Molecular dynamics simulations of cesium adsorption on illite nanoparticles

Laura N Lammers; Ian C Bourg; Masahiko Okumura; Kedarnath Kolluri; Garrison Sposito; Masahiko Machida

doi:10.1016/j.jcis.2016.11.084

Molecular dynamics simulations of cesium adsorption on illite nanoparticles

J Colloid Interface Sci. 2017 Mar 15:490:608-620. doi: 10.1016/j.jcis.2016.11.084. Epub 2016 Nov 29.

Authors

Laura N Lammers¹, Ian C Bourg², Masahiko Okumura³, Kedarnath Kolluri⁴, Garrison Sposito⁵, Masahiko Machida⁶

Affiliations

¹ Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, USA; Department of Environmental Science, Policy, and Management (ESPM), University of California, Berkeley, Berkeley, USA. Electronic address: lnlammers@berkeley.edu.
² Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, USA; Department of Civil and Environmental Engineering (CEE) and Princeton Environmental Institute (PEI), Princeton University, Princeton, USA. Electronic address: bourg@princeton.edu.
³ Center for Computational Science and e-Systems, Japan Atomic Energy Agency, Kashiwa, Japan. Electronic address: okumura.masahiko@jaea.go.jp.
⁴ Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, USA. Electronic address: kedar.kolluri@gmail.com.
⁵ Department of Environmental Science, Policy, and Management (ESPM), University of California, Berkeley, Berkeley, USA. Electronic address: gsposito@berkeley.edu.
⁶ Center for Computational Science and e-Systems, Japan Atomic Energy Agency, Kashiwa, Japan. Electronic address: machida.masahiko@jaea.go.jp.

PMID: 27930922
DOI: 10.1016/j.jcis.2016.11.084

Abstract

The charged surfaces of micaceous minerals, especially illite, regulate the mobility of the major radioisotopes of Cs (¹³⁴Cs, ¹³⁵Cs, ¹³⁷Cs) in the geosphere. Despite the long history of Cs adsorption studies, the nature of the illite surface sites remains incompletely understood. To address this problem, we present atomistic simulations of Cs competition with Na for three candidate illite adsorption sites - edge, basal plane, and interlayer. Our simulation results are broadly consistent with affinities and selectivities that have been inferred from surface complexation models. Cation exchange on the basal planes is thermodynamically ideal, but exchange on edge surfaces and within interlayers shows complex, thermodynamically non-ideal behavior. The basal planes are weakly Cs-selective, while edges and interlayers have much higher affinity for Cs. The dynamics of NaCs exchange are rapid for both cations on the basal planes, but considerably slower for Cs localized on edge surfaces. In addition to new insights into Cs adsorption and exchange with Na on illite, we report the development of a methodology capable of simulating fully-flexible clay mineral nanoparticles with stable edge surfaces using a well-tested interatomic potential model.

Keywords: Geochemistry; Molecular dynamics simulations; Radiocesium.