CO2 capture and zeolite synthesis via hydrothermal treatment of inertized rock wool

The management of rock wool waste poses a growing challenge, with global production exceeding 2.5 million tons annually. Thermal inertization converts this fibrous hazardous waste into safe glassy products; however, high-value applications of the inerted product remain limited. This study is a preliminary investigation into a sustainable valorization pathway for thermally inertized mineral wool, focusing on CO2 recovery during low-temperature (130 °C) alkaline hydrothermal synthesis. A comparative assessment was performed between synthesis in a CO2-enriched atmosphere and ambient air. Results revealed CO2 as a key parameter controlling crystallization pathways and zeolite yield, along with CO2 fixation through carbonation. Synthesis in air predominantly yielded 11-Å tobermorite and transient carbonates (vaterite), with limited zeolite (analcime) formation. Conversely, the CO2-enriched atmosphere suppressed tobermorite, favoring Na-P and phillipsite zeolites alongside stable calcite. The CO2-based process proved superior across all key metrics. Zeolitic yields were nearly fourfold higher, resulting in a cation exchange capacity of 40.7 ± 1.6 compared to 12.3 ± 0.9 cmol(+)/kg in air. Furthermore, CO2-synthesis demonstrated an 86% increase in carbon capture efficiency (4.49 wt% vs. 2.41 wt%), driven by stable mineral carbonation. Overall, the proposed hydrothermal pathway provides a promising laboratory-scale strategy for End-of-Waste upcycling while enabling CO2 sequestration, demonstrating that a CO2-rich environment enhances zeolite crystallization and increases CO2 retention.