A review on ex situ mineral carbonation

Harnessing Ash for Sustainable CO2 Absorption: Current Strategies and Future Prospects

This review explores the potential of using different types of ash, namely fly ash, biomass ash, and coal ash etc., as mediums for CO2 capture and sequestration. The diverse origins of these ash types - municipal waste, organic biomass, and coal combustion - impart unique physicochemical properties that influence their suitability and efficiency in CO2 absorption. This review first discusses the environmental and economic implications of using ash wastes, emphasizing the reduction in landfill usage and the transformation of waste into value-added products. Then the chemical/physical treatments of ash wastes and their inherent capabilities in binding or reacting with CO2 are introduced, along with current methodologies utilize these ashes for CO2 sequestration, including mineral carbonation and direct air capture techniques. The application of using ash wastes for CO2 capture are highlighted, followed by the discussion regarding challenges associated with ash-based CO2 absorption approach. Finally, the article projects into the future, proposing innovative approaches and technological advancements needed to enhance the efficacy of ash in combating the increasing CO2 levels. By providing a comprehensive analysis of current strategies and envisioning future prospects, this review aims to contribute to the field of sustainable CO2 absorption and environmental management.

From black to green: Quantifying the impact of economic growth, resource management, and green technologies on CO2 emissions

In an exploration of environmental concerns, this groundbreaking research delves into the relationship between GDP per capita, coal rents, forest rents, mineral rents, oil rents, natural gas rents, fossil fuels, renewables, environmental tax and environment-related technologies on CO2 emissions in 30 highly emitting countries from 1995 to 2021 using instrumental-variables regression Two-Stage least squares (IV-2SLS) regression and two-step system generalized method of moments (GMM) estimates. Our results indicate a significant positive relationship between economic growth and CO2 emissions across all quantiles, showcasing an EKC with diminishing marginal effects. Coal rents exhibit a statistically significant negative relationship with emissions, particularly in higher quantiles, and mineral rents show a negative association with CO2 emissions in lower and middle quantiles, reinforcing the idea of resource management in emissions reduction. Fossil fuels exert a considerable adverse impact on emissions, with a rising effect in progressive quantiles. Conversely, renewable energy significantly curtails CO2 emissions, with higher impacts in lower quantiles. Environmental tax also mitigates CO2 emissions. Environment-related technologies play a pivotal role in emission reduction, particularly in lower and middle quantiles, emphasizing the need for innovative solutions. These findings provide valuable insights for policymakers, highlighting the importance of tailoring interventions to different emission levels and leveraging diverse strategies for sustainable development.

Calcium carbonate synthesis from Kambara reactor desulphurization slag via indirect carbonation for CO2 capture and utilization

In this work, industrial Kambara reactor desulphurization slag (KR slag) was indirectly carbonated. The effects of leaching time, leaching temperature, leaching agent types, and leaching agent concentration on the leaching ratio of calcium from KR slag were investigated. Subsequently, precipitated calcium carbonate (PCC) was synthesized by bubbling CO2 gas (flow rate of 15 mL/min) into 400 mL leaching solutions at 40 °C for 120 min with magnetic stirring at 300 rpm. It is found that calcium in KR slag can be selectively extracted using a diluted solution of ammonium acetate (CH3COONH4) or ammonium chloride (NH4Cl), while ammonium sulfate ((NH4)2SO4) solution is not suitable as leaching agent due to the formation of slightly soluble calcium sulfate (CaSO4). The leaching ratio of calcium is improved by extending the leaching time or increasing the leaching solvent concentration. However, leaching temperature has little effect on calcium extraction. After carbonating the NH4Cl- and CH3COONH4-leachate for 120 min, calcite and vaterite type PCC with a purity of 99% is synthesized. Each gram of KR slag can produce 0.794 g and 0.803 g PCC using NH4Cl and CH3COONH4 leaching agents respectively. Calculations show that 349.6 kg CO2 is captured by per ton of KR slag. The CO2 capture capacity of KR slag is significantly higher compared with previously studied materials.

Experimental study on characterization of lime-based mineral carbonation reaction and CO2 sequestration

This paper reports for the first time the use and application of a novel technique in the characterization of mineral carbonation reaction and CO2 sequestration in soil stabilization using flow meters. Soils based on SiO2 with two different sizes were tested. Lime (Ca(OH)2) was used as the reactant. Instant CO2 flow rate (L/min), total CO2 volume (L), temperature (°C), and absolute pressure (kPa) were monitored and recorded for 1 h by flow meters connected to the mold inlet and outlet. It was determined that the mineral carbonation reaction started in the first seconds and ended before the 5th minute. The mineral carbonation is a short-term and potential reaction, and it is not a time-dependent reaction. It is separated from other carbonation reactions with these characteristics. The highest CO2 captured value was obtained in the soil mixed with 5% lime, where fines were not used. The second highest CO2 captured value was obtained in soil mixed with 1% lime, where fines were not used. CO2 captured with 1% lime is more than CO2 captured with 5% lime in the soil containing fines. Accordingly, 1-5% lime can be used in soil carbonation studies. According to the soil properties, the highest CO2 captured and the CO2 efficiency was achieved with the use of 6-7% water by weight.

Amine-Assisted Simultaneous CO2 Absorption and Mineral Carbonation: Effect of Different Categories of Amines

The hybrid technology of CO₂ capture-mineral carbonation (CCMC) using alkaline streams has emerged in recent years. However, thus far, there has been no comprehensive study revealing the mechanisms of the simultaneous CCMC process regarding the choice of amine types and sensitivity of parameters. Combining with the analysis of multistep reaction mechanisms for different amines, we investigated a representative from each category in CCMC using calcium chloride to simulate the alkaline resource after leaching, i.e., primary (ethanolamine, MEA), secondary (diisopropanolamine, DIPA), tertiary (diethylethanolamine, DEAE), and triamine (diethylenetriamine, DETA), respectively. In the adsorption step, increasing the amine concentration beyond 2 mol/L reduced the absorption efficiency of DEAE due to the hydration mechanism, motivating a rational choice of concentration. In CCMC sections, when the amine concentration increased, only DEAE exhibited an increased carbonation efficiency of up to 100%, while DETA showed the lowest conversion. The carbonation of DEAE demonstrated the least sensitivity to temperature. The crystal transformation experiments suggested that over time, the produced vaterite could completely transform to calcite or aragonite, except those from DETA. Thus, with rationally chosen conditions, DEAE was demonstrated ideal for CCMC. These findings obtained in this work provided a theoretical foundation for designing future CCMC processes.

Trends in Research and Development for CO2 Capture and Sequestration

Technological and medical advances over the past few decades epitomize human capabilities. However, the increased life expectancies and concomitant land-use changes have significantly contributed to the release of ∼830 gigatons of CO₂ into the atmosphere over the last three decades, an amount comparable to the prior two and a half centuries of CO₂ emissions. The United Nations has adopted a pledge to achieve "net zero", i.e., yearly removing as much CO₂ from the atmosphere as the amount emitted due to human activities, by the year 2050. Attaining this goal will require a concerted effort by scientists, policy makers, and industries all around the globe. The development of novel materials on industrial scales to selectively remove CO₂ from mixtures of gases makes it possible to mitigate CO₂ emissions using a multipronged approach. Broadly, the CO₂ present in the atmosphere can be captured using materials and processes for biological, chemical, and geological technologies that can sequester CO₂ while also reducing our dependence on fossil-fuel reserves. In this review, we used the curated literature available in the CAS Content Collection to present a systematic analysis of the various approaches taken by scientists and industrialists to restore carbon balance in the environment. Our analysis highlights the latest trends alongside the associated challenges.

Enhanced precipitation of magnesium carbonates using carbonic anhydrase

Carbonate precipitation, as part of the carbon dioxide (CO₂) mineralization process, is generally regarded as a high-temperature, high-pressure, and high-purity CO₂ process. Typical conditions consist of temperatures around 120 °C and a pressure of 100 bar of pure CO₂, making the process costly. A major challenge facing carbonate precipitation is performing the reaction at low temperatures and low partial pressures of CO₂ (p_CO2) such as 25 °C and CO₂ flue gas concentration. In this work, we investigated the effect of carbonic anhydrase (CA) to favor magnesium (Mg) carbonate precipitation at low temperatures and low p_CO2. CA is an enzyme that accelerates CO₂ hydration promoting its conversion into HCO₃^- and then CO₃^2-. This increases supersaturation with respect to Mg-carbonates. A geochemical model was implemented and used to identify supersaturated conditions with respect to Mg-carbonates. Tests were run at 25, 40, and 50 °C and at 1 bar of either pure CO₂ or 10 vol% CO₂ and 90 vol% N₂. The concentration of 10 vol% CO₂ was chosen to resemble CO₂ concentration in flue gas. In selected tests, the CA enzyme was added directly as bovine CA or through microalgae (Scenedesmus obliquus). Experiments were run for 48 hours; 24 hours to reach equilibrium, then another 24 hours until the supersaturated conditions were established. After 48 hours the experiments were interrupted and the solids were characterized. Results show that the addition of CA, either directly or through Scenedesmus obliquus, enhances Mg-carbonate precipitation. Regardless of the temperature, the precipitates were made entirely of nesquehonite (MgCO₃-3H₂O) when pure CO₂ was used. Otherwise, a solid solution containing brucite (Mg(OH)₂) and MgCO₃-3H₂O was formed. Overall, these findings suggest that CA can promote carbonate precipitation at low temperatures, pressures, and CO₂ purity. The enzyme is effective when added directly or supplied through microalgae, opening up the possibility for a CO₂ mineralization process to be implemented directly at a combustion plant as a CO₂ storage option without preliminary CO₂ capture.

Capture and Reuse of Carbon Dioxide (CO2) for a Plastics Circular Economy: A Review

Plastic production has been increasing at enormous rates. Particularly, the socioenvironmental problems resulting from the linear economy model have been widely discussed, especially regarding plastic pieces intended for single use and disposed improperly in the environment. Nonetheless, greenhouse gas emissions caused by inappropriate disposal or recycling and by the many production stages have not been discussed thoroughly. Regarding the manufacturing processes, carbon dioxide is produced mainly through heating of process streams and intrinsic chemical transformations, explaining why first-generation petrochemical industries are among the top five most greenhouse gas (GHG)-polluting businesses. Consequently, the plastics market must pursue full integration with the circular economy approach, promoting the simultaneous recycling of plastic wastes and sequestration and reuse of CO2 through carbon capture and utilization (CCU) strategies, which can be employed for the manufacture of olefins (among other process streams) and reduction of fossil-fuel demands and environmental impacts. Considering the previous remarks, the present manuscript’s purpose is to provide a review regarding CO2 emissions, capture, and utilization in the plastics industry. A detailed bibliometric review of both the scientific and the patent literature available is presented, including the description of key players and critical discussions and suggestions about the main technologies. As shown throughout the text, the number of documents has grown steadily, illustrating the increasing importance of CCU strategies in the field of plastics manufacture.