Hydrothermal conversion of chrysotile asbestos using near supercritical conditions

Our plain-English summary of Hydrothermal conversion of chrysotile asbestos using near supercritical conditions, by K. Anastasiadou, D. Axiotis, E. Gidarakos (Journal of Hazardous Materials, 2010).

The study

• Authors: K. Anastasiadou, D. Axiotis, E. Gidarakos
• Journal: Journal of Hazardous Materials
• Published: 2010;179(1-3):926-32
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The present research investigates, develops and evaluates the transformation of chrysotile asbestos into a non-hazardous material, such as forsterite, using an economically viable and safe method. The aim of this study is to convert fibrous chrysotile asbestos into an anhydrous magnesium silicate with a non-hazardous lamellar morphology using supercritical steam. The treatment method is characterized as hydrothermal in a temperature and pressure range of 300-700 degrees C and 1.75-5.80 MPa, respectively. Small amounts of asbestos (2.5 g) were treated in each experiment. Deionised water was used as the treatment solution. The treatment duration varied from approximately 1-5 h. Additional experiments took place using solutions of distilled water and small amounts of acetic acid, with the aim of attaining optimal treatment conditions. Crystal phases of the samples were determined by X-ray diffraction (XRD). The main phases present in the treated samples were forsterite, enstatite, and chrysotile asbestos. Lizardite and periclase were also found. The morphology of the treated chrysotile asbestos fibers was identified by scanning electron microscope (SEM). The fibrous form of chrysotile asbestos was converted into non-fibrous form of forsterite. In fact, none of the fibrous-needle-like morphology, with length equal to or greater than 5 microm and diameter less than 3 microm, which was responsible for the toxicity of the original material, was visible in the solid phase. The dissolution of magnesium from chrysotile asbestos was measured using volumetric determination by titration with EDTA. Leaching of magnesium into the liquid phase was observed. Clearly, the highest concentrations of dissolved magnesium are observed after hydrothermal treatment of chrysotile asbestos using acetic acid 1% (8.4-14.6%). Lowest concentrations of dissolved magnesium are obtained after hydrothermal treatment of chrysotile asbestos without using additives. Observing the results of the hydrothermal treatment using additives, the mineralogical conversion does not depend on the presence of a small quantity of weak organic acid (<1%). The addition of acetic acid 1% during hydrothermal treatment did not involve changes in the conditions of the chrysotile asbestos' mineral conversion.

2010 Elsevier B.V. All rights reserved.

In plain English

This was a laboratory experiment by researchers in Crete, Greece. It tested whether chrysotile asbestos could be turned into a non-fibrous mineral called forsterite by heating it with water under pressure, near supercritical steam conditions. Chrysotile from the Asbestos Mines of Northern Greece was ground. Samples of 2.5 g were heated with deionised water in a sealed 70 ml reactor at 300 to 700 °C for about 1 to 5 hours, and some runs added 1% acetic acid. X-ray diffraction showed conversion to forsterite at 650 °C and no chrysotile after 3 hours at 690 °C. No chrysotile was detected after 1 hour at 700 °C, though the authors noted any remaining amount would be below the instrument's detection limit. Electron microscope images showed no needle-like fibres 5 micrometres or longer and under 3 micrometres wide. Acetic acid raised the share of magnesium dissolved (8.4% to 14.6%, against 1.6% or less with water alone) but did not change the conversion conditions. The authors concluded the chrysotile was completely converted into forsterite. They noted that their energy comparisons applied to laboratory scale, not industrial use.

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 treating chrysotile asbestos samples with hot pressurised water (hydrothermal treatment) in a high pressure reactor
• Who was studied: Ground chrysotile asbestos samples (2.5 g per experiment) supplied by the Asbestos Mines of Northern Greece. Before treatment the samples also contained small amounts of dolomite and calcium sulfate. Eighteen sets of operating conditions are listed in Table 1. No people or animals were studied.
• Exposure: Chrysotile asbestos treated with deionised water (20 to 25 mL) at 300 to 700 °C for 1 to 5 hours. Table 1 lists pressures from 1.75 to 7.40 MPa. Some runs (300 to 650 °C) added 1% acetic acid.
• Main results:
  • With water alone, conversion of chrysotile into forsterite was seen at 650 °C, and chrysotile was absent after 3 hours at 690 °C.
  • Total conversion of chrysotile into forsterite was reported at 700 °C in 1 hour.
  • For the 700 °C, 1 hour sample, chrysotile was not detected by X-ray diffraction. Any chrysotile present would be below the instrument's lowest detectable limit.
  • Scanning electron microscope images of the treated sample showed no fibrous, needle-like particles 5 micrometres or longer and less than 3 micrometres in diameter.
  • With 1% acetic acid, 8.4% to 14.6% of the magnesium dissolved into the liquid.
  • Without additives, dissolved magnesium was lowest: the text gives less than 1%, and Table 2 lists values from less than 1% up to 1.6% at 700 °C.
  • Adding 1% acetic acid did not change the conditions needed to convert the chrysotile.
  • At laboratory scale, a furnace for conventional thermal treatment at 1200 °C needs 1200 to 6000 W. The controller for the hydrothermal process needs 400 W.
• The authors' conclusion: The authors concluded that chrysotile asbestos was completely neutralized and converted into forsterite. They also concluded that low concentrations of acetic acid did not improve the conversion but did increase the magnesium released.
• Limitations the authors state:
  • The authors stated that their energy-use results apply to laboratory-scale treatment, not industrial application.
  • The authors noted that X-ray diffraction cannot rule out chrysotile below the instrument's detection limit.

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, Forsterite, Silicate, X-Ray Diffraction (XRD), Lizardite.

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