Paléosiderurgic slags as anthropic analogues for studying stability of low activity nuclear vitrified wastes

International audienceSeveral type of analogues have been proposed for slagged wastes, among them glasses from archaeometallurgical sites. A world-wide database on 1500 samples whith ages varying from a few years to more than 2000 years, has been built, allowing the characterisation of iron slags, including location and deposit conditions, age of the site, type of technology, chemical analysis and petrological studies.The use of archaeometallurgical slags as anthropic analogues presents several advantages. Firstly, the chemical compositions of several slagged wastes (REFIOM, low activity nuclear vitrified wastes, ...) are remarkably close to some archaeometallurgical slags.Secondly, their structure is heterogeneous, some parts being totally vitreous while others are more or less crystallized, as slagged wastes. Among their complex mineralogy, it appears that some minerals (spinels, such as hercynite, melilite ...) are able to trap specifically transition elements, which they concentrate at high levels. For instance, when archaeometallurgical slags are crystallized, they show a high speed crystallizing pattern (dendritic, skeletal crystals), a situation which can occur when elaborating slagged wastes.Thirdly, archaeometallurgical slags are widely found in Europe. Their age ranges from 100 to more than 2000 years. They can be found under different climatic environments, ranging from cold to hot - dry or hot - wet climates. They occur in different depositing conditions such as weathering zones (oxidizing conditions), drainage zones (open system), beneath the water table (more reducing conditions), buried in diversified soils or as colluvions (reducing conditions). The study of glass natural alteration shows that, despite of the wide variability of samples from the point of view of chemical composition as well as deposition conditions, the process of alteration seems to be the same for all slags. A fracturing and peeling phenomenon is superimposed to the chemical alteration, allowing the leaching solution to be always in contact with unaltered glass. An acid alteration occurs, with alcaline-earth cation departure from the glass. In a confined medium (buried samples or in cracks) the altering solution becomes basic (this is also verified by laboratory leaching tests) and glass tends to be dissolved. In cracks, neoformed phases, especially Fe and Mg hydroxides, appear