Adsorption properties of ammonia-modified wheat straw on aquatic cadmium

In order to solve the problem of chromium-contaminated wastewater, urea ammoniated modified wheat straw was prepared as a kind of Cd ²⁺ sorbent. The characterization before and after modification was observed by scanning electron and Fourier transform infrared spectroscopy, and the effects of different initial pH and dosage concentration on adsorption capacity of Cd ²⁺ by wheat straw before and after modification were studied. The adsorption kinetics and isothermal characteristics of wheat straw were fitted by kinetic and thermodynamic models. The results showed that the structure of the ammoniated wheat straw (N1) was loose, the pores were enlarged, the surface was grafted with primary amide group, and the activity of each functional group was enhanced, which was conducive to improving the adsorption capacity of Cd ²⁺. The optimum conditions for Cd ²⁺ adsorption on wheat straw after ammoniation modification were pH of 6, temperature of 25 ℃ and sorbent dosage of 1/300 g/mL. Under these conditions, the removal rate and the biggest saturated adsorption capacity were 74.32% and 11.29 mg/g, respectively. At different temperatures, the adsorption kinetics of Cd ²⁺ on wheat straw modified by ammonia could be described by the quasi-second order kinetic equation, which was shown as the endothermic reaction. The thermodynamic process could be described by Langmuir model, indicating that the adsorption on Cd ²⁺ was dominated by chemical adsorption.