State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, 210008, Nanjing, China.
College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
Environ Sci Pollut Res Int. 2022 Sep;29(45):68680-68691. doi: 10.1007/s11356-022-20315-w. Epub 2022 May 11.
Lead (Pb) is one of the top metal pollutants worldwide, and its distribution between liquid and solid phases of soils is strongly controlled by its adsorption on minerals, organic matter, and their composites. This paper presented the effect of fulvic acid (FA) coexistence on the distribution of Pb(II) at the solid-liquid interface of four minerals, which provided reference for how to use humic substances to remove toxic Pb(II) in soils. The free Pb of suspensions, measured by Pb ion selective electrode, was used to characterize the complexation of FA with Pb at various pH. The adsorption isotherms of Pb(II) by montmorillonite, kaolinite, goethite, and gibbsite with and without FA were studied with batch experiments. Results indicated that the free Pb decreased and complexed Pb(II) increased with the increase of FA concentration in Pb(II)-FA solutions, whether the initial concentration of Pb(II) was 0.1 or 1 mM. Pb hydrolysis was low and the free Pb concentration in pure lead solution without FA was generally unchanged with increasing solution pH at pH < 6.0. But free Pb decreased with the increase of pH in the presence of FA, suggesting that the complexation ability of FA with Pb increased with the increase of solution pH. The adsorption of Pb(II) by the minerals without FA followed the order: montmorillonite > kaolinite ≈ goethite > gibbsite at pH5.0. The Pb(II) adsorption by montmorillonite and kaolinite significantly enhanced with 1 g/L FA, while significantly inhibited with 3 g/L FA at low initial Pb(II) concentration. However, the effect of FA on Pb(II) adsorption by montmorillonite was greater than that of kaolinite, which was mainly related to the crystal layer structure, adsorption area, and cation exchange capacity of the minerals. The Pb(II) adsorption by goethite and gibbsite was significantly enhanced by the addition of both 1 g/L and 3 g/L FA, and the enhancement was more evident in goethite system. The effect of FA on the distribution of Pb(II) between solid and liquid phases of the minerals was determined by the factors such as the initial concentration ratio of FA to Pb(II), the adsorption capacity of minerals for FA, and the number of soluble complexes of FA with Pb. Therefore, the distribution of FA between solid and liquid of four minerals affected the distribution of Pb(II) between solid and liquid phases of the minerals greatly. The results can provide an important reference for understanding the distribution of Pb(II) and the dynamics and mobility of active components in polluted soils.
铅 (Pb) 是世界上主要的金属污染物之一，其在土壤固液相中的分布强烈受其在矿物、有机物及其复合物上吸附的控制。本文研究了腐殖酸 (FA) 共存对四种矿物固液界面上 Pb(II) 分布的影响，为利用腐殖质去除土壤中有毒的 Pb(II) 提供了参考。通过 Pb 离子选择电极测量悬浮液中的游离 Pb，以表征 FA 在不同 pH 值下与 Pb 的络合。采用批量实验研究了 FA 共存时 Pb(II) 在蒙脱石、高岭石、针铁矿和三水铝石上的吸附等温线。结果表明，无论 Pb(II) 的初始浓度是 0.1 还是 1 mM，在 Pb(II)-FA 溶液中 FA 浓度增加时，游离 Pb 减少，络合态 Pb(II)增加。在没有 FA 的情况下，在 pH 值低于 6.0 时，Pb 水解程度较低，并且在纯 Pb 溶液中没有 FA 时，游离 Pb 浓度通常保持不变。但在有 FA 的情况下，随着溶液 pH 值的升高，游离 Pb 减少，表明 FA 与 Pb 的络合能力随溶液 pH 值的升高而增加。在 pH 值为 5.0 时，没有 FA 存在时四种矿物对 Pb(II) 的吸附顺序为：蒙脱石>高岭石≈针铁矿>三水铝石。在低初始 Pb(II)浓度下，FA 的加入量为 1 g/L 时，蒙脱石和高岭石对 Pb(II)的吸附明显增强，而 FA 的加入量为 3 g/L 时，吸附明显受到抑制。然而，FA 对蒙脱石中 Pb(II)吸附的影响大于高岭石，这主要与矿物的晶体层结构、吸附面积和阳离子交换能力有关。添加 1 g/L 和 3 g/L FA 均可显著增强针铁矿和三水铝石对 Pb(II)的吸附，而在针铁矿体系中增强效果更为明显。FA 对矿物固液相中 Pb(II)分布的影响取决于 FA 与 Pb(II)的初始浓度比、矿物对 FA 的吸附能力以及 FA 与 Pb 的可溶性络合物数量等因素。因此，四种矿物中 FA 在固液相之间的分布极大地影响了矿物固液相中 Pb(II)的分布。该结果可为深入了解污染土壤中 Pb(II)的分布以及活性成分的动力学和迁移性提供重要参考。
