Towards a detailed comprehension of the inertisation processes of amphibole asbestos: in situ high-temperature behaviour of fibrous tremolite

Thermal behaviour of fibrous tremolite from Maryland, USA has been investigated in situ up to breakdown temperature. Tremolite can be found both as primary constituent and as contaminant in Asbestos Containing Materials (ACMs). The products of breakdown are subcalcic diopside and calcium-rich clinoenstatite in a 2:1 ratio, traces of hematite plus minor silica-rich amorphous material. Thermal expansion follows a regular trend up to 723 K before the onset of Fe2+ oxidation/OH- deprotonation which is completed at 1023 K. At 923 K the Fe3+ migration starts towards M(1) and the corresponding counter-migration of Mg to M(2) and M(3). At T close to structure breakdown, M(2) shows a significant site-scattering reduction possibly consistent with the occurrence of minor vacancies. In fully oxidised tremolite, Fe3+ is allocated prevalently at M(1) and subordinately at M(3). As it is well-known that M(1), along with M(2), is the most exposed octahedral site at the surface of amphiboles, most of the Fe3+ is available for participating in the Fenton-like reactivity of oxidised tremolite, potentially making it dangerous for human health. This point should be properly taken into account in the evaluation of the safety of thermally decomposed tremolite-containing ACMs, in particular in the case of accidentally incomplete treatments.