Carbon Capture and Utilization By Three-Step Aqueous Phase Mineralization

The increase in greenhouse gasses concentration in the atmosphere has contributed to global warming in recent decades. Carbon sequestration is one of the solutions to control the CO₂ concentration in atmosphere.  A pH-swing mineral carbonation is the process of extracting magnesium or calcium from mineral rock, followed by precipitation of extracted minerals in separate reactors. The process was found to be feasible method for potential industrial application to reduce CO₂ emission by carbon sequestration. This study investigates production of value-added materials for a three-series mineralization reactor in aqueous phase. Magnesium, iron and small portions of some other minerals were extracted from magnesium silicate rock, were precipitated in two steps by increasing the pH from 0.5 up to 10. Product analysis showed that in each step, high purity stable solids such as silica, iron hydroxide II and III, hydrated magnesium carbonate were produced. The CO₂ source was Na₂CO₃ which was the product generated from the scrubbing reaction between a power plant's flue gas and NaOH to serve as a potential carbon capture method. Mass balance for the mineral sequestration process was investigated for future scale up. CO₂ uptake was determined by magnesium carbonate elemental analysis.  It was calculated that for each ton of sequestrated CO₂ approximately 3.22 ton of serpentine rock (mainly (Mg₃Si₂O₅(OH)₄) was required and also 25 m³ of 1M NaOH, 35 m³ of 1M Na₂CO₃ and 80 m³ of 1M HCl were utilized. The resultant value-added products from the process would be 3.1 ton of 99.74% pure nesquehonite (Mg₂CO₃∙3H₂O) and 0.82 ton of iron oxide and hydroxide with 90% purity. Crystalline structure, particle size distribution and morphology of hydrated magnesium carbonate produced, were strongly dependent on the last precipitation reactor conditions including temperature, feeding flow rate, mixing speed and base concentration. Additionally, different composition and crystalline structure of magnesium carbonate produced in the last precipitation step in different temperature ranging 0 to 60 ºC, shows that the process is capable of producing value-added products including nesquehonite, hydromagnesite and dypingite under a wide range of ambient temperature.  In future investigations, carbon footprint of the process chain will be studied.