Study on the thermal decomposition of crocidolite asbestos

Abstract

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.

Utilisation of cement-asbestos wastes by thermal treatment and the potential possibility use of obtained product for the clinker bricks manufacture

“…This is pseudomorph of crocidolite asbestos after its thermal decomposition and dehydroxylation process. However, the temperature 700°C is sufficient for the thermal decomposition of crocidolite, which was confirmed by previous studies [39], where was found that crocidolite asbestos undergoes dehydroxylation process in the temperature range 400-450°C. Because the in situ diffraction experiment (HT-XRD) was carried out in dynamic conditions, this observation suggests that calcination of cement-asbestos at 700°C should already be sufficient for thermal utilisation of asbestos-containing materials.…”

“…In this case lower water absorption was obtained in comparison to the reference material (2.7 vs. 3.3 %). Also, the value of open porosity was the lowest [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] MPa, thus the standard requirements are fulfilled. It should be noted that the addition of 10 wt% of cement-asbestos did not reduce the compressive strength of ceramic material as compared to the sample with 5 wt% of this waste.…”

The Use of Asbestos Wastes as a Fillers on Sorel Cement

“…Dicalcium silicate (belite) Ca 2 SiO 4 and a small amount of ettringite 3CaO•Al 2 O 3 •3CaSO 4 •32H 2 O were also identified [24]. The material was calcined at 700°C for 2 h, then ground in a ball mill for 4 h. The calcination temperature was chosen to ensure thermal decomposition (dehydroxylation process) of the asbestos minerals [27,28] contained in the cement-asbestos and, on the other hand, to limit the thermal decomposition of calcite, which occurs at a temperature range of 800 to 900°C. To confirm the thermal decomposition of asbestos minerals included in the cement-asbestos material, material obtained after calcination was studied by the FT-IR method and compared with the IR spectrum of raw cement-asbestos (Figure 3).…”

A Low Temperature Detoxification Method for Treatment of Chrysotile-Containing Waste Roofing Slate

“…Asbestos minerals can be decomposed by dehydroxylation and recrystallization at temperatures that depend on mineral type [2]. Thermal decomposition of chrysotile theoretically follows the reaction path given below [6] …”

“…In the study, chrysotile was fully decomposed into sellaite (MgF 2 ) and magnesium silicofluoride (MgSiF 6 ) by reaction with the acidic gas at 150 • C for 30 min. Tabata et al [16] proposed an asbestos decomposition method using recycled supernatant obtained from fly ash treatment with sulfur, Ca(OH) 2 , and water at 0.6 MPa at 160 • C for 1-2 h. The supernatant was mixed with asbestos in a ball mill at room temperature. After mixing, more than 99.9% of asbestos was decomposed.…”