Selective transport of cesium and strontium ions through polymer inclusion membranes containing calixarenes as carriers

Cs+ and Sr2+ are selectively removed over Na+ from acidic aqueous solutions with high Na+ concentrations by using membranes designed to selectively transport one of the two cations. To this end, calix[4]arene derivatives were used as carriers in polymer inclusion membranes (PIMs). The synthesis and characterization of new calix[4]arene derivatives (a bisamide (2) and three bisesters (3, 5 and 6)) used for the separation of Sr2+ are described. Another bisester (4) was employed for the same separation. In addition, a calix[4]arene-crown-6 (7) was incorporated into the membrane for Cs+ extraction. The concentration of each membrane component (polymer, carrier and counter-ion) was optimized and the permeability coefficients (P, m sec(-1)) of Cs+, Sr2+ and Nat were determined. A synergistic effect between the calixarenes and dinonylnaphtalenesulfonic acid, used as counterion, (DNNS, 8) was observed. High selectivity of Cs+ over Na+ and of Sr2+ over Na+ were obtained with compounds 7 and 3, respectively. The best P for Sr2+ was obtained with compound 4. A long-term experiment was carried out to demonstrate the durability of PIMs. PIMs are compared to classical supported liquid membranes.