Mineral carbonation is a sequence of natural processes that can be summarized as a net reaction of carbon dioxide (CO₂) with metal-bearing minerals, producing stable carbonates. The rapid increase in anthropogenic CO₂ emissions has created an imbalance in the carbon cycle which natural mineral carbonation is not able to offset by itself. The severity of the problem now requires the use of an array of carbon sequestration techniques, such as Carbon Dioxide Capture and Storage (CCS) and Carbon Dioxide Removal (CDR) in addition to drastically reduced greenhouse gas emissions. Mineral carbonation has been drawing attention as a potentially sustainable technology to reach carbon neutrality, by storing CO₂ as carbonate minerals that are stable over a long period of time. Thus, many recent studies have focused on characterizing the chemical reactions that occur during mineral carbonation and developing methods to improve its efficiency, however, mostly under laboratory conditions.

The Mariana forearc presents a unique opportunity to study these processes in a natural system, as mineral carbonation occurs as authigenic carbonate precipitates in the serpentinized muds from large mud volcanoes. We analysed samples collected from three serpentinite mud volcanoes – Yinazao, Asùt Tesoru and Fantangisña – during the IODP 366 expedition to characterize the C, O and Ca isotopic composition of these authigenic carbonates. They consist of rhombohedral calcite and aragonite needles and spherulites found predominantly in the core’s top meters. At Yinazao aragonite occurs in the mud volcano’s summit, showing a δ¹³C of ~0±0.9‰, δ^44/40Ca of ~0±0.5‰, and δ¹⁸O ~5±0.3‰, while calcite is found on the mud volcano’s flank, with higher values of δ¹³C and δ^44/40Ca (~2.9±0.08‰ and 1.4±0.06‰, respectively), and lighter δ¹⁸O (~1.7±0.43‰). As for Asùt Tesoru and Fantangisña we also found aragonite needles and spherulites on the mud volcanoes’ flank and summit, respectively, with similar δ¹³C, δ^44/40Ca and δ¹⁸O isotopic signatures compared to the ones from Yinazao.

These results emphasise the importance of these mud volcanoes as ideal models to study mineral carbonation reactions in a naturally occurring system. Importantly, they show that seawater is the major source of carbon for the authigenic carbonate precipitation. This precipitation is the result of the reaction between seawater with the highly alkaline fluids sourced by serpentinization reactions that ascend through the mud volcanoes.

This knowledge highlights the importance of mineral carbonation as a potentially effective approach for both CDR and CCS, as well as the need for further studies in natural systems. Additionally, it shows that understanding how mineral carbonation occurs naturally may be the key to overcoming many of the challenges we currently face when developing efficient carbon sequestration technologies.

How to cite: Freitas, M., Geilert, S., Heuser, A., Wallmann, K., and Magalhães, V. H.: Exploring Carbon Sequestration through Mineral Carbonation in Serpentinite Mud Volcanoes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1143, https://doi.org/10.5194/egusphere-egu24-1143, 2024.

Until recently, efforts to understand the fluid dynamics processes occurring in flowing fractures have generally excluded chemical reactions or only explored one reaction: dissolution or precipitation. This has hindered our progress in predicting the CO₂ storage potential in a given system because it has limited our understanding of in situ carbon mineralization. Identifying the influence of fluid flow in fractures on geochemical reactions is particularly important for CO₂ mineralization in low-permeability rocks, such as ultramafic rocks (e.g. peridotite), which will rely on fractures to act as primary conduits for CO₂ distribution and mineralization. We are working towards bridging this knowledge gap by conducting experiments using an advanced high-P, high-T microfluidics setup that permits real-time visualization of carbon mineralization in a coupled dissolution-precipitation regime under flowing conditions.

In order to understand fundamental regimes of coupled dissolution and precipitation relevant to mineral carbonation, experiments have been conducted in an analog setup where the dissolution of gypsum (CaSO₄) by a carbonate solution is coupled to the precipitation of calcite (CaCO₃). The fracture model used in the experiments included a primary channel and dead ends, which define advection and diffusion-dominated zones. We conducted experiments under different flow conditions, and the results revealed key factors that affect optimal carbonation. The amount, morphology, and geochemistry of carbonate mineralized was strongly influenced by the fluid flow rate. These results suggest that the rate of CO₂ injection could be an important parameter to consider during in situ carbon mineralization operations.

How to cite: Nisbet, H., Chen, M., Neil, C., and Viswanathan, H.: A microfluidic approach to understanding coupled dissolution-precipitation during CO2 storage in fractured systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2945, https://doi.org/10.5194/egusphere-egu24-2945, 2024.

Seismic low-frequency shadow (LFS) is a zone in the seismic data that is characterized by strong anomalously low-frequency energy compared to its surroundings and it occurs beneath a body that strongly attenuates the energy of the propagating seismic waves. LFS can be used as a tool to monitor the migration of CO₂ in a reservoir. To demonstrate this on the Sleipner field, North Sea, where a large amount of CO₂ is being sequestered in the deep saline Utsira Formation. A spectral decomposition analysis of time-lapse 3D seismic data of the Sleipner field, North Sea, was carried out using the continuous wavelet transform. We examined the common frequency stacks corresponding to frequencies 10 Hz, 14 Hz, 30 Hz, and 40 Hz for the occurrence of LFS in the pre-and post-CO₂ injection cases data. We did not find any signatures corresponding to LFS in the pre-CO2 injection
scenario. In the post-CO₂ injection cases, LFSs were detected below the reservoir base at frequencies lower than 30 Hz. It is shown that the seismic low-frequency shadows are not artefacts but occur due to attenuation of the high-frequency components of the propagating seismic waves in the CO₂-saturated Utsira Formation. The low-frequency shadows are localized anomalies at the base of the formation; hence it can be applied to study the behaviour of CO2 when stored in a reservoir.

How to cite: Anthony, E. and Bohlen, T.: Low-frequency shadow (LFS) as a tool for CO2 sequestration of Sleipner field North Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3234, https://doi.org/10.5194/egusphere-egu24-3234, 2024.

Carbon Dioxide Removal (CDR) approaches are essential to achieve the Paris 2015 global warming targets, as emphasized by the Intergovernmental Panel on Climate Change (IPCC) in their reports from 2021 onwards. With European legislation and ethical constraints in mind, a desirable approach to contribute to meeting ambitious climate goals would require to find safe, effective and sustainable storage sites on European territory, e.g. to avoid additional CO₂ footprint for transportation or other processing steps needed.

Given that the (admittedly substantial) storage capacity of Mesozoic sandstones forming the continental socket of wider parts of Europe (with a potential to host 270 Gt of carbon dioxide) has been widely accepted, there still remain doubts that these deep, warm reservoirs are the ideal place for storage of supercritical CO₂, in particular since the overburden strata are heavily fractured and far less impermeable than what would be ideal and safe – let alone the elevated temperatures in several kilometres where Buntsandstein formations encounter conditions where carbon dioxide remains in its supercritical state for geological times. In contrast, oceanic basalts have been demonstrated to host CO₂ both as structural (pore volume) and mineral (precipitation as carbonate minerals) traps in a sustainable manner. In large water depth the CO₂ is stable as pure carbon dioxide, and when dissolved in seawater, the carbonated equivalent is heavier than pure seawater and unlikely to escape.

With that in mind various European regional scenarios have been (re-)visited in order to assess feasibility and potential of storage. We have focused on the North Atlantic Volcanic Province (NAVP) with an estimated volume of extrusives close to 1.8 Mill. km³. The NAVP comprises various mafic and ultramafic regions between Iceland, the UK and Norway, including ocean crust, vesicular basalt and other igneous rock originating from the opening of this part of the Atlantic Ocean. We identified various corridors using ArcGIS Pro in combination with the Carbfix Mineral Storage Atlas and quantified the storage potential and associated cost in case CDR was to be carried out in these areas. Despite the large uncertainty in such numbers, the study serves to compare (among others) the Vøring and Møre basins, the Aegir ridge, Shetland and Faroer islands and neighbouring facies, and the Rockall basin and ridge. Farther from industrial centres we also investigated Iceland and the Reykjanes ridge. The work carried out is part of the AIMS³ project as part of the research mission CDRmare (www.cdrmare.de).

How to cite: Kopf, A., Dunger, M., and Elfil, M.: Marine basalt complexes within reach of Europe – quo vadis?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16924, https://doi.org/10.5194/egusphere-egu24-16924, 2024.

Permanent carbonate mineralisation in basalt is a promising solution for Carbon Capture and Storage of anthropogenic greenhouse gases without the risk of leakage. While this process is known to occur at relatively low temperatures below 100°C, new research on Large Igneous Provinces (LIPs) and young rift basins suggests that much of the thermogenic gases mobilised during contact metamorphism can remain trapped and mineralised in the sills that mobilised them. This discovery is the result of two distinct drilling investigations on land (KARIN) and at sea (IODP Exp 385). It shows that basalts may not only trigger the sudden release of thermogenic gas, but also represent an important carbon sink. The two examples of carbonate trapping in sills presented here are from the Karoo and Guaymas basins. Results indicate that a large fraction of epimagmatic fluids charged with thermogenic gas systematically penetrated inside the sills during cooling. Our numerical solutions suggest that in both cases the higher permeability of the sill acquired during cooling and crystallisation compared to that of its host, ultimately dictates the fate of the thermogenic gas that accumulated in the igneous bodies.

How to cite: Galerne, C., Jörg, H., Cheviet, A., Bach, W., Lenhardt, N., Zhang, J., wiggers, C., Kahl, W.-A., Kopf, A., Buatier, M., and Götz, A.: Natural carbon sequestration process into shallow sill intrusions – numerical modelling, land-based and IODP drilling investigations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9786, https://doi.org/10.5194/egusphere-egu24-9786, 2024.

The basaltic crust attracts increasing attention as a promising lithology for CO₂ storage, due to its common occurrence, its vast storage capacity in pores, and its chemical composition rich in divalent cations - required to bind the dissolved CO₂ in form of carbonate minerals. The availability of divalent cations for carbonate mineralization critically depends on the dissolution kinetics of the basaltic host rock. Numerous laboratory experiments have been conducted on a variety of rock forming minerals to investigate these dissolution kinetics and mechanisms under various experimental conditions. In the case of heterogeneous materials, such as polymineralic rocks, the identification and quantification of rate determining parameters is challenging and requires further investigations.

In our experiments, we analyze the dissolution behavior of an intact, micro-crystalline basalt sample, typical for mid ocean ridge basalts, in contact with CO₂-charged water under temperature and pressure conditions relevant to offshore CO₂ storage. We combine flow-through dissolution experiments with Raman coupled Vertical Scanning Interferometry (RcVSI) in order to obtain spatially resolved images of both the topography and the chemical composition of the rock surface. The consecutive topography measurements by VSI allow us to quantify spatial differences in surface reactivity and examine their relation to chemical and structural properties provided by Raman spectroscopy. The data show significant differences in dissolution rates both between the different minerals and within single phenocrysts. Furthermore, the spatial heterogeneities in surface reactivity indicate an important influence of the rock texture as well.

This combination of measurements provides the means to investigate the dissolution kinetics of polymineralic rocks and to determine differences in the dissolution kinetics of different minerals simultaneously. The results provide important information about rock internal parameters that contribute to the overall dissolution behavior of the rock. The results improve our understanding of dissolution processes that are critical to the efficiency of carbonate mineralization for long-term CO₂ storage in submarine basaltic aquifers.

How to cite: Lange, I., Toro, M., Ostertag-Henning, C., Hansen, C., Lüttge, A., Kopf, A., and Bach, W.: Dissolution experiments on a polyphase basalt surface under conditions relevant to offshore CO2 storage., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18314, https://doi.org/10.5194/egusphere-egu24-18314, 2024.

How fracture initiate and propagate at the nanoscale controls the specific surface area available for fluid-rock interactions. Fracturing creates surface area and flow pathways, which control the flow mixing properties and reactivity. However, how fractures form at the nanoscale in basaltic glasses remains enigmatic. Here, we implement molecular dynamics simulations to reproduce fracture propagation in amorphous basalt. These simulations require large systems and long simulation times and are therefore currently depending on interatomic potentials rather than ab initio calculations. We have developed a machine-learned interatomic potential for basaltic glass that allow using molecular dynamics simulations to simulate fracture propagation at the nanoscale. This interatomic potential reproduces the mechanical properties of bulk solid and molten basalt over a wide range of temperatures and pressures. During a molecular dynamics simulation, bonds are formed and broken as the atoms and ions move. As a result, various species may form and migrate into the glass or towards the surface. In order to study how a basalt surface changes over time we looked at the cation-anion species on the surface and measured how long each species lived on the surface before the coordination changes. Our results show that the process zone around propagating cracks in basaltic glasses at the nanoscale is much larger than for instance when quartz breaks, and that cavities open ahead of the crack tip, and grow with time until they coalesce. A similar propagation process has been observed in fracture experiments on silica glasses at nanometer scale using atomic force microscopy and is reminiscent of the ductile fracturing process observed in metals. By training the interatomic potentials with water and carbon dioxide as fluids, we also aim to study how dynamic fractures may damage a basaltic glass and how the water and carbon dioxide enter these fractures in the wake of rupture. These simulations are relevant for carbon mineralization where a coupling between dissolution of the basalt and precipitation of carbonate minerals may lead to nanoscale fracturing of the rock.

How to cite: Guren, M. G., Sveinsson, H. A., Caracas, R., Malthe-Sørenssen, A., and Renard, F.: Large scale molecular modelling of basalt surfaces and fracturing in basaltic glass, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11861, https://doi.org/10.5194/egusphere-egu24-11861, 2024.

The Nesjavellir high temperature geothermal reservoir, located in southwest Iceland, was one of the test sites for the 'Geothermal Emission Control' (GECO) project. The project involves the reinjection of exhaust gases from geothermal power plants into the subsurface for permanent storage. Numerical modelling and field data from the nearby CarbFix2 storage site at Hellisheiði indicate that even at high temperatures (< 280°C), large quantities of CO₂ can be mineralised. To complement these data, we investigated the potential for CO₂ sequestration in the Nesjavellir reservoir by conducting a 260 °C batch reaction experiment using a basaltic drill core sample and effluent water from the Nesjavellir injection well. We also simulated the experiment using the PHREEQC geochemical modelling program and observed significant inconsistencies between the modelled and experimental results. The experiment produced a secondary mineral assemblage dominated by zeolites, chlorites and anhydrite, with no carbonates observed. In contrast, the model predicted the formation of calcite, which did not occur during the experiment. This discrepancy is due to the model's inability to handle solid solutions and non-ideal phases adequately. During the experiment, Ca was primarily incorporated into anhydrite and a Na-Ca-zeolite, which resembles a solid solution of wairakite and analcime. However, the model did not consider this phase, which resulted in Ca being incorporated into calcite instead of zeolite.

The experimental results are consistent with previous studies that show limited carbon mineralization at higher temperatures (> 180 °C) due to the competition between carbonates and silicates for the uptake of divalent cations. In addition, a comparison with the numerical model shows that simulations of high-temperature CO₂ sequestration can be misleading as they may not be able to reproduce the complexity of non-ideal silicate mineral formation, resulting in an overestimation of carbonate formation.

How to cite: Berndsen, M., Erol, S., Akın, T., Akın, S., Nardini, I., Immenhauser, A., and Nehler, M.: High-temperature CO2 mineralisation in basaltic rocks: Inconsistencies between laboratory experiments and numerical modelling , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16943, https://doi.org/10.5194/egusphere-egu24-16943, 2024.

Basaltic rock dissolution release trace and toxic elements to the aqueous phase; this process has been extensively studied in Icelandic geothermal systems. There is little information regarding their fate as a result of subsurface carbon mineralization. Samples collected from the CarbFix pilot and CarbFix2 monitoring wells at the Hellisheidi geothermal field (Iceland) were measured over time as dissolved CO₂ and H₂S were injected into the subsurface basalts. Results suggest that the release of any trace elements were likely scavenged into several secondary phases, including carbonate and sulfide minerals.

Although these fluids are not meant for human consumption, the aqueous trace element concentrations were generally below the WHO, EU, and Iceland drinking water standards, with a few exceptions. There were peaks in Fe during both injection experiments at the CarbFix pilot site in 2012 that exceeded proposed drinking water values, which were not sustained once the gas injections finished. In addition, As concentrations were significantly elevated at the start of the CarbFix2 gas injection in 2014, but concentrations have since greatly reduced over time to levels at or below drinking water standards although injection continued.

How to cite: Clark, D. E., Galeczka, I. M., Snæbjörnsdóttir, S. Ó., Oelkers, E. H., Sigfússon, B., Gunnarsson, I., and Gíslason, S. R.: Trace metal scavenging from CO2-H2S injection into basaltic rocks at the CarbFix pilot and CarbFix2 sites, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20514, https://doi.org/10.5194/egusphere-egu24-20514, 2024.

Understanding how in-situ mineralization of CO₂ affects the porosity and permeability of the host rock is critical to assessing the viability of basalt reservoirs as carbon dioxide repositories. Precipitating carbonate minerals have the potential to fill primary porespace and decrease permeability, reducing injectivity and overall reservoir capacity. Laboratory experiments that induce carbon mineralization in basalt under controlled conditions can inform how fluid transport properties evolve in geological storage reservoirs.

Here, we present time-resolved 3D datasets acquired using a novel x-ray transparent cell that allows carbon mineralization in basalt to be documented on the grain scale through time using x-ray microtomographic imaging (µCT). Our 4DµCT data aim to document the formation of carbonate mineral species, via ion exchange between dissolved inorganic carbon and the divalent cations of primary minerals in the basalt sample. We use the 4DµCT dataset to track sample deformation, changes in porosity, and to model the permeability evolution on the grain scale. Our 4DµCT data (Figure, below), and other post-reaction analyses, document the in-situ formation of carbonate mineral species.

Our experiments utilise cylindrical cores of basalt with a diameter of 10 mm and a central 2 mm bore and react these with water-dissolved CO_2. The second phase of the experiments is a switch of injection fluid to an aqueous solution of NaHCO₃ equilibrated with CO₂ During the ongoing experiment, the sample has been repeatedly sealed to maintain fluid pressure, disconnected from benchtop apparatus, and imaged using a µCT scanner. 

Exceptionally long operando experiments such as ours can be of particular use in assessing reservoir potential of prospective carbon mineral storage sites by recreating subsurface conditions unique to each location. The apparatus can investigate the evolution of physical rock properties over time periods relevant to field operations (months/years).

How to cite: Watt, I., Butler, I., Fusseis, F., Molnar, I., Gilgannon, J., Haszeldine, S., and Gilfillan, S.: Lab-based assessment of engineered CO­2 mineralization in mafic rock reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21955, https://doi.org/10.5194/egusphere-egu24-21955, 2024.

Carbon capture and storage (CCS) is essential for meeting the UK’s legally binding net-zero targets by 2050. In-situ mineralisaton of CO₂ in mafic rock has been established as a rapid, secure, and affordable method of geological CO₂ storage by the Carbfix projects in Iceland.

In this study, we use geochemical, stratigraphic, and volumetric analyses to assess the suitability of UK onshore mafic and ultramafic formations for in-situ mineral storage of CO₂. We find that the total Mg²⁺, Ca²⁺, Fe_tot. oxide content of some UK formations is comparable to the geological reservoirs utilised by Carbfix in Iceland. We determine the volumes of the studied formations using a combination of boreholes, digitised cross sections and GIS calculated surface areas. We find that there are significant volumes of reactive rock available for CO₂ mineral storage in the UK.

Using a method developed by Callow et al. (2018) we determine the reactive surface area within connected pore volumes in the most suitable formations for in-situ CO₂ mineral storage. Our results indicate that onshore UK formations have the theoretical potential to store multiple gigatonnes (Gt) of CO₂. This is equivalent to the storage of decades’ worth of annual UK industrial CO₂ emissions. 

Our findings highlight that in the Antrim Lava Group alone, there is between 1.6 and 21.9 million km² of reactive surface area available for CO₂ mineral storage. This equates to a potential theoretical CO₂ storage capacity of between 8 and 110 GtCO₂. These results demonstrate that the theoretical CO₂ mineral storage capacity of onshore mafic and ultramafic rocks in the UK far exceeds the CO₂ storage requirement for the UK to achieve net-zero GHG emissions by 2050. Future research efforts should prioritise the investigation of connected porosity, reactive surface area, impact by alteration and mineralisation rates specific to the formations identified by this study.

How to cite: Montgomery, A. W., Holdsworth, C., Martin-Roberts, E., Watt, I., and Gilfillan, S.: The geological potential of in-situ CO2 mineral storage within onshore UK formations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21858, https://doi.org/10.5194/egusphere-egu24-21858, 2024.

Currently, Taiwan is actively spearheading the development of technologies associated with achieving net-zero emissions. The government has set ambitious targets aimed at reducing greenhouse gas emissions and steering toward a more sustainable, low-carbon economy. But suffers from high urbanization and densely populated, the CO₂ sequestration site is still needing careful evaluation. Whether geological sequestration storage or mineralization sequestration, the lab work for feasibility assessment is an indispensable key step before pilot. In this work we build up a tandem reaction system which the autoclave can be used to high-pressure and well-temperature controlled. Continuously flux CO₂ gas to maintain system pressure for simulate carbon dioxide perfusion. A long-term water/rock reactions were performed in different minerals or water bodies. The mass flow controller (MFC) was set up to control the flow rate, while a pressure sensor and a pressure gauge were set up inside the autoclave for on-line and real-time pressure measurements during the experiment. The results were carried out by Scanning Electron Microscope-Energy Dispersive X-Ray Spectrometry (SEM-EDS) and Thermogravimetric analysis (TGA) for evaluating CO₂ mineralization sequestration possibility. Most importantly, this work is a very limited research case for realistic water/rock reaction parameter experiment in Taiwan. We looking forward this contribution to be representative study for further core-flooding experiment.

How to cite: Yang, W.-T., Kao, L. C., and Liou, S. Y. H.: Study on water/rock effect of CO2 mineralization sequestration system development, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20210, https://doi.org/10.5194/egusphere-egu24-20210, 2024.

Subsurface fluid flow and solute transport are pivotal in addressing pressing energy, environmental, and societal challenges, such as the geological storage of carbon dioxide (CO2). Basaltic rocks have emerged as highly suitable geological substrates for injecting large volumes of CO2 with emission reduction and carbon mineralization purposes. This preference is attributed to their widespread occurrence at Earth's surface, high concentrations of cation-rich silicate minerals, reported fast mineralization rate, and often favorable characteristics such as porosity, permeability, and injectivity. The mineralization process within basaltic rocks is intricately linked, involving the dissolution of silicate minerals and the subsequent precipitation of carbonate minerals. During this chemical interplay, silicates play a crucial role by contributing vital calcium (Ca), magnesium (Mg), and iron (Fe) ions essential for the precipitation of carbonate minerals, including Ca-, Mg-, and Fe-carbonates. Understanding the consequences of mineral nucleation and growth in porous media and the fate of subsurface flow and transport necessitates spatial and temporal knowledge of solid precipitation locations and amounts. Only then can the reactive transport models provide precise and realistic predictions on the intricate interplay between transport mechanisms and reaction kinetics and, therefore, advection-diffusion-reaction (ADR). However, accurately representing the dynamics and dimensionality of mineral nucleation and growth in porous media is still challenging. There is a continued need for theoretical development to precisely predict the occurrences where ADR coupling occurs in the space and time domains. We conducted an integrated investigation involving experimental and numerical approaches to gain deeper insights into the spatial distribution of secondary mineral growth. Laboratory experiments under static (batch reactors) and dynamic (columnar flow cells) conditions at elevated pressure and temperature explored variations in aqueous solutes, pH, thermodynamic conditions, and residence time. Despite numerical predictions suggesting the formation of MgFeCa-carbonates in CO2-basalt interactions at higher temperatures, our laboratory findings primarily indicated the growth of calcium carbonates, namely calcite and aragonite. The lack of MgFeCa-carbonates, such as ankerite, siderite, and magnesite, remains elusive but is presumed to be associated with the concurrent occurrence of clay fractions, particularly smectites, consistently observed in batch-type experiments. Columnar flow experiments revealed the spontaneous formation of a limited number of large crystals at various locations, rationalized by the overarching influence of probabilistic mineral nucleation. This underscores the need for a new probabilistic approach to accurately model kinetics and crystal growth distribution in numerical simulations, where dynamic ADR may steer geochemical reactions towards favorable or unfavorable regions in terms of carbon mineralization efficiency.

How to cite: Nooraiepour, M., Masoudi, M., Haile, B. G., and Hellevang, H.: From numerical expectations to experimental observations: Unraveling the complexities in CO2-basalt interactions and mineral growth in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3927, https://doi.org/10.5194/egusphere-egu24-3927, 2024.

The urgent need for net-negative greenhouse gas emissions in the face of climate change is driving the global energy transition. Essential to this transition is the growing demand for critical metals, which leads to the need for more sustainable mining activities. Carbon mineralization via ultramafic-type minerals and tailings is one of the many strategies that can effectively reduce the carbon footprint associated with mining. The process involves the liberation of cations through dissolution and the subsequent precipitation of carbonate minerals to capture and store CO₂ permanently. In this context, the rate and capacity of cation liberation are crucial, dictating the suitability of ultramafic mine wastes for carbon sequestration.

Our earlier research focused on the characterization of 'labile cations,' derived from transient, early-stage dissolutions, which signify a critical aspect of the reactivity and carbon capture potential of ultramafic tailings. Labile cations, predominantly governed by mineral content, are essential for rapid and cost-effective carbon capture using these tailings. Despite recognizing the concept of labile cations, understanding the sources and controls of labile Mg in ultramafic minerals, rocks, and tailings remains limited. Moreover, there is a pressing need for the development of efficient, user-friendly, and cost-effective experimental, numerical, and technical tools. Addressing this, our study employs batch dissolution experiments and data science techniques, including Multiple Linear Regression (MLR) and Principal Component Analysis (PCA), to assess carbon mineralization reactivity. We report on the extraction of labile Mg from various sources such as serpentine, hydrotalcite group minerals, serpentinite, and ultramafic tailings, examining the impact of factors like grain size, ore heterogeneity, and brucite content.

Mineral content is a primary control on labile Mg content. Interestingly, labile Mg content is quite variable within mineral groups. For instance, within the serpentine group, chrysotile and lizardite contribute notably higher Mg than antigorite. Likewise, the reactivity of hydrotalcite minerals is influenced more by the nature of their divalent and trivalent cations rather than by anion species. We also find that the original rock composition and mineral alteration progression are crucial in determining brucite abundance, serpentine type, and labile Mg accessibility. MLR and PCA analysis highlights the critical role of mineralogy and reactive surface area in predicting carbon mineralization reactivity. Overall, the results from this study offer significant advancements in the assessment of carbon mineralization potential in ultramafic mine wastes. These insights are instrumental in refining both ex-situ and in-situ carbonation strategies and extend their applicability to a broader range of alkaline solid wastes for CO₂ capture and storage.

How to cite: Lu, X. and Dipple, G.: The Quantification of Ultramafic Mine Waste Reactivity for Carbon Mineralization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12028, https://doi.org/10.5194/egusphere-egu24-12028, 2024.

To achieve a low-carbon economy, storing carbon dioxide in the Earth's crust by converting it into minerals within basalt rocks is a promising method. This study explores CO₂ interaction with Saudi scoriaceous (SB) and dense (DB) basalts to assess their capacity for CO₂ storage. SB contains augite, olivine, clinopyroxene, and enstatite, while DB is composed of anorthite, augite, olivine, orthopyroxene, and diopside.

SB and DB samples were aged in a supercritical CO₂/brine system at 50°C and 1450 psi for a month. Interfacial tension (IFT) was studied across various pressures at 50°C, and contact angles were measured at room conditions and under the specific conditions of 1450 psi and 50°C. Surface compositional analysis of SB and DB was conducted using scanning electron microscopy (SEM), x-ray fluorescence (XRF), and x-ray diffraction (XRD) before and after CO₂ exposure. Micro-CT scans were performed pre- and post-exposure to assess in situ mineralization. DB, characterized by minimal porosity and permeability, showed potential for CO₂ interaction predominantly on fractured surfaces. However, the DB core sample lacked fractures, so the surface area was the primary place of interaction. In contrast, SB displayed considerable porosity and permeability, indicating a broader area for potential CO₂ interaction.

The results from the IFT measurements revealed a pressure-sensitive pattern, with significant alterations at lower pressures and smaller ones at higher pressures, essential for assessing CO₂ storage potential. Under standard conditions, SB and dense DB exhibited water-wetting properties. However, in a supercritical CO₂/Brine environment, their wettability significantly changed: contact angles increased from 32.9° to 85.8° for DB, and  from 42.6° to 104° for SB, indicating a move towards intermediate water wetness in a CO₂ environment. These results highlight the potential for CO₂ storage in basaltic formations and the complex dynamics of CO₂-brine-rock interactions. Micro CT and SEM analyses showed dissolution, precipitation, and surface variations in the rocks during brine-CO₂ exposure. Specifically, SB demonstrated considerable changes in pore structure and surface, indicating a substantial interaction with CO₂. On the other hand, DB, being non-porous in nature, primarily exhibited surface changes. These post-exposure transformations confirm effective CO₂ interaction with the rocks, further supporting the feasibility of CO₂ sequestration in basalt rocks.

Our in-depth understanding of changes in interfacial tension, wettability, and rock morphology is crucial for safely and efficiently storing CO₂ in basaltic rocks. This knowledge contributes to environmental sustainability and innovative climate change mitigation, marking a significant step towards a greener future in Saudi Arabia.

How to cite: Murtaza, M., Whattam, S., Fawad, M., Saraih, N. A., Kamal, M. S., Abu-Mahfouz, I. S., Hussain, S. M. S., and Kaminski, M. A.: Assessing CO2 Mineralization and Sequestration Potential in Saudi Basaltic Rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20955, https://doi.org/10.5194/egusphere-egu24-20955, 2024.

In the island of Evia (Aegean, Greece), big peridotitic masses crop out in the central and north parts displaying different extents of serpentinization. These rocks were frequently subjected to CO₂-metasomatism [1,2] forming magnesite deposits that have been exploited for several years for industrial purposes (currently by Grecian Magnesite and TERNA Mag companies). The non-carbonated ultramafic rock types mostly appear in the broader areas of Pagondas, Dafni, Psachna, Makrimalli, Artaki and Vatondas. These are predominantly divided into serpentinized harzburgites/lherzolites and serpentinites, whereas scarce occurrences of garnet-bearing serpentinites are rarely evident close to the Pagondas locality in spatial association with rodingites [3]. The mineralogy [mostly serpentine ± (clino- and ortho-) pyroxenes ± olivine ± garnet] and geochemistry (i.e. high MgO, FeO and occasionally CaO contents) of representative rock samples from the Pagondas and Psachna-Makrimalli regions indicate that they can react with carbonated water in order to crystallize carbonate mineral phases. This is also shown by thermodynamic calculations with PERPLE_X software [4], which simulate the natural carbonation of Central Evia ultramafic rocks, revealing that they have the physicochemical potential to form specific carbonate minerals (siderite, magnesite and calcite) at T ≤ ~390^oC. Thus, it is concluded that in Central Evia the petrological properties and relatively high quantities of serpentinized peridotites, offer a potentially viable option for their exploitation as reservoir rocks during in-situ CO₂-storage. These non-carbonated ultramafic outcrops are located proximal to: (a) the Western and Eastern coastline of Evia Island (i.e. ~6 km far from the Evoikos Gulf and ~20 km far from the Aegean Sea), (b) the Central Evia groundwaters [5],  (c) the Edipsos hot-springs in Northern Evia [6] and (d) areas with industrial activities close to the city of Chalkida. Hence, their geographical distribution could contribute to the financial viability of such storage scenarios lowering the logistic costs and contributing to sustainable development through actions for the mitigation of climate change.

References: [1] Karkalis, C. 2022: PhD-Thesis National and Kapodistrian University of Athens, Department of Mineralogy and Petrology, 371p; [2] Grieco et al., 2023: Minerals, 13(2), 159; [3] Karkalis et al., 2022: Lithosphere, 2022 (1): 9507697; [4] Connolly, J.A.D., 2009: Geochem Geophys 10, Q10014; [5] Voutsis et al., 2015: J. Geochem. Explor., 159, 79-92; [6] Kanellopoulos et al., 2016:  Proc. 14th Intern. Congress Geol. Soc. Greece, Thessaloniki, May 2016, 50(2), 720-729

How to cite: Karkalis, C., Magganas, A., Koukouzas, N., and Koutsovitis, P.: Serpentinized ultramafic rocks of Evia Island (Greece) as potential reservoirs for CO2 mineralization based on a petrological research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10093, https://doi.org/10.5194/egusphere-egu24-10093, 2024.