Cation exchange in the system CaII or MgII + complexing‐agent + zeolite‐NaA: Equilibria in water‐ethanol

The ion-exchange behaviour of CaII and MgII with zeolite NaA in ethanol-water systems has been studied. The ion-exchange isotherms show that the affinity of the zeolite for CaII and MgII ions decreases with increasing ethanol content, i.e. decreasing dielectric constant of the media. When adding nitrilotriacetate (NTA) as a complexing agent, the selectivity of zeolitic NaA for CaII and MgII ions was found to decrease. The exchange phenomena observed are discussed in relation with water distribution and cation coordination preferences. Cation-anion coordination in mixed solvents was studied using 35Cl NMR.