Separation of strontium from the raffinate solution of TEHDGA-actinide partitioning process: Batch extraction and process development

The extractant N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (TEHDGA) has been evaluated for extraction of strontium from the raffinate solution of TEHDGA-actinide partitioning process. Actinide partitioning of HLW using 0.2 M TEHDGA + 30% isodecyl alcohol/n-dodecane, carried at our unit at engineering scale, selectively separates trivalent ‘f’ group elements from HLW leaving all the elements including strontium in the raffinate. Strontium from the raffinate was extracted using 0.3 M TEHDGA + 5% isodecyl alcohol/n-dodecane, isodecyl alcohol has been used as a phase modifier whose concentration was optimized to 5% (v/v) to obtain maximum extraction of strontium (D3.1–3.8M = 23) without third phase formation in the given extraction conditions. The stoichiometry of the extracted complex was found to depend on initial aqueous nitric acid concentration and obtained as Sr(NO3)2(TEHDGA)2(HNO3)2. Fission products, such as Mo, Pd, and Zr, co-extracted during extraction process were scrubbed with 3.5 M nitric acid containing 0.2 M oxalic acid and 0.05 M HEDTA. Complete stripping of strontium was achieved with 0.01 M nitric acid. Quantitative recovery of strontium was obtained in a single contact of extraction, two contacts of scrubbing and two contacts of stripping each at O/A = 1.

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► 0.3 M TEHDGA + 5% isodecyl alcohol/n-dodecane used for separation of strontium from SHLW solution.
► Stoichiometry of the extracted complex determined as Sr(NO3)2(TEHDGA)2(HNO3)2.
► Co-extracted fission products (Zr, Mo, and Pd) were scrubbed with 0.2 M oxalic acid + 0.05 M HEDTA/3.5 M nitric acid.
► High recovery and purity of strontium was obtained with this process.