Obtaining of Clinoptilolitic Extrudates for Environmental Applications I. Rheological Characterization for the Zeolitic Pastes

The natural zeolites powders with high content of clinoptilolite can be used in the polluted water treatment processes. In order to bring these ceramic materials to the desired shape, for example by extrusion, all information about the rheological properties are imperative. The purpose of this paper is to present the rheological aspects regarding the obtaining of new natural zeolites based extrudated materials, containing a high amount of clinoptilolite, an abundant material in Romania. The influence of two parameters was assessed: the amount of stearine and the presence of cationic surfactant, both at a constant solid fraction. It was noticed that all unmodified clinoptilolite based pastes present a tixotropic pseudoplastic non-newtonian fluid behaviour. As the stearine concentration in the composition of the pastes rises, their dynamic viscosity decreases; in parallel, the pseudoplastic character decreases and a viscoelastic effect appears. This behaviour confirms the lubricant function of the stearine for this system. The pastes become more workable by stearine adding. Applying the Ostwald de Waele rheological model, the parameters of this model for all the pastes were determined. The clinoptilolite pastes modified with cationic surfactant showed a more complex behaviour (dilatant with a viscoelastic element). The conclusion is that the cationic surfactant plays a binding role.