Vol.:(0123456789) 1 3 Journal of Radioanalytical and Nuclear Chemistry https://doi.org/10.1007/s10967-018-6310-6 Sorption of Am(III) on clays and clay minerals: A review Daniel R. Fröhlich 1  · Ugras Kaplan 2 Received: 13 August 2018 © Akadémiai Kiadó, Budapest, Hungary 2018 Abstract The problem connected to the long-term storage of high-level nuclear waste has initiated an extensive search for suitable host rock formations and backfll materials to guarantee an isolation of hazardous nuclear elements from the biosphere for thousands of years. Besides other alternatives, clays and clayey materials have been in the focus of various sorption studies. With respect to long-term predictions of migration processes, the transuranium elements and fssion products are of particular interest. The present review gives a detailed summary of sorption studies conducted during the past decades describing the impact of various geochemical parameters on the immobilization of Am(III) by diferent clays and clay minerals. Keywords Americium · Sorption · Clay minerals · Nuclear waste disposal Introduction The search for suitable host rock formations for the fnal disposal of high-level nuclear waste has lead to strong scientifc efort worldwide with the aim of weighing the advantages and disadvantages of diferent potential host rocks. Besides rock salt and crystalline formations (e.g. granite), clay rocks are considered and investigated in various countries (e.g. Belgium [ 1], China [ 2], France [3], Germany [4], and Switzerland [5]). Furthermore, the potential backfll material bentonite, which is considered in various nuclear waste repository scenarios, is mainly constituted of clay (typically 60–80% montmorillonite) as well. Positive characteristics of clays include a high sorption capacity for heavy metals and the self-healing of cracks due to swelling. Therefore, a strong retardation of radio- nuclides, when released from their primary containment during storage, is assumed. With respect to long-term pre- dictions and any safety assessment, the long-lived radio- nuclides, which will determine the long-term radiotoxicity of the waste material, are of particular interest. These include the transuranium elements Np, Pu and Am, whose geochemistry and migration behavior is thus of high importance. The relevant geochemical processes include sorption onto and difusion in the clay, complexation reactions with poten- tial ligands in the deep waters, and dissolution/precipitation reactions. All of these processes are strongly dependent on the characteristic geochemical conditions of the potential storage site. Important parameters include pH, redox poten- tial, ionic strength, temperature and inorganic (especially carbonate) or organic ligands (e.g. humic substances) which are ubiquitous found in natural waters. Due to the strongly reducing conditions expected in the near-feld of a nuclear waste repository, resulting from the corrosion of the steel containments, + 3 (Pu, Am) and + 4 (Np) will be the predominant oxidation states of the tran- suranium elements [6]. Therefore, various studies during the past decades have focused on the interaction between trivalent actinides with clays. Compared to Pu(III), Am(III) ofers a strong advantage through its redox stability, which simplifes the chemical handling. Diferent modeling approaches to describe the uptake mechanisms of actinides by various sorbents, including clays, have been the topic of a very extensive review by Geckeis et al. [7]. The present work is a continuation of the * Daniel R. Fröhlich daniel.froehlich@partner.kit.edu 1 Institute of Physical Chemistry, Ruprecht-Karls-University Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany 2 Karlsruhe, Germany