Příprava syntetických zeolitů na bázi VEP

Abstract

Dissertation thesis deals with the design of a methodology for the synthesis of zeolites from secondary energy products, specifically high-temperature fly ashes from ČEZ, a. s. Brown coal fly ashes, which were taken directly from transfer chutes, are a by-product of the Ledvice, Mělník, Trmice, Prunéřov, Tušimice power plants and the Trmice heating plant. Black coal fly ashes from the electrostatic and mechanical separators are a by-product of the Dětmarovice power plant. The fly ashes were characterized by X-ray fluorescence spectrometry supplemented with Fe and Al determination by atomic absorption spectrometry, X-ray diffraction analysis, LOI determination, etc. On the basis of optimal properties, fly ash from the electrostatic precipitator of the Ledvice power plant was used in the experiments that were carried out to determine the optimal physical and chemical parameters of zeolite synthesis. Microwave and combined (microwave and convection) syntheses were performed. This study presents a three-phase hydrothermal synthesis of high-purity sodalite in suspension. Initially, the fly ashes were microwave decomposed for 150 min at 120 ℃ in 4M NaOH. The Si/Al ratio was 1:1.5, and the solid-to-liquid ratio (S/L) was 1:5. Microwave digestion was performed in the Milestone UltraCLAVE IV autoclave reactor. The mixing intensity was 70% and cross-shaped magnetic stirrers were used. In the second stage, the mixtures were convectively heated for 24 h at 120 ℃ in a Memmert UF 110PLUS drying oven. The S/L ratio was 1:40. Additionally, 30 mL of 30% LiCl was added to the mixture. The mixtures were stirred manually. The final convective crystallization at 70 ℃ lasted 24 h. The efficiency and reproducibility of the methodology were tested for nine high-temperature fly ashes. The synthesis products were analyzed by X-ray powder diffraction at both qualitative and quantitative levels. Under the specified optimal conditions, pure-phase sodalite (>99 wt.%) was prepared from the nine fly ashes. The formation of rhombododecahedral crystals of synthetic sodalite was confirmed by scanning electron microscope images.