Purification of Na-smectite and preparation of oriented samples for diffusion experiments

Purification of Na-smectite and preparation of plated-oriented samples (membranous samples) were carried out, and a compacted smectite sample for diffusion experiment, of which orientation of smectite particles and interlayer aperture were controlled, was manufactured for trial. Mineral analyses and measurements of the basal spacing of the purified Na-smectite for oriented and powder samples by X-ray Diffractometry (XRD) and measurements of the dry densities for the plated-oriented samples were carried out. A Na-bentonite, Kunipia-P (a product of the Kunimine Industries Co. Ltd.), of which smectite (montmorillonite) content is almost 100 wt.%, was used as an initial material in the purification of Na-smectite, and after exchangeable cations in the interlayer of smectite were perfectly exchanged with Na+ ions, purification of the smectite and removal of soluble salts were carried out. Next, plated-oriented samples were prepared in the same way as preparation of oriented sample, and a compacted smectite sample for diffusion experiment was manufactured for trial using the plated samples. Furthermore, after the compacted smectite sample for diffusion experiment manufactured for trial was saturated with 0.01 M-NaCl, the basal spacing distribution was measured for the sample depth by XRD. The recovery of finally obtained purified Na-smectite was 80.55% to the initial weight of Kunipia-P which was used as an initial material, and it was identified that the purified Na-smectite, a homogeneously arranged Na-smectite, has no impurity and is a dioctahedral smectite from XRD profiles and peak positions for oriented and powder samples. The dry density of the plated-oriented samples was 1.86±0.18 Mg/m3, and it was clarified that the plated-oriented samples with thinner than 0.5 mm in thickness are better in order to obtain samples with high-dry density and the samples with thinner than 1 mm in thickness are desirable from the viewpoint of manufacturing in the plated samples such as cutting. A compacted smectite sample for diffusion experiment, of which orientation of smectite particles and interlayer aperture were controlled, was manufactured for trial using the plated samples. Consequently a compacted smectite sample with a dry density of about 1.8 Mg/m3 and with only 2 water layers of interlayer aperture could be successfully manufactured for trial. This study was carried out under JAEA Nuclear Fuel Cycle Creative Engineering Research Promotion System (successor of Japan Nuclear Cycle Development Institute Innovative Research Promotion System). (author)