Analysis of Rare Earth Elements in Base Metal Ores by ICP-OES

Importance of the Topic

Rare earth elements (REEs) play a vital role in defense, energy and various industrial applications due to their unique physical and chemical properties. Although REEs are widespread in the earth’s crust, they often occur in low concentrations that require sensitive and selective analytical methods for accurate quantification. Inductively coupled plasma optical emission spectrometry (ICP-OES) is favored for its speed, robustness and multi-element capability, but REE analysis in complex ore matrices presents significant spectral interferences that must be overcome.

Objectives and Study Overview

This study evaluates the performance of the Agilent 5800 Vertical Dual View ICP-OES in the determination of 16 REEs in base metal and rare earth ore samples. Key aims include:

• Overcoming spectral interferences through advanced background correction and wavelength selection.
• Validating accuracy and precision using three certified reference materials (CRMs) and four natural ore samples.
• Demonstrating high-throughput analysis with minimized maintenance.

Methodology

Sample preparation involved microwave digestion of 0.250 g ore in HNO3 and HCl using a CEM MARS 6 iWave system and EasyPrep vessels. Calibration employed matrix-matched standards (0.01–10 mg/L) with correlation coefficients >0.9999. IntelliQuant Screening was used for rapid semiquantitative assessment and optimal wavelength selection. Background correction techniques included Fitted Background Correction (FBC), Fast Automated Curve-Fitting Technique (FACT) and off-peak correction. Method detection limits (MDLs) were determined as three times the standard deviation of ten 10 ppb blank spikes.

Instrumentation

• Agilent 5800 VDV ICP-OES with SeaSpray nebulizer, double-pass cyclonic spray chamber and demountable torch.
• AVS 7 switching valve and SPS 4 autosampler for rapid, low-carryover sample introduction.
• Vista Chip III CCD detector providing continuous wavelength coverage (167–785 nm).
• CEM MARS 6 iWave microwave digestion system and EasyPrep iWave vessels.

Main Results and Discussion

• MDLs ranged from 0.0014 to 0.0036 μg/mL in solution (0.28–0.73 μg/g in solid).
• CRM recoveries for all REEs were within ±10% of certified values, demonstrating method accuracy.
• Four ore samples showed reproducible precision (RSD <15%) and sample-to-sample measurement time of 1 min 1 s.
• Long-term stability over five hours (≈100 samples) maintained recoveries within ±10% with RSD <3%.

Benefits and Practical Applications

The 5800 VDV ICP-OES offers:

• High resolution and advanced detection for reliable REE analysis in complex matrices.
• Simplified method development with IntelliQuant Screening and automated background correction.
• Enhanced throughput and reduced maintenance via AVS 7 sample introduction.
• Robust plasma stability and repeatable torch alignment for routine mining laboratory operations.

Future Trends and Potential Applications

• Integration of machine learning for real-time spectral deconvolution and interference correction.
• Development of compact ICP-OES systems for in-field ore grade monitoring.
• Expansion to other challenging sample types such as battery materials and environmental matrices.
• Automated workflows combining microwave digestion and ICP-OES for high-throughput laboratories.

Conclusion

The Agilent 5800 VDV ICP-OES, combined with advanced optics, detection technology and intuitive software tools, provides accurate, precise and high-throughput determination of REEs in complex ore matrices. The method’s robustness, low detection limits and streamlined operation make it well suited for routine mining and geological applications.

References

1. Van Gosen B.S., Verplanck P.L., Seal R.R. II, Long K.R. and Gambogi J. (2017) Rare-earth elements, in Schulz K.J. et al. (eds), Critical Mineral Resources of the United States—Economic and Environmental Geology and Prospects for Future Supply. U.S. Geological Survey Professional Paper 1802, chap. O, O1–O31.
2. Agilent Technologies (n.d.) IntelliQuant Screening. Publication 5994-1518EN.
3. Agilent Technologies (n.d.) ICP Expert Software. Publication 5994-1517EN.
4. Natural Resources Canada (n.d.) Canadian Certified Reference Materials Project. Available from NRCan NRCAN website.
5. Agilent Technologies (n.d.) Fitted Background Correction (FBC)—Fast, accurate and fully automated background correction. Publication 5991-4836EN.
6. Agilent Technologies (n.d.) Real-time spectral correction of complex samples using FACT spectral deconvolution. Publication 5991-4837EN.