Abstract
The engineered removal of atmospheric CO
2
is now considered a key component of mitigating climate warming below 1.5 °C. Mineral carbonation is a potential negative emissions technique that, ...in the case of Iceland’s CarbFix experiment, precipitates dissolved CO
2
as carbonate minerals in basaltic groundwater settings. Here we use calcium (Ca) isotopes in both pre- and post-CO
2
injection waters to quantify the amount of carbonate precipitated, and hence CO
2
stored. Ca isotope ratios rapidly increase with the pH and calcite saturation state, indicating calcite precipitation. Calculations suggest that up to 93% of dissolved Ca is removed into calcite during certain phases of injection. In total, our results suggest that 165 ± 8.3 t CO
2
were precipitated into calcite, an overall carbon storage efficiency of 72 ± 5%. The success of this approach opens the potential for quantification of similar mineral carbonation efforts where drawdown rates cannot be estimated by other means.
Carbon capture and storage (CCS) provides a solution toward decarbonization of the global economy. The success of this solution depends on the ability to safely and permanently store CO₂. This study ...demonstrates for the first time the permanent disposal of CO₂ as environmentally benign carbonate minerals in basaltic rocks. We find that over 95% of the CO₂ injected into the CarbFix site in Iceland was mineralized to carbonate minerals in less than 2 years. The result contrasts with the common view that the immobilization of CO₂ as carbonate minerals within geologic reservoirs takes several hundreds to thousands of years. Our results, therefore, demonstrate that the safe long-term storage of anthropogenic CO₂ emissions through mineralization can be far faster than previously postulated.
•Results from injection of CO2-H2S gas mixture at the CarbFix2 site, SW-Iceland.•Soluble gas mixture was captured in water and injected into hot basaltic reservoir.•The injected CO2 and H2S was ...mineralized within months providing safe and long term storage of the gases.•The cost of the integrated method is US $25/ton of the gas mixture at the CarbFix2 site.
One of the main challenges of worldwide carbon capture and storage (CCS) efforts is its cost. As much as 90% of this cost stems from the capture of pure or nearly pure CO2 from exhaust streams. This cost can be lowered by capturing gas mixtures rather than pure CO2. Here we present a novel integrated carbon capture and storage technology, installed at the CarbFix2 storage site at Hellisheiði, Iceland that lowers considerably the cost and energy required at this site. The CarbFix2 site, located in deeper and hotter rocks than the original CarbFix site, permits the continuous injection of larger quantities of CO2 and H2S than the original site. The integrated process consists of soluble gas mixture capture in water followed by the direct injection of the resulting CO2-H2S-charged water into basaltic rock, where much of the dissolved carbon and sulfur are mineralized within months. This integrated method provides the safe, long-term storage of carbon dioxide and other acid gases at a cost of US $25/ton of the gas mixture at the CarbFix2 site and might provide the technology for lower CCS cost at other sites.
Abstract
Basalts are recognized as one of the major habitats on Earth, harboring diverse and active microbial populations. Inconsistently, this living component is rarely considered in engineering ...operations carried out in these environments. This includes carbon capture and storage (CCS) technologies that seek to offset anthropogenic CO
2
emissions into the atmosphere by burying this greenhouse gas in the subsurface. Here, we show that deep ecosystems respond quickly to field operations associated with CO
2
injections based on a microbiological survey of a basaltic CCS site. Acidic CO
2
-charged groundwater results in a marked decrease (by ~ 2.5–4) in microbial richness despite observable blooms of lithoautotrophic iron-oxidizing Betaproteobacteria and degraders of aromatic compounds, which hence impact the aquifer redox state and the carbon fate. Host-basalt dissolution releases nutrients and energy sources, which sustain the growth of autotrophic and heterotrophic species whose activities may have consequences on mineral storage.
New methods have been developed and applied successfully for the determination of dissolved inorganic, organic and total carbon in water samples. The new methods utilize two instrumental setups, ...Reagent-Free™ Ion Chromatography (RF™-IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Dissolved inorganic carbon (DIC) was measured in untreated samples along with Cl
−, F
− and SO
4
2− using RF™-IC and by in-line mixing with 0.1
M HNO
3 to enhance CO
2 removal in the nebulizer, followed by ICP-AES analysis. Total dissolved carbon (TDC) was measured by in-line mixing with 0.1
M NaOH following ICP-AES analysis. Dissolved organic carbon (DOC) was obtained as the difference between DIC and TDC. Only non-volatile organic carbon could be detected by the present method. The workable limits of detection obtained in the present study were 0.5
mM (RF™-IC) and 0.1
mM (ICP-AES) for dissolved inorganic and organic carbon, respectively. The power of the new methods lies in routine analysis of DIC and DOC in samples of natural waters of variable composition and salinity using analytical techniques and facilities available in most laboratories doing water sample analysis. The techniques are sensitive and precise, can be automated using gas-tight sample vials and auto-samplers, and are independent of most elemental interferences with the exception of chloride overload by saline samples when using RF™-IC. The new methods were successfully applied for analysis of DIC and DOC in selected samples of natural and synthetic waters.
Display omitted
•Geothermal power plants represent well-constrained systems to study the time-resolved precipitation of amorphous silica.•Heterogeneous nucleation, followed by surface controlled ...growth, leads to a botryoidal silica layer.•Silica layer grows over 1 g m−2 day-1 by addition of silica monomers from solution.•μm-sized silica particles form via homogeneous nucleation in the fluid and are deposited and subsequently cemented.•Silica particles aggregate to form μm- to mm-sized 3D structures which are subsequently cemented together.
Amorphous silica is a common precipitate in modern and ancient hot springs and in geothermal power plants, yet the corresponding precipitation rates and mechanisms are still highly debated, primarily due to the plethora of parameters that can affect the reactions in natural waters. Here, we report the results from a first ever industrial-scale time-resolved (1 day to 10 weeks) study of silica precipitation conducted at the Hellisheiði geothermal power plant (SW-Iceland). We show that such in-work pipelines of a geothermal power plant are ideal environments to investigate silica precipitation because the physicochemical conditions are well constrained and constantly monitored. Our results document that amorphous silica forms via two distinct precipitation modes: (1) the fast deposition of continuous botryoidal silica layers and (2) the growth of 3D fan- or ridge-shaped silica aggregates. The continuous layers grow by heterogeneous nucleation and subsequent surface controlled growth by monomer addition. In contrary, the 3D aggregates form through homogeneous nucleation of silica nano- and microparticles in solution, followed by deposition and cementation on the surface of the botryoidal layer. From the time-resolved data, silica precipitation rates of over 1 g m−2 day-1 are derived. Over time, this deposition of silica on pipelines and fluid handling equipment is detrimental to geothermal power production. Our data does not only help improve our understanding of silica precipitation from geothermal fluids, but the determined silica precipitation mechanisms and rates help improve mitigation strategies against silica scaling inside in-work geothermal power plants.
Field scale reactive transport models of CO
2
and H
2
S mineral sequestration in basalts were developed with a focus on Reykjavík Energy’s ongoing CarbFix and SulFix sour gas re-injection tests at ...Hellisheidi geothermal power plant, SW-Iceland. Field data, such as drill cuttings and a calcite cap-rock overlying the high-temperature geothermal reservoir, suggest that mineral CO
2
and H
2
S sequestration already plays an important role within Hellisheidi geothermal system. The data indicate CO
2
sequestration to be most intensive from 550–800-m depth below surface, while H
2
S sequestration is most intensive below 800-m depth. Injecting and precipitating CO
2
and H
2
S into nearby formations with the objective of imitating and accelerating natural sequestration processes should therefore be considered as an environmentally benign process. Reactive transport simulations predict rapid and efficient mineralization of both CO
2
and H
2
S into thermodynamically stable minerals, with calcite, magnesite, and pyrrhotite being the favored carbonate and sulfide minerals to form. At intermediate depths and low temperatures (25–90
∘
C), calcite is the main CO
2
sequestering carbonate predicted to form, while magnesite is the only carbonate predicted to form at high temperatures (
>
250
∘
C). Despite only being indicative, it is concluded from this study that the capture and sequestration of CO
2
and H
2
S from geothermal power plants are a viable option for reducing their gas emissions and that basalts may comprise ideal geological CO
2
and H
2
S storage formations.
We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO
2
) and hydrogen sulfide (H
2
S) from Hengill volcanic system, Iceland. Soil CO
2
and H
2
S ...efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722 g m
−2
day
−1
, respectively. The soil temperature was measured at each sampling site and used to evaluate the heat flow. The chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic/hydrothermal component and air. Most of the diffuse CO
2
degassing is observed close to areas where active thermal manifestations occur, northeast flank of the Hengill central volcano close to the Nesjavellir power plant, suggesting a diffuse degassing structure with a SSW–NNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H
2
S efflux values are in general very low or negligible along the study area, except those observed at the northeast flank of the Hengill central volcano, where anomalously high CO
2
efflux and soil temperatures were also measured. The total diffuse CO
2
emission estimated for this volcanic system was about 1,526 ± 160 t day
−1
of which 453 t day
−1
(29.7 %) are of volcanic/hydrothermal origin. To calculate the steam discharge associated with the volcanic/hydrothermal CO
2
output, we used the average H
2
O/CO
2
mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4–240.2) as a representative value of the H
2
O/CO
2
mass ratios for Hengill fumarole steam. The resulting estimate of the steam flow associated with the gas flux is equal to 40,154 t day
−1
. The condensation of this steam results in thermal energy release for Helgill volcanic system of 1.07 × 10
14
J day
−1
or to a total heat flow of 1,237 MW
t
.
In high-temperature geothermal fields, precipitation of amorphous silica from solution to form silica scales is the main obstacle to efficient heat extraction from the hot fluids. The silica deposits ...cause operational problems and may even clog pipelines and injection drillholes. The rate of silica-scale formation can be reduced by ageing amorphous silica super-saturated waters, thus allowing the aqueous silica in excess of saturation to polymerize. Polymeric silica shows less tendency to precipitate from solution than monomeric silica. Studies of separated water from the Nesjavellir geothermal power station, Iceland, indicate that silica-scale formation can be avoided during heat extraction by rapid cooling of the water in “capillary heat exchangers”, followed by ageing the water for 1–2
h and subsequently mixing it with condensed steam. It is thus possible to avoid scale formation during injection of the amorphous silica super-saturated water leaving the heat exchanger.
PDF
