黍糠、菜籽饼生物炭的制备及其对重金属镉(Cd2+)的吸附

利用黍糠、菜籽饼在不同温度下制备生物炭,以确定最佳制备温度及最佳吸附材料。结果表明,2种生物炭对镉(Cd~(2+))的吸附效果随制备温度上升而升高,黍糠生物炭的吸附效果更好。综合考虑产出率、吸附效果与能耗,得到最佳生物炭材料为黍糠,最佳制备温度为600℃。经2种生物炭吸附后,Cd~(2+)溶液的pH值均呈上升趋势,而黍糠生物炭调节pH值的能力更强。2种生物炭清洗后的吸附效果均有下降,表面沉淀是未清洗的生物炭对重金属离子吸附作用的机理之一。600℃黍糠生物炭对Cd~(2+)的吸附符合Langmuir吸附等温线,表明黍糠生物炭对Cd~(2+)的吸附为单分子层的吸附,且吸附剂表面均匀。使用扫描电镜(SEM,Scanning Electron Microscope)、多通道比表面积和孔径分析仪(BET,Multi-channel specific surface area and pore size analyzer)、傅里叶变换红外光谱(FT-IR,Fourier Transform Infrared Spectroscopy)和综合热分析仪(STA,Synchronous Thermal Analyzer)对黍糠生物炭进行了表征。结果表明,黍糠原材料具有丰富的官能团,随热解温度升高,脂肪族官能团逐渐弱化消失,而芳香性结构与官能团逐渐凸显出来,因而能更多地吸附重金属Cd~(2+)。黍糠生物炭对重金属的吸附不主要依赖比表面积和孔隙结构,而是多种化学作用的结果,如表面沉淀、与官能团络合和阳离子-π键吸引。

On the preparation of pyrolysis of the millet bran biochar and the rapeseed cake biochar and their adsorption behavior of Cd2+

This paper is inclined to identify and determine the optimum pyrolysis temperature as well as the best feedstock for the biochar adsorbent behavior,as well as its fabrication derived from the millet bran and rapeseed cake through slow pyrolysis under the different temperatures. The results from our experiment and fabrication demonstrate that the adsorption of cadmium ions (Cd2 + ) by the two biochars can be enhanced with the increase of the pyrolysis temperature and the adsorption capacity by the biochar derived from the millet bran much more efficiently than that from the rapeseed cake derived biochar. Through a comprehensive evaluation including those of the yield rate,the adsorption capacity and the optimal fabrication temperature to produce the millet bran derived biochar should be set up at the temperature of 600 ℃ by choosing Cd2 + as the best adsorbent. And,then,in the adsorption experiment,the solution pH can be increased from its initial value 4 with the millet bran derived biochar to reach a better pH adjustment value. In addition,the surface precipitation tends to play an important role in Cd adsorption by different biochars (remaining unwashed),whose adsorption capacity would like to decrease evidently through the deash treatment. Besides,the adsorption of the millet bran derived biochar produced at the temperature of 600 ℃ also proves in accordance with the Langmuir adsorption model,which implies that the adsorption of Cd2 + should be of monolayer adsorption with its surface of the adsorbent being homogeneous. Furthermore,it has to be pointed out that in the given experiment,it is necessary to use some few kinds of analysis instruments including SEM,BET,FT-IR and STA. The experiment results also indicate that the smooth surface of the feedstock may turn to be rough and porous on account of the fine biochar structure which had been formed in the pyrolysis process. What is more,the FT-IR spectra may reveal that the millet bran feedstock is abundant with the functional groups. Nevertheless, with the increase of the pyrolysis temperature,most of the aliphatic group may turn to be weakening and even disappearing while the aromatic function groups and their structures may turn to play the prominent role that may contribute to the Cd2 + adsorption through the complexion with the aromatic groups and cation-π interaction. On the other hand,the Cd2 + adsorption by biochar tends to prove their main attribution to the surface precipitation, the complexion with the functional groups and cation-π interaction rather than the specific surface area and the biochar's pore structure.