The researchers from the University of Modena and Reggio Emilia in Italy have proposed a method to transform hazardous mineral wool waste – widely used for thermal and acoustic insulation in construction and industry – into usable materials. Over 2.5 million tons of this type of wool produced annually worldwide becomes a problematic waste at the end of its useful life as the fine glass fibers can be harmful to the respiratory tract. This material is usually melted down at high temperatures, turning it into safety glass. However, its life cycle typically ends here: the material ceases to be hazardous, but remains unclaimed and continues to accumulate but the Italian researchers have found a method to return the material to economic circulation.
The key to the solution is found in composition of the resulting glass containing high levels of silicon, aluminum, and calcium. It is from these elements that zeolites, porous materials used for water and gas purification can be produced. In this way, the waste effectively transforms into raw material for production of in-demand sorbents.
To test this idea, the scientists ground the material into powder, added an alkaline solution, and heated the resulting mixture to 130°C – relatively mild conditions that we can get, if necessary, using waste heat from the production process itself. The experiments were conducted in two configurations: in plain air and in an environment with elevated carbon dioxide levels. At various stages (24, 48, 72, and 96 hours), the samples were removed and the composition of the resulting substances analyzed.
The comparison revealed a significant difference. When processing took place in plain air, tobermorite was primarily formed from starting material, a mineral coating particles with thin, plate-like crystals. However, zeolites almost never formed – their share did not exceed 2.4% of the weight. Carbon dioxide from the air was incorporated into the process but formed unstable compounds breaking down over time, so the carbon in the material did not bind.
When CO₂ was added to the system, the process was different: tobermorite ceased to be the primary product, and zeolites (in particular, sodium-containing varieties and sodium phillipsite) actively formed in its place. Their share reached almost 10%, approximately a fourfold increase. Simultaneously, the properties of the material also improved, increasing its ability to capture ions, which is especially important for water purification and contaminant removal.
At the same time, the carbon dioxide capture effect also increased. In a CO₂ environment, it converted to stable calcite and retained within the structure of the material. Ultimately, the proportion of bound carbon dioxide reached approximately 4.5% by weight, about 86% higher than in air experiments. Some of the carbon was apparently also bound in amorphous material, further enhancing the overall effect.
Finally, it turned out that environment with elevated carbon dioxide levels also reduces environmental risks. In the samples obtained without adding CO₂, a relative accumulation of toxic elements such as cadmium and lead was observed. This did not occur in the system with carbon dioxide.
Thus, the researchers’ laboratory studies have demonstrated that in the that mineral wool waste can not only be rendered harmless, but also converted into a useful resource. Instead of accumulating after remelting, this material is able to serve as a raw material to produce sorbents and simultaneously participate in carbon dioxide capture, closing the cycle.
