Ion effects on the extraction of cesium (I) by 1,3-Diisopropoxycalix [4] arenecrown-6(BPC6) and the highly efficient extraction under neutral conditions

The effect of ion species and concentration on the extraction percent of Cs+ by 1,3-Diisopropoxycalix [4] arenecrown-6 (BPC6) in octanol/water solvent extraction system has been studied by molecular dynamics simulations and experiments. The results show that the anionic species play an important role on the enhancement of the extraction percent of Cs+. Specifically, the order in which anions promote the extraction percent is different at different total anion concentrations. At a relatively low anion concentration of 0.5 M, the extraction percent follows the sequence: ClO4−> I−> NO3−> Br−> Cl−> SO42−> F−. At a relatively high concentration of 2 M, the extraction percent of Cs+ follows the following sequence: I−> ClO4−> Br−~ NO3−> Cl−> SO42−> F−. It is indicated that the extraction percent is dominated by the anion’s interface propensity, which is the probability of anion distribution in the interface compared to the water phase. However, at low concentration of anions, strong coordination effect of NO3− promotes the extraction effect compared to Br−. At the high anion’s concentration, the stronger salting-out capacity of Br− leads to a considerable increase of extraction percent. In addition, the cations also slightly affect the extraction percent. The extraction percent is affected by both cations’ concentration and the salt-out effect. On this basis, a neutral Cs+ extraction system has been established, and one stage extraction percent could reach 62.5%.