Supercritical Carbon Dioxide Extraction of Uranium from Acidic Medium Employing Calixarenes

Abstract

Various calixarenes were evaluated for the supercritical fluid extraction of uranium from nitric acid medium. The extraction efficiency was found to be affected by various parameters, namely pressure, temperature, CO₂ flowrate, extraction time, and molarity of nitric acid. The addition of HPFOA (pentadecafluoro-n-octanoic acid) for the production of CO₂-phillic fluorinated counter ion enhanced the extraction efficiency. Under optimized conditions (pressure of 200 atm, temperature of 323 K, 30 minutes of static time followed by 30 minutes of dynamic time, CO₂ flowrate of 2 mL min⁻¹, nitric acid molarity of 0.1 M) for uranium: calixarene: HPFOA mole ratio of 1:5:10, highest extraction efficiency could be obtained with p-tert.-butyl calix[6]arene (79.9%). Solvent extraction study with hexane as the organic phase indicated the formation of [UO₂ (calixarene)]²⁺. In order to assess the suitability of the developed method to extract uranium in the presence of a host of other ions, extraction efficiency for other metal ions was estimated.

Keywords:

• calixarene
• carbon dioxide
• counter ion
• supercritical fluid extraction
• uranium

ACKNOWLEDGEMENTS

The authors wish to acknowledge the Board of Research in Nuclear Sciences, Department of Atomic Energy, Goverment of India, India, for financial support. Thanks are due to Dr. B.S. Tomar, Head, RACD for his continuous support. We also acknowledge the encouragement from Dr. Pradeep Kumar. Thanks are also due to S. Jeyakumar for his involvement during IC analysis.

Notes

# mean of three repetitions, Average standard deviation = ±4%.

The extraction efficiency values are mean of two repetitions.

The results are mean of two repetitions.