添加小麦秸秆生物炭对黄土吸附苯甲腈的影响

摘要

Benzonitrile was selected as the target pollutant to investigate the effect of biochar produced from wheat residue at different temperatures on the adsorption of benzonitrile onto loess soil. The results showed that the adsorption equilibrium of benzonitrile onto loess was about 8h without biochar, and after the addition of biochar into loess soil, the adsorption equilibrium time of benzonitrile was shortened, meanwhile, with the increase of pyrolysis temperature of biochar added into soil, the adsorption equilibrium time was obviously reduced, while the saturation adsorption amount of benzonitrile onto loess soil was also significantly increased. The kinetic data showed that the adsorption of benzonitrile onto loess soil could be better described by a pseudo-second-order kinetic model, the boundary layer control and intraparticle diffusion were both involved in the adsorption process. Besides, the adsorption equilibrium data were well described by the Freundlich isothermal model. The saturated adsorption capacity was improved as temperature increased with or without the biochar, suggesting a spontaneous endothermic process. The average adsorption free energy E was between 1.865and 3.171kJ/mol, which indicated that adsorption of benzonitrile onto loess was physical adsorption with or without biochar. Thermodynamic parameter analysis showed that Gibbs free energy was less than zero, while Entropy (ΔHθ) and Enthalpy (ΔSθ) were greater than zero, indicating an endothermic process for adsorption of benzonitrile onto loess soil. The results indicated that the adsorption process of benzonitrile onto loess with the addition of biochar involved a surface adsorption, diffusion within the particles, and external film diffusion mechanism.%选择苯甲腈为目标污染物,研究添加不同热解温度制备小麦秸秆生物碳对黄土吸附苯甲腈的影响.研究表明:不加生物炭黄土对苯甲腈的吸附约8h达到平衡,而加入生物炭后,黄土对苯甲腈的吸附时间缩短,并随着加入生物炭热解温度的升高,吸附平衡时间缩短越明显,同时,黄土对苯甲腈的饱和吸附量也显著增加;添加生物炭黄土对苯甲腈的动力学吸附数据显示较好的符合了准二级动力学方程;无论是否添加生物炭,苯甲腈在黄土上的吸附都符合Freundlich吸附的等温模型,随系统温度升高,添加生物炭黄土对苯甲腈的饱和吸附量也显著增加,表明该吸附过程为吸热反应;苯甲腈在黄土上的吸附等温线符合C-型吸附等温模式.计算结果显示,平均吸附自由能E介于1.865~3.171kJ/mol,表明苯甲腈在黄土上的吸附,无论是否添加生物炭,都以物理吸附为主;热力学参数计算结果显示,无论是否添加生物炭,黄土对苯甲腈的吸附过程中吉布斯自由能ΔGθ均小于0、熵变ΔSθ和焓变ΔHθ均大于0,表明土壤对苯甲腈的吸附为自发进行的吸热过程.研究结果说明,添加生物炭黄土对苯甲腈的吸附过程包含表面吸附和颗粒内部扩散、外部液膜扩散等机制.