The measurement of moisture content in mineral ore samples

Significance of the Topic

Accurate determination of moisture in oil shale and other mineral ores is critical for developing reliable calibration models in energy and resource analysis. Moisture content can significantly affect spectroscopic predictions of oil yield and material properties, making robust, rapid and non-destructive measurement techniques indispensable in both research and industrial settings.

Objectives and Study Overview

This study aimed to evaluate near-infrared (NIR) diffuse reflectance spectroscopy as a quantitative tool for moisture analysis in oil shale samples. By exposing prepared samples to controlled humidity environments and correlating spectral features with gravimetric moisture uptake, the work sought to establish a predictive relationship for non-bonded hydroxyl absorption bands, particularly at 1900 nm.

Methodology

Sample Preparation and Humidity Control:

• Oil shale powders were oven-dried at 105 °C to constant weight and then equilibrated in desiccators over saturated salt solutions to achieve relative humidity levels from 0 to approximately 97% at 22–24 °C.
• Ten discrete humidity conditions were established using common salts (e.g., LiCl, NaCl, K₂SO₄), with silica beads providing a zero-humidity baseline.

Spectral Acquisition and Data Processing:

• NIR diffuse reflectance spectra were collected from 2300 to 1300 nm using a Cary 500 UV-Vis-NIR spectrophotometer equipped with a Praying Mantis diffuse reflectance accessory.
• Instrument settings included a 5 nm spectral bandwidth, double beam mode, 0.3 s integration time, and reduced slit height; powdered KBr served as a background for baseline correction.
• Raw reflectance data were converted to pseudo-absorbance (log10 1/R) and subjected to second-derivative enhancement using an 11-point Savitzky–Golay algorithm to resolve overlapping bands.

Instrumentation

• Cary 500 UV-Vis-NIR Spectrophotometer
• Praying Mantis Diffuse Reflectance Accessory
• Cary 400/500 Extended Sample Compartment

Main Results and Discussion

Analysis of second-derivative spectra revealed the combination band of non-bonded –OH at 1900 nm to increase proportionally with sample moisture uptake, while the overtone bands at 1400 nm and bonded –OH at 2200 nm showed no clear trend. Plotting the integrated area under the 1900 nm feature against gravimetric moisture content yielded a strong linear correlation, demonstrating the band’s suitability for quantitative moisture determination in oil shale.

Benefits and Practical Applications

• Non-destructive and rapid moisture assessment without the need for chemical reagents.
• Improved calibration of NIR models for oil yield prediction by compensating for moisture variations.
• Potential for real-time monitoring in industrial processes involving mineral drying and handling.

Future Trends and Potential Uses

Advances in chemometric modeling and portable NIR instrumentation may enable on-site moisture analysis in mining and processing facilities. Integration with automated sampling systems and machine-learning algorithms could further enhance accuracy and throughput. Extending this approach to other mineral matrices and building composite models for multi-component analysis represents another promising direction.

Conclusion

This work validates NIR diffuse reflectance at 1900 nm as a reliable marker for moisture content in oil shale. The established linear relationship between non-bonded –OH band intensity and water uptake offers a practical route for routine, non-destructive moisture analysis, supporting both laboratory research and industrial quality control.

References

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