EDXRF analysis of coal fly ash as loose powders Ling Yok Ung, Application Specialist

Importance of the Topic

Fly ash from coal combustion contains heavy metals and poses environmental and health risks. Rapid and accurate quantification of its elemental composition is essential for quality control, regulatory compliance, and valorization in construction materials.

Objectives and Study Overview

The study aims to establish a fast, precise, and reliable protocol for analyzing loose coal fly ash powders using energy dispersive X-ray fluorescence (EDXRF), focusing on key oxides (Na2O, MgO, Al2O3, SiO2, P2O5, SO3, K2O, CaO, TiO2, Mn3O4, Fe2O3).

Methodology and Instrumentation

• Instrument: Thermo Scientific ARL QUANT'X EDXRF spectrometer with Silicon Drift Detector (SDD) and 50 W Rh/Ag X-ray tube.
• Excitation: Multiple filters and voltages (4–50 kV) in vacuum; no sample spinning.
• Sample preparation: ~1 g loose powder in plastic cups sealed with 4 µm polypropylene film.
• Calibration: Ten oxide standards covering representative concentration ranges; calibration curves built relating X-ray intensity to oxide concentration.
• Analysis time: Total live time 2 minutes per sample (e.g., 80 s low Z, 40 s mid Z).

Main Results and Discussion

• Calibration performance: R2 values above 0.975 for all oxides; RMSE values ranged from 0.008 to 1.736.
• Accuracy: Analysis of reference material (ARM 013) showed close agreement with certified values, with deviations within acceptable limits.
• Repeatability: 1-sigma precision (%RSD) below 1.3% for all oxides, demonstrating high reproducibility.

Benefits and Practical Applications

• Non-destructive, minimal sample preparation.
• Rapid screening for routine quality control in power plants and construction materials.
• Potential for process monitoring, waste management, and regulatory reporting.

Future Trends and Potential Applications

• Integration with automated sample handling for high-throughput analysis.
• Extension to in-situ measurements and portable EDXRF systems for field analysis.
• Combining chemometric approaches to refine elemental speciation and trace element detection.

Conclusion

The ARL QUANT'X EDXRF spectrometer provides a swift, accurate, and repeatable method for analyzing loose coal fly ash powders. High calibration linearity and low RSD values confirm its suitability for environmental monitoring and industrial quality control.

Instrumentation Used

Thermo Scientific ARL QUANT'X EDXRF spectrometer equipped with a 30 mm2 Si drift detector, 50 W Rh/Ag X-ray tube, nine primary beam filters, and a 10-position autosampler.

References

• Natural Resources Defense Council. Coal Ash: Fly Ash, Bottom Ash, and Boiler Slag. 2025.