Removal of cadmium(II) from aqueous solutions by a novel sulfide-modified nanoscale zero-valent iron supported on kaolinite: Treatment efficiency, kinetics and mechanisms

作者：Gao, Runqin; Hu, Peiwei^*; Dai, Yanni; Zhang, Yan; Liu, Liu; Yang, Wenzhao

来源：Applied Surface Science, 2022, 602: 154353.

DOI：10.1016/j.apsusc.2022.154353

• Kaolinite
• Sulfide-modified nanoscale zero-valent iron
• Cd(II) removal
• Chemical precipitation
• Surface complexation

Nano zero-valent iron (nZVI) had great potential in water pollution remediation, but the instability and easy agglomeration limited its application. To improve the dispersion and antioxidant properties of the nZVI, kaolinite-supported sulfide-modified nZVI (S-nZVI@Kaol) was synthesized for the removal of cadmium (II) (Cd (II)) in aqueous solution. The structure and morphology of the samples were characterized by field emission scanning electronic microscopy (FE-SEM) and X-ray diffraction (XRD), the elemental distribution and micro-structure of the S-nZVI@Kaol were accomplished by transmission electron microcopy (TEM) and energy dispersive X-Ray spectroscopy (EDX), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that S-nZVI was successfully loaded on kaolinite with a core-shell structure. The S-nZVI had higher specific surface area and lower magnetism compared with nZVI. The adsorption process of S-nZVI@Kaol for Cd(II) conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm model better, and the maximum adsorption capacity was 104.7 mg.g(-1). When the S/Fe molar ratio (M-S/Fe) was 0.3, and the Fe/Kaol mass ratio (m(Fe/Kaol)) was 50:50, S-nZVI@Kaol had the best removal efficiency for Cd(II). A higher solution pH (3.0-9.0) was beneficial for the removal of Cd(II). Adsorption thermodynamics studies showed that removing Cd(II) by composites was a spontaneous endothermic process. The mechanisms of the removal of Cd(II) involved electrostatic gravitation, chemical precipitation of CdS, and surface complexation.