Thermal inertization of amphibole asbestos modulates Fe topochemistry and surface reactivity

摘要

This study discloses the morphological and chemical-structural modifications that occur during thermal degradation of amphibole asbestos. Low-iron tremolite and iron-rich crocidolite were heated at temperatures ranging from r.t. to 1200 degrees C. Heating promoted a complex sequence of iron oxidation, migration and/or clustering and, finally, the for-mation of brittle fibrous pseudomorphs consisting of newly formed minerals and amorphous nanophases. The effects of the thermal modifications on toxicologically relevant asbestos reactivity were evaluated by quantifying carbon-and oxygen-centred, namely hydroxyl ((OH)-O-center dot), radicals. Heating did not alter carbon radicals, but largely affected oxygen-centred radical yields. At low temperature, reactivity of both amphiboles decreased. At 1200 degrees C, tremolite structural breakdown was achieved and the reactivity was further reduced by migration of reactive iron ions into the more stable TO4 tetrahedra of the newly formed pyroxene(s). Differently, crocidolite breakdown at 1000 degrees C induced the formation of hematite, Fe-rich pyroxene, cristobalite, and abundant amorphous material and restored radical reactivity. Our finding suggests that thermally treated asbestos and its breakdown products still share some toxicologically relevant properties with pristine fibre. Asbestos inertization studies should consider morphology and surface reactivity, beyond crystallinity, when proving that a thermally inactivated asbestos-containing material is safe.