Hydrothermal synthesis of mesoporous tobermorite from fly ash with enhanced removal performance towards Pb2+ from wastewater

The mesoporous tobermorite with high removal efficiency of Pb2+ was hydrothermally synthesized from fly ash (FA). The physicochemical characteristics of the synthesized tobermorite were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller specific surface area analyzer, and Fourier transform infrared spectroscopy (FTIR). It was found that the specific surface area and pore volume of the mesoporous tobermorite were 29.98 m2/g and 0.1325 cm3/g, respectively, which were much higher than those of FA. The tobermorite showed high removal efficiency for Pb2+ of 99.93%, and the adsorption kinetic data for Pb2+ adsorption on tobermorite were better fitted with the pseudo-second-order model. Besides, the Langmuir isotherm model provided better description of the Pb2+ adsorption isotherm, and the maximum adsorption capacity for Pb2+ adsorption on tobermorite was 266.67 mg/g, which was much higher than that on FA (86.13 mg/ g). What's more, the adsorption mechanisms of the tobermorite towards Pb2+ were analyzed by XRD, SEMenergy dispersive spectroscopy, and FTIR. It was found that the high adsorption capacity of the tobermorite towards Pb2+ was ascribed to its mesoporous structure, a mass of -OH, the ion-exchange of Ca2+ with Pb2+, and the precipitation of 2PbCO3.Pb(OH)2. This work presents the tobermorite synthesized from FA as an effective and low-cost adsorbent towards Pb2+, and provides a potential application method of FA in treatment of industrial wastewater containing Pb2+