Enhanced adsorption of Cd(II) from aqueous solution by a magnesium oxide–rice husk biochar composite

In this study, a magnesium oxide–rice husk biochar composite (MgO–BCR) was successfully prepared by a MgO impregnation method, and its adsorption performance was investigated in Cd(II) aqueous solution. A pseudo-second-order kinetic model described the Cd(II) adsorption behaviour on BCR and MgO–BCR well, while a Langmuir adsorption isotherm was more suitable for Cd(II) adsorption on the adsorbent. The fitting results of the monolayer model indicated that the number of ions captured by per site varied between 0.97 and 1.09. The calculated thermodynamic parameters indicated that Cd(II) adsorption onto MgO–BCR was spontaneous and endothermic. Characterisation of the adsorbent revealed that in situ precipitation, surface complexation, and electrostatic attraction contributed to the Cd(II) adsorption. The adsorption capacities of rice husk biochar (BCR) and MgO–BCR for Cd(II) reached 6.36 and 18.1 mg/g, respectively. The results demonstrated that MgO–BCR composite could be used as an effective and eco-friendly adsorbent to enhance the removal of Cd(II) from aqueous solution.