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Geological Sequestration of CO2: Mechanisms and Kinetics of CO2 Reactions in Mafic and Ultramafic Rock Formations

Investigators:

Principal Investigator: Gordon E. Brown, Jr., Professor, Department of Geological & Environmental Sciences; Co-Investigators: Dennis K. Bird, Professor, Department of Geological & Environmental Sciences; Tom Kendelewicz, Senior Research Associate, Department of Geological & Environmental Sciences; Kate Maher, Assistant Professor, Department of Geological & Environmental Sciences; Wendy Mao, Assistant Professor, Department of Geological & Environmental Sciences; Natalie Johnson, Ph.D. Student, Department of Chemical Engineering; Robert J. Rosenbauer, Research Scientist, U.S. Geological Survey, Menlo Park, CA; Pablo García Del Real, M.S. Student, Department of Geological & Environmental Sciences, Stanford University. Abstract We investigated the interactions between CO2-rich fluids and Mg-silicate minerals using experiments to provide information on reaction rates and to identify potential catalysts for the reactions, and studies of natural analogues to assess the conditions that lead to massive carbonation of ultramafic rocks and thus the potential for field-scale implementation. Key findings from our exploratory work include the following: (1) Mineral transitions that occur during alteration of basalt and serpentinites are efficient and could result in complete removal of CO2 from circulating fluids under the correct conditions. However, these reactions also result in extremely high net volume changes and dramatic reductions in porosity and permeability that prevent the continual removal of CO2 unless the dissolution and precipitation reactions occurred in different zones and the precipitation reactions were accompanied by substantial hydrofracturing. This emplacement mechanism is consistent with our observations from Red Mountain, CA Magnesite District and the findings of Boschi et al. (2009); (2) The use of organic acids (e.g., salicylic acid) as activators caused the rate of olivine dissolution to increase by a factor of 3, while the rate of MgCO3 precipitation increased by an order of magnitude at the highest concentration of salicylic acid (1 g/L) and decreased by an order of magnitude (relative to pure water) at lower concentrations of salicylic acid (0.1 g/L). The presence of organic acids in natural systems is also indicated by the carbon isotopic composition of the magensite from Red Mountain. The negative carbon isotope signature (δ13C = -11.6 ± 2.4 ‰) of the magnesite (MgCO3) is consistent with CO2 derived from degradation of organic matter and/or decarboxylation reactions and thus indicates that organic acids were likely present during the conversion of Mg-silicates to magnesite. While the exact role of organic acids has not yet been precisely determined, the effects of aqueous organic ligands on the dissolution rate, solubility, and stability of Mg-silicates relative to carbonate minerals are likely to be of first-order importance in optimizing the industrial utility of geologic sequestration of CO2 in ultramafic and mafic rock formations. Our experimental work and characterization studies of natural analogues inspired us to expand our research using the techniques that we developed during our exploratory research to submit a full GCEP proposal focused on the reactivity of CO2 in both ultramafic/mafic rocks and in saline aquifers.

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Introduction Injection of CO2 into the subsurface has become an important strategy for both enhanced energy extraction and for the disposal of harmful waste products derived from energy generation (Orr, 2009). For enhanced oil and gas recovery (EOR) and enhanced geothermal systems (EGS), a waste stream of supercritical CO2 is circulated through a subsurface reservoir to displace oil and gas (Jessen et al., 2005), or as a working fluid for a geothermal power plant (Pruess, 2006). During the conversion of fossil fuels to energy, the resulting waste stream containing CO2 (and possibly SOx and NOx and an array of heavy metals and metalloids) would be injected into the subsurface as a means of reducing the emission of a harmful greenhouse gas, CO2, to the atmosphere (Benson and Cole, 2008). As a consequence of these strategies, anthropogenic waste streams will be introduced into a variety of natural systems that were nominally in a state of chemical equilibrium. As the CO2 and associated by-products interact with the subsurface minerals and dissolve into local fluids, the ensuing chemical reactions will transform the subsurface environment. To understand the nature of these transitions, for our GCEP exploratory research we have conducted several experimental and characterization studies, including (1) preliminary characterization of a natural analogue (Red Mountain, CA); (2) an experimental study of the conversion of Mg-rich olivine to Mg-carbonate in the presence of CO2-rich aqueous fluids, and (3) in situ ambient pressure photoelectron spectroscopy on the interaction of CO2 and water with MgO surfaces. In addition, we assembled a geochemical modeling framework that will be used to interpret and guide experimental results and in the analysis of field-scale natural analogue systems. Background Although sedimentary formations provide ample storage volume for CO2, any viable long-term sequestration scenario must optimize mineralogical trapping of CO2 in stable mineral phases (carbonates). Mineralogical sequestration involves the reaction of CO2 with silicates rich in Mg and/or Ca, which are abundant in mafic rocks (basalts) and ultramafic rocks (peridotites and their metamorphic equivalent serpentinites) and thermodynamically convenient for the formation of carbonate minerals (Lackner, 2002). Over the past several years papers have been published which discuss the advantages of CO2 injection into ultramafic rock formations, including deep-sea basalts (Goldberg et al., 2008; Oelkers et al., 2008) and peridotites (Kelemen & Matter, 2008; Andreani et al., 2009). Carbonation reactions are exothermic, and rates are favorable over experimental time scales. In addition, mafic and ultramafic rocks are abundant and widely distributed in the Earth’s crust (Matter and Kelemen, 2009). The potential advantages are (1) rapid conversion of CO2 to stable carbonate minerals thus reducing the risk of CO2 release, (2) potential blockage of upward CO2 migration due to impermeable (and previously undisturbed) sediment cover, (3) the possibility of CO2-hydrate accumulation when escaped CO2 contacts cool overlying formation water or seawater, and (4) development of substantial fracture networks due to the initial emplacement processes. Nature has performed relevant experiments—in-situ carbonation is particularly common in some mafic and most ultramafic rocks, which contain abundant metal cations

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(i.e. Ca, Mg, Fe) and have sufficient permeability and pore space to react with CO2-rich fluids (Oelkers et al., 2008), forming calcite, dolomite, magnesite, and/or siderite (Matter and Kelemen, 2009). In order to assess the feasibility of both ex situ and in situ mineral carbonation strategies, our research has focused on (1) experimentally determining the optimal (yet realistic) conditions for both the dissolution rate of olivine and precipitation rate of magnesite, and (2) analyzing a natural deposit where CO2-rich fluids have interacted with ultramafic rocks to form massive magnesite (MgCO3) deposits in order to determine the operative geochemical and mechanical processes that facilitated these massive carbonation events. Our investigation has found that organic acids play a key role in facilitating mineral carbonation. However, additional work is required to understand the nature of the interaction between the organic acids and Mg-silicates and Mg-carbonates, and the mechanical processes that fractured and breciated the ultramafic rocks to create the massive pure magnesite breccias we observe in the field system. These key areas will be our continued focus. Results Kinetics of Mg-silicate carbonation Although there have been a number of studies addressing the injection of CO2 into mafic and ultramafic rock formations and the resulting mineral fluid interactions (Wogelius & Walther, 1991; Giammar et al., 2005; Hansen et al., 2005; Bearat et al., 2006; Hanchen et al., 2006; Alexander et al., 2007; Goldberg et al., 2008; Hanchen et al., 2008; Kelemen & Matter, 2008; Oelkers et al., 2008; Andreani et al., 2009; Flaathen et al., 2009; Matter et al., 2009), none have employed an integrative approach that combines experimental studies of CO2 (+H2O) interaction with mineral surfaces, surface science characterization of reaction products and reaction intermediates, thermodynamic considerations and field studies of natural analogs of mineral carbonation reactions. Our experimental approach has yielded much needed information on surface chemical changes of Mg-containing minerals upon reaction with CO2 and water, including the important effect of surface passivation. Our recently initiated experimental studies of the interaction of CO2-rich fluids with olivine will yield baseline kinetic data on mineral carbonation that will be compared with planned studies of the effects of organic acids and natural enzymes on reaction kinetics.

Experiments involving the interactions between the common Mg-silicate mineral

olivine (Mg2SiO4) and CO2-rich fluids were conducted using rotating autoclaves at 60˚C and 100 bar of CO2 pressure. The unique apparatus contains a sampling valve connected to a flexible gold cell inside the autoclave, thus allowing for the removal of fluid samples throughout the duration of the experiment without taking the experiment down from reaction conditions. The resulting samples were analyzed using ICP-AES for elemental composition and a titration to determine the alkalinity, the data from which allow us to track the reaction progress. The batch-style reactions ensure that we are able to study the kinetics at both near and far from equilibrium conditions. We have performed a number of experiments at the conditions mentioned above, utilizing the rocking autoclaves, all with a powdered olivine sample from a mine in Twin Sisters, Washington that has been

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sieved to 200 mesh. The surface area of the powder as determined by BET is 1.1 m2/g but the wide range of particle size introduces significant error into that measurement. Solids were analyzed before and after reaction using x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy with energy dispersive analysis. Three experiments of note each contained olivine, CO2, and an aqueous solution of either distilled water, 1.0 g/L salicylic acid, or 0.1 g/L salicylate buffered with salicylic acid to a pH of 3. In all cases, sufficient CO2 was added to fully saturate the aqueous solution with 10-15 mL of excess in the supercritical phase. The experiments were conducted for 30 to 40 days.

XRD analysis confirmed the formation of magnesite (MgCO3) in two of the three

experiments, and solution chemistry shows that both of these experiments surpassed MgCO3 saturation (Figure 1). The experiment with 1 g/L salicylic acid reached saturation first and had the highest extent of reaction (29 ± 4%) based on quantitative XRD analysis. The experiment with the buffered salicylic acid solution did not reach saturation, and very weak magnesite peaks were observed in the XRD spectrum. SEM images of the carbonated solids show ferrous magnesite formations as well as an abundance of precipitated amorphous silica (SiO2) (Figure 2). In all reactions, the system reached saturation for amorphous silica within the first several days.

Figure 1: Time-resolved magnesite saturation indices for three experiments. A saturation index of 1 indicates thermodynamic saturation.

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The time-resolved magnesium concentrations for all experiments show an unexpected trend. Initially fast Mg release (olivine dissolution) ends after 2 or so days, at which point the Mg concentration becomes nearly constant for 1-20 days, depending on the conditions. After this lag, Mg is again released quickly into solution until saturation is exceeded, at which point the concentrations again level out since the rate discrepancy between precipitation (fast) and dissolution (slow) maintains the system at thermodynamic saturation. The observed saturation is likely higher than the calculated value because of ion pairing in solution.

Many other groups have found that the addition of organic acids increases the rate of dissolution of silicate minerals. We found that the dissolution of olivine over 2 days was actually slower with salicylic acid than without, but that the overall rate of conversion was higher with salicylic acid than without (Table 1). Salicylic acid also complexes with magnesium ions in solution, increasing the thermodynamic saturation of magnesite. The rates calculated from solution chemistry and the extent of reaction show an important point: the experiment with the most rapid initial dissolution ended up reacting with CO2 the least. Thus, when modeling these systems, we must not assume that the initial olivine dissolution rate corresponds to the overall rate of carbonation.    

Our future experimental work will involve both batch and flow through studies of

the interaction of CO2-rich fluids, with and without organic acids, including acetic acid, with various Mg-silicates (olivine, orthopyroxene, antigorite, chrysotile) representative of ultramafic and mafic rocks and their alteration products and with minerals representative of deep saline aquifers and cap rocks, followed by detailed characterization studies of reaction products and thermodynamic and kinetic modeling studies.

Figure 2: SEM images of carbonated olivine. A: Edge of a 100 µm sheet made predominantly of amorphous silica with crystalline magnesite nodules on the surface. B,C: close-up view of morphology of the silica as well as the magnesite nodules.  

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Table 1: Summary of selected results from Olivine + CO2 ± Salicylic Acid experiments

Initial pH

Other additions Extent of carbonation

Olivine dissolution rate over 24 hours (mol s-1 cm-2)

Apparent MgCO3 appearance rates (mol s-1 cm-2)

4.3 1 g/L salicylic acid 29 ± 4% 5.0 x 10-13 1.1 x 10-13 4.5 none 7 ± 2% 8.8 x 10-13 2.6 x 10-14 4.5 0.1 g/L salicylate

buffered to pH of 3 <3% 1.4 x 10-12 4.5 x 10-15

Natural Analogues of CO2 Interactions with Mafic and Ultramafic rocks  

Although stratigraphic sequences of basalts provide high permeability aquifers for CO2 transport (Goldberg et al., 2008), their potential for mineral sequestration of CO2 is significantly less than ultramafic rocks due to the abundance of reactive Mg-rich phases (olivine and serpentine) in the latter (Lackner 2002; Marini, 2007; Kelemen and Matter, 2008). Subsurface concentrations of magnesite (MgCO3) forming world-class economic deposits called Kraubath type deposits, demonstrate the efficiency of mineral carbonation in ultramafic rocks (Pohl, 1990; Abu-Jaber and Kimberley, 1992). Characteristics of these deposits include pure cryptocrystalline magnesite in economic veins up to 45 m in thickness, structural lengths of 4 km, and mining depths of ~300 m. Such large concentrations of mineral carbonation illustrate a thermodynamically, kinetically, and structurally favored process, and their worldwide occurrence suggests that physical and chemical conditions for their formation are not unique to any one geologic locality. The carbonation appears to have formed at shallow crustal levels and low-temperatures, where cyclic hydraulic fracturing and brecciation maintained high permeability and porosity (Fig. 3C,D; Abu-Jaber and Kimberley, 1992; Boschi et al., 2009; etc.).

Furthermore, massive bodies of carbonate do not exhibit extensive metasomatic reactions with the ultramafic rocks that host the veins (Fig. 3D), suggesting that magnesite mineralization was rapid, precluding reaction of the CO2-mineralizing fluids with the ultramafic host rocks, and thus indicating that the source of Mg2+ for magnesite mineralization was not derived from immediate host rocks that provided the open flow paths (Boschi et al. 2009; our present observations).  

In view of the geologic evidence, we have chosen the Red Mountain Magnesite Mining District, one of the world's largest magnesite deposits (Bodenlos, 1950) located ~100 km SE of San Francisco, California, as our type locality for evaluating natural mineralogical CO2 sequestration (Figure 3). The deposit is in variably serpentinized ultramafic rocks of the Jurassic Coast Range ophiolite belt exposed at Del Puerto, CA (Bodenlos, 1950). It is a classic example of the geologic features summarized above, and is well exposed in outcrops, glory holes, cross-cuts, and underground workings (Figure 3), providing an excellent opportunity to characterize the interaction of geochemical and

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structural processes. Our objectives are to evaluate the physical and chemical processes responsible for this extraordinary CO2 mineralization and to explore engineering approaches that replicate the natural phenomena of permeability and porosity generation and carbonate mineralization in these ultramafic rocks.  

Our characterization of the Red Mountain deposit to date has consisted of petrographic analysis, X-ray Diffraction (XRD), and stable and radiogenic isotopic analyses of the carbonate to understand the origin of the fluids, the CO2 and the solutes. We also conducting a preliminary geochronologic investigation using both Nd/Sm and U/Pb radioactive dating systems to determine the age of the carbonate veins and ideally the timescale over which they formed. Three main occurrences of ultramafic rocks were distinguished: 1) uncarbonized serpentinitized peridotite in contact with magnesite (Figure 4A), 2) angular fragments of serpentinite of varying size (i.e. few microns to 2 cm) with dissolution/reaction rims of carbonate (Figure 4B), and 3) relict grains thoroughly replaced by carbonate (Figure 4C). The majority of the massive magnesite is cryptocrystalline and was confirmed by XRD analyses to be devoid of other mineral phases (Figure 4D). This pure cryptocrystalline magnesite coupled with the extensive re-

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breciation of magnesite (e.g., Figures 3C, D) suggests rapid precipitation and cyclic hydrofracturing of the veins. We hypothesize that mechanical energy generated by fluid-phase separation or volumetric changes during decompression of CO2-rich fluids at shallow crustal depths provides the work to exceed tensile strengths of the host rocks, thus generating porosity and permeability through hydraulic brecciation and fracturing. By combining our observations and data from the experimental and natural system studies, our future work will focus on the development of a coupled thermodynamic,

Figure 4. A. Hand specimen showing the sharp contact between serpentinized peridotite and a carbonate vein. The photomicrograph in cross-polarized light shows distinctive 3rd order birefringence colors of olivine in typical mesh texture with serpentine. The contact between the ultramafic and the carbonate is sharp in thin section as well. Notice the isopachous texture of clear- to pastel-colored fibrous to bladed grains in the carbonate vein. Nodular cryptocrystalline magnesite in the vein can be identified as the dark brown-colored areas with “cauliflower” texture surrounded by the bladed coarser magnesite. B. Photomicrograph in crossed polars shows the 1st order interference colors of a serpentine grain that presents a corona texture as carbonization occurs; magnesite is the cementing cryptocrystalline matrix in this breccia. C. Photomicrograph in crossed polars showing the relict serpentine grains thoroughly carbonized. The brighter areas still contain small fragments of serpentine but pervasive dissolution converts them to carbonate. D. Hand sample of pure cryptocrystalline magnesite; notice the typical conchoidal fracture and its resemblance to porcelain.

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hydrologic and mechanical model of the Red Mountain deposit in order to test our above hypothesis for the apparent rapid and massive sequestration of CO2 in ultramafic sequences. This approach will enable us to determine feasibility and approaches for injecting CO2 into these types of deposits, which although represent less storage volume than saline aquifers, present the opportunity to permanently remove CO2 from circulating fluids.

In order to better understand fluid circulation and sources of water and solutes,

carbon, oxygen, and neodymium isotope analyses have also been performed on the magnesite samples, providing useful information on the paragenesis of the carbonates. The δ18OSMOW values of 26.0 ± 2.1 ‰ and δ13CPDB values of -11.6 ± 2.4 ‰ are consistent with a meteoric fluid source and carbon derived from the breakdown of organic matter. The isotope values are also similar to other magnesite deposits from around the world suggesting a similar origin (Figure 5).

Geothermometric calculations using the O isotope fractionation between magnesite and water (Aharon, 1998) further suggest that the minimum precipitating temperature of the magnesite is 30°C and the maximum 116°C. The organic signature of the C associated with the magnesite suggests that a fraction of the CO2 is derived from organic matter decomposition and that organic acids were likely present in the fluid.

Figure 5: δ18O and δ13C of petroleum reservoirs (open symbols). Fields corresponding to seafloor carbonate formed in basalts (blue) and magnesite in ultramafic rocks worldwide (purple) are shown for references.

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However, typical groundwaters do not contain the elevated DIC presumably required to generate the rapid precipitation of the massive amounts of magnesite observed. One possibility is that decarboxylation of organic acids may be the source of the elevated CO2. The suggestion that organic acids were associated with the system is interesting given our findings from the experimental studies, where dissolution rates were greatest for lower concentrations of salicylic acid, but carbonation rates much higher at elevated salicylic acid concentrations. Given the hypothesized mechanism for carbonate emplacement at Red Mountain, CA, it would be useful for us to know the duration over which the cyclic brecciation occurred. Unfortunately there are very few approaches for dating carbonate minerals older than about 500,000 years. However, in collaboration with a group at Boston University, we are developing two new chronometers (Nd/Sm and U/Pb) for carbonate dating that could be used to place constraints on the timescale of carbonation. Our first analyses of Red Mountain magnesite did not result in enough spread in the isochron to produce an age, but additional samples are being considered. However, we did find surprisingly low εNd values suggesting that a substantial fraction of the Nd was not from the ultramafic rocks. In future work, Nd and Sr isotope mixing diagrams may provide additional insight into the fraction of solute derived from reaction with ultramafic rocks, information which could be further used to constrain our model for the genesis of the carbonate. Conclusions  

Our work on the interaction between CO2 and Mg-silicates has revealed a number of new findings with respect to the feasibility of mineral carbonation as a mechanism for permanently storing anthropogenic CO2 as a stable carbonate phase. First, our experimental work has found that organic acids, such as those commonly found in natural waters and deep saline aquifers, are capable of both enhancing and potentially inhibiting dissolution and precipitation reactions. Our studies of natural analogues also indicate the presence of organic acids in the system, although their exact role has not yet been determined. The olive carbonation experiments suggest that while some organic acids enhance mineral-fluid reaction rates in the presence of CO2, there is a threshold of organic acid concentrations (> ca. 0.1 g/L for salicylic acid) and/or pH above which mineral dissolution rates may actually be suppressed, possibly due to interactions between the organics and the mineral surface. In contrast, our initial findings suggest that magnesite precipitation rates are potentially enhanced by several orders of magnitude at higher salicylic acid concentrations. A review of published values for organic acid concentrations in continental brines typical of saline aquifers (the other proposed storage reservoir for CO2), also suggests that oil field brines contain organic acid concentrations up to 10,000 mg/L (Kharaka and Hanor, 2007), a substantial portion of the total alkalinity. Quantifying the role of organic acids in promoting or inhibiting mineral dissolution-precipitation reactions in CO2 + water (± SOx, NOx) systems will be a continued focus of our research.

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The second important aspect of our exploratory research has been the observations of substantial mineral carbonation accompanied by repeated brecciation events within the serpentinized ultramafic rocks of the Red Mountain Magnesite District. Our current model suggests that mechanical energy generated by fluid-phase separation or volumetric changes during decompression of CO2-rich fluids at shallow crustal depths provides the work to exceed tensile strengths of the host rocks. As a result, repeated hydraulic brecciation and fracturing generate porosity and permeability allowing fluids to deposit substantial amounts of magnesite. Further characterization studies will be used to constrain a coupled thermodynamic, hydrologic and mechanical model of the Red Mountain deposit in order to test our hypothesis for the apparent rapid and massive sequestration of CO2 at this locality. If the processes we observe at Red Mountain can be engineered for CO2 sequestration, we believe that ultramafic rock sequences provide an alternative strategy for permanent CO2 sequestration in areas that lack access to deep saline aquifer storage capacity.

Finally, during the course of our GCEP project our team has developed substantial experience working with the experimental and natural systems relevant to assessing the fate of CO2 in the subsurface. We have also developed a strong collaboration with the CO2 sequestration team at the U.S. Geological Survey in Menlo Park, CA (Bob Rosenbauer, Burth Thomas and Yousif Kharaka) who are involved in field scale sequestration tests. Thus, as a direct result of this exploratory project, which has involved 2 graduate students and will likely result in 2 to 3 manuscripts submitted within the year, we have decided to expand our project to consider the other main proposed subsurface storage reservoir for CO2, saline aquifers. In February, 2010, we submitted a full GCEP proposal to investigate CO2 reactivity in saline aquifers and to conduct new research into the engineering aspects of CO2 sequestration in ultramafic rocks based on the chemical and hydrologic mechanisms we have discerned in our exploratory research. Publications and Abstracts Brown, Jr., G. E., Bird, D. K., Kendelewicz, T., Maher, K., Mao, W., Johnson, N.,

Rosenbauer, R. J., and García Del Real, P. (2009) Geological Sequestration of CO2: Mechanisms and Kinetics of CO2 Reactions with Mafic and Ultramafic Rock Formations. 2009 Annual Report to the Global Climate and Energy Project, Stanford University, Stanford, CA. (URL: http://www.stanford.edu/~gebjr/).

Johnson, N. C, B. Thomas, K. Maher, D. K. Bird, R. B. Rosenbauer, and G. E. Brown, Jr. (2009) Kinetics of olivine carbonation at 60°C and 100 bar. Abstr. Prog. Geol. Soc. Am. Ann. Mtg., Portland, OR.

Johnson, N. C, B. Thomas, K. Maher, T. Kendelewicz, D. K. Bird, R. B. Rosenbauer, and G. E. Brown, Jr. (2010) Kinetics of Mg-silicate carbonation for the geologic storage��� of carbon dioxide. Abstr. ACS Ann. Mtg., San Francisco, CA.

Johnson, N. C, B. Thomas, K. Maher, D. K. Bird, R. B. Rosenbauer, and G. E. Brown, Jr. (in prep) Kinetics of olivine carbonation at 60°C and 100 bar. Geochim. Cosmochim. Acta.

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García Del Real, P. Maher, G. E. Brown D. K. Bird (in prep) CO2 Sequestration in Ultramafic Rocks: Geological, Physical, and Chemical Constraints from the Red Mountain Magnesite District, California.

Contacts Gordon E. Brown, Jr.: gordon.brown@stanford.edu Dennis K. Bird: dkbird@stanford.edu Tom Kendelewicz: kendelewicz@stanford.edu Kate Maher: kmaher@stanford.edu Wendy Mao: wmao@stanford.edu Natalie Johnson: nataliej@stanford.edu Robert J. Rosenbauer: brosenbauer@usgs.gov Pablo García Del Real: gdelreal@stanford.edu References Abu-Jaber, N. S. and M. M. Kimberley (1992) Origin of ultramafic-hosted vein

magnesite deposits. Ore Geol. Rev. 7, 155-191. Aharon, P., (1988), A stable-isotope study of magnesite from the rum jungle uranium

field, Australia: Implications for the origin of strata-bound massive magnesite: Chemical Geology, 69, 127-145.

Alexander, G., Maroto-Valer, M. M. & Gafarova-Aksoy, P. (2007)Evaluation of reaction variables in the dissolution of serpentine for mineral carbonation. Fuel 86(1-2), 273-281.

Andreani, M., L. Luquot, P. Gouze, M. Godard, E. Hoise, and B. Gibert (2009) Experimental Study of Carbon Sequestration Reactions Controlled by the Percolation of CO2-Rich Brine through Peridotites, Environ. Sci. Technol. 43(4), 1226-1231.

Bearat, H., McKelvy, M. J., Chizmeshya, A. V. G., Gormley, D., Nunez, R., Carpenter, R. W., Squires, K. & Wolf, G. H. (2006) Carbon sequestration via aqueous olivine mineral carbonation: Role of passivating layer formation. Environ. Sci. Technol. 40(15), 4802-4808.

Benson, S. M. and D. R. Cole (2008) CO2 sequestration in deep sedimentary formations, Elements 4(5), 325-331.

Bodenlos, A. J., (1950) Geology of the Red Mountain magnesite district, Santa Clara and Stanislaus Counties, California. Calif. Jour. Mines Geol. 46, 223-278.

Boschi, C., A. Dini, L. Dallai, G. Ruggieri, and G. Gianelli (2009) Enhanced CO2-mineral sequestration by cyclic hydraulic fracturing and Si-rich fluid infiltration into serpentinite at Malentra (Tuscany, Italy). Chem. Geol. 265, 209-226.

Flaathen, T. K., Gislason, S. R., Oelkers, E. H. & Sveinbjörnsdóttir, A. E. (2009) Chemical evolution of the Mt. Hekla, Iceland, groundwaters: A natural analogue for CO2 sequestration in basaltic rocks. Appl. Geochem. 24, 463-474.

Giammar, D. E., Bruant, R. G. & Peters, C. A. (2005) Forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide. Chem. Geol. 217(3-4), 257-276

Goldberg, D. S., T. Takahashi, and A. L. Slagle (2008) Carbon dioxide sequestration in deep-sea basalt, Proc. Nat. Acad. Sci. U.S.A. 105(29), 9920-9925.

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Hanchen, M., Prigiobbe, V., Baciocchi, R. & Mazzotti, M. (2008)Precipitation in the Mg-carbonate system-effects oft emperature and CO2 pressure. Chem. Eng. Sci. 63, 1012-1028.

Hanchen, M., Prigiobbe, V., Storti, G., Seward, T. M. & Mazzotti, M. (2006) Dissolution kinetics of fosteritic olivine at 90-150 degrees C including effects of the presence of CO2. Geochim. Cosmochim. Acta 70(17), 4403-4416

Hansen, L. D., Dipple, G. M., Gordon, T. M. & Kellett, D. A. (2005) Carbonated serpentinite (listwanite) at Atlin, British Columbia: A geological analogue to carbon dioxide sequestration. Canad. Mineral. 43, 225-239.

Jessen, K., A. R. Kovscek, and F. M. Orr (2005) Increasing CO2 storage in oil recovery, Energy Conv. Manag. 46(2), 293-311.

Kelemen, P. B. and J. Matter (2008) In situ carbonation of peridotite for CO2 storage. Proc. Nat. Acad. Sci. USA 105(45), 17295-17300.

Lackner, K.S.(2002), Carbonate chemistry for sequestering fossil carbon, Annu. Rev. Energ. Environ. 27, 193-232.

Marini, L. (2007) Geological Sequestration of Carbon Dioxide: Thermodynamics, Kinetics, and Reaction Path Modeling. Vol. 11, Developments in Geochemistry. Elsevier, Amsterdam, 453 p.

Matter, J. M. and P. B. Kelemen (2009) Permanent storage of carbon dioxide in geological reservoirs by mineral carbonation, Nature Geoscience 2(12), 837-841.

Oelkers, E. H., S. R. Gislason, and J. Matter (2008) Mineral Carbonation of CO2, Elements, 4(5), 333-337.

Orr, F. M. (2009) Onshore Geologic Storage of CO2, Science 325(5948), 1656-1658. Pohl, W. (1990) Genesis of magnesite deposits--models and trends. Geologische

Rundschau 79, 291-299. Pruess, K. (2006) Enhanced geothermal systems (EGS) using CO2 as working fluid - A

novel approach for generating renewable energy with simultaneous sequestration of carbon, Geothermics 35(4), 351-367.

Wogelius, R. A. & Walther, J. V. (1991)Olivine dissolution at 25˚C - Effects of pH, CO2, and organic acids. Geochim. Cosmochim. Acta 55(4), 943-954.