Morphological changes during enhanced carbonation of asbestos containing material and its comparison to magnesium silicate minerals

Our plain-English summary of Morphological changes during enhanced carbonation of asbestos containing material and its comparison to magnesium silicate minerals, by G. Gadikota, C. Natali, C. Boschi, et al (Journal of Hazardous Materials, 2014).

The study

• Authors: G. Gadikota, C. Natali, C. Boschi, A.H. Park
• Journal: Journal of Hazardous Materials
• Published: 2014;264:42-52
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The disintegration of asbestos containing materials (ACM) over time can result in the mobilization of toxic chrysotile ((Mg, Fe)3Si2O5(OH)4)) fibers. Therefore, carbonation of these materials can be used to alter the fibrous morphology of asbestos and help mitigate anthropogenic CO2 emissions, depending on the amount of available alkaline metal in the materials. A series of high pressure carbonation experiments were performed in a batch reactor at PCO2 of 139atm using solvents containing different ligands (i.e., oxalate and acetate). The results of ACM carbonation were compared to those of magnesium silicate minerals which have been proposed to permanently store CO2 via mineral carbonation. The study revealed that oxalate even at a low concentration of 0.1M was effective in enhancing the extent of ACM carbonation and higher reaction temperatures also resulted in increased ACM carbonation. Formation of phases such as dolomite ((Ca, Mg)(CO3)2), whewellite (CaC2O4·H2O) and glushinskite (MgC2O4·2H2O) and a reduction in the chrysotile content was noted. Significant changes in the particle size and surface morphologies of ACM and magnesium silicate minerals toward non-fibrous structures were observed after their carbonation.

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In plain English

This was a laboratory experiment. The authors tested whether reacting asbestos-containing material (ACM) with carbon dioxide could change its fibrous structure. The material was a sample of corrugated cement–asbestos slate from Italy. Samples were reacted for 3 hours under carbon dioxide at 139 atm, at 90, 125 or 185 degrees Celsius, in deionized water or in sodium oxalate or sodium acetate solutions. Carbonation was highest with 0.1 M sodium oxalate (11.4%). The other results were 6.3% for 1.0 M sodium acetate, 4.7% for 0.1 M sodium acetate and 1.5% for deionized water. With oxalate, the mean particle diameter of the material fell about 20-fold. New minerals formed, including whewellite, glushinskite and dolomite. X-ray analysis showed weaker chrysotile signals, and the authors reported fewer fibers in the treated solids. Under the oxalate conditions, the ACM, serpentinite and chrysotile reached 10–11% carbonation and olivine 20%. The authors concluded that the structure of ACM particles can be altered to non-fibrous phases. They noted that small or poorly crystalline new phases were hard to detect.

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: high-pressure, high-temperature batch-reactor carbonation of asbestos-containing material, compared with magnesium silicate minerals
• Who was studied: No people were studied. The main material was a sample of corrugated cement–asbestos slate collected from Italy, which the authors inferred was about 10 years old and contained around 10% clino-chrysotile. For comparison, the authors used serpentinite (95% lizardite) and chrysotile from Montecastelli Pisano, Tuscany, Italy, and Twin Sisters olivine from Washington State, USA.
• Exposure: No human exposure was studied. The treatment was carbonation with carbon dioxide at 139 atm for 3 hours. Conditions tested were reaction temperatures of 90, 125 and 185 degrees Celsius, and solvents of deionized water, 0.1 M sodium oxalate, 0.1 M sodium acetate and 1.0 M sodium acetate.
• Main results:
  • In the temperature experiments (1.0 M sodium acetate), carbonation of ACM was highest at 185 degrees Celsius, at about 6%.
  • At 185 degrees Celsius, 0.1 M sodium oxalate gave the highest extent of ACM carbonation, 11.4%.
  • Extents of ACM carbonation were 6.3% in 1.0 M sodium acetate, 4.7% in 0.1 M sodium acetate and 1.5% in deionized water.
  • The mean particle diameter of ACM reacted in 0.1 M sodium oxalate decreased 20-fold, from 183.73 to 9.03 (unit symbol lost in the text; context indicates micrometres).
  • ACM reacted in 0.1 M sodium oxalate formed whewellite (calcium oxalate) and glushinskite (magnesium oxalate). With acetate, dolomite formed.
  • X-ray powder diffraction showed reduced chrysotile peak intensity in treated ACM compared with untreated ACM.
  • In all cases, fewer fibers were present in the carbonated solids.
  • Under the 0.1 M sodium oxalate conditions, ACM, serpentinite and chrysotile reached 10–11% carbonation, while olivine reached 20%.
  • For the chrysotile mineral sample, the mean particle diameter increased from 18.11 to 54.41 after carbonation. The authors attributed this to newly precipitated phases such as glushinskite.
• The authors' conclusion: The authors concluded that, at 90–185 degrees Celsius, the structure of ACM particles can be altered to non-fibrous phases. They also concluded that adding oxalate or acetate improved the treatment.
• Limitations the authors state:
  • Phases making up less than 4–5% of a sample were hard to detect by X-ray powder diffraction.
  • A broad hump in the X-ray patterns of reacted samples, covering the range of the carbonate peaks, prevented highly accurate identification of carbonate peaks.
  • Metastable carbonates without a characteristic crystal shape were hard to detect by electron microscopy.
  • Experiments ran for only 3 hours. The authors expected larger structural changes with longer reaction times.

Topics

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

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