Adsorption performance and mechanistic study of heavy metals by facile synthesized magnetic layered double oxide/carbon composite from spent adsorbent

To reuse the spent magnetic MgAl-layered double hydroxide after humic acid adsorption, this work provided a simple calcination method to prepare the magnetic layered double oxide/carbon (Mag-LDO/C) nanocomposite. The characterization results indicated the Mag-LDO/C was a carbonaceous composite with a large number of functional groups and superparamagnetic property. Then the adsorption performance of Mag-LDO/C for heavy metals was studied by batch experiments. The Mag-LDO/C exhibited excellent removal efficiencies for Cd(II), Pb (II), and Cu(II) with maximum adsorption capacities of 386.1, 359.7, and 192.7 mg/g, respectively. The batch sorption data were studied by the pseudo-second-order kinetic equation and the Langmuir isothermal model, and they matched well. According to the zeta potentials, X-ray diffraction patterns, and X-ray photoelectron spectra of Mag-LDO/C after heavy metals adsorption, the interaction mechanisms were ascribed to the precipitation, surface complexation, and electrostatic attraction. After reaction, the solid-liquid separation of Mag-LDO/C could quickly achieve using a magnet. Additionally, the Mag-LDH/C exhibited excellent adsorption capacities in various simulated wastewater and well sorption recyclability, proving the valuable applications of Mag-LDO/C synthesized from spent adsorbent for metal ions removal in actual water environment.