[Adsorption Characteristics and Mechanism of Ammonia Nitrogen in Water by Nano Zero-valent Iron-modified Biochar]

The adsorption performances of ammonia nitrogen (NH⁺₄-N) in water by unmodified biochar are ineffective. In this study, nano zero-valent iron-modified biochar (nZVI@BC) was prepared to remove NH⁺₄-N from water. The NH⁺₄-N adsorption characteristics of nZVI@BC were investigated through adsorption batch experiments. The composition and structure characteristics of nZVI@BC were analyzed using scanning electron microscopy, energy spectrum analysis, BET-N₂ surface area (SSA), X-ray diffraction, and FTIR spectra to explore the main adsorption mechanism of NH⁺₄-N by nZVI@BC. The results showed that the composite synthesized at the iron to biochar mass ratio of 1:30 (nZVI@BC1/30) performed well in NH⁺₄-N adsorption at 298 K. The maximum adsorption amount of nZVI@BC1/30 at 298 K was remarkably increased by 45.96% and reached 16.60 mg·g^-1. The pseudo-second-order model and Langmuir model fitted well with the adsorption process of NH⁺₄-N by nZVI@BC1/30. There was competitive adsorption between coexisting cations and NH⁺₄-N, and the sequence of coexisting cations to the adsorption of NH⁺₄-N by nZVI@BC1/30 was Ca²⁺> Mg²⁺> K⁺> Na⁺. The adsorption mechanism of NH⁺₄-N by nZVI@BC1/30 could be mainly attributed to ion exchange and hydrogen bonding. In conclusion, nano zero-valent iron-modified biochar can improve the adsorption performance of NH⁺₄-N and enhance the application potential of biochar in the field of nitrogen removal from water.