稀酸稀碱洗脱处理对生物炭结构及吸附四环素性能的影响

Effects of the washing treatment using diluted acid and base on the structure of biochar and its adsorption performance on tetracycline

生物炭制备过程中部分无机灰分以及热解副产物会附着在生物炭的表面,这些被附着的灰分及热解副产物会随生物炭一起进入环境中,由于其性质较活跃,在环境中易发生变化,会在一定程度上影响生物炭的结构及其对污染物的吸附行为。以稀酸、稀碱两种溶液作为洗脱剂,对纤维板生物炭进行洗脱处理以去除灰分及热解副产物。通过对比洗脱前后生物炭的元素含量、比表面积以及表面官能团,以探究洗脱处理对生物炭结构的影响;通过对比洗脱前后生物炭对四环素的吸附去除率和等温吸附研究,以考察洗脱处理对生物炭吸附性能的影响;通过对洗脱液的紫外分光光谱表征,以探究洗脱处理对生物炭表面热解副产物的去除效果。结果表明,洗脱处理后生物炭的碳含量相对减少,含氧官能团含量增加,极性增加;洗脱前后拟合的吸附模型表明,生物炭对四环素的吸附过程主要是多分子层吸附,生物炭吸附四环素的主要吸附机理是π-π堆积作用。此外,相对于灰分的去除,洗脱处理去除具有芳香结构的有机热解副产物才是生物炭吸附性能降低的主要原因。

The by-products(i.e., tar and coke) produced during the biomass pyrolysis could be adsorbed by biochar. These adsorbed pyrolysis by-products and the ash on the biochar surfaces would be brought to the environment along with the biochar during its applications. Due to their active nature, they are easy to react each other in the environment, thereby both the properties and the adsorption behavior on the pollutants of the biochar would be affected to a certain extent. Therefore, it is necessary to remove the ash, as well as the adsorbed pyrolysis by-products using the washing treatment and the effects of the washing treatment on the structure of the biochar and its adsorption performance were investigated. In this study, two washing solvents, namely, the diluted acid solution and diluted base solution, were used as washing agents to soak the fiberboard biochar. The effect of the washing treatment on the structure of biochar was investigated by comparing the element content, specific surface area, and functional groups of the fiberboard biochar samples before and after the washing treatment. In addition, the effect of the washing treatment on the adsorption performance of biochar was examined by comparing the removal rates of tetracycline adsorption using biochar samples before and after the washing treatment. The adsorption mechanism was then studied by the adsorption isotherm analysis, i.e. Langmuir and Freundlich models. The results showed that, after the washing treatment, the C content decreased while both the content of O-containing functional groups and the polarity of the biochar increased. Moreover, the adsorption ability of biochar after the washing treatment decreased. Compared with the ash removal, the removal of by-products with aromatic structure was the primary reason for the decrease of the adsorption ability. Finally, the adsorption isotherm analysis indicated that the tetracycline adsorption process of biochar is mainly the multi-molecular layer adsorption, and the main adsorption mechanism is π-π interactions.