To study the sorption behaviors of Zn2+ on different biochars, a series of sorption experiments were conducted. Figure 1 shows the kinetics and isotherms of Zn2+ sorption on different biochars. From Fig. 1a we find that sorption reactions between Zn2+ and most biochars can reach equilibrium at 48 h, the sorption capacities of Zn2+ on biochars produced at 550 °C were higher than those of Zn2+ on biochars produced at 350 °C. Figure 1c shows that the maximum sorption capacities of Zn2+ on raw biochars decreased in the following order: PN550 (25.9 mg g−1) > WS550 (20.4 mg g−1) > WS350 (16.0 mg g−1) > PN350 (3.0 mg g−1). It seems that biochars with higher ash contents were more effective on Zn immobilization. From Fig. 1c,d we find that, the maximum sorption capacities of Zn2+ on de-ashed biochars were lower than those of Zn2+ on their corresponding raw biochars. Especially for biochars produced at 550 °C, the maximum sorption capacities of Zn2+ on biochars decreased by more than 80% when the ash was removed. These results suggested the important role of ash on Zn immobilization by biochar. Among de-ashed biochars, WS350D had the highest sorption capacity (9.4 mg g−1), which may be due to the more oxygen-containing functional groups WS350D had compared with other biochars. Kinetics experiments show that sorption reactions between Zn2+ and most biochars can reach equilibrium at 48 h, thus the equilibrium time for the following experiments was set to be 48 h. As PN550, WS350, and WS550 had considerable sorption capacities of Zn2+, several kinetics models (pseudo-first and pseudo-second-order models35, Elovich model3637, and intraparticle diffusion model3839) and isotherms models (Langmuir, Frendlich, and Langmuir-Frendlich models40) were performed on kinetics and isotherms data of these biochars, the fitting results were shown in Supplementary Tables S2 and S3.