Abstract
Thorium, a major element in thorium matrix, quenches uranium fluorescence when it is present above the ratio (Th/U) of 2000 in conventional pellet fluorimetry determination of uranium. A single step ‘sample digestion cum thorium fluoride precipitation’ with NH4HF2 has been developed for separation of bulk thorium as hydrated thorium fluoride precipitates. Uranium in aqueous solution is extracted into ethyl acetate and stripped into pyrophosphate medium (pH ∼ 7), prior to its laser induced fluorimetry determination. Optimizations of certain parameters such as the effects of fluoride flux, mineral acid, temperature and time, stripping solution, diverse ions etc. are discussed in detail. The method has been validated by analyzing a set of synthetic mixtures and certified reference materials of rock samples such as SY-2, SY-3, GSP-2, NKT-1 and CG-2 doped with a large excess of thorium. This method has been applied for the determination of microgram to nanogram uranium in thorium rich rocks and synthetic nuclear grade ThO2 with high degree of accuracy and precision. This is the improvement of the existing method which involves two liquid-liquid solvent extraction separation of thorium and uranium using the chelating agent 2,3-dihydroxynaphthalene at the different pH, compared to one solvent extraction separation of uranium in the present method, because separation of thorium by precipitation as its fluoride has already been carried out during sample digestion step itself. The proposed method involving ammonium hydrogen fluoride in combination with laser induced fluorimetry is simple, rapid, cost effective and more eco-friendly.
Acknowledgments
The authors are thankful to Head, Chemistry Group, AMD, Hyderabad and Dr. Vijay Kumar, In-charge, Chemistry Laboratory, AMD, Jamshedpur for constant encouragement, support and motivation to do the work. The authors express their sincere thanks and gratitude to Directors, AMD, Hyderabad and NIT, Jamshedpur for their kind permission to do research work leading to a Ph.D. (SKP). The authors are also thankful to Additional Directors (OP-I and R&D), AMD, Hyderabad, Regional Director and Dy. Regional Director, AMD, Eastern Region, Jamshedpur for providing necessary facilities to carry out the work.
Author contributions: Susanta Kumar Pradhan: Conceptualization, Methodology, Validation, Writing - original draft. Balram Ambade: Supervision, Writing - review & editing.
Research funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest statement: There are no conflicts to declare.
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