13C partition during bacterial ureolysis and formation of CaCO3: a tool to study CO2 sequestration?

Category Environmetal Geology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Millo, Christian; Dupraz, Sebastien; Ader, Magali; Menez, Benedicte
Holding Date 28 September 2008

It is well established that bacterial hydrolysis of urea can induce precipitation of considerable amounts of calcium carbonate. Formation of CaCO3 results from the progressive increase in both concentration of dissolved inorganic carbon (DIC) and pH during bacterial ureolysis. Theoretically, this chemical process could be used as a novel strategy for the sequestration of CO2: due to rising pH, CO2 is expected to diffuse into the precipitation medium, forming HCO3- that is then fixed as solid CaCO3. To verify this theoretical perspective, we investigated the 13C partition between urea, DIC, CaCO3 and CO2 during hydrolysis of urea induced by Bacillus pasteurii in artificial groundwater. We used urea with a δ13C value of -49 per mil. To detect a possible atmospheric CO2 sequestration, we analyzed DIC and CaCO3 formed during total ureolysis in capped and uncapped vials, respectively. The δ13C values of DIC formed in capped vials lie close to -42 per mil, whereas those of CaCO3 span between -57 and -55 per mil. The δ13C values of DIC formed in uncapped vials vary between -28 and -9 per mil, whereas those of CaCO3 range between -57 and -53 per mil. On the whole, DIC and CaCO3 formed in uncapped vials are 13C-enriched with respect to those formed in capped vials. Such a 13C-enrichment would point to sequestration of atmospheric CO2 (the typical δ13C value of which is -7.8 per mil) in both DIC and CaCO3. However, the mass balance of carbon suggests that this 13C-enrichment is rather due to degassing of isotopically light CO2 from the sample solutions. These results show that 13C tracing is a promising tool to investigate the potential use of microbiological processes for geological sequestration of CO2.