Rapid determination of uranium on solid matrices by synergistic in situ chelation supercritical fluid extraction and UV absorption spectroscopy

The extraction and spectrophotometric quantitation of UO2(NO3)2 · 6H2O from different solid matrices is compared using ethanol solutions and supercritical carbon dioxide containing various combinations of 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octadione (FOD), tri-n-butylphosphate (TBP), and ethanol. The matrix is shown to have a tremendous effect on the extractability of ethanol from different solid matrices with achievable recoveries as follows: polypropylene/polyester > glass wool > cotton > clay. A synergistic increase in the recovery of U(VI) from Kaolin is observed when ethanol is used in combination with FOD or a mixture of FOD and TBP. Compared to liquid extraction, the SFE method yields higher recoveries, is significantly faster, is of equal or greater precision, and greatly reduces the amount of organic solvents used. Additionally, the UV absorption of the uranium · FOD complex is linear over three orders of magnitude in concentration (ppb to ppm) and makes direct UV monitoring of the amount of uranium extracted feasible.