Calcium-based CO2 indirect mineralization of alkaline industrial solid wastes: State-of-the-art technologies

CO 2 indirect mineralization plays a vital role in the CO 2 sequestration step of carbon capture, utilization, and storage (CCUS) technology, while also serving as an effective pathway for valorizing alkaline industrial solid wastes. This review systematically summarizes the global research progress on calcium-based CO 2 indirect mineralization of alkaline industrial solid wastes, establishing a comprehensive framework covering solid waste characteristics, core mechanisms, typical technical routes, and key industrialization pathways. Firstly, the review takes steel slag (SS), carbide slag (CS), phosphogypsum (PG), coal fly ash (CFA), and municipal solid waste incineration fly ash (MSWI FA) as representative substrates. It systematically analyzes their key physicochemical characteristics, and all five types show good CO 2 sequestration potential due to high calcium content. Secondly, this review details the mechanisms and regulation for indirect mineralization's core steps: (1) Ammonium salts are promising for Ca 2+ leaching due to recyclability, though efficiency loss and ammonia escape remain to be solved; (2) Targeted high-purity, functionalized CaCO 3 can be directionally prepared via synergistic regulation of pH, temperature, and chemical additives. Additionally, the review integrates advanced technologies and development status of the five typical wastes. To address challenges of high energy consumption, cost, and environmental risks, it emphasizes life cycle assessment (LCA) for carbon footprint quantification and process economic optimization, identifying reagent recycling and high-value products as keys to industrialization. This review aims to provide a solid scientific foundation and important engineering insights for advancing calcium-based CO 2 indirect mineralization of alkaline industrial solid wastes.