生物炭对西北黄土吸附壬基酚的影响

Effect of Biochar on Adsorption Behavior of Nonylphenol onto Loess Soil in Northwest China

以壬基酚（nonylphenol,NP）为目标污染物,采用批量实验法研究其在添加不同温度制备的小麦秸秆生物炭的黄土中的吸附动力学、吸附热力学,以及粒径、pH等影响因素.结果表明,不添加生物炭黄土吸附NP的快反应时间为10 h,而加入生物炭后,黄土对NP吸附的快反应时间缩短,为6 h;且快反应阶段添加生物炭黄土明显比不添加生物炭黄土对NP的吸附量多,但碳化温度不同的生物炭在此阶段吸附量差别较小.黄土和添加生物炭黄土对NP的吸附平衡时间均为16 h且符合准二级动力学模型.无论是否添加生物炭,NP在黄土上的热力学吸附过程都较好地符合Freundlich等温吸附模型,符合L-型吸附等温模式;随着系统温度的升高,黄土和添加生物炭的黄土对NP的饱和吸附量都呈增大趋势;NP的吸附自由能ΔGθ〈0,焓变ΔHθ〉0,熵变ΔSθ〉0,表明此吸附是一个自发吸热且混乱程度增大的吸附过程.在同一温度下,随着生物炭碳化温度的升高,NP在添加生物炭黄土中的吸附量逐渐增大.添加生物炭黄土的粒径越小,对NP的吸附量越大.pH值为4~7时,添加生物炭黄土吸附量随pH值的增大而增加;pH为7~10时,吸附量又随pH值增大而减小;表明添加生物炭黄土在中性范围内对NP的吸附效果最好,酸性和碱性都不利于NP的吸附.

In the present study,nonylphenol（ NP） was selected as the target pollutant to investigate the effect of biochar produced from wheat residue at different temperatures on loess soil based on the batch experiments. The research basically included adsorption kinetic,thermodynamic and some influencing factors such as biochar with different pyrolysis temperature,particle size and pH value.The results showed that the adsorption reaction of NP onto loess soil without biochar was 10 h during fast reaction,and after the addition of biochar into loess soil,the fast reaction time of NP adsorption was shortened. Meanwhile,in the fast stage the adsorption reaction of NP onto loess soil with biochar was significantly higher than loess soil without biochar,while the difference of adsorption capacity was small at different carbonization temperatures. The adsorption reaction of NP onto loess soil by adding biochar could be well described by the pseudo-second-order kinetics model and reached equilibrium in 16 h. The kinetic data showed that the adsorption of NP accorded well with the Freundlich isotherm model. The saturated adsorption capacity was improved as temperature increased with or without biochar. Thermodynamic parameter analysis indicated Gibbs free energy ΔGθ 〈0, entropy ΔHθ 〉0 and enthalpy ΔSθ〉 0,demonstrating it was a spontaneous,endothermic and chaos-increasing adsorption process. At the same temperature,the adsorption capacity of NP in loess soils increased dramatically with the increase of carbonization temperature. The smaller particle size of the loess with the addition of biochar,the better the adsorption of NP. When the pH value was 4 to 7,the adsorption capacity of NP onto loess soil by adding biochar showed an increasing trend; in the pH range of 7 to 10,the adsorption saturation capacity decreased with the increase of pH value. Therefore,the adsorption of NP on loess with the addition of biochar had the best adsorption effect in the neutral range. Acid and alkalinity were not conducive to the adsorption of NP.