1 School of Energy and Environment, Inner Mongolia University of Science and Technology, Baotou, 014010, China.
2 School of Energy and Environment, Inner Mongolia University of Science and Technology, Baotou, 014010, China. zhengchunli1979@163.com.
3 Inner Mongolia Engineering Research Center of Evaluation and Restoration in the Mining Ecological Environment, Inner Mongolia University of Science and Technology, Baotou, 014010, China. zhengchunli1979@163.com.
4 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC, H3G 1M8, Canada.

In this study, aged biochar (CCB350 and CCB650) were obtained from pyrolysis of corn stalk biochar (CB350 and CB650) at the degree of 350 °C and 650 °C by artificial oxidation with hydrogen peroxide (H₂O₂). Also, the mechanism of Pb²⁺ and Cd²⁺ on fresh and aged biochars was analyzed qualitatively and quantitatively by batch adsorption experiments combined with characterization. The adsorption isotherm results showed that aging treatment decreased the adsorption capacity of Pb²⁺ and Cd²⁺ and inhibited the competitive adsorption behavior of heavy metals. In the single-metal system, precipitation and cation exchange were considered as the main adsorption mechanisms for CB350 and CB650, with a ratio of 40.07-48.23% and 38.04-57.19%, respectively. Competition between Pb²⁺ and Cd²⁺ increased the relative contribution of mineral precipitation, but decreased the contribution of cation exchange mechanism. Aging resulted in the rise of the contribution of surface complexation to the adsorption of Pb²⁺ and Cd²⁺ on biochars, especially in low-temperature biochars, but weakened the contribution of mineral precipitation to the adsorption. Further, the contribution of other adsorption mechanisms was significantly enhanced for high-temperature aged biochars. These results are important to evaluate its long-term application prospects in the natural environment.