Treatment of airborne asbestos and asbestos-like microfiber particles using atmospheric microwave air plasma

Our plain-English summary of Treatment of airborne asbestos and asbestos-like microfiber particles using atmospheric microwave air plasma, by A. Averroes, H. Sekiguchi, K. Sakamoto (Journal of Hazardous Materials, 2011).

The study

• Authors: A. Averroes, H. Sekiguchi, K. Sakamoto
• Journal: Journal of Hazardous Materials
• Published: 2011;195:405-13
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Atmospheric microwave air plasma was used to treat asbestos-like microfiber particles that had two types of ceramic fiber and one type of stainless fiber. The treated particles were characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The experiment results showed that one type of ceramic fiber (Alumina:Silica=1:1) and the stainless fiber were spheroidized, but the other type of ceramic fiber (Alumina:Silica=7:3) was not. The conversion of the fibers was investigated by calculating the equivalent diameter, the aspect ratio, and the fiber content ratio. The fiber content ratio in various conditions showed values near zero. The relationship between the normalized fiber vanishing rate and the energy needed to melt the particles completely per unit surface area of projected particles, which is defined as η, was examined and seen to indicate that the normalized fiber vanishing rate decreased rapidly with the increase in η. Finally, some preliminary experiments for pure asbestos were conducted, and the analysis via XRD and phase-contrast microscopy (PCM) showed the availability of the plasma treatment.

Copyright © 2011 Elsevier B.V. All rights reserved.

In plain English

This was a laboratory engineering study in Japan. It tested whether hot air plasma made with 1 kW of microwave power could change airborne fibers so they were no longer fiber-shaped. The authors first treated three asbestos-like test fibers: two ceramic fibers (IBI wool and Fibermax) and a stainless steel fiber (SMF300UE). Under the electron microscope, many treated particles became spheres, except for Fibermax. At lower particle feed and swirl air flow rates, the share of fiber-shaped material in IBI wool and the stainless fiber fell to almost zero. For Fibermax it fell only to about 0.7 or 0.5, depending on conditions. The authors then ran preliminary tests on pure chrysotile, amosite and crocidolite. After treatment, the X-ray signals of chrysotile mostly disappeared. Those of amosite and crocidolite remained, though reduced, and some fibers were still seen in both. A second light-microscope method did not detect asbestos after treatment. The authors concluded that the method suited pure chrysotile but needed improvement for amosite and crocidolite. They noted that clumping of the asbestos fibers disturbed steady feeding.

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 engineering experiment: fiber particles were treated with atmospheric microwave air plasma, followed by preliminary tests on pure asbestos
• Who was studied: Materials, not people. These were three asbestos-like microfiber materials: IBI wool and Fibermax (ceramic fibers) and SMF300UE (stainless fiber). The study also used three pure asbestos samples (chrysotile, amosite, crocidolite) from the Japan Association for Working Environment Measurement. The work was done at the Tokyo Institute of Technology, Japan. For each sample, 100 to 200 particles were imaged by SEM.
• Exposure: The fibers were treated with atmospheric microwave air plasma (2.45 GHz, 1000 W input power). The particle feed rate and the swirl air flow rate (about 8 to 14 L/min) were varied. The fibers tested were the three microfibers and pure chrysotile, amosite and crocidolite.
• Main results:
  • Electron microscopy showed many spherical particles after the microfibers were treated, except for Fibermax.
  • X-ray diffraction showed no phase change for IBI wool and Fibermax, but did show a phase change for the stainless fiber.
  • The fiber content ratio of IBI wool and SMF300UE fell to almost zero at a lower particle feed rate and a lower swirl air flow rate.
  • The fiber content ratio of Fibermax fell only to about 0.7 when the particle feed rate was varied, and to 0.5 at the lowest swirl air flow rate.
  • For the microfibers, the normalized fiber vanishing rate went down as the energy needed per unit surface area to melt the particles went up.
  • In the pure asbestos after treatment, electron microscopy still showed some fibers in amosite and crocidolite but not in chrysotile.
  • By X-ray diffraction, the chrysotile peaks mostly disappeared after treatment and new forsterite and enstatite peaks appeared. The amosite and crocidolite peaks remained but decreased.
  • In the treated pure asbestos, asbestos was detected by X-ray diffraction but not by phase-contrast microscopy (dispersion staining).
  • The normalized fiber vanishing rate for the pure asbestos was small.
• The authors' conclusion: The authors concluded that the method was suited to pure chrysotile and needs improvement, especially for pure amosite and pure crocidolite. They suggested it has potential for treating airborne asbestos in exhaust gas from asbestos disposal stations.
• Limitations the authors state:
  • A high standard deviation made the trends in particle size weak and hard to interpret.
  • The predicted relationship between energy and fiber vanishing rate still needs to be checked with a numerical model.
  • The pure asbestos particles stuck together in bunches. This disturbed steady feeding and may explain the needle-shaped particles left in amosite and crocidolite.
  • The pure asbestos results did not reach full fiber removal. The authors attributed this to bunching that increased the fiber diameter.

Topics

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Aspect Ratio (Length-to-diameter ratio).

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