Abstract: Rice straw was pyrolyzed into biochar at four different temperatures (200, 400, 600, and 800℃). Mineral structure, surface properties and elemental composition of the biochars were analyzed with the aid of XRD, FTIR and SEM/EDS, and characteristics of the biochars adsorbing cyromazine in wastewater were studied, so as to provide some references for treatment of cyromazine-containing wastewater and utilization of crop straws as resource. Results show that the biochars contain mineral crystals, like quartz, calcite and potassium chloride, and some major elements, like C, O and Si; They were porous in structure and rich in oxygen-containing functional group. Biochars prepared at 600℃ or more in pyrolyzation were higher in specific surface area and their adsorption of cyromazine significantly higher, too. Fitting with Langmuir equation showed that the maximum cyromazine adsorption capacity of the biochar prepared at 200, 400, 600 and 800℃ of pyrolyzation temperature  was 4200 and 6365, 144865 and 167084 mg•kg^-1, respectively, of which the last two were quite close to that of the commodity activated carbon (177305 mg•kg^-1), and 16.8 and 20.1 times as higher asthan that of the equivalent amount of rice straw. The kinetic curve of biochar adsorbing cyromazine fitted well the first order kinetics equation. In solution with the initial concentration of cyromazine being 100 and 200 mg•L^-1, it took the biochars produced at 600 and 800℃ about 5 and 8 hours, respectively, to reach equilibrium in cyromazine adsorption. In solutions, 500 mg•L^-1 in initial concentration of cyromazine, 5 - 10 in pH and 1 - 100mmol•L^-1 NaNO₃ in supportive electrolyte, no significant effects of pH value and ion strength were observed on the adsorption of cyromazine by the biochar produced at 600 and 800℃.

Key words: rice straw based biochar, surface properties, adsorption, cyromazine