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| Adsorption of Pb(Ⅱ) by organic sheep manure fertilizer and organic seaweed fertilizer at different decomposition stages |
| Received:January 21, 2021 |
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| KeyWord:organic fertilizer;seaweed;sheep manure;heavy metal;adsorption isotherm;adsorption kinetic |
| Author Name | Affiliation | E-mail | | HAN Jiayi | College of Tropical Crops, Hainan University, Haikou 570110, China | | | WANG Yuyang | College of Tropical Crops, Hainan University, Haikou 570110, China | | | ZHAO Qingjie | College of Tropical Crops, Hainan University, Haikou 570110, China | qingjiezhao@hainanu.edu.cn | | WU Weidong | College of Tropical Crops, Hainan University, Haikou 570110, China | | | LI Jianhong | School of Environmental and Chemical Engineering, Foshan University, Foshan 528000, China | | | FAN Qiuyun | College of Forestry, Hainan University, Haikou 570110, China | | | WU Zhipeng | College of Tropical Crops, Hainan University, Haikou 570110, China | |
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| Abstract: |
| The screening of commercial organic fertilizers with excellent and long-lasting immobilization effects for remediating heavy metal contamination in farmlands has received increasing attention. In this study, the basic properties of commercial organic fertilizers of sheep manure(SM) and seaweed(SW) at different stages of decomposition(0, 6, and 12 months) were analyzed by chemical analysis, sorption -desorption analysis, thermogravimetric and differential thermogravimetric analysis, and Fourier transformation infrared spectroscopy analysis. The sorption mechanism of organic fertilizers on Pb(Ⅱ) in an aqueous solution system was further investigated. The results showed that the organic carbon content and pH value of the SW fertilizer were higher compared with the SM fertilizer, while the cation exchange capacity(CEC), oxygen-carbon ratio, and base saturation were lower. As the decomposition process proceeded, the oxygen-carbon ratio and CEC of the SW fertilizer increased significantly, and the content of the functional groups decreased, whereas the functional group contents increased in the SM fertilizer. The easily decomposable compounds(e. g., cellulose, hemicellulose, aliphatic substances, etc.) in both organic fertilizers decreased as the decomposition proceeded. The maximum sorption amount(qm) of Pb(Ⅱ) in the SM fertilizer was 198.7 mg·g-1 when it was not decomposed, and the qm of Pb(Ⅱ) decreased with increasing decomposition to 61.6 mg· g-1 at 12 months of decomposition, whereas the qm of Pb(Ⅱ) of the SW fertilizer gradually increased from 118.7 mg·g-1 to 147.1 mg·g-1. The sorption kinetics of Pb(Ⅱ) on SW and SM fertilizers was expressed well by the pseudo-second-order model. The Langmuir model provided a better fit for the two fertilizers, which indicated that the Pb(Ⅱ) adsorption of the fertilizers was via the surface monolayer adsorption and mainly attributed to geochemical sorption. The geochemical sorption of Pb(Ⅱ) by organic fertilizers was mainly based on ion exchange adsorption(41.4%~47.1%) and hydrogen bonding adsorption(36.5%~47.3%). The correlation analysis revealed that the qm of Pb(Ⅱ) adsorbed by organic fertilizer was correlated with the CEC, base saturation, and oxygen-carbon ratio of the fertilizer. The sorption capacity of organic fertilizer for Pb(Ⅱ) could be enhanced by increasing the number of exchangeable active sorption sites and oxygen-containing functional groups on the surface of the organic fertilizer. The SW fertilizer has a high sorption capacity for Pb(Ⅱ) and good durability to adsorb Pb(Ⅱ); therefore, it is suitable as a commercial organic fertilizer for the stable remediation of Pb(Ⅱ) contamination in farmland. |
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