Crucial parameters determining efficient use of fly ashes from energy sector as raw materials for dedicated advanced applications

Abstract

This paper describes the physicochemical properties of three types of samples: fly ashes received directly from the coal power plant (FA_PP), fly ashes coming from commercial warehouses (FA_Mix) and the commercial cenospheres (FA_Cen). The main goal of our studies was to identify crucial parameters of fly ashes decisive to use these materials for such advanced applications as synthesis of zeolites or structured catalysts as well as to choose optimal ways of their effective chemical valorization. The chemical composition of the studied samples was determined by XRF, the phase composition - by both XRD and Raman spectroscopy. Textural properties - by using jointly SEM-EDS and low-temperature nitrogen adsorption. The grain size distribution was determined by laser diffraction analysis. DRIFT spectroscopy was used to examine the functional features of the analyzed samples. Physicochemical properties of the functional materials obtained from ash samples (containing i.a. NaX zeolites) were determined by the XRF, XRD and DRIFT. The obtained results confirmed a decrease of the Si/Al ratio from 1.94 to 1.34, accompanying NaX zeolite synthesis starting from FA_Cen ashes and from 2.27 to 2.13 starting from FA_Mix. XRD measurements performed for the obtained preparations showed intense reflections characteristic of NaX zeolite only in the case of FA_Mix ashes used as a starting material. The differences in synthesis progress were mainly influenced by the content ratio of the glassy to crystalline phases and by such textural properties as: specific surface area and particle size distribution. The reported results clearly confirm the complex nature of the tested materials and their evident potential to be used for synthesis of such functional materials as e.g. zeolites.