Remarkable structural effects on the extraction behavior of uranium from sulfuric acid medium using di-alkylhydrogen phosphonates: Insights from EXAFS and DFT computations

[Display omitted] •Demonstration of method for the separation of uranium from sulfuric acid medium.•First reports on the recovery of U(VI) from analytical waste contains sulfuric acid along with phosphoric acid by DalHPs.•First investigations on the extraction mechanism of U(VI)-DalHPs complexes.•EXAFS studies insights that the three ligands are coordinated to uranyl sulfate moiety. The structural effects of the carbon chain on the extraction of uranium have been examined by dialkylhydrogen phosphonates (DalHPs). The extraction of uranium by 0.55 M solutions of DalHPs in n-dodecane (n-DD) was investigated as a function of aqueous phase sulfuric and phosphoric acid concentration (0.1–6 M), and the obtained results were compared with 0.55 M solution of tri-n-butyl phosphate (TBP) in n-DD system under similar experimental conditions. The batch distribution data for the extraction of uranium from sulfuric acid and phosphoric acid medium indicated that DalHPs showed dual extraction behavior, i.e., cation exchange at lower acidities and solvation at higher acidities. The extraction of uranium from the sulfuric acid medium was found to be higher than that from the phosphoric acid medium. The extracted U-DalHPs complexes were characterized by extended X-ray absorption fine structure (EXAFS) and the local atomic structure was discerned. The coordination number of uranium was derived from the EXAFS fitting data for various sulfuric acid concentrations. Density functional theory (DFT) computations were performed to understand the electronic structure and binding affinity of U-DalHPs. An acid-dependent extraction mechanism was derived computationally to understand the complexation of U-DalHPs. The trends observed in the distribution ratios of uranium, and the coordination number deduced from EXAFS fitting was found to be in good agreement with the DFT computations. These investigations have opened up new avenues for use of DalHPs for the extraction/recovery of heavy metal ions from sulfuric acid medium.