An evolved fluorimetric determination of uranium in rock/mineral sample solutions containing hydrolysable elements such as Nb, Ta, Zr and Ti sequestered by bi-fluoride

The aim of the present paper is to develop a novel method for fluorimetric determination of uranium in rock/mineral solutions containing hydrolysable elements such as Nb, Ta, Zr and Ti sequestered by bi-fluoride. These rocks/minerals are decomposed with ammonium bi-fluoride (NH4HF2) and sulfuric acid (H2SO4) mixture. Uranium in such mineral solutions is selectively extracted into ethyl acetate with 2,3-dihydroxynaphthalene at pH 10-12 in the presence of cetyltrimethylammonium bromide, prior to its pellet fluorimetric determination. Optimizations of certain parameters such as the effects of fluoride fluxes, mineral acids, masking agents and diverse ions are discussed in detail. This method is applied for the determination of uranium in synthetic mixtures and a set of in-house reference refractory minerals including certified reference material X1807 with a high degree of accuracy and precision. The results for the refractory minerals using the proposed method are in excellent agreement with results obtained by other standard methods. The novelty of the proposed method is that the decomposition mixture (NH4HF2/H2SO4) inhibits the hydrolysis of hydrolysable elements by formation of their soluble fluoro complexes, and the separation of uranium using the complexing agent 2,3-dihydroxynaphthalene is more eco-friendly compared to existing the conventional solvent extraction system using aluminum nitrate as the salting out agent.