A new approach to the decontamination of asbestos-polluted waters by treatment with oxalic acid under power ultrasound

Our plain-English summary of A new approach to the decontamination of asbestos-polluted waters by treatment with oxalic acid under power ultrasound, by F. Turci, M. Tomatis, S. Mantegna, et al (Ultrasonics Sonochemistry, 2008).

The study

• Authors: F. Turci, M. Tomatis, S. Mantegna, G. Cravotto, B. Fubini
• Journal: Ultrasonics Sonochemistry
• Published: 2008;15(4):420-427
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A suspension of chrysotile asbestos fibres in aqueous 0.5M oxalic acid was subjected to power ultrasound with the aim to disrupt and detoxify the mineral by the leaching action of oxalic acid on its structural cations acting simultaneously with a vigorous acoustic cavitation. Sonication was performed in a "cavitating tube", a vertical hollow vibrating cylinder made of titanium, operating at 19.2 kHz and 150 W. Treatment lasted from 2.5 to 21 h. Scanning electron microscopy (SEM) showed that the joint action of the chelating agent and ultrasound (though not of either when applied independently) mostly converted asbestos fibres into micrometric aggregates and nano-sized debris, whose morphology totally differed from asbestos fibres. When treated suspensions were filtered through CA membranes (pore size 0.20 microm), more than half of the asbestos went through the filter because it had either been brought in solution or dispersed in the form of extremely small particles. Most of the structural metal ions were brought into solution (ICP-AES). After the treatment the BET surface area of the recovered solid was tenfold greater than the original. The crystalline fraction of residual solids, though resembling the original sample in XRD, was shown by micro-Raman spectra to be made of antigorite, a polymorph form of serpentine. Furthermore, as the length of these antigorite fibrils lay outside the fibre range rated as a health hazard under worldwide regulations, our procedure can be employed for the decontamination of chrysotile-polluted waters and sediments.

In plain English

This was a laboratory experiment on a mineral sample, not a study of people. The authors suspended a commercial chrysotile asbestos sample from the San Vittore mine at Balangero, Italy, in 0.5 M oxalic acid and treated it with power ultrasound (19.2 kHz, about 150 W) for 2.5, 13 or 21 hours. For comparison, chrysotile was sonicated in pure water. Oxalic acid alone was not tested here; the authors cited their earlier work for that. Ultrasound alone shortened the fibres but partly preserved their fibrous structure. With oxalic acid plus ultrasound for 21 hours, the original fibre shape was completely destroyed and replaced by round particles of 20 to 200 micrometres. A few ultra-small chrysotile fibrils, under 1 micrometre long, were still seen. By 21 hours, over 60% of the starting weight passed through the filter, either dissolved or as extremely small particles, according to the authors. Raman spectra showed the crystalline residue was antigorite, a non-asbestos serpentine mineral, rather than chrysotile. The authors concluded that the method would be applicable to detoxify chrysotile dispersed in water, because the remaining fibrils fell outside the lengths classified as hazardous under safety regulations.

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 (chemical and ultrasound treatment of an asbestos mineral sample, with ultrasound-only comparison runs)
• Who was studied: A commercial chrysotile asbestos sample (classified 6D) from the San Vittore disused asbestos mine, Balangero, Italy; 500 mg per run
• Exposure: Chrysotile suspended in 0.5 M oxalic acid (or in pure water for comparison) and treated with ultrasound at 19.2 kHz, input power about 150 W, for 2.5, 13 or 21 hours; ultrasound-only runs lasted 2.5 and 13 hours
• Main results:
  • Ultrasound alone, without oxalic acid, greatly changed fibre length, but the fibrous structure was partially preserved.
  • After 21 hours of ultrasound with oxalic acid, the original chrysotile shape was completely destroyed, leaving round particles of 20 to 200 micrometres.
  • After the 21-hour treatment, a few ultra-small chrysotile fibrils (length under 1 micrometre, diameter under 100 nm) were still seen on top of these particles.
  • With ultrasound plus oxalic acid, the solid recovered on the filter after 21 hours had lost more than 60% of the starting weight. The Results section calls this material 'in the solution'.
  • The authors stated that the material passing the 0.20-micrometre filter had either been dissolved or dispersed as extremely small particles.
  • With ultrasound plus oxalic acid, about half of the weight loss (35%) occurred in the first 2 hours.
  • Magnesium released into the liquid with ultrasound plus oxalic acid was 77 micrograms after 2.5 hours, which the authors describe as about 40% of the magnesium.
  • Magnesium released into the liquid with ultrasound plus oxalic acid rose to 199 micrograms after 13 hours and 203 micrograms after 21 hours.
  • Sonication in pure water released little magnesium (less than 10 micrograms), even after 13 hours.
  • Specific surface area with ultrasound alone doubled after 13 hours (from 15 to 34 square metres per gram).
  • Specific surface area with ultrasound plus oxalic acid rose about tenfold in 2.5 hours (to 140 square metres per gram) and reached 160 square metres per gram after 21 hours.
  • X-ray diffraction showed that the crystal structure of the treated samples was still consistent with a serpentine mineral structure.
  • Micro-Raman spectra of the sample treated for 21 hours with ultrasound plus oxalic acid indicated that the crystalline residue was antigorite (a non-asbestos serpentine), not chrysotile.
• The authors' conclusion: The authors concluded that combined ultrasound and oxalic acid greatly changed chrysotile, which may lead to progressive detoxification. Because the few remaining fibrils fell outside the lengths classified as hazardous under WHO, EU and NIOSH rules, they concluded the method would be applicable as it stands to detoxify chrysotile dispersed in water.
• Limitations the authors state:
  • The authors observed a few minor changes in the X-ray diffraction patterns of treated chrysotile but did not study them, saying this was beyond the purpose of the work.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Balangero mine, Balangero, about 20 km north of Turin, Piedmont

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Ultrasound, Chrysotile, Cation, Cavitation, Scanning Electron Microscopy (SEM), Crystalline, Antigorite, Serpentine Group.

Related studies

• The combination of oxalic acid with power ultrasound fully degrades chrysotile asbestos fibres — F. Turci, M. Tomatis, et al. (2007)
• Chrysotile asbestos detoxification with a combined treatment of oxalic acid and silicates producing amorphous silica and biomaterial — A. Valouma, A. Verganelaki, et al. (2016)
• New detoxification processes for asbestos fibers in the environment — F. Turci, M. Colonna, et al. (2010)
• Growth of carbon structures on chrysotile surface for organic contaminants removal from wastewater — B.R.S. Lemos, É.A.R. Soares, et al. (2016)
• The effects of naturally occurring acids on the surface properties of chrysotile asbestos — E.P. Holmes, L.M. Lavkulich (2014)
• Chrysotile asbestos is progressively converted into a non-fibrous amorphous material by the chelating action of lichen metabolites — S.E. Favero-Longo, F. Turci, et al. (2005)

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