A novel decomposition technique of friable asbestos by CHClF2-decomposed acidic gas

Abstract

Asbestos was widely used in numerous materials and building products due to their desirable properties. It is, however, well known that asbestos inhalation causes health damage and its inexpensive decomposition technique is necessary to be developed for pollution prevention. We report here an innovative decomposition technique of friable asbestos by acidic gas (HF and HCl) generated from the decomposition of CHClF 2 by the reaction with superheated steam at 800 °C.Chrysotile-asbestos fibers were completely decomposed to sellaite and magnesium silicofluoride hexahydrate by the reaction with CHClF 2 -decomposed acidic gas at 150 °C for 30 min. At high temperatures beyond 400 °C, sellaite and hematite were detected in the decomposed product. In addition, crocidolite-asbestos containing wastes and amosite-asbestos containing wastes were also decomposed by CHClF 2 -decomposed acidic gas at 500 °C and 600 °C for 30 min, respectively. The observation of the reaction products by phase-contrast microscopy (PCM) confirmed that the resulting products did not contain any asbestos.

Thermal decomposition of different types of asbestos

“…4. In the temperature range 600-800°C, chrysotile Mg 3 (OH) 4 Si 2 O 5 -regardless of origin and deposit-losses the chemical bonded water (Fig. 4, strong endothermic peak with T max 700-730°C).…”

“…The other five asbestos forms belong to the amphibole type, having chain structure. Minerals such as actinolite, tremolite, crocidolite (fibrous form of riebeckite), anthophyllite, and amosite (fibrous form of grunerite) are found in this group [1][2][3][4].…”

“…The methods which are able to change the harmful properties of asbestos minerals through the destruction of the fibrous structure should be considered. Dissolution in acids [4,[12][13][14][15][16][17], hydrothermal treatment [18,19], mechanochemical treatment with high-energy milling process [20], fiber melting and vitrification with fluxes or the use of plasma technology [21,22] are the main among the described methods in technical literature.…”

“…In the case of chrysotile asbestos [Mg 3 (OH) 4 Si 2 O 5 ], which was the most abundant and most widely investigated, results reported in several studies [6,7,[32][33][34][35][36] show that chrysotile with the loss of chemical combined water transforms into an anhydrous phase (metachrysotile) around 500-750°C (with a maximum rate above 700°C). Rapid recrystallization of anhydrous phase occurs after this stage at above 800°C.…”

Thermal decomposition of asbestos-containing materials

“…There are different ways of disposing of these wastes. Dissolution in acids or bases [8][9][10][11][12], hydrothermal [13] or mechanochemical treatment [14,15] as well as fibre melting with further vitrification [16,17] are methods that have been described in the technical literature. One of these methods could also be thermal treatment [18][19][20][21].…”