(306f) Impact of Reactive Conditions on WTE Ash for Recovery of Critical Elements and Waste Management

In the United States, approximately 292.8 million tons of municipal solid waste (MSW) is generated annually, with nearly half ending up in landfills. A significant portion of this waste, about 9%, consists of valuable materials, including metals and critical elements. Driven by rapid economic growth and increasing demand in high-technology industries, the global need for metals particularly precious, critical, and rare earth elements (REEs) continues to rise. To address the challenges of high import costs, supply risks, and the depletion of natural resources, it is imperative to explore alternative sources of these elements. Waste-to-Energy (WTE) ash presents a promising opportunity in this context, as it contains many of these elements in concentrations comparable to those found in natural ores.

This study investigates the recovery of valuable elements from WTE ash through its thermal treatment with additives derived from other industrial waste streams. Specifically, gypsum waste from the construction and demolition sector and spent Fluidized Catalytic Cracking (FCC) catalyst from chemical industries. Thermal experiments were conducted at temperatures up to 1000 °C with 15, 30, and 50 wt.% of these additives under reactive conditions, aiming to understand their influence on the transformation of elemental compounds into more extractable forms.

Characterization techniques including X-ray diffraction (XRD), thermal analysis, and gas chromatography, along with thermodynamic simulations using HSC Chemistry software, were employed to examine the phase transformations, elemental compound formation, and gaseous products. Initial findings demonstrated that these additives significantly influenced the behavior of both common and critical elements, promoting the formation of oxides, sulfides, alumino-silicates and other compounds. These transformations were accompanied by changes in the oxidation states of the elements, making them more amenable to recovery via acid leaching.

To gain clearer insight into the interactions between additives and specific elemental species, a simplified model system was also developed using selected compounds representative of precious and REE elements. This approach enabled more precise understanding of the reaction mechanisms and interactions between the additives and the target elements under controlled conditions.

This presentation will provide comparative results across different experimental conditions, to elucidate the mechanisms driving elemental transformations and oxidation state changes and the recovery efficiency of these elements. These findings will contribute to broader efforts in enhancing resource recovery from WTE residues and integrating such processes into circular economy strategies.