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UBC Theses and Dissertations

Uranous sulfate precipitation as a novel route to uranium purification in extractive metallurgy Burns, Alexander D.


Uranous sulfate can be crystallized from uranium(IV)-containing solutions by raising the temperature and adding sulfuric acid. Several important aspects of the process have never been investigated, however, making its successful application as a real-world extractive metallurgy technology far from certain. This dissertation addresses several fundamental questions surrounding the crystallization of uranous sulfate from acidic process solutions. The effects of various parameters on the solubility of uranous sulfate and the kinetics of its precipitation are demonstrated, including temperature, acid concentration, and agitation, based on the results from a series of bench-scale experiments. The effects of various impurities on the selectivity and efficiency of the crystallization process are also determined. Two new uranous sulfate x-hydrate polymorphs, the hexahydrate and the octahydrate, are characterized using single-crystal x-ray diffraction, vibrational spectroscopy, and chemical assay data, and an understanding of the conditions under which they form is developed. The thermal stability and decomposition characteristics of uranous sulfate tetrahydrate, hexahydrate, and octahydrate are demonstrated through fundamental thermodynamic calculations and through the examination of thermal analysis data. The fundamental kinetics of uranium(IV) oxidation in acidic solutions are quantified through the interpretation of experimental data under various conditions of acidity, temperature, and oxygen partial pressure. Finally, a hydrometallurgy flow sheet incorporating uranous sulfate precipitation is presented, and the viability of the complete process is demonstrated experimentally, including electrolytic reduction, precipitation, filtration, drying, and calcining. This work demonstrates that uranous sulfate precipitation is viable as a hydrometallurgical process technology, and that further work is justified.

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