Abstract
AbstractThermal 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.
Highlights
The study of the thermal stability of amphiboles, and of the fibrous ones in particular, has received increasing interest in recent years (Della Ventura et al, 2017; 2018a; Oberti et al, 2019)
In the present work we focus on the in situ analysis of the structure modifications occurring in tremolite fibres upon heating using the same well-characterised sample from Maryland, USA analysed by Pacella et al (2010) and Pacella et al (2020)
The quantitative phase analysis (QPA) of the sample cooled down at RT indicates the occurrence of ∼2:1 weight ratio subcalcic diopside and associated calcium-rich clinoenstatite plus traces of hematite
Summary
The study of the thermal stability of amphiboles, and of the fibrous ones in particular, has received increasing interest in recent years (Della Ventura et al, 2017; 2018a; Oberti et al, 2019). In a recent paper (Pacella et al, 2020) the products of riebeckite and tremolite fibres heated at several temperatures, including above those of the breakdown of their structures, have been analysed ex situ by PXRD.
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