摘要
以玉米秸秆为原料,在不同温度下(280℃和320℃),分别采用水热炭化法和热裂解炭化法制备秸秆水热炭和热裂解炭,对比分析了两种生物质炭的结构差异,并结合等温吸附模型和吸附动力学模型研究了秸秆水热炭和热裂解炭对铅离子的吸附机制。结果表明:随着反应温度的升高,水热炭的脱氢效果更显著,形成了无序的晶体结构及丰富的表面含氧官能团;热裂解炭的脱氧效果更显著,其表面含氧官能团较少,且形成了有序的晶体结构。水热炭的孔隙率先增大、后减小,呈现致密、平滑的表面形貌;热裂解炭的孔隙率持续增加,具有显著的中孔结构特征,呈现粗糙多孔的表面形貌。秸秆水热炭和热裂解炭分别在4 h和10 h达到吸附平衡,理论平衡吸附量分别可达214.16 mg/g和133.99 mg/g。秸秆热裂解炭对铅离子吸附符合准一级动力学模型和Freundlich等温吸附模型,表明其吸附反应为多分子层吸附过程;而秸秆水热炭对铅离子吸附符合准二级动力学模型和Langmuir等温吸附模型,表明其吸附反应为单分子层吸附过程。结合两种生物质炭的结构特征可知,热裂解炭主要依靠铅离子在其孔隙内的扩散运动进行物理吸附,其中大尺寸中孔的存在更有利于铅离子克服空间障碍进入孔隙,但吸附能力相对较弱,且容易脱附。络合反应是水热炭脱除水中铅离子主要机制,即含氧官能团与铅离子结合形成络合物的化学吸附,其吸附能力较强,且不容易脱附。
Heavy metal pollution of soil and water has seriously threatened human life and health,and Pb^2+is one of the most difficult heavy metals to deal with because of its strong toxicity,difficult degradation and easy enrichment.Corn straw was used as raw material to prepare hydrochar and pyrochar at different temperatures(280℃and 320℃),respectively.The structural differences of the two kinds of biochar were compared and analyzed,and based on this,Pb^2+adsorption mechanism of hydrochar and pyrochar from straw was studied by combining isothermal adsorption model and adsorption kinetic model.The results showed that the dehydrogenation effect of hydrochar was more significant,forming rich surface oxygen functional groups and disordered crystal structure with the increase of hydrothermal temperature.The porosity of hydrochar was firstly increased and then decreased,finally presenting a regular and dense appearance;however,the deoxidization effect of pyrochar was more remarkable,it had fewer surface oxygen functional groups,forming a more ordered crystal structure.The porosity of pyrochar continued to increase,showing a rough porous surface morphology.Adsorption equilibrium of straw hydrochar and pyrochar was reached at 4 h and 10 h respectively,and the theoretical equilibrium adsorption capacity was 214.16 mg/g and 133.99 mg/g;Pb^2+adsorption of straw pyrochar was in accordance with pseudo first-order kinetic model and Freundlich isotherm adsorption model,indicating that the adsorption reaction was a multi molecular layer adsorption process;however,Pb^2+adsorption of straw hydrochar conformed to the pseudo second-order kinetic model and Langmuir isotherm adsorption model,indicating that the adsorption reaction was a single molecular layer adsorption process.Combined with the structural characteristics of the two kinds of biochar,it was found that straw pyrochar mainly relied on the diffusion movement of Pb^2+within its pores to remove Pb^2+from water,and the existence of large-scale mesopores was more conducive to Pb^2+to overcome the space barrier and enter the pores,however,the physical adsorption capacity was relatively weak and easy to desorb;in addition,complexation reaction was the main Pb^2+removal mechanism of straw hydrochar,in other words,the oxygen-containing functional groups exchanged with Pb^2+to form complexes,and chemical adsorption capacity was strong and not easy to desorb.
作者
刘冬冬
李金铭
赵博骏
朱俊昊
陈光
董良杰
LIU Dongdong;LI Jinming;ZHAO Bojun;ZHU Junhao;CHEN Guang;DONG Liangjie(Key laboratory of Straw Biology and Utilization,Ministry of Education,Jilin Agricultural University,Changchun 130118,China;College of Engineering and Technology,Jilin Agricultural University,Changchun 130118,China;Department of Chemical and Biochemical Engineering,Western University,London N6A5B7,Canada)
出处
《农业机械学报》
EI
CAS
CSCD
北大核心
2020年第12期304-314,共11页
Transactions of the Chinese Society for Agricultural Machinery
基金
国家自然科学基金项目(51806080)
2020年度吉林省博士后科研人员择优项目
吉林省教育厅“十三五”科学技术项目(JJKH20200325KJ)。
关键词
秸秆
水热炭
热裂解炭
结构表征
铅吸附
straw
hydrochar
pyrochar
structure characterization
Pb^2+absorption
