Thermochemical destruction of asbestos-containing roofing slate and the feasibility of using recycled waste sulfuric acid

Our plain-English summary of Thermochemical destruction of asbestos-containing roofing slate and the feasibility of using recycled waste sulfuric acid, by S.N. Nam, S. Jeong, H. Lim (Journal of Hazardous Materials, 2014).

The study

• Authors: S.N. Nam, S. Jeong, H. Lim
• Journal: Journal of Hazardous Materials
• Published: 2014;265:151-7
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In this study, we have investigated the feasibility of using a thermochemical technique on ∼17% chrysotile-containing roofing sheet or slate (ACS), in which 5N sulfuric acid-digestive destruction was incorporated with 10-24-h heating at 100°C. The X-ray diffraction (XRD) and the polarized light microscopy (PLM) results have clearly shown that raw chrysotile asbestos was converted to non-asbestiform material with no crystallinity by the low temperature thermochemical treatment. As an alternative to the use of pricey sulfuric acid, waste sulfuric acid discharged from a semiconductor manufacturing process was reused for the asbestos-fracturing purpose, and it was found that similar removals could be obtained under the same experimental conditions, promising the practical applicability of thermochemical treatment of ACWs. A thermodynamic understanding based on the extraction rates of magnesium and silica from a chrysotile structure has revealed that the destruction of chrysotile by acid-digestion is greatly influenced by the reaction temperatures, showing a 80.3-fold increase in the reaction rate by raising the temperature by 30-100°C. The overall destruction is dependent upon the breaking-up of the silicon-oxide layer - a rate-limiting step. This study is meaningful in showing that the low temperature thermochemical treatment is feasible as an ACW-treatment method.

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In plain English

This was a laboratory study from South Korea. It tested whether a combined acid-and-heat treatment could destroy chrysotile asbestos in waste roofing slate, which the article describes as a mixture of asbestos with cement containing about 17% chrysotile. The slate waste came from a government-registered hazardous waste treating company. Raw chrysotile from a mine in Jecheon city was also tested. Ground samples were placed in 5 N sulfuric acid and heated at 100°C for 10 and 24 hours. After treatment, X-ray diffraction of the raw chrysotile no longer showed its original crystal pattern. Under polarized light microscopy, fibrous chrysotile was not observed and the material had turned into a fine particulate form. In tests on raw chrysotile, the magnesium release rate, calculated from magnesium extracted in the first 10 minutes, was 80.3 times as high at 100°C as at 30°C. Waste sulfuric acid from an electronics company, diluted to 5 N, gave X-ray results very similar to commercial acid, with no chrysotile peak detected after 24 hours. The authors concluded the technique is viable but cautioned that high impurity levels in waste acids may affect treatment.

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 testing a chemical treatment (sulfuric acid digestion combined with heating) of asbestos-containing waste
• Who was studied: samples of asbestos-containing roofing slate waste obtained from a government-registered hazardous waste treating company in South Korea, plus raw chrysotile fiber from a mine in Jecheon city, South Korea; no people were studied
• Exposure: chrysotile asbestos (about 17% in the roofing slate) treated with 5 N sulfuric acid heated at 100°C for 10 and 24 hours. Commercial acid was compared with waste sulfuric acid from an electronics company, which was about 30 N before dilution to 5 N. Magnesium release from raw chrysotile was measured at 30, 50, 70 and 100°C.
• Main results:
  • For raw chrysotile after treatment, X-ray diffraction showed only a broad hump with no characteristic chrysotile diffraction angles, which the authors took to mean the product no longer had the original crystallinity
  • Under polarized light microscopy, fibrous chrysotile was not observed in treated raw chrysotile or treated slate; the material had changed to a fine particulate form
  • The temperature comparison of reaction rates was based on the amount of magnesium extracted from raw chrysotile in the first 10 minutes
  • For raw chrysotile, these 10-minute magnesium extraction rates at 50°C, 70°C and 100°C were 3.9-fold, 12.6-fold and 80.3-fold the rate at 30°C
  • At 100°C, approximately 75% of the magnesium in the 1 g raw chrysotile sample was released in 10 minutes
  • Based on activation energies, the authors calculated it was 1.77 times more difficult to break down the silicon-oxygen structure than the magnesium (brucite) layers, making silicon-oxide breakdown the rate-limiting step
  • After 24-hour treatment of the roofing slate, the chrysotile peak was not detected with either waste or commercial sulfuric acid, and the two X-ray patterns were very similar overall
• The authors' conclusion: The authors concluded that the low-temperature thermochemical treatment destroyed chrysotile in both pure form and mixed with cement. They considered it a viable technique for disposing of asbestos-containing wastes more sustainably, and found that the waste sulfuric acid could replace commercial acid without noticeable loss of removal efficiency.
• Limitations the authors state:
  • Treatment results may be affected by high amounts of impurities in waste acids
  • The amount of raw chrysotile available was limited, which constrained the reaction dosage in the temperature experiments

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, X-Ray Diffraction (XRD), Polarized Light Microscopy (PLM), Non-Asbestiform.

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• Change of carcinogenic chrysotile fibers in the asbestos cement (eternit) to harmless waste by artificial carbonatization: petrological and technological results — M. Radvanec, L. Tuček, et al. (2013)
• Crystal chemistry of the high temperature product of transformation of cement-asbestos — A. Viani, A.F. Gualtieri, et al. (2013)
• Microwave-assisted acid treatment for the mineral transformation of chrysotile as an alternative for asbestos waste management — S. Essih, L. Pardo, et al. (2024)
• Optimal management program for asbestos containing building materials to be available in the event of a disaster — Y.C. Kim, W.H. Hong (2017)

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