Reactivity of Alkaline Lignite Fly Ashes Towards CO_2 in Water

摘要

The reaction kinetics between alkaline lignite fly ashes and CO_2 (pCO_2=0.01 -0.03 MPa) were studied in a laboratory CO_2 flow-through reactor at 25-75 ℃. The reaction is characterized by three phases that can be separated according to the predominating buffering systems and the rates of CO_2 uptake. Phase 1 (pH > 12, < 30 min) is characterized by the dissolution of lime, the onset of calcite precipitation and a maximum uptake, the rate of which seems to be limited by dissolution of CO_2. Phase II (pH < 10.5,10-60 min) is dominated by the carbonation reaction. CO_2 uptake in phase III (pH < 8.3) is controlled by the dissolution of periclase (MgO) leading to the formation of dissolved magnesium-bicarbonate. Phase I could be significantly extended by increasing the solid-liquid ratios and temperature, respectively. At 75 ℃ the rate of calcite precipitation was doubled leading to the neutralization of approximately 0.23 kg CO_2 per kg fly ash within 4.5 h, which corresponds to nearly 90% of the total acid neutralizing capacity.