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The synthesis of zeolites through microwave-assisted hydrothermal alkaline activation processes allows for a faster recycling of fly ash. Although both the microwave and conventional methods of zeolite synthesis yield the same products, the dissolution of silica and aluminium is faster in microwave-assisted zeolite synthesis. The method hastens the conversion of of synthesized zeolites such as NaPl, KM-phillipsite, and F linde zeolites since the high retention capacities of NH+4 are reached after just a few minutes.

This study focuses on the behavior of major and trace water-soluble impurities in fly ash during leaching processes. The objective is to assess potential decontamination procedures in order to reduce the content of undesirable species in coal combustion by-products and to increase their potential industrial applications. Fourteen flyashes were selected for this study. Major impurities considered were lime and portlandite, sulfate, and some potentially hazardous trace elements such as As, Ba, Be, Cd, Co, Cr, Cu, Ge, Mn, Mo, Ni, Pb, Se,Th, U, V,and Zn.Water was used for the extraction experiments,with asolvent/fly ash ratio of 50 mL/g. An hydrite was completely dissolved in all fly ashes studied, except the Cercs and Escatron flyashes. Lime and portlandite were completely dissolved or carbonated from all flyashes with exception of the Cercs flyash. Bulk calcium contents were reduced from 9% to 18% in all fly ashes with the exception of the Compostilla and Espiel fly ashes (4-5%). From 17% to 79% ofthe sulfur was extracted from the bulk content. The results show a relatively higher extraction for S, Se, As, B, Mo, and Ca, and an intermediate extraction for As, Ge, Cd, Li, Sr, Na, V, Cr, Sn, P, and Ba. The results suggest that the alkalinityis induced during the extraction mainly by free lime. The high alkalinity accounts for the high Al and Si concentrations in the leachates and the relatively low mobility of sometrace elements, with the exception of As, B, Mo, and Se. [ABSTRACT FROM AUTHOR]

This article summarizes the results obtained from the physical, chemical, and mineralogical characterization of 14 fly ash samples. Major features that influence the utilization of each fly ash for zeolite synthesis are evidenced, and several fly ash types were selected as potential high-quality starting material for zeolite synthesis and ceramic applications. The main parameters influencing this selection were relatively small grain size; high Al and Si contents; high glass content; low CaO, S, and Fe contents; and relatively low heavy metal concentration. The Compostilla and Dou He fly ashes have high potential applications because of the low content of major impurities (such as Ca, Fe, and S) and the low content of soluble hazardous elements. The Espiel, Escucha, Los Barrios, As Pontes, Soto de Ribera, Meirama, Narcea, and Teruel fly ashes have important application potential, but this potential is slightly limited by the intermediate content of nonreactive impurities, such as Fe and Ca. The La Robla fly ash is of moderate interest, since the relatively high Ca and Fe oxide contents may reduce its potential applications. Finally, the Puertollano fly ash also has limited application because of the very high concentration of some heavy metals such as As, Cd, Ge, Hg, Pb, and Zn. From a mineralogical point of view, the Compostilla, Espiel, and Soto de Ribera fly ashes show the highest aluminum-silicate glass content and, consequently, the highest industrial application potential. [ABSTRACT FROM AUTHOR]