A fast method for recycling fly ash: Microwave-assisted zeolite synthesis

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 phillipsite-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 far 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.