Crystal chemistry of the high temperature product of transformation of cement-asbestos

Our plain-English summary of Crystal chemistry of the high temperature product of transformation of cement-asbestos, by A. Viani, A.F. Gualtieri, S. Pollastri, et al (Journal of Hazardous Materials, 2013).

The study

• Authors: A. Viani, A.F. Gualtieri, S. Pollastri, C. Rinaudo, A. Croce, G. Urso
• Journal: Journal of Hazardous Materials
• Published: 2013;248-249:69-80
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In this work, the high-temperature inertization product of a representative batch of samples of cement-asbestos (CA) from different localities in Italy have been characterized with a multidisciplinary approach. All the raw CA samples were heated at 1200°C for 15 min. After firing, they underwent a series of solid state reactions leading to global structural changes of the matrix. Effects of annealing time and temperature on the crystallization kinetics were thoroughly investigated. Both factors acted in favour of equilibrium. Three classes of CA were identified with the aid of phase diagrams and of specific plots relating chemical and mineralogical parameters. This result was considered of importance in view of the potential use of transformed cement-asbestos as a secondary raw material. In principle, the content of CA packages removed from the environment and their corresponding heat-treated products can be classified simply using XRF. This method allows for the selection of appropriate fractions in function of the most suitable recycling solution adopted. Samples belonging to the class called larnite-rich, turned out to be of great interest as possible candidate for substituting a fraction of cement in many building materials and innovative green cement productions.

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In plain English

This laboratory study examined what cement-asbestos becomes after high-temperature treatment intended to transform its asbestos. The authors collected 27 cement-asbestos samples from sealed packages removed from 27 locations in Italy. Of these, 23 came from corrugated slates and the rest from water tanks, pipes and partition boards. All samples were heated at 1200°C for 15 minutes. Selected samples were also heated at 1200°C for 30 minutes and at 1250°C for 15 minutes. In selected samples examined after heating, infrared spectra no longer showed the characteristic bands of asbestos minerals. Micro-Raman spectra of transformed fibres showed none of the typical bands of chrysotile and crocidolite. The heated products fell into three classes, distinguished by their chemical and mineralogical compositions and named larnite-rich, bredigite–merwinite-rich and akermanite-rich. The authors concluded that, once calibrated for the heating cycle used, X-ray fluorescence analysis of only four chemical elements allows the material to be classified correctly. They also considered the larnite-rich class a viable substitute for a fraction of cement in building materials. They noted that their mean values lack rigorous statistical value.

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 mineralogical characterization of cement-asbestos samples before and after heat treatment (XRF, X-ray powder diffraction, SEM/EDS, FTIR, micro-Raman)
• Who was studied: 27 cement-asbestos (CA) samples from sealed packages removed from 27 different locations in Italy; 23 from corrugated slates, the others from water tanks, pipes and partition boards
• Exposure: Heat treatment of cement-asbestos at 1200 °C for 15 min (all samples); selected samples also at 1200 °C for 30 min and at 1250 °C for 15 min. The article states that magnesium in the starting material is hosted by chrysotile.
• Main results:
  • In selected samples examined by FTIR, heating at 1200 °C, even for short times, was sufficient to complete the asbestos transformation; the characteristic absorption bands of asbestos minerals disappeared (the authors present this as confirming earlier results)
  • Micro-Raman spectra of transformed asbestos fibres showed none of the typical bands of chrysotile and crocidolite; bands of calcium–magnesium silicates were detected instead
  • Three classes of heated product were identified. The first, larnite-rich, had larnite usually above 55 wt% with little or no akermanite and bredigite. The second, bredigite–merwinite-rich, had larnite and bredigite each between 15 and 30 wt%, akermanite of 20 to 30 wt%, and the highest merwinite contents. The third, akermanite-rich, had larnite below 20 wt% and C/S below 1 (samples 10, 12, 16, 22, 24).
  • In larnite-rich samples, larnite abundance was more than three times higher than in bredigite- and merwinite-rich samples
  • Mean CaO/SiO2 (C/S) ratio after 1200 °C for 15 min, with standard deviations: akermanite-rich 0.85 (0.12), bredigite-rich 1.14 (0.10), belite (larnite)-rich 1.54 (0.11), all samples 1.23 (0.30)
  • Samples heated at 1200 °C for 15 min showed a threshold for lime formation at a C/S ratio of about 1.43
  • Both longer time and higher temperature moved the products toward equilibrium; treatment at 1250 °C appeared more effective than 30 min at 1200 °C, and the three classes could still be distinguished
  • The authors report that preliminary tests showed up to 30 wt% of the larnite-rich material could be used in larnite–sulphoaluminate–brownmillerite (LSB) cement production
• The authors' conclusion: The authors concluded that, once a calibration curve for the thermal treatment has been established, XRF analysis of only four chemical elements, on raw or transformed material, allows correct classification. They also concluded that the larnite-rich class could substitute for a fraction of cement in many building materials.
• Limitations the authors state:
  • The mean values for the classes cannot be considered to have rigorous statistical value
  • Standard deviations of the overall means are very high and may be biased by the limited number of observations
  • For the 1250 °C treatment, the limited number of data prevented rigorous consideration of point dispersion
  • The phase diagram used considers only three oxides, so the roles of aluminium, iron and sulphur are neglected
  • The laboratory furnace had no control of gas concentrations

Topics

Medical terms in this study, explained in our Lexicon: Multidisciplinary Team.

Related studies

• In vitro biodurability of the product of thermal transformation of cement-asbestos — A.F. Gualtieri, A. Viani, et al. (2012)
• Recycling the product of thermal transformation of cement-asbestos for the preparation of calcium sulfoaluminate clinker — A. Viani, A.F. Gualtieri (2013)
• Recycling of the product of thermal inertization of cement-asbestos for various industrial applications — A.F. Gualtieri, C. Giacobbe, et al. (2011)
• The transformation sequence of cement-asbestos slates up to 1200 degrees C and safe recycling of the reaction product in stoneware tile mixtures — A.F. Gualtieri, C. Cavenati, et al. (2008)
• Thermochemical destruction of asbestos-containing roofing slate and the feasibility of using recycled waste sulfuric acid — S.N. Nam, S. Jeong, et al. (2014)
• Sustainable bio-hydrothermal sequencing treatment for asbestos-cement wastes — D. Spasiano, V. Luongo, et al. (2019)

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