Recycling of Potential Hazardous Stone Wool into a Non-Hazardous New Stone Wool

Mineral wool products are man-made vitreous fibres (MMVFs), such as glass wool and stone wool, mainly used for thermal and acoustic insulation. Demolition of buildings generates mineral wool (MW) waste. With regard to the intended recycling of materials, the European Union's circular economy package currently foresees a landfill ban for certain waste streams by 2030. As a result, Austria will have a landfill ban for MMVFs from 2027. This paper presents an investigated route for the recycling of MW waste into new mineral wool (wool2wool). The recycling route aims to conserve valuable and limited landfill volume and enables the reduction of primary resource consumption and CO2 emissions. The investigation was based on pH-dependent leaching tests of the fibres according to ÖNORM EN 14429 and hydrogeochemical modelling using LeachXS/Orchestra to identify the solubility-controlling mechanisms. The next step was a thermochemical treatment using correction materials to adjust the chemical composition, followed by rapid cooling through a spinning process. Another focus was on the theoretical determination of the dynamic viscosity to ensure suitable flow behaviour during fibre production. The chemical composition of the mineral wool produced was analysed, and it was shown that the target formulation could not be achieved for all elements within the permitted variation. The variations were due to the dissolution of the kiln lining, which had a more significant influence on the experiment than expected. Overall, the recycling pathway showed a high potential for CO2 savings, resource savings and other environmental benefits by recycling waste that is currently landfilled.