Adsorption Process of Ammonia Nitrogen in Solution by the Modified Biochar from Corn Straw

The biochar was prepared by pyrolyzing corn straw at 773 K temperature under an oxygen-limited condition. Then, the gained biochar samples were further modified with MgCl2 solution through mixing method for 3 h at the speed of 120 rpm. The physicochemical properties of the modified biochar from corn straw were investigated by surface area analysis, elemental analysis, scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy spectra. The adsorption experiments of ammonia nitrogen in aqueous solution by modified biochar were carried out. The results showed that the modified biochar contains high surface area, rough surface and a lot of oxygen-containing functional groups. The adsorption process fits well with the pseudo-second-order kinetics equation and Langmuir isotherm equation. The adsorption mechanism of modified biochar to NH4 + ion in aqueous solution includes ion exchange and physical adsorption. The ion exchange is primary in the process of adsorption.