Extraction of ¹³⁷Cs from Acidic Feed by Centrifugal Contactors Using a Solution of Calix[4]arene-bis-1,2-benzo-crown-6 in Phenyltrifluoromethyl Sulphone

Extraction of ¹³⁷Cs from 1.6 L of diluted aqueous simulated high-level waste (SHLW) (at 1 M HNO₃) was carried out using a two-stage centrifugal contactor system (bowl volume 200 mL) into 2 × 10⁻³ M solution of calix[4]arene-bis-1,2-benzo-crown-6 in phenyltrifluoromethyl sulphone. Batch extraction studies were done to optimize the conditions for the centrifugal contactor runs. Extraction and stripping experiments were carried out at 2000 rotations per minute, keeping the organic and aqueous flow rate at 15 mL/min. Alamine 336 was used at a very low concentration (0.4 vol %) to effect efficient stripping of the extracted radiocesium. The studies were carried out using SHLW as well and the results indicated quantitative extraction and stripping in the first stage of operations while the repeat runs suggested lower extraction as well as stripping efficiencies.