Pertraction of radio-cesium from acidic feeds across supported liquid membranes containing calix-crown-6 ligands in a fluorinated diluent

Abstract

Supported liquid membranes containing a solution of four calix-crown-6 ligands viz., calix[4]arene-bis-crown-6 (CC), calix[4]arene-benzo-bis-crown-6 (CBC), calix[4]arene-naphtho-bis-crown-6 (CNC), and bis-(octyloxy)calix[4]arene-mono-crown-6 (CMC) in a fluorinated diluent, phenyltrifluoromethyl sulfone (PTMS) along with small fraction of Alamine 336, were employed for the pertraction of radio-cesium from nitric acid feed solutions. The transport efficiency of the membranes followed the trend: CNC⪢CBC>CC⪢CMC. While 4.0×10−3M solutions of CBC, CC and CMC were used for the transport studies and near quantitative Cs(I) transport was seen at tracer scale after 4h using CBC, transport studies with CNC were carried out at 1.0×10−3M due to solubility limitations. The mass transport rates for Cs(I) reported here is the fastest in a calix-crown-6 based SLM and shown to be promising for applications in nuclear waste remediation. Acid co-transport was observed with all the calix-crown-6 ligands which increased sharply if the membranes were used for longer time. 137Cs spiked simulated high level waste (SHLW) was used as the feed to result in >60% transport of the metal ion and <3% acid co-transport after 5h when the CBC based SLM was used to suggesting effectiveness of the transport system for applications in the back end of the nuclear fuel cycle. Transport parameters such as permeability coefficient (P) and diffusion coefficient (Do) were also determined. The SLM was found to have limited stability to suggest that fresh membranes need to be used for better performance.