A integrated route for CO₂ capture in the steel industry and its conversion into CaCO₃ using fundamentals of Solvay process

In this work we propose the transformation of CO₂ into calcium carbonate utilizing steel slag and the waste heat generated in the steel industry. The necessary chemicals, aqueous NH₄Cl and solid NaHCO₃, were obtained as products of a bench scale Solvay process. Our approach is divided into four steps: (i) CO₂ capture using ammoniated brine, (ii) Ca²⁺ lixiviation from steel slag, through the reaction with NH₄Cl_(aq), (iii) CaCO₃ precipitation by reacting the leachate with NaHCO₃, and (iv) NaCl and NH₃ reclamation. Steel slag is utilized as the source of calcium. A small amount of heat is required by the overall process, which could be also provided by waste heat from the steel industry. Laboratory scale experiments showed that nearly 95 wt% of NaCl and NH₃ necessary for the mineral carbonation can be regenerated, therefore minimizing costs. At the end of this process, 98 wt% pure CaCO₃ is obtained, and up to 94 wt% of the extracted Ca²⁺ was precipitated with no need for pH adjustments. Finally, we observed that, depending on the source of the steel slag, 86 kg of high purity CaCO₃ could be obtained from 38 kg of CO₂ and 1000 kg of steel slag.