Fluorine Estimation in Fluorspar Using WD-XRF: A Comprehensive Guide

Central Laboratory, Mitra S.K. Private Limited

Fluorspar (CaF₂) is a strategically important industrial mineral widely used in steelmaking, ceramics, cement production, and hydrofluoric acid manufacturing. Its commercial value is directly governed by fluorine content, making accurate determination of F essential for reliable grade classification and process control. Wavelength-Dispersive X-ray Fluorescence (WD-XRF) is recognized as one of the most precise and stable techniques for fluorine quantification. Its superior spectral resolution, reduced peak overlaps, and ability to measure light elements make it highly suitable for analyzing complex mineral matrices like fluorspar. Additional advantages include fast throughput, high repeatability, minimal sample destruction, and reduced human error. Despite the inherent challenge of fluorine’s low-energy X-rays—which are easily absorbed—WD-XRF overcomes this through optimized instrumental design: vacuum atmosphere, XS-55 analyzing crystal, and sensitive flow proportional counters dedicated to light elements.

Why WD-XRF Works:

• High spectral resolution
• Vacuum atmosphere for better F detection
• Stable optics for repeatability
• Suitable for both low- and high-grade fluorspar

Fusion Beads: The Preferred Sample Preparation

Fusion beads eliminate particle-size effects and mineralogical bias, producing a uniform glass disc ideal for WD-XRF.

Typical fusion: 1 g sample + 10 g Li₂B₄O₇–LiBO₂ flux + LiBr, fused at 1050–1100 °C to form a clear, crystal-free bead.

Chemical Reactions During Fusion of CaF₂ With Lithium Borate Flux

During fusion, CaF₂ reacts with lithium borate flux to form calcium metaborate Ca(BO₂)₂, lithium fluoroborate LiBF₄, and additional LiBO₂. These species stabilize Ca²⁺ and F⁻ ions within the molten borate network, allowing complete dissolution and formation of a clear, homogeneous bead.

Calibration Curve Data:

CRM	Fluorine (%)
CRM-1	45.67
CRM-2	34.03
CRM-1 (Diluted)	22.84
CRM-2 (Diluted)	17.02

WD-XRF vs Wet Classical Chemistry:

Sample No.	Wet Classical Chem (%)	WD-XRF (%)	Deviation (%)
S-782	6.13	6.06	−1.14%
S-647	8.44	8.33	−1.30%
S-783	13.65	13.75	+0.73%
S-890	15.94	15.65	−1.82%
A-1	46.87	46.52	−0.75%

All results fall within acceptable analytical deviation, demonstrating strong correlation between classical wet chemistry and WD-XRF.

Conclusion:

WD-XRF, when combined with high-quality fusion bead preparation, offers a robust, accurate, and highly reproducible method for fluorine estimation in fluorspar. It eliminates matrix effects, ensures superior measurement stability, and supports reliable process control in industries where fluorine content is critical. This method stands as the preferred analytical approach for laboratories aiming for precision, speed, and long-term consistency in fluorspar evaluation.

Contributed by : Alakata Saha https://www.linkedin.com/in/msk-alakta-saha-81a7121b3/

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