Carbonate Precipitation in Artificial Soils as a Sink for Atmospheric Carbon Dioxide

Turnover of C in soils is the dominant flux in the global C cycle and is responsible for transporting 20 times the quantity of anthropogenic emissions each year. This paper investigates the potential for soils to be modified with Ca-rich materials (e.g. demolition waste or basic slag) to capture some of the transferred C as geologically stable CaCO3. To test this principal, artificial soil known to contain Ca-rich minerals (Ca silicates and portlandite) was analysed from two sites across NE England, UK. The results demonstrate an average C content of 30±15.3 Kg C m^-2 stored as CaCO3, which is 3 times the expected organic C content and that it has accumulated at a rate of 25 ± 12.8 t C ha^-1 a^-1 since 1996. Isotopic analysis of the carbonates gave values between -6.4 and -27.5‰ for δ13C and -3.92 and -20.89‰ for δ18O respectively (against V-PDB), which suggests that a combination of carbonate formation mechanisms are operating including the hydroxylation of gaseous CO2 in solution, and the sequestration of degraded organic C with minor remobilisation/precipitation of lithogenic carbonates. This study implies that construction/development sites may be designed with a C capture function to sequester atmospheric C into the soil matrix with a maximum global potential of 290 Mt C a^-1.