The metallurgy dross of the past: analogues to forecast the behaviour of present wastes in the course of their future aging

The production of wastes is continuously increasing. Since they are a potential source of pollution, they must be stabilised, generally by vitrification. In order to know the long term behavior of these new products, several ways have been investigated, and among them, the study of analogues, either natural or resulting from the human activity. In this paper, are studied metallurgy drosses of the past which are regularly found during archaeological excavations; their ages range from 100 to 4000 years. The mineralogical, macroscopical and chemical characterisation of these materials and of some vitrified present wastes (from municipal wastes incineration plants and nuclear wastes), showed a great analogy of chemical and mineralogical composition between these present wastes and these materials of the past. Both are generally made of similar mineral phases (spinels, silicates, sulfides, metallic alloys), surrounded by a glassy matrix, and containing in many cases high percentages of contaminants. This matrix being the main cohesion factor of these materials, which brings them to weathering resistance. This led to study the glass weathering mechanisms. The results have shown a continuous weathering in three successive steps: the departure of large glass cations (Ca, Mg), the dissolution of the glassy structure, the precipitation of new phases. The average speeds range from 20 to 180 mm/1000 years, showing a good resistance of these materials in a natural environment. Future investigations should concern the study of a global site including its surroundings, in order to know the behaviour of contaminants after weathering during a period of several hundred years. These metallurgical sites of the past may thus be considered as analogues to forecast the future behaviour of abandoned industrial sites. (authors)