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• Applied voltage and calcium addition increased biogas yield and CO 2 sequestration. • Wollastonite and CaCl 2 exhibited different CO 2 sequestration performances. • Wollastonite showed a better CO 2 sequestration effect with 2.22% CO 2 in biogas. • The contribution of chemical and biological CO 2 sequestration was clarified. The combination of microbial electrolytic cells and anaerobic digestion (MEC-AD) became an efficient method to improve CO 2 capture for waste sludge treatment. By adding CaCl 2 and wollastonite, the CO 2 sequestration effect with mineral carbonation under 0 V and 0.8 V was studied. The results showed that applied voltage could increase dissolved chemical oxygen demand (SCOD) degradation efficiency and biogas yield effectively. In addition, wollastonite and CaCl 2 exhibited different CO 2 sequestration performances due to different Ca2+ release characteristics. Wollastonite appeared to have a better CO 2 sequestration effect and provided a wide margin of pH change, but CaCl 2 released Ca2+ directly and decreased the pH of the MEC-AD system. The results showed methane yield reached 137.31 and 163.50 mL/g SCOD degraded and CO 2 content of biogas is only 12.40 % and 2.22 % under 0.8 V with CaCl 2 and wollastonite addition, respectively. Finally, the contribution of chemical CO 2 sequestration by mineral carbonation and biological CO 2 sequestration by hydrogenotrophic methanogenesis was clarified with CaCl 2 addition. The chemical and biological CO 2 sequestration percentages were 46.79 % and 53.21 % under 0.8 V, respectively. With the increased applied voltage, the contribution of chemical CO 2 sequestration rose accordingly. The findings in this study are of great significance for further comprehending the mechanism of calcium addition on CO 2 sequestration in the MEC-AD system and providing guidance for the later engineering application. [ABSTRACT FROM AUTHOR]

Water Flooding (WF) and CO 2 Foam Flooding EOR (CFF) processes are exergy intensive and CO 2 emissive in nature. Hence, the objective of this work is to investigate the ways to attain decarbonization and to evaluate hydrogen requirement for attaining energy transition during WF and CFF processes under different operational conditions. This was performed by using exergy-based evaluation metrics (i.e., Exergy-Return on Exergy-Investment (ERoEI), carbon emissions and hydrogen intensity). It was found that CFF process was 1.69 times more exergy intensive than WF process. Further, for every barrel of oil produced, WF process had net-CO 2 emission of 5.18 kg, while CFF process had net-CO 2 sequestration of 814.5 kg. Moreover, during CFF process, reducing the surfactant concentration from 2.5 wt% to 0.5 wt% had correspondingly decreased CO 2 emissions from 70% to 31%. Further, to attain energy transition during production operations, it was evaluated that WF process requires 1.7 times more hydrogen than CFF process. [Display omitted] • Decarbonization & energy transition was carried out on CO 2 foam flooding EOR process. • Performed sensitivity analysis on various field operations using evaluation metrics. • Manufacturing of surfactants & Injection pumps consumed 66% of total exergy invested. • By using H 2 as fuel source in field operations, the CO 2 emissions are reduced by 62%. • CO 2 foam flooding EOR process sequestrated 27 times more mass of CO 2 than it emitted. [ABSTRACT FROM AUTHOR]

CO 2 sequestration is an effective method for dealing with the global climate crisis, and carbonation curing is considered an effective method of sequestering CO 2 and improving the mechanical properties of cement-based materials (CBM). Regarding modified magnesium-coal based solid waste backfill material (MB), to explore its carbonation curing performance and CO 2 sequestration capacity, its uniaxial compression strength (UCS), carbonation depth, microstructure, CO 2 transport performance, CO 2 uptake capacity, and carbonation efficiency are analyzed and characterized using UCS tests, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) analysis. The results show that the early UCS of the MB is significantly improved by carbonation curing. The UCS at 7 days is 10.91 times higher than that of the MB without carbonation curing, and the UCS increases as the concentration and modified magnesium slag-based cementitious material (MC) content increase. Carbonation curing makes the microstructure of the MB significantly denser and reduces the porosity, pore diameter, and permeability. The formation of carbonated products such as calcium carbonate and hydration products makes the microstructure more compact, which is the main reason for the rapid increase in the early UCS of the MB. The maximum CO 2 uptake capacity of the MB through carbonation curing is 14.3%, and the carbonation efficiency is up to 92.2%. Therefore, carbonation curing of MB has broad application potential in improving the UCS and sequestering CO 2. [ABSTRACT FROM AUTHOR]

A large amount of CO 2 will be emitted after the burning of fossil fuels, causing global warming and glacier melting which will bring a huge threat to the living environment. Atmospheric clearance through the capture, utilization or storage of CO 2 is one of the technologies for dealing with global climate change. In order clarify the mechanization of supercritical CO 2 fracturing, the tight sandstone cores in the Jinqiu Gas field, Sichuan Basin were used to carry out the effect research of supercritical CO 2 on fracture toughness. The results show that after the treatment of tight sandstone on supercritical CO 2 , the degradation degree of I-type fracture toughness decreases by 23.6%−33.6% when the soaking days reach 15 days. At the same reaction time, the fracture toughness under 20 MPa and 60 ℃ is lower by 3∼11% than that under 10 MPa and 50 ℃. Meanwhile, the geometric fracture trajectories of sandstone samples before and after the treatment of supercritical CO 2 treatment are observed. Before the treatment, the S max was 1.46 mm and the fracture angle was 10.24°, but after the treatment, the parameters were 0.93 mm and 3.41°, respectively. The fracture trajectories after multiple polishing were observed by SEM imaging, which shows that the fractures can propagate directly through the mineral particles after the supercritical CO 2 treatment, which causes the transcrystalline fracture. It is conducive to initiating, propagating, and destroying I-type fractures under smaller external loads. The results further improve the mechanism of CO 2 on fracture toughness of tight sandstone, which is useful to explore the feasibility of CO 2 fracturing of low-pressure tight sandstone, and provide theoretical support for the safety of CO 2 fracturing and CO 2 geological sequestration of tight sandstone. [ABSTRACT FROM AUTHOR]

The shells of Pinctada fucata are composed of CaCO 3 and several organic molecules. The organic molecules containing chitin and proteins play a significant role in shell mineralization. Nacrein was the most abundant acid-soluble protein in the nacreous layer of P. fucata. Nacrein has a carbonic anhydrase (CA) domain that catalyzes the reversible conversion of CO 2 to HCO 3 -. A nacre powder (NP) directly obtained from the crushed shells of P. fucata showed CA activity (K m = 3.44 mM and k cat / K m = 920 M−1 s−1). Furthermore, the powder was thermally stable at temperatures over 70 °C and was reusable after the 10th cycle of catalysis. Fluorescence detection showed that nacrein was exposed on the surface of the powder. This result suggested that nacrein was localized on the powder surface and provided CA activity to the powder. The shell of P. fucata is a readily available material because it is industrial waste in the pearl aquaculture. Recently, CA has attracted attention as a promising material for CO 2 sequestration to mitigate global warming. We propose the use of NP as a reasonable and competitive biocatalyst for CO 2 sequestration. [Display omitted] • Nacre powder (NP) was obtained by crushing industrial waste shell of Pinctada fucata. • Carbonic anhydrase activity (CA) was identified in NP. • NP was thermally stable enzyme at temperatures over 70 °C. • NP was reusable after 10 cycles of catalysis. • CA was displayed on the surface of NP and provided CA activity to it. [ABSTRACT FROM AUTHOR]

• The liquid CO 2 -seawater system in unsealed submarine sediments is simulated. • Liquid CO 2 hydrate conversion capacity is identified from driving force and contact ability. • "Comfort zone" for submarine CO 2 hydrate sequestration is identified. • The influences of sediment type and CO 2 -seawater ratio are revealed. CO 2 hydrate provides an important way for the long-term stable way for CO 2 sequestration, but the current understanding of CO 2 hydrate formation behavior from liquid CO 2 and seawater in submarine sediments is still unclear. In this work, we constructed the unsealed submarine sediments and examined the effects of multiple factors on CO 2 hydrate formation from two perspectives: driving force of hydrate formation and CO 2 -water contact ability. "T-p comfort zone" that CO 2 could be more sequestrated as hydrate was identified, and if CO 2 is injected in the appropriate area, the floating CO 2 from deep sediments could always flow in the relatively "comfort zones" and eventually be more solidified. The relations of CO 2 -water distribution and quantity in sediments further determined the hydration rate and capacity. Due to the better dispersibility, the maximum CO 2 storage density of 66.8 kg/m3 in hydrate form was obtained in silt system at 60 vol% CO 2 , which was 60 % higher than the sandy system. The addition of 25 wt% clay inhibited the hydrate quantity to 40 kg/m3. Our results present the friendly CO 2 sequestration conditions and optimized path in unsealed marine sediments. [ABSTRACT FROM AUTHOR]

Hydrate-based CO 2 sequestration (HBCS) under seafloor with huge storage capacity and long-term mechanical stability is attractive for large-scale carbon reduction. However, as representative geochemical constituents of marine sediments, swelling clay minerals still play ambiguous roles in hydrate phase transition and sedimentary structure stability. In this study, pore-scale behaviors of hydrate deposition and reservoir structure evolution in the presence of montmorillonite (MMT), a representative swelling clay, was investigated using low-field nuclear magnetic resonance (LNMR) technique. Total inter-particle interaction energy of 195.4 K b T ensured the dispersion of clay in 0.5 wt% MMT system, which facilitated homogeneous hydrate formation by providing nucleation sites and surface electric fields, improving hydrate conversion from 78.2 % to 89.6 %. Weak water activity caused by strong water absorption of swelling clay resulted in a 14.4 % reduction in CO 2 storage capacity of high-concentration (10.0 wt%) MMT reservoir. Hydrate phase transition accompanied by the migration of MMT particles and liquid water synergistically contributed to sedimentary structure evolution. Migration of MMT-rich fluid with high viscosity could cause irreversible geologic damages by exacerbating sedimentary skeleton deformation. This work reveals the interaction between swelling clay and CO 2 hydrate at microscopic scale, providing new perspectives for effective implementation of CO 2 geologic sequestration in marine sediments. [Display omitted] • Revealing the interaction of swelling clay with CO 2 hydrate from the pore scale. • The presence of montmorillonite improves the homogeneity of hydrate distribution. • Concentrated clay fluids provide mass transfer resistance for hydrate formation. • Clay agglomeration and migration can cause irreversible damage to the reservoir. • A small amount of clay allows for homogeneous and dense hydrate-based CO 2 storage. [ABSTRACT FROM AUTHOR]

• In CO 2 sequestration, pore volume is reduced due to dissolution and pressure. • CO 2 decreases rock's fracture resistance and elasticity. • Pressure during CO 2 sequestration causes new micro-fractures and pores. • High-feldspar rocks show greater dissolution and weakening in CO 2 sequestration. Tight sandstone reservoirs have huge potential for geological sequestration of CO 2. In the process of CO 2 injection, the stability and safety of the reservoir pore structure and physical properties are the basis for CO 2 sequestration. However, due to the interaction between CO 2 -water-rocks, the mineral composition and physical properties of the reservoir can be affected, leading to changes in the pore structure of the rocks and destabilizing the reservoir under high-pressure environments. The changes in pore distribution, rock surface microstructure, and rock mechanical properties of cores with different mineral compositions treated with carbonated water under different confining pressures were investigated through nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and rock mechanics experiments. The effects of the dynamic CO 2 sequestration process on the pore structure of the tight reservoir and the physical properties of the rocks were analyzed. The results demonstrate that following CO 2 injection, the pore volume of the rock decreased due to the generation of debris by chemical dissolution and the plastic deformation of the pore structure was more significant under high pressure, resulting in pore closure and a reduction in pore space. Concurrently, the dissolution of gap-fillers, such as chlorite and kaolinite, between mineral grains in the pore space occurred, and the formation of microfractures. The formation of microfractures decreased the overall stability of the rock. Additionally, feldspar is easily dissolved chemically under CO 2 -water conditions, and this process is more pronounced in rocks with a higher feldspar content. The compressive strength and elastic modulus of these rocks are significantly reduced. Consequently, in the context of CO 2 geological sequestration, it is recommended that rocks with a high quartz content, a low feldspar content, a moderate porosity, and stable physicochemical properties be selected as injection targets. Furthermore, a phased injection strategy should be employed to accommodate the structural changes in the rocks due to pressure and to enhance the injection efficiency, thereby optimizing the long-term geological sequestration of CO 2 and its safety. [ABSTRACT FROM AUTHOR]

Geological CO 2 sequestration (GCS) in shale reservoirs is considered an imperative approach to reducing CO 2 emissions and mitigating greenhouse gas effects, with the wettability of reservoir rocks playing a critical role in this process. In this study, we comparatively investigated the wetting characteristics of H 2 O on the organic matter (graphene) and inorganic matter (hydroxylated quartz) surfaces of shale in a CO 2 atmosphere utilizing molecular dynamics (MD) simulations and focused on elucidating the effects of CO 2 pressure, temperature, and salinity on wettability from the perspectives of the H 2 O droplet contact angle (CA), gas-water density distributions and interaction energy. The results demonstrate that the H 2 O droplet is gradually stripped from the graphene surface by CO 2 with increasing CO 2 pressure, inducing a wetting transition from intermediate-wet to strongly CO 2 -wet, while the hydroxylated quartz surface consistently exhibits a strongly H 2 O-wet state. This significant discrepancy in wetting behaviors can be attributed to the differential adsorption capabilities of CO 2. The hydrophilicity of graphene and quartz surfaces is enhanced with increasing temperature for the given CO 2 pressure condition, and the wettability alteration is more pronounced above the CO 2 critical temperature for graphene, while the opposite is observed for quartz. The H 2 O CA in the CO 2 -H 2 O-shale systems only slightly increases with increasing salinity, which is related to the spatial effect of ions in the brine. The results of this work indicate that the CO 2 -wet feature of shale organic matter during GCS is favorable for the adsorption trapping of CO 2 but unfavorable for capillary trapping, while the opposite is true for inorganic matter. This study sheds light on the phenomena and regularity of the wettability alterations of shale organic and inorganic matter by CO 2 injection, and the results gained are expected to furnish new insights into CO 2 sequestration-enhanced gas recovery (CS-EGR) and gas-water two-phase flow at the nanoscale. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigates the synergistic effects of CO 2 mixing and CO 2 curing on the CO 2 uptake capacity of Portland cement. After a normal mixing or ten minutes of CO 2 mixing, samples underwent 0.5, 1, or 3 days of CO 2 curing at a 10 % CO 2 concentration. Hydration and carbonation characteristics were assessed by means of a thermogravimetry analysis, reacted water and CO 2 uptake measurements, pore solution analysis, X-ray diffractometry, and Rietveld-refinement-based quantification. The CO 2 -mixed samples displayed an escalating trend in terms of CO 2 uptake with longer curing times and greater reaction degrees compared to normally mixed samples. In addition, extended CO 2 curing durations resulted in decreased levels of portlandite and increased amounts of crystalline carbonates, alongside a reduction in the ratio of amorphous to crystalline carbonates. Subsequently, improvements in the compressive strength were noted with longer CO 2 curing durations. • The effects of CO2 mixing and CO2 curing on Portland cement were investigated. • CO2 mixing resulted in increasing trends of CO2 uptake with curing age. • CO2 mixing facilitated the reaction of clinkers at early curing age. • CO2 curing exceeding 1 day strengthened microstructure by larger CO2 uptake. • CO2 mixing and CO2 curing can fix CO2 in cement during fresh and hardened states. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular dynamics was used to study transport of CO 2 -hydrocarbon-H 2 O in shale. • Multiscale shale system with nano and bulk pores was constructed. • CO 2 has better storage potential in inorganic nanopores of shale gas reservoirs. • The swelling effect of CO 2 is significant on light components in the nanopore. • Heavy components tend to be trapped in the nanopore during CO 2 huff-n-puff. CO 2 huff-n-puff (HNP) is an attractive enhanced oil recovery (EOR) technique in shale development due to its low cost, high efficiency, and environmentally friendly feature. Molecular dynamics (MD) simulations have been widely used to investigate the mechanisms of CO 2 HNP process. However, the process of CO 2 HNP is highly complex, involving the CO 2 adsorption and transport in multiscale porous media, while considering the effect of different hydrocarbon compositions of shale oil. In this work, we developed a novel multiscale model (nano + bulk) with the modified Eagle Ford shale oil and water as the reservoir fluid. We investigated the adsorption behaviors and transport dynamics of CO 2 in the CO 2 HNP process. We quantitatively evaluated the CO 2 swelling effect and its miscibility with hydrocarbons. Our results show the preferential adsorption to the graphene wall is pentane < CO 2 < octane. CO 2 can effectively desorb the light and intermediate hydrocarbons from the graphene wall. In addition, CO 2 has good swelling effect and miscibility with the light and intermediate components. Due to the large molecular diameter and the strong interactions with the nanopore wall, the heavy components tend to be trapped in the nanopore after the CO 2 HNP process. However, CO 2 has similar swelling effect on the light and heavy components, indicating that the heavy components in the bulk pore can be effectively swelled and produced. Different from the unstable diffusion edge in the inorganic nanopores, CO 2 has a stable diffusion edge in the organic nanopores. From the adsorption perspective, CO 2 has favorable sequestration performance in the inorganic nanopores in shale gas reservoirs. This work provides a comprehensive understanding of the CO 2 HNP process and practical implications for CO 2 sequestration in shale reservoirs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanical Activation of Red Mud using a high-energy planetary ball mill. • Mechanically-activated Red Mud adsorbs 18.28 mg/g CO 2 (60 ml/min, 5 h) under ambient conditions. • Avrami's Fractional Kinetic Model provides the best fit in the kinetic study, suggesting Physisorption and Chemisorption. • The highest adsorption rate constant, k a is 1.8 h−1, and the lowest desorption rate constant, k d is 6.86 day−1) • The adsorption mechanism involves surface and pore diffusion, along with reactions at active sites. Greenhouse gas emissions and the growing stockpiles of red mud, an alkaline industrial waste with potential for CO 2 sequestration, present significant environmental challenges. This article aims to enhance the CO 2 sequestration capacity of red mud by mechanically activating its surface using a high-energy planetary ball mill for extended grinding periods. The novelty of the study lies in investigating the CO 2 sequestration capacity and evaluating its kinetics includingadsorption and desorption on feed and mechanically-activated red mud under atmospheric temperature and pressure for the first time via a direct gas–solid carbonation route using a fixed bed column. The effect of ball size (10,8 and 6 mm) used in high-energy planetary ball mills while mechanical activation, CO 2 flow rate (20–80 ml/min), and reaction time (1–5 h) on the CO 2 capture has been studied. Apart from this, experimental data on CO 2 sequestered (1–5 h) and the extent of CO 2 desorption (7–35 days) are fitted to various kinetic models, including pseudo-first-order, pseudo-second-order, and Avrami's fractional order models. Results showed that the CO 2 sequestration capacity of feed red mud is 3.75 mg/g, while the capacity of mechanically-activated red mud increased to 18.28 mg/g, with an adsorption time of 5 h at ambient temperature and pressure. The most suitable fit is attained with Avrami's fractional order model, suggesting that both physisorption and chemisorption contribute to enhancing the CO 2 sequestration capacity of red mud. The mechanism for this process has also been proposed along with the suitable characterizations. [ABSTRACT FROM AUTHOR]

Facing the huge gap between the growing CO 2 emissions and net-zero emissions target to mitigate global warming, the long-term storage of excess CO 2 becomes an intractable issue. Sequestering CO 2 in the oceans as clathrate hydrates is a promising solution. Many unanswered questions still exist at the molecular level regarding how ions in seawater kinetically affect the formation of CO 2 hydrates, particularly the dual effect: as the concentration rises, salt ions shift from being a promoter of hydrate formation to becoming an inhibitor. Herein, we report the homogeneous nucleation process of CO 2 hydrates in saline solutions via molecular dynamics simulations. Consistent with experimental findings, our results show that nucleation is promoted within certain salt concentration ranges; however, the evidence suggests that ions do not act as nucleation sites. Multiple ion-induced variations in the aqueous phase are analyzed, including changes in the mobility, structure, and CO 2 solubility. We find that the presence of ions strengthens the hydrophobic interactions among the dissolved CO 2 molecules, which are associated with the salting-out phenomenon, accounting for the promoting effect of salts at low concentrations. However, as the salt concentration increases, this advantage is offset, leading to the inhibiting effect at high salt concentrations. We demonstrate that anions are inevitably involved in the construction of the solid hydrate phase. Their presence disrupts the native tetrahedral connectivity of water molecules and imparts negative charges to the solid phase, thereby attracting cations. In addition to advancing our understanding of the intricate interactions among water, guest, and additive molecules to germinate ordered solid structures, these findings can accelerate the development and utilization of sustainable hydrate-based applications. [Display omitted] • Molecular resolution into CO 2 hydrate spontaneous nucleation in saline solution. • Concentration-dependent dual effect of ions on the formation of CO 2 hydrate. • A new method for tracking hydrate nucleation process. • Ions enhance the hydrophobic interactions among dissolved CO 2 molecules. • Cation and anion exhibit different interference patterns in the growth of hydrate. [ABSTRACT FROM AUTHOR]

• Pressure, temperature, and salinity did not affect residual trapping of sandstone. • CO 2 had higher sweep efficiency compared to N 2. • Residual trapping characteristic curve was independent of gas type. • Rock wettability induced by different gases had minor impact on residual trapping. • Pore structure had a dominant role in gas capillary trapping. Capillary entrapment plays a pivotal role in the long-term and secure storage of CO 2 in subsurface formations. Previous research has indicated that capillary entrapment of gases in porous media is predominantly influenced by the wettability of the rock and its pore structure. However, there is some ambiguity regarding the influence of pore surface hydrophilicity and pore structure on the efficiency of gas capillary entrapment. Certain literature has reported comparable gas entrapment efficiencies for different gas types within the same rock, despite the change in rock wettability due to different fluid pairs. Conversely, other studies suggested that gas capillary entrapment efficiency is contingent upon the type of injected gas. Therefore, this study aims to investigate gas capillary entrapment efficiency using different gases, specifically CO 2 and N 2 , in rocks exhibiting varying degrees of hydrophilicity and pore structure, namely sandstone and carbonate rocks. High-pressure, high-temperature core flooding experiments were conducted to examine drainage/imbibition cycles under reservoir conditions. Gas saturation profiles along the core length were derived from X-ray scan results obtained during the experiments, while contact angles were measured to quantify rock sample wettability under experimental conditions. In-depth characterization of the rock samples was achieved through NMR surface relaxometry measurements to ascertain pore size distribution and average pore sizes, along with the collection and analysis of thin sections to obtain two-dimensional images for further insights into pore and pore throat sizes. Our findings suggest compelling evidence that gas type does not significantly influence gas residual trapping efficiency in the tested sandstone and carbonate rocks but does impact sweep efficiency within the rock. Furthermore, residual trapping efficiency increased under conditions favoring snap-off trapping, characterized by a high pore body-throat aspect ratio. Thus, while changes in rock wettability due to different injected gas types had negligible effects on the capillary trapping efficiency of specific samples, pore structure emerged as the predominant factor. [ABSTRACT FROM AUTHOR]

The increasing CO 2 emissions from heavy industries have presented a growing threat to the global environment. The critical solution is to develop CO 2 sequestration technologies, especially the fast speed CO 2 fixation methods. In this study, the CO 2 uptake performances of hydrated cement paste under various environment parameters coupling with high temperature were evaluated through accelerated carbonation experiments. The results show that high temperature is an effective way to improve CO 2 sequestration efficiency, in which the waste heat accompanied by the emitted CO 2 can be used as the source of high temperature. Based on this, appropriate vapor and liquid water addition during carbonation can further improve the CO 2 sequestration performance of powder samples. Moreover, the hydration and carbonation products and the porosity before and after carbonation were evaluated, high temperature and vapor acceleration method facilitated aragonite generation and higher porosity reduction. Scale-up test of recycled aggregates on CO 2 sequestration under optimum carbonation conditions was evaluated, and the results show the CO 2 sequestration performance of recycled aggregates was stable in different input scales, which could sustain the CO 2 sequestration amount of 80kg/t-cem. [ABSTRACT FROM AUTHOR]

Dark fermentation of cheese whey (CW) for the production of biohydrogen generates an acidic effluent, containing high concentrations of volatile fatty acids, which needs to be further treated before disposal and possibly further valorised. This study develops a dual-chamber Microbial Electrolysis Cell (MEC) that achieves simultaneously the reduction of the organic content of this effluent to environmentally acceptable levels, along with bio-electrochemical reduction of CO 2 to CH 4. The MEC was operated for 140 days and the effect of the following conditions on the MEC performance was examined: (a) the feed concentration of the acidic fermentate (in the range 6–81 g COD /L), (b) the conductivity of the feed modified via KCl addition (range 2–22 mS/cm), (c) the MEC operation mode (with or without catholyte renewal) and (d) the solids content (modified via CW filtration prior to its use). The results showed that high COD removal (>95 %) was achieved in all cases, along with a CH 4 production of up to 1.1 mmol/g CODconsumed. The best performance of the cell was obtained for a feed COD concentration of ∼30 g COD /L and a feed conductivity of ∼15 mS/cm; these conditions resulted in a COD removal exceeding 99 %, a CH 4 production of 1.1 mmol CH4 /g CODconsumed and a net energy production of 15.8 % compared to the energy demand of the system. The electrochemical study of the system revealed that higher and lower feed COD concentrations were characterized by higher internal resistances. The results indicate that the MEC can be exploited for further treatment and valorization of a high-strength effluent along with the production of CH 4 with an energy surplus, as an efficient waste-to-energy technology. [Display omitted] • High organic load removal was achieved in all cases (>95 % COD removal). • Energy gain reached up to 199 % relative to the expenditure due to applied potential. • Optimal performance was obtained at moderate conditions (30 g COD /L, 15 mS/cm). • Catholyte renewal enables treatment of the undiluted (63 g COD /L) waste. • Fermentative bacteria contained in the acidified cheese whey inhibit MEC operation. [ABSTRACT FROM AUTHOR]

• Direct synthesis of N-doped porous carbons (PCs) using PAN and NaNH 2 simplifies production. • Optimized sample PN-3 shows a high specific surface area (SSA) of 2490 m2/g. • PN-3 exhibits significant CO 2 adsorption: 7.15 mmol/g at 273 K, 4.56 mmol/g at 298 K. • Outstanding CO 2 /N 2 selectivity (∼102) surpasses many other N-doped carbons. • Modest heat of adsorption (39.10 kJ/mol) allows energy-efficient regeneration. N-doped porous carbons (PCs) are extensively researched for CO 2 capture and separation under flue gas conditions, but their complex and expensive preparation methods hinder widespread industrial use. Herein, we present a direct approach for synthesizing N-doped PCs by utilizing polyacrylonitrile (PAN) and NaNH 2 as precursors, without the need for any solvents. The utilization of NaNH 2 as both a porogen and nitrogen supply during carbonization is primarily responsible for the formation of the well-developed pore structure and high specific surface area of N-doped PCs. The optimized sample "PN-3" demonstrated excellent textural features with an excellent specific surface area (SSA) of 2490 m2/g, a pore volume of 2.0559 cm3/g, a well-defined pore size distribution (PSD), and abundant micropores (<1 nm). In addition, PN-3 has the highest pyrrolic nitrogen content (∼40.1 at.%), resulting in a significant capacity for CO 2 adsorption (7.15 mmol/g at 273 K/1bar, 4.56 mmol/g at 298 K/1 bar, 26.2 mmol/g at 298 K/ 40 bar). Furthermore, it exhibits an outstanding CO 2 /N 2 selectivity (∼102) based on the ideal adsorbed solution theory (IAST) at 273 K, surpassing the performance of most of previously reported biomass and polymer-derived N-doped carbons in terms of CO 2 adsorption and separation. In addition, the adsorption process is characterized by a modest heat of adsorption (39.10 kJ/mol) and a steady cyclic pattern of CO 2 adsorption–desorption under flue gas settings (15 % CO 2 and 85 % N 2). This indicates that the adsorption is mostly governed by physisorption, which allows for an energy-efficient regeneration process. In summary, this study showcases the successful production of highly PCs that can effectively adsorb CO 2 , enlightening the way toward establishment of a cost-effective and facile synthetic protocol for achieving CO 2 capture/separation at the commercial scale. [ABSTRACT FROM AUTHOR]

This study evaluated the role of cellulose nanofibers (CNF) in reducing the carbonation degradation of alkali-activated slag (AAS) samples. AAS samples prepared with different dosages of CNF (0 %, 0.10 %, and 0.80 % by weight of the binder) were exposed to natural and accelerated carbonation for up to 90 days. The effects of carbonation on the microstructure of AAS paste samples were monitored using FTIR, XRD, TGA, MIP, and BSE/SEM. It was observed that after 90 days of natural carbonation, the control batch exhibited a reduction in compressive strength, whereas the CNF batches showed an enhancement. Notably, the CNF-containing batches maintained consistent strength over time, with no reduction in strength. Similarly, after 90 days of accelerated carbonation, CNF 0.10 % and CNF 0.80 % showed an increase in compressive strength compared to the control batch. Despite this enhancement in compressive strength, microstructural studies indicated that the addition of CNF increased the extent of carbonation, leading to a higher amount of CaCO 3 formation and C–S–H/C-A-S-H decalcification compared to the control batch. The beneficial effects of CNF on the strength despite increased C–A–S–H decalcification are attributed to their reinforcing effects and the ability to form composites with CaCO 3. [ABSTRACT FROM AUTHOR]

CO 2 injection into unconventional gas reservoir has been recognized as a promising approach to enhance unconventional gas recovery (CO 2 -EUGR) and sequester CO 2 geologically. The CO 2 -EUGR is a complex multi-physics coupling process. To accurately assess the effectiveness of different injection strategies, this paper firstly presents a non-isothermal compositional two-phase flow model coupling with geomechanics, in which a multicomponent adsorption kinetics is incorporated to separate free phase and adsorbed phase. A hybrid numerical approach combining EbFVM and GFEM is used for numerical solutions. The performance of different injection strategies for CO 2 -EUGR is evaluated. The results indicate that CO 2 injection is able to improve CH 4 recovery significantly, over 90 % of injected CO 2 can be adsorbed in reservoirs, The performance of CO 2 -EUGR is permeability dependent, the displacement effect occurs earlier when reservoir permeability is higher; Increase in temperature of injected gas and mixed CO 2 /N 2 injection can further improve CH 4 recovery, especially for low permeability gas reservoirs; Mixed gas injection also enables displacement effect to occur earlier; Cyclic injection can hardly lead to increase in CH 4 production, especially when reservoir permeability is higher, while it can cause an increase in amount of adsorbed CO 2 during injection period. Based on these findings, a geothermal-assisted CO 2 -EUGR method is proposed. • An efficient non-isothermal compositional model coupling with geomechanics is developed for CO 2 -EUGR. • The performance of different CO 2 injection strategies is evaluated quantitatively. • The occurring of displacement effect and performance of CO 2 -EUGR depend on reservoir permeability. • Increasing temperature of injected gas and mixed CO 2 /N 2 injection can further improve CH 4 recovery. [ABSTRACT FROM AUTHOR]

The persistently high global CO 2 emissions are exacerbating the greenhouse effect issue. Scientists have explored methods such as carbon sequestration via subsea hydrate formation in response to global warming. However, this method faces a series of challenges when injecting CO 2 on a large scale, including the slow formation rate of CO 2 hydrates and potential leakage risks. Specially, the direct injection of promoters could lead to excessively high concentrations of additives close to the injection wells. This would consequently accelerate the local hydrate conversion, potentially causing reservoir blockage problems. The current study proposes a novel strategy involving additives that exhibit varying effects with concentrations. The high-concentration areas close to the wellbore can maintain the permeability by inhibiting hydrate formation; while the reduced concentration further away upon gas migration facilitates the rapid formation of CO 2 hydrates. We successfully demonstrate the spatial and temporal differences in hydrate formation when using such additives. This can also facilitate the rapid formation of a dense hydrate cap layer over the reservoir, potentially preventing the leakage of CO 2 gas. A new type of additive based on egg albumin was developed, which possesses the dual function and exhibits good biocompatibility and specific reservoir stability. • Spatial and temporal differences in the formation of CO 2 hydrates were identified. • A dual-function additive for hydrate-based carbon sequestration was proposed. • The additive was effective in maintaining the reservoir mechanical stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The displacement behavior of different fluids at the pore scale is visually demonstrated. • The CH 4 spatial and temporal distribution rules in different pore spaces are characterized by NMR. • The dispersion properties of different displacing fluids are investigated. • The entrance/exit effect leads to an expansion of the CO 2 dispersion coefficient by 11.3 % to 23.4 %. Visual characterization of the spatial and temporal distribution patterns of displacing fluids and CH 4 within the pore space and exploration of the differences in sweep effect on CH 4 are key to predicting the scale of CO 2 geological sequestration and production capacity within the reservoir. There are large differences in the displacement efficiency of CH 4 in the pore space by different components of the displacing fluid. In this study, the more cost-effective displacing fluid injection scheme is explored on the basis of CO 2 sequestration and enhanced gas recovery. Thus, the displacement behavior and dispersion characteristics of CO 2 , gas mixture (50 % CO 2 + 50 % N 2) and N 2 at the pore scale are investigated. N 2 has the highest overall sweep efficiency during displacement, but it also causes the greatest degree of mixing. In contrast, liquid and supercritical CO 2 has the weakest diffusion ability and the lowest overall sweep efficiency on CH 4 , but cause the least mixing. In addition, it is found that the dispersion coefficients of all three displacing fluids become smaller with increasing pressure, with the entrance/exit effect causing the CO 2 dispersion coefficients to increase by 11.3 % to 23.4 %. [ABSTRACT FROM AUTHOR]

Exploitation of natural gas hydrates provides an alternative way to address energy crisis. Dilute CO 2 gas (13–30mol%CO 2 with remaining N 2 /Air) injection into CH 4 hydrates for hydrate swapping (SW) allows cheaper and more practical CH 4 recovery and in-situ CO 2 sequestration. However, the roles of N 2 /Air in dilute CO 2 gas during exploitation remain unknown. It is unclear whether depressurization should be coupled after SW and continued below CH 4 hydrate stability pressure. This work employed multistep depressurization (MD) to dissociate the mixed hydrates formed after SW from 86.5 to 97.9 bar at 0.7–1.2 °C in bulk-water and sandpack with CH 4 hydrate saturation of 4.1–25.3 %. Effects of N 2 /Air on exploitation were investigated by examining hydrate morphologies and gas compositions. Morphological results in bulk-water indicated higher N 2 fraction in 20mol%CO 2 /N 2 triggered more CO 2 -rich hydrate reformation and CH 4 -rich hydrate dissociation. Exploitation results in sandpack indicated 13mol%CO 2 /N 2 produced the highest CH 4 swapping percent (46.6 %) and CO 2 hydrate sequestration percent (29.1 %). Air exerted weaker promoting effects on exploitation compared with equivalent N 2. The promotion of N 2 /Air on exploitation was dominated by dilute CO 2 gas injection altering mixed hydrate equilibrium which varied with time-dependent gaseous compositions during MD. l -methionine of 3000 ppm had stronger promoting effects on CO 2 sequestration in sandpack than bulk-water depending on mass transfer and water availability. Ceasing points (13.9–31.4 bar) suggested MD could be continued below CH 4 /above CO 2 hydrate stability pressures and before water production. For the first time, this study provided insights into the roles of N 2 /Air to determine injection gas types and depressurization schemes for efficient and safe hydrate exploitation in gas-rich hydrate-bearing sediment. [Display omitted] • The roles of N 2 /Air in exploitation of CH 4 -rich hydrate are studied. • CO 2 -rich hydrate reformation above CH 4 hydrate stability pressure is observed. • CH 4 -rich hydrate dissociation above CH 4 hydrate stability pressure is observed. • l -methionine of 3000 ppm efficiently enhances CO 2 sequestration in low-water system. • Ceasing points of multistep depressurization are decided in bulk-water and sandpack. [ABSTRACT FROM AUTHOR]

In this present investigation, the freshwater microalga Nannochloropsis oculata TSD05 was used to demonstrate multiforius environmental applications viz., bioremediation of tannery effluent, carbon sequestration, and green renewable biodiesel production from treated microalgal biomass. The microalga Nannochloropsis oculata TSD05 was exhibited unique heavy metal reduction capabilities and reduced significant amount of heavy metals viz., 96.62% of copper (Cu2+), 99.9% of chromium (Cr3+), 98.36% of zinc (Zn2+), 98.71% of cadmium (Cd2+), 97.96% of lead (Pb2+), 98.88% of Cobalt (Co2+), and 98.76% of nickel (Ni2+). The biosorption capacity rate (q max) of heavy metals reduction and highest R2 of 97.84% exhibited at 12 days of effluent treatment by Langmuir and Freundlich isotherm models. The phytotoxicity analysis was tested againt treated tannery effluent using Vigna radiate, Sapindus muukorossi seeds and 98.45%, 99.05% seeds were germinated. The Nannochloropsis oculata TSD05 microalga was utilized 98.45% of CO 2 by biofixation kinetics, 372 mg g−1 of lipid, 3.65 mg mL−1 of biomass and 4.64 mLg−1 of biodiesel were produced. The produced biodiesel was confirmed and identification of 18 fatty acid methyl ester (biodiesel) compounds using GCMS. The recognition of 17 functional groups was identified using FTIR analysis and the microalga Nannochloropsis oculata TSD05 potential for sustainable and renewable green energy production. The potential future application of Nannochloropsis oculata TSD05 is to increase lipid production and biodiesel yield. Scaling up the bioremediation process can also validate these microalga's feasibility for use in wastewater treament. Enhancing heavy metal biosorption and carbon sequestration efficiency through genetic engineering could also maximize environmental benefits. [Display omitted] • Nannochloropsis oculata TSD05 strain achieved 97.84% heavy metals biosorption from tannery effluent. • Nannochloropsis oculata TSD05 utilized and sequestered 98.45% of carbon dioxide. • The microalgal biomass produced 3.65 mg mL−1, 372 mg g−1 lipid yield, and 4.64 mL/g biodiesel. [ABSTRACT FROM AUTHOR]

• Sealing mechanism of ultra-high T/P CO2-rich reservoirs analyzed in the South China Sea. • Hydraulic failure occurred after the capillary failure. • Capillary leakage is not effectively reducing reservoir pressure. Global industry drillings targeted at deep-burial hydrocarbons have renewed the record of maximum sustainable overpressure in sedimentary basins. However, the influence of extremely high overpressure on natural fluid accumulation and artificial waste sequestration is not yet completely understood. To better understand the motion characteristics of the highly overpressured CO 2 -rich fluid, the CO 2 retention capacity was quantified, and the CO 2 -rich fluid motion trails were evaluated in an ideal natural laboratory in the Yinggehai Basin. The hydraulic sealing capacity was higher than the capillary sealing capacity in the highly overpressured stratum. Relative to the situations of no breach or solely breached by capillary failure, the superposition of capillary and hydraulic failures resulted in the caprock integrity breakage by faults (or fractures), diapirs, and pipes. Meanwhile, the high expulsion flux of CO 2 -rich fluid caused the consumption of chlorite to generate illite in the caprock of dual-breached fields. The CO 2 -rich fluid flux of capillary invasion was limited by the inherently low permeability of caprock, which may be insufficient for a dramatic change of hydrogen ions or electron activities to induce remarkable chlorite dissolution in the caprock of the sole-breached field. [ABSTRACT FROM AUTHOR]

Coal-fired power generation has always been a major energy supply source globally. However, a large amount of CO 2 is emitted with the combustion of coal resources, and fly ash, a by-product of coal combustion, is also accumulated in large quantities. The application of CO 2 mineralization in fly ash can not only reduce CO 2 emission but also effectively manage industrial waste, thereby promoting environmental sustainability. This paper used the mechanical ball milling method to activate fly ash and investigated the effects of ball milling time and speed on the CO 2 sequestration in fly ash. At 30 min ball milling time and 400 r/min ball milling speed, the modified fly ash achieves a good CO 2 sequestration capacity of 81.70 g CO2 /kg FA. Compared with raw fly ash, the CO 2 consumption of treated fly ash is higher at 75.41 mmol/mL. The specific surface area and pore volume of treated fly ash are larger at 1.57 m2/g and 4.33 cm3/kg respectively, which is beneficial for enhancing mass transfer capacity and the carbonation effect. As the ratio of mineralized product/coal increases from 0.5 to 4, the crossing-point temperature increases from 157.20 °C to 165.15 °C. Based on the experimental results, the paper discussed the mechanism of ball milling activation to enhance the carbonation effect of fly ash. This study provides theoretical references for the environmentally friendly utilization of fly ash. [Display omitted] • The CO2 mineralization behavior in fly ash by mechanical activation was studied. • Effects of ball milling time and speed on physicochemical properties in fly ash were analyzed. • The application potential of mineralized product produced by treated fly ash was discussed. [ABSTRACT FROM AUTHOR]

The magnesium tailings, whose main phase composition is serpentine [Mg 3 Si 2 O 5 (OH) 4 ], has lower reactivity than common minerals and solid waste, but rich magnesium content. It is of great significance for CO 2 emission reduction and ecological environment protection to solve the problem of low leaching rate and carbon sequestration efficiency of Mg2+ in the tailings. The strengthening effect of external field (microwave and ultrasound) and pretreatment (impregnation-calcination) on leaching of magnesium tailings and its mechanism were studied, which significantly improved the leaching efficiency of Mg2+ in tailings. The idea of CO 2 heterophase absorption and sequestration was put forward, and the efficient of CO 2 mineralization was achieved by using the leaching product, magnesium-rich leaching solution. The results showed that pretreatment of impregnation and calcination and external field (microwave and ultrasound) could promote the leaching reaction of magnesium tailings. Reaction mechanism analysis showed that microwave can accelerate the reaction rate, pretreatment and ultrasound induction can reduce the adverse effect of product layer on the reaction, and promote the leaching of Mg2+. The optimum leaching parameters (acetic acid concentration of 4 mol/L, temperature of 80 °C, liquid-solid ratio of 20, tailings particle size <125 μm, microwave power of 1000 W and ultrasound power of 500 W) were determined, and 66.64 % of Mg2+ leaching efficiency was achieved in 120 min. The CO 2 heterophase absorption and sequestration method achieves high level fixation of CO 2 from gas phase to solid phase at normal temperature and pressure, and forms a carbon sequestration product MgCO 3 ∙3 H 2 O with long-term stability. • Impregnation-calcination coupling microwave and ultrasound promote tailings leaching. • A novel process for converting CO 2 to MgCO 3 ∙3H 2 O is proposed. • Efficient CO 2 sequestration is achieved for magnesium tailings under mild conditions. [ABSTRACT FROM AUTHOR]

CO 2 sequestration in geological formations is an efficient step towards mitigating climate change by reducing global warming. The CO 2 emitted from natural sources and anthropogenic activities is injected into geological formations. The flow and transport of CO 2 during sequestration operations require in-depth knowledge of the effects of the type of geological formation. The present work analyses the CO 2 migration and storage in a heterogeneous deep saline aquifer with variable porosity and evolving permeability under non-isothermal flow conditions while upscaling the capillary pressure using the Leverett J-function. The developed numerical model is history-matched with CO 2 gas saturation profiles reported using analytical and numerical approaches. The novelty of the present work lies in its ability to capture fine-scale heterogeneities in the aquifer, which is modelled through variation in the porosity (ϕ) distribution and the permeability (k). The thermal-hydraulic numerical analysis projected a pronounced effect of the degree of heterogeneity arising from the variation in porosity and permeability on pressure buildup along the top of the formation decreasing from a maximum of about 6.41 MPa at the injection well to about 0.933 MPa at 1200 m and affecting gas characteristics and transmission. The thermal front could only propagate to a maximum extent of about 142 m from the injection well in aquifers, while gas plume lengths migrated to a maximum plume length of about 1010 m. The permeability and porosity of the aquifer are critically observed to vary during the sequestration by a ratio (k/k 0) of about 1.07 to 1.01 and a percentage of about 0.791 % – 3.136 % in the low permeable conditions. Maximum effective storage of CO 2 by a factor of 0.95 observed in low-permeable heterogeneous aquifers with normally distributed porosity affirms maintenance of optimum gas injection rates below the fracture gradient in these formations to sequester the CO 2 economically. • The present work analyzes numerically the effect of formation heterogeneities on field-scale CO 2 sequestration. • Higher aquifer permeabilities promote gas migration with maximum plume length for uniform random distribution. • Pore pressure buildup in heterogeneous aquifers affect the lateral gas migration in the bottom zones. • Modification in porosity, permeability and effective storage of CO 2 are higher for low-permeable heterogeneous aquifers. [ABSTRACT FROM AUTHOR]

The hydrate-based CO 2 sequestration provides an alternative solution for reducing CO 2 emissions. However, the hydrate film that forms preferentially at the CO 2 -water interface can severely restrict hydrate conversion rate. How to enhance CO 2 hydrate formation remains a crucial question. Here, we constructed static and shear flow contact models of liquid CO 2 and brine in a cubic cavity and investigated their hydrate growth behavior at different subcoolings from perspectives of morphology and kinetics. For static contact, nucleation usually occurs at the CO 2 -brine interface, and high subcooling increases the degree of hydrate film wrinkling and the CO 2 hydrate formation amount. The shear flow can delay the explosive growth of hydrates and tends to nucleate in bottom water; meanwhile, the continuous flow causes the overall extrusion deformation of hydrate film until the injection hole is blocked. Compared to static contact, this forced CO 2 -H 2 O contact caused by film deformation enhanced the CO 2 hydration amount by 2.68–3.62 times at the subcoolings of 6.94–3.25 K. Increasing the flow rate can further delay hydrate appearance and enhance hydrate growth. We also speculate on the hydration patterns of CO 2 in sediment pores under static and flowing conditions, and think that maintaining long-term flow can be an effective means to improve CO 2 hydrate storage and prevent blockage occurring in the pore throat. Our work provides new insights into the growth behavior of CO 2 hydrate for future CO 2 storage in submarine sediments. • The model of continuous shear flow contact of liquid CO 2 and seawater in marine environment is constructed. • The relationship between induction time and injection rate is revealed. • Subcooling and shear flow cause hydrate film deformation with morphological difference. • Shear flow can significantly enhance CO 2 hydration formation. [ABSTRACT FROM AUTHOR]

Sequestrating the CO 2 into deep geological formations is a profound approach to reduce green-house gas and thus mitigate climate change. In this context, ceiling the energy consumption, enhancing the CO 2 trapping to facilitate further dissolution and mineralization, and expanding the CO 2 sequestration capacity have gained extensive interests. Here, we explore the roles of pore heterogeneity and fluid properties in optimizing energy consumption and maximizing CO 2 sequestration effectiveness by computational modeling. We validate the modeling results through microfluidic experiments. We discover that placing the low Pore-Throat-Ratio layer at the middle fosters 7 % reductions of energy consumptions per pore volume, and a Ca<4.0 × 10−5 saves 8 % energy consumption per kgCO 2. The High-Median-Low heterogeneous pores optimally perform not only in residual CO 2 generation (22%PV) and conservation (7%PV) but also in CO 2 sequestration capacity (67%PV). Regarding fluid properties, the enlarged hydrophilicity and viscosity ratio with reduced density difference and interfacial tension increase the residual CO 2 and energy consumption while suppress the sequestration capacity. The presence of gravity especially when Bo > 6 × 10−5 promotes the residual CO 2 generation and conservation yet burdens the energy consumptions. This work bridges the gap between energy consumption and CO 2 sequestration effectiveness by uncovering the significant roles of pore heterogeneity and fluid properties. • Nearly 10 % energy consumption reduction is achieved at proper pore heterogeneity or fluid properties. • The HML heterogeneous pores optimally perform not only in residual CO 2 trapping but also in sequestration capacity. • The decrease of B o · C a − 1 expands the residual CO 2 trapping and energy consumption but suppresses the sequestration capacity. • The presence of the gravity promotes the residual CO 2 trapping yet burdens the energy consumptions. • Technology developed in this study is applicable in fields in terms of energy storage, development and utilization. [ABSTRACT FROM AUTHOR]

Methane (CH 4) hydrates exist on the seabed globally. This study explores the novel concept of methane recovery by CO 2 exchange into CH 4 hydrate through depressurization-assisted CO 2 injection. For the first time, we demonstrate the effectiveness of CH 4 recovery and CO 2 sequestration using l -Leucine amino acid. Three different approaches of additive injection to assess feasible methane recovery were studied. The investigation focuses on the thermodynamic region between CH 4 and CO 2 phase equilibrium lines in the presence of 0.5 wt% leucine. The amino acid system shows a 5 % increase in CH 4 recovery compared to the pure sediment system. Gas exchange kinetics suggest equilibration of released methane and injected CO 2 , prompting recrystallization into mixed hydrate. CO 2 consumption correlates with initial CH 4 hydrate conversion, with higher methane conversion resulting in lower CO 2 intake. The amino acid system promotes quicker hydrate dissociation and greater stability of mixed hydrates, preventing induced melting during depressurization. Ex-situ Raman analysis performed after the CO 2 exchange in 0.5 wt% Leucine system resulted in a four-wave number upward shift at 2919 cm−1 indicating partial distortion of small cages. The Large (L)/Small (S) cage intensity ratio of CH 4 hydrate after swapping is 0.57, suggesting a 50 % methane replacement by CO 2 with preferential CO 2 occupying large cages. [Display omitted] • First time employment of l -Leucine amino acid for studying CH 4 /CO 2 gas exchange in hydrates. • Three different experimental approaches studied for CH 4 /CO 2 gas exchange. • 0.5 wt% Leucine enhanced methane recovery by 5 % between CH 4 and CO 2 equilibrium curves. • CO 2 -methane exchange kinetics with fluctuations in recovery and a correlation between CO 2 consumption and initial CH 4 hydrate conversion was established. • Ex-situ Raman analysis shows CO 2 replaced 50 % of large sI cages. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) injection into deep coal seams holds considerable significance in both carbon mitigation and enhanced recovery of clean coalbed methane (CBM). The CO 2 -coal interaction leads to changes in the physicochemical properties, potentially impacting the stability of the target sequestration coal reservoir. This study applied the nanoindentation, scanning probe microscopy (SPM), X-ray diffraction (XRD), and electron probe X-ray Micro-Analyzer (EPMA) techniques to probe the micromechanical property change and damage mechanism of coal subjected to ScCO 2 injection. The result shows that the load-displacement behavior of the tested coal changes with continuous ScCO 2 treatment, and the mechanical strength significantly weakens after 4 days of ScCO 2 treatment. The nanoindentation test indicates that the peak and creep displacements of tested coal increased by 168.79 % and 1046.32 % respectively with 4-day ScCO 2 treatment, inferring that the coal deformation increases and changes from elastic to plastic after ScCO 2 injection. As the ScCO 2 treatment time increases, Young's modulus and hardness of coal exhibit an exponential decay trend and rapidly decrease by 77.77 %∼89.76 % and 68.37 %∼81.63 % respectively after the initial 3-day treatment, followed by a slow decrease with the ScCO 2 duration prolonging. The XRD and EPMA results show that the carbonate minerals reacted preferentially with ScCO 2 , and silicate minerals experienced gradual dissolution, while the amorphous carbon fluctuated almost unchanged in the tested coal. Carbonate minerals in tested coal have decreased by 70.68 % within the first 1-day ScCO 2 treatment, making the most significant contribution to the initial rapid weakening of coal mechanics. The mineral distribution is closely related to the mechanical anisotropy of coal, which is confirmed by the phenomenon that the coal anisotropy gradually weakens with the mineral reaction process. It is inferred that the mineral component and distribution of coal seams are important indicators for evaluating the intensity of physical and chemical reactions in ScCO 2 -injected reservoirs, which directly determines the mechanical damage behavior of sequestration reservoirs. This research provides basic support for site selection and safety assessment of carbon sequestration in deep coal seams. • Nanomechanics of coal was probed using nanoindentation, SPM and EPMA. • Mechanical behavior changes in coal induced by ScCO 2 treatment were quantified. • The ScCO 2 treatment reduces strength and mechanical heterogeneity of coal. • Linking coal minerals and morphology to mechanical property alterations. [ABSTRACT FROM AUTHOR]

The gas adsorption/desorption-induced coal deformation effect is a significant factor governing the evolution of coalbed permeability. Current theoretical investigations typically coal bulk and fracture deformation induced by gas are equivalent, neglecting the matrix-fracture interactions. Based on internal adsorption stress, this paper proposes Internal Differential Strain Coefficient (IDSC) to quantitatively characterize the relationship between coal bulk and fracture strain under equilibrium conditions. Coupling this coefficient constructs a binary gas permeability evolution model considering matrix-fracture interactions. Through numerical simulations of CO 2 -ECBM processes under various internal differential strain circumstances using this model, dynamic evolution patterns of diverse parameters are obtained. The research findings indicate that along the direction of CO 2 injection, matrix-fracture interactions exhibit a complex trend of initially increasing, then decreasing and then increasing, and the increase in internal differential strain levels results in a downward trend in permeability peak. Additionally, the evolutionary characteristics of CH 4 recovery and cumulative CO 2 storage rising with increasing internal differential strain levels were obtained on time scales using a fixed-point monitoring methodology. Inspired by the aforementioned laws, this paper discusses the macroscopic influence of burial depth on the effects of internal differential strain, providing new theoretical support for CO 2 sequestration injection methods in deep coal seams. • A coefficient capable of quantitatively analyzing the internal differential strain in the CO 2 -ECBM process is proposed. • Based on IDSC, a model describing the evolution of coal seam permeability in CO 2 -ECBM process is established. • Analyzed the influence of internal differential strain on the permeability of coal beds in the CO 2 -ECBM process. • Analyzed the influence of internal differential strain characteristics on CO 2 injection capacity. [ABSTRACT FROM AUTHOR]

The use of alkaline solid waste to CO 2 capture is a potential way to upgrade the recycling of solid waste and reduce CO 2 emission. In previous work, we proposed a novel wet grinding carbonation technique to achieve rapid carbonation of sintering red mud (SRM). Herein, the effect of wet grinding carbonation of SRM (WGCS) replacement rate (0 %, 5 %, 10 %, 15 %, 20 % and 25 %) on the hydration and hardening of Portland cement was further explored, such as rheology, compressive strength, hydration products and water transfer properties. The plastic viscosity and yield stress of carbon sequestered paste rose together with the WGCS replacement rate, which was due to the decreased D 50 of SRM after wet grinding carbonation. When the WGCS replacement rate was 15 %, the 56 d compressive strength of carbon sequestered mortar was increased by 14.1 %. The microscopic characterization showed that the nucleation of calcite crystals and the pozzolanic reaction of silica-rich gels clearly improved the microstructure compactness. The electric flux and porosity of cement mortar was decreased by 25.7 % and 11.4 %, respectively. In terms of environmental and economic benefits, the CO 2 sequestration of carbon sequestered mortar reached as high as 24.7 kg/m3 and the CO 2 emission was reduced by 30.9 %. [Display omitted] • WGCS was prepared by a novel wet grinding carbonation technique. • WGCS contained tiny calcite and silica gel without CaCO 3 layer coverage. • The 56 d compressive strength of CSM-15 was increased by 14.1 %. • Water transfer properties of CSM-15 have been greatly enhanced. • The CO 2 sequestration of cement mortar reached 24.7 kg/m3. [ABSTRACT FROM AUTHOR]

In this research, an internal carbonation curing method was proposed to achieve inside-outside synergistic carbon capture and performance improvement of cement-based materials. Potassium glycine (KG) solution with various concentrations was used as the CO 2 carrier. The results indicate that the addition of CO 2 -rich KG solution increases 7-d and 28-d compressive strength by 29.8% and 16.2%, as well as achieving an overall CO 2 uptake of 4∼11% in cement paste. However, at higher KG concentrations, the rapidly generated amorphous calcium carbonate covers the surface of cement particles, which shortens the setting time and inhibits early-age hydration. The presence of carbamate in CO 2 -rich KG solution improves the stability of metastable CaCO 3 polymorphs and prolongs the period of dissolution-recrystallization. Calcite generated by the slowed recrystallization within 14 days having a filling and binding ability in the cement matrix, significantly reducing porosity and providing a secondary strengthening effect. [ABSTRACT FROM AUTHOR]

Utilizing depressurization combined with CO 2 replacement for extracting natural gas hydrates (NGHs) is vital for sustainable energy and carbon sequestration. In this study, a NGH reservoir numerical model was developed to investigate the impacts of depressurization combined with CO 2 replacement on hydrate extraction at a field scale. Findings reveal an increase in methane production with reduced bottom hole pressure. When the bottom hole pressure is 3.5 MPa, the methane production reaches its maximum at 1.71 × 106 m3. Methane hydrates near production and injection wells decompose first, with deeper hydrates decomposing more easily. Higher differential pressures between injection and production enhance methane extraction and CO 2 hydrate formation. However, excessive pressure differential (1.5 MPa) can lead to CO 2 breakthrough across reservoir barriers, adversely affecting the purity of methane. At 1800 d, the methane purity is only 36.2 %. Optimal methane extraction and CO 2 sequestration occur at higher injection temperatures (9 °C) below the CO 2 hydrate phase equilibrium temperature. Temperatures above this equilibrium adversely affect both processes. The study validates the feasibility of depressurization with CO 2 replacement for extracting hydrates in the Shenhu area, offering theoretical guidance for synergistic offshore methane extraction and CO 2 sequestration techniques. • Studied the process of depressurization combined with CO 2 replacement for extracting NGH on a mine scale. • Unveiled the mechanisms behind the variations in extraction under different state parameters. • Considered the impact of geothermal gradient on the extraction of NGH. • Injection of CO 2 can enhance the gas production rate in depressurization extraction. [ABSTRACT FROM AUTHOR]

The invasion of formation water during marine hydrate production gravely affects gas productivity. CO 2 hydrate caps effectively inhibit water invasion while sequestering CO 2 , which is considered an excellent prospective application. However, forming field-scale artificial CO 2 hydrate caps remains a global challenge. This study proposed an innovative method for forming an artificial CO 2 hydrate cap. The fracture length, injection time, production pressure, and production well distance, which are all factors that affect sealing capacity and production enhancement, were optimized. Results indicated that the sealing capacity exhibited a trend of initially increasing and subsequently decreasing with fracture length. The injection time was positively correlated with the sealing capacity and was sufficient to seal both vertically and horizontally once it reached 4 years. In addition to sequestering CO 2 , the CO 2 hydrate cap enhanced gas production by 146.56 % and reduced water production by 37.47 % compared to direct depressurization. CO 2 invasion occurred when the well spacing was too close, while being distant was not favorable for pressure propagation and heat utilization by the CO 2 hydrate cap. This method simultaneously achieves multiple goals for energy and environmental, providing essential implications for the future commercial application of marine hydrates. [Display omitted] • A novel method for forming field-scale CO 2 hydrate cap is proposed. • Optimal fracture length and injection time are suggested for sufficient sealing cap. • Favorable production well spacing under the CO 2 hydrate cap is revealed. • Sequestering CO 2 while increasing gas production and decreasing water production. [ABSTRACT FROM AUTHOR]

The construction industry is a major contributor to CO 2 emissions, accounting for 5–7 % of worldwide CO 2 emissions. Biochar, a carbon-based material derived from waste, is considered an effective way to sequester carbon dioxide. This study investigated the effect of different biochar content on shotcrete under various curing conditions (carbonation, normal and low temperature). Flowability, compressive strength, splitting strength and microstructure of sprayed biochar shotcrete were conducted. Combined carbonation depth, thermogravimetric, and X-ray diffraction (XRD) were used to analyze the carbon sequestration of the biochar sprayed concrete materials from both macro and microscopic perspectives. In addition, the effect of low temperature on the performance of biochar shotcrete was considered. Results show that biochar fills the pores of the concrete and makes the microstructure denser when 5 % biochar replaces cement. Meanwhile, the compressive and splitting strength of concrete has been enhanced. The addition of 10 % biochar has a greater carbon sequestration capacity, although it can somewhat weaken the mechanical properties of concrete. Furthermore, low temperature hurt the performance of concrete. These results demonstrate the potential of combining biochar with shotcrete. It also provides a new direction for improving buildings' overall carbon sequestration performance. [Display omitted] • Effect of biochar content on the mechanical properties of shotcrete was compared. • Carbon sequestration of biochar shotcrete under carbonation curing was analyzed. • Temperature affecting the properties of biochar shotcrete was investigated. [ABSTRACT FROM AUTHOR]

Sorption-induced swelling reduces porosity and permeability in porous media, impacting long-term CO 2 storage injectivity. This study employs an innovative coarse-grained model to couple fluid flow with sorption-induced solid deformation at the pore-scale. Our model preserves the advantages of molecular dynamics in simulating complex fluid-solid interaction under nano-confinement while extending the time and length scales. Adjusting the gas-solid interaction energy controls solid swelling and gas slippage at pore walls. Gas permeability curves demonstrate a linear decline with the increasing gas-solid interaction energy in both swelling and non-swelling nanoporous media, with the former experiencing a greater drop. Surprisingly, in the regime of weak gas-solid interactions, swelling is not yet initiated and the porosity and permeability of flexible porous media increase, possibly due to gas flow-induced pore throat opening. Nanoporous media with lower initial porosity experience a greater permeability decline during swelling. The relationship between permeability and porosity changes shows a linear increase characterized by different slopes with varying initial porosities. These findings provide valuable insights into the complex interactions among gas transport, solid deformation, and porosity changes in nanoporous media, with implications for understanding and optimizing gas production and CO 2 storage in realistic geological environments. • An innovative coarse-grained model couples gas transport with solid swelling. • Permeability of low-porosity nanoporous media is more sensitive to swelling. • Permeability changes generally correlate linearly with porosity variations during swelling. • Permeability-porosity correlation is affected by the initial pore structure. [ABSTRACT FROM AUTHOR]

• The reactivity of basalt from Poland in CO 2 -water-basalt system was carried out. • An experiment on geochemical reactor was carried out for 65 days at 293 K and 0.43 MPa. • Partial dissolution and conversion of minerals was achieved. • Tight intrapore transport pathways have been clogged with secondary minerals. • A transformation of the macroporosity and morphology of the sample was achieved. The aim of the work was to identify the basic structural properties of basalts from the Central European Volcanic Province in Poland in the context of assessing the possibility of permanent CO 2 storage. The research was carried out on rock samples from three Polish basalt mines. An experiment on the reactivity of minerals contained in basalt was carried out in the original geochemical reactor. In an isolated system with a capacity of 100 cm3, proper analyzes of mineral carbonation were carried out for 65 days at a temperature of 293 K and a pressure of 0.43 MP. The pressure, pH and temperature of the process were recorded. The mechanism of structural changes that occurred in pores of different diameters was determined. SEM microscopic analyzes showed a transformation of the macroporosity and morphology of the sample. The formation of new voids and transport channels was observed, which resulted from the partial dissolution and conversion of minerals. At the same time, the pore surface area in the transitional pores and finest micropores has been reduced, indicating that the surface area of these pores have been overbuilt and the tight intrapore transport pathways have been clogged. The gravimetric measurements of the sorption capacity of basalt in relation to gaseous CO 2 were also conducted. After the mineral carbonation process, the efficiency of CO 2 accumulation decreased, which confirmed that the previously free pore space had been filled. Comprehensive scanning, structural and sorption studies confirmed the migration and multi-track transformation of minerals from basalt. [ABSTRACT FROM AUTHOR]

Underground hydrogen storage (UHS) is an effective means to solve large-scale hydrogen energy storage. The depleted gas reservoirs can be used as the potential UHS targets due to its huge storage space, good sealing ability, and the existing facilities. CO 2 can be injected as the cushion gas to reduce the hydrogen loss, improve energy storage efficiency and achieve carbon sequestration. This work proposes a novel method to estimate the hydrogen storage capacity in depleted gas reservoirs using CO 2 as cushion gas. The multi-components (H 2 -CO 2 -CH 4 -H 2 O) material balance equations are further developed by integrating the edge/bottom water and water invasion, gas (e.g., CO 2 , H 2 , CH 4) dissolution in formation water as well as caprock breakthrough and fault instability. The maximum UHS operating pressure can be determined by calculating the caprock-breakthrough pressure and the fault-instability pressure. A numerical model is established to validate the proposed UHS capacity model in this work. The impact of dominated factors on the UHS capacity is discussed. The proposed method has been applied to evaluate the UHS capacity of a depleted gas reservoir in the Sichuan Basin of China. Results show that the model validation verifies the accuracy of the proposed model since the average error is only 1.76% between the analytical model developed in this work and the numerical model. The maximum pressure threshold presents the most significant impact on the UHS capacity, followed by CO 2 cushion gas volume, formation temperature and water body size. The maximum pressure threshold of formation is determined to be 42 MPa. The hydrogen storage capacity under different CO 2 cushion gas injection conditions is calculated. The UHS capacity is increased by 7.76% and 8.61% with dissolution when V CO2_inj is 3000 × 104 m3 and 4000 × 104 m3. The UHS capacity of Well #P4 is 6076 × 104 m3 when V CO2_inj is 4000 × 104 m3 based on the proposed model in this work. This work provides an effective approach to evaluate the hydrogen storage capacity and improve hydrogen storage efficiency by using CO 2 as cushion gas considering caprock breakthrough, fault slip and gas dissolution. The established model provides important references for calculating the storage capacity of gas storage facilities in oil and gas reservoirs with edge and bottom water as well as for gas storage in aquifers. • A novel model is proposed to calculate the H 2 storage capacity in depleted gas reservoirs using CO 2 as cushion gas. • CO 2 can be injected as the cushion gas to reduce H 2 loss, enhance storage efficiency and achieve carbon sequestration. • The developed analytical model in this work is validated with the numerical model. • Field case highlights the practical potential of the proposed method for estimating the UHS capacity. [ABSTRACT FROM AUTHOR]

The employment of solid waste, notably coal gangue, in carbon-negative backfill mining technology for mineralization and filling in coal mine gobs, is recognized as a productive method for carbon sequestration and waste management, with research primarily dedicated to engineering advanced mineralized backfill materials. Under this background, four variables, including the ratio of gangue to solids (R G-S), water-cement ratio (R W-C), ratio of fly ash to solid wastes providing calcium (Ca) (R A-Ca), and ratio of flue gas desulfurization (FGD) gypsum to carbide slag (R F-CS) were defined to formulate gangue-based mineralized backfill materials, with orthogonal experiments assessing their effects on CO 2 sequestration and mechanical characteristics. The results indicate that R W-C consistently emerges as the primary factor influencing both the amount of sequestered CO 2 and the mechanical properties of gangue-based solid waste mineralized backfill materials. The amount of sequestered CO 2 demonstrates a direct proportionality to R W-C and mechanical strength demonstrates an inverse relationship with R W-C. After 45 minutes of stirring and carbon sequestration, samples in various groups exhibited an maximum sequestered CO 2 amount of 18.96 g·kg−1, with a maximum sequestration rate of 0.20 g·kg−1·min−1. The process of CO 2 sequestration enhances the compressive properties of mineralized backfill materials derived from gangue based solid wastes. [Display omitted] • Mineralized backfill materials enable waste disposal and CO 2 absorption. • The water-cement ratio affects mineralized backfill materials the most. • The optimal amount of sequestered CO 2 per sample is 18.96 g·kg−1 in 45 min. • CO 2 sequestration improves the strength of mineralized backfill materials. • Adding gangue improves CO 2 sequestration and the mechanical properties. [ABSTRACT FROM AUTHOR]

This study systematically investigated the influence of varying carbon dioxide (CO 2) dosages and steel slag (SS) replacement rates on the fresh and hardened properties of concrete through the injection of CO 2 gas during the mixing process. The composition of hydration products, degree of hydration, and the evolution of microstructural characteristics within the CO 2 -SS-cement system were analyzed. The results showed that CO 2 addition during the mixing process enhanced early strength in SS concrete. For concrete with a 10 wt% SS replacement rate, the incorporation of CO 2 ranging from 0.4 wt% to 1.2 wt% of the total mass of cementitious materials resulted in notable compressive strength increases of 1.26%–12.47%, 0.64%–6.14%, and 11.79%–18.24% at ages of 1 d, 3 d, and 7 d, respectively. CO 2 rapidly reacted with SS to form calcite-type CaCO 3 and promoted the generation of C-S-H through synergistic hydration with cement. However, a high CO 2 dosage (1.2 wt%) led to issues such as microcrack propagation and interface loosening due to CaCO 3 deposition, which could be mitigated to some extent by appropriately increasing the SS content. • CO 2 -mixing and steel slag synergistically improve early strength of concrete. • Increasing steel slag content alleviates adverse effects of high CO 2 dosage. • CO 2 -mixing enhanced the early cement hydration. [ABSTRACT FROM AUTHOR]

Natural Hydraulic Lime (NHL), as a low-carbon binder, possesses a significantly higher carbon sequestration potential compared to cement-based materials. This study aims to elucidate the accelerated carbonation mechanism of NHL5 by investigating the evolution of phase composition and microstructure during the accelerated carbonation process, as well as the preferential reactivity of different carbonatable components. Different hydration levels of NHL5 paste were achieved by controlling various steam curing durations (with a water-to-binder ratio of 0.5); accelerated carbonation conditions included 3±1 % CO 2 , 25±3°C, and 70±5 % relative humidity. The results indicate that higher hydration levels positively impact the mechanical properties of samples after carbonation. The compressive strength of the sample with carbonation curing 28 after 7 days of steam curing (S7C28) reached 45.6 MPa, and the carbon sequestration per unit mass increased. Specifically, S7C28 achieved an increase in carbon sequestration from 71.8 g/kg to 364.3 g/kg after 28 days of incomplete carbonation, while the high degree of hydration also limited the diffusion of CO 2. Qualitative and quantitative analyses confirm that the carbonation reactivity in NHL5 paste follows the order: Ca(OH) 2 >C-S-H gel>C 2 S. The continuous generation of carbonation by-products, such as calcite and silica gel, fills the pores of the samples, enhancing their strength. These results suggest that higher hydration levels in NHL5 significantly promote the effectiveness of carbonation curing at a 3 % CO 2 concentration, leading to improvements in mechanical performance, carbon sequestration capacity, and microstructural characteristics. • A higher degree of hydration facilitates the attainment of superior mechanical properties after carbonation curing but restricts the diffusion of CO 2. • The sequence of carbonation reaction activity for carbonatable substances in NHL5 paste is as follows: Ca(OH) 2 > C-S-H > C 2 S. • A higher degree of hydration can enhance the carbonation capacity of NHL5 paste. • The carbonation reaction products, calcite and silica gel, fill and refine the pores, enhancing the mechanical properties of the paste. [ABSTRACT FROM AUTHOR]

This study assessed the feasibility of in-situ CO 2 mixing in a wollastonite-blended cementitious composite by evaluating its mineral carbonation performance. Wollastonite (CS) polymorphs were synthesized and used to replace ordinary Portland cement with up to 30 wt%. The results showed that amorphous CaCO 3 , calcite, and monocarboaluminate were formed as carbonation products. The wollastonite-blended cementitious composite with a 20 % replacement of β-CS exhibited the highest CaCO 3 production of 22.5 wt%, which was mainly attributed to amorphous CaCO 3. β-CS showed a superior mineral carbonation ability to α-CS because the Ca-depleted silicate layer formed by the dissolution of β-CS accelerated the formation of amorphous CaCO 3. Moreover, CS retarded the early-stage formation of ettringite and monocarboaluminate by delaying gypsum dissolution. The wollastonite-blended cementitious composites exhibited superior compressive strength exceeding 40 MPa. These results demonstrate that the mineral carbonation of wollastonite-blended cementitious composite can be accomplished through in-situ CO 2 mixing, especially with β-CS replacement, which has significant potential as a CO 2 storable binder. • Two polymorphs of wollastonite (CS) were synthesized and compared for carbonation. • For wider applicability (ready-mixed concrete), in-situ CO 2 mixing has been firstly applied. • Intended carbonation produced amorphous CaCO3, calcite, and monocarboaluminate. • CS-blended cement system was proved as a sufficient building materials [ABSTRACT FROM AUTHOR]

Listvenites form by metasomatic transformation of variably serpentinized peridotites to carbonate-quartz rocks due to extensive reaction with CO 2 -bearing aqueous fluids. This transformation sequesters large amounts of carbon since listvenites commonly contain >30 wt% CO 2. Although volumetrically a rare rock type, they occur in many ophiolites throughout much of the geological record, with preserved examples from the Archean to the present. Listvenites are highly interesting because they can form in the forearc mantle wedge, modulating deep carbon cycling. They further are natural analogues for optimal carbon sequestration by mineral carbonation. Here we elucidate the influence of different controlling variables and feedback mechanisms on natural listvenite formation, investigate which prerequisites and geodynamic settings are favorable, and discuss related implications for the deep carbon cycle and engineered CO 2 storage by mineral carbonation. Using thermodynamic fluid infiltration-fractionation models that simulate idealized, step-wise carbonation flow-through experiments, we quantify expected changes in volume, mass, solute transfer (e.g. Mg, Si mobility), redox conditions and pH with reaction progress in dependence of protolith composition, infiltrated fluid composition, temperature and pressure. The models agree well with experiments and natural observations of high- T carbonation but have limitations at low temperature (T ≲ 130–150 °C) where kinetic effects in experiments limit the approach to equilibrium. Our modeling and assessment of typical CO 2 concentrations in metamorphic/hydrothermal fluids highlight that listvenite formation requires high time-integrated fluid flux, which in turn requires dynamic renewal of permeability despite reactive volume expansion. As most known listvenites crop out along tectonic contacts between crustal and ultramafic rocks in ophiolites that delineate major orogenic sutures, key factors controlling CO 2 supply are deviatoric stress and related deformation. Listvenite microstructures indicate that important hydro-mechanical-chemical feedback processes allowing continued fluid flux during carbonation are brittle fracturing and vein formation, reaction-enhanced ductile deformation, and local mass redistribution due to solute transfer. These feedback processes critically influence carbon flux pathways and the extent of CO 2 sequestration, but are not yet well understood as they are challenging to reproduce experimentally and by modeling. The CO 2 source for listvenite formation is most commonly inferred to be metamorphic devolatilization and/or dissolution of carbonate ± organic carbon bearing meta-sediments. Less commonly reported are mantle or magmatic CO 2 sources. First-order thermodynamic modeling indicates that listvenites may be a direct consequence of meta-sediment devolatilization in subduction zones, while their formation at low pressure conditions requires rapid, large scale ascent and cooling of deep sourced fluids along shear or fault zones. The latter setting is reminiscent of induced mineral carbonation by subsurface CO 2 injection. The microstructural and chemical record of listvenites thus provides a means to investigate hydro-mechanical-chemical feedbacks during carbonation reaction progress at scales that cannot be achieved in laboratory experiments. Understanding these mechanisms is crucial for developing and validating strategies of engineered subsurface CO 2 sequestration by mineral carbonation. [ABSTRACT FROM AUTHOR]

Mixed siliciclastic‑carbonate depositional systems are prone to differential diagenesis due to lithological heterogeneity. However, unlike pure carbonate and/or siliciclastic counterparts, the diagenesis within mixed clastic‑carbonate successions remains poorly known. This study integrates sedimentological and petrographic analysis with porosity-permeability measurements to understand diagenetic variability and its impact on fluid flow in the Oligocene-Miocene mixed clastic‑carbonate system (lower part of Musayr Fm) in Midyan Basin, Red Sea, Saudi Arabia. Sedimentological observations highlight that siliciclastic intervals comprise conglomerates, coarse- to fine-grained sandstones and subordinate mudstones whereas mixed siliciclastic‑carbonate intervals are composed of shell, ooids and microbialites-dominated facies. Petrographic analysis indicates presence of several diagenetic processes in siliciclastic intervals including dissolution of unstable silicate grains (feldspar), formation of pore filling and/or grain-replacive kaolinite, precipitation of calcite and/or dolomite, and replacement of dolomite by silica. The siliciclastic strata exhibit minimal compaction fabrics with no stylolites and are characterized by higher permeability (average = 1884 md) and porosity (average = 18.7 %). On the other hand, mixed siliciclastic‑carbonate intervals underwent micritization, sparry calcite formation, dolomitization of micrite and bioclasts, and replacement of sparry calcite by pyrite and Fe-oxides. Wavy stylolite seams were also observed in ooid facies reflecting moderate chemical compaction. In addition, the porosity (average = 6.6 %) and permeability (average = 93 md) are magnitudes lower than siliciclastic counterparts. Significant differences between porosity and permeability of siliciclastic and mixed intervals are partly linked to relatively intense diagenetic alteration (higher cementation and chemical compaction) in mixed units. Understanding such diagenetic heterogeneity in mixed systems has important implications for identification of reservoir and non-reservoir zones and may provide useful insights for hydrocarbon exploration and carbon sequestration in the analogous strata in the subsurface. • Mixed siliciclastic-carbonate successions are lithogically variable depositional systems. • Unlike clastic and carbonate counterparts, diagenesis in mixed systems is poorly understood. • Sedimentological, petrographic, and porosity-permeability analyses of syn-rift mixed systems in the Red Sea. • Mixed siliciclastic-carbonate beds experienced severe diagenetic alterations compared to interbedded siliciclastics. • Diagenetically variable behavior in mixed successions may facilitate subsurface CO 2 storage. [ABSTRACT FROM AUTHOR]

• Surface modification of nanoparticles is key for the successful implementation of foam for subsurface applications. • Previous research has focused on enhanced oil recovery, with limited exploration of novel nanoparticles for CO2 sequestration. • Hydrophilic nanoparticles increase foam drainage, while partially hydrophobic nanoparticles prevent foam rupture. • Surface grafting of nanoparticles introduces additional mechanisms for bubble interaction and preventing coalescence. Foams are used as an enhanced oil recovery (EOR) method to reduce the mobility of injected gaseous phases. However, foam stability is often compromised under harsh reservoir conditions, leading to drainage of the aqueous phase and gas diffusion. Incorporating nanoparticles, particularly SiO 2 , has been found to enhance foam stability due to their surface chemistry and natural abundance. To create stable nanofluids at high temperatures and low concentrations, nanoparticles need to have their surfaces altered, allowing particles and molecules to interact and keep the nanoparticle-stabilized foam in the reservoir for extended periods. This review paper highlights the use of novel nanoparticles for stabilizing foams for EOR and CO 2 sequestration. It also discusses the modification of nanoparticles to improve foam stability in porous media, focusing on the impact of surface groups and hydrophobicity. Additionally, it covers how to alter nanoparticle surfaces by adding different functional groups or long-chain molecules to stabilize nanofluids in various conditions. The review also delves into how charge interactions and the hydrophilic or partially hydrophobic nature of nanoparticles affect foam stability. Overall, incorporating novel nanoparticles with surfactants has the potential to optimize oil recovery and CO 2 sequestration by improving foam stability. This perspective article explores the potential of using newly modified nanoparticles to stabilize foams and provides a comprehensive review of recent advancements in utilizing modified nanoparticles for foam stabilization, with a focus on surface-modified novel nanoparticles and their influence on stabilizing foams. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) emissions contribute significantly to global warming, driving interest in carbon capture and storage (CCS) strategies. One promising approach involves injecting flue gas (CO 2 + N 2) into marine sediments to form hydrates, facilitating CO 2 storage. However, understanding the kinetics of hydrate formation and dissociation, especially under varying salinity conditions, remains crucial. In this study, we investigate these dynamics under isochoric and isothermal conditions, using the gas mixture of 25% CO2/75% N2 and addition of three different amino acids (L-leucine, L-methionine, L-tryptophan) at 1.0 wt% to enhance hydrate formation. Our findings reveal that L-leucine significantly accelerates hydrate kinetics, doubling hydrate yield compared to pure water, both in saline and non-saline conditions. Moreover, pressure driving force exerted a noticeable influence on gas uptake kinetics, with higher driving force accelerating the process. Morphological observations indicate hydrate formation within and above sediments, suggesting potential for practical application. Interestingly, CO 2 selectivity within hydrate cages decreases with increased pressure driving force, attributed to heightened N 2 dissolution in water and CO 2 -N 2 competition for hydrate cages. Gas chromatographic analysis confirms the preferential selectivity of CO 2 in larger cages, with hydrate phase gas doubling compared to feed gas. The introduction of salinity (3.5 wt% NaCl) slightly decreases overall hydrate yield. Additionally, hydrate dissociation studies highlight L-leucine's potential to slow gas release, enhancing its suitability for hydrate-based CO 2 capture and sequestration. These findings underscore the scientific significance of understanding hydrate kinetics and salinity effects in advancing hydrate based CCS technology. [Display omitted] • CO 2 sequestration from flue gas using gas hydrates investigated in silica sand with and without 3.5% NaCl. • Formation and dissociation kinetics of CO 2 /N 2 hydrates assessed in presence of three amino acids. • 1 wt% Leucine effective in saline and non-saline environment for hydrate-based CO 2 sequestration. • Driving force and salinity effect on gas uptake and separation factor documented in the study. [ABSTRACT FROM AUTHOR]

The growing emphasis on sustainability in environmental health, climate change, and water usability has driven the exploration of economically and environmentally friendly approaches to enhance wastewater quality. Algae-mediated natural precipitation of minerals in wastewater, driven by these organisms' carbon utilization in photosynthesis, has emerged as a promising wastewater treatment (WWT) method due to its sustainability and cost-efficiency benefits. This study examines the impact of varying carbon content in bicarbonate forms on algae activity in mediating CaCO 3 precipitation and how pH in algae-mediated solutions influences calcite precipitation. Solutions with different Ca2+ and HCO 3 − concentrations were prepared, and algae growth curves were established to ensure solution suitability. The experiments, conducted in two sets, employed ANOVA and t -test analyses for samples with common calcium concentration. Results indicated that increasing HCO3- concentration positively correlates with algae mediation and CaCO 3 precipitation, while elevating pH from 9.8 to 11.0 negatively correlates with calcite precipitation. In conclusion, HCO 3 − additions were effective in enhancing algae-mediated calcite precipitation in wastewater. Recommendations include ensuring proportionate HCO 3 − additions to calcium content to optimize mineral precipitation without detrimental effects on algae. [Display omitted] • Need for economic and eco-friendly wastewater treatment. • Utilization of algae for mediating mineral precipitation. • Increasing HCO 3 − concentration boosts algae mediation and CaCO 3 precipitation. • pH shows an inverse relationship with calcite precipitation. [ABSTRACT FROM AUTHOR]