TC Measurement and Elemental Composition Analysis of Fly Ash – Quantitation by TOC and XRF

Importance of the Topic

The accurate determination of carbon content in fly ash is critical for both environmental monitoring and industrial quality control. Fly ash, a by‐product of thermal power and waste incineration plants, contains significant amounts of metal oxides and residual carbon from incomplete combustion. Precise carbon quantification enhances the reliability of X-ray fluorescence (XRF) analysis for all other elements, ensuring proper assessment of material composition and supporting compliance with regulatory requirements.

Objectives and Study Overview

This study demonstrates a combined approach using a Total Organic Carbon (TOC) analyzer and XRF spectrometry to improve quantitative analysis of fly ash samples. By using the total carbon (TC) value obtained from the TOC measurement as a calibration standard, the work aims to achieve accurate quantitation of carbon alongside major and trace elements via the Fundamental Parameters (FP) method in XRF.

Methodology

The experimental workflow involved four fly ash samples (A, B, C, D) plus a heat‐treated blank sample:

• TOC measurement: 100–500 mg of powder was analyzed using the TOC‐L CSH analyzer coupled with the SSM‐5000A solid sample combustion unit. Total carbon (TC) was measured in triplicate to assess reproducibility.
• XRF spectrometry: Qualitative analysis covered elements from beryllium to uranium. Quantitative determinations applied the FP method, with TC values fixed from the TOC data and other elements reported as oxides.
• Calibration: Carbon CKα intensities from XRF were plotted against TC values to generate a carbon calibration curve. For comparison, a calibration using Loss on Ignition (LOI) was also created.

Instrumentation Used

• Shimadzu TOC-L CSH Total Organic Carbon Analyzer
• Shimadzu SSM-5000A Solid Sample Combustion Unit
• Shimadzu XRF-1800 Sequential X-ray Fluorescence Spectrometer (4 kW Rh target)

Main Results and Discussion

TOC measurements yielded TC values ranging from 0.354% to 5.940% across samples, with coefficients of variation near 1%. Incorporating these TC values in the XRF FP quantitation reduced bias in major oxides: neglecting carbon led to overestimations of SiO2 by 3.5% and Al2O3 by 1.4% in sample A. The XRF-based carbon calibration curve against TC displayed excellent linearity and 0.15% accuracy, outperforming the LOI-based curve (0.39%). Comprehensive oxide data for SiO2, Al2O3, Fe2O3, CaO and trace oxides down to ppm levels confirmed the method’s broad dynamic range.

Benefits and Practical Applications

The combined TOC + XRF approach offers:

• Accurate carbon quantitation at low levels, improving overall compositional accuracy.
• Elimination of uncertainties inherent in LOI for carbon and moisture.
• Capability to analyze principal and trace elements in a single workflow.
• Applicability to fly ash, incineration ash, soils, composts, and metallurgical slags.

Future Trends and Opportunities

Advances may include integration with automated sample preparation, enhanced detector technologies for light elements, and coupling with chemometric tools for multivariate calibration. Extending this TOC + XRF methodology to other complex matrices and real-time process monitoring promises to broaden its industrial and environmental applications.

Conclusion

The use of TOC solid sample measurement to supply accurate TC values for XRF FP quantitation significantly enhances element analysis of fly ash, resolving the traditional challenge of carbon detection. This streamlined method provides precise major‐and‐trace element data in a single analytical sequence and is readily applicable to diverse inorganic materials.

References

• Ochi H., Okashita H.: Shimadzu Review, Vol.45 (1-2), 51 (1988).
• Shimadzu Application News No. O035, O040.
• TOC / TN / TP Application News No.4,5,14, First Edition: Jun.2013.