Combined X‐ray microanalytical study of the Nd uptake capability of argillaceous rocks

Argillaceous rocks are considered as suitable host rock formation to isolate the high-level radioactive waste from the biosphere for thousands of years. Boda Claystone Formation, the possible host rock formation for the Hungarian high-level radioactive waste repository, has geologically and mineralogically been studied in detail, but its physico-chemical parameters describing the retention capability of the rock needed further examinations. Studies were performed on thin sections subjected to 72 h sorption experiments using inactive Nd(III). Nd(III) has been used as a chemical analogue for transuranium elements of the radioactive waste to examine the ion uptake capability of the micrometre size mineral phases occurring in the rock. The elemental mapping of synchrotron radiation-based microscopic X-ray fluorescence (micro-XRF) combined with scanning electron microscopy energy dispersive X-ray analysis (SEM/EDX) has sufficient sensitivity to study the uptake capability of the different mineral phases on the microscale without the necessity of applying radioactive substances. Elemental maps were recorded on several thousand pixels using micrometre magnitude spatial resolution. By interleaving micro-XRF and SEM/EDX data sets from the same sample area and applying multivariate methods, calcite and clay minerals could be identified as the main mineral phases responsible for Nd(III) uptake without using additional microscopic X-ray diffraction mapping. It should be highlighted that the ion uptake capability of dolomite containing calcium and magnesium could be distinguished from the characteristics of calcite only by the interleaving of micro-XRF and SEM/EDX data sets. The presence of minerals was verified by applying microscopic X-ray diffraction point measurements. Copyright © 2015 John Wiley & Sons, Ltd.