Upgrading the glassy slag from waste disposal by thermal plasma treatment

Our plain-English summary of Upgrading the glassy slag from waste disposal by thermal plasma treatment, by M. Lázár, M. Hnatko, J. Sedláček, et al (Waste Management, 2018).

The study

• Authors: M. Lázár, M. Hnatko, J. Sedláček, M. Čarnogurská, T. Brestovič
• Journal: Waste Management
• Published: 2018;78:173-182
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The paper reports on the experimental results obtained from the production of glassy slag by the plasma smelting of a mixture of two different wastes. The combination of two wastes with different chemical compositions is a promising way to optimise the energy consumption in the disposal process. Asbestos-cement roof tiles (ACRTs) and fly ash from fluidised-bed boilers (with a weight ratio of 1:1) were used for the preparation of glassy (vitrified) slag. The thermal process facilitated a 14.4% reduction of the weight of the original mixture and a 72% volume reduction of the waste. The glassy slag is then adopted as a raw material in the production of porous materials intended for various architectural applications, thus eliminating the necessity for its further disposal. The formation of a porous glass-ceramic matrix, using the vitrified slag containing CaSO4 as the pore-forming agent, is described in detail. A glass-ceramic foam with 66% porosity is formed by the rapid heating of the mixture of glassy slag and a 1 wt% of CaSO4, consisting of crystallised calcium aluminosilicate (Ca2Al2SiO7, Ca0.88Al1.77Si2.23O8). The thermal conductivity of the prepared porous material, measured by a laser flash thermal analysis, is 0.22 W·m-1·K-1.

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In plain English

This was a laboratory engineering experiment, not a study of people or health. The authors crushed asbestos-cement roof tiles from the dismantled roof of a family house, in which chrysotile fibres were seen under an electron microscope. They mixed the tiles in equal weights with fly ash from fluidised-bed boilers and melted 5.7 kg of the mixture in a plasma reactor at 1420 to 1440 degrees Celsius for 28 minutes. The resulting glassy slag weighed 14.4% less and took up 72% less volume than the starting mixture. X-ray analysis found chrysotile in crystal form only in the material before melting, and the slag was non-crystalline (amorphous). In water leaching tests of the slag, most metals were below the limits for inert waste listed in the article's table (Slovak Decree 372/2015 Coll.). The authors then ground the slag, added 1% calcium sulphate and heated it quickly to make a foam. The foam had 66% porosity, against 77% for a commercial foam glass. Its thermal conductivity was 0.22 W/m·K, higher than the commercial product's 0.038. The authors concluded that the product could be considered for thermal insulation.

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 (plasma smelting of waste, then foaming of the resulting slag)
• Who was studied: No people were studied. Material: asbestos-cement roof tiles from the dismantled roof of a family house, mixed 1:1 by weight with fly ash from fluidised-bed boilers; 5.7 kg of the mixture was smelted (Slovakia)
• Exposure: Asbestos-cement roof tiles containing chrysotile fibres, crushed to less than 5 mm and melted with fly ash in a DC plasma reactor
• Main results:
  • Smelting reduced the weight of the original mixture by 14.4% and its volume by 72%
  • X-ray diffraction confirmed chrysotile in the crystal phase only in the input material before smelting; the glassy slag was amorphous
  • In water leaching tests of the glassy slag, most measured metals were below the limits for inert waste listed in the article's results table (Slovak Decree 372/2015 Coll.)
  • The glass-ceramic foam made from the slag plus 1 wt% calcium sulphate had 66% volumetric porosity (density 0.998 g per cubic cm)
  • A commercial foam glass (PERINSUL S) had 77% volumetric porosity
  • The prepared foam's thermal conductivity (0.22 W/m·K) was higher than that of the commercial foam glass (0.038 W/m·K)
• The authors' conclusion: The authors concluded that, given its thermal conductivity, the glass-ceramic product could be considered for use as a thermal insulation material
• Limitations the authors state:
  • The pore structure of the prepared foam was uneven compared with commercial foam glass
  • The increase in Al2O3 in the slag was likely due to contamination from the furnace wall
  • Smelting is costly because of the high melting temperatures

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement.

Related studies

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• The origin and future of oxidative stress pathology: From the recognition of carcinogenesis as an iron addiction with ferroptosis-resistance to non-thermal plasma therapy — S. Toyokuni (2016)
• Non-thermal plasma induces a stress response in mesothelioma cells resulting in increased endocytosis, lysosome biogenesis and autophagy — L. Shi, F. Ito, et al. (2017)
• Microwave thermal inertisation of asbestos containing waste and its recycling in traditional ceramics — C. Leonelli, P. Veronesi, et al. (2006)
• Non-combustible waste vitrification with plasma torch melter — J.K. Park, Y.P. Moon, et al. (2001)

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