Cesium Adsorption on Clay Minerals:  An EXAFS Spectroscopic Investigation

Abstract

Cesium adsorption on the clay minerals vermiculite and montmorillonite is described as a function of surface coverage using extended X-ray adsorption fine structure spectroscopy (EXAFS). Cesium (Cs) possessed a variable coordination environment consisting of Cs-O distances between 3.2 and 4.3 A; however, disorder typical of the Cs coordination environments prevented the resolution of all oxygen shells. On the basis of the influence of Cs loading and exchangeability on this structural arrangement, we could recognize both inner-sphere and outer-sphere adsorption complexes. The shorter Cs-O bond distance belongs to outer-sphere complexes typical of hydrated ions. In inner-sphere complexes, partially or fully dehydrated Cs coordinates directly to siloxane groups of the clay minerals forming longer Cs-O bonds. The inner-sphere adsorption complexes may have occurred within the interlayer or at frayed edge sites and were less extractable than the outer-sphere complexed Cs. Both coordination number ratios and linear combination fitting of EXAFS spectra were useful in estimating the fractions of inner-sphere and outer-sphere adsorption complexes. Our results show that X-ray absorption spectroscopy (XAS), and particularly EXAFS, is a valuable technique for exploring the type of Cs binding in environmental samples.

The seasonal variations of atmospheric 134,137Cs activity and possible host particles for their resuspension in the contaminated areas of Tsushima and Yamakiya, Fukushima, Japan

“…In general, water-soluble cesium ions from SO 4 2− are considered to be adsorbed or attached to mineral particles in a soil environment (Bostic et al 2002;Dumat and Staunton 1999;Mukai et al 2014). These mineral particles were shown to act as resuspended host particles in an atmospheric environment by the previous investigations of the global fallout from atmospheric nuclear weapon tests (e.g., Igarashi et al 2005;Masson et al 2010).…”

Organically modified clay with potassium copper hexacyanoferrate for enhanced Cs+ adsorption capacity and selective recovery by flotation

“…Cs + , Sr 2+ , Co 2+ ) 10,11 and other hazardous contaminants are readily available, low cost, and therefore suitable for scale-up. In particular, montmorillonite, a member of the smectite clays composed of two tetrahedral silica sheets surrounding a central octahedral sheet of alumina in a 2-1 layered structure, has been extensively adopted as a very efficient Cs + adsorbent with an adsorption capacity in the range 57-104 mg/g [10][11][12][13] . This relatively high adsorption capacity results from favourable structural properties including high cation exchange capacity (CEC), large surface area, high swelling capacity, good chemical and mechanical stability 10,14 .…”

Study of Heavily Adhesive Cs in Soil Environment

“…Furthermore, the wedge-shaped part similar to the frayed-edge site generally appeared after long-term pedogenetic weathering is already available both in the open spaces A and B. The frayed-edge site is known to capture Cs with much greater affinity than the expanded layers [7,26]. It is reasonably inferred that such local molecular sites characteristic for the open spaces A and B are responsible for the heavily adhesive Cs adsorption observed here.…”

“…These radioactive nuclides were carried by wind and fell out on the land surface, by which soil contamination occurs [3]- [5]. Two years having passed, the radionuclide of our largest concern is 137 Cs with the half-life of ~ 30 years because of its harmful influences on human life for decades [6], [7]. The radioactive Cs deposited on the terrestrial areas is estimated to be ~ 22 % of the total release that largely remains in soil [8].…”