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

Abstract

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 (DTc ∼ 2.03) and ∼99% recovery of technetium 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 mechanism like, H+aq. + TcO4−aq. + DCH18C6org = HTcO4.DCH18C6org up to 4.0 M feed acidity and HTcO4.DCH18C6org + H +aq. + NO3−aq = DCH18C6org.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.