Synthesis of novel zeolites produced from fly ash by hydrothermal treatment in alkaline solution and its evaluation as an adsorbent for heavy metal removal

In this study, zeolites (FA6, FA12, and FA24) were prepared from JIS Type-II fly ash (FA) by alkaline hydrothermal treatment, and their physicochemical characteristics were investigated. In addition, their adsorption capability for heavy metals ions (Hg2+ and Pb2+) was evaluated. Zeolites have Hydrosodalite and/or Zeolite P structure, and the specific surface area of FA24 was greater than that of FA6 and FA12. A higher amount of heavy metals ions was adsorbed by FA24 than by FA6 and fA12. After adsorption using FA24, the binding energy of Pb2+ was detected, on the other hand, the binding energy of Hg2+ was not detected under our experimental conditions. These results suggest that FA24 surface properties shows a low adsorption capability of Hg2+. In addition, ion exchange with sodium ions in the adsorbent was also related to the adsorption capability of heavy metals ions (correlation coefficient: 0.965-0.973). A pH of approximately 5 was found to be optimal for the adsorption of heavy metals ions under our experimental conditions.