A novel heat-treated humic acid/MgAl-layered double hydroxide composite for efficient removal of cadmium: Fabrication, performance and mechanisms

Heat-treated humic acid/MgAl-layered double hydroxide composite (HA/MgAl-LDH) was fabricated through a coprecipitation method and used as an adsorbent for the removal of Cd in aqueous solution. The composite was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) technique and X-ray photoelectron spectroscopy (XPS). These results indicated that the composite (HA/MgAl-LDH) had a rough surface, a large specific surface area and many functional groups. A series of experiments were conducted to ascertain the adsorption performance of HA/MgAl-LDH, including the additive amount of HA/MgAl-LDH, pH and ionic strength. The adsorption dynamics of HA/MgAl-LDH followed a pseudo-second-order model, suggesting that the process of Cd removal was chemical adsorption. Adsorption isotherms followed the Langmuir model of monolayer adsorption, and the maximum theoretical adsorption capacity calculated for Cd was 155.28 mg/g. Moreover, the adsorption mechanism of Cd was investigated by characterization and batch experimental analysis. Cd was absorbed on the surface of HA/MgAl-LDH by surface complexation and chelating interactions, and surface complexation was the main route of Cd removal. In addition, HA/MgAl-LDH has excellent treatment efficiency in actual wastewater. In short, HA/MgAl-LDH is a promising material for the removal of Cd from aqueous media because of its low cost, high efficiency, and easy operation.