Biochar(BC) was made by pyrolysis of rice husk, bamboo and Chinese fir sawdust at different temperature, which respectively labeled DBC, ZBC and MBC in turn. The physicochemical properties of the product were characterized by Fourier transform infrared spectroscopy(FT-IR), scanning electron microscope(SEM), energy dispersive X-ray(EDS) and X-ray diffraction(XRD). The adsorption characteristic and mechanism of BC to U(Ⅵ) were studied by batch adsorption experiments. The results showed that, as the temperature increased from 300 ℃ to 700 ℃, the pH value and ash content of the three kinds of biochars increased, but the yield decreased. Meanwhile, the characterization of both ZBC and DBC was also changing with increasing pyrolysis temperature, such as the crystallinity of the carbon fiber and content of oxygen-containing functional groups decreased, the proportions of inorganic elements and pore shapes increased, and the surface was rougher. The adsorption processes on the three kinds of BCs were more consistent with the pseudo-second-order kinetic model(R22>0.96), and the adsorption equilibrium time was 3 h at reaction temperature 25 ℃, pH value 4, solid-liquid ratio 1:1(g:L). The adsorption isotherms of the three kinds of BCs were more consistent with Langmuir model, which indicated that chemical adsorption was the main process. The largest adsorption capacity of ZBC700 was 18.55 mg/g. The abilities of ZBC and DBC to adsorb U(Ⅵ) were enhanced with increasing pyrolysis temperature, simultaneously, the contribution utility of cation-π and ion exchange was increasing. Nevertheless, the relationship between the ability of MBC to adsorb U(Ⅵ) and pyrolysis temperature was not obvious, and the adsorption capacities of ZBC and DBC were higher than that of MBC at the same pyrolysis temperature.
