Eco-friendly zeolites for innovative purification of water from cationic dye and heavy metal ions

Along with industrial development, coal consumption and the amount of waste fly ash increase, negatively impacting the environment. Fly ash contains silicon and aluminum oxides, and could serve as a substrate for the synthesis of zeolite. The novelty of this study was to assign a potential of fly ashes from lignite combustion in three energy blocks operating on circulating fluidized bed boilers to convert them into zeolites. The X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy; pore volume, size and specific surface area tests; thermal analysis; leaching test; and radioisotope activity analysis were applied to characterize the materials. Zeolites were synthesized using hydrothermal and fusion methods modified in the molar concentration of NaOH, the ratio of NaOH to raw material, drying and heating temperatures, and treatment time. Both, hydrothermal and fusion synthesis were found to result in the efficient formation of the zeolite Linde Type A, gismondine, and sodalite; with the largest specific surface area of zeolite developed after fusion synthesis (132 m(2) g(-1)). The zeolite had surpassingly high efficiency of adsorption of cationic impurities from post-production wastewater, ranging from 85% to 97% and from 89% to 100%, when tested with methylene blue and lead ions, respectively. The costs of zeolite production were estimated to range from 3.82 to 6.36 $ per 1 kg, thus reducing the price of commercial zeolite by up to 99.5%. The new engineering method of zeolite is an attractive alternative to the storage of hazardous byproducts from coal-fired power plants. Eco-zeolite is also a technological innovation in the cleaning of post-production wastewater from harmful impurities, while water reuse in a closed circuit. Our studies provide tools for novel and integrated environmental management in line with the 'Cleaner Production' goal to reduce the production of waste, while improving use efficiency of energy, resources, and water.