Given the known carcinogenic effects, asbestos minerals are considered as general health hazard. Therefore, the elimination of asbestos materials from the environment is necessary. Asbestos minerals should be entirely transformed to a non-hazardous material. One of these methods is destructing the fibers structure of asbestos minerals by thermal treatment. Asbestos minerals are naturally occurring hydrous silicates, so that they decompose to release water by heating at high temperatures which may lead to changes in crystal structure and the formation of new phases without the dangerous properties. In this article, thermal behavior of asbestos minerals is investigated to observe the disappearance of this hazardous structure and to characterize products obtained by this way. Ten samples of asbestos minerals (six chrysotile samples from different locations, two samples of crocidolite, one amosite, and one tremolite) from different locations were tested. Mineralogical and morphological data (X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy) were obtained before and after differential thermal analysis.

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The thermal behaviour of two crocidolite asbestos samples was characterized. Infrared spectroscopy (FT-IR), powder X-ray diffraction, scanning electron microscopy and thermal analysis (DTA and TG) with evolved gas analysis were carried out on samples of crocidolite asbestos as received and after heating in order to observe their structural changes and dehydroxylation process. The results show that the dehydroxylation process of crocidolite asbestos occurs at different temperatures and is in the range 400-650°C. This temperature is dependent on the origin of asbestos samples and may be associated with an increased amount of magnesium in the structure of asbestos. For the sample which comes from the Republic of South Africa, the dehydroxylation process occurs at lower temperature in contrast to Russian crocidolite asbestos sample from cement-asbestos material. However, this temperature range is lower than those reported by some authors, who state that the decomposition temperature of crocidolite should be at least 900°C. This finding may have a significant influence on thermal utilization of asbestos materials, e.g. cementasbestos, because the temperature of the heat treatment in the utilization process should be as low as possible.

Asbestos is the common name applied to a group of natural, fibrous silicate minerals, which were once one of the most popular raw materials to be used in building materials. Asbestos was mainly used for the production of assortment asbestos-cement products. Today it is generally known that asbestos belongs to the group of hazardous materials and shows carcinogenic activity. In Poland, asbestos-containing materials are stored in special landfills. This is not the final solution to the asbestos problem because the fibrous structure of asbestos is still maintained. Therefore, methods based on recycling must be found which will be able to destroy asbestos' dangerous fibrous structure. One of these methods may be thermal decomposition, where chemically combined water is released from the asbestos materials during heating. This leads to changes in the crystal structure and to the formation of new mineral phases. The aim of the preliminary research presented in this study was to determine the thermal behaviour as well as the structural and phase transformations of asbestos-cement materials during heating to high temperature. In the present study, three different types of asbestos-containing materials from Poland were examined. Differential thermal analysis, thermogravimetry with evolved gas analysis, X-ray diffraction, infrared spectroscopy and scanning electron microscopy were used to study the thermal decomposition of asbestos-cement samples. It was found that there were no significant differences between the type of asbestos-cement samples used-their thermal decomposition takes place in a similar way.

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