Modifications induced by the thermal treatment of asbestos actinolite

Asbestos is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) therefore many countries have banned asbestos use. Asbestos actinolite is currently the only asbestos mineral that has not been fully characterized from the thermal point of view. In order to compensate for this gap in scientific literature, in this paper it is reported for the first time a systematic study of the thermal behaviour of actinolite asbestos, using thermogravimetric and differential scanning calorimetry (TGA/DSC) supplemented by powder X-ray diffraction (XRPD), and scanning and transmission electron microscopy combined with energy dispersive spectrometry (SEM/TEM/EDS). The deep knowledge of thermal behaviour of asbestos actinolite may deliver data relevant for the understanding of the crystal-chemical transformations of asbestos through thermal treatment and for the identification of asbestos mineral fibres in bulk natural samples using thermal analysis. For the first time, in this manuscript it is shown that the collapse of the actinolite occurs in two endothermic events followed by the formation of augite and cristobalite at approximately 1100 °C. Moreover, in this paper is shown that after thermal treatment actinolite asbestos preserves the same external fibrous habit although the structure is completely changed at molecular level: this phenomenon, known as pseudomorphosis, leads to the complete transformation of asbestos minerals into non-hazardous silicates.