Adsorption of heavy metal cations using coal fly ash modified by hydrothermal method

In this study, the adsorption properties of synthetic zeolite produced from Brazilian coal fly ash were investigated for some heavy metal cations (Zn, Cu, Mn and Pb). The batch method has been employed, using metal concentrations in solution ranging from 100 to 3000 mg/l. Preliminary statistical analysis has indicated that temperature and time of synthesis of zeolites were the most important variables that affect the their adsorption capacity. Results lead to the conclusion that a hydrothermal treatment can increase from 2 to 25 times the adsorption capacity (CA) of the coal ash comparing to its original capacity. The ion-exchange characteristic of the zeolites was determined using Langmuir, Freundlich and Dubinin–Kaganer–Radushkevich isotherms. The adsorption increases as cation concentrations in aqueous solution increases. The preference order observed for adsorption is Pb > Cu > Zn > Mn.