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 CaCO(3). 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 CaCO(3), which is three 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 parts per thousand and -27.5 parts per thousand for delta(13)C and -3.92 parts per thousand and -20.89 parts per thousand for delta(18)O, respectively (against V-PDB), which suggests that a combination of carbonate formation mechanisms are operating including the hydroxylation of gaseous CO(2) 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). (C) 2009 Elsevier Ltd. All rights reserved.