Heterogeneity and hierarchy of clinoptilolite porosity

The porous structure of the raw and the modified clinoptilolite has been investigated by nitrogen adsorption method, polarized light, scanning electron and atomic force microscopy as well as by thermogravimetric analysis. The relative moisture, specific gravity, bulk density and inter-particle porosity have been tested using thermostatic, pycnometric and hydrostatic weighing methods. The geometric method has been used to calculate the external surface area of the clinoptilolite crystallites in the clinoptilolite rock and to evaluate the volume of the clinoptilolite framework channels. Generally two types of porosities such as primary porosity and secondary one are observed. The primary porosity may be defined as microporosity presented by nanotube system of the clinoptilolite 3-dimensional aluminosilicate framework. The secondary porosity is formed by meso- and macropores, where the first ones are presented by slot pores determined mainly by cleavability of the zeolite crystallites. Total volume of the zeolite channels equals 0.332 cm3/g which has been obtained using a geometric method. Micropores volumes of the raw and the acid-treated samples are 0.0031 and 0.0342 cm3/g by nitrogen adsorption, respectively. According to thermogravimetric analysis the structural water lost at 150-750 °C placed the pore volume 0.087 cm3/g with the surface area 360 m2/g.