Search

Ex-situ mineral carbonation, a CCU process, is one possible approach for the decarbonisation of emission-intensive industry with hard-to-abate process emissions like the cement industry. The chemical reaction ensures long-term binding of carbon dioxide in minerals with the effect of storing otherwise emitted CO 2 long term. As a major hurdle for CCU processes is often their economic viability, to create incentives for the usage of this process, these carbonated mineral products must become marketable. A separation approach for the reaction products of this process and possible utilization paths are presented. The separation results in three different fractions, each enriched in either the reaction products amorphous silica or magnesium/calcium silicate or unreacted peridotite. The fractions enriched with reaction products are tested as supplementary cementitious material in cement or as a filler in rubber and paper. The application tests show promising results, comparable or even better than the conventional product. Additionally, based on the laboratory explorations, we present initial economic and environmental investigations showing potential carbon footprint reductions of up to 27% for blended cement with a total global reduction potential of 681 Mt CO2e /a. Also, potential carbon footprint reductions of 52% can be achieved by using carbonation products as fillers in rubber and 197% in paper, respectively. While the costs for the utilization of carbonated minerals have been calculated to be higher than for the conventional products, CO 2 emission certificates could ensure the same price for cement and even lower costs for the substitution of fillers in paper and rubber. [Display omitted] • The technical feasibility of the separation of the carbonation products by centrifugal classification has been proven. • Yield of the separation process can be optimized by better liberation of the particles. • Application tests for cement, paper or rubber show the potential of the carbonated and separated products as a (partial) substitute. • The modeled industrial process – in this case a cement plant with carbonation products as clinker substitute – is ecological and economical feasible. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Mineral carbonation techniques for iron and steel by-products are reviewed. • Technological advances have enhanced process efficiency and economic feasibility. • Processes are assessed for economic, environmental, and health impacts. [ABSTRACT FROM AUTHOR]

Due to the depletion of river sand, the construction industry is eager to develop upcycling techniques for transforming secondary by-products derived from construction and demolition (C&D) waste into quality fine aggregates. This paper presents a study of replacing river sand with enhanced recycled fine aggregate through a wet carbonation process developed by the authors previously. The fine recycled concrete aggregate (FRCA) ranging from 0.15 to 5 mm was prepared by demolishing a concrete with a known mixture design. After wet carbonation, the particle size, water absorption, and density of the FRCA were tested and compared with the original samples. The chemical characteristics of the original and carbonated FRCA (C-FRCA) were analyzed by a series of experiments. The results showed that (1) an increase of carbonation products and a significant reduction of hydration products; (2) microscopic observation of the C-FRCA showed a surface layer densified by calcite after wet carbonation; and (3) no significant strength loss were observed when replacing up to 50% river sand by C-FRCA in mortar specimens. The potential environmental and economic impacts were also analyzed. [Display omitted] • Wet carbonation significantly improved the quality of FRCA. • The carbonation efficiency of wet carbonation excelled conventional carbonation methods. • Up to 50% river sand replacement ratio was achieved by carbonated FRCA. [ABSTRACT FROM AUTHOR]

Highlights • Carbonation of concrete mixes with high incorporation ratios of recycled concrete aggregates (RCA), and/or fly ash (FA). • Sequestration of a high amount of CO 2 in concrete, by producing a concrete with high rate of carbonation. • Service life of concrete made with high volumes of FA and RCA. Abstract This paper mainly focuses the effect of high incorporation ratios of fly ash (FA) and recycled concrete aggregates (RCA) on the carbonation resistance of concrete. The aim of using high volumes of these non-traditional materials is to decrease the use of natural resources and capture CO 2. For that purpose, the carbonation resistance of low- and high-strength concrete mixes produced with various incorporation ratios of FA, fine RCA and coarse RCA, jointly and individually, is obtained and related with compressive strength, water absorption and chloride ion penetration. The results show that the carbonation depth of concrete increased up to 3 and 6 times when incorporating 30% and 60% of FA, respectively, and 100% of RCA led to up to 2.7 times increment. Therefore, the concrete cover for mixes made with FA and/or RCA should be increased in order to obtain an equivalent service life to that of conventional concrete. In spite of this fact, it is recommended to incorporate FA in RCA concrete because, in most concrete mixes, the carbonation depth due to the combined effect of both RCA and FA was lower than the sum of the values due to each effect. Additionally, the results show that, although the carbonation rate of concrete mixes containing high volumes of FA and RCA is high, their service life is also relatively high and the concrete reinforcement can be protected for up to 50 years. [ABSTRACT FROM AUTHOR]

The production of ordinary portland cement (OPC) is a CO 2 intensive process. Specifically, OPC clinkering reactions not only require substantial energy in the form of heat, but they also result in the release of CO 2 ; i.e., from both the decarbonation of limestone and the combustion of fuel to provide heat. To create alternatives to this CO 2 intensive process, this paper demonstrates a new route for clinkering-free cementation by the carbonation of fly ash; i.e., a by-product of coal combustion. It is shown that in moist environments and at sub-boiling temperatures, Ca-rich fly ashes react readily with gas-phase CO 2 to produce robustly cemented solids. After seven days of exposure to vapor-phase CO 2 at 75 °C, such formulations achieve a compressive strength of around 35 MPa and take-up 9% CO 2 (i.e., by mass of fly ash solids). On the other hand, Ca-poor fly ashes due to their reduced alkalinity (i.e., low abundance of mobile Ca- or Mg-species), show limited potential for CO 2 uptake and strength gain—although this deficiency can be somewhat addressed by the provision of supplemental/extrinsic Ca agents. The roles of CO 2 concentration and processing temperature are discussed, and linked to the progress of reactions and the development of microstructure. The outcomes create new pathways for achieving clinkering-free cementation while enabling the beneficial utilization (“upcycling”) of emitted CO 2 and fly ash; i.e., two abundant, but underutilized industrial by-products. [ABSTRACT FROM AUTHOR]

Carbon dioxide is one of the main if not the most potent greenhouse gases responsible for climate change. Scientists put great efforts to tackle this problem and carbon dioxide capture seems to be a promising solution. The present study proposes a novel method of carbon dioxide capture using black liquor, a side stream from the paper and pulp industry. Its content in sodium hydroxide makes it an attractive candidate for carbon dioxide capture via carbonation. The black liquor was prepared from oat husks, a non-woody biomass, using the soda-pulping process. To estimate its carbon dioxide absorption capacity, a mixture of nitrogen and carbon dioxide (70:30%) was sparged into a bubble column reactor and computational fluid dynamics simulations of this setup were used to evaluate the mixing process. The formation of carbonate and bicarbonate ions throughout the carbonation process was followed using a Fourier-Transform Infrared (FTIR) probe and a pH meter. The absorption capacity was measured from the weight increase of the reactor. It was found to be around 30 g of carbon dioxide/L of black liquor. The carbonate and bicarbonate species in black liquor before and after carbonation were further characterized with 13C Nuclear Magnetic Resonance (NMR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and optical microscopy. Using industrial side-streams might enable an economically feasible process without the need for production of virgin absorbents or their recovery. Furthermore, this capturing process, which is performed at atmospheric conditions might reduce the overall energy consumption. The results demonstrated that black liquor could be an attractive absorbent for carbon dioxide, paving the way for a circular and resource-efficient economy. • Carbon dioxide capture using black liquor as the absorbent. • Non-woody black liquor captures 30 g of carbon dioxide per liter. • Sodium carbonates and bicarbonates were formed. • Bubble column stirred reactor for carbon dioxide absorption. [ABSTRACT FROM AUTHOR]

The large amount of carbon dioxide emitted during the life span of cement-based materials makes a great contribution to the increasingly severe global warming. Due to their abnormally large annual production, sequestering carbon dioxide using cement-based materials has become one of the most efficient ways for cement industry to reduce net carbon dioxide emissions. Meanwhile, the production and accumulation of solid wastes has been causing widely occupation of the land space and threatening the ecological balance and human health. Considering that most solid wastes are rich in calcium and magnesium, and can be easily used in cement-based materials, the carbonation treatment of solid wastes not only uptakes a large amount of carbon dioxide, but also mitigates the accumulation of excessive solid wastes, which is the core of achieving carbon neutrality in cement industry. In this paper, the carbonation potential and the state-of-art carbonation techniques of various solid wastes are comprehensively reviewed, and a pathway to reach net-zero carbon dioxide emission for cement-based materials is proposed. Then physical, chemical and microbiological methods to enhance the carbonation degree of solid wastes are summarized, with both advantages and disadvantages of each method are given. In the end, the challenges and perspectives of the utilization of solid wastes to sequester carbon dioxide in cement-based materials are proposed. • The carbonation treatment of solid wastes is the core of achieving carbon neutrality in cement industry. • The carbonation potential and the state-of-art carbonation techniques of various solid wastes are comprehensively reviewed. • Methods to improve the carbonation reaction degree are summarized from physical, chemical and microbial aspects. • A pathway to reach net-zero CO 2 emission for cement-based materials is proposed. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2 ) is the predominant greenhouse gas on Earth and its atmospheric concentration is increasing at an exponential rate due to human activities. Cement production contributes about 7% of the total worldwide CO 2 emissions, and thus finding a practical way to reduce the greenhouse gas emission is essential. Construction and demolition (C&D) waste rich in calcium hydroxide and calcium silica hydrate is considered to be a potential calcium source for CO 2 sequestration, forming thermodynamically stable carbonate minerals. In the past decade, a major research effort was to study the influencing factors affecting the effectiveness of active carbonation of C&D waste. In this paper, active carbonation techniques adopted for crushed concrete aggregate and waste cement derived from the C&D waste, and the resulting properties of the CO 2 cured concrete aggregate and cement waste are discussed. In addition, special features of concrete block products as a potential medium for CO 2 sequestration are also highlighted. Lastly, based on the environmental benefit and cost analysis of CO 2 sequestration through C&D waste and concrete block are also presented. We concluded that the mineral carbonation of C&D waste is technically feasible, economical and environmentally friendly approach of a future carbon sequestration strategy. [ABSTRACT FROM AUTHOR]

Fly ash carbonation is a feasible alternative method for CO 2 reduction and heavy metal stabilization. There are four main mechanisms for fly ash carbonation to stabilize heavy metals. However, due to differences in heavy metals and fly ash, the stability of heavy metals is also different. Especially, the properties of supercritical CO 2 are greatly changed compared with those of non-supercritical CO 2 , and the influence of this change on the four mechanisms is still unclear. In this paper, carbonation experiments of different fly ash were conducted in the transition from non-supercritical to supercritical, and leaching characteristics of Cu, Zn, Pb, Cr, Cd, and Ni were investigated to explore stabilization mechanisms. Our research showed that physical encapsulation was a physical phenomenon that had stabilizing effects on all heavy metals. Chemical reaction was aimed at heavy metals that reacted with CO 3 2-. Pb, Zn, and Cu belonged to the isomorphism with Ca, and adsorption precipitation was formed by the isomorphism substitution during carbonation process. Supercritical CO 2 enhances the three mechanisms. And mechanical force broke up sintered surface of fly ash, exposing more active sites to enhance the three mechanisms. On the other hand, under supercritical state, the solubility of CO 2 increased, resulting in the speciation transformation of heavy metals. Under the above mechanisms, there were two trends regarding stability of heavy metals in fly ash. One trend was a gradual increase in stability, and the other trend an initial increase in stability followed by a peak at the critical point and then a decrease. [Display omitted] • Supercritical CO 2 enhances encapsulation, reaction, and adsorption. • Supercritical CO 2 greatly reduces the pH of the solution. • There are two trends regarding the stability of heavy metals in fly ash. • Properties of heavy metal and CO 2 , composition of fly ash determine stability. [ABSTRACT FROM AUTHOR]

• Ambient pressure carbonation can promote CO 2 utilization in reinforced concrete. • Ambient pressure carbonation can enhance the performances of reinforced concrete. • The carbonation-cured reinforced concrete has higher corrosion resistance. Carbonation curing of concrete is an emerging technology that sequesters CO 2 in cement matrix while improving the material properties. Given the fact that concrete is the world's most used man-made material, its CO 2 utilization capacity is high. Since majority of concrete products are reinforced with steel, CO 2 utilization potential will be tremendously enhanced if all reinforced concrete can be treated by carbonation curing. However, the carbonation corrosion becomes a concern. This paper is to show if carbonation curing of reinforced concrete could be performed under ambient pressure, the concrete structure would be more corrosion resistant. It was found that reinforced concrete product so produced could attain 11 % CO 2 uptake based on cement content. The rebar corrosion behavior in the carbonation-cured concrete was examined using a natural ponding test and an accelerated impressed current (IC) test independently. Results suggested that the ambient pressure carbonation improved concrete resistance to the chloride-induced corrosion due to the densified carbonate-rich surface layer. In the natural ponding test, a lower macrocell current and a lower total corrosion value were observed in the carbonation-cured concrete during the 33-month wet-dry cyclic exposure of a chloride solution. The chloride contents at the rebar location in carbonation-cued concrete were also decreased. In addition, carbonation curing was found to delay the corrosion-initiation stage. The IC-accelerated corrosion test verified that carbonation curing improved the concrete resistance to chloride penetration by lowering the current and inhibiting the corrosion-propagation, leading to an enhanced structural integrity and an extended service life after corrosion initiation. [ABSTRACT FROM AUTHOR]

• The cement pastes were further cured in water after two different CO 2 concentrations (3% and 20%) curing. • The calcite was the main product generated in CO 2 -cured pastes. • The cement pastes cured at a higher CO 2 concentration exhibited a higher compressive strength at all curing ages. • The CO 2 -cured cement pastes, the porosity and pore size distribution became lower because of the formation of CaCO 3. Understanding the effect of formed calcium carbonate and highly polymerization of silicates on the microstructure of cement paste exposed to early CO 2 curing and further hydration process is crucial to comprehend the mechanisms of CO 2 curing. In this paper, the cement pastes were further cured in water after CO 2 curing under two CO 2 concentrations (3% and 20%) and the carbonation depth, compressive strength, composition and morphology of the formed products were characterized. The results showed that calcite was the main product generated in CO 2 -cured pastes and its content was increased with the increasing CO 2 concentration. The formed calcium carbonate provided additional nucleation sites and accelerated the hydration of C 3 S in further water curing. Furthermore, calcium carbonate was consumed by C 3 A to form calcium aluminate monocarbonate, which delayed the transformation of ettringite to monosulfate during further water curing. The decarbonation temperature of the formed calcium carbonate was increased with the increase of the CO 2 concentration, but it was decreased in further water curing due to participating the further hydration process. The early carbonation curing improved the polymerization of silica gel, which was decreased in the subsequent hydration due to the formation of C-S-H. The CO 2 -cured sample showed higher early compressive strength and comparable long-term compressive strength compared to the conventional samples due to the lower porosity. [ABSTRACT FROM AUTHOR]

• Carbonation treatment reduces free CaO and capture CO 2 effectively. • "Double carbonation" mitigates strength loss caused by incorporation of HFA. • "Double carbonation" delays the strength development brought by pozzolanic effect. Carbonation treatment of fly ash (FA) is proposed as a promising method for stabilization of hazardous residues and CO 2 sequestration. This paper aims to investigate the performance of cement mortar incorporating carbonated FA and the synergistic effect with carbonation curing. The results show that the content of free CaO and the hydration heat were reduced apparently by carbonation treatment. The synergy of carbonation treatment and carbonation curing compensated for the strength loss caused by FA incorporation, but can also delayed strength development brought by pozzolanic effect. CO 3 2- on the surface of FA introduced by carbonation treatment competed with Cl− for binding AFm, consequently lead to decreased resistance of chloride ion penetration. Carbonation curing mitigated this degradation by improving the pore structure of cement mortar significantly. In summary, carbonation curing can be an appropriate complement to carbonation treatment of FA for performance improvement of cement-based materials and more efficient CO 2 sequestration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water-to-CO 2 ratio decreases with increase in CaO/SiO 2 ratio. • Impact of CaO/SiO 2 & interlayer space on CO 2 adsorption capacity in Wollastonite • Insights on atmospheric and accelerated carbonation of C–S–H. • Scalable & portable parallel GCMC implementation. The paper deals with the understanding of the CO 2 capacity of adsorption through the anhydrite cement compound, i.e., CaO·SiO 2 structure. The Wollastonite structure is prepared with various CaO/SiO 2 ratios for the atomistic simulations. Subsequently, simulations of binary adsorption of H 2 O and CO 2 have been performed to arrive at C–S–H structure. The CaO/SiO 2 ratio is varied from 0.66 to less than 1.5 in the present study. The interlayer spacing between CaO sheets is considered as 13.5 Å. The impact of the electrostatic charges has been explored using available CLAY_FF and CSH_FF potentials. The outcomes have been successfully examined and compared with experimental results. To understand the capacity adsorption of CO 2 and selectivity effect on C–S–H forming, numerical experiments have been performed using CO 2 concentrations from 10 ppm up to 1,000,000 ppm at 20 °C. These numerical experiments allow understanding of the selectivity of H 2 O and CO 2 in binary mixture adsorption, and the capacity of CO 2 adsorption in the Wollastonite atomic structure. According to the physisorption simulations, the CO 2 adsorption capacity depends not only on CO 2 concentration but also the Wollastonite structure. The possible CaCO 3 precipitation and C–S–H structure are addressed. [ABSTRACT FROM AUTHOR]

• Effect of calcination conditions were studied for up to 100 reaction cycles. • Raising calcination temperature adversely affected the sorbent cyclic performance. • Partial limestone calcination greatly altered the sorbent CO 2 capture capability. • Uncalcined portion of the sorbents, after being calcined, retained high reactivity. • A method was proposed to estimate the sorbent utilization at different conditions. This paper investigates the effect of calcination temperature and duration on the cyclic CO 2 capture performance of natural lime-based sorbents. Tests showed that increasing calcination temperature considerably reduced the sorbent reactivity over the first few calcination-carbonation cycles. No significant variation in performance was observed when a sorbent remained at the calcination temperature after completing limestone decomposition. On the other hand, incomplete limestone calcination significantly altered the sorbent cyclic utilization and CO 2 carrying capacity. A semi-empirical method is proposed to estimate the fast reaction-controlled carbonation extent at different reaction cycles, calcination extents and temperatures. This method is shown to work well for two different naturally-derived limestones exposed to different calcination conditions. [ABSTRACT FROM AUTHOR]

• The process of carbonation curing and related chemical reactions are reviewed. • Different strategies of carbonation curing optimization are elaborated. • Matrix of cement-based composite is densified, and matrix/fiber interface is improved by carbonation curing. • Durability in different aspects are enhanced by carbonation curing. • Corrosion and alkali-silica reaction potential by carbonation curing are discussed. To tackle the rising CO 2 concentration in atmosphere, technologies of carbon sequestration are emerging. As one of these technologies, carbonation curing of cement-based composite at early age shows a great potential because its wide application and benefits to provide cement-based composite with enhanced mechanical properties and durability. However, carbonation curing is mostly investigated on lab-scale, due to two main challenges that should be addressed before it can be widely applied for industrial-scale production: (1) CO 2 sequestration rate is still low, which is around 20 %–50 % of the theoretical potential because of the limitation of CO 2 diffusion into matrix during the carbonation curing; and (2) the effect carbonation curing on the durability of cement-based composites and the underlying mechanisms remains unclear, especially for some critical aspects such as alkali-silica reaction, corrosion, and sulfate attack. Therefore, this paper focuses on discussing: (1) factors affecting CO 2 sequestration in cement-based composite during each stage of carbonation curing and the optimization methods of carbonation curing for high CO 2 sequestration rate without mitigating mechanical properties and durability, and (2) effects of carbonation curing on different aspects of durability and the corresponding mechanisms. Based on the review, future studies on addressing current challenges are inspired to comprehend and promote the carbon sequestration by carbonation curing of cement-based composites. [ABSTRACT FROM AUTHOR]

• Life cycle assessment of mineral carbonation technology finds net carbon abatement. • Suitable technology for carbon capture and utilisation of waste-to-energy CO 2 flue. • Technology produces solid carbonates for land reclamation, avoiding sand import. • Carbon abatement improves with serpentine sourced from geographically nearer regions. • Waste heat from other industries can be used to further improve carbon abatement. Carbon capture and utilization (CCU) is one of the key pathways to abate carbon emissions. In this paper, the carbon abatement potential of a CO 2 mineralization technology for CCU in Singapore is studied. Requiring mild reaction conditions, this technology uses 10 %–15 % (v/v) CO 2 flue from a waste-to-energy plant and serpentine mineral (Mg 3 Si 2 O 5 (OH) 4), to convert CO 2 into solid carbonates or sand, which can then be used for purposes such as land reclamation. To study its carbon abatement potential more holistically, the life cycle or net carbon emissions were analysed by employing life cycle assessment (LCA) methodology. The results show that the CO 2 mineralization technology abates 115.78 kg CO 2 -eq per tonne of CO 2 input. The results also indicate that the major sources of emissions are from the land and sea transportation of serpentine mineral feedstock, the thermal activation of the feedstock, and carbon capture processes. Possible ways to increase the carbon abatement potential of this technology were explored, which included the sourcing of serpentine mineral from nearer regional locations, electrification of land transport for shipping serpentine, use of waste heat for thermal activation, and use of renewable energy to power the processes. [ABSTRACT FROM AUTHOR]

• The effectiveness of flue gas, as a CO 2 source, to improve the RCAs was evaluated. • Similar microstructures of RCAs treated by flue gas and mixed CO 2 gas were found. • Mechanical properties of the RAC containing carbonated RCAs were enhanced. • Flue gas from cement plant can be effectively used for RCAs carbonation. CO 2 source is one of the limiting factors for popularizing the accelerated carbonation technology in recycled concrete aggregates (RCAs) improvement. In this paper, the feasibility of using flue gas (CO 2 content of 20 %) from cement plant as alternative CO 2 source to improve RCAs was systematically studied and evaluated. Results showed that the carbonation extent and physical properties of the RCAs treated by flue gas were obviously improved and were comparable to those treated by commercial mixed gas with CO 2 content between 20 % and 100 %. Based on the results of thermal gravimetric (TG), fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis, calcium hydroxide and calcium silicate hydrates in RCAs were significantly transformed into calcium carbonate at the optimal gas flow rate (5 L/min) after 168 h of treatment. The workability, compressive strength and flexural strength of concrete incorporating carbonated RCAs treated by flue gas were comparable with those treated by mixed CO 2 gas, but were much better than those of concrete containing non-carbonated RCAs at all the replacement rate. Finally, the environmental impact and economic feasibility using flue gas to improve RCAs were evaluated based on a combined waste recycling system. All indicated that flue gas could be effectively utilized as CO 2 source to improve RCAs. [ABSTRACT FROM AUTHOR]