Reactive Crystallization of Dolomite by CO₂ Microbubble Injection into Concentrated Brine

Abstract

In this study, utilizing the minute gas-liquid interfaces around CO₂ microbubbles as novel reaction fields where the crystal nucleation proceeds predominantly, a crystallization technique that enables the synthesis of dolomite（CaMg（CO₃）₂）fine particles with a Mg/Ca ratio of 1.0 was developed. In the regions around the gas-liquid interfaces of CO₂ microbubbles, the local increase in the concentrations of Ca^2＋, Mg^2＋, and CO₃^2－ because of the electric charge on microbubble surface and the acceleration of CO₂ mass transfer are caused by minimizing the bubble size. CO₂ microbubbles with an average bubble size of 40 μm were continuously supplied to the concentrated brine coming from salt manufacture discharge in Japan using a self-supporting bubble generator, and CaMg（CO₃）₂ was crystallized within a reaction time of 120 min. The CO₂ flow rate varied in the range between 1.49 and 23.8 mmol/（l･min）. For comparison, the reactive crystallization with the injection of CO₂ bubbles at d_bbl of 200, 300, 800 or 2000 μm was performed using a dispersing bubble generator. The results indicated that minimizing the bubble formation and increasing the CO₂ flow rate can achieve the high-yield crystallization of CaMg（CO₃）₂ fine particles with a higher Mg/Ca ratio.