Synthesis of zeolite from Italian coal fly ash: Differences in crystallization temperature using seawater instead of distilled water Claudia Belviso * , Francesco Cavalcante, Saverio Fiore Laboratory of Environmental and Medical Geology, IMAA-CNR, Tito Scalo (PZ), Italy article info Article history: Accepted 10 November 2009 Available online 19 January 2010 abstract In this study Italian coal fly ash was converted into several types of zeolite in laboratory experiments with temperatures of crystallization ranging from 35 up to 90 °C. Distilled and seawater were used during the hydrothermal synthesis process in separate experiments, after a pre-treatment fusion with NaOH. The results indicate that zeolites could be formed from different kind of Italian coal fly ash at low tem- perature of crystallization using both distilled and seawater. SEM data and the powder patterns of X-ray diffraction analysis show that faujasite, zeolite ZK-5 and sodalite were synthesized when using both dis- tilled and seawater; zeolite A crystallized only using distilled water. In particular the experiments indi- cate that the synthesis of zeolite X and zeolite ZK-5 takes place at lower temperatures when using seawater (35 and 45 °C, respectively). The formation of sodalite is always competitive with zeolite X which shows a metastable behaviour at higher temperatures (70–90 °C). The chemical composition of the fly ash source could be responsible of the differences on the starting time of synthesized zeolite with distilled water, in any case our data show that the formation of specific zeolites takes place always at lower temperatures when using seawater. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Coal fly ash is the most abundant coal combustion by-product, partly used in concrete and cement manufacturing yet more than half of it disposed of in landfills since it finds no other applica- tion. The huge production of fly ash is extremely worrying be- cause of this kind of disposal and several investigations have been carried out in order to try to exploit this waste material. Over the last few years fly ash has been gaining ground in the synthesis of zeolites. This is due to the fact that the main fly ash component is amorphous aluminosilicate glass, which is the prevalent reactive phase. The synthesizing process for zeolite from fly ash involves an alkaline treatment using both KOH and NaOH at high temperatures (Holler and Wirsching, 1985; Henmi, 1987; Shih and Chang, 1996; Lee et al., 2001; Murayama et al., 2002). The processes involved are hydrothermal reaction (Holler and Wirsching, 1985; Henmi, 1987; Shih and Chang, 1996; Lee et al., 2001; Murayama et al., 2002; Tanaka et al., 2003), hydro- thermal processes with a pre-treatment fusion to improve the conversion of fly ash into zeolite (Shigemoto et al., 1993, 1994; Berkgaut and Singer, 1996; Chang and Shih, 1998; Rayalu et al., 2000), and molten-salt methods (Park et al., 2000a,b) or methods which involve the utilization of microwaves (Querol et al., 1997; Slangen et al., 1997; Katsuki et al., 2001; Inada et al., 2005). Distilled water was used in all the experiments conducted with these different methods. In this work four samples of coal fly ash from Italian thermo- electric power plants were used for synthesizing zeolites by hydro- thermal activation after a pre-treatment fusion with NaOH. The experiments involved were performed at different temper- atures of crystallization – from 35 to 90 °C – by using both seawater and distilled water, separately. The utilization of seawater could cut down the costs for a large-scale use of distilled water and reduce drastically the costs to attain the incubation temperature using warm seawater from powder plants, generally located near the sea. Our data show that X-type zeolite, ZK-5-type zeolite and soda- lite form at lower temperatures when using seawater, and A-type zeolite is synthesized only when using distilled water. The forma- tion of sodalite is competitive with X-type zeolite which is highly metastable at higher temperatures. These results do not agree with the very few data available in literature on the synthesis of zeolite using seawater. Lee et al. (2001) show the results of the hydrothermal process (without a pre-treatment fusion) used in order to form Na-P1-type zeolites with incubation temperatures above 100 °C. When comparing the patterns of the products, the authors of this article report that the use of seawater neither disturbs nor accelerates the zeolite for- mation, and the amount of zeolite synthesized with seawater is comparable with that synthesized with distilled water. Our study can provide a starting-point to develop a new eco- nomically advantageous method for production of useful materials 0956-053X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2009.11.015 * Corresponding author. Tel.: +39 0971427224; fax: +39 0971427222. E-mail address: belviso@imaa.cnr.it (C. Belviso). Waste Management 30 (2010) 839–847 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman