FIELD STUDY ON CO2 FIXATION BY SERPENTINITE ROCK-BED

摘要

The sequestration of atmospheric CO_2 could be an effective means of mitigating global warming. The groundwater and surface water associated with serpentinite shows alkaline conditions and is associated with natural carbonate minerals. A technology to sequester atmospheric CO_2 could be based on the reactions forming these carbonate minerals. Ca-carbonate and Mg-hydrocarbonate associated with the serpentinite in the Kamuikotan metamorphic belt, Hokkaido, northern Japan, precipitate around alkaline springs on landslide deposits, on the surface and in fractures in weathered serpentinite. The carbonates yield ~(14)C ages from 22,700 yBP to modern. These carbonates sometimes co-exist with serpentine mousse which is white to pale brown in color. The relationship between δ ~(18)O and δ D values of the serpentine is similar to that of deweylite, which is a serpentine formed at low temperature. The temperature of oxygen isotopic equilibrium between co-existing deweylite and water is approximately 16 ℃ corresponding to the annual average atmospheric temperature in Hokkaido. The relationships of δ ~(18)O among deweylite, water and carbonate suggest low-temperature formation of the carbonate. From these facts it is concluded that the alkaline water associated with serpentinite reacts with atmospheric CO_2 under surface conditions and has continued from at least 22,700 yBP to the present. In addition, the system of serpentinite and groundwater could continue to keep itself alkaline and carbonate stable safely for a long period.