花生壳生物炭对硝态氮的吸附机制研究

Adsorption of nitrate nitrogen by peanut shell biochar

以花生壳为原料,300℃热解条件下制得生物炭。通过批量平衡吸附试验,结合吸附前后FTIR、XPS图谱表征分析探索硝态氮(NO-3-N)在生物炭表面的吸附机制。结果表明,生物炭对NO-3-N的吸附显著受溶液pH值影响,当pH<6时有利于吸附的进行。随溶液初始NO-3-N浓度增加,生物炭对其吸附量逐渐增加,在初始浓度800 mg·L-1的吸附体系中,最大吸附量达40 mg·g-1,Freundlich方程可较好地拟合(R2=0.975)生物炭对NO-3-N等温吸附过程,吸附为非均一的多分子层吸附;生物炭对NO-3-N的吸附可在30 min达到平衡,伪二级动力学方程能够较好地描述吸附动力学过程,表明吸附以化学吸附为主。FTIR、XPS图谱分析表明,生物炭表面分布的羟基(-OH)、芳香环羰基(-C=O)及脂肪族醚类(-O-)等官能团参与了吸附过程,且与之相连的C原子结合能均增加。结合生物炭表面金属离子分布状况,综合分析认为,通过氢键形成和金属桥键作用是生物炭对NO-3-N吸附的主要机制。

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 adsorption quantity by biochar increased gradually with initial concentrations of NO-3-N. At the initial concentration of 800 mg·L-1, the maximum adsorption capacity was 40 mg·g-1. Freundlich equation could be well fitted（R2=0.975）to the NO-3-N isothermal adsorption. Adsorption of NO-3-N by biochar was non-uniform multilayer process and could reach the equilibrium in 30 min. Pseudo secondary dynamic equation 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 distributed on the surface of biochar, were involved in the adsorption process, and that the binding energy of C atoms connected to those functional 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.