| Title | CarbFix: CO2 Sequestration in Basaltic Rock, Hellisheidi SW-Iceland |
|---|---|
| Authors | Helgi A. Alfredsson, Eric H. Oelkers and Sigurdur R. Gislason |
| Year | 2012 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | CO2 sequestration, mineral carbonation, basalt, geochemical modeling |
| Abstract | A number of recent studies have advocated the injection of CO2 into basaltic rocks to promote mineral carbonation due to their abundance in divalent metal cations and their high reactivity. This study assesses this possibility through a set of reactive path modeling calculations. Two gas mixtures were considered 1) pure CO2 and 2) a 75%-24.2%-0.8% mixture of CO2-H2S-H2. It is assumed that these gases are dissolved into a representative basaltic groundwater prior to their injection into the subsurface. The injected water is assumed to have a temperature of ~25 °C and is equilibrated with ~25 bar pressure of the CO2 gas, and ~14 bar pressure of the CO2-H2S-H2 mixture. The injected fluid will have a total CO2 concentration of ~0.8 and a pH of 3.7 for the pure CO2 gas and total CO2 concentration of ~0.42 and a pH of 4.0 for the gas mixture. Model calculations reacted these fluids with basaltic glass, the most abundant constituents of many basalts. Reaction path modelling shows that 1-2 moles of basaltic glass are needed to lower the CO2 concentration of each liter down to natural pre-injection concentrations, but less than 1 mole is needed for the H2S rich fluid. Major carbonates formed were Ca-Mg-Fe-carbonate and dolomite at pH below 5, whereas ankerite and calcite formed later at higher pH. Associated minerals at lower pH were chalcedony, kaolinite and iron hydroxide, followed by smectite and zeolites at higher pH. Modelling result suggest that the first sulfur bearing phase to precipitate is elemental sulfur, followed by greigite and mackinowite upon further basaltic glass dissolution. |