(182c) A New Aqueous Mineral Carbonation Process Utilizing Bipolar Membrane Electrodialysis

A new aqueous mineral carbonation process which utilizes bipolar membrane electrodialysis was proposed. The proposed process consists of four unit operations, (a) acid leaching of alkaline metals (Ca²⁺ /Mg²⁺) from mineral compounds, (b) carbonate precipitation by addition of Na₂CO₃, (c) acid /alkaline regeneration from salt solution with bipolar membrane electrodialysis, and (d) Na₂CO₃ generation via absorption of CO₂ into NaOH. In the acid leaching step, alkaline metals are extracted from mineral compounds such as alkaline rocks, concrete waste, and steel making slag. In this operation, HNO₃ solution is adopted as a leaching solution. In the carbonation sedimentation step, by adding Na₂CO₃ solution into the leaching solution, sediment of carbonate such as CaCO₃ or MgCO₃ is obtained and NaNO₃ solution is remained. In the acid /alkaline regeneration step, HNO₃ solution and NaOH solution are regenerated from NaNO₃ solution via bipolar membrane electrodialysis treatment. Regenerated HNO₃ solution is then recycled to the acid leaching step. In the Na₂CO₃ generation step, regenerated NaOH solution is contacted with the gaseous CO₂ to form Na₂CO₃ solution. Exhaust gas from power plant can be directly used without compression. Experimental studies were conducted to confirm the technical feasibility of this process. Results demonstrate that the combination of acid leaching and carbonation sedimentation enhances the utilization of alkaline metals in mineral compounds. Also, HNO₃ and NaOH were successfully regenerated from NaNO₃ solution. This result suggests that acid and alkaline solution can be used cyclically in this process.