간접 탄산화(indirect method) 및 양이온 공급원으로 사문암(serpentinite)을 이용하여 광물탄산화 연구를 수행하였다. 이산화탄소와 사문암 내 알칼리 토금속(칼슘과 마그네슘)의 탄산화 반응을 통해 고 순도의 탄산칼슘과 탄산마그네슘을 합성할 수 있었다. 마그네슘 추출을 위해 황산암모늄을 사용하였고 Mg 추출률 향상을 위해 황산암모늄 농도, 반응온도 및 사문암과 추출 용매의 비(고액비) 등 여러 반응 변수를 검토하였다. 본 연구로부터 2 M 황산암모늄을 사용하여 300℃ 반응온도에서 고액비(5 g/66 mL) 실험을 진행한 경우 약 80 wt% 이상의 Mg를 얻을 수 있었다. Mg 추출률은 추출 용매 농도 및 반 응온도와 비례하여 증가하였다. 사문암의 Mg 추출 과정에서 얻어진 암모니아(NH3)는 회수하여 탄산화 과정에서 필요한 pH 복원제(pH swing agent)로 활용하였다. 본 연구를 통해 약 1.78 M 암모니아를 회 수할 수 있었고 지구화학 모델링을 통해 사문암의 Mg 추출 과정의 핵심 단계를 해석하고자 하였다.

Carbon dioxide has steadily increased in atmosphere since the industrial revolution, and it is the main cause of the global warming. In this study, carbon dioxide is stored in the form of insoluble calcium carbonate through indirect carbonation using paper sludge ash (PSA) as a raw material and acids (acetic acid and hydrochloric acid) as solvents. Acid is very efficient to extract calcium from PSA, which is as high as 55%. However, since the pH of calcium extractant obtained using acid is as low as 6 and carbon dioxide is not present in the form of CO32- at the low pH, carbonation reaction does not occur to form calcium carbonate. Sodium hydroxide, therefore, is added into the calcium extractant to increase pH up to 13. The amount of sodium hydroxide is calculated based on the equivalent of calcium in the extractant. Then, carbon dioxide is injected into the calcium extractant for 30 minutes at a flow rate of 0.05 L/min. The calcium extractant is prepared in advance using 40 g of PSA and 1L of 0.7 M acid, and 35mL of 50% sodium hydroxide is added into the extractant to adjust pH. During carbonation, liquid samples are taken at designated intervals to measure pH and calcium concentration. After the carbonation is completed, white solids are collected to dry at 105℃ for 12 hours, which weigh 30.0 g and 33.1 g from the extractants using acetic acid and hydrochloric acid, respectively. The white solids are found to be highly pure calcite by XRD analysis. Based on the solid mass, the amounts of carbon dioxide sequestrated in PSA are calculated to be 330.4 kg CO2/ton PSA and 363.7 kg CO2/ton PSA using acetic acid and hydrochloric acid as solvents, respectively.