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| Sorption and co-sorption of methylene blue and Pb(Ⅱ) onto rice husk-based biochars modified by nitric acid via microwave heating |
| Received:March 05, 2016 |
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| KeyWord:biochar;adsorption isotherm;adsorption kinetics;co-sorption |
| Author Name | Affiliation | E-mail | | CHE Xiao-dong | Department of Municipal Engineering, Nanjing Tech University, Nanjing 211816, China | | | DING Zhu-hong | Department of Environmental Science, Nanjing Tech University, Nanjing 211816, China | dzhuhong@njtech.edu.cn | | HU Xin | State Key Laboratory of Analytical Chemistry for Life Science, Center of Material Analysis, Nanjing University, Nanjing 210093, China | | | CHEN Yi-jun | State Key Laboratory of Analytical Chemistry for Life Science, Center of Material Analysis, Nanjing University, Nanjing 210093, China | |
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| Abstract: |
| Biochars derived from various biomass feedstocks through slow pyrolysis/carbonization in an oxygen limited environment have been considered as promising low-cost and sustainable sorbents for organic and inorganic contaminants' removal from aqueous solution. The related researches show that appropriate chemical modification of the pristine biochars will improve its adsorption capacity greatly. In this work, rice husk, a common agricultural by product, was chosen as a feedstock to prepare biochars through the pyrolysis at 600℃ and 300℃ under oxygen-limited conditions. The resulting pristine biochars were oxidated by nitric acid via microwave heating and water-bath heating, respectively, to obtain four kinds of modified biochars. Then, the batch adsorption experiments of a cationic dye-methylene blue(MB) and a heavy metal ion-Pb(Ⅱ) onto the modified biochars were carried out to compare the adsorption effect of different biochars. The results indicated that the modified biochars exhibited greater adsorption capacity for Pb(Ⅱ) and MB than the pristine biochars, and the experimental data could be well fitted by the Langmuir and Freundlich isotherm model(R2>0.90). Kinetic data showed that the adsorption of Pb(Ⅱ) and MB onto the modified biochars followed well with the pseudo-second order kinetic model, and the adsorption reached equilibrium in about 2 h. In the pH range of 2~6, the removal of Pb(Ⅱ) increased with the increase of solution pH and reached the maximum at pH 6. The removal rates of MB also increased with pH increasing from 4 to 8, and the maximum value was observed at pH 8. The co-adsorption experimental results showed that the adsorption of Pb(Ⅱ) onto modified biochars was greatly decreased with increasing molar ratio of MB/Pb(Ⅱ), suggesting the possible competitive adsorption of MB and Pb(Ⅱ) onto biochars. Biochars modified with different heating methods had different adsorption performances for Pb(Ⅱ) and MB. |
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