Synthesis of zeolite from fly ash: application to adsorption of COD from cheese whey wastewater

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Abstract
In this study, raw fly ash (RFA) was used to synthesize zeolite (the zeolitized fly ash, ZFA) via a two-step process (alkaline fusion-hydrothermal synthesis). RFA and ZFA were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared. The prepared ZFA was employed as the adsorbent in the batch adsorption of chemical oxygen demand (COD) from cheese whey wastewater. The effect of operational parameters on the adsorption process was investigated. The results showed that the adsorption efficiency increases with the increase of pH, contact time, adsorbent dosage, and temperature. The optimum conditions were determined as pH of 11, a contact time of 20 min (q(e) = 330.088 mg/g), and adsorbent dosage of 0.4 g for COD adsorption on ZFA. Kinetic analysis of the COD adsorption on ZFA indicated that the adsorption process was controlled by the Morris-Weber-order model. Moreover, the isotherm models were subjected to the experimental data of the COD adsorption on ZFA. The results revealed that the COD adsorption on ZFA involved physical adsorption with good adsorption characteristics. The calculated values of the thermodynamic parameters such as Delta H degrees, Delta S degrees, and Delta G degrees revealed that the adsorption of COD on ZFA was feasible, spontaneous, and endothermic. In fact, high adsorption efficiency can be obtained in a short time using ZFA as the adsorbent for the COD removal from cheese whey wastewater.