Enhanced Removal of Pb²⁺, Cu²⁺, and Cd²⁺ by Amino-Functionalized Magnetite/Kaolin Clay

The amino-functionalized magnetite/kaolin clay (MKC) was synthesized via a simple solvothermal method and used to remove Pb²⁺, Cu²⁺, and Cd²⁺ from aqueous solutions. In comparison, the kaolin clay (KC) and MKC were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning and transmission electron microscopy with energy dispersive spectrometry. The results indicated amino-functionalized MKC was formed with Fe₃O₄ particles adhering to the surface by interactions with negatively charged KC. The optimal experimental conditions were evaluated, and the adsorption performance of MKC for Pb²⁺, Cu²⁺, and Cd²⁺ was far better than that of KC. This was mainly caused by adding an amino group, in which the amino group displayed complexing ability toward metal ions. In kinetic data representation, the pseudo-first-order, pseudo-second-order, and Elovich models were employed, and the second one gave the better fitting. Langmuir, Freundlich, and Dubinin–Radushkevich models were chosen for isotherm data correlation, of which the first one showed better suitability. The X-ray photoelectron spectroscopy analysis of MKC before and after adsorption further revealed that the adsorption mechanisms of Pb²⁺, Cu²⁺, and Cd²⁺ could be a combined reaction of complexation between functional groups and metal ions and electrostatic attraction. In addition, MKC can be rapidly separated using only a magnet after the adsorption process