Impact of Selective Iron Removal by DIBK-Based Multistage Solvent Extraction on Radionuclide Measurement Accuracy in Fe-Rich Metal Matrices

This study evaluates a multistage solvent extraction method using diisobutyl ketone (DIBK) to selectively remove iron from metal matrices and to improve the reliability of beta-emitting radionuclide analysis. DIBK was chosen due to its low solubility in water, which enables efficient back-extraction of Fe using distilled water. The experimental design consisted of two steps: Step 1 assessed the extraction and recovery behavior of Fe into the organic phase, while Step 2 examined the remaining Fe and coexisting elements (Ni, Sr, and Re, as a stable surrogate for Tc) in the aqueous HCl phase. Samples containing 10–700 mg of Fe showed high recovery efficiencies of 93–99% with a single extraction, and samples exceeding 900 mg required two to three additional back-extraction steps to achieve recovery above 95%. Ni remained predominantly in the aqueous phase with 90–100% stability, and Sr exhibited nearly complete recovery in all stages. Re showed partial co-extraction (65–90%), indicating the need for optimization of acid concentration and phase ratios. Subsequent radiochemical analyses of 55Fe, 63Ni, 90Sr, and 99Tc demonstrated recovery yields of approximately 90%, 90%, 100%, and 80%, respectively, all within acceptable analytical error ranges. Overall, the DIBK-based process provides an effective and reproducible pretreatment method for Fe-rich samples.