample preparation as fused beads undoubtedly dilutes the sample 10 times, implying that the trace element levels are extremely low in the actual fused beads. This explains the low precision of traces, particularly for Cr₂O₃ and V₂O₅. Measurement time can be adjusted further based on the application, for example, by enhancing counting time to increase precision for trace elements.

The 200 W version of the ARL OPTIM’X Spectrometer reduced total counting time by a factor of 2.5 while maintaining the same accuracy and precision. The total analysis time would be reduced to about three minutes in this case.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

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