CO2 Mineral Sequestration Research Articles

Modeling Kinetics of CO2 (Carbon Dioxide) Mineral Sequestration in Heterogeneous Aqueous Suspensions Systems of Cement Dust

The necessity to reduce CO2 emission in the environment has encouraged people to search for solutions for its safe capture and storage. Known methods for carbon dioxide mineral sequestration are based primarily on the use of its binding reaction with metal oxides, mainly earth metals. Increasingly important, due to the availability and price, are processes based on the suspension of various wastes such as fly ash, cement dust or furnace slag. Due to the complexity of the mineral sequestration of CO2 in water-waste suspensions, an important issue is to determine the reaction mechanisms. This applies mainly to the initial period of the transformation phase of mineral wastes, and consequently with the occurrence of a number of transition states of ionic equilibria. The mechanisms and reaction rates in the various stages of the process of CO2 mineral sequestration in heterogeneous systems containing selected wastes are defined herein. This paper presents a method of modeling kinetics of this type of process, developed on the basis of the results of the absorption of CO2 thanks to the aqueous suspension of fly ash and cement dust. This allowed for the transfer of obtained experimental results into the mathematical formula, using the invariant function method, used to describe the processes.

A review on ex situ mineral carbonation.

The increased CO2 quantities in the environment have led to many harmful effects. Therefore, it is very important to decrease the CO2 levels in the environment. CO2 capture along with safe and permanent storage using mineral CO2 sequestration method can play an important role to reduce carbon emissions into the environment. Mineral sequestration is a stable storage method that provides long-term storage and an appropriate substitute for the more popular geological storage method. The process is most suited for places where there is a lack of underground cavities for underground geological storage. Minerals rich in Ca and Mg are used predominantly in carbonation reactions. In addition, those alkaline wastes that are rich in Mg and Ca such as cement waste, steel slag and many process ashes can also be employed in CO2 sequestration. Mineral carbonation could be used for the sequestration of billions of tonnes of CO2 every year. However, various drawbacks related to mineral carbonation still need to be addressed, such as resolving the slow rate of reactions, necessity of large amounts of feedstock, decreasing the high overall cost of CO2 sequestration and reducing the huge energy requirements to accelerate the carbonation reaction. This study explores a number of carbonation methods, parameters that control the process and future potential applications of carbonated products.

Mineral sequestration of CO2 from Vernasca Ca-looping demo system: scale up to a pilot

In recent years, carbon sequestration into thermodynamically stable carbonates has been developed as a promising carbon capture, utilization and storage (CCUS) method, especially, when alkaline industrial wastes are used as sorbents. The use of industrial wastes to sequester CO2 plays a dual role in environment protection, creating opportunities not only for capture and disposal of CO2 but also for recycling of wastes and promoting the transition to circular economy. The CLEANKER project (Horizon 2020 Project Clean clinker production by Calcium looping process) aims to build a CO2 mineralization pilot incorporated into Ca-looping demo system in Vernasca cement plant and use the re-carbonated wastes in concrete applications. Different types of wastes such as burnt oil shale (BOS) from Eesti, Balti and Auvere power plants as well as from Enefit280 oil producing unit in Estonia, concrete demolition wastes (CDW), cement by-pass dust (CBD) from Robilante, Italy, blast furnace slag (NSF) from Bremen, Germany were tested first in laboratory scale via dry and wet direct carbonation routes under the conditions of CO2-rich model gas flow of 70 – 100% CO2, simulating the Ca-looping system. The results show that selected types of BOS and cement wastes could be used as efficient binders in both dry and wet CO2 mineralization systems with binding capacities up to 0.18 kg of CO2 per kg of BOS and up to 0.24 kg of CO2 per kg of CBD. The activating effect of hydration as a pre-treatment method showed that at lower operating temperatures, the same level of CO2 capture can be achieved, thereby rendering the carbonization processes of similar industrial wastes more energy efficient. Moreover, the CO2 mineralization tests with BOS in a 46 L concrete mixer confirmed the applicability of wet carbonization process also in larger scale. Based on the results, the most promising materials, BOS and CBD, were selected for in the proposed CO2-mineralization process in wet conditions at ambient temperature. The pilot (200 L) was designed based on a commercially available concrete mixer integrated into CLEANKER Ca-looping demo system and equipped with CO2 inlets and outlets, as well as CO2, temperature and moisture sensors to detect the reaction progress. The re-carbonated wastes will be tested via concrete casting in order to demonstrate the quality of the commercial product in the following stages of the project.

Simultaneous Co2 Mineral Sequestration and Rutile Beneficiation by Using Titanium-Bearing Blast Furnace Slag: Process Description and Optimization

Simultaneous Co2 Mineral Sequestration and Rutile Beneficiation by Using Titanium-Bearing Blast Furnace Slag: Process Description and Optimization

Separation of Products from Mineral Sequestration of CO2 with Primary and Secondary Raw Materials

Rising levels of greenhouse gases (GHG) in our atmosphere make it necessary to find pathways to reduce the amount of GHG, especially emissions of CO2. One approach is carbon capture and utilization by mineralization (CCUM). With this technology, it is possible to bind CO2 chemically from exhaust gas streams in magnesium or calcium silicates. Stable products of this exothermic reaction are carbonates and amorphous silica. Being amongst the biggest emitters of CO2, the cement industry has to find ways to reduce emissions. Geological mapping in Europe has been carried out to find suitable feedstock material, mainly olivines but also slags, to perform lab‑scale carbonation tests. These tests, conducted in a 1.5 L autoclave with increased pressure and temperature, have been scaled up to a 10 L and a 1000 L autoclave. The outcomes of the carbonation are unreacted feed material, carbonate, and amorphous silica, which have to be separated to produce substitutes for the cement industry as pozzolanic material (amorphous silica) or a value‑added product for other applications like paper or plastics (magnesite/calcite with bound anthropogenic CO2). Therefore, a process for the separation of ultrafine carbonation product was developed, consisting mainly of classification and flotation.

Numerical Simulation of Effects of Microbial Action on CO2 Geological Storage in Deep Saline Aquifers

CO2 geological storage (CGS) is a crucial strategy for meeting CO2 emission reduction targets. However, the effect of microbial action on CGS in deep saline aquifer is unclear. In this paper, numerical simulations based on previous experimental data were conducted to investigate CO2 solubility-trapping and mineral-trapping by microbial-mediated process in CGS demonstration base in Ordos, north of China. The simulation results reveal that the presence of a microbial community has a positive influence on CGS, mainly in terms of the amount of CO2 that can be injected and the manner by which it is stored. With the effect of microbial action, the amount of injected CO2 was increased by 23.33% and the CO2 mineral sequestration increased from 1.12 to 2.05%. In addition, microbial action plays different roles at different stages of CGS. In the initial stage of CO2 injection, the microbial action promotes dissolution of calcite, oligoclase and clay minerals such as chlorite and kaolinite, providing a favorable condition (more K+, Ca2+, Na+, Mg2+, Fe2+ and HCO3−) for CO2 mineral-trapping. In the following stage of CGS, microbial action accelerates the precipitation of carbon-fixing minerals such as calcite and siderite, enhancing the CO2 storage security in deep saline aquifer. As such, secondary minerals such as ferroan dolomite and dawsonite were observed in advance in microbially mediated CO2–saline–sandstone interactions, further indicating that microbes play a positive role in CO2 mineral-trapping. Consequently, the microbial action can promote mineral capture of CO2 and increase the CO2 storage security in deep saline aquifer. These conclusions can provide a reference and basis for the suitability assessment of CGS in such deep saline aquifer like Erdos, China.

Carbon-Dioxide and Hydrogen-Sulfide Removal from Simulated Landfill Gas Using Steel Slag

Municipal solid waste landfills are a source of major greenhouse gases such as methane (CH4) and carbon dioxide (CO2) and emit a trace amount of hydrogen sulfide (H2S). Recently, steel slag has extensively been used for mineral CO2 sequestration to minimize the CO2 releases to the atmosphere. This study explores the potential of basic oxygen furnace (BOF) steel slag to simultaneously remove CO2 and H2S from landfill gas (LFG). Various batch and column tests were conducted to evaluate the CO2 and H2S removal potential of the BOF slag under various conditions such as moisture content and particle size of the BOF slag. The three different particle sizes of BOF slag (coarse, as-is, and fine) were exposed to continuous flow of a synthetic LFG [50% CO2, 48.25% CH4, and 1.75% H2S by volume (v/v)] in a column reactor to evaluate the effect of particle size on CO2 and H2S removal capacity of the slag. Similarly, the BOF slag was exposed to synthetic LFG as well as 20% (v/v) of H2S alone in batch reactors at varying moisture contents (10%–30% by weight) to evaluate the effect of moisture content on the CO2 and H2S removal capacity of the slag. A significant H2S removal of 27 g H2S kg−1 BOF slag and CO2 removal of 76 g CO2 kg−1 BOF slag were obtained in the batch reactor. The fine BOF slag (<0.106 mm) showed the maximum CO2 removal (300 g CO2 kg−1 BOF slag) and H2S removal (38 g H2S kg−1 BOF slag) upon exposure to continuous synthetic LFG flow in the column reactor. The quantitative X-ray diffraction (QXRD) analysis showed the highest increase in carbon (77.5 g C kg−1 BOF slag) and sulfur (28 g S kg−1 BOF slag) contents in the fine BOF slag, which was consistent with the mass balance of carbon and sulfur from CO2 and H2S uptake in column tests. The major reaction product with H2S was elemental sulfur depicted by the significant increase in the sulfur content in the X-ray fluorescence analysis. The key minerals involved in carbonation reactions were lime, portlandite, and larnite, as these minerals showed significant reduction in weight percentage (100%, 82%, and 80%, respectively) in the QXRD analysis. Overall, BOF slag showed promising results in mitigating CO2 and H2S from LFG.

CO2 mineral sequestration by using blast furnace slag: From batch to continuous experiments

CO2 mineral sequestration is a promising strategy to combat global warming. Indirect CO2 mineral sequestration was proposed in our previous study by using blast furnace slag as feedstock. As the continuity of this research, the continuous experiment process was carried out in a self-designed rotary kiln, and the results were compared with those of the batch experiment. The results showed that several problematic situations, such as the formation of kiln rings, insufficient mass, and heat transfer, occurred in the continuous experiment. A “returning charge” operation by adding an inert component into the feedstock was suggested for the prevention of ring formation and achieved good results. The reaction conditions for the continuous experiment were harsher than those of the batch experiment due to the scale-up effects. Preliminary analysis of CO2 net-emission reduction was conducted based on the continuous experimental results. It was shown that the net reduction of CO2 emissions amounted to 36 kg for 1000 kg of blast furnace slag processed. The results demonstrated in this study can act as guidance for pilot- or industrial-scale applications of indirect CO2 mineral sequestration technologies, especially for process parameter optimization and equipment design.

The potential of FBC fly ashes to reduce CO2 emissions

The production of electricity and heat in Poland is the reason why the commercial power industry is the largest emitter of CO2. At the same time, significant amounts of solid by-products of combustion, which can be used to bind CO2 by mineral carbonation, are generated during the production processes. The article presents the results of research on mineral sequestration of CO2 (suspension-CO2) using fluidized bed combustion (FBC) fly ashes from hard coal combustion. The analyzed fluidized bed combustion (FBC) fly ashes were characterized by a significant free CaO content (1.7–6.8%) and a high CO2 binding potential ranging from 9.7 to 15.7%. In the case of fluidized bed combustion (FBC) fly ashes suspensions, the basic product of the carbonation process is calcium carbonate, which is clearly indicated by the results of the phase composition determination of solidified suspensions of fluidized bed combustion (FBC) fly ashes. The degree of carbonation, i.e. the degree of CO2 binding, calculated on the basis of the calcium carbonate content, in the analyzed suspensions was up to 1.1%. Mineral carbonation also reduces the leachability of pollutants such as: Zn, Cu, Pb, Ni, As, Hg, Cd, Cr, Cl, and SO42-. The pH is also reduced from about 12 to about 9. Aqueous suspensions of fluidized bed combustion (FBC) fly ashes with introduced CO2 can potentially be used in underground mining. These activities are in line with the concepts of Carbon Capture and Utilization and the idea of circular economy.

In-situ CO2 sequestration and nutrients removal in an anaerobic digestion-microbial electrolysis cell by silicates application: Effect of dosage and biogas circulation

For overcoming high CO2 content in biogas and high NH4+ and PO43− concentrations in digestate of anaerobic digestion - microbial electrolysis cell (AD-MEC), in-situ CO2 sequestration and nutrients removal were investigated in AD-MEC by combined application of wollastonite and magnesium silicate. Wollastonite of 20 g/L and magnesium silicate of 40 g/L was the optimal dosage for CO2 sequestration and nutrients removal in the AD-MEC, which decreased CO2 content from 11.5% to 7.8%, and removed NH4+ and PO43− by 47.4% and 92.1%, respectively, by forming calcite and struvite precipitates. Higher silicates dosage enhanced little in CO2 sequestration and nutrients removal probably owing to the limitation of proton inventory for Ca2+ and Mg2+ release. Biogas circulation slightly deteriorated mineral CO2 sequestration and nutrients removal in AD-MEC, but enhanced CH4 production from 164.8 mL CH4/g CODr to 261.5 ± 5.1 mL CH4/g CODr. Integrating biogas circulation with silicates application in AD-MEC resulted in the CH4 content reached 96.7% ± 0.4%. High-throughput sequencing revealed that Geobacter was the dominant bacterial genus, while hydrogenotrophic methanogens of Methanobacterium and Methanomassiliicoccus dominated in archaeal communities on both anode and cathode in the AD-MEC with silicates addition. In conclusion, the combined application of wollastonite and magnesium silicate is an attractive way to improve the performance of AD-MEC by achieving in-situ mineral CO2 sequestration and nutrients removal.

Soil and geologic formations as antidotes for CO2 sequestration?

AbstractRapid and far‐reaching transitions are required to combat climate change and its impacts. Carbon capture and storage within mineral deposits is a promising solution to remove CO2 from the atmosphere. In‐situ geological storage and ex‐situ mineral sequestration are practically sufficient for sequestering all the anthropogenic CO2. Recent research reports that more than 95% of injected CO2 was mineralized into carbonates in two years by using in‐situ geological approach, and mining wastes and secondary minerals were recycled as resources for ex‐situ CO2 sequestration. However, geological activity is the major risk of in‐situ storage, while high energy consumption and associated cost may limit the application of ex‐situ carbonation. Significant technical breakthroughs of mineral and geological CO2 sequestration are therefore of vital importance to realize a “net‐zero CO2 emissions” and even “carbon‐negative” society.

In-situ mineral CO2 sequestration in a methane producing microbial electrolysis cell treating sludge hydrolysate

Microbial electrolysis cell (MEC) has excellent CH4 production performance, however, CO2 still remains in the produced biogas at high content. For achieving in-situ CO2 sequestration and thus upgrading biogas, mineral carbonation was integrated into a MEC treating sludge hydrolysate. With 19 g/L wollastonite addition, in-situ mineral CO2 sequestration was achieved by formation of calcite precipitates. CH4 content in the biogas was increased by 5.1 % and reached 95.9 %, with CH4 production improved by 16.9 %. In addition, the removals of polysaccharide, protein, and chemical oxygen demand (COD) of the MEC were increased by 4.4 %, 6.7 %, and 8.4 %, respectively. The generated precipitates rarely accumulated on bio-cathode, and did not significantly affect the morphology of cathode biofilm. However, integrating mineral carbonation resulted in a higher relative abundance of Methanosarcina on anode and slightly decreased the ratio of Methanobacterium to Methanosaeta on cathode, which should be noticed. In conclusion, integrating mineral carbonation is an attractive way to improve the performance of MEC by achieving in-situ CO2 sequestration, accompanied with CH4 production enhancement.

An efficient methodology to use hydrolysate of phosphogypsum decomposition products for CO2 mineral sequestration and calcium carbonate production

There is an urgent need to find new, improved ways to reduce CO2 emissions and treat phosphogypsum (PG) waste. This research proposes an energy-efficient methodology for the production of pure calcium carbonate and CO2 mineral sequestration (CMS) by hydrolysate of PG decomposition products. The technical feasibility of this process and the influence of process variables on CMS were investigated using online experiments. Pure calcium carbonate was obtained by CO2 separation and mineralization using the hydrolysis solution of PG decomposition products. A carbonization rate greater than 90% was obtained when the liquid phase absorption reached saturation. In addition, lower temperatures and higher CO2 partial pressures favoured CMS. To confirm the operating strategy underlying calcium carbonate crystallization, real-time experiments data obtained from process analytical technologies (PATs) and solutions of population balance equations were used to determine parameters of crystallization kinetic models. The match between model simulation experiments and online experimental results throughout the crystallization process confirms the robustness of our findings.

A Review of CO2 Storage in View of Safety and Cost-Effectiveness

The emissions of greenhouse gases, especially CO2, have been identified as the main contributor for global warming and climate change. Carbon capture and storage (CCS) is considered to be the most promising strategy to mitigate the anthropogenic CO2 emissions. This review aims to provide the latest developments of CO2 storage from the perspective of improving safety and economics. The mechanisms and strategies of CO2 storage, focusing on their characteristics and current status, are discussed firstly. In the second section, the strategies for assessing and ensuring the security of CO2 storage operations, including the risks assessment approach and monitoring technology associated with CO2 storage, are outlined. In addition, the engineering methods to accelerate CO2 dissolution and mineral carbonation for fixing the mobile CO2 are also compared within the second section. The third part focuses on the strategies for improving economics of CO2 storage operations, namely enhanced industrial production with CO2 storage to generate additional profit, and co-injection of CO2 with impurities to reduce the cost. Moreover, the role of multiple CCS technologies and their distribution on the mitigation of CO2 emissions in the future are summarized. This review demonstrates that CO2 storage in depleted oil and gas reservoirs could play an important role in reducing CO2 emission in the near future and CO2 storage in saline aquifers may make the biggest contribution due to its huge storage capacity. Comparing the various available strategies, CO2-enhanced oil recovery (CO2-EOR) operations are supposed to play the most important role for CO2 mitigation in the next few years, followed by CO2-enhanced gas recovery (CO2-EGR). The direct mineralization of flue gas by coal fly ash and the pH swing mineralization would be the most promising technology for the mineral sequestration of CO2. Furthermore, by accelerating the deployment of CCS projects on large scale, the government can also play its role in reducing the CO2 emissions.

Utilization of phosphogypsum in CO2 mineral sequestration by producing potassium sulphate and calcium carbonate

Industrial activities for the phosphoric acid production cogenerate a large amount of phosphogypsum waste, emitting significant quantities of toxic gas in the surrounding environment. In the context of recovered materials to handle greenhouse gases more precisely CO2 as one of the most toxic gases responsible for the global climate change, an affordable and effective method for CO2 mineral sequestration using phosphogypsum by-product is developed in this investigation. The obtained results show the high efficiency of portlandite Ca(OH)2 resulting from the dispersion of phosphogypsum in alkaline potash solution followed by releasing of potassium sulphate as a co-product. Furthermore, the carbonation experiments show a total conversion of the Ca(OH)2 to calcium carbonate as final product at ambient temperature and atmospheric pressure. The approach suggested in this research shows permanent and safe solution to face the storage of phosphogypsum and carbon dioxide, which were causes a serious problems for the ecosystems and human health. As well as, the valorization of the co-products in different fields, e.g., potassium sulphate as a fertilizer while calcium carbonate has various uses as raw material for construction.

Spontaneous Serpentine Carbonation Controlled by Underground Dynamic Microclimate at the Montecastelli Copper Mine, Italy

Understanding low temperature carbon sequestration through serpentinite–H2O–CO2 interaction is becoming increasingly important as it is considered a potential approach for carbon storage required to offset anthropogenic CO2 emissions. In this study, we present new insights into spontaneous CO2 mineral sequestration through the formation of hydromagnesite + kerolite with minor aragonite incrustations on serpentinite walls of the Montecastelli copper mine located in Southern Tuscany, Italy. On the basis of field, petrological, and geochemical observations coupled with geochemical modeling, we show that precipitation of the wall coating paragenesis is driven by a sequential evaporation and condensation process starting from meteoric waters which emerge from fractures into the mine walls and ceiling. A direct precipitation of the coating paragenesis is not compatible with the chemical composition of the mine water. Instead, geochemical modeling shows that its formation can be explained through evaporation of mine water and its progressive condensation onto the mine walls, where a layer of serpentinite powder was accumulated during the excavation of the mine adits. Condensed water produces a homogeneous film on the mine walls where it can interact with the serpentinite powder and become enriched in Mg, Si, and minor Ca, which are necessary for the precipitation of the observed coating paragenesis. The evaporation and condensation processes are driven by changes in the air flow inside the mine, which in turns are driven by seasonal changes of the outside temperature. The presence of “kerolite”, a Mg-silicate, is indicative of the dissolution of Si-rich minerals, such as serpentine, through the water–powder interaction on the mine walls at low temperature (~17.0 to 18.1 °C). The spontaneous carbonation of serpentine at low temperature is a peculiar feature of this occurrence, which has only rarely been observed in ultramafic outcrops exposed on the Earth’s surface, where instead hydromagnesite predominantly forms through the dissolution of brucite. The high reactivity of serpentine observed, in this study, is most likely due to the presence of fine-grained serpentine fines in the mine walls. Further study of the peculiar conditions of underground environments hosted in Mg-rich lithologies, such as that of the Montecastelli Copper mine, can lead to a better understanding of the physical and chemical conditions necessary to enhance serpentine carbonation at ambient temperature.

Provenance and Sediment Maturity as Controls on CO2 Mineral Sequestration Potential of the Gassum Formation in the Skagerrak

In order to meet the increasing demand to decarbonize the atmosphere, storage of CO2 in subsurface geological reservoirs is an effective measure. To maximize storage capacity, various types of saline aquifers should be considered including dynamic storage options with open or semi-open boundaries. In sloping aquifers, assessment of immobilization potential for CO2 through dissolution and mineralization along the flow path is a crucial part of risk evaluations. The Gassum Formation in Skagerrak is considered a nearshore CO2 storage option with layers shallowing northwards. In this study, petrographic data and provenance analysis provide the basis for estimating reactivity of the sandstones with respect to CO2 immobilization potential. These analyses are integrated with seismic interpretation, well-log analysis and sedimentological observations of sedimentary facies to estimate mineral distribution and corresponding reactivity in the proposed injection area. Here the Gassum Formation comprises south-prograding, shoreface-fluvial para-sequences, sourced from northern hinterlands. Pronounced differences in the mineralogical maturity in the studied area are identified and explained by the sediment transport distances and the type of sediment source. This is possible because the U-Pb ages of zircon grains in the sediments can be used to pinpoint the areas where they originate from in the Fennoscandian Shield, such as Telemarkia (gneissic) or Idefjorden (granitic) terranes. Of special importance are the most reactive mineral phases like albite and Fe-rich chlorite, of which the feldspar occurs in largest abundance and the grain-coating chlorite has largest surface area. Their distribution is partly controlled by provenance, so their abundance decreases basinwards with increasing sediment maturity. The abundance of fluvial sandstones presumably increases northwards in basal parts of para-sequences, while shoreface sandstones comprise the top part of sandy units. CO2 injected in the proposed area will migrate upwards within the reservoir and up-dip along the seal, towards more immature sediments (i.e. higher contents of albite and chlorite) and higher proportions of Telemarkian-derived sediment. Thus, the mineralization potential increases along the migration path, while kinetic reaction rates will decrease in shallower, lower temperature regions. Identifying these parameters is important to estimate the CO2 mineral sequestration potential and ensure safe storage of CO2.

Mineral CO2 Sequestration by Carbonation of Glauberite

CO2 mineral sequestration has significant advantages such as safety and permanence, but its industrial application is limited by high costs. Combining CO2 mineral sequestration with existing industrial processes can make it economically viable by integrating ore extraction, crushing and grinding, and avoiding the construction of new carbonation plant. In this paper, CO2 mineral sequestration was combined with the leaching of sodium sulfate from glauberite. The dissolution behavior and carbonation process of glauberite ore were studied in detail. The influences of key parameters such as ammonia dosage, CO2 pressure and temperature were also investigated. The results showed that under the optimal conditions (ammonia dosage 110%, CO2 pressure 5 bar, temperature 100°C), the carbonation rate of glauberite can reach 93.4%, while the concentrations of sodium ion and sulfate ion were 25.8g/L and 53.8g/L, respectively. The increase of ammonia dosage and CO2 pressure contributed to the dissolution and carbonation of glauberite. Temperature, however, affected them in two very different ways.

Reaction of pseudowollastonite with carbonate-bearing fluids: Implications for CO2 mineral sequestration

The kinetics of silicate carbonation in aqueous solutions are typically sluggish, especially at neutral to alkaline conditions. This hampers the complete understanding of the mechanisms and parameters that control mineral carbonation during carbon capture and storage (CCS). Here we study the hydrothermal dissolution and carbonation of pseudowollastonite (psw; α-CaSiO3), one of the most reactive silicates known, under a range of geochemical conditions ranging from acidic to strongly alkaline pH, presence/absence of different background alkali metal ions and carbonate sources (K2CO3 and Na2CO3, pH ~13, or NaHCO3 and KHCO3, pH ~9). We show that in addition to amorphous silica precipitation, the formation of secondary Na + Ca- or K + Ca-silicates in the presence of Na+ and K+ background ions, respectively, fosters the progress of psw carbonation. However, the formation of Ca-containing secondary crystalline silicates and Ca-containing amorphous silica is shown to be a strong handicap for a fully effective carbonation. In all cases a higher conversion into CaCO3 (up to ~70 mol%) is achieved when using bicarbonate salts (i.e., lower initial pH). By using a reactor with a pressurized CO2-solution, with and without Na+ or K+ background ions, rapid and nearly complete conversion of psw with a CaCO3 yield ~92 mol% is achieved because, in addition to the initial low pH (~3.7) that favored α-CaSiO3 dissolution, abundant Ca-free non-passivating amorphous silica formed along with calcite. These results imply that the presence (e.g., use of sea water during CO2 injection or mixing with saline formation solutions) or the release of different alkali metal ions (e.g., after feldspar and/or basaltic glass dissolution) in combination with a reaction-induced pH increase during in situ CCS scenarios may strongly limit carbonation due to the capture of alkaline-earth metals in secondary silicates and a reduction in reaction rates. In turn, our results show that the high conversion achieved in pure CO2-aqueous systems, while relevant for ex situ CCS, may not reflect the actual conversion in multicomponent natural systems following reactive transport during in situ CCS. Moreover, the precipitation of secondary silicate and calcium carbonate phases have a direct cementing effect, which could be detrimental for in situ CCS, as it would likely reduce host rock permeability, but would be relevant and beneficial for the setting of novel CaSiO3-based non-hydraulic cements with reduced CO2 footprint.

Thermodynamic Modelling and Experimental Validation of CO2 Mineral Sequestration in Mandla Basalt of the Eastern Deccan Volcanic Province, India

Abstract Deccan basalt contains primary silicates rich in Ca, Mg, and Fe ions, suitable for CO2 sequestration. Previous, basalt-water-CO2 interaction studies were focused on other than Deccan basalt types. However, such studies on the Deccan basalt are rare. Thus, present basalt-CO2 water saturated interaction modelling under hydrothermal-like conditions was carried out on the Deccan basalt of the Mandla area to understand apposite pCO2 and time parameters. Modelling results were further validated by experiments run in a laboratory time framework. Present results show negative entropy (ΔS) and enthalpy (ΔfH) that suggest feasibility of plagioclase, pyroxene and magnetite dissolution. Obtained negative Gibb’s free energy (ΔfG), ΔfH and ΔS values for calcite, dolomite and magnesite indicate spontaneous reaction, whereas, positive ΔfG and negative ΔfH and ΔS values of the siderite suggest non-spontaneous and opposing reactions. Calcite is the first carbonate mineral to form, but, at a faster rate. Magnetite dissolution begins after a time lag (not initiated along with the plagioclase and pyroxene). X-ray Powder Diffraction results of post-experiment residues revealed formation of calcite, aragonite, ankerite, huntite, siderite, smectite, chlorite, smectite/chlorite mixed layers and chabazite. Scanning electron microscopic images show tiny calcite crystal growth over the larger calcite crystal and incipient-disordered calcite with imperfections on crystal faces. Thus, basalt carbonation is mainly controlled by time, but temperature, pCO2 and pH played sub-ordinate role. Largely, thermodynamic models do not agree well with the experimental results as numerical models indicate larger carbonate growth. Additionally, transition state theory based models work well to predict dissolution rates for most of the minerals, but, they overpredict growth of the secondary minerals.