Experimental and theoretical studies (DFT) on technetium extraction as HTcO4 using dicyclohexano-18-crown-6 in a blend of isodecyl alcohol and n-dodecane from acidic medium

Fundamental studies on technetium extraction from acid medium using a versatile supramolecule, dicyclohexano-18-crown-6 (DCH18C6) in isodecyl alcohol-n-DD diluent system from acidic nuclear waste have been reported here. It was observed that the maximum extraction (D-Tc similar to 2.03) and similar to 99% recovery of techne-tium can be achieved when an organic phase of 0.4 M DCH18C6 in 50% isodecyl alcohol + n-dodecane was used to extract technetium from 4.0 M HNO3 solution followed by three successive stripping contact with water. Two types of mechanisms are found to be operative depending on the acidity of feed solution, an extraction mech-anism like, H+ (aq.) + TcO4q-. + DCH18C6(org) = HTcO4.DCH18C6(org) up to 4.0 M feed acidity and HTcO4. DCH18C6(org) + H-aq.(+) + NO3aq = DCH18C6(org).HNO3 + TcO4- (aq.)+ H (+)(aq). for feed acidity beyond 4.0 M HNO3. Almost identical interaction energies of adducts DCH18C6-HTcO4 & DCH18C6-HNO3 obtained in the DFT calculations. The extraction is driven by low hydration energy of pertechnate compared to nitrate up to 4.0 M HNO3 and beyond 4.0 M HNO3 concentration of nitrate dominates the hydration energy effect causing decrease in the technetium extraction irrespective of the equal interaction energies.

Automated summary

This study presents fundamental research on the extraction of technetium from acid nuclear waste using a supramolecule called dicyclohexano-18-crown-6 (DCH18C6) in a isodecyl alcohol-n-DD diluent system. The authors found that the highest extraction and recovery of technetium (D-Tc approximately 2.03 and ~99% recovery) were achieved when using an organic phase containing 0.4 M DCH18C6 in 50% isodecyl alcohol + n-dodecane to extract technetium from a 4.0 M HNO3 solution. Different extraction mechanisms were identified based on the acidity of the feed solution. The study also revealed the importance of hydration energy in the extraction process.