Efficiency Enhancement by pH Swing in Indirect Carbonation using Paper Sludge Ash and Acid = Efficiency Enhancement by pH Swing in Indirect Carbonation using Paper Sludge Ash and Acid

다국어 초록 (Multilingual Abstract)

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 CO₃ ^2- 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.