M.A. Avilés

Reversibility of La and Lu sorption onto smectites: Implications for the design of engineered barriers in deep geological repositories

The sorption reversibility of La and Lu (considered as actinide analogues) onto a set of smectites (bentonite FEBEX; hectorite, HEC; MX80; saponite, SAP; Otay montmorillonite, SCa-3; and Texas montmorillonite, STx-1) was studied to estimate actinide retention by smectites that are candidates for use as engineered barriers in deep geological repositories. The sorption distribution coefficients (K(d)) and the reversibility parameters (desorption distribution coefficients (K(d,des)), adjusted distribution coefficients (K(d,adj)), and desorption rates (R(des))) were determined from batch tests in two ionic media: deionized water and Ca 0.02 mol L(-1). The latter simulates possible conditions due to the presence of concrete leachates. The results varied greatly depending on the ionic medium, the lanthanide concentration and the clay structure. The high values of K(d,des) obtained (up to 1.1 x 10(5) and 9.2 x 10(4) L kg(-1) for La and Lu in water, and 2.8 x 10(4) and 4.1 x 10(4)L kg(-1) for La and Lu in the Ca medium) indicate the suitability of the tested smectites for lanthanide (and therefore, actinide) retention. Based on all the data, SCa-3, HEC and FEBEX clays are considered the best choices for water environments, whereas in Ca environments the suitable clays depended on the lanthanide considered.

Amber, beads and social interaction in the Late Prehistory of the Iberian Peninsula: an update

The identification of archaeological amber has been used in Iberian prehistory to evidence long-distance exchanges and engage Iberia in networks that connect western Europe with central and northern Europe, the emergence of social complexity, and the consolidation of trade networks. However, until now, no comprehensive analytical study of the Iberian amber has been produced to support any of the interpretive models currently in use. This paper approaches the analysis of Iberian Peninsula amber artefacts by considering their provenance (based on FTIR characterization), chronology, and spatial relationship with other exotica. Our work increases the number of analyzed artefacts to 156 (24%), out of the c. 647 currently known for the Iberian Peninsula. Based on these new data and a review of Murillo-Barroso and Martinón-Torres (2012), this overview outlines amber consumption patterns from the 6th to 2nd millennia BCE and demonstrates long-distance amber exchange connecting Iberia with the Mediterranean region from the Neolithic period onwards.

Isosymmetric structural phase transition of the orthorhombic lanthanum gallate structure as a function of temperature determined by Rietveld analysis

High energy planetary ball milling has been used to synthesize pseudo-cubic highly-pure LaGaO3 in one hour from its oxide components in an air atmosphere. Calcination at different temperatures led to the crystallization of lanthanum gallate in an orthorhombic structure with its local lanthanum coordination number environment changing from 12 to 7 when the temperature was increased. This change was attributed to the thermal expansion of the Ga–O bonds that varied non-monotonically inducing GaO6 tilting. Rietveld analysis, Raman spectroscopy, and transmission electron microscopy were used to elucidate the LaGaO3 structures at different temperatures.