Removal of Heavy Metals from Wastewaters with Biochar Pyrolyzed from MgAl-LDH-Coated Rice Husk: Mechanism and Application

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 was conformed to the Langmuir-Freundlich model and PSO kinetics model, indicating single-layer chemical adsorption. Besides, the theoretical maximum adsorption capacities for Cd(II) and Cu(II) were 112.40 and 101.39 mg g –1 , respectively. The adsorption of Cd(II) and Cu(II) by MgAl–LDH@RHB was dominated by surface precipitation and ion exchange. Our 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.