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Using circulating fluidized bed combustion (CFBC) ash discharged from thermal power plants, we identified factors affecting mineral carbonation to sequester CO2 and produced autoclaved aerated concrete (AAC). To use CFBC ash as a raw material for AAC, free-CaO, which causes volume expansion, was replaced through hydration and carbonation. During the raw material replacement process, carbonation behavior was confirmed through pH and temperature. A Ca(OH)2 to liquid ratio similar to a fly ash to liquid ratio of 0.25 is considered to provide sufficient diffusion distance, and the reaction rate may increase due to the rise in water temperature caused by Ca2+ leaching. Additionally, the results of XRD, XRF, TG-DTA, and SEM analyses indicate that hydration and carbonation reactions were stably achieved in the materials, suggesting that CO2 sequestration allows the materials to be used as alternative raw materials. After identifying the characteristics of the CFBC ash and the substituted material, AAC was manufactured through pressurized carbonation. The weight change rate, carbonation depth, ventilation rate, pore structure, and compressive strength of the manufactured AAC were measured. As a result, the alternative raw material exhibited higher permeability and a larger pore size range in the specimens compared to the original material, indicating easier CO2 penetration into the specimens. Consequently, this experiment suggests the potential of using the material in AAC production by providing a theoretical basis for solving volume expansion issues associated with concrete admixtures and CO2 sequestration in waste materials. [ABSTRACT FROM AUTHOR]

Kumdykolite is a polymorph of albite that has been predominantly identified within crystallized melt inclusions in high-temperature metamorphic rocks. This study reports a new occurrence of kumdykolite that formed during internal mineral carbonation within amphibole-hosted fluid inclusions in post-collisional hornblendite from the Dabie orogen, central China. Amphibole in the hornblendite trapped CO2-rich fluid inclusions at the magmatic stage, and mineral carbonation, referring to the reaction of mineral rich in divalent cations and CO2 into carbonate, occurred in situ within the fluid inclusions due to the interaction between trapped CO2-rich fluids and host amphibole during cooling of the hornblendite. Kumdykolite was produced along with calcite, dolomite, chlorite, talc, a SiO2 phase (quartz or cristobalite), a TiO2 phase (rutile or anatase), and mica during internal mineral carbonation within the fluid inclusions. It is estimated that kumdykolite in the fluid inclusions crystallized under near-surface conditions, which are significantly different from the conditions of crystallization proposed in previous studies. It is further inferred that kumdykolite may crystallize metastably across the stability field of albite, and the presence of kumdykolite is not indicative of extreme thermobaric and fluid-absent conditions. [ABSTRACT FROM AUTHOR]

Mineral carbonation is a promising CO2 sequestration strategy that can utilize industrial wastes to convert CO2 into high-value CaCO3. This review summarizes the advancements in CO2 mineralization using typical industrial wastes to prepare ultrafine CaCO3. This work surveys the mechanisms of CO2 mineralization using these wastes and its capacities to synthesize CaCO3, evaluates the effects of carbonation pathways and operating parameters on the preparation of CaCO3, analyzes the current industrial application status and economics of this technology. Due to the large amount of impurities in solid wastes, the purity of CaCO3 prepared by indirect methods is greater than that prepared by direct methods. Crystalline CaCO3 includes three polymorphs. The polymorph of CaCO3 synthesized by carbonation process is determined the combined effects of various factors. These parameters essentially impact the nucleation and growth of CaCO3 by altering the CO2 supersaturation in the reaction system and the surface energy of CaCO3 grains. Increasing the initial pH of the solution and the CO2 flow rate favors the formation of vaterite, but calcite is formed under excessively high pH. Vaterite formation is favored at lower temperatures and residence time. With increased temperature and prolonged residence time, it passes through aragonite metastable phase and eventually transforms into calcite. Moreover, polymorph modifiers can decrease the surface energy of CaCO3 grains, facilitating the synthesis of vaterite. However, the large-scale application of this technology still faces many problems, including high costs, high energy consumption, low calcium leaching rate, low carbonation efficiency, and low product yield. Therefore, it is necessary to investigate ways to accelerate carbonation, optimize operating parameters, develop cost-effective agents, and understand the kinetics of CaCO3 nucleation and crystallization to obtain products with specific crystal forms. Furthermore, more studies on life cycle assessment (LCA) should be conducted to fully confirm the feasibility of the developed technologies. [ABSTRACT FROM AUTHOR]

Mineral carbonation is a promising CO2 sequestration strategy that can utilize industrial wastes to convert CO2 into high-value CaCO3. This review summarizes the advancements in CO2 mineralization using typical industrial wastes to prepare ultrafine CaCO3. This work surveys the mechanisms of CO2 mineralization using these wastes and its capacities to synthesize CaCO3, evaluates the effects of carbonation pathways and operating parameters on the preparation of CaCO3, analyzes the current industrial application status and economics of this technology. Due to the large amount of impurities in solid wastes, the purity of CaCO3 prepared by indirect methods is greater than that prepared by direct methods. Crystalline CaCO3 includes three polymorphs. The polymorph of CaCO3 synthesized by carbonation process is determined the combined effects of various factors. These parameters essentially impact the nucleation and growth of CaCO3 by altering the CO2 supersaturation in the reaction system and the surface energy of CaCO3 grains. Increasing the initial pH of the solution and the CO2 flow rate favors the formation of vaterite, but calcite is formed under excessively high pH. Vaterite formation is favored at lower temperatures and residence time. With increased temperature and prolonged residence time, it passes through aragonite metastable phase and eventually transforms into calcite. Moreover, polymorph modifiers can decrease the surface energy of CaCO3 grains, facilitating the synthesis of vaterite. However, the large-scale application of this technology still faces many problems, including high costs, high energy consumption, low calcium leaching rate, low carbonation efficiency, and low product yield. Therefore, it is necessary to investigate ways to accelerate carbonation, optimize operating parameters, develop cost-effective agents, and understand the kinetics of CaCO3 nucleation and crystallization to obtain products with specific crystal forms. Furthermore, more studies on life cycle assessment (LCA) should be conducted to fully confirm the feasibility of the developed technologies.

Highly plastic clays pose significant challenges in engineering projects. Various techniques have been employed to enhance their properties, though many face difficulties related to implementation and environmental impact. This study examines the effect of CO2-induced magnesium carbonate on improving the geotechnical behavior of plastic clay. CO2-induced magnesium carbonate was produced via mineral carbonation and used to improve the behavior of highly plastic natural clay. CO2 gas was injected into a sodium hydroxide solution to produce carbonate ions (CO32−). Magnesium carbonate was precipitated on a laboratory scale by adding magnesium sulfate solution to the carbonate ion solution. Clayey soil samples were obtained from test pits in the Meyghan Plain near Arak, Iran. The clay samples were treated with different percentages of the produced magnesium carbonate. Various parameters of the treated and untreated samples, including index properties, unconfined compressive strength, consolidation behavior, and swelling potential, were studied. It was found that the liquid limit and plasticity index of the treated clay decreased as the magnesium carbonate content increased. The soil classification changed from high plastic clay (CH) to low plastic silt (ML) with the addition of 15% magnesium carbonate to the highly plastic clay. The unconfined compressive strength of the treated clay increased. Additionally, the consolidation behavior and swelling index of the treated clay improved as the magnesium carbonate content increased. This study confirms that CO2-induced magnesium carbonate is a promising material for improving the behavior of highly plastic clays, offering a sustainable approach to environmental management. [ABSTRACT FROM AUTHOR]

Mineral carbonation, which precipitates dissolved carbon dioxide (CO2) as carbonate minerals in basaltic groundwater environments, is a potential technique for negative emissions. The Leizhou Peninsula in southwest Guangdong province has extensive basalt, indicating a promising potential for CO2 storage through rapid mineralization. However, understanding of the basic geological setting, potential, and mechanisms of CO2 mineralization in the basalts of the Leizhou Peninsula is still limited. The mineralization processes associated with CO2 storage at two candidate sites in the area are investigated in this paper: Yongshi Farm and Tianyang Basin (of the dried maar lake). Petrography, rock geochemistry, basalt petrophysical properties, and groundwater hydrochemistry analyses are included in the study. Numerical simulation is used to examine the reaction process and its effects. The results show that basalts in the study areas mainly comprise plagioclase, pyroxene, and Fe–Ti oxides, revealing a total volume fraction exceeding 85%. Additionally, small amounts of quartz and fayalite are available, with volume fractions of 5.1% and 1.0%, respectively. The basalts are rich in divalent metal cations, which can form carbonate minerals, with an average of approximately 6.2 moles of metal cations per 1 kg of rock. The groundwater samples have a pH of 7.5–8.2 and are dominated by the Mg–Ca–HCO3 type. The basalts demonstrate a porosity range of 10.9% to 28.8%, with over 70% of interconnected pores. A 20-year geochemical simulation revealed that CO2 injection dissolves primary minerals, including anorthite, albite, and diopside, while CO2 mineralization dissolves precipitation secondary minerals, such as calcite, siderite, and dolomite. Furthermore, a substantial rise in pH from 7.6 to 10.6 is observed in the vicinity of the injected well, accompanied by a slight reduction in porosity from 20% to 19.8%. Additionally, 36.8% of the injected CO2 underwent complete mineralization within five years, revealing an increasing percentage of 66.1% if the experimental period is extended to 20 years. The presence of abundant divalent metal cations in basalts and water-bearing permeable rocks in the Leizhou Peninsula supports the potential for mineral carbonation in basalts, as indicated by the geochemical simulation results. Additional research is necessary to identify the factors that influence the CO2 mineralization, storage, and sensitivity analysis of basalt in the Leizhou Peninsula. [ABSTRACT FROM AUTHOR]

This study investigates the effect of the particle size and solid-to-liquid ratio on the dissolution rate of magnesium (Mg) and silicon (Si) in heat-activated lizardite. The investigation was conducted under specific conditions: without the presence of sodium bicarbonate (NaHCO3), at a moderate temperature (40 °C), and under elevated CO2 pressure (100 bar). The aim was to isolate the dissolution reactions and enhance comprehension of the factors constraining the overall yields in the Albany Research Center (ARC) mineral carbonation process. Our study disclosed two distinct dissolution regimes: an initial stage with a rapid initial rate of Mg extraction, resulting in the fraction of Mg extracted ranging from 30 to 65% during the first 20 min of the experiment, following which the dissolution rate decreases dramatically. The initial rapid dissolution stage is primarily driven by the low pH of the supernatant solution, resulting from CO2 dissolution, leading to a higher concentration of protons that extract Mg2+ cations. However, as the heat-activated lizardite dissolution progresses, the pH increases due to the high level of leached Mg2+, and a diffusion barrier forms due to the precipitation of amorphous silica. This phenomenon ultimately slows down the mineral's dissolution rate during the latter stages of particle dissolution. [ABSTRACT FROM AUTHOR]

Natural silicates are promising sources of divalent cations, which are necessary for the mineralization of CO2 in the form of carbonates. The kinetics of natural talc dissolution was studied in flow-through reactors at 25°C in solutions of hydrochloric, citric, and oxalic acids at pH 3. An increase in the rate of talc dissolution in the presence of organic ligands of citrate and oxalate by about 3–4 times is characteristic of only the initial stage of mineral dissolution. The stationary rates of talc dissolution were detected ~30–40 h after the start of the experiment and were ~3E–10–16 mol/cm2 s. [ABSTRACT FROM AUTHOR]

As per the recommendations of the Intergovernmental Panel on Climate Change, global warming should be restricted to below 2°C to mitigate the consequences of severe climate change. This study investigates an innovative carbon sequestration method that involves the electrolysis of concentrated seawater to produce alkali solutions and hydrogen gas for mineral carbonation. The optimal conditions were examined with a focus on factors such as electrode materials, current density, and electrolyte flow rate. The study demonstrated the potential for CO2 reduction and the formation of valuable metal carbonates (Mg(OH)2, MgCO3, and CaCO3) via accelerated mineral carbonation. With 1 m3 of concentrated seawater, 1.35 kg of CO2 was removed and 10.3 and 1.1 kg of Mg(OH)2 and CaCO3 were precipitated, respectively. This method is an economically viable and energy-efficient alternative to conventional mineral carbonation, which requires substantial resources. [ABSTRACT FROM AUTHOR]

The observation of photosynthetic biofilms growing on the Fine Residue Deposit (FRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa suggests that processed kimberlite supports bacterial growth. The presence of this biofilm may aid in the acceleration of weathering of this ultra-mafic host material - a process that can sequester CO2 via carbon mineralization. Laboratory and field trial experiments were undertaken to understand the microbe-mineral interactions occurring in these systems, and how these interactions impact geochemical cycling and carbonate precipitation. At laboratory scale it was discovered that using kimberlite as a growth supplement increased biomass production (up to 25-fold) and promoted microbiome diversity, while the inoculation of FRD systems aided in the aggregation, settling, and dewatering of kimberlitic slurries. Field trial studies combining photosynthetic biofilms (cultured in 3 × 1,000 L bioreactors) with FRD material were initiated to better understand microbially enhanced mineral carbonation across different depths, and under field environmental conditions. Over the 15-month experiment the microbial populations shifted with the kimberlitic environmental pressure, with the control and inoculated systems converging. The natural endogenous biosphere (control) and the inoculum accelerated carbonate precipitation across the entire 40 cm bioreactor depth, producing average 15-month carbonation rates of 0.57 wt.% and 1.17 wt.%, respectively. This corresponds to an annual CO2e mine offset of ~4.48% and ~ 9.2%, respectively. Millimetre-centimetre scale secondary carbonate that formed in the inoculated bioreactors was determined to be biogenic in nature (i.e., possessing microbial fossils) and took the form of radiating colloform precipitates with the addition of new, mineralized colonies. Surficial conditions resulted in the largest production of secondary carbonate, consistent with a ca. 12% mine site CO2e annual offset after a 15-month incubation period. [ABSTRACT FROM AUTHOR]

Using mining waste for CO2 sequestration presents a promising solution for managing waste and reducing greenhouse gas emissions. This article provides a comprehensive overview of established CO2 sequestration methods that can be applied to mining waste eligible for such application. Three techniques were considered: 1) passive mineral carbonation; 2) a nature-based solution (NBS); and 3) carbon capture, utilisation, and storage (CCUS). Passive mineral carbonation involves exposing mining waste rich in Ca and Mg silicates to atmospheric CO2. NBS explores the reclamation of disposal areas, estimating the carbon sequestration by topsoil, organic amendments, and revegetation. CCUS presents some storage possibilities with CO2 injection into waste piles and utilisation by incorporating waste and CO2 into cement products. Furthermore, an innovative proposal for injecting CO2 into surface and underground coal mining waste disposal areas was described as a potential action. The strategies presented in this article can be considered to offset CO2 emissions from mining projects while also contributing to waste management and more sustainable production. [ABSTRACT FROM AUTHOR]

Mineral carbonation is one of the known methods for carbon capture, utilization, and storage (CCUS). Slag from the steel industry is studied as a common source of CaCO3 via mineral carbonation owing to its high Ca content. Despite numerous preliminary studies, the optimal factors governing the mineral carbonation of steelmaking slag, such as extraction and carbonation remain unexplored. In this study, we optimized the factors for Ca extraction and carbonation, as CaCO3 produced under these optimized factors possesses commercial value due to its high purity. The extraction and carbonation experiments were performed on two types of slag samples, specifically non-magnetic steelmaking and pig iron slag, utilizing the chosen factors for each procedure. NH4Cl was chosen as the extractant because of its high calcium selectivity and inhibition of gel formation. Precipitates with Ca content ≥ 98% were obtained by extracting and carbonating them. The crystalline form and particle size of CaCO3 in the precipitates were determined by the pH control. The findings of this study will be used to improve the design of precipitated calcium carbonate (PCC) production processes and increase the economic value of their output. [ABSTRACT FROM AUTHOR]

The surge in global industrialization has significantly increased greenhouse gas concentrations in the Earth's atmosphere, with carbon dioxide (CO2) being the predominant contributor to about two-thirds of the greenhouse effect. Landfill gas (LFG), resulting from the biodegradation of municipal solid waste (MSW), mainly consists of methane (CH4) and CO2. To counteract uncontrolled CO2 emissions from waste decomposition, an innovative, low-cost biogeochemical cover (BGCC) system for landfills utilizing biochar-amended soil and basic oxygen furnace (BOF) slag for CO2 carbonation has been developed. Despite the effectiveness of BOF slag in CO2 removal, its limited availability near landfill sites presents sustainability challenges, necessitating the search for viable alternatives within the BGCC system that can achieve efficient CO2 sequestration through direct aqueous mineral carbonation. This review explores various carbon sequestration techniques, identifying potential alkaline industrial solid wastes as substitutes for BOF slag, and evaluates these materials—namely cement kiln dust (CKD), blast furnace (BF) slag, coal fly ash (CFA), and concrete waste—for their compatibility with the BGCC system. CKD is highlighted as having the highest carbonation potential based on its capacity for direct aqueous carbonation, with a comparative analysis revealing substantial differences in the carbonation capacities of the materials. Given the fine-grained nature of the selected materials, the review also emphasizes the need to integrate them into barrier soil layers or use them as standalone layers within the BGCC. In conclusion, this review accentuates the potential of alternative materials in achieving effective CO2 sequestration within BGCC, thereby addressing the challenges related to the availability of BOF slag and promoting sustainable landfill management practices. [ABSTRACT FROM AUTHOR]

In recent years, the building industry has looked for technological ways to protect the environment and preserve natural resources. Since the COVID-19 epidemic, there has been a shortage of building materials, which has caused construction costs to go up. This has made it more important for sustainable development to be based on the principles of the circular economy. This gives an opportunity to utilise various reliable materials as substitutes, like construction and demolition (C&D) waste. (C&D) wastes are made up of a large chunk of all solid waste, which causes many environmental problems. The most important factor in the struggle against climate change is the reduction of CO2 emissions from the construction sector. At the same time, globally, climate change caused in part by carbon dioxide (CO2) emissions is an important problem that requires innovative carbon sequestration strategies. Because C&D waste is alkaline-rich (e.g., calcium hydroxide and calcium-silicate-hydrate (C-S-H)), it can be used to sequester CO2 by converting it into thermodynamically stable carbonates. Temperature, partial pressure of CO2, time, process route, humidity, and the water-to-solid ratio (w/s) can affect the CO2 sequestration over the C&D wastes. [ABSTRACT FROM AUTHOR]

Natural Mg phyllosilicates are potential sources of divalent cations, which are necessary for the mineralization of CO2 into carbonates. The influence of inorganic () and organic (oxalate and citrate) ligands on the dissolution kinetics of talc and serpentine was studied in experiments in a flow-through reactor at 25°C. The dissolution rates of natural silicates r (mol cm–2 s–1) in solutions of various composition were calculated at the stationary stage of dissolution after a rapid initial stage, which is characterized by the formation of a surface leached layer depleted in magnesium. The presence of ligands increases the dissolution rate of magnesium silicates due to the formation of surface complexes, which leads to magnesium separation from the surface and transfer into solution. The initial incongruent stage may be the most promising for the development of carbonation technologies, because the minimum removal of the network-forming elements prevents the undesirable formation of secondary minerals (for example, clays), which exclude divalent cations from the carbonation process and greatly reduce the permeability of rocks. [ABSTRACT FROM AUTHOR]

To shift towards a sustainable steel production practice, circular economy principles can be applied in the value chain by valorizing the 2 in flue gases and the generated steel slags to produce stable silicates and carbonates via mineral carbonation, leading to long-term stable carbon sequestration. Carbonated slags can then be considered as a carbon capture, utilization and storage technology. However, it is important to quantify the environmental benefits and economic viability to evaluate a system's sustainability. This study aims (1) to evaluate the environmental and economic impacts of steel slag mineral carbonation and (2) to identify hotspots and process parameters of the systems. In this study, lab-scale experimental mineral carbonation data is upscaled to a TRL 6 scenario via an upscaling simulation with a power law learning curve. Subsequently, life cycle assessment and life cycle costing are performed to quantify the environmental and economic performances in agriculture. Contribution analyses are performed to ascertain the hotspots and process parameters of the systems. The results obtained in this study can encourage industrial symbiosis among different stakeholders in and around the steel industry to promote a more sustainable steel manufacturing value chain, incorporating circular economy principles. [ABSTRACT FROM AUTHOR]

CO2 sequestration via mineralization of steel slag has received widespread attention due to its ability to achieve in-situ CO2 sequestration in steel industries and high-value utilization of steel slag. The final CO2 sequestration capacity of steel slag is closely related to the reaction parameters (i.e., reaction duration, reaction temperature, CO2vol concentration, and liquid-solid ratios) of mineralization. The reaction parameters may have synergistic effects on the ability of steel slag to sequestrate CO2. Therefore, the single-factor (one-factor-at-a-time) experimental strategy can't obtain optimal process parameters. Herein, response surface methodology and the Box-Behnken Design were employed in determining optimal conditions. It is found that the combined effects of CO2 concentration in combination with reaction temperature and liquid-solid ratio significantly influence the sequestration process (P = 0.0082 and P < 0.0001, respectively). Conversely, the combined effects of reaction duration with liquid-solid ratio and CO2 concentration were found to be less significant (P = 0.6905 and P = 0.6114, respectively). The reasons behind this observation can be ascribed to the focus of this research on the later stages of the reaction, during which it proceeds smoothly. Additionally, alterations in temperature, liquid-solid ratio, and CO2 concentration not only affect the initial pH, CO2 dissolution rate and quantity, and reaction kinetics but also alter the patterns of their collective impact on CO2 sequestration. The CO2 capture could reach 179.1 g-CO2/kg-steel slag at the optimal condition (i.e., 56.14 °C reaction temperature, 6.66 ml/g liquid-solid ratio, 44.53 wt.% CO2 concentration, and 286.73 mins reaction time), compared to single-factor stepwise optimization, which improves by about 9.84 %. Implementing this optimized mineralization process could enable the Chinese steel industry to capture an estimated 27.4 million tons of CO2 annually, based on an annual production of 153 million tons of steel slag.

An assessment of the levelised cost and associated CO2-eq emissions for the thermal activation of serpentine mine tailings to be used as activated feedstock for CCUS processes via mineral carbonation, is reported here for the first time. Two main technological scenarios were assessed, based on either direct fuel sources heating (natural gas and hydrogen) or indirect, CST-based heating with a back-up burner and storage to provide continuous operations, for a 200 ton/hr of processed ore and a targeted roasting ore temperature of 700°C. For CST-based systems, 3 different solar input scales, namely 50, 150 and 450 MWth, were considered, and simulations performed over a year timeline with a 10 minutes time step, using Mt Keith Nickel mine in Western Australia as the reference location. The analysis highlighted that the proposed CST-hybrid plant layout can achieve similar cost to that of fuel-only cases with current Australian fuel prices for natural gas and hydrogen, with lower CO2-eq emissions, and a parity cost with fuel-only scenarios of some 16 USD/GJ. The proposed CST-hybrid plant layout was also identified as the potential, preferred route over direct CST routes to achieve 24/7 continuous heat supply while retaining fine tuning of activation temperature, given a very narrow temperature window of activation for the chosen mine tailings for mineral carbonation processes.

The observation of photosynthetic biofilms growing on the Fine Residue Deposit (FRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa suggests that processed kimberlite supports bacterial growth. The presence of this biofilm may aid in the acceleration of weathering of this ultra-mafic host material – a process that can sequester CO2 via carbon mineralization. Laboratory and field trial experiments were undertaken to understand the microbe–mineral interactions occurring in these systems, and how these interactions impact geochemical cycling and carbonate precipitation. At laboratory scale it was discovered that using kimberlite as a growth supplement increased biomass production (up to 25-fold) and promoted microbiome diversity, while the inoculation of FRD systems aided in the aggregation, settling, and dewatering of kimberlitic slurries. Field trial studies combining photosynthetic biofilms (cultured in 3 × 1,000 L bioreactors) with FRD material were initiated to better understand microbially enhanced mineral carbonation across different depths, and under field environmental conditions. Over the 15-month experiment the microbial populations shifted with the kimberlitic environmental pressure, with the control and inoculated systems converging. The natural endogenous biosphere (control) and the inoculum accelerated carbonate precipitation across the entire 40 cm bioreactor depth, producing average 15-month carbonation rates of 0.57 wt.% and 1.17 wt.%, respectively. This corresponds to an annual CO2e mine offset of ~4.48% and ~ 9.2%, respectively. Millimetre-centimetre scale secondary carbonate that formed in the inoculated bioreactors was determined to be biogenic in nature (i.e., possessing microbial fossils) and took the form of radiating colloform precipitates with the addition of new, mineralized colonies. Surficial conditions resulted in the largest production of secondary carbonate, consistent with a ca. 12% mine site CO2e annual offset after a 15-month incubation period.

Most of the geologic CO2 entering Earth's atmosphere and oceans is emitted along plate margins. While C-cycling at mid-ocean ridges and subduction zones has been studied for decades, little attention has been paid to degassing of magmatic CO2 and mineral carbonation of mantle rocks in oceanic transform faults. We studied the formation of soapstone (magnesite-talc rock) and other magnesite-bearing assemblages during mineral carbonation of mantle peridotite in the St. Paul's transform fault, equatorial Atlantic. Clumped carbonate thermometry of soapstone yields a formation (or equilibration) temperature of 147 ± 13 °C which, based on thermodynamic constraints, suggests that CO2(aq) concentrations of the hydrothermal fluid were at least an order of magnitude higher than in seawater. The association of magnesite with apatite in veins, magnesite with a d13C of -3.40 ± 0.04°, and the enrichment of CO2 in hydrothermal fluids point to magmatic degassing and melt-impregnation as the main source of CO2. Melt-rock interaction related to gas-rich alkali olivine basalt volcanism near the St. Paul's Rocks archipelago is manifested in systematic changes in peridotite compositions, notably a strong enrichment in incompatible elements with decreasing MgO/SiO2. These findings reveal a previously undocumented aspect of the geologic carbon cycle in one of the largest oceanic transform faults: Fueled by magmatism in or below the root zone of the transform fault and subsequent degassing, the fault constitutes a conduit for CO2-rich hydrothermal fluids, while carbonation of peridotite represents a vast sink for the emitted CO2. [ABSTRACT FROM AUTHOR]

Mining waste is generated in vast quantities globally, which can have negative environmental consequences. This study highlights the utilization of iron ore mining waste as feedstock material in the preparatory step of an indirect aqueous mineral carbonation for carbon sequestration. The role of reactive cations (Ca2+, Mg2+, and Fe2+) was investigated in view of their elution behavior to improve carbonation efficiency. An elution experiment was carried out for the divalent cations using different acids (oxalic, HCl, acetic, and formic acid) at different concentration solutions (up to 1.5 M) and times (up to 100 min) at ambient temperature. The initial analysis confirmed the presence of divalent cations in the sample. The elution approach at ambient temperature resulted in the elution efficiency of Fe2+ (30.4%), Mg2+ (54%) using oxalic acid, and Ca2+ (98%) using HCl at a relatively short time between 50 and 100 min. It was found that for the iron ore mining waste, oxalic acid and HCl were best suited as elution agents for the Fe2+ and Mg2+, and Ca2+, respectively. The CO2 sequestration potential was calculated to be 131.58 g CO2/kg residue. A further carbonation step using a complexing agent (1,10 phenanthroline) confirmed the formation of siderite and magnesite along with phenanthroline hydrates. Findings have shown that the indirect mineral carbonation of the iron mining waste with complexing agent might improve carbonation efficiency, thus indicating that this material is useful for long-term carbon capture and storage applications. [ABSTRACT FROM AUTHOR]

In the pursuit of sustainable solutions for carbon dioxide CO2 sequestration and emission reduction in the steel industry, this study presents an innovative integration of steelmaking slag with the modified Solvay process for sodium bicarbonate (NaHCO3) synthesis from saline brines. Utilizing diverse minerals, including electric arc furnace (EAF) slag, olivine, and kimberlite, the study explored their reactivity under varied pH conditions and examined their potential in ammonium regeneration. SEM and WDXRF analyses were utilized to acquire morphological and chemical compositions of the minerals. Advanced techniques such as XRD and ICP-OES were employed to meticulously analyze mineralogical transformations and elemental concentrations. The findings demonstrate that steelmaking slag, owing to its superior reactivity and pH buffering capabilities, outperforms natural minerals. The integration of finer slag particles significantly elevated pH levels, facilitating efficient ammonium regeneration. Geochemical modeling provided valuable insights into mineral stability and reactivity, which aligned with the ICP-OES results. This synergistic approach not only aids in CO2 capture through mineral carbonation but also minimizes waste, showcasing its potential as a sustainable and environmentally responsible solution for CO2 mitigation in the steel industry. [ABSTRACT FROM AUTHOR]

Mineral carbonation stands out not only as an effective method for reducing CO2 emissions but also as a strategic approach to upcycling industrial waste. This study introduces a novel procedure for generating high-purity nano-calcium carbonate (nCaCO3) from waste cement powder, deploying hydrochloric acid (HCl), and sodium hydroxide (NaOH), both obtained through the electrolysis of sodium chloride (NaCl). Our approach, aimed at both environmental preservation and techno-economic feasibility, encompasses optimizing calcium extraction conditions through rigorous analysis of variables such as HCl concentration, solid-to-liquid ratio, and reaction temperature, subsequently proposing a rate law for the extraction process. Furthermore, the method emphasizes the production of high-purity CaCO3 by meticulously removing metallic impurities from the extracted solution with 1.0 M NaOH, culminating in pure calcium hydroxide and the generation of nCaCO3 particles with superior purity (>99 %) and a uniform particle size (80–140 nm). An exhaustive environmental and economic assessment indicates that our process, while consuming varying energy levels based on operational potentials, anticipates a significant reduction in CO2 emissions by 46.1 %, alongside a competitive production cost (335 USD/ton of nCaCO3), thereby demonstrating substantial advantages over traditional methods in terms of sustainability, efficiency, and cost-effectiveness.

Cementitious materials as a medium of carbon capture, and utilization (CCU) have recently attracted considerable attentions. Atmospheric CO2 can be absorbed in hardened concrete, which can be also accelerated by early age CO2 curing. Compared to the CO2 curing of concrete materials, in-situ CO2 mixing technology can be widely applied because it can be used in a batch plant without an additional curing facility. In this study, the CO2 mixing time was set as the primary variable to elucidate the precipitation of the carbonate phases in the early stages and its effect on cement hydration. The dissociated CO2 is directly mineralized into calcium carbonate (CaCO3) in calcite phase. In addition, the longer the CO2 mixing time, the greater the precipitation of calcite (i.e., CCU capacity), thereby densifying the internal microstructure and improving early strength development. Interestingly, a certain amount of calcite converted to monocarboaluminate—an important factor for quantitatively assessing the degree of mineral carbonation in cementitious materials.

The release of carbon dioxide (CO2) into the earth's atmosphere is a substantial global environmental concern that arises from the processes of industrialization and urbanization. The increase in atmospheric CO2 concentrations has resulted in the phenomenon of global warming and subsequent alterations in climate patterns. Accelerated CO2 sequestration in cementitious materials is currently the subject of extensive research as a highly efficacious approach to mitigating the carbon footprint of the concrete industry. The sequestration procedure entails the transformation of gaseous CO2 into carbonate minerals. The review presented in this paper outlines the most recent carbonation (i.e., CO2 sequestration) techniques, such as mineral carbonation, accelerated CO2 curing (ACC), pre-carbonation, and carbonation mixing, that have been recently explored. The potential of mineral carbonation of industrial wastes and the advantages of their incorporation in the concrete matrix is investigated. Carbonation technologies and their effect on the performance of cementitious composites are reported. Information on life cycle assessment are also included to evaluate the environmental impact associated with the production of carbonated materials. Various commercialized CO2 utilization technologies in construction sector, such as CarbonCure, Solidia, Carbstone, Calera, and Carbon8 are reviewed. Moreover, this review offers a thorough insight into the carbonation technologies, evaluating their advantages, limitations, and the existing gaps in research.

Over the previous two decades, a diverse array of geochemical negative emissions technologies (NETs) have been proposed, which use alkaline minerals for removing and permanently storing atmospheric carbon dioxide (CO2). Geochemical NETs include CO2 mineralization (methods which react alkaline minerals with CO2, producing solid carbonate minerals), enhanced weathering (dispersing alkaline minerals in the environment for CO2 drawdown) and ocean alkalinity enhancement (manipulation of ocean chemistry to remove CO2 from air as dissolved inorganic carbon). CO2 mineralization approaches include in situ (CO2 reacts with alkaline minerals in the Earth's subsurface), surficial (high surface area alkaline minerals found at the Earth's surface are reacted with air or CO2-bearing fluids), and ex situ (high surface area alkaline minerals are transported to sites of concentrated CO2 production). Geochemical NETS may also include an approach to direct air capture (DAC) that harnesses surficial mineralization reactions to remove CO2 from air, and produce concentrated CO2. Overall, these technologies are at an early stage of development with just a few subjected to field trials. In Part I of this work we have reviewed the current state of geochemical NETs, highlighting key features (mineral resources; processes; kinetics; storage durability; synergies with other NETs such as DAC, risks; limitations; co-benefits, environmental impacts and life-cycle assessment). The role of organisms and biological mechanisms in enhancing geochemical NETs is also explored. In Part II, a roadmap is presented to help catalyze the research, development, and deployment of geochemical NETs at the gigaton scale over the coming decades.

The escalating global warming has intensified concerns about climate change and prompted a swift shift towards worldwide carbon neutrality and a sustainable future. Among various carbon capture, utilization, and storage technologies, mineral carbonation enables the transformation of waste materials into valuable construction resources while mitigating their adverse impacts on the environment and public health. During the past two decades, mineral carbonation has found widespread application in carbon sequestration, primarily employing industrial by-products, notably those generated within the iron and steel sector. The inherent properties of these by-products, characterized by alkalinity, reactivity for carbonation, widespread availability, and substantial quantities, hold great potential for carbon mitigation. Developing efficient and resilient carbon sequestration protocols utilizing iron and steel by-products is vital, as it addresses key challenges associated with mineral carbonation, such as high costs, slow reaction kinetics, and environmentally detrimental feedstock mining.In this review paper, various carbonation techniques for iron and steel by-products are evaluated and summarized. Different stages of essential carbonation processes are examined, along with their detailed physicochemical mechanisms. The review also explores recent technological advancements in this field, including the utilization of additives, supercritical carbonation, microwave irradiation, and ultrasonic enhancement, while assessing their potential to enhance process efficiency and sustainability. Additionally, the paper critically assesses representative processes from economic, environmental, and health perspectives. By providing an in-depth discussion of scalability, industrial implementations, economic feasibility, environmental toxicity, health impacts, and current technical barriers, this paper presents a comprehensive summary that addresses challenges, opportunities, prospects, and key insights in the field of mineral carbonation using iron and steel by-products. This effort represents a unique contribution to fill critical knowledge gaps in the mineral carbonation of iron and steel by-products, encompassing state-of-the-art technical advances and addressing their economic, environmental, and health implications.

Carbon capture, utilization and storage (CCUS) technologies are utmost need of the modern era. CCUS technologies adoption is compulsory to keep global warming below 1.5 °C. Mineral carbonation (MC) is considered one of the safest and most viable methods to sequester anthropogenic carbon dioxide (CO2). MC is an exothermic reaction and occur naturally in the subsurface because of fluid-rock interactions with serpentinite. In serpentine carbonation, CO2 reacts with magnesium to produce carbonates. This article covers CO2 mitigation technologies especially mineral carbonation, mineral carbonation by natural and industrial materials, mineral carbonation feedstock availability in Pakistan, detailed characterization of serpentine from Skardu serpentinite belt, geo sequestration, oceanic sequestration, CO2 to urea and CO2 to methanol and other chemicals. Advantages, disadvantages, and suitability of these technologies is discussed. These technologies are utmost necessary for Pakistan as recent climate change induced flooding devastated one third of Pakistan affecting millions of families. Hence, Pakistan must store CO2 through various CCUS technologies.

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Human survival is threatened by the rapid climate change due to global warming caused by the increase in CO2 emissions since the Second Industrial Revolution. This study developed a secondary cement product production technology by replacing cement, a conventional binder, with calcium silicate cement (CSC), i.e., CO2 reactive hardening cement, to reduce CO2 emissions and utilize CO2 from the cement industry, which emits CO2 in large quantities. Results showed that the carbonation depth, compressive strength increase rate, and CO2 sequestration rate increased as the CSC content increased, suggesting that CSC can be applied as a secondary cement product. [ABSTRACT FROM AUTHOR]

As a rapidly evolving technology, carbon capture and storage (CCS) can potentially lower the levels of greenhouse gas emissions from the oil and gas industry. This paper provides a comprehensive review of different aspects of CCS technology, including its key components, the methods and stages of carbon storage, implied environmental effects, and its pros and cons. This paper also investigates the utilization of CCS as an alternative method to water injection into oil reservoirs. It also probes the technical and operational challenges of implementing CCS technology in the oil and gas industry. Additionally, this paper examines the regulatory and policy issues associated with CCS, including incentives and frameworks for promoting the deployment of CCS technology. Finally, in this paper the potential benefits of CCS are discussed, including reducing the carbon footprint of the oil and gas industry, enhancing energy security, and supporting the transition to a low-carbon economy. [ABSTRACT FROM AUTHOR]

Abstract Microbiological weathering of coarse residue deposit (CRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa enhanced mineral carbonation relative to untreated material. Cultures of photosynthetically enriched biofilm produced maximal carbonation conditions when mixed with kimberlite and incubated under near surface conditions. Interestingly, mineral carbonation also occurred in the dark, under water-saturated conditions. The examination of mineralized biofilms in ca. 150 µm-thick-sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron—scanning electron microscopy-energy dispersive x-ray spectrometry demonstrated that microbiological weathering aided in producing secondary calcium/magnesium carbonates on silicate grain boundaries. Calcium/magnesium sulphate(s) precipitated under vadose conditions demonstrating that evaporites formed upon drying. In this system, mineral carbonation was only observed in regions possessing bacteria, preserved within carbonate as cemented microcolonies. 16S rDNA molecular diversity of bacteria in kimberlite and in natural biofilms growing on kimberlite were dominated by Proteobacteria that are active in nitrogen, phosphorus and sulphur cycling. Cyanobacteria based enrichment cultures provided with nitrogen & phosphorus (nutrients) to enhance growth, possessed increased diversity of bacteria, with Proteobacteria re-establishing themselves as the dominant bacterial lineage when incubated under dark, vadose conditions consistent with natural kimberlite. Overall, 16S rDNA analyses revealed that weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation. Enhanced weathering and carbonate-cemented microcolonies demonstrate that microorganisms are key to mineral carbonation of kimberlite.

Mineral technology has attracted significant attention in recent decades. Mineral carbonation technology is being used for permanent sequestration of CO2 (greenhouse gas). Temperature programmed desorption studies showed interaction of CO2 with Mg indicating possibility of using natural feedstocks for mineral carbonation. Soaking is effective to increase yields of heat-activated materials. This review covers the latest developments in mineral carbonation technology. In this review, development in carbonation of natural minerals, effect of soaking on raw and heat-activated dunite, increasing reactivity of minerals, thermal activation, carbonations of waste materials, increasing efficiency of carbonation process and pilot plants on mineral carbonation are discussed. Developments in carbonation processes (single-stage carbonation, two-stage carbonation, acid dissolution, ph swing process) and pre-process and concurrent grinding are elaborated. This review also highlights future research required in mineral carbonation technology.

In this study, municipal solid waste incineration (MSWI) fly ash was subjected to mineral carbonation with the aim of investigating CO2 sequestration in waste material. The conducted study follows the trend of searching for alternatives to natural mineral materials with the ability to sequestrate CO2. The mineral carbonation of MSWI fly ash allowed for the storage of up to 0.25 mmol CO2 g−1. Next, both carbonated and uncarbonated MSWI fly ashes were activated using an alkaline activation method by means of two different activation agents, namely potassium hydroxide and potassium silicate or sodium hydroxide and sodium silicate. Mineral carbonation caused a drop in the compressive strength of alkali-activated materials, probably due to the formation of sodium and/or potassium carbonates. The maximum compressive strength obtained was 3.93 MPa after 28 days for uncarbonated fly ash activated using 8 mol dm−3 KOH and potassium hydroxide (ratio 3:1). The relative ratio of hydroxide:silicate also influenced the mechanical properties of the materials. Both carbonated and uncarbonated fly ashes, as well as their alkali-activated derivatives, were characterized in detail by means of XRD, XRF, and FTIR. Both uncarbonated and carbonated fly ashes were subjected to TG analysis. The obtained results have proved the importance of further research in terms of high-calcium fly ash (HCFA) utilization. [ABSTRACT FROM AUTHOR]

The heterogenous mineralogy of ultramafic deposits hosting mining operations makes it challenging to accurately determine the waste rock's mineral carbonation potential (MCP). Additionally, the significantly higher carbonation capabilities of olivine than serpentine add to the difficulty. To address this issue, in this work, a new and unique tool called the MCP calculator was developed as a Microsoft ExcelTM spreadsheet to accurately determine the amount of anthropogenic CO2 that a given rock mass can sequester through mineral carbonation. The program estimates the modal mineral abundance of ultramafic rocks to aid in MCP estimation. This tool is designed to be cost-effective and tailored for use by the mining industry, utilising abundant lithogeochemical data to evaluate their deposit as a potential substrate for industrial mineral carbonation operations. The paper introduces the MCP calculator, outlines a framework for developing the MCP parameter, and presents an example of its application. The calculator is specific to the mineral assemblage investigated at the Turnagain ultramafic complex in northern British Columbia but can be adjusted to study comparable deposits. The paper acknowledges that using waste rock in a mineral carbonation operation requires economic and practical decisions beyond the scope of the research. [ABSTRACT FROM AUTHOR]

Waste concrete powder (WCP) is emerging as a potential method of adoption for CO2 sequestration due to its ability to chemically react with carbon dioxide and trap it within its structure. This study explores the application of artificial intelligence (AI) and the Marine Predators Algorithm (MPA) to maximize the absorption of CO2 from waste concrete powder generated by recycling plants for building and demolition debris. Initially, a model is developed to assess CO2 uptake according to carbonation time (CT) and water-to-solid ratio (WSR), utilizing the adaptive neuro-fuzzy inference system (ANFIS) modeling approach. Subsequently, the MPA is employed to estimate the optimal values for CT and WSR, thereby maximizing CO2 uptake. A significant improvement in modeling accuracy is evident when the ANOVA method is replaced with ANFIS, leading to a substantial increase of approximately 19% in the coefficient of determination (R-squared) from 0.84, obtained through ANOVA, to an impressive 0.9999 obtained through the implementation of ANFIS; furthermore, the utilization of ANFIS yields a substantial reduction in the root mean square error (RMSE) from 1.96, as indicated by ANOVA, to an impressively low value of 0.0102 with ANFIS. The integration of ANFIS and MPA demonstrates impressive results, with a nearly 30% increase in the percentage value of CO2 uptake. The highest CO2 uptake of 3.86% was achieved when the carbonation time was 54.3 h, and the water-to-solid ratio was 0.27. This study highlights the potential of AI and the MPA as effective tools for optimizing CO2 absorption from waste concrete powder, contributing to sustainable waste management practices in the construction industry. [ABSTRACT FROM AUTHOR]

This work compares the mechanical properties of two geomaterials: forsterite and magnesite. Various physical conditions are considered to investigate the evolution of stress–strain relationships for these two polycrystals. A molecular-scale study is performed on three-dimensional models of forsterite and magnesite. Three different temperatures (300 K, 500 K, and 700 K) and strain rates (0.001, 0.01, and 0.05 ps−1) are considered to initiate deformation in the polycrystals under tensile and compressive forces. The polycrystalline structures face deformation at lower peaks at high temperatures. The Young's modulus values of forsterite and magnesite are found to be approximately 154.7451 GPa and 92.84 GPa under tensile forces and these values are found to be around 120.457 GPa (forsterite) and 77.04 GPa (magnesite) for compressive forces. Increasing temperature reduces the maximum strength of the polycrystalline structures, but forsterite shows higher ductility compared to magnesite. Strain rate sensitivity and the effect of grain size are also studied. The yield strengths of the forsterite and magnesite drop by 7.89% and 9.09% when the grain size is reduced by 20% and 15%, respectively. This study also focuses on the changes in elastic properties for different pressures and temperatures. In addition, from the radial distribution function (RDF) results, it was observed that the peak intensity of pairwise interaction of Si–O is higher than that of Mg–O. Finally, it is found that the formation of magnesite, which is the product of mineral carbonation of forsterite, is favorable in terms of mechanical properties for the comminution process. [ABSTRACT FROM AUTHOR]

Mineral carbonation is a technology for capturing and storing CO2 in solid minerals. When mineral carbonation is used to produce construction materials, the quantification of the CO2 uptake of these products is of the utmost importance, as it is used to calculate the CO2 footprint of the product and/or carbon offset. The CO2 uptake is generally determined by measuring the CO2 content of a material before and after accelerated carbonation. This approach, however, does not take hydration and dehydroxylation reactions into account that may occur during carbonation, and it can therefore under- or overestimate the CO2 uptake. Thus, a more accurate and practical method to determine CO2 uptake, which also accounts for hydration and dehydroxylation reactions, is proposed in this paper. This method is based on analytical methods to determine the dry mass and the CO2 content of the solid products before and after carbonation, and on the calculation of the CO2 uptake by the following equation: CO2 uptake (wt.%) = CO2 carbonated (wt.%) × (weight after carbonation (g)/weight before carbonation (g) − CO2 initial (wt.%), with CO2 carbonated being the CO2 content in g/100 g dried carbonated material, and CO2 initial being the CO2 content in g/100 g dried initial material, i.e., before carbonation. The "weight before carbonation" is the dry weight of the initial material, and the "weight after carbonation" is the product's dry weight after carbonation. In this paper, we show that up to 44% under- or overestimation of CO2 uptake can occur when hydration and dehydroxylation reactions are not taken into account during mineral carbonation. [ABSTRACT FROM AUTHOR]

This study focuses on the utilization of mineral carbonation as a means to capture carbon dioxide (CO2) from the atmosphere. The approach involves using various composites consisting of an inert matrix with an active phase. To evaluate the efficiency of mineral carbonation for CO2 sequestration, three composites were synthesized based on calcium-rich and calcium/magnesium-rich minerals using sol–gel techniques. The results obtained from the characterization techniques used, namely X-ray diffraction, infrared spectroscopy and scanning electron microscopy, demonstrate the formation of composite materials such as calcium oxide and calcium/magnesium oxides. After the bubbling process, these techniques confirmed the formation of stable calcium and magnesium carbonates. In addition, to assess the efficiency of the synthesized composites in CO2 capture, a Bernard's Calcimeter was used to determine the operating parameters favouring the mineral carbonation reaction. Analysing these operating parameters reveals that under atmospheric pressure and at room temperature, increasing the mass of the compound used leads to an increase in the percentage of captured CO2 up to 0.5 g, but this rate remains relatively constant when the mass is increased to 1 g. Additionally, increasing the particle size results in a higher CO2 capture rate. The initial pH of the solution plays a crucial role in promoting mineral carbonation, as an increase in the initial pH also leads to an increase in the CO2 fixation rate. It is essential for the medium to be basic, as this is one of the critical parameters contributing to the enhanced CO2 sequestration rate through the mineral carbonation method. [ABSTRACT FROM AUTHOR]