Effective utilization of waste ash from MSW and coal co-combustion power plant-Zeolite synthesis

The solid by-product from power plant fueled with municipal solid waste and coal was used as a raw material to synthesize zeolite by fusion-hydrothermal process in order to effectively use this type of waste material. The effects of treatment conditions, including NaOH/ash ratio, operating temperature and hydrothermal reaction time, were investigated, and the product was applied to simulated wastewater treatment. The optimal conditions for zeolite X synthesis were: NaOH/ash ratio = 1.2:1, fusion temperature = 550 °C, crystallization time = 6-10 h and crystallization temperature = 90 °C. In the synthesis process, it was found that zeolite X tended to transform into zeolite HS when NaOH/ash ratio was 1.8 or higher, crystallization time was 14-18 h, operating temperature was 130 °C or higher. The CEC value, BET surface area and pore volume for the synthesized product at optimal conditions were 250 cmol kg−1, 249 m2 g−1 and 0.46 cm3 g−1 respectively, higher than coal fly ash based zeolite. Furthermore, when applied to Zn2+ contaminated wastewater treatment, the synthesized product presented larger adsorption capacity and bond energy than coal fly ash based zeolite, and the adsorption isotherm data could be well described by Langmuir and Freundlich isotherm models. These results demonstrated that the special type of co-combustion ash from power plant is suitable for synthesizing high quality zeolite, and the products are suitable for heavy metal removal from wastewater.