Dissolution Behaviors and Circular Economy Potential of Waste-to-Energy Fly Ash for Carbon Sequestration and Electrodeposited Zn Recovery

Abstract

While coal-fired power plants are being phased out, waste-to-energy (WTE) facilities remain important during the clean energy transition, providing both waste management and energy recovery. This study presents a mild, modular process that integrates zinc recovery with CO2 mineralization from WTE fly ash (FA). Feedstock characterization showed high Ca (25 wt·%) and Zn (1.2 wt·%) contents. A two-step leaching strategy, DI water washing followed by mild acid leaching (pH 3, HNO3), effectively partitioned Ca and Zn into distinct streams, increasing the Ca/Zn ratio from 20 in raw ash to 223.6 in the water-soluble fraction and 13.6 in the acid-soluble fraction. Electrochemical recovery from the acidic leachate achieved 99% Zn2+ removal under ambient conditions, yielding a cathodic deposit with an estimated Zn content of 58 wt·% that may serve as an intermediate feedstock for further refining. Subsequent carbonation of the Ca-rich stream yielded CaCO3 with 77 wt·% purity and 99.5% Ca removal efficiency. Integration of Zn recovery with CO2 mineralization enables simultaneous valorization of metals and carbonates within a single workflow, minimizing cross-contamination and maintaining compatibility with existing WTE plant infrastructure. The process operates without highly acidic leaching conditions, elevated temperatures, or complex chemical separation steps, supporting scalability to continuous-flow or staged reactor configurations. By coupling resource recovery with carbon sequestration, this approach offers a pathway toward net-negative emissions when paired with CO2 captured from WTE flue gas. The results highlight the potential for WTE FA valorization to contribute to circular-economy objectives and carbon reduction targets through the production of value-added products from an underutilized waste stream.