木质纤维素基重金属吸附剂的制备技术研究进展

分析了木质纤维素的组成成分和结构性质,归纳出木质纤维素基吸附剂的制备路线,系统总结了木质纤维素预处理、化学改性技术方法的最新研究进展,阐述了制备过程中主要因素的影响;结合表征手段揭示了其吸附机理,介绍了其吸附及再生研究方法。结果表明,为提高木质纤维素对重金属的吸附效果,可通过化学改性在其纤维素上引入活性官能团。但纤维素被封闭在由半纤维素和木质素构成的致密网状结构内,加之其结晶度较高,使得改性效果较差,因此,在化学改性前需要先进行预处理。目前的预处理技术除了包括物理、化学和生物技术,还有微波、超声等新兴技术;化学改性技术主要包括单体接枝和直接改性。原材料和试剂的种类与用量、反应温度和反应方式等因素对制备过程影响较显著。木质纤维素基吸附剂对重金属离子的吸附机理主要是表面络合和离子交换,目前吸附研究主要采用间歇式静态吸附法,再生研究主要采用溶剂再生法。最后,指出了木质纤维素基吸附剂的制备、吸附和再生过程中存在的问题及今后的发展方向。

Research progress on preparation techniques of lignocellulose-based heavy metal adsorbents

Lignocellulose-based adsorbents are widely used for heavy metal wastewater treatment due to their abundant availability, richness in natural resources, low cost, and renewability of raw materials. This study analyzed the composition and morphological structures of lignocellulose and summarized the preparation of lignocellulose-based adsorbents according to the up-to-date advances in pretreatment and chemical modification techniques. Meanwhile, the main factors that affected the preparation process were analyzed. Furthermore, characterization methods were adopted to reveal the adsorption mechanism. Adsorption and regeneration methods were then demonstrated in the study. The results indicated that reactive functional groups could be introduced to cellulose through chemical modification to enhance the adsorption capacity of lignocellulose for heavy metals. However, the cellulose was enclosed in a dense network which is composed of hemicellulose and lignin, and possesses high crystallinity; both of these lead to a poor chemical modification performance. Thus, it was necessary to conduct the pretreatment before chemical modification. In addition to physical, chemical, and biological methods, current pretreatment techniques included new methods such as microwave and ultrasound. Modification techniques mainly included monomer grafting and direct modification. Factors such as types and amounts of raw materials and reagent and reaction temperature and modes had a significant impact on the preparation process. The adsorption mechanism of lignocellulose-based adsorbents for heavy metals was mainly complexation and ion exchange. Current adsorption studies adopt mainly intermittent static adsorption methods and the solvent regeneration method was often used in the regeneration research. Finally, this study concluded existing problems of the preparation, adsorption, and regeneration of lignocellulose-based adsorbents, and suggestions were also made for future developments.