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The aim of the article is mathematical modelling of the carbonation process that has been based on results of research conducted both in accelerated and natural conditions. The article covers short characteristic of carbonation, its processes and effects. Also critical review of articles that concern carbonation mathematical models was included in the paper. Assuming the self-terminating nature of carbonation the hyperbolic model of carbonation was formulated. Such a model describes the carbonation progress as the process unlimited in time but with the restricted range in concrete depth that is limited by the value of a model asymptote. Presented results cover research on carbonation of concrete with a different water-cement ratio and different types of binders and duration times of early curing. Investigations have been conducted as accelerated (1% concentration of CO ) as well as in long-term exposures in natural conditions. The obtained results confirmed statistically that hyperbolic model is a well-founded approach when the modelling concrete carbonation process is concerned

Carbon dioxide (CO 2 ) is a significant contributor to global warming and environmental issues, necessitating the development of practical storage solutions. As an alternative to CO 2 storage in subsurface formations, mineral carbonation, which offers long-term CO 2 storage and advantages like thermodynamics and energy economy, is gaining popularity. Also, the possible repurposing of carbonated solid waste in the building and construction industry contributes to the reduction of CO 2 . However, large-scale implementation of natural mineral carbonation remains a challenge. This study investigates the comparative advantages and disadvantages of direct solid-gas and direct aqueous carbonation, two carbon capture and storage (CCS) methods for combating atmospheric CO 2 emissions. The research focuses on reaction kinetics, capture efficiency, recovery efficiency, leakage security, and cost-effectiveness. Both methods have the potential to capture CO 2 efficiently, but they differ in their effectiveness and feasibility. Direct solid-gas carbonation exhibits higher reaction rates and capture efficiency, while direct aqueous carbonation has lower energy requirements and is easier to implement at ambient temperature and pressure. Further research is essential to fully understand the comparative merits and drawbacks of direct solid-gas and aqueous carbonation and devise strategies to minimize their environmental impact. Furthermore, to ensure economic feasibility, future research should focus on lowering CO 2 sequestration costs, increasing the scale of captured CO 2 usage in industrial processes, and developing a circular economy by transforming captured CO 2 into valuable metal carbonates.

Steel slag is a solid waste product generated during the carbonation stage of steelmaking. It has high levels of heavy metals and substantial amounts of free calcium and magnesium oxide, making it unsuitable for use as a cement material. Furthermore, the disposal of steel slag in landfills requires many resources and can seriously contaminate the surrounding environment. One method of reducing its negative environmental impact is carbonation, which involves reacting steel slag with carbon dioxide to form stable minerals. However, many parameters influence the carbonation efficiency of steelmaking slag, including temperature, time, particle size, pressure, CO2 concentration, liquid-to-solid ratio, moisture content, humidity, additives, etc. To this end, this paper comprehensively reviews the most important steel slag carbonation-influencing factors. Moreover, it compares the characteristics from two perspectives based on their causes and effects on carbonation. Finally, this article reviews earlier studies to identify the factors that affect steel slag carbonation and the potential of carbonated steel slag as a sustainable construction material. Based on previous research, it systematically examines all the elements for future work that need to be improved.

The RILEM TC 281–CCC ‘‘Carbonation of concrete with supplementary cementitious materials’’ conducted a study on the effects of supplementary cementitious materials (SCMs) on the carbonation rate of blended cement concretes and mortars. In this context, a comprehensive database has been established, consisting of 1044 concrete and mortar mixes with their associated carbonation depth data over time. The dataset comprises mix designs with a large variety of binders with up to 94% SCMs, collected from the literature as well as unpublished testing reports. The data includes chemical composition and physical properties of the raw materials, mix-designs, compressive strengths, curing and carbonation testing conditions. Natural carbonation was recorded for several years in many cases with both indoor and outdoor results. The database has been analysed to investigate the effects of binder composition and mix design, curing and preconditioning, and relative humidity on the carbonation rate. Furthermore, the accuracy of accelerated carbonation testing as well as possible correlations between compressive strength and carbonation resistance were evaluated. One approach to summerise the physical and chemical resistance in one parameter is the ratio of water content to content of carbonatable CaO ( w /CaO reactive ratio). The analysis revealed that the w /CaO reactive ratio is a decisive factor for carbonation resistance, while curing and exposure conditions also influence carbonation. Under natural exposure conditions, the carbonation data exhibit significant variations. Nevertheless, probabilistic inference suggests that both accelerated and natural carbonation processes follow a square-root-of-time behavior, though accelerated and natural carbonation cannot be converted into each other without corrections. Additionally, a machine learning technique was employed to assess the influence of parameters governing the carbonation progress in concretes.

Mineral carbonation can simultaneously realize the effective treatment of CO 2 and iron and steel slag; thus, it is of great significance for the low carbon and sustainable development of iron and steel industry. In this article, the researches of mineral carbonation process using iron and steel slag as feedstock are reviewed, and the carbonation reaction mechanism and the parameters affecting the reaction rate and carbonation degree are analyzed. Furthermore, the effect of different enforcement approaches, such as ultrasonic enhancement, mixed calcination, microbial enhancement, and cyclic coprocessing on mineral carbonation reaction, is introduced. The additional effects of mineral carbonation, such as solving the problem of poor volume stability of steel slag, weakening the leaching of heavy metal ions, and reducing the pH of the leachate, are also illustrated. Moreover, issues related to mineral carbonation technology that should be emphasized upon soon, such as the production of valuable products, use of industrial wastewater, aqueous phase recycling use, multiparameter coupling analysis, and research on the properties of carbonation residues, are also discussed, which contribute some perspectives to the future development of mineral carbonation of iron and steel slag. Graphical abstract

In order to assess the potential CO 2 capture ability of recycled concrete aggregates (RCAs) subjected to accelerated carbonation, an empirical prediction model has been developed in relation to carbonation conditions and the characteristics of RCAs. In this study, two sources of RCAs were used: RCAs from a designed concrete mixture and RCAs obtained from crushing of old laboratory concrete cubes. Two types of carbonation approaches were employed: (A) pressurized carbonation in a chamber with 100% CO 2 concentration and (B) flow-through carbonation at ambient pressure with different CO 2 concentrations. Four groups of RCAs particles with sizes of 20–10, 5–10, 2.36–5 and <2.36 mm were then tested and evaluated. It was found that a moderate relative humidity, a CO 2 concentration higher than 10%, a slight positive pressure or a gas flow rate of >5 L/min were optimal to accelerate the RCAs carbonation. Moreover, the CO 2 uptake of fine RCAs particles was faster than that of large RCAs particles. The developed model was able to predict the CO 2 uptake in relation to relative humidity, particle size, carbonation duration and cement content of the RCA under the tested carbonation conditions.

Carbon dioxide utilization for enhanced metal recovery (EMR) during mineralization has been recently developed as part of CCUS (carbon capture, utilization, and storage). This paper describes fundamental studies on integrating CO₂ mineralization and concurrent selective metal extraction from natural olivine. Nearly 90% of nickel and cobalt extraction and mineral carbonation efficiency are achieved in a highly selective, singlestep process. Direct aqueous mineral carbonation releases Ni2+ and Co2+ into aqueous solution for subsequent recovery, while Mg2+ and Fe2+ simultaneously convert to stable mineral carbonates for permanent CO₂ storage. This integrated process can be completed in neutral aqueous solution. Introduction of a metal-complexing ligand during mineral carbonation aids the highly selective extraction of Ni and Co over Fe and Mg. The ligand must have higher stability for Ni-/Co- complex ions compared with the Fe(II)-/Mg- complex ions and divalent metal carbonates. This single-step process with a suitable metal-complexing ligand is robust and utilizes carbonation processes under various kinetic regimes. This fundamental study provides a framework for further development and successful application of direct aqueous mineral carbonation with concurrent EMR. The enhanced metal extraction and CO₂ mineralization process may have implications for the clean energy transition, CO₂ storage and utilization, and development of new critical metal resources.

This research proposes a novel deep breathing analogy (DBA) accelerated carbonation process. Inspired by the breathing mechanism of human lungs, the DBA method involves injecting pure CO 2 into a reaction chamber at a specific pressure (inspiration) and subsequently evacuating the gas from the chamber to a negative pressure (exhalation). This process is repeated to remove excess water from the chamber and restore optimal carbonation conditions, which further enhances the efficiency of carbonation for the sample. The effectiveness of this method is evaluated based on weight gain, proportion of captured CO 2 and carbonation depth. Results show that the DBA method significantly reduces the inhibition of carbonation. Based on the test results, a correlation between the proportion of captured CO 2 and carbonation depth is established. Additionally, a more accurate prediction model for pressurized carbonation is proposed and the economic potential of concrete carbonation is studied.

Carbonation-induced reinforced steel concrete corrosion is a prominent concern related to engineering design and maintenance. The Durability Index (DI) approach was developed in South Africa to address this concern and enhance the durability performance of reinforced concrete structures. This approach relies on durability index tests, which are associated with transport mechanisms linked to specific deterioration processes. The carbonation of concrete is primarily influenced by the microstructure and transport characteristics of the concrete. Environmental exposure conditions also influence the rate of carbonation. The focus of the research reported here was to develop a carbonation model that could predict the rate of carbonation of concrete exposed to, or sheltered from, rain, with the permeability coefficient ( k ) from the Oxygen Permeability Index (OPI) test (DI test) as the key unifying variable. The model development was based on natural carbonation data and the drying profiles (experimentally measured) of 48 different concretes. Concrete microstructure was varied by varying the water-to-cement ratio, curing conditions, and by using SCMs. The resulting carbonation model was able to predict the rate of carbonation of concrete, allowing for different exposure conditions. A unique feature of this model is its use of a single material property, the ' k ' value, to effectively address both CO 2 diffusion and the drying process within concrete. The model displayed sensitivity towards the influence of variation in CO 2 concentration, concrete microstructure, and the environmental exposure conditions, making this a simplified, effective and practical concrete carbonation prediction model.