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 ~ 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. + DCH18C6_org = HTcO₄.DCH18C6_org up to 4.0 M feed acidity and HTcO₄. DCH18C6_org + H ⁺_aq. + NO₃^–_aq = 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.