Sardinian natural clinoptilolites are examined to evaluate their adsorption for the metals, copper, cadmium, lead and zinc, as well as ammonium removal. The natural material is either used as received or once converted into the sodium form. Equilibrium data for each species and the natural material are obtained. The corresponding behavior is quantitatively correlated using classical isotherms, whose parameters are estimated by fitting the equilibrium data. Breakthrough experiments of lead solutions are also performed. Fixed-bed runs are simulated using a mathematical model which includes axial dispersion as well as a new approximate rate law for non-linear adsorption and diffusion in spherical adsorbent particle based on an equivalent film resistance model.