Measurement of the sorption of actinides on minerals using microanalytical techniques

Abstract

The use of advanced surface-analytical techniques t o study the sorption of the actinides uranium and plutonium on to rocks and their consistuent minerals, in the context of radioactive waste disposal, is described. Nuclear microprobe analysis was used t o quantify the extent of sorption of actinides via Rutherford back-scattering (RBS); data on the minerals o n which sorption had occurred were provided by particleinduced X-ray emission. Both surface and su b-surface concentrations of actinides were measurable. Secondary-ion mass spectrometry (SIMS) was used to measure qualitatively the distribution of sorbed actinides and their penetration rates into minerals. The equipment used at Harwell is described. Complementary use of both techniques in parallel is highly advantageous; RBS is used to quantify actinide surface loadings, w i t h limited lateral and depth resolution, but, allied to SIMS, which has excellent spatial resolution, samples can be analysed both quantitatively and with high spatial resolution. Concentrations of uranium and plutonium sorbed o n t o minerals can be routinely determined w i t h sensitivities d o w n to 1 ng cm-*. The data obtained are used to identify the minerals in a rock that are important for actinide sorption.

Heterogeneous reduction of uranyl by micas: Crystal chemical and solution controls

“…A number of studies have used micro-analytical techniques (including Rutherford backscattering spectroscopy) to study the sorption of U VI on micas and chlorite in polished-rock thin sections (Dran et al, 1988;Berry et al, 1989Berry et al, , 1991Berry et al, , 1993Berry et al, , 1994Berry et al, , 1995Smyth et al, 1980). Two interesting findings for granitic rocks were that (1) biotite and chlorite concentrated U relative to the non-mafic assemblage and (2) the sorption of U depended on mica orientation and increased with increasing exposure of edges as opposed to basal-plane surfaces.…”

The Use of Microanalytical Techniques to Measure the Distribution of Uranium and Plutonium Sorbed on Rocks and Minerals

“…The surfaces of the sections were then examined using the nuclear microprobe and SIMS. The application of both techniques at Harwell to studying actinide distributions on rocks has been discussed in detail in an earlier paper [5]. A brief summary is given below.…”

“…Two different SIMS instruments have been used in this work; the Cameca IMS 3F ion microscope and a gallium microprobe instrument based on a quadrupole mass spectrometer. Technical aspects of each machine and their application to determining uranium and plutonium distributions on rock surfaces have been described in detail elsewhere [5].…”

“…Rutherford backscattering has been used to investigate the sorption of actinide analogues (uranium and thorium) onto granite minerals and calcite [2], In pre-vious papers [3][4][5], we have described the application of nuclear microprobe analysis and SEMS to study the sorption of uranium onto various rocks and minerals. In this paper, data on uranium and plutonium loadings on minerals are presented.…”

Application of microanalytical techniques to the study of aqueous ion sorption phenomena on mineral surfaces

“…**Present address: Centro Regional de Estudios Nucleares, Univer- For the study of aqueous ion sorption on mineral substrates, proton induced X-ray emission and scattering spectrometry seem to be the most powerful tools because of their abilities to detect low concentration levels and to determine depth profiles. Some works have been published in this field from the beginning of the nineties in which the depth incorporation of a heavy element in a light substrate is followed by ion beam analysis [3][4][5][6]. In recent published works concerning high level radioactive waste disposal, ion beam analysis was applied to materials constituting the engineered barrier system as apatite in order to study the sorption mechanism [7] or to investigate possible thermal diffusion of simulated transuranium elements [8,9].…”