Low-Temperature Pyrolysis of Crocidolite and Amosite using Calcium Salts as a Flux

Abstract

Two kinds of materials, sprayed-on crocidolite and sprayed-on amosite, containing crocidolite and amosite respectively, were treated with aqueous acetic acid solution, the pH of which was adjusted with an ammonium acetate buffer at 5, in order to remove soluble components of cement. The liquids were filtrated with a membrane filter, and the residue collected as crocidolite samples and amosite samples, respectively. The Crocidolite and amosite thus obtained were heated up to 600-1300? C for 1h. Then, power X-ray diffraction XRD experiment, scanning electron microscopic SEM observation, and thermal analysis TGDTA were carried out for these burned specimens in order to observe the change of the burned materials and melting behaviors together with their thermal properties. In addition, CaCO 3 and CaCl 2 were mixed with the respective sprayed-on asbestos and sprayed-on crocidolite, and a TGDTA measurement was conducted on these mixtures. Based on the SEM observation and XRD experiment on the specimens used in the TGDTA measurements, we tried to decompose the crocidolite and amosite, applying the method of low-temperature decomposition, the applicability of which was previously confirmed in the study on the case of chrysolite. The temperature of the TGDTA measurement could be raised up to 1000? C, and it became evident that in the cases of specimens where CaCl 2 was added, all the asbestos fibers had decomposed, but not in any other specimen. The crocidolite specimen became rounded in shape when it was heated up to 1000? C, and it looked as if it was densified due to burning. CaCO 3 and CaCl 2 were added to this burned crocidolite, and decomposition of the material after burning was examined. In a DTA thermogram, an endothermic peak was recognized, which corresponds to the formation of a melt of CaCO 3 -CaO-CaCl 2 as summarized in the previous report. Thus it is experimentally verified that burned crocidolite decomposes at high temperatures.

Thermal decomposition of different types of asbestos

“…3. In the region 3,000-4,000 cm 3,681-3,686 cm -1 can be assigned to the surface Mg-OH stretch vibration, whereas the second band can be linked to the inner Mg-OH stretch vibration [38]. This confirms the assignment of the OH doublet to the external and internal Mg-OH groups in chrysotile asbestos [33].…”

“…11). It may be caused by the loss of chemical bonded water [37] or in accordance with Fujishige et al [38] by partially melted fibers. The second way was confirmed by TG analysis (Fig.…”

“…[31]. According to Fujishige et al [38] weight loss of crocidolite was not observed above *700°C. However, on DTA curve, the authors observed strong endothermic peak (T max * 930°C) without weight change.…”

“…The main mineral compound which was formed from crocidolite after thermal treatment (isothermal firing) may be acmite } follows a very similar pattern to previously described asbestos, but requiers higher temperature. The final products of amosite decomposition above 900°C (at isothermal soaking) are a spinel, hematite, magnetite, and cristobalite [31,38]. The thermal analysis of tremolite mainly shows an endothermic peak at *950°C due to the dehydroxylation reaction [6].…”

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

“…Recent papers revealed that the addition of calcium salts was effective to decrease the decomposition temperatures of asbestos [17,18]. At low temperatures, the calcium salts gave a melt which acted as a flux.…”