Importance of cation exchange for colloid-associated transport of organic cations on clays

自20世纪80年代至今，人们一直在研究天然和人工胶体对地下水中污染物的胶体相关输送（共输送）的可能性。特别是，非极性、疏水物质向天然和人工有机以及无机胶体的共运输的潜力在实验上得到了很好的证明。然而，有机污染物往往以离子形式存在于水生环境中。特别是含碳量小的有机碳在含水层中的吸附，从而也使阳离子的环境和输运行为不以疏水吸附为特征，而以离子交换为特征。因此，对污染物迁移的预测可能会导致对流动性的低估和高估。尽管有机阳离子通过离子交换和类似疏水吸附的吸附滞后在粘土上具有很高的吸附电位，但阳离子交换作为共运输过程中的吸附机制尚未得到系统的研究。目前还没有关于阳离子交换对有机离子向粘土胶体共输运的重要性的基础研究。本建议的目的是通过实验方法系统地量化和评估有机阳离子在粘土胶体上共输运的重要性。为此，在不同规定的条件（pH、离子强度、有机阳离子的价态和停留时间）下，以一价和二价有机阳离子作为吸附剂和黏土矿物（伊利石、高岭石和蒙脱土）为粒径200、500和1000 nm的黏土矿物（伊利石、高岭石和蒙脱土）在硅酸盐基质中进行了批式和柱式实验。了解共输运的复杂性为估计有机污染物在粘土矿物存在下的环境潜力提供了基础。此外，该项目还为后续复杂材料的实验室实验和实地研究提供了方法学基础。

The potential for colloid-associated transport (co-transport) of pollutants in groundwater caused by natural and artificial colloids has been subject of research since the 1980s up to the present day. In particular, the potential for co-transport of nonpolar, hydrophobic substances to natural and artificial organic but also inorganic colloids is experimentally well documented. However, organic pollutants often occur in the aquatic environment as ionic species. Especially with small contents of organic carbon in the aquifer sorption and thus also environmental and transport behavior of cations is not characterized by hydrophobic sorption but by ion exchange. Predictions on the transport of pollutants can then lead to both underestimation and overestimation in mobility. Despite the high adsorption potential of organic cations on clays by ion exchange and a sorption hysteresis similar to hydrophobic sorption, cation exchange has not yet been systematically investigated as a sorption mechanism during co-transport. There are no fundamental studies on the importance of cation exchange for co-transport of organic ionic species to clay colloids. The aim of this proposal is to systematically quantify and evaluate the importance of co-transport of organic cations on clay colloids by experimental laboratory methods. For this purpose, batch and column experiments with monovalent and divalent organic cations as sorbent and clay minerals (illites, kaolinites and montmorillonite) of the size fractions 200, 500 and 1000 nm under different defined conditions (pH, ionic strength, valence of organic cations and residence times) are carried out in/with a silicate matrix. Understanding the complexities of co-transport provides a foundation for estimating the environmental potential of organic pollutants in the presence of clay minerals. In addition, the project provides the methodological basis for subsequent experimental laboratory experiments on complex materials and in field studies.