The thermal transformation of man made vitreous fibers (MMVF) and safe recycling as secondary raw materials (SRM)

This work describes the high temperature reaction sequence of commercial Man Made Vitreous Fibers(MMVF) Cerafiber, Superwool, Rock wool and Glass wool which may be used as substitute for asbestosin some industrial applications. Knowledge of the reaction path and transformation sequence is veryimportant to assess whether carcinogenic crystalline phases are formed during devitrification, whichmay occur when used as insulators. In addition, knowledge about the nature of the phases formed at hightemperature is mandatory to assess if thermally transformed MMVF can be safely recycled as secondaryraw material (SRM). In this scenario, this study provides useful information for the optimization of theindustrial annealing process aimed to attain a safe, recyclable product.The results of this work show that one of the high-temperature products of Cerafiber and Superwoolis cristobalite which is classified as a carcinogenic. It was possible to define the temperature interval atwhich Cerafiber and Superwool fibers can be safely used as thermal insulators (e.g. insulators in tunneland/or roller kilns, etc.). As cristobalite is formed in both synthetic fiber products at temperatures higherthan 1200 ◦C, their use should be limited to devices operating at lower temperatures.Rock and Glass wool melt upon thermal treatment. As far as the industrial process of inertization isconcerned, a maximum firing temperature of 1100 and 600 ◦C is required to melt Rock wool and Glasswool, respectively, with the high-temperature products that can be safely recycled as SRM. Recycling ofthese products in stoneware tile mixtures were subsequently attempted. The addition of 1–2 wt.% of themelts of Rock and Glasswool gave promising results in terms of viscous sintering reactions and resistanceto staining with the only weak characteristic being the color properties of the fired bodies which tend toworsen.