Hydraulic and Mass-Transfer Performance of a 20-Mm-Diameter Annular Centrifugal Contactor for the Solvent Extraction of Cesium by Bis(2-Propyloxy)Calix[4]-Crown-6 in n-Octanol

A calixcrown extraction process using bis(2-propyloxy)calix[4]-crown-6 (iPr-C[4]C-6) as extractant and n-octanol as diluent for the separation of cesium from Chinese High Level Liquid Waste (HLLW) has been developed at INET. Chinese HLLW is acidic defense waste with high salt content, which is now stored in underground stainless steel tanks. The intention is to use a process to extract cesium from HLLW conducted on multistage 20-mm-diameter annular centrifugal contactors (ACCs), so it is necessary to study the hydraulic and mass-transfer performance of a 20-mm-diameter ACC for the extraction system. In this work, the effects of the parameters such as the rotor speed, the diameter of heavy weir, and the acid concentration on the hydraulic performance were investigated. An operational envelope of the 20-mm-diameter ACC for the n-octanol/aqueous solution system was identified. The mass-transfer efficiency of the single stage 20-mm-diameter ACC for the extraction and stripping of cesium with iPr-C[4]C-6 in n-octanol was studied by varying several parameters, such as the rotor speed, the total flow rate, and the flow ratio. The extraction stage efficiency is greater than 95% at suitable operating conditions for extracting Cs⁺ with 0.025 mol/L of iPr-C[4]C-6 in n-octanol from HNO₃ solution containing Cs⁺. The stripping stage efficiency of Cs⁺ (< 90%) is lower than the extraction stage efficiency of Cs⁺.