Recycling of the product of thermal inertization of cement-asbestos for various industrial applications

Our plain-English summary of Recycling of the product of thermal inertization of cement-asbestos for various industrial applications, by A.F. Gualtieri, C. Giacobbe, L. Sardisco, et al (Waste Management, 2011).

The study

• Authors: A.F. Gualtieri, C. Giacobbe, L. Sardisco, M. Saraceno, M.L. Gualtieri, G. Lusvardi, C. Cavenati, I. Zanatto
• Journal: Waste Management
• Published: 2011;31(1):91-100
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Recycling of secondary raw materials is a priority of waste handling in the countries of the European community. A potentially important secondary raw material is the product of the thermal transformation of cement-asbestos, produced by prolonged annealing at 1200-1300 °C. The product is chemically comparable to a Mg-rich clinker. Previous work has assured the reliability of the transformation process. The current challenge is to find potential applications as secondary raw material. Recycling of thermally treated asbestos-containing material (named KRY·AS) in traditional ceramics has already been studied with successful results. The results presented here are the outcome of a long termed project started in 2005 and devoted to the recycling of this secondary raw materials in various industrial applications. KRY·AS can be added in medium-high percentages (10-40 wt%) to commercial mixtures for the production of clay bricks, rock-wool glasses for insulation as well as Ca-based frits and glass-ceramics for the production of ceramic tiles. The secondary raw material was also used for the synthesis of two ceramic pigments; a green uvarovite-based pigment [Ca(3)Cr(2)(SiO(4))(3)] and a pink malayaite-based pigment [Ca(Sn,Cr)SiO(5)]. The latter is especially interesting as a substitute for cadmium-based pigments. This work also shows that KRY·AS can replace standard fillers in polypropylene plastics without altering the properties of the final product. For each application, a description and relevant results are presented and discussed.

Copyright © 2010 Elsevier Ltd. All rights reserved.

In plain English

This laboratory study tested reusing KRY·AS, the material produced by heating cement-asbestos slates for a long time at high temperature, in industrial products. The material came from a sealed pack of 61 cement-asbestos slates removed from an industrial site and heated for 40 hours, including 21 hours at 1200 °C. This article did not itself test the material for asbestos fibers or toxicity. The authors relied on earlier work for its non-hazardous nature. Clay bricks made with 10 to 30 wt% KRY·AS had fired strength above the stated commercial minimum. However, bricks with more than 10 wt% failed efflorescence (surface salt) tests. Glasses for insulating wool made with 30 or 40 wt% KRY·AS had calculated melting temperatures of 1290 and 1240 °C, respectively. Green and pink ceramic pigments were also made. Polypropylene plastics with 20 or 40 wt% KRY·AS behaved much like those with a standard calcium carbonate filler, apart from higher shrinkage. Iron in the material colored several products. The authors concluded that the treated material can safely be recycled.

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 materials-testing study of recycling thermally treated cement-asbestos (KRY·AS) into bricks, insulating-wool glasses, frits and glass-ceramics, ceramic pigments, and plastic filler. The non-hazardous nature of the material was not tested in this article; the authors relied on earlier work for it.
• Who was studied: No people were studied. The test material came from one standard sealed pack of 61 cement-asbestos slates removed from an industrial site. The same powder batch was used for all applications.
• Exposure: Cement-asbestos slates heated in an industrial kiln for 40 hours, including 21 hours at 1200 °C. The asbestos fiber type in this pack is not stated in this article. The heated product was added to product mixtures at these levels: 10, 20 and 30 wt% (bricks), 30 and 40 wt% (wool glasses), 30 and 40 wt% (frits and glass-ceramics), 20 wt% (pink pigment) and 20 and 40 wt% (plastics).
• Main results:
  • Clay bricks: fired bricks containing KRY·AS had modulus of rupture values of 179, 178 and 188 kg/cm2 at 10, 20 and 30 wt%, compared with 159 kg/cm2 with none. All values were above 100 kg/cm2, which the article cites as the minimum for commercial products.
  • Clay bricks: bricks with more than 10 wt% KRY·AS failed efflorescence tests, so the authors advised that additions not exceed this percentage. Bricks with 20% and 30% tended to develop cracks.
  • Insulating-wool glasses: the glasses were prepared by melting at 1350 °C. The calculated melting temperature was 1290 °C for mixture 1 (30 wt% KRY·AS) and 1240 °C for mixture 2 (40 wt% KRY·AS). The authors stated these glasses could be used only for insulating wool in kilns operating up to 1200 °C.
  • Frits and glass-ceramics: technological properties such as thermal expansion were comparable to those of Ca-based frits, except for color. Both were light green because of iron in KRY·AS.
  • Pigments: a green uvarovite-based pigment was stable in standard stoneware tile mixtures fired at 1200 °C. A pink malayaite-based pigment was made from a batch containing 20 wt% KRY·AS; the fired product was 66.1 wt% malayaite.
  • Plastics: polypropylene with 20 or 40 wt% KRY·AS had properties similar to polypropylene with the same amounts of calcium carbonate filler. The only marked difference was higher linear shrinkage: 1.45% versus 1.37% at 20 wt%, and 1.25% versus 1.15% at 40 wt%. The product was brown.
• The authors' conclusion: The authors concluded that cement-asbestos thermally treated at 1200 to 1300 °C yields a product that can safely be recycled as a secondary raw material. They also stated that the process offers a conclusive solution to the asbestos problem. The safety claim rests on earlier work, not on tests reported in this article.
• Limitations the authors state:
  • The authors did not report all experimental details in the paper; they said these were available on request.
  • The high iron content of KRY·AS affects the color of the final products, which the authors said limits some uses.
  • The melting temperatures of the insulating-wool glasses limit their maximum operating temperature.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Containing Material (ACM).

Related studies

• 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)
• Recycling the product of thermal transformation of cement-asbestos for the preparation of calcium sulfoaluminate clinker — A. Viani, A.F. Gualtieri (2013)
• Treatment and recycling of asbestos-cement containing waste — F. Colangelo, R. Cioffi, et al. (2011)
• In vitro biodurability of the product of thermal transformation of cement-asbestos — A.F. Gualtieri, A. Viani, et al. (2012)
• Crystal chemistry of the high temperature product of transformation of cement-asbestos — A. Viani, A.F. Gualtieri, et al. (2013)
• Biological effects and comparative cytotoxicity of thermal transformed asbestos-containing materials in a human alveolar epithelial cell line — F. Giantomassi, A.F. Gualtieri, et al. (2010)

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