Effect of crown ethers on the ion-exchange behavior of alkaline earth metals. Toward improved lon exchange methods for the separation and preconcentration of radium

The effect of selected crown ethers on the uptake of alkaline earth cations by sulfonic acid and diphosphonic acid-based cation-exchange resins from hydrochloric acid media is examined. The effect observed is shown to vary with the hydrophobicity of the crown ether, Water-soluble crown ethers enhance the sorption of certain cations, thereby improving the selectivity of the resin for other alkaline earths over calcium ion, an apparent result of a synergistic interaction between crown ether present in the resin phase and the ionic functional groups of the resin. In the presence of more hydrophobic crown ethers, a decrease in cation sorption is often observed, a result of the exclusion of the crown ether from the resin phase and the formation of cation-crown complexes in the solution phase, The result can be a reversal of the selectivity sequence ordinarily exhibited by the resin.