Hydrothermal synthesis of zeolitic material from circulating fluidized bed combustion fly ash for the highly efficient removal of lead from aqueous solution

The utilization of coal fly ash derived from circulating fluidized bed combustion (CFBFA) still faces great challenges because of its unique characteristics. In this study, a zeolitic material with Na-P1 zeolite as the main phase was successfully synthesized via a hydrothermal method by using CFBFA as the raw material. The effects of hydrothermal temperature, time, and added CTAB amount on the characterizations of synthesized materials were investigated by XRD, SEM, and XPS. The properties of the optimal zeolitic material and its adsorption performance for Pb²⁺ in aqueous solution were evaluated. The influences of pH, initial concentration, dosage, and temperature on Pb²⁺ adsorption were also examined. Results revealed the following optimal parameters for the synthesis of zeolitic material:NaOH concentration of 2 mol·L^-1, solid-to-liquid ratio of 1:10 g·ml^-1, hydrothermal temperature of 110℃, hydrothermal time of 9 h, and CTAB amount of 1 g (per 100 ml solution). The adsorption capacities of the zeolitic material reached 329.67, 424.69, and 542.22 mg·g^-1 when the pH values of aqueous solution were 5, 6, and 7, respectively. The Pb²⁺removal efficiency can reach more than 99% in aqueous solution with the initial concentrations of 100-300 mg·L^-1 under pH 6 and suitable adsorbent dosage. The adsorption and kinetics of Pb²⁺ on the zeolitic material can be described by Langmuir isotherm and pseudo-second-order kinetic models, respectively. The ion exchange between Pb²⁺ and Na⁺ and chemisorption are the main adsorption mechanism. All these findings imply that the synthesis of low-cost adsorbent for Pb²⁺ removal from weak acid and neutral aqueous solution provides a highly effective method to utilize CFBFA.