【兴大报告 Xing Da Lecture 546】

题  目：Aspects of environmental actinide chemistry

报告人: Prof. Horst Geckeis

Director of the Institutefor Nuclear Disposal (INE) and Professor for Radiochemistry at the KarlsruheInstitute of Technology (KIT), Institute for Inorganic Chemistry, Faculty ofChemistry and Biosciences

时　间：2018年5月18日(星期五)下午2:00

地　点：化学楼A204/206

主请人：刘春立

报告摘要：

Sincetheir application in various technologies, notably in nuclear energy, actinideelements have gained significant interest by environmental scientists (e.g. [1,2]). Besides uranium and thorium, also transuranium elements, notably plutonium, can be found in the natural environment. While the naturogenic plutonium isotopes ²⁴⁴Pu and ²³⁹Pu are only abundant atultra-trace levels in the earth crust, antropogenic releases between the 1950s and the 1970s via nuclear weapon tests and from military processing installationsinto the environment amount to more than 20 tons ^[3]. In addition, quite a number of countries using nuclear energy have decided to dispose spentnuclear fuel in a geological repository without separating uranium andplutonium. Understanding environmental actinide behaviour is certainly of highrelevance not only to appraise actinide propagation in the biosphere but alsoto assess their behaviour in a deep geological repository over long timescales.

It is well known, that plutonium exists in its tetravalent oxidation state in manyenvironmental compartments and thus is considered of low mobility. This isconsistent with observations made for plutonium already abundant in theenvironment, where e.g. plutonium deposited as weapon test fallout can be foundlocated in narrow regions of sediment layers ^{[3, 4]}. However,formation of colloidal species, complexation with organic ligands, redoxtransitions have been reported to enhance the mobility of the early actinideseries elements under specific conditions (e.g. [5, 6]). Respective reactionsare often characterized by strong kinetic hindrances.

Frequently, lanthanides, uranium or thorium are taken as surrogates for americium,neptunium and plutonium. Such analogies, though being adequate in some cases,may be misleading in other cases. Ionic radii vary and thus speciation insolution can strongly differ. The capability of forming e.g. covalent bondings significantly varies between 4f and 5f elements and within the 5f elementseries (see e.g. [7, 8]). Consequently, thermodynamic data and speciationschemes of chemical homologies are not always applicable, but have to be determined element specific.

Our knowledge on actinide environmental chemistry has certainly improved tremendously over the years. There is, however, still space for research on agroup of radioelements with exciting properties.

[1] A.Yu.Romanchuk et al., 2016, Russ. Chem. Rev., 85, 995

[2] A. B.Kersting, 2013, Inorg. Chem. 52, 3533

[3] H.Geckeis, M. Zavarin, B. Salbu, O. Lind, L. Skipperud, 2018, Environmentalchemistry of plutonium in P. A. Stevens, D.L. Clark, Plutonium Handbook, in print

[4]Saito-Kokubu, et al. 2008, Journal of Environmental Radioactivity, 99, 211

[5] A.B.Kersting et al., 1999, Nature, 397, 56

[6] A.P.Novikov et al., 2006, Science, 314, 638

[7] M.L.Neidig et al., 2013, Coord. Chem. Rev., 257, 394

[8]T. Vitova et al., 2017, Nature Comm., 8, 16053