Selective Separation and Recovery of Mo(VI) by Hybrid Microcapsules Containing Organic Extractants-10179

The content of molybdenum in high level vitrified waste is limited. The selective separation and recovery of Mo(VI) from HLLWs containing highly concentrated HNO3 are very important in relation to the volume reduction of radioactive wastes, partitioning of nuclides and to make efficient use of resources. The organic extractant LIX63 (5,8-diethyl-7-hydroxy-6-dodecanone oxime) is effective for the extraction of Mo(VI). The selective uptake of Mo(VI) from nitric acid solution was studied by using microcapsules (MCs), LIX63HALG and LIX63Ca-HALG. The characterization of LIX63HALG and LIX63Ca-HALG was examined by a scanning electron microscope (SEM), and the uptake and recovery of Mo(VI) were investigated by batch and column methods, respectively. The particle sizes of LIX63HALG and LIX63Ca-HALG were about 1.2 mm and 0.9 mm in diameter. Fine droplets of LIX63 were uniformly encapsulated in the matrices. The uptake rate of Mo(VI) for both MCs was fairly fast and the uptake attained equilibrium within 5 h; the uptake percentage was above 99% within 3 h in the presence of 1 M HNO3. The order of the Kd value for different metal ions at 1 M HNO3 was Mo(VI) >> W(VI) > Cr(VI) > Re(VII) >> Se(IV). The uptake of Mo(VI) was followed by a Langmuir adsorption isotherm, and the maximum uptake capacity of Mo(VI) for LIX63HALG was estimated to be 0.54 mmol/g. In a similar way, the maximum uptake capacity of Mo(VI) for LIX63Ca-HALG was estimated to be 0.73 mmol/g. The breakthrough curve of Mo(VI) for the column packed with LIX63HALG had S-shaped profiles, and 5% breakpoint and breakthrough capacity were estimated to be 24 cm and 0.11 mmol/g, respectively. The 5% breakpoint and breakthrough capacity of Mo(VI) for the column packed with LIX63Ca-HALG were estimated to be 15 cm and 0.19 mmol/g, respectively. The adsorbed Mo(VI) was effectively eluted with 5 M HNO3. LIX63CaALG exhibited a relatively high uptake percentage of 99.9% for Mo(VI). Thus, the LIX63-MCs were effective for the separation and recovery of Mo(VI) from HLLWs containing highly concentrated HNO3. WM2010 Conference, March 7-11, 2010 Phoenix, AZ