Removal of heavy metals from wastewaters with biochar pyrolyzed from MgAl-layered double hydroxide-coated rice husk: Mechanism and application

[Display omitted] •A novel nano-sized MgAl–LDH@RHB functional biochar was synthesized.•MgAl–LDH@RHB shows higher adsorption capacity than original biochar.•Mg2+ exchange and surface precipitation mainly contribute to Cd and Cu removal.•Cd(II) and Cu(II) are adsorbed on MgAl–LDH@RHB as CdCO3 and CuSO4. This study reports a MgAl–LDH rice husk biochar composite (MgAl–LDH@RHB) with a regular hydrotalcite structure synthesized by a simple hydrothermal method, which was then used to remove Cd(II) and Cu(II) from water. The influencing factors on the adsorption performance were determined through batch adsorption experiments, and the adsorption characteristics and cycling capacity were evaluated with eight models and adsorption–desorption experiments. The results showed that the adsorption of Cd(II) and Cu(II) by MgAl–LDH@RHB conformed to the Langmuir-Freundlich model and PSO kinetics model, indicating single-layer chemical adsorption. In addition, the experimental maximum adsorption capacities for Cd(II) and Cu(II) were 125.34 and 104.34 mg g−1, respectively. The adsorption of Cd(II) and Cu(II) by MgAl–LDH@RHB was dominated by surface precipitation and ion exchange. The findings reveal the mechanism for the heavy metal removal by MgAl–LDH@RHB and provide a theoretical reference for agricultural waste disposal and water pollution control.