Leaching properties of bitumen-salt mixtures produced by sedimentation, in water

After the selection of highly radiation resistant types of bitumen for application in radioactive waste management, NaCl grains were introduced into heated bitumen by a new sedimentation technique. Prepared samples were leached with distilled water and the influence of the amount of NaCl, sample geometry, temperature and preirradiation were studied. These experiments showed that a large amount of salt can be embedded in bitumen by the proposed sedimentation method. Leaching rates depended on the salt content and decreased with time and probably with the grain size and were influenced by previous radiation treatment of the bitumen. A dynamic leaching procedure yielded higher leaching rates than static methods; leaching rates were, however, higher than those calculated by diffusion models. Discrepancies can be explained by the existence of microcracks and microholes in the bitumen matrix. Although the determined leaching rates agreed well with published values obtained by other bituminized samples, better retention of embedded salts may be expected by using softer kinds of bitumen which reduce the number of defects. (Auth.)