Article pubs.acs.org/IECR
Design of a Fission 99Mo Recovery Process and Implications toward Mo Adsorption Mechanism on Titania and Alumina Sorbents Dominique C. Stepinski,*,† Amanda J. Youker,† Elizabeth O. Krahn,† George F. Vandegrift,† Pei-Lun Chung,‡ and Nien-Hwa Linda Wang‡ †
Nuclear Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
‡
ABSTRACT: Molybdenum-99 is the parent of the most widely used medical isotope technetium-99m. Proliferation concerns have prompted development of alternative Mo production methods utilizing low enriched uranium. Alumina and titania sorbents were evaluated for separation of Mo from concentrated uranyl nitrate solutions. System, mass transfer, and isotherm parameters were determined to enable design of Mo separation processes under a wide range of conditions. A model-based approach was utilized to design representative commercial-scale column processes. The designs and parameters were verified with bench-scale experiments. The results are essential for design of Mo separation processes from irradiated uranium solutions, selection of support material, and process optimization. Mo uptake studies show that adsorption decreases with increasing concentration of uranyl nitrate; however, examination of Mo adsorption as a function of nitrate ion concentration shows no dependency, indicating that uranium competes with Mo for adsorption sites. These results are consistent with reports indicating that Mo forms inner-sphere complexes with titania and alumina surface groups.
1. INTRODUCTION Refractory sorbents have been widely recognized as supports for tetraoxoanions.1−11 The interactions between metal oxides (Mo, Cr, W, V, Re, Mn) and refractory oxides (such as Al2O3, TiO2, or SiO2) have been widely elucidated in the context of catalyst preparation.1−10,12,13 In radiochemical separations these supports have been used to a lesser extent due to the less favorable kinetics in comparison to ion-exchange resins. The notable exception is the application of alumina in the production of 99Mo.14−17 Our interest in adsorption of Mo on titania surfaces stems from its applications in separation of 99 Mo, the parent of the most commonly used radiopharmaceutical imaging agent 99mTc,18,19 from an irradiated uranyl nitrate solution. Nearly all of the 99Mo supply is produced in research, test, or isotope-production reactors by irradiation of highly enriched uranium (HEU) targets.19 The use of HEU has caused worldwide concerns over the use and transport of this weapons grade material and generation of larger than necessary radioactive waste inventories. The use of HEU is a proliferation concern that the US National Nuclear Security Administration (NNSA), Office of Material Management and Minimization (MMM), is vested in mitigating by converting research reactors and medical isotope production facilities worldwide to low enriched uranium (LEU, enriched to
