Synthesis of ZSM-5 Molecular Sieve from Coal Gasification Fine Slag and Its Adsorption Mechanisms for Pb2+ in Aqueous Solution
Coal gasification fine slag (CGFS), a solid waste from entrained-flow coal gasification, is characterized by fine particles and high silicon and aluminum content. This study proposes a simple and economical hydrothermal synthesis of ZSM-5 molecular sieve using CGFS as raw material. Impurities were removed by acid washing, followed by alkaline extraction of silicon and aluminum species. The extracted Si-Al precursors were crystallized hydrothermally at 170 °C for 48 h, yielding ZSM-5 with a high specific surface area of 358 m2/g. Adsorption experiments showed that the synthesized ZSM-5 exhibited excellent Pb2+ removal performance: at 25 °C, the removal efficiency for a 50 mg/L Pb2+ solution reached 83.7%, with an adsorption capacity of 104.625 mg/g under optimized conditions. The adsorption process is mainly governed by chemisorption mechanisms, including surface complexation, precipitation, and ion exchange. Thermodynamic analyses indicated that Pb2+ adsorption is spontaneous and endothermic, consistent with multilayer chemisorption. The synthesized ZSM-5 shows promising potential for application in the treatment of lead-containing wastewater, offering a high-value utilization route for coal-based solid waste.