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| Research progress on preparation techniques of lignocellulose-based heavy metal adsorbents |
| Received:September 12, 2019 |
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| KeyWord:lignocellulose;heavy metal;pretreatment;modification;microwave heating;adsorption;regeneration |
| Author Name | Affiliation | | DU Zhao-lin | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | CHEN Hong-an | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | AN Yi | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | GUO Xiao-yan | The College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China |
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| Abstract: |
| 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. |
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