Lippold Holger, Lippmann-Pipke Johanna
Institut für Interdisziplinäre Isotopenforschung, Permoserstr. 15, 04318 Leipzig, Germany.
J Contam Hydrol. 2009 Oct 13;109(1-4):40-8. doi: 10.1016/j.jconhyd.2009.07.009. Epub 2009 Aug 11.
Migration of contaminants with low affinity for the aqueous phase is essentially governed by interaction with mobile carriers such as humic colloids. Their impact is, however, not sufficiently described by interaction constants alone since the humic carriers themselves are subject to a solid-liquid distribution that depends on geochemical parameters. In our study, co-adsorption of the REE terbium (as an analogue of trivalent actinides) and humic acid onto three clay materials (illite, montmorillonite, Opalinus clay) was investigated as a function of pH. (160)Tb(III) and (131)I-labelled humic acid were employed as radiotracers, allowing experiments at very low concentrations to mimic probable conditions in the far-field of a nuclear waste repository. Humate complexation of Tb was examined by anion and cation exchange techniques, also considering competitive effects of metals leached from the clay materials. The results revealed that desorption of metals from clay barriers, occurring in consequence of acidification processes, is generally counteracted in the presence of humic matter. For all clay materials under study, adsorption of Tb was found to be enhanced in neutral and acidic systems with humic acid, which is explained by additional adsorption of humic-bound Tb. A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid-liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal-humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.
与水相亲和力较低的污染物的迁移主要受与腐殖质胶体等移动载体的相互作用控制。然而，仅靠相互作用常数并不能充分描述它们的影响，因为腐殖质载体本身会受到取决于地球化学参数的固液分配的影响。在我们的研究中，研究了稀土铽（作为三价锕系元素的类似物）和腐殖酸在三种粘土材料（伊利石、蒙脱石、奥帕林努斯粘土）上的共吸附随pH值的变化。用(160)Tb(III)和(131)I标记的腐殖酸作为放射性示踪剂，使实验能够在极低浓度下进行，以模拟核废料处置库远场的可能条件。通过阴离子和阳离子交换技术研究了铽的腐殖酸盐络合作用，同时也考虑了从粘土材料中浸出的金属的竞争效应。结果表明，酸化过程导致的金属从粘土屏障中的解吸，在腐殖质存在的情况下通常会受到抑制。对于所有研究的粘土材料，发现在中性和酸性体系中，腐殖酸会增强铽的吸附，这可以通过腐殖质结合的铽的额外吸附来解释。测试了一种常用的复合方法（线性加和模型）在基于二元子系统测定的数据重建三元体系（铽/腐殖酸/粘土）中铽的固液分配方面的适用性。该模型可以定性地解释腐殖酸随pH值的影响，但无法定量再现我们的实验数据。看来基本过程（金属吸附、金属-腐殖酸盐络合、腐殖酸吸附）不能被认为是相互独立的。讨论了可能的原因。
