Impact of gypsum waste on MSW and WTE ash for material recovery and syngas enhancement

Waste-to-energy (WTE) ash, traditionally viewed as a disposal challenge with landfill costs of approximately $70 tonnes⁻¹, is emerging as a valuable feedstock for resource recovery. This study explores the potential of combining Municipal Solid Waste (MSW) ash with gypsum waste to enhance recovery of valuable elements from MSW ash, modifying the oxidation state of key elements through an appropriate thermal treatment. These objectives can be achieved by utilizing energy generated during thermal processing of MSW. The work focuses on the recovery of manganese (Mn), a representative critical element, but also aluminum (Al) and iron (Fe) are investigated. Adding gypsum waste increased Mn₃O₄ levels approximately by 50 %, facilitating easier recovery of Mn via acid extraction thus enhancing the efficiency of the process. Furthermore, the possibility of adding gypsum waste to the gasification of MSW was investigated in a lab-scale reactor showing a 36 % increase in carbon dioxide (CO₂) and 58 % in hydrogen (H₂) yields at 900 °C in the produced syngas, indicating improved hydrogen conversion and energy efficiency. Increase in temperature also improved the impact of gypsum with 900 °C, providing increased syngas improvements over 800 °C. Thus, this approach, combining gypsum waste with MSW and their thermal treatment, presents a promising avenue for enhancing the environmental sustainability of WTE systems.