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

Our plain-English summary of A novel decomposition technique of friable asbestos by CHClF2-decomposed acidic gas, by K. Yanagisawa, T. Kozawa, A. Onda, et al (Journal of Hazardous Materials, 2009).

The study

• Authors: K. Yanagisawa, T. Kozawa, A. Onda, M. Kanazawa, J. Shinohara, T. Takanami, M. Shiraishi
• Journal: Journal of Hazardous Materials
• Published: 2009;163(2-3):593-9
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

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 degrees C. Chrysotile-asbestos fibers were completely decomposed to sellaite and magnesium silicofluoride hexahydrate by the reaction with CHClF(2)-decomposed acidic gas at 150 degrees C for 30 min. At high temperatures beyond 400 degrees C, sellaite and hematite were detected in the decomposed product. In addition, crocidolite containing wastes and amosite containing wastes were decomposed at 500 degrees C and 600 degrees C for 30 min, respectively, by CHClF(2)-decomposed acidic gas. The observation of the reaction products by phase-contrast microscopy (PCM) and scanning electron microscopy (SEM) confirmed that the resulting products did not contain any asbestos.

In plain English

This laboratory study tested a way to break down friable asbestos. The method used acid gases (hydrogen fluoride and hydrogen chloride) made by decomposing CHClF2, a type of Freon, with superheated steam at 800 degrees C. It did not study people or health effects. Ten-gram samples of three materials were each treated for 30 minutes: purchased chrysotile fibers, crocidolite-containing waste from lagging, and amosite-containing waste from fireproofing. Chrysotile was completely decomposed at 150 degrees C, the lowest temperature the equipment could hold. Crocidolite needed 500 degrees C for complete decomposition. The amosite waste was almost decomposed at 600 degrees C. A tiny X-ray signal that may correspond to amosite remained, but no amosite fibers were seen by microscope, and under a Japanese standard method the authors concluded amosite was decomposed. The authors concluded the method works at much lower temperatures than melting treatment. In the chrysotile test, they estimated that only 6.29% of the decomposed gas was effectively used on the chrysotile. They also said the capacity of Japan's existing Freon plants would be very small compared with all friable asbestos waste.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment testing a chemical method for decomposing asbestos materials (not a study of people or health outcomes)
• Who was studied: Three asbestos samples treated as friable asbestos: chrysotile fibers purchased from Wako Pure Chemical Industries (containing brucite as an impurity); crocidolite-containing wastes collected from lagging materials (over 60 mass% crocidolite, with calcite and quartz); amosite-containing wastes collected from fireproofing materials (30 mass% amosite, 3 mass% chrysotile, with calcite and quartz). Each test used a 10 g sample.
• Exposure: Treatment of the asbestos samples with acidic gas (HF and HCl) produced by decomposing CHClF2 (Freon) with superheated steam at 800 degrees C. The asbestos reactor was held at temperatures from 150 to 800 degrees C, and gas was supplied for 30 minutes.
• Main results:
  • Chrysotile fibers were completely decomposed at 150 degrees C for 30 minutes, turning into magnesium silicofluoride hexahydrate and sellaite. 150 degrees C was the lowest controllable temperature of the reactor.
  • In the treated chrysotile product (150 degrees C), no chrysotile fibers were detected by phase-contrast microscopy; only fine particles were observed.
  • Complete decomposition of crocidolite in the crocidolite-containing waste required 500 degrees C. The product consisted of hematite, fluorite and quartz.
  • In the crocidolite waste treated at 500 degrees C, no blue-colored (crocidolite) fibers were detected by phase-contrast microscopy.
  • Amosite-containing waste was almost decomposed at 600 degrees C for 30 minutes. A tiny X-ray diffraction peak that may correspond to amosite was still detected in the treated product.
  • In the amosite waste treated at 600 degrees C, colored amosite fibers were not detected by phase-contrast microscopy. Based on Japanese Industrial Standard JIS A 1481: 2006, the authors concluded that amosite was decomposed. The chrysotile in this waste was already decomposed below 550 degrees C.
  • In the chrysotile experiment, about 6.29% of the decomposed gas was effectively used to decompose the chrysotile (90 litres of CHClF2 for 10 g of chrysotile). The article gives this figure only for chrysotile.
  • The authors calculated that Japan's 30 existing Freon plants could ideally decompose 549 tons of chrysotile a year. They compared this with 17,019 tons of friable asbestos sent to controlled landfill and 1,315 tons treated by melting in Japan in 2004.
• The authors' conclusion: The authors concluded that they had developed a new technique for decomposing friable asbestos using acidic gas from CHClF2 decomposition. In their account, chrysotile, crocidolite and amosite were decomposed at 150, 500 and 600 degrees C respectively for 30 minutes, much lower temperatures than the traditional melting method, and Freon and friable asbestos were decomposed at the same time.
• Limitations the authors state:
  • The efficiency of gas use in the chrysotile experiment was low, which the authors attributed to placing a very small chrysotile sample in a large reaction tube.
  • The capacity of this technique using existing Freon plants is very small compared with the total amount of friable asbestos waste.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Friable, Chrysotile, Hematite, Crocidolite, Amosite, Scanning Electron Microscopy (SEM).

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