Kinetics of the Ba2+/Na+ exchange on a mixed phillipsite–chabazite–rich tuff

The kinetics of Ba2+/Na+ ion exchange on a mixed tuff, containing both phillipsite and chabazite, was studied. A fixed bed experimental apparatus was used and the breakthrough curves were determined varying the Ba2+ concentration in the inlet solution in the range 0.77-17.5 eq-m-3. The experimental results showed that the tuff under consideration is very selective towards Ba2+, with very steep breakthrough curves. A diffusional model, based on the linear driving force (LDF) approximation, was used to interpret the experimental data. The model takes into account both fluid-particle and intra-particle resistances to diffusion, and considers the fact that the tuff contains different zeolites, having different ion exchange properties. Its use allowed to evaluate the internal and the external mass transfer coefficients, and it appeared that, except in one of the experimental runs, their values do not depend on the composition of the liquid phase, confirming the validity of the LDF approximation.