During the last decade, the pilot CarbFix project in the Iceland rift zone has provided highly promising results for permanently storing CO₂ as carbonates in basalts. A key question is whether this method can be applied in other basaltic formations worldwide where the rocks are older, the porosities are lower, the chemical compositions are different, and/or the temperatures are lower. Storing CO₂ in the subsurface necessitates injectivity, where two essential properties are permeability and porosity. In basaltic formations, porous volumes are typically found as vesicle zones, near lava flow boundaries and in flow tops, or fractures. Currently, it appears that the permeability necessary for injecting fluids in basalts is dominated by fractures. The Faroe Islands, in the North Atlantic, consist of layered basalts of Paleogene age. The aim of this study is to examine the potential of the Faroe Island Basalt Group (FIBG) as a CO₂ reservoir. To evaluate the reservoir properties of the FIBG we interpret and integrate new and existing data at multiple scales, including satellite images, UAV photogrammetric surveys, and field mapping. We have determined the distribution of large-scale lineaments (faults and dykes), flow-scale fractures, and the interaction between them in three dimensions. Here, we focus on the Malinstindur Formation, a compound basalt sequence, which is a potential pilot injection sequence because of its permeability potential. Large-scale mapping of the FIBG volcanostratigraphy is used to map the depth of the Malinstindur Formation and to determine the presence of large strike-slip faults across the archipelago. In addition, large-scale structural lineaments exhibiting a preferred EW-trending orientation are mapped. In addition, fracture analyses on different scales (from islands to outcrops), have been conducted to investigate how lava flow architectures, regional stress, and faults control fracture distribution and connectivity. The results of these analyses show that (1) the fracture density decreases with flow thickness, (2) the orientation of the internal fractures follows the same as those of the sets of regional scale lineaments, and (3) there is no link between the fracture intensity in the basalts and the distance to the regional scale lineaments. This study will serve as a foundation for determining the subsurface distribution of the Malinstindur Formation and the fracture distribution and connectivity at potential injection sites in order to estimate the potential for permanent CO₂ storage within the Faroe Islands.

How to cite: Johannesen, R., Galland, O., Ólavsdóttir, J., Kjøll, H. J., Eidesgaard, Ó., and Planke, S.: Fractured basalts as reservoirs for permanent CO2 storage on the Faroe Islands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12801, https://doi.org/10.5194/egusphere-egu25-12801, 2025.

Offshore basalt flow sequences represent potential permanent CO₂ sequestration sites along volcanic rifted margins. The International Ocean Discovery Program (IODP) Expedition 396 drilled six basement sites on the Vøring volcanic margin in 2021, recovering more than 350 m of basaltic basement cores and 15 m of granite cores. The cores have been extensively analyzed following the IODP shipboard procedures (e.g., velocity, density, porosity, and magnetic susceptibility measurements). In addition, shore-based petrographic, geochemical, CT scanning, and multi-fluid permeability and flow measurements (nitrogen, brine, liquid and gaseous CO₂) have been performed to assess reservoir properties. A standard suite of conventional wireline logs along with borehole image (acoustic and resistivity) logs were acquired in four holes. High-resolution 2D and locally 3D seismic reflection data have been acquired across all sites during three surveys (2020, 2022, and 2024) using R/V Helmer Hansen. In total, four HR3D P-Cable cubes with a total areal extent of 62 km² and c. 2700 km of HR2D data have been collected. The seismic data are interpreted using the concepts of seismic volcanostratigraphy and igneous seismic geomorphology combined with conventional horizon interpretation and core-log-seismic integration. On the Skoll High, the igneous seismic geomorphology of the Top Basalt horizon reveals two distinct domains: a pitted surface in the west, and a faulted surface in the east. Cross-cutting faults and fracture systems are well imaged in borehole data and the 3D seismic data. Borehole data show that the Inner Seaward Dipping Reflectors (SDR) were emplaced in subaerial and coastal environments, including vesicular flow tops and deposition of inter-basalt volcaniclastic sedimentary horizons. Vesicles are observed to be both open or filled with carbonates and clay minerals within different layers, however, laboratory measured matrix permeability of mini-core plugs is typically low and in the milli to micro-darcy range; brine permeability measurements are indicating even lower. Multiple scales of fracturing are identified within the cores and image logs, and Strontium residual salt analysis revealed that they have an important impact on permeability by enhancing fluid communication between flows. In conclusion, the integrated interpretation suggests that the Vøring Margin basalt sequences may have reservoir potential in fractured intervals and flow tops, but reservoir-scale injection testing linked to fracture network parameterization is required for large-scale assessment.

How to cite: Lebedeva-Ivanova, N., Bünz, S., Berndt, C., Millett, J. M., Betlem, P., Zastrozhnov, D., Rosenqvist, M., Polteau, S., and Planke, S.: High-resolution 2D and 3D seismic imaging and core-log-seismic integration of seaward dipping reflectors on the Vøring volcanic rifted margin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12935, https://doi.org/10.5194/egusphere-egu25-12935, 2025.

The widespread and substantive occurrence of basalt in ocean basins has long been recognised as a potential reservoir for CO₂ removal via mineralization having stability over extended periods of geological time. Due to the significant cost of fully exploring this potential, more recent attention has focused on geochemically equivalent rocks in more accessible terrestrial terranes. Examples occur in ophiolite sequences, terrestrial volcanic environments, and even in stable cratonic settings that have undergone considerable metamorphism. There have been abundant studies of the hydrogeology of crystalline rock in general by the nuclear waste and mining industries, and for water supply, which clearly illustrate that flow and transport are governed in these rock types by a sparse network of discrete fractures having relatively small aperture (10s to a few 100 μm with a total void volume of <0.01%), embedded in a rock matrix of virtually zero permeability (<10^-18 m²)  and very low effective porosity (<0.05% to ∼0.8%). Thus, although the geochemical suitability of the rock is required, the injection permeability, CO₂ transport mechanisms, and pore volumes available for mineralization may be the more limiting factors to commercial viability. Examples will be presented illustrating the need for hydrogeological characterization of appropriate rock bodies, and more complete analysis of the process of matrix diffusion under complex geochemical conditions.

How to cite: Novakowski, K., O'Connor, S., Maidment, G., and Sánchez-Roa, C.: Hydrogeological challenges for carbon mineralization in terrestrial mafic/ultramafic rock bodies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14364, https://doi.org/10.5194/egusphere-egu25-14364, 2025.

Mineral carbon storage in basalt has been proven as an effective means of durable and verifiable geologic carbon sequestration. Here we describe and investigate a novel technology aimed at optimizing subsurface mineralization: water-alternating-gas (WAG), or cycled injections of free-phase CO₂ (e.g., supercritical) and water. Incorporating injection of supercritical CO₂ (scCO₂) into basalt can minimize water demand, increase per-well injection capacity, and expand the feasible range of basalt carbon storage. Cycling water between injection of scCO₂ can accelerate geochemical reactions and shorten mineralization timeframes. We model aqueous-phase, scCO₂-only, and WAG injections into subsea and onshore basalt sites using the STOMP-CO₂ simulator. We simulate WAG injections into various basalt reservoirs to investigate injection parameters and reservoir characteristics that accelerate mineralization during WAG injections. Results indicate that optimized WAG injections can double mineralization compared to traditional scCO₂-only using half as much water as an aqueous-phase approach. WAG scenarios improve mineralization the most relative to the scCO₂-only injection and increase feasible per-well injection rates relative to aqueous-phase approaches. Our results indicate that WAG has the potential to optimize carbon mineralization in basalt and substantially advance the scalability of this technology.

How to cite: Nelson, C. and Goldberg, D.: Water-alternating-gas injections for optimized mineral carbon storage in basalt., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1840, https://doi.org/10.5194/egusphere-egu25-1840, 2025.

The Ivrea-Verbano Zone (IVZ) in the western Southern Alps offers a unique opportunity to study an exhumed, almost complete section of continental crust, including a Lower Permian transcrustal magmatic system. Among these features is the Layered Series, a sequence of ultramafic and mafic cumulates located between the localities of Balmuccia and Vocca in the Sesia Valley. These rocks formed during the early stages of magmatic underplating in the Lower Permian. Here we report previously undocumented occurrences of carbonated peridotites and pyroxenites in this area.

High resolution drone mapping and field observations reveal carbonation zones associated with fault-controlled fluid flow. Petrographic analysis shows the formation of serpentine, talc and carbonate minerals (magnesite, siderite and calcite) replacing olivine and pyroxene. In peridotites, reaction fronts between replacing phases and olivine and pyroxenes show sharp, well-defined boundaries, whereas in pyroxenites they show more gradual transitions, indicating differences in fluid reactivity between lithologies. The rocks are also characterized by volume expansion, which seems to have induced fracturing and facilitated further fluid-rock interactions, possibly creating a feedback loop that promotes alteration. Furthermore, the presence of talc in meter scale fault zones may affect their mechanics by promoting aseismic slip.

Serpentinization and carbonation could have taken place either during (a) Jurassic rifting, (b) final exhumation related to tectonic activity along the Insubric line, or (c) recent, near surface alteration. Detailed mineralogical and microstructural studies are underway to quantify the origin, timing and evolution of the CO₂-rich fluids and the temperature/pressure conditions under which these transformations occurred.

How to cite: Venier, M., Beltrame, M., Corradetti, A., Del Rio, M., Hawemann, F., Müntener, O., Narduzzi, F., Pistone, M., Toy, V., and Ziberna, L.: Carbonated ultramafic rocks in the Balmuccia layered series, Ivrea-Verbano Zone, Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16486, https://doi.org/10.5194/egusphere-egu25-16486, 2025.

Earth’s basaltic repositories are among the premier CO2 storage spaces. The Deccan Traps in India, the world’s largest basaltic flow deposits, offer one of the viable options for CO2 sequestration due to their extensive availability and the heterogeneity of texture and mineralogy. Laboratory investigations and field implementation of CO2 treated basalts show the release of divalent cations upon reaction with and formation of stable carbonates upon reaction with CO2 and brine. However, this varies with the varying composition and texture of the samples atspecific conditions of pressure, temperature, and CO2 injection rates. To guarantee long-term sustainability, it’s crucial to formulate a viable model that includes using the sample with maximum divalent cations, high porosity, and permeability and calculate its storage capacity.

This research work utilizes the samples collected from the field to calculate their storage capacity and compare how textural difference can bring about change in storage mechanism of CO2 in the sample. The comparison between storage capacity calculated for samples showed that each mechanism plays a crucial role in CO2 storage in basalts of varying composition and porosity. Moreover, through in-situ experiments, we can identify the mechanism best suited for the basalts of the Deccan Trap formations. Thus, results acquired from storage estimation and in-situ experiments will together guide to make mindful decision while choosing the sites for CO2 capture for maximum storage and avoid any potential leakage risks or gas escape.

How to cite: Kumar, T., Nagarkoti, N., Jamwal, V. D., and Sharma, R.: Estimating the Sensitivity of Storage capacity to the Fraction of Free Pore Volume and Surface Adsorption in Mafic Rocks: A case study from Deccan Basalts, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19143, https://doi.org/10.5194/egusphere-egu25-19143, 2025.

Abstract. Carbon mineralization is the process of converting CO₂ into stable carbonate minerals through chemical reactions with reactive minerals such as silicates or oxides. This study investigates the carbon mineralization potential of wollastonite for carbon dioxide (CO₂) sequestration through geochemical modelling. For this purpose, geochemical simulation was conducted using kinetic batch modelling under varying conditions, including temperatures ranging from 35 to 90 °C, pressures between 100 to 200 atm, and salinities from 0 to 2 mol/L NaCl for 20 days using PHREEQC (Version 3.7.3, USGS). The kinetic batch modelling results were explained that wollastonite dissolution increased with higher pressures and salinities, within the tested ranges of 100 – 200 atm and 0 – 2 mol/L NaCl, respectively. However, as the temperature increased from 35 to 90 °C, calcium concentration decreased by 55 % for 0 M salinity (Pure water). Besides, it is clear from the finding that carbonation efficiency shows a minimal variation (±1%) with changes in pressure at a constant temperature of 65°C in pure water, whereas it improved significantly by 52 % with changes in temperature from 0 to 90 °C at constant pressure on 150 atm in pure water. These results provide important understanding into the CO₂ mineralization processes of calcium silicates such as wollastonite under geological carbon sequestration (GCS) conditions. They contribute to a deeper understanding of how injected CO₂ behaves and interacts geochemically within subsurface environments, emphasizing the potential of these silicate minerals for efficient carbon capture and storage.

Keywords: Geological carbon sequestration; Kinetic batch modelling.

How to cite: Gupta, K. D., Katre, S., and Nair, A. M.: Geochemical Modelling for Carbon Mineralisation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14981, https://doi.org/10.5194/egusphere-egu25-14981, 2025.

CO₂ sequestration through mineralisation in mafic-ultramafic rocks is gaining momentum as a secure means of CO₂ storage over geological timescales^1,2. Currently, CarbFix in Iceland operates the world’s leading geologic CO₂ sequestration project. Here, we present the results of novel imaging of the CO₂ mineralisation process within a subsample of basalt core obtained from CarbFix Hellisheiði KB-01 well, using an in-house developed, X-ray transparent cell³.

CO₂ mineralisation was induced in the core using CO₂-saturated solution at 10 bar CO₂ and under 170 °C. The process was imaged through X-ray computed microtomography (XCT) on a weekly basis for a period of 12 weeks. During the experiment, the composition of the CO₂ saturated solution which was pumped through the core sample was modified as follows: deionised water (first 5 weeks), followed by 6.3 mM NaHCO₃ (4 weeks), followed by 0.64 M NaHCO₃ solution (3 weeks). Visual inspection of the acquired XCT and analysis of the fluid composition of the reaction outlet allowed the rock/fluid interaction to be determined over the experiment duration.

Over the first 5 weeks, increased porosity within the core sample was observed, indicating that CO₂-induced dissolution was occurring. On the introduction of NaHCO₃, the porosity within the core sample was observed to decrease. Based on both image analysis and the reduction in cations with the outlet fluid, we attribute this to precipitation of CO₂ to form stable carbonate phases. Hence, our results indicate that at the studied conditions, rapid dissolution and precipitation over the duration of months occurred.

Planned future work will involve correlating the acquired XCT images with Energy Dispersive Spectroscopy (EDS) to accurately segment the different phases precipitated in the core sample and to identify the exact mineral composition of the precipitates. Using analysis of XCT and EDS images, we will match the observed microstructure development to the chemical composition of the regions where the microstructures are observed. This will provide the first complete 4D microscale imaging of fluid-rock interaction during CO₂ mineralisation, and allow prediction of the maximum amount of CO₂ uptake in a given formation based on its microstructure and mineralogy.

References

1-Khudhur, F. W. K., MacDonald, J. M., Macente, A. & Daly, L. The utilization of alkaline wastes in passive carbon capture and sequestration: Promises, challenges and environmental aspects. Science of The Total Environment 823, 153553 (2022).

2-Raza, A., Glatz, G., Gholami, R., Mahmoud, M. & Alafnan, S. Carbon mineralization and geological storage of CO2 in basalt: Mechanisms and technical challenges. Earth Sci Rev 229, 104036 (2022).

3-Watt, I. D. et al. X-ray translucent reaction cell for simulation of carbon mineral storage reservoir environments. International Journal of Greenhouse Gas Control 137, 104195 (2024).

How to cite: Khudhur, F. W. K., Butler, I. B., Fusseis, F., Watt, I. D., and Gilfillan, S. M. V.: Qualitative observations of microstructure development during CO2 mineralisation in basalt obtained from CarbFix, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17987, https://doi.org/10.5194/egusphere-egu25-17987, 2025.

Geological CO₂ sequestration in basalt formations represents a promising approach to mitigate climate change through secure carbon dioxide storage via mineral carbonation. This study investigates mineral dissolution, precipitation, and their influence on pore structure change during sequestration in basalt formations through batch experiments under controlled conditions (P: 8 MPa, T: 100 °C). The experiments were conducted in an autoclave system containing brine, where basalt sample (2 cm width and 9 cm height) was partially submerged to mimic a CO₂-brine boundary during CO₂ injection in basaltic formation.

CT imaging technique was employed to compare changes in pore structure in basalt before and after the experiment. To evaluate impact of basalt-brine-CO₂ reaction on pore structure, regions of interest (ROIs) were defined, focusing on the reacted zone and the transient zone, where mineral precipitation was most prominent. The reacted zone exhibited the formation of reddish minerals, likely iron oxide minerals, compared to unreacted zone. The transient zone, located at the CO₂-brine interface, displayed the deposition of white minerals. These findings demonstrated that mineral dissolution/precipitation varied spatially, leading to heterogeneous changes in pore structure and fluid flow characteristics. The significant precipitation observed in the transient zone caused pore connectivity reduction, potentially impacting permeability and flow pathways. This study would contribute to an understanding of fluid flow behavior during long-term CO₂ storage in basalt.

How to cite: Han, G., Bang, J.-H., Song, K., Jo, H., Kim, K.-Y., and Kang, C.-U.: Investigating the Impact of Mineral Dissolution and Precipitation on Fluid Flow Characteristics in Basalt After CO2 Injection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15278, https://doi.org/10.5194/egusphere-egu25-15278, 2025.

Permanent storage of CO₂ as carbonates in basalt deposits utilises natural weathering reactions between silicate minerals and carbonic water. By studying how CO₂-enriched water has altered basalt in 43 samples from the Vøring Margin, offshore Norway, we demonstrate the pathways and reactions of CO₂ within a basalt reservoir.

The pore spaces occupied by carbonates in the samples were studied through μ-CT (computer tomography) studies on three minicores and detailed microanalyses on 32 thin sections via scanning electron microscopy (SEM), electron microprobe analysis, and electron backscatter diffraction (EBSD). Single crystal X-ray diffraction on 15 samples determined the type of carbonate minerals and precipitation ages were determined for two samples through U/Pb-radiomeric dating. δ¹⁸O and δ¹³C-isotope analyses were used to determine the fluid origin in 11 samples.

Three types of carbonate precipitation were characterised based on the pore structures they fill and the associated mineralogy. Type I carbonates, seen in 18 thin sections, fills vesicles, mainly along lava flow margins. SEM analyses showed that all vesicles are initially coated with a smectite layer which incorporates most of the Mg²⁺ and Fe²⁺ from dissolving silicate minerals. As pH and Ca concentrations increase, calcite precipitates in some vesicles. The secondary mineral assemblage and precipitation order fit with low-temperature alteration of basalt with pore water and atmospherically balanced CO₂ levels (pH≥8). Type II carbonates appear in seven thin sections as <500μm calcite crystals surrounded by clay minerals in the basalt groundmass. The porous carbonate crystals containing clay inclusions suggest formation through coupled dissolution-precipitation reactions. Thus, Type II carbonates result from the replacement of primary minerals like olivine with mostly clays and some calcite under similar conditions as Type I. δ¹⁸O and δ¹³C-isotope analyses indicate a meteoric fluid origin for the Type I carbonates and U/Pb dating of Type I and II calcites indicates precipitation occurred within 10 Ma after lava emplacement (47.3 ± 6.9 Ma and 43.3 ± 5.1 Ma, respectively). Type III carbonates are only observed in two thin sections and show partial replacement of clinopyroxene by calcite, following micro-fractures in the minerals. Near-complete replacement of olivine by calcite and some siderite through coupled dissolution-precipitation reactions is also observed. This indicates reducing conditions at a slightly higher CO₂ concentration (pH: 6-7) closer to what we expect in a CO₂ injection scenario. EBSD analysis of Type III calcite reveals no clear relationship between the crystal orientation of the calcite and the mineral it replaces. This suggests that chemical rather than crystallographic factors lead to the preferential dissolution of clinopyroxene and olivine over plagioclase. Microprobe analysis indicates varying trends in Ca-substitution within all three calcite types by either Mg (approximately 0-4.5%) or Mn (approximately 2-16%), likely linked to local variations in fluid chemistry or temperature within the reservoir.

In conclusion, the results show that CO₂ storage primarily occurs in vesicles along lava flow margins, but CO₂ can also migrate into the micro- and nano-pore networks of the basalts, enhancing storage potential. Coupled dissolution-precipitation reactions between silicate minerals and carbonates may further increase available storage space.

How to cite: Rosenqvist, M., Dunkel, K., Planke, S., Nogueira, L. P., Polteau, S., and Menegon, L.: Porosity structures and local compositional variations associated with natural CO2 sequestration in basalts offshore Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11073, https://doi.org/10.5194/egusphere-egu25-11073, 2025.

Peridotites and serpentinites (ultramafic rocks) serve as natural reservoirs of Mg²⁺, which can react with carbonate ions during mineral carbonation to form Mg-carbonates and permanently sequester atmospheric CO₂. Whole rock analyses of a large number of ultramafic rocks from various environments show that Ni concentrations in these rocks can reach 10.000 mg/kg^[1]. In contrast, mid-ocean ridge basalts (MORB), also recognized as a promising feedstock for mineral carbonation, have an average Ni content of 200 mg/kg^[2,3].

The fate of Ni during ex situ mineral carbonation is still poorly understood. This issue is critical, as the large-scale application of mineral carbonization may pose ecotoxicological risks by mobilizing specific metallic elements naturally occurring in ultramafic rocks. To elucidate possible Ni mobility during ex situ mineral carbonation, 15 grams of powdered serpentinized peridotite was carbonated in a batch-type reactor for 96 hours at 185°C and a PCO₂ of 100 bar. The experiment resulted in the dissolution of the forsterite and the extensive crystallization of magnesite, demonstrating that the serpentinized peridotite is a highly effective natural material for permanent CO₂ storage in ex situ carbonation processes. Ni released during the dissolution of forsterite was mainly incorporated in newly formed Ni-rich phyllosilicates (more than 98%) and a small portion was mobilized into carbonating fluid (less than 2 %), reaching a concentration of ~18 mg/kg after 96 hours.

We thus recommend monitoring the formation of potential Ni-rich phases during carbonation as well as the concentration of Ni in the carbonating fluids, particularly in future large-scale mineral carbonation projects using ultramafic rocks. Experimental results indicate that both CO₂ sequestration and the synthesis of Ni-rich phyllosilicates can be achieved through ex situ mineral carbonation. Further work is needed to evaluate the stability of the newly formed phases and to assess their long-term potential for nickel immobilisation.

^[1]Kierczak, J., Pietranik, A., & Pędziwiatr, A. (2021). Ultramafic geoecosystems as a natural source of Ni, Cr, and Co to the environment: A review. Science of The Total Environment, 755, 142620.

^[2]Snæbjörnsdóttir, S. Ó., Sigfússon, B., Marieni, C., Goldberg, D., Gislason, S. R., & Oelkers, E. H. (2020). Carbon dioxide storage through mineral carbonation. Nature Reviews Earth & Environment, 1(2), 90-102.

^[3]McDonough, W. F., & Sun, S. S. (1995). The composition of the Earth. Chemical geology, 120 (3-4), 223-253.

How to cite: Cieślik, B., Lacinska, A., Pietranik, A., Pędziwiatr, A., Turniak, K., and Kierczak, J.: Towards a better understanding of nickel mobilization and phase composition changes during ex situ mineral carbonation of serpentinized peridotites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10361, https://doi.org/10.5194/egusphere-egu25-10361, 2025.

Society’s persistent dependence on fossil fuels has resulted in significantly increased atmospheric CO₂ concentration that contribute to severe global warming. It is now essential to remove excess CO₂ from the atmosphere to mitigate climate change. Enhanced weathering offers a promising solution by accelerating natural chemical weathering processes in which atmospheric CO₂ dissolves in rainwater, reacts with rocks, and is converted into alkalinity–effectively storing CO₂ securely over decades. Modelling indicates that increased weathering rates by selecting highly reactive rocks and expanding reactive surface area could remove up to 2 Gt of CO₂ annually [1]. The mining industry, extracts and processes huge tonnages of ore-bearing and overburden rocks, generating large amounts of freshly exposed, reactive surface area which can enable enhanced weathering. Substantial amounts of annual mine tailing and industrial waste production and higher reaction rates due to its relatively hot climate make India one of the most favourable places to implement enhanced weathering research. In India, many ore deposits are hosted by silicate rocks with high proportions of Mg- and Ca-bearing minerals.

Here we report the results of an investigation into the reactivity of Indian mine waste, including chromite mine tailings and peridotite, serpentinite, pyroxenite, and ultrabasic host rock samples from the Sukinda chromite mine in India. We also explore the potential of carbon capture of industrial waste, such as steel slag from the iron and steel industries and coal fly ash from coal-based thermal power plants.  A series of laboratory experiments were conducted whereby crushed rock, slag, and coal fly ash samples were reacted with CO₂-enriched water at room temperature and atmospheric pressure (100% CO₂). XRD, XRF and thin section studies have been conducted on the rock samples and ICP-MS, IC used for chemical analysis of the reaction liquids. Surface area normalized dissolution rates were measured across various grain sizes, mineral compositions, and solution chemistries. Among the mine waste samples, peridotite shows high reactivity with the CO₂-saturated water and reflects the significant potential to sequestrate carbon dioxide (63kg CO₂/tonne rock) in comparison to other host rocks (<5kg CO₂/tonne rock). Additionally, basic oxygen furnace (BOF) slag demonstrated promising future possibilities as an effective carbon capture medium (70kg CO₂/tonne rock) within the human timescale.

[1] Kelemen, P. B., McQueen, N., Wilcox, J., Renforth, P., Dipple, G., & Vankeuren, A. P. (2020). Engineered carbon mineralization in ultramafic rocks for CO2 removal from air: Review and new insights. Chemical Geology, 550, 119628.

How to cite: Maitra, A., Teagle, D., and Matter, J.: Carbon Capture through Enhanced Weathering of Indian Industrial and Mine Waste Materials, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3146, https://doi.org/10.5194/egusphere-egu25-3146, 2025.

Enhanced weathering, in which mafic and ultramafic rocks react with CO₂ to form stable carbonates, is a promising negative emission technology for long-term carbon sequestration. A key challenge that prevents large-scale implementation of the technology is the slow rate of the process. In-situ study of mineral weathering has led to new insights on how to enhance the process, but the equipment required to carry out these experiments has set a high barrier to entry [1]. To address this challenge, we developed a microreactor made from silicon and glass using standard cleanroom processes (Figure 1a) [2]. Our reactor can withstand temperatures and pressures relevant to enhanced weathering [3] and, to our knowledge, we are the first to demonstrate live optical imaging of individual mineral particles during enhanced weathering.

In our experiments, we studied the size and morphology of olivine particles during dissolution in sulfuric acid. Olivine was loaded in the microreactor (Figure 1b) and a flow of 0.1M sulfuric acid was introduced at the inlet using a syringe pump. A second pressure-regulated syringe pump at the outlet maintained a back pressure of 115 bar while the temperature was controlled at 185°C using a heating element.

Preliminary results show two distinct morphological changes: particle shrinkage (Figure 1c) and fracture (Figure 1d). The fracture likely results from stresses generated between the parent mineral and precipitated phases during mineral replacement reactions [4]. Fracturing is hypothesized to enhance the carbonation process by continuously exposing fresh reactive surfaces, leading to a potential millionfold enhancement of reaction rate under certain conditions [5]. While previous studies, such as those by Zhu et. al., have visualized similar fracturing in olivine using in-situ synchrotron X-ray microtomography [1], the reliance on synchrotron facilities has limited the accessibility of such analysis. The microreactor, with its optical transparency, may be a powerful alternative for studying fracturing in real-time without requiring a synchrotron, potentially offering a more easily accessible and cheaper method for investigating fracturing.

Future research will involve exploration of conditions that optimize weathering such as temperature, pressure, pH, and chemical composition. We expect that the microreactor will provide further insight into parameters that control weathering and phenomena like fracture and may lead to strategies to enhance carbonation rates, contributing to the development of more efficient negative emission technologies.

[1] Zhu, W., et al. Experimental evidence of reaction-induced fracturing during olivine carbonation, Geophys. Res. Lett. 2016 .
[2] Kleinsmit, M.H. et al. Microreactor, system and method for investigating a solid-fluid chemical reaction in a microreactor. World Intellectual Property Organization, WO 2025/005863 A2, 2025.
[3] Kleinsmit, L., et al. Microreactors for in-situ study of olivine dissolution rates under conditions relevant to enhanced weathering, Goldschmidt conference, 2024.
[4] Putnis, A. Mineral Replacement Reactions, Rev. Mineral. Geochem. 2009.
[5] Rudge, J. F., et al. A simple model of reaction-induced cracking applied to serpentinization and carbonation of peridotite, Earth Planet. Sci. Lett. 2010.

How to cite: Kleinsmit, L., Loessberg-Zahl, J. T., Vollenbroek, J. C., Tiggelaar, R. M., Bomer, J. G., Knops, P. C. M., and Odijk, M.: Live optical imaging of dissolution of olivine under conditions relevant to enhanced weathering in a microreactor., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15822, https://doi.org/10.5194/egusphere-egu25-15822, 2025.