Properties of aluminium slags

The decontamination process of metallic aluminium through metal melting, results in a nuclear waste product referred to as aluminium slag. In order to gain information regarding the physico chemical properties of these slags and to better understand how to treat these wastes, different techniques were used to characterise the slags. Water intrusion test revealed an apparent density around 1.64 g cm-3 and an open porosity around 3.9%. This test also allowed to highlight the reactivity of the sample in contact with distilled water, as some sulphur-based gas was produced in small quantity during the test. However, this reaction did not hamper the tests, except from a slight increase of the uncertainty. The reaction of the sample, when brought into contact with water, was also observed after the preparation of the sample for Scanning Electron Microscopy coupled with an Energy Dispersive Spectroscopy. After polishing the sample, until a mirror finish, some material bled from the interior of the sample after a few days and were deposited on its surface. Three distinct types of morphology could be discerned on the sample surface. The first morphology represented a well dispersed high density particles (composed of Fe, Cr, Mn and Si) in a metallic aluminium matrix. In addition, some particles were found containing Zn, Cu (possibly brass) and Ni. The second morphology, more concentrated to specific areas in the sample as compared to the first one, contained numerous cracks and had a certain porosity. It also appeared to include or surround some of the particles of the previous type. The main constituents were: Al, O, Na, Mg, K, Ca and Si of which the latter is highly localised to specific areas. The third morphology clearly lied on top of the sample surface and represented the accumulated deposition of material on the sample surface. EDS count intensity maps of the area showed a main composition of Na and O suggesting NaOH. Other elements which were encountered are Cl and K. No sulphur was detected in all morphologies. From X-Ray diffractometer, a good agreement was found for the reference peaks of metallic aluminium (PDF 04 0787), MgAl2O4 (PDF 21 1152) and graphite (PDF 08-0415). The graphite signal originated from the used embedding resin. Several peaks were unassigned and were unable to be identified given the current knowledge of the elements present within the sample.