Abstract: Wheat straw activated carbon (AC) coated with iron oxide (FeCl₃ solution) as activator was prepared to obtain strong nitrate adsorption capacity, and response surface methodology (RSM) was applied to determine the optimal preparation condition for AC to have maximized adsorption capacity. According to RSM, the optimal condition is 527 ℃ of carbonization temperature and 92.5% of chemical weight ratio (FeCl₃/wheat straw). The adsorption capacity of FAC, prepared at the optimal condition was higher than that of wheat straw bio-char (WBC) prepared at the same condition without chemical activation. Plenty of pores with varying sizes were developed at the surface of FAC because of FeCl₃ activation. The surface of FAC had more iron content, the specific surface area and pore volume increased, and a large amount of iron oxide was introduced into the FAC pores, and the saturation magnetization value was 4.12 emu·g^-1 with good magnetic responds. The N₂ adsorption-desorption isotherm would become combination of types Ⅱ and IV with an adsorption hysteresis loop and contains a large number of pores that like the narrow slot. The pore structures of WBC and FAC were mainly micropore and mesopore and the pore volume of FAC was larger than that of WBC. With the increase of the nitrogen concentration, the amount of nitrogen adsorbed onto FAC was rising rapidly, the Langmuir maximum nitrogen adsorption capacity of FAC was 14.68 mg·g^-1 (65.01 mg·g^-1 for NO₃^- ions). Nitrate adsorption capacity decreased with an increase in pH. With the increase of FAC content, the removal rate of nitrate increased to about 90%. The nitrate uptake was rapid in the beginning and followed by a slower removal that gradually reached a plateau, and this equilibrium was established after 120 min. The Kinetic studies showed that a pseudo second-order rate equation fit the experimental data well. Therefore, FAC could be used for nitrate removal from water and be separated from water readily by using magnetic separation, providing a method to improve the ecological environment (crop straw using and water pollutant removing efficiently).

Key words: wheat straw, activated carbon, FeCl₃ activation, response surface methodology, nitrate removal