Development of a new pH-swing CO2 mineralization process with a recyclable reaction solution

A new CO₂ mineral sequestration process using the pH swing of a weak base–strong acid solution was proposed. In this process, an alkaline-earth metal was extracted selectively from silicate waste material, such as steelmaking slag or waste concrete, in an acidic condition using a weak base–strong acid solution. The reacted solution containing alkaline-earth metal ions and a weak-base, behaves as a CO₂ absorbent. The acidic extraction solution was regenerated from the basic absorbent solution by precipitating the alkaline-earth metal with CO₂ as the carbonate. The thermodynamic analysis of this process shows that a series of reactions proceeds spontaneously and the overall reaction is exothermic. The feasibility of the proposed process was confirmed using steelmaking slag as a silicate material and ammonium chloride solution as a weak base–strong acid solution. It was confirmed that this series of reaction proceeds successfully under mild conditions. Calcium ions were extracted selectively from steelmaking slag using an ammonium chloride solution, and the reacted solution absorbed CO₂ followed by the precipitation of CaCO₃ at 80 °C. On the basis of these experimental analyses, the energy consumption of the proposed process was roughly estimated as 300 kWh/ton-CO₂.