Thermal decomposition of chrysotile-containing wastes in a water vapor atmosphere

Abstract

A simple thermal decomposition technique to convert asbestos-containing wastes (ACWs) into non-asbestos products has been developed by heating ACWs in a water vapor atmosphere. It was confirmed that cement slates containing 18 mass % chrysotile were converted into non-asbestos products by the thermal treatment in a water vapor atmosphere at 800°C for 2 h. In contrast, the thermal treatments in air required temperatures as high as 900°C to convert the cement slates into non-asbestos products. It should be noted that any chrysotile particles were not detected by the phase-contrast microscopic observation in the products after the thermal treatments in a water vapor atmosphere at temperatures beyond 800°C but three or less chrysotile particles remained after the thermal treatments in air at high temperatures beyond 900°C. In a water vapor atmosphere, ACWs were successfully converted into non-asbestos products at low temperatures below 800°C for 2 h by accelerated solid-state reactions between decomposed products of chrysotile and cement components to form calcium magnesium silicates. This technique may contribute to large-scale decomposition of ACWs with low energy consumption in comparison with the traditional melting method.

Thermal decomposition of different types of asbestos

“…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.…”

Water vapor-assisted solid-state reaction for the synthesis of nanocrystalline BaZrO₃ powder

“…According to the thermodynamic data represented by L'vov, 28) the vapor pressure of Ba(OH) 2 in the 1 atm water vapor atmosphere is calculated to be 9.2 © 10 ¹6 atm at 800°C. 13) This value is 36 orders of magnitude higher than the other alkaline-earth hydroxides at the same temperature. Therefore, in the water vapor atmosphere, the contact areas between the reactants are increased by gas-phase transport, and then BaZrO 3 formation is promoted.…”

Thermal decomposition of asbestos-containing materials

“…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]. Asbestos minerals are naturally occurring hydrous silicates; thus they decompose to release chemically combined water by heating at high temperatures, which may lead to changes in the crystal structure and the formation of new phases without dangerous properties.…”