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| Phosphorus Adsorption by and Forms in Fe-modified Biochar |
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| KeyWord:Fe-modified biochar; adsorption; phosphorus forms; pH |
| Author Name | Affiliation | | JIANG Xu-tao | School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
China Water Resources Beifang Investigation, Design and Research CO. LTD, Tianjin 300222, China | | CHI Jie | School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China |
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| Abstract: |
| Biochar has great potential to adsorb phosphorus, and its phosphorus forms are important for phosphorus release and bioavailability. In this study, wheat straw derived biochar was used to examine the changes of elements and surface functional groups, phosphorus adsorption and forms in biochar after modification. Modification obviously decreased C mass fraction, but increased O and Fe mass fractions in the biochar. The content of carboxyl in biochar significantly increased, while basic functional groups decreased after modification. Modification led to the equilibrium time of phosphorus adsorption by biochar increasing from 60 min to 120 min. The maximum adsorption capacity of phosphorus by Fe-modified biochar was 10.1 mg·g-1, which was 19.4 times that of unmodified biochar. The content of exchangeable phosphorus in unmodified biochar accounted for 82.1% of the total adsorption, suggesting that the adsorption mechanism was mainly physical adsorption. However, the content of iron-bound phosphorus in Fe-modified biochar was 66.7% of the total adsorption, while exchangeable phosphorus only 26.6%, implying that phosphorus was adsorbed by chemical adsorption. Increasing initial pH enhanced the removal percentage of phosphorus by Fe-modified biochar until pH7, and then decreased. The pH dependence of phosphorus removal rates was closely related to the content of exchangeable phosphorus. Increased pH might promote iron-bound phosphorus transform into occluded phosphorus. |
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