PhD ABSTRACT.
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Mots clés : mâchefers, REFIOM, métaux lourds, comportement à long terme, extraction séquentielle, extraction à pH imposé. |
Abstract : one ton of incinerated municipal solid wastes give about 300kg of bottom ash and 50kg of APC (Air Pollution Control) residues which are mainly constituted of oxides and silico-aluminate compounds. A non-negligeable part of these residues are soluble compounds (NaCl, KCl, CaCl2, CaSO4...) and heavy metals (Pb, Zn, Cd...) which are harmful elements in view of their disposal or valorisation. We first characterized the composition of the residues and the physico-chemical mechanisms in case of lixiviation. Sequential extractions have been used to define the speciations of heavy metals and major constituents. Heavy metals are mainly associated with calcite and anhydrite and these mineral compounds are solubilised in acid conditions. These extractions were associated with pH-stat extractions to predict the behaviour of the residues in time. We then used simple scenarios and simulations : in the case of non exceptional conditions of disposal, the chlorides are the first compounds which are released to the environment. The carbonatation phenomenon in open air quickly reduced (some months) the pH of the residues leachate to about pH = 8,5, wich is fortunately in most cases the pH of the minimum solubilisation of heavy metals. A kinetic approach confirms this result. The rain is then the only possible source of protons and the decrease of the leachates pH proceeded very slowly (about hundred to thousand years). The remaining metals, associated with oxydes or inside the alumino-silicate mould cannot be released to the environment, except under special condition of disposal. Key words : bottom ash, APC residue, heavy metal, long-term behaviour, sequential extraction, pH-sta extraction. |
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