Adsorption Performance of Two Kinds of Biochar for Cd<sup>2+</sup> in Water

Abstract

Cadmium is one of the most widely distributed and toxic pollutants in nature, and the remediation of Cd pollution is still a difficult and serious task. In this paper, the biochar derived from walnut shells and sunflower seed shells were prepared at 700°C. The two kinds of biochar were characterized by SEM and FTIR, and the effects of pH, adsorption time, initial concentration on the adsorption of Cd²⁺ in aqueous solution were investigated. The adsorption kinetics were studied and the experimental data was also fitted with the isotherm equilibrium models. The results showed that the adsorption amount of Cd²⁺ increased with the pH when the solution pH was between 2 and 7. The maximum adsorption amount of Cd in water was up to 12.94 mg•g^-1 and 21.11 mg•g^-1 for BWS and BSS. The adsorption kinetics of Cd²⁺ on the BWS and BSS followed pseudo-second-order kinetics. The Langmuir adsorption isotherm was used to describe the adsorption equilibrium process isotherms. Thermodynamic studies showed that the adsorption reaction was spontaneous, endothermic and entropy increasing. The analysis of microstructural characteristics indicated that complexation and ion exchange are the main mechanisms of cadmium adsorption on the two kinds of biochar. And the surface of the BSS contained a large number of functional groups. Compared with the BSS exhibited better Cd²⁺ adsorption capacity. The results of this research are important for the resourceful use of waste and the purification of heavy metals in water.