The recovery of strontium from acidic medium using novel strontium selective extractant: An experimental and DFT study

[Display omitted] •BOC8A/NO -An efficient solvent medium for Sr2+ separation from acid medium.•Aliphatic NO diluents reported for the first time in hydrometallurgy.•Ion dissociation mechanism is operative for the Sr2+ extraction.•Recovery of Sr2+ from loaded BOC8A/NO phase by 0.01 M HNO3 solution.•DFT study supported expt. results of high affinity of diprotonated BOC8A for Sr2+. In view of the limited solvent system known for the Sr2+ extraction from acidic media, extraction and recovery of 90Sr from acidic medium using novel Octabenzyloxyoctakis[[[(N,N-diethylamino)carbonyl)]methyl]oxy]calix[8]arene (BOC8A) extractant in nitro alkane medium are presented in this paper. BOC8A and nitro alkanes have been synthesized and characterized by 1H NMR, 13C NMR, FTIR and GC–MS techniques. Solvent composition of 0.01 M BOC8A in nitro octane (NO) has been optimized for substantial amount of extraction of strontium from feed acidity of 3.5−4 M nitric acid, (D3.5−4 M HNO3 = 7.1–7.8). Poor extraction of Pu4+, Ba2+, Na+ and UO22+ and negligible extraction of Am3+, Cs+, Ru3+, Nd3+, Zr2+ and trivalent lanthanides are observed. Ion dissociation mechanism was found to be operative involving an extractable complex having Sr2+, BOC8A and HNO3 in a ratio of 1:1:2. About 99 % of Sr2+ from the loaded solvent was recovered with 0.01 M HNO3. DFT calculations were used to predict the structures of free, protonated BOC8A and its complex with Sr2+. DFT result showed reorientation in conformation of BOC8A due to protonation resulting in the Sr2+ extraction from acidic medium with significantly high interaction energy between Sr2+ and diprotonated form of BOC8A.