Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland.
Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.
Environ Sci Process Impacts. 2022 Sep 21;24(9):1343-1359. doi: 10.1039/d2em00028h.
The adsorption of thallium (Tl) onto phyllosilicate minerals plays a critical role in the retention of Tl in soils and sediments and the potential transfer of Tl into plants and groundwater. Especially micaceous minerals are thought to strongly bind monovalent Tl(I), in analogy to their strong binding of Cs. To advance the understanding of Tl(I) adsorption onto phyllosilicate minerals, we studied the adsorption of Tl(I) onto Na- and K-saturated illite and Na-saturated smectite, two muscovites, two vermiculites and a naturally Tl-enriched soil clay mineral fraction. Macroscopic adsorption isotherms were combined with the characterization of the adsorbed Tl by X-ray absorption spectroscopy (XAS). In combination, the results suggest that the adsorption of Tl(I) onto phyllosilicate minerals can be interpreted in terms of three major uptake paths: (i) highest-affinity inner-sphere adsorption of dehydrated Tl on a very low number of adsorption sites at the wedge of frayed particle edges of illite and around collapsed zones in vermiculite interlayers through complexation between two siloxane cavities, (ii) intermediate-affinity inner-sphere adsorption of partially dehydrated Tl on the planar surfaces of illite and muscovite through complexation onto siloxane cavities, (iii) low-affinity adsorption of hydrated Tl, especially in the hydrated interlayers of smectite and expanded vermiculite. At the frayed edges of illite particles and in the vermiculite interlayer, Tl uptake can lead to the formation of new wedge sites that enable further adsorption of dehydrated Tl. On the soil clay fraction, a shift in Tl(I) uptake from frayed edge sites (on illite) to planar sites (on illite and muscovite) was observed with increasing Tl(I) loading. The results from this study show that the adsorption of Tl(I) onto phyllosilicate minerals follows the same trends as reported for Cs and Rb and thus suggests that concepts to describe the retention of (radio)cesium by different types of phyllosilicate minerals in soils, sediments and rocks are also applicable to Tl(I).
铊（Tl）在层状硅酸盐矿物上的吸附在土壤和沉积物中 Tl 的保留以及 Tl 向植物和地下水潜在迁移中起着关键作用。特别是云母类矿物被认为能强烈结合单价 Tl（I），这与它们对 Cs 的强烈结合类似。为了深入了解 Tl（I）在层状硅酸盐矿物上的吸附，我们研究了 Tl（I）在 Na-和 K-饱和伊利石和 Na-饱和蒙脱石、两种云母、两种蛭石以及一种天然富铊土壤粘土矿物部分上的吸附。宏观吸附等温线与 X 射线吸收光谱（XAS）对吸附 Tl 的表征相结合。综合来看，结果表明，可以根据三个主要的吸收途径来解释 Tl（I）在层状硅酸盐矿物上的吸附：（i）在伊利石的磨损颗粒边缘的楔形和蛭石夹层的塌陷区周围，通过两个硅氧烷腔之间的络合作用，对脱水 Tl 进行最高亲和力的内球吸附，在非常少的吸附位点上进行吸附，（ii）对部分脱水 Tl 进行中等亲和力的内球吸附，在伊利石和云母的平面表面上进行吸附，通过与硅氧烷腔络合，（iii）对水合 Tl 的低亲和力吸附，特别是在蒙脱石和膨胀蛭石的水合夹层中。在伊利石颗粒的磨损边缘和蛭石夹层中，Tl 的吸收会导致形成新的楔形位点，从而能够进一步吸附脱水 Tl。在土壤粘土部分，随着 Tl（I）负载量的增加，观察到 Tl（I）吸收从磨损边缘位点（在伊利石上）向平面位点（在伊利石和云母上）转移。本研究的结果表明，Tl（I）在层状硅酸盐矿物上的吸附与 Cs 和 Rb 的报道趋势相同，因此表明描述不同类型的土壤、沉积物和岩石中的（放射性）铯被不同类型的层状硅酸盐矿物保留的概念也适用于 Tl（I）。
