A Fast Method for Recycling Fly Ash:  Microwave-Assisted Zeolite Synthesis

Abstract

Zeolitic material was synthesized from fly ash by conventional and microwave-assisted hydrothermal alkaline activation experiments. The zeolite synthesis was studied as a function of temperature, time, and activation solution concentration. K+-Na+/NH4 + exchange properties of the zeolitic material synthesized were studied as a function of time and zeolite type. The zeolitic material synthesized from the same fly ash by changing the synthesis parameters contained: NaP1, hydroxysodalite, hydroxycancrinite, analcime, tobermorite, and nepheline hydrate using NaOH as an activation agent and F linde zeolite, kalsilite, and phil lipsite-KM zeolite from KOH activation. Synthesis yields and zeolite types obtained from the microwave and conventional experiments were very similar, but the activation time needed was drastically reduced by using microwaves (from 24−48 h to 30 min). Consequently, the industrial application of the synthesis process is enhanced by the microwave-assisted method. From this point of view, the most interesting zeolites synthesized are NaP1, KM-phillipsite, and F linde zeolites since the NH4 + retention capacities obtained for the activation products were close to 20 and 30 mg of NH4 + g-1. The experiments performed also showed that high NH4 + retention capacities are attained after a few minutes of equilibrium with NH4 +-rich solutions.

Formation of linde F zeolite by KOH treatment of coal fly ash

“…Although there has been no report on the CEC of FA-derived linde F zeolite, Querol et al reported that 23.1 mg g -1 (1.4 meq g -1 ) of ammonium (NH4 + ) ions was adsorbed on the FA-derived linde F zeolite. 6) Further study is needed in order to elucidate the adsorption of various harmful ions on linde F zeolite.…”

Resource recovery from coal fly ash waste: an overview study

“…The zeolitization of CFA by microwave heating has also been reported to be useful for shortening the reaction time. 66) Microwaves are absorbed directly by water as the solvent, which enables more rapid heating than by conventional heating processes. The electromagnetic waves induce water dipole rotation, probably activating water molecules by the breaking of hydrogen bonds.…”

Synthesis of merlinoite from Chinese coal fly ashes and its potential utilization as slow release K-fertilizer

“…Synthesis of zeolites from coal fly ash is one of the promising applications of fly ashes with high added value [9]. Since the initial studies of zeolite synthesis from fly ash by Höller and Wirsching (1985) [10], various methods and patents have been proposed, improved and applied by many authors to synthesize different types of zeolites , among which direct conversion is a common synthesis method [19,[22][23][24][25]. Due to the peculiar structural properties of zeolites, they have a wide range of industrial applications, such as ion exchange, and gas and water adsorption, among others [35,36].…”