Reactivity of Alkaline Lignite Fly Ashes Towards CO2 in Water

• Published in: Environmental science & technology Vol. 42; no. 12; pp. 4520 - 4526
• Main Authors: Back, Martin, Kuehn, Michael, Stanjek, Helge, Peiffer, Stefan
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.06.2008
• Subjects: Alkalies - chemistry; Applied sciences; Carbon - chemistry; Carbon Dioxide - chemistry; Coal Ash; Exact sciences and technology; Particulate Matter - chemistry; Pollution; Remediation and Control Technologies; Water - chemistry; Fly ash; Carbon dioxide; Carbonation; Acid neutralizing capacity; Kinetics; Reactor; Chemical reactivity; Dissolution; Neutralization
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es702760v

The reaction kinetics between alkaline lignite fly ashes and CO2 (pCO2 = 0.01−0.03 MPa) were studied in a laboratory CO2 flow-through reactor at 25−75 °C. The reaction is characterized by three phases that can be separated according to the predominating buffering systems and the rates of CO2 uptake. Phase I (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 CO2. Phase II (pH < 10.5, 10−60 min) is dominated by the carbonation reaction. CO2 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 °C the rate of calcite precipitation was doubled leading to the neutralization of approximately 0.23 kg CO2 per kg fly ash within 4.5 h, which corresponds to nearly 90% of the total acid neutralizing capacity.