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Detoxification of chrysotile asbestos and asbestos cement, via silylation processes, in acidic and alkaline conditions

Valouma Aikaterini

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Summary

AbstractThe development of this master thesis, was primarily imposed by the ever increasing need for detoxification of asbestos and materials containing asbestos (Asbestos Containing Material - ACMs), with potential application in site.The silicates mineral occupying 90% of the Earth's surface, are the largest in volume category minerals. The term "asbestos" designates a family of silicate minerals with fibrous form. Ιn the 20th century different types of asbestos have been widely used in industry and construction, due to the exceptional physical and chemical properties. The most prevalent class of asbestos is the chrysotile asbestos, known as "white asbestos". In all of the worldwide materials containing asbestos, those produced by chrysotile exceed 90%.In the early 1960s, asbestos was implicated to cause damage to human health. Several years later, in 1988, appeared in Greece the first legislative framework for the prohibition of asbestos-containing materials. Nowadays, asbestos is considered one of the most important factors of carcinogenesis, particularly for mesothelioma and lung cancer caused by chronic exposure to fibers which enter the human body through the respiratory system. The perceived incrimination for carcinogenicity has led many countries to take strong measures to restrict the use and gradually complete closure. Greece was ranked 7th in the world in production of asbestos and placed high in the rankings involving the export of chrysotile. It was only in 2000 that the operation of the Asbestos Mines of Northern Greece were closed down, from which more than 70 million tons of serpentine were excavated in 18 years. Out of those one million tons of chrysotile asbestos were produced. In addition, plants containing materials were operating for decades. These sites remain abandoned until today, costing the health of local residents and need immediate remediation.Although various treatments have been developed for the asbestos detoxification, most of them are either limited to laboratory scale, or are very expensive to implement. Thereby the most widespread method is the deposition of asbestos-containing materials in HWL's (hazardous waste landfills), without prior treatment to reduce the toxicity of the material. Furthermore, this method is very expensive to the Greek standards, since a HWL does not operate in Greece, thus resulting in an increase in cost by transporting asbestos-containing materials abroad.This thesis investigates potential detoxification of pure chrysotile asbestos through silylation processes, and its applicability to asbestos. The chrysotile samples used for the preparation of this master thesis, originate from Asbestos Mines of Northern Greece and from the old asbestos cement factory of A.B.E.A. located in Chania. Through a series of experiments in chrysotile, selected compositions perform optimally for performing the experiments in asbestos cement. The oxalic acid dihydrate (Ox) chosen as one of the reactants is characterized by a moderate acidity and toxicity. Furthermore, the pure water glass (potassium silicate), the tetraethoxysilane (TEOS) and Ox, used in the experimental procedure do not cause adverse effects on the environment and are cost effective.FTIR, XRD, SEM and stereoscope analyses indicated that in less than 20 days, in pure chrysotile and on the surface of the fibers of asbestos, the silylation processes have transformed the layer of brushite Mg (OH)2 into an amorphous silicate mineral. In the experiments that magnesium oxalate was used the formation of a new mineral, the magnesium oxalate (Glushinskite) was observed. The procedures achieving the best results were tested on asbestos fibers. Furthermore, coatings comprised of (a) oxalic acid with TEOS and (b) oxalic acid with pure water glass were applied to cement tiles containing asbestos. Originally, the fibers were trapped and then, the brushite layer surrounding them was cleaved. The results indicate that the treatment of the asbestos based cement tiles was successful. Therefore, this method can be further studied, for a potential in situ application, at low cost.

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