Accurate determination of halogens in geological materials using an automated pyrohydrolysis system with a liquid nitrogen cold trap.

Background: Accurately determining the content of halogens (F, Cl, Br, and I) in geological samples, especially ultra-trace amounts of I, remains a challenging task owing to their inherent volatility. Traditional pyrohydrolysis techniques face the challenges of incomplete sample decomposition and released halogen recovery. Moreover, the pyrohydrolysis mechanism of geological samples has never been investigated. Hence, a robust method of fully decomposing geological samples, achieving the complete recovery of volatile halogens, and elucidating the related reaction mechanisms is required.

Results: An automated pyrohydrolysis system was constructed to extract halogens from geological materials. Two innovative techniques were applied simultaneously during sample preparation to obtain high-quality data, namely a double-layer quartz pyrohydrolytic tube that ensured the complete decomposition of geological samples and a liquid nitrogen cold trap that facilitated the complete recovery of volatile halogen compounds. The captured halogens were determined by ion chromatography and inductively coupled plasma mass spectrometry. The obtained results were highly consistent with those obtained using noble gas and radiochemical neutron activation analysis methods. Moreover, the reaction mechanism of basalt (BHVO-2) with the accelerator (VO) was investigated in detail using X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy.

Significance: This study demonstrates the effectiveness of simultaneously employing a double-layer quartz pyrohydrolytic tube and liquid nitrogen cold trap in pyrohydrolysis for halogen analysis, eliminating the need for the neutron activation technology. Additionally, elucidating the reaction mechanisms enhances the advancement and refinement of analytical techniques.