Adsorption of nitrate nitrogen by peanut shell biochar
Peanut shell was used to prepare biochar through low-oxygen pyrolysis(300 ℃). FTIR and XPS results of the biochar before and after batch equilibrium adsorption test showed that adsorption of NO -3 -N on the biochar was significantly affected by pH. The NO -3 -N ad-sorption quantity by biochar increased gradually with initial concentrations of NO -3 -N. At the initial concentration of 800 mg·L-1, the maxi-mum adsorption capacity was 40 mg·g-1. Freundlich equation could be well fitted(R2=0.975)to the NO -3-N isothermal adsorption. Adsorp-tion of NO-3-N by biochar was non-uniform multilayer process and could reach the equilibrium in 30 min. Pseudo secondary dynamic equa-tion could effectively describe the adsorption kinetics, indicating that the adsorption was mainly chemical adsorption. FTIR and XPS results also suggested that the functional groups such as hydroxyl(-OH), aromatic ring carbonyl(-C=O), and aliphatic ether(-o-), which dis-tributed on the surface of biochar, were involved in the adsorption process, and that the binding energy of C atoms connected to those func-tional groups increased. Considering the distribution of metal ions on the biochar surface, it is concluded that formation of hydrogen bond and metallic bond would be the main chemical mechanism of NO -3-N adsorption by biochar.
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