Influence of Pyrolysis Temperature on Characteristics and Zn²⁺ Adsorptive Mechanism of Crayfish Shell Biochars

In order to investigate the physicochemical properties of biochar at different pyrolysis temperatures and under-lying adsorption mechanism of Zn²⁺ on biochar.Crayfish shell biochar were prepared at 300, 400, 500, 600℃ by the limited oxygen slow pyrolysis (LS300, LS400, LS500 and LS600).The original biochar and zinc-loaded biochar were char-acterized by using scanning electron microcopy with energy spectrum analysis (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraxtion (XRD).Then, the Zn²⁺ adsorption property and mechanism of crayfish shell biochar was proposed based on the results of adsorption experiment and characterization.Results indicated that the higher the pyrolysis temperature, the yield of crayfish shell biochar decreased, while the ash content, pH, the pore diameter, and the aromaticity were increased.The adsorption kinetics was well fit to the pseudo-second order model.For LS600, adsorption equilibrium was reached at 7 h, and adsorption equilibrium of the other three types biochar were reached at 24 h.The isothermal adsorption of LS600 was well consistent with the Langmuir isotherm model, and LS600 displayed the best adsorption effect on Zn²⁺, with its adsorption rate up to 462.50 mg·g^-1.Isothermal adsorption of LS300, LS400 and LS500 were well described by Freundlich isotherms model.The adsorption mechanism of crayfish shell biochar on Zn²⁺ mainly includes cation exchange, the surface complexation of oxygen-containing functional groups, the combination of π electrons and precipitating action.