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

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.

Automated summary

This study synthesized kaolinite-supported sulfide-modified nano zero-valent iron (S-nZVI@Kaol) for the removal of cadmium in water. The results showed that the composite material had good adsorption performance and stability, and its removal efficiency was affected by the solution pH value and the composition ratio of the material.