Synthesis and Characterization of NaX Zeolite from Coal Gangue and Its Efficacy in Cd and Pb Remediation in Water and Soil

Zhibing Chang; Yinuo Yan; Lu Bai; Nan Guo; Zhenguo Xing; Chunwei Lu

doi:10.1021/acsomega.4c07708

Synthesis and Characterization of NaX Zeolite from Coal Gangue and Its Efficacy in Cd and Pb Remediation in Water and Soil

ACS Omega. 2024 Dec 16;9(52):51237-51252. doi: 10.1021/acsomega.4c07708. eCollection 2024 Dec 31.

Authors

Zhibing Chang¹, Yinuo Yan¹, Lu Bai^{2

3}, Nan Guo^{2

3}, Zhenguo Xing^{2

3}, Chunwei Lu¹

Affiliations

¹ School of Chemical and Environmental Engineering, China University of Mining and Technology, Beijing 100083, China.
² State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing 102211, China.
³ National Institute of Clean-and-Low-Carbon Energy (NICE), Beijing 102211, China.

Abstract

Alkaline fusion is a pivotal process influencing the cost of synthesizing zeolite from coal gangue. This study examined the effects of alkaline fusion temperature (X ₁), treatment duration (X ₂) and the NaOH/coal gangue weight ratio (X ₃) on the composition and properties of the products, as well as their adsorption capacities for Cd²⁺ (q _e,Cd) and Pb²⁺ (q _e,Pb). Response surface methodology (RSM) was employed to analyze the interactions among these factors, and the adsorption mechanisms for Cd²⁺ and Pb²⁺ were investigated using X-ray diffraction, scanning electron microscopy-EDS, Fourier transform infrared, X-ray photoelectron spectroscopy, and N₂ adsorption-desorption techniques. The results reveal that (1) under optimized conditions-X ₁ of approximately 800 °C, X ₂ of around 2.8 h and X ₃ of 1.2-the maximum q _e,Cd and q _e,Pb for the synthesized NaX zeolite can reach 181.3 and 419.9 mg/g, respectively. (2) The RSM models indicate that increasing the X ₃ value can lower the required X ₁. For q _e,Cd and q _e,Pb of 150 and 350 mg/g, respectively, with X ₂ fixed at 2 h, increasing X ₃ from 0.976 to 1.134 and from 0.900 to 1.289 enables a reduction in X ₁ from 800 to 600 °C. (3) NaX zeolite primarily adsorbs Cd²⁺ and Pb²⁺ through ion exchange, allowing these ions to enter the zeolite's cage structure. Pb²⁺ can also precipitate as hydrocerussite (Pb₃(CO₃)₂(OH)₂) within the zeolite channels, while Cd²⁺ has a more significant impact on the [SiO₄] and [AlO₄] tetrahedra. (4) The synthesized NaX zeolite effectively reduces the exchangeable Cd content in contaminated soil from 3.51 to below 1.5 mg/kg. The remediation performance of the NaX zeolite for Cd and Pb in water and soil can be further enhanced by optimizing its Si/Al ratio and pore structure.