Microwave-assisted acid treatment for the mineral transformation of chrysotile as an alternative for asbestos waste management

Our plain-English summary of Microwave-assisted acid treatment for the mineral transformation of chrysotile as an alternative for asbestos waste management, by S. Essih, L. Pardo, J.A. Cecilia, et al (Environmental Geochemistry and Health, 2024).

The study

• Authors: S. Essih, L. Pardo, J.A. Cecilia, L. Dos Santos-Gómez, R.M.P. Colodrero, M. Pozo, G. Calero, F. Franco
• Journal: Environmental Geochemistry and Health
• Published: 2024;46(9):332
• Read it: PubMed · Publisher · Free full text

Abstract

In this work, the effect of microwave-assisted acid treatments on the morphological and crystallochemical characteristics of chrysotile fibers is investigated. A low concentration of nitric acid (0.2 N) is used to remove Mg2+-species located in the octahedral sheet of its structure, thereby causing a crystallo-chemical change forming a skeleton of non-crystalline amorphous silica. This skeleton maintains an elongated morphology but characterized by rounded -not sharp-edges and porous surfaces whose physical resistance under stress is reduced when compared with the initial fibers of chrysotile, favoring a lower pathogenicity of the fibers. Thus, microwave-assisted acid treatment rise as a low-cost, fast and effective option in avoiding the dangerousness associated with asbestos waste management.

© 2024. The Author(s).

In plain English

This laboratory study tested whether a short microwave-heated acid treatment could alter chrysotile asbestos fibers, as an option for asbestos waste management. The authors placed 0.13 g of natural chrysotile from Quebec, Canada, in 50 mL of dilute (0.2 N) nitric acid and heated it in a microwave at 700 W for 8, 12, 16 or 20 minutes. X-ray analysis showed the crystal structure breaking down, with complete amorphization after 20 minutes. The ratio of magnesium plus aluminum to silicon fell from 1.46 in untreated chrysotile to 0.51 after 8 minutes and 0.12 after 20 minutes, leaving mostly silica. Surface area rose from 10.0 square meters per gram in untreated chrysotile to 248.5 after 20 minutes. Treated fibers had rough, porous surfaces and rounded edges. After 20 minutes of treatment and one minute of gentle grinding, no traces of fibrous shape remained. The article reports no tests on cells, animals or people. The authors concluded the material was easily breakable, suggesting the fibers' pathogenicity had been inactivated. They said a more in-depth study would be necessary.

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 on mineral fibers: microwave-assisted acid treatment of chrysotile, followed by X-ray diffraction, infrared spectroscopy, nitrogen adsorption surface-area measurement, and electron microscopy with chemical analysis. No biological or toxicity testing is reported.
• Who was studied: A natural chrysotile sample from Quebec, Canada, untreated and after microwave-assisted acid treatment for 8, 12, 16 and 20 minutes. No human or animal subjects.
• Exposure: Chrysotile fibers (0.13 g) immersed in 50 mL of 0.2 N nitric acid and microwave-irradiated at 700 W for 8, 12, 16 or 20 minutes. The article's comparison table gives the temperature as 100 ºC.
• Main results:
  • X-ray diffraction showed amorphization of the chrysotile structure that increased with treatment time and was complete after 20 minutes.
  • Specific surface area (BET) rose from 10.0 square meters per gram for untreated chrysotile to 248.5 square meters per gram for the 20-minute-treated sample. The value was 249.2 at 16 minutes.
  • The (Mg + Al)/Si ratio was 1.46 for natural chrysotile.
  • The (Mg + Al)/Si ratio decreased to 0.51 after 8 minutes of treatment.
  • The (Mg + Al)/Si ratio reached a minimum of 0.12 after 20 minutes. Silica content stayed constant.
  • After 12 minutes of treatment, fibers appeared dispersed, with lengths between 0.5 and 3 µm and thickness around 0.2 µm.
  • After 16 and 20 minutes of treatment, sample surfaces were very rough and porous, with very rounded edges.
  • After 20 minutes of treatment followed by 1 minute of gentle grinding in an agate mortar, no remnants of fibrous morphology were seen under the electron microscope.
• The authors' conclusion: The authors concluded that the treated amorphous silica skeletons did not retain the physical resistance of natural chrysotile and were easily breakable. They wrote that this suggests the fibers' pathogenicity has been inactivated, and that the treatment can be an economical, fast and effective alternative for managing asbestos waste.
• Limitations the authors state:
  • The authors stated that a more in-depth study would be necessary.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Crystalline.

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