Coupling Mineralization and Product Characteristics of Steel Slag and Carbon Dioxide

Crude steel production in China exceeds 1 billion tons per year, and steel slag production accounts for 10%–15% of the crude steel mass. Although slag presents certain hydration activity, it is still difficult to be used as a building material because the particles contain a large amount of active calcium oxide and magnesium oxide, which are easy to hydrate and expand besides presenting low stability. The heap stock is increasing at a rate of 80 Mt/a because of the limitation of application scenarios. Moreover, every 1 ton of crude steel is associated with an emission of 1.8 tons of carbon dioxide (CO2), which becomes a greenhouse gas, because it cannot be reused at the moment. In this investigation, CO2 was used to cure steel slag particles, and the coupling mineralization reaction between them was used to convert active calcium oxide and magnesium oxide in steel slag into carbonate forms and, thus, allow the processing of steel slag particles into fine building aggregate. Two particle size ranges of 0.6–2.36 and 2.36–4.75 mm were selected as representative particle sizes. Mineralization was carried out under a temperature of 25 °C, relative humidity of 75%, a CO2 concentration of 20%, and a time of 24 h. The carbon fixation rate of steel slag was 9.68%. The quality of steel slag fine aggregate as a product met the GB/T 14684-2011 construction sand grade II standard. The application of this technology is expected to improve the stability of steel slag particles, the utilization rate as a building material, and the resource utilization level of CO2. It is expected to realize the full, high-value-added resource utilization of steel slag and CO2 absorption and solve the supply shortage problem of fine aggregate for construction in China, which has potential economic and environmental benefits.