In situ ESEM study of the thermal decomposition of chrysotile asbestos in view of safe re cycling of the transformation product

The thermal transformation of asbestos into non-hazardous crystalline phases and their recycling is a promising solution for the “asbestosproblem”. The most common asbestos-containing industrial material produced worldwide is cement-asbestos. Knowledge of the kinetics ofthermal transformation of asbestos fibers in cement-asbestos is of paramount importance for the optimization of the firing process at industrialscale. Here, environmental scanning electron microscopy (ESEM) was used for the first time to follow in situ the thermal transformation ofchrysotile fibers present in cement-asbestos. It was found that the reaction kinetics of thermal transformation of chrysotile was highly slowed downin the presence of water vapor in the experimental chamber with respect to He. This was explained by chemisorbed water on the surface of thefibers which affected the dehydroxylation reaction and consequently the recrystallization into Mg-silicates. In the attempt to investigate alternativeand faster firing routes for the decomposition of asbestos, a low melting glass was mixed with cement-asbestos and studied in situ to assess towhich extent the decomposition of asbestos is favored. It was found that the addition of a low melting glass to cement-asbestos greatly improvedthe decomposition reaction and decreased the transformation temperatures.