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Efficient and simultaneous immobilization of fluoride and lead in water and tea garden soil by bayberry tannin foam loaded zirconium.
Abstract
Nowadays, human activities intensified the combined pollution of fluoride and lead in acidic tea garden soil. The key to eliminating this combined pollution is to immobilize pollutants simultaneously, thus preventing their migration from tea garden soil to tea trees. In this paper, the natural product bayberry tannin was employed as raw material to fabricate functional materials (TF-Zr) for simultaneous adsorption of fluorine (F) and lead (Pb) in water and soil by the reactivity of tannin with Pb2+ and the affinity of Zr with F. SEM-Mapping, EDS, FT-IR, XPS were utilized to probe the immobilization mechanisms. The results showed that TF-Zr could simultaneously and efficiently adsorb F– and Pb2+ from water with the adsorption capacity of 5.02 mg/g (Pb) and 4.55 mg/g (F). The adsorption processes were both in accordance with the proposed secondary kinetic adsorption model. Besides, the presence of F– promoted the adsorption of Pb2+ by TF-Zr. The materials were applied into tea garden soil to explore its effect on the variation of F and Pb forms in the soil. It was found that the proportion of water-soluble fluorine, exchangeable fluorine and exchangeable lead in the tea garden soil decreased significantly, while the proportion of residual fluorine and lead increased evidently, illustrating TF-Zr possessed eximious fixation effect on the highly reactive fluorine and lead in the soil and facilitated their conversion to the more stable residue state. Therefore, TF-Zr can be used for the efficient and simultaneous immobilization of fluorine and lead in water and tea garden soil.
Full-text study online at https://www.nature.com/articles/s41598-024-71767-8
EXCERPTS:
Introduction
With the intensification of human activities, various pollutants have entered the environment one after another, causing serious environmental pollution in water and soil1. More seriously, the pollution has changed to combined pollution, which is mainly manifested by heavy metals, other inorganic and organic pollutants2,3. Recently, the combined pollution of fluorine and lead in tea garden soil is particularly prominent in China. Qin et al. found that the average value of total fluorine content in a tea garden soil in China was 945 mg/kg, which was higher than the national average value of total soil fluorine4. Guo et al. tested 150 tea gardens in Fujian Province, China, for soil heavy metals and found that 70% of the tea gardens had soil lead levels exceeding the organic tea garden limit (NY 5199-2002) (50 mg/kg)5. As the tea tree grows, fluorine and lead in soil can be enriched into tea leaves6,7. Various diseases in human bodies may caused by drinking tea polluted by lead and fluorine8,9. Research has shown that the absorption of heavy metals and fluorine by tea trees comes from water in soil10,11,12. Meanwhile, the bioavailability of fluoride and lead is greatly increased in acidic tea plantation soils13,14,15, which also potentially increases the migration of fluoride and lead from soil to tea tree and into human body through the food chain16,17. Therefore, achieving the immobilization of lead and fluorine in water and soil is the key to solving the combined pollution of fluorine and lead in tea garden soil, which is of great significance for soil ecology and human health and safety.
The addition of chemical stabilizers is one of the most common means of reducing the bio-availability of lead and fluorine in soil. Currently, a number of absorptive materials obtained from natural sources or from waste products have been reported to immobilize lead and fluorine in soil, such as chitosan, sludge and diatomite18,19,20. However, these absorbents have complex compositions and limited adsorption capacity. Therefore, more materials have been developed to increase the immobilization capacity for lead and fluorine in soil. For example, aluminum humate prepared by Huang et al. was able to significantly reduce the water-soluble fluorine content in tea plantation soil21. Different charcoals reported by Gao could also effectively reduce the content of water-soluble and exchangeable fluorine in soil, which in turn significantly reduced the accumulation of fluorine in tea plants. Biochar loaded with iron lanthanides (BC/Fe-La) and aluminum lanthanides (BC/Al-La) prepared by Fan et al. were able to reduce water-soluble fluorine in soil by 87.58% and 90.17%, respectively22. Chemical stabilizers can also change the morphology of heavy metal Pb and reduce the ionic mobility and bioavailability of Pb. For example, Zhang and Xia et al. achieved in situ immobilization of Pb in soil by preparing a chemical stabilizer23,24. The MgO-loaded fish scale biochar (MgO-FB) prepared by Qi et al. was effective in immobilizing Pb and other heavy metals in soil25. Although a series of chemical stabilizers have been developed for controlling fluorine or heavy metal Pb contamination in soils, few efficient chemical stabilizers have been reported for using in the combined contamination of fluorine and Pb in acidic tea garden soil, meanwhile reducing the biological effectiveness of fluorine and Pb. Plant tannins are natural and easily extractable polyphenols that can chelate with various heavy metal ions26. However, tannin molecules are water-soluble and need to be modified when used as heavy metal adsorbents. In addition, Zr (IV) is highly electropositive and it shows excellent affinity for the highly electronegative F–27. Both Singh et al. and Liu et al. reported that Zr (IV) is able to complex with F28,29. Cho et al. prepared hydrated zirconia chitosan bead composites, which were able to achieve simultaneous adsorption of fluorine and lead in aqueous solutions, but the adsorption efficiency needs to be improved, and the effect of its application in soil has not been explored30.
Therefore, in this paper, the natural product bayberry tannin was used as raw material to prepare functional materials for simultaneous immobilization of fluorine (F) and lead (Pb) by using the efficient chelation of tannin with Pb and the strong affinity of Zr with F. Firstly, the adsorption properties of the prepared materials on F– and Pb2+ and their influencing factors were investigated in aqueous solution, and the mechanism of the adsorption of F– and Pb2+ by the materials was revealed. Then, the material was applied to tea garden soil to investigate its stabilization effect on F and Pb in tea garden soil. This study may provide new ideas for the management of the combined pollution of fluorine and heavy metal Pb in water and soil, and provide guidance for reducing the biological effectiveness of F and Pb in tea garden soil…
Conclusion
In this study, the adsorption properties of TF-Zr on Pb2+ and F– in water were evaluated. It was found that TF-Zr had a good adsorption capacity for both Pb2+ and F–, which was because Pb2+ and F– was effectively combined with hydroxyl group and Zr ion on the surface of TF-Zr. Besides, the presence of F– promoted the adsorption of Pb2+ by TF-Zr owing to the enhancement of electrostatic effect. Moreover, it was identified that when the TF-Zr material was applied to tea garden soil, the forms of Pb and F in soil changed greatly from highly active state to the most stable residual state, which indicated that the material could effectively and simultaneously prevent the pollution of Pb and F in soil and control their migration to tea trees.