Carbon mineralization of steel and iron-making slag: Paving the way for a sustainable and carbon-neutral future

Carbon mineralization technology has emerged as a promising method for permanently sequestering CO₂ by transforming it into a thermodynamically stable solid carbonate material. Recently, alkaline industrial waste, particularly from steel and iron-making processes, has been identified as a proper feedstock due to its high potential for CO₂ storage and the ability to reduce landfill strain significantly. In this context, this review focuses on the possibilities and challenges associated with the carbon mineralization of steel and iron-making slag. Given that the composition and characteristics of feedstock play crucial roles in carbon mineralization, in-depth examinations of the generation of by-products and the corresponding physicochemical properties were conducted. In the context of the carbon mineralization process, our primary focus was on ex-situ carbon mineralization, which encompasses both direct and indirect carbonation routes, while elucidating the intricate mechanisms underlying both types of carbonation. Current challenges such as low leaching efficiency rates, slow kinetics, complex slag structures and silicate passivation phenomena are also addressed. For practical applications, it is essential to integrate valuable material production with the carbon mineralization process. Accordingly, various methods for producing precipitated calcium carbonates, construction materials with heavy-metal stabilization, valuable element recovery, and possible integration with hydrogen production processes, were introduced. Lastly, we provide an overview of the current state of the art of carbon mineralization technology and suggest future research directions.