功能化秸秆基吸附剂对污染土壤浸出液中铅的吸附分离机理研究

With the development of the industry, soil was seriously polluted by heavy metals, especially by lead. It had been reported that leaching method is an efficient way to remove the heavy metals permanently from soil. However, large volume of leachate containing lead ion was produced during this process. Harmless and resourceful treatment of the leachate became a significant problem to be solved. During the methods of waste water treatment, biosorption have attracted much attention due to the low cost and simple operation. However, biosorption still rest on the experiment. Basic research, especially the separation mechanism about the lead adsorption in real wastewater treatment is not enough, which restrict its industry application. In this project, multi-functionalized straws were prepared by chemical modification methods and used as sorbent to treat the acid leaching solution of heavy metal polluted soil. Adsorption performances and mechanisms of lead ions on the functionalized straw were discussed. Strong and weak interfering ions were determined, inherent laws that affects the adsorption affinity was revealed. Competitive adsorption process and mechanism between lead ions and other metals in the leaching solution under dynamic condition were studied. Dynamic model for lead ion sorption were established, which would enrich and develop the theory of heavy metals sorption on biosorbents. Parameters of the pre-column and processing column were optimized to separate lead ions and the other metal ions from the leachate. Separation and recovery system were established to recycle the metals. The investigation of this project would provide theoretical basis and technical support for harmless and resourceful treatment of soil polluted heavy metal.

随着我国工业发展，重金属特别是铅污染土壤严重。化学浸出法能高效去除污染土壤中的铅，但会产生大量含低浓度铅的浸出废液，其无害化和资源化处理成为亟待解决的难题。在低浓度含铅废液处理的众多技术中，以秸秆为材料的生物吸附法因成本低、操作简单备受关注，然而目前生物吸附法还处在试验阶段，对实际废液中铅吸附分离的基础研究尤其是机理研究不够，限制了其应用。本项目以铅污染土壤的浸出液为研究对象，采用化学改性法制备多功能化秸秆基吸附剂；探讨各功能化吸附剂对铅吸附的行为和机理，筛选影响铅吸附的干扰离子，揭示影响吸附亲和力的内在规律；研究浸出液中铅与干扰离子之间的动态竞争吸附分离过程和机理，建立铅吸附的动力学模型，丰富和发展生物材料对重金属的吸附理论；优化预处理柱分离干扰离子和处理柱分离铅离子的条件，构建分离回收体系，实现浸出液中铅及其它金属的分离回收，为重金属污染土壤修复的无害化及资源化提供理论依据和技术支撑。

本项目以铅污染土壤浸出液为研究对象，采用化学接枝法制备磷酸、胺基和羧基等功能化的秸秆，研究了改性前后秸秆对铅离子的吸附性能和机理。结果表明，改性后吸附剂的稳定性增强，吸附过程中有机质的释放量显著降低，不同秸秆由于结构不同在吸附过程中有机质释放量有所区别，但释放源主要来自于秸秆中的木质素和半纤维素；改性吸附剂对铅离子的吸附容量、吸附速率和选择性显著提高，不同官能团改性吸附剂对不同金属离子表现出不一样的吸附亲和力。羧基改性秸秆对金属离子的吸附亲和力顺序为：Pb2+>Cu2+>Cd2+>Zn2+>Mg2+>Ca2+>Na+；胺基改性的顺序为：Cu2+>>Pb2+>Zn2+≈Cd2+>>Mg2+≈Ca2+>Na+；磷酸改性的为：Pb2+>Cu2+>Cd2+>Zn2+>Mg2+>Ca2+>Na+，吸附亲和力顺序主要受金属离子特性和吸附剂表面特性影响。改性吸附剂对Pb2+的吸附符合Langmuir等温吸附模型，为单分子吸附，吸附过程符合准二级动力学模型，吸附机理以静电吸附、配位吸附为主。动态吸附结果表明在所研究的范围内流速、初始浓度等因素会影响金属离子吸附的穿透曲线，但对吸附容量影响较小；由于不同功能化吸附剂对不同金属离子的吸附亲和力不同，复杂体系中出现了显著的竞争取代效应，实现了高吸附亲和力金属离子的选择性吸附，竞争取代的动力学过程符合色谱分离的高斯方程；在竞争取代过程中，铅离子吸附的主要干扰离子为铜离子，常见其它共存离子干扰小；改性秸秆填充柱的再生实验表明被吸附的铅离子可高效洗脱，洗脱液中的铅离子可采用化学沉淀法进行回收，常用沉淀剂磷酸钠、硫化钠和硫酸钠的沉淀率均高于99%。基于动态吸附研究的结果，构建了污染土壤浸出液中低浓度铅离子的选择性分离回收体系，优化了预处理柱胺基功能化秸秆填充柱和处理柱磷酸功能化秸秆柱的分离条件，实现了污染土壤浸出液中低浓度铅离子的分离回收。以上研究将丰富和发展生物材料对重金属的吸附理论，同时也为为重金属污染土壤修复的无害化及资源化提供理论依据和技术支持。