Using Coal Fly Ash and Wastewater for Microwave Synthesis of LTA Zeolite The reuse of industrial wastes from a coal-fired power plant and a plasma electro- lytic oxidation process was attempted to realize a zero discharge. The batch com- position was adjusted by adding sodium hydroxide and sodium aluminate. A sin- gle-mode microwave oven equipped with reflux condenser was used for crystalli- zation under atmospheric pressure. The synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, BET, thermogravimetric anal- ysis, and cation-exchange capacity (CEC) measurement. Analytical results indi- cated that Na-A zeolite with a defined maximum crystallinity could be success- fully synthesized by hydrothermal treatment of fly ash with wastewater. Due to the high CEC, the product can be applied for gas purification and soil remediation processes. Keywords: Coal fly ash, Industrial waste, Plasma electrolytic oxidation, Wastewater treatment, Zeolite LTA Received: April 10, 2014; revised: May 01, 2014; accepted: June 05, 2014 DOI: 10.1002/ceat.201400225 1 Introduction The abundance of amorphous aluminosilicate in fly ash as a by-product of coal-fired power stations makes it an important source material for synthetic zeolites. Zeolitic aluminosilicates are valuable inorganic porous materials that can be synthesized by various techniques and serve for a wide range of diverse applications as adsorbent, catalyst, adsorbent in the form of powder, formed particulates, and membranes [1–6]. Over the last few decades, the synthesis of different zeolites from fly ash has been of great interest to many researchers. Two well-known activation processes are generally employed for the conversion of coal fly ash (CFA) to zeolite. The first one is a two-step pro- cess, in which pretreatment fusion at high temperature is fol- lowed by a hydrothermal process. Different zeolites including Na-A [7–9], Na-X [10–14], and Na-P [15] were synthesized by means of this indirect two-stage method. The second method is a direct hydrothermal process, in which the fusion step is eliminated [16] and different zeolites such as Na-A [17, 18], Na-Y [19], Na-P [20–23], and hydroxy sodalite [24] are synthesized. The direct and indirect zeolitization processes of CFA are being studied in terms of type and concentration of the alkaline solutions, solution/solid ratio, aging time, mixing technique, and time, temperature, and pressure of the crystalli- zation reaction using different thermal sources such as conven- tional and microwave techniques. Numerous publications including review articles [25–27] indicate the increasing inter- est in using fly ash as a source of Si and Al for manufacturing different porous zeolitic aluminosilicates. All methodologies for zeolitization of CFA involve three ma- jor stages of dissolution, nucleation, and crystal growth. The conventional techniques for synthesis of different zeolites from CFA are very time-consuming taking 12–48 h on average. Cur- rently, microwave-assisted hydrothermal processes are being considered as one of the most effective techniques for chemical synthesis including zeolite crystallization [28–30]. Most studies utilized deionized, distilled, or industrial water during the synthesis, but few reports analyzed different sources of water. Belviso et al. [10] synthesized zeolite X from CFA and seawater by pretreatment fusion with NaOH followed by hy- drothermal crystallization. Results obtained with seawater and distilled water were compared in [10]. The synthesis yield at different crystallization temperatures was higher using sea- water. Hussar et al. [31] synthesized zeolite A by hydrothermal process using sodium silicate, sodium aluminate, and the by- product of an aluminum etching process. The chemical com- position of the aluminum etching by-product consisted of the main oxides of Al 2 O 3 (92 %), Na 2 O (6 %), and SiO 2 (0.5 %). Their results indicated that a higher synthesis reaction temper- ature and a longer reaction time led to improved synthesis of zeolite A. The effect of taking industrial waste brine solution instead of ultrapure water was investigated during the synthesis of zeolite by Musyoka et al. [24]. They used CFA as silicon feedstock and high-halide brine obtained from the retentate effluent of a reverse-osmosis mine water treatment plant. The brine con- tained high sodium and potassium levels and low concentra- tions of toxic elements. In addition, there was a trace of alumi- num equal to 48.38 mgL –1 and no silicon. The use of brine as a Chem. Eng. Technol. 2014, 37, No. 9, 1–10 ª 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Jamshid Behin 1,2 Syed Salman Bukhari 1 Vahid Dehnavi 1 Hossein Kazemian 1 Sohrab Rohani 1 1 Western University (UWO), Department of Chemical and Biochemical Engineering, London, ON, Canada. 2 Razi University, Department of Chemical Engineering, Kermanshah, Iran. – Correspondence: Dr. Sohrab Rohani (srohani@uwo.ca), Dr. Hossein Kazemian (hossein.kazemian@uwo.ca), Western University (UWO), Department of Chemical and Biochemical Engineering, London, ON, N6A 589, Canada. Research Article 1