Reactivity of alkaline lignite fly ashes towards CO2 in water.
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 degrees 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 degrees 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.
Back
Martin
M
Department of Hydrology, University of Bayreuth, BayCEER, D-95440 Bayreuth, Germany. martin.back@uni-bayreuth.de
Kuehn
Michael
M
Stanjek
Helge
H
Peiffer
Stefan
S
D000468:Alkalies / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D060729:Coal Ash; D052638:Particulate Matter / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D000468:Alkalies; D060729:Coal Ash; D052638:Particulate Matter; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon