Key Takeaways & Executive Findings
- •• • ZSM-5 synthesized from CGFS achieved a high specific surface area of 358 m2/g, enabling superior adsorption performance for Pb2+ removal. • • At 25 °C, the ZSM-5-1 sample achieved 83.7% removal efficiency for a 50 mg/L Pb2+ solution, corresponding to an adsorption capacity of 104.625 mg/g. • • Pb2+ adsorption is spontaneous and endothermic, dominated by chemisorption mechanisms including surface complexation, precipitation, and ion exchange. • • Increasing acid concentration during pretreatment enhances silicon extraction and impurity removal, while excessive alkali concentration reduces crystallinity and surface area, potentially inducing clinoptilolite formation.
Abstract
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.
1. Introduction
Coal gasification, a cornerstone of the coal chemical industry, generates vast quantities of coal gasification fine slag (CGFS), a solid waste rich in silicon and aluminum but also containing heavy metals. Conventional disposal methods, such as landfilling, pose significant environmental and safety risks, while the high silica-alumina content of CGFS remains underutilized. Existing synthesis routes for zeolites from coal-based wastes often rely on high-temperature alkali fusion followed by hydrothermal treatment, which are energy-intensive and may not yield high-purity products. The challenge lies in developing a cost-effective and scalable method to convert CGFS into valuable materials while mitigating its environmental footprint.
This study addresses this bottleneck by proposing a simple hydrothermal synthesis process that integrates acid washing to remove impurities, alkaline extraction to recover silicon and aluminum, and subsequent crystallization at 170 °C for 48 h. The resulting ZSM-5 exhibits a high specific surface area of 358 m2/g, demonstrating excellent Pb2+ adsorption capacity (104.625 mg/g) and removal efficiency (83.7% for a 50 mg/L solution). By optimizing acid and alkali concentrations, the process achieves high crystallinity and surface area, offering a sustainable pathway for high-value utilization of CGFS in wastewater treatment.
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JIAO Facun, YU Jie, GAO Shengtao, ZHANG Yuanchun, LIU Tao, MAO Lirui, WU Chengli, LI Hanxu, DONG Zhongbing (2026). Synthesis of ZSM-5 Molecular Sieve from Coal Gasification Fine Slag and Its Adsorption Mechanisms for Pb2+ in Aqueous Solution. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60659-7
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Frequently Asked Questions
What is the maximum Pb2+ adsorption capacity of the synthesized ZSM-5, and under what conditions was it achieved?
The synthesized ZSM-5-1 sample achieved a Pb2+ adsorption capacity of 104.625 mg/g at 25 °C for a 50 mg/L Pb2+ solution, with a removal efficiency of 83.7%. These results were obtained under optimized synthesis conditions, including acid washing and hydrothermal crystallization at 170 °C for 48 h.
How does the acid concentration during pretreatment affect the synthesis and final properties of ZSM-5?
Increasing acid concentration facilitates silicon extraction and reduces impurities, leading to higher purity ZSM-5. However, excessive alkali concentration during synthesis reduces crystallinity and surface area, and may induce the formation of clinoptilolite, which is detrimental to adsorption performance.
What are the dominant adsorption mechanisms for Pb2+ removal by the synthesized ZSM-5?
The adsorption process is primarily governed by chemisorption, involving surface complexation, precipitation, electrostatic attraction, and ion exchange. Thermodynamic analyses indicate that the adsorption is spontaneous and endothermic, consistent with multilayer chemisorption.
What is the specific surface area of the synthesized ZSM-5, and why is it important for adsorption?
The synthesized ZSM-5 exhibits a high specific surface area of 358 m2/g. This large surface area provides abundant active sites for Pb2+ adsorption, contributing to the high removal efficiency and capacity observed in the study.
What are the potential scalability and economic implications of using CGFS as a raw material for ZSM-5 synthesis?
CGFS is an abundant and low-cost solid waste, making it an economically attractive raw material. The proposed hydrothermal synthesis process is simple and economical, potentially enabling large-scale production of ZSM-5 for wastewater treatment while addressing environmental concerns associated with CGFS disposal.
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