Carbonation Reaction Research Articles

Microstructural Evolution of Calcium Sulfoaluminate Cement during the Wet-Carbonation Process

Calcium sulfoaluminate (CSA) cement, as a type of low-carbon cement, can contribute to further reduction in carbon emissions with carbonation technologies. However, the detailed microstructure development of CSA cement during the carbonation process has been rarely analyzed. In this paper, wet carbonation was applied to CSA cement to investigate the microstructure evolution of carbonation products and carbon absorption capacity of CSA cement by means of pH measurement, X-ray diffraction (XRD) measurement, thermogravimetric (TG) measurement, Fourier-transformed infrared spectroscopy (FT-IR) measurement and scanning electron microscope measurement. During the carbonation process, the formed ettringite product and the dicalcium silicate clinker were carbonated immediately to generate calcium carbonate crystals, silica gel and aluminum hydroxide (AH3) gel. With the trend of pH increasing first and notably decreasing later, the coupling interaction between the hydration and carbonation reactions of CSA cement was revealed. From the XRD and TG results, three types of calcium carbonate crystal forms (calcite, vaterite and aragonite) were detected, and the content of calcium carbonate increased with the increase in carbonation time. FT-IR analysis further confirmed the existence of calcium carbonate, silica gel and AH3 gel with their characteristic vibrations. Moreover, the microstructure of carbonation products with different morphologies was observed. The application of wet carbonation to CSA cement provides a more comprehensive insight to the carbonation mechanism of this low-carbon cement.

Effect of Glycine on the Wet Carbonation of Steel Slag Used as a Cementitious Material.

The wet carbonation process of steel slag (SS) is envisaged to be an effective way to sequestrate CO2 and improve the properties of SS as a supplementary cementitious material. However, the carbonation process still struggles with having a low carbonation efficiency. This paper studied the effect of glycine on the accelerated carbonation of SS. The phase composition change of carbonated SS was analyzed via XRD, FT-IR, and TG-DTG. The carbonation process of SS is facilitated by the assistance of glycine, with which the carbonation degree is increased. After 60 min of carbonation, SS with glycine obtained a CO2 sequestration rate of 9.42%. Meanwhile, the carbonation reaction could decrease the content of free calcium oxide in SS. This significantly improves the soundness of SS-cement cementitious material, and the compressive strength of cementitious materials that contain carbonated SS with glycine is improved. Additionally, the cycling performance of glycine in the successive wet carbonation process of SS was investigated. Multicycle experiments via solvent recovery demonstrated that although the promotion effect of glycine was reduced after each cycle, compared with the SS-water system, the carbonation process could still be facilitated, demonstrating that successive wet carbonation via solvent recovery has considerable potential. Herein, we provide a new idea to facilitate the wet carbonation process of SS and improve the properties of SS-cement cementitious material.

Performance evaluation of carbonated cement paste derived from hydrated Portland cement based binders as supplementary cementitious material

The production of concrete has gone up from 2.3 billion m3 in 2002 to 14 billion m3 in 2020. At the same time, the amount of construction and demolition waste generated annually has reached levels of 3 billion tons, with concrete rubble making up a major portion of it. This study investigates the performance of carbonated fines derived from hydrated cement paste of different binders. Four cement paste blends, containing Portland cement (PC) and blends of Portland cement with fly ash (FA30), perlite (PL30) and metakaolin (MK30) at a 30 % cement replacement level, were cured for 90 days prior to subjecting them to a carbonation reaction. The R3 test gauged pozzolanic reactivity, while calorimetry, XRD, and TGA studied hydration characteristics. Compressive strength of mortar samples prepared using the same binder composition as paste was also measured at different ages. Carbonated fines exhibited notable pozzolanic activity compared to waste hydrated cement paste. The reactivity of carbonated fines derived from different binders were similar, however slightly higher reactivity was measured for fines comprising of reactive SCM in the precursor material (hydrated paste). Mixes with carbonated fines demonstrated enhanced kinetics, exhibiting over 25 % higher compressive strength at 3 and 7 days compared to the fly ash control mix. Similar compressive strength characteristics were observed in mortar mixes with different carbonated fines, indicating a limited impact of the various binder types from which the fines originated.

Carbonation kinetics of calcium-based solids at the centimeter scale for moving bed applications

Countercurrent moving bed reactors were recently proposed to capture CO2 from dispersed sources using calcium materials. Due to disparities with Calcium Looping systems in particle size and solids residence times, additional investigations are required to identify reaction controlling steps and kinetic parameters. This study examines the carbonation reaction of centimeter-scale CaO and Ca(OH)2-derived-CaO pebbles under conditions relevant to moving bed applications. To this end, the impact of carbonation temperature (450–650 °C) and CO2 concentration in the inlet gas (2.5–7.5 %v) was evaluated in TGA, employing particle sizes from 0.26 to 1.65 cm. The obtained results were fitted to a shrinking core model where the rate-determining step is CO2 diffusion through the gas volume that occupies the pores of the solid CaCO3-rich layer formed during carbonation. The experimental findings can be predicted using the effective porosity of the materials as the sole fitting parameter.

Study on the physical encapsulation mechanism of heavy metals in fly ash carbonation solidification based on synthetic pellets

The physical encapsulation mechanism prevents the leaching of heavy metals by forming calcium carbonate-encapsulated fly ash through the reaction of carbon dioxide and calcium oxide. However, current research in this area primarily involves qualitative analysis, focusing on various methods to enhance the fixation effect of heavy metals. There is a lack of quantitative description regarding how physical encapsulation solidifies heavy metals, and the solidification mechanism of heavy metals is challenging to verify through macroscopic experiments. In this paper, a method for synthesizing small fly ash particles into pellets is proposed to quantitatively study the mechanism of physically encapsulating heavy metals. The data from the carbonation reaction and leaching reaction are fitted using the shrinking core model. The depth of carbonation increases with the lengthening of carbonation time, and the physical encapsulation strengthens the immobilization of heavy metals. The leaching of heavy metals after carbonation can be categorized into three stages based on the shrinking core model: external diffusion, internal diffusion, and chemical reaction control. Synthetic pellets enhance all three stages, especially the external diffusion, which is not detectable with fly ash powder. The fitting results of the experimental data for the carbonation reaction of the enlarged synthetic pellets and the shrinking core model are both above 0.9. This indicates that the primary barrier to leaching of heavy metals is the physical encapsulation formed by the carbonation reaction following the shrinking core model. The physical encapsulation serves as the primary mechanism for the solidification of heavy metals during the carbonation process.

Accelerated carbonation of waste paper fly ash by liquid process (NaHCO3) for stabilization of Ba and Pb

The increase of energy valorization of paper sludge waste and biomass due to their high calorific value by incineration leads to an increase of waste paper fly ash (WPFA) quantities, which are in most cases considered as hazardous, and must be dealt with accordingly. The Alternative options for the management of WPFA, such as stabilization/solidification, vitrification or sintering, are not fully developed or either costly. In the present study, accelerated carbonation technology was used to reduce the hazardous nature of WPFA by improving the stabilization of metallic and metalloids trace elements (MMTE), especially Barium (Ba) and Lead (Pb) leaching. The accelerated carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under controlled temperature and humidity conditions. The use of water saturated with 25% sodium bicarbonate (NaHCO3) improved the carbonation of WPFA and the stabilization of Ba and Pb. Batch leaching tests based on thermodynamic equilibrium was used to evaluate the solubility of the MMTE as a function of pH and at the natural pH of non‑carbonated and carbonated WPFA. Thermogravimetry, X-ray diffraction, scanning electron microscopes and energy dispersive spectroscopy analyses were performed to investigate the evolution of carbonation over time and its effect on the chemical and mineralogical properties of WPFA. After 30 days of accelerated carbonation, the leaching concentration of Ba and Pb was below the French legal limit. The leaching concentration of Ba and Pb from carbonated samples decreased 99% and 99.5% respectively. The leaching and release potential behavior of carbonated WPFA were further evaluated using the four-step sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR). The speciation of MMTE underwent significant transformation, shifting predominantly from the soluble fraction to the carbonated fraction as a result of the carbonation reaction.

Modification of magnesium hydroxide for improved performance in CO2 sequestration

Magnesium hydroxide (Mg(OH)2) can gain strength through carbonation, presenting a potential for its use as a cementitious component. This study proposes a novel method to increase the reactivity and carbonation performance of Mg(OH)2 via the use of acetate-based solution as modifier, which was recovered and reused repeatedly. Modification improved the microstructure and reactivity of Mg(OH)2, increasing the carbonation degree and compressive strength. After 7 days of carbonation curing, the compressive strength of modified Mg(OH)2 pastes was about twice that of unmodified Mg(OH)2 pastes (24.6 vs. 12.9 MPa). The interaction between modifiers and Mg(OH)2 enabled the increased dissolution of Mg(OH)2 and subsequent carbonation reaction. The differences in the reactivity of modified and unmodified Mg(OH)2 led to variations in their carbonation products. The differences in the morphology of the observed carbonation products could further affect the carbonation process. The findings of this study could pave the way enabling the use of Mg(OH)2 as a cementitious binder, meanwhile providing permanent CO2 sequestration within building components.

Mechanism of interaction between hydration–carbonation of C2S

The physical and microscopic properties of γ-C2S and β-C2S under hydration, carbonation, and hydration–carbonation cycle reactions were investigated. The hydration–carbonation cycle reaction facilitated the carbon sequestration of C2S, and the generation of CaCO3 filled the pores of the matrix and enhanced the matrix density in the carbon fixation reaction process. In the subsequent hydration and reaction process, the formation of hydration products increased the number of pores in the matrix and reduced the matrix density. Post-hydration, γ-C2S slurry became powder and had no mechanical strength. However, after carbonation reaction and two carbonation–hydration cycles, γ-C2S exhibited better mechanical properties than β-C2S.

Cobalt substitution slows forsterite carbonation in low-water supercritical carbon dioxide.

Cobalt recovery from low-grade mafic and ultramafic ores could be economically viable if combined with CO2 storage under low-water conditions, but the impact of Co on metal silicate carbonation and the fate of Co during the carbonation reaction must be understood. In this study, in situ infrared spectroscopy was used to investigate the carbonation of Co-doped forsterite ((Mg,Co)2SiO4) in thin water films in humidified supercritical CO2 at 50 °C and 90 bar. Rates of carbonation of Co-doped forsterite to Co-rich magnesite ((Mg,Co)CO3) increased with water film thickness but were at least 10 times smaller than previously measured for pure forsterite at similar conditions. We suggest that the smaller rates are due to thermodynamic drivers that cause water films on Co-doped forsterite to be much less oversaturated with respect to Co-doped magnesite, compared to the pure minerals.

Does lack of CO2 control in environmental chambers influence the strength and stiffness of hydraulic lime mortars?

This study investigates the influence of carbon dioxide (CO2) control in environmental chambers, where hydraulic lime mortar specimens are typically cured before strength testing according to EN1015-11:2019. To do this, three sets of identical mortar samples were cast. Two sets were cured in an environmental chamber that offered the same temperature and relative humidity but different CO2 conditions. In the first chamber, carbonation reactions used the ambient CO2 trapped in the hermetically sealed chamber air. The second chamber was connected to an external carbon dioxide supply, which maintained a constant CO2 concentration, above ambient laboratory levels, during curing. A third set of samples was cured under laboratory conditions to serve as a reference. Following the 35-day curing period, the dynamic elastic modulus and flexural and compressive strengths of sample sets were obtained. Subsequent X-ray diffraction analysis gives additional insights into the material composition for each curing regime. Results indicate that controlling carbon dioxide to above ambient levels leads to noticeably higher stiffness and strength in samples. This suggests that implementing CO2 control as a part of standard curing conditions may enable more reliable estimates of strength and stiffness development in lime mortars, with respect to laboratory conditions.

Utilizing ZrO2 as an Alkali Metal-Based Adsorbent Support to Lower Energy Consumption in Direct Air Capture

Alkali metal-based adsorbents are used in the direct air capture of CO2, but the process is hindered by high energy demands, mainly due to the slow adsorption and desorption kinetics of CO2, This necessitates the use of a catalytic support like ZrO2 to reduce the energy barrier associated with the reaction. This study uses both density functional theory and experimental approaches to explore how ZrO2 support interacts with H2O during the carbonation reaction. The findings suggest that the presence of [ZrO(OH)]+ and OH- on the monoclinic ZrO2 (001) surface greatly speeds up the dissociation of H2O, reducing energy use in CO2 capture and increasing thermal efficiency. The catalytic role of ZrO2 is further confirmed through analyses using thermogravimetric-mass spectrometry (TG-MS) and X-ray photoelectron spectroscopy (XPS).

An Ab initio based OH initiated oxidation kinetics of glycerol carbonate: A promising biofuel component

The global energy demand is steadily increasing because of the population explosion and economic growth. Fossil fuels supply around 85 % of global primary energy demand. On one hand, fulfilling the increasing energy demands is a big challenge for the next few decades. On the other hand, the continued burning of fossil fuels leads to higher CO2 emissions, severely impacting global warming. Therefore, the policymakers vow to shift from conventional fuels to renewable resources for economic, environmental, and future energy security reasons. In this context, biofuels from lignocellulosic biomass and/or carbon-neutral fuels produced in the sustainable carbon cycle can close the carbon cycle and reach net zero-carbon emission. Recently, glycerol carbonate has been proposed as a promising fuel or fuel additive for future sustainability. Therefore, we investigated the hydrogen abstraction reactions of glycerol carbonate (GC) by OH radicals using high-level ab initio and variational transition state theory calculations. We mapped out the potential energy surface using the CCSD(T)/cc-pV(D, T)Z//MP2/cc-pVTZ level of theory. We used the ab initio parameters to obtain the site-specific rate coefficients by employing the variational transition state theory. We observed that every hydrogen atom in GC displays a unique reactivity with OH radicals. We derived branching ratio of each channel that are difficult to access experimentally. The overall rate coefficients exhibit a strong non-Arrhenius behaviour, which can be represented as:kovCVT/SCT(T)=3.39×10−20×T2.659×e−750.0Jmol−1RTcm3moleculesThis is the first reported rate data for the glycerol carbonate and OH radicals reaction.

Enhancing mechanical properties of dredged sludge through carbonation stabilization employing steel slag: An eco-friendly and cost-effective approach

Carbonation stabilization presents an efficacious and eco-friendly soil stabilization method with extensive applicability. Because market costs play a crucial role in determining the recycling of dredged sludge, this research investigates the potential use of solid waste steel slag as a cost-effective alternative stabilizing agent. The objective is to promote the wider adoption of carbonation stabilization technology for the reuse of dredged sludge. This investigation examined the alteration patterns of unconfined compressive strength and CO2 uptake in steel slag carbonation stabilized soils (CS) under varying steel slag contents, stabilization moisture contents, and carbonation durations. Furthermore, a detailed analysis of micro-mineral composition and micro-pore structure evolution during the carbonation process was conducted employing X-ray diffraction (XRD), thermogravimetric and derivative thermogravimetric analysis (TG-DTG), and mercury intrusion porosimetry (MIP). The outcomes revealed a positive linear association between the unconfined compressive strength of CS specimens and their CO2 uptake across different steel slag contents and carbonation durations. Through XRD and TG-DTG assessments, the carbonation byproducts in CS specimens were identified as calcite-type CaCO3, with an increasing concentration of CaCO3 correlating with the increase of steel slag content and carbonation duration. MIP testing revealed that a 72-hour carbonation period could diminish the total porosity of steel slag dredged soils from 40.96% to 34.53%. The strength of CS specimens predominantly derives from the carbonation reaction of steel slag, which enhances the soil's mechanical attributes through the cementing and pore-filling impacts of CaCO3 crystal growth on the soil matrix.

Enhancing the Performance and Sustainability of Cementitious Composites through the Optimized Use of Steel Slag: Particle Size and Activation Techniques

The utilization of industrial by-products such as steel slag in cementitious materials not only mitigates environmental impact but also enhances material properties. This study investigates the dual influence of steel slag particle size on the compressive strength and carbonation efficiency of cementitious composites. Through a systematic experimental approach, steel slag particles were incorporated into cement at varying sizes, and the resulting composites were subjected to mechanical and carbonation tests. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are conducted in this paper. The findings reveal a positive correlation between increased particle size and compressive strength, attributed to the improved interfacial transition zone and packing density. Conversely, smaller particle sizes exhibited enhanced carbonation efficiency, likely due to the increased surface area facilitating the carbonation reaction. The presence of higher silica and calcium content in finer particles was confirmed by EDX, which contributed to the accelerated carbonation process. This study underscores the importance of particle size optimization in designing sustainable cementitious materials with balanced mechanical performance and carbon sequestration potential. The insights gained from the advanced analytical techniques offer a comprehensive understanding of the mechanisms at play, paving the way for the strategic use of steel slag in eco-friendly construction practices.

The role of fluocerite in the genesis of bastnäsite: mechanistic insights and transformation pathways.

Fluocerite is a rare earth element (REE) fluoride found as an accessory mineral in magmatic-hydrothermal REE ore deposits, including alkaline complexes and carbonatites, where it is often associated with REE-fluorocarbonates. This study investigates the crystallisation kinetics, mechanisms and energetics of fluocerite (REEF3) and its role as a precursor phase of bastnäsite, one of the key minerals used for the extraction of REE. Fluocerite was synthesized by reacting pure fluorite (CaF2) with La-, Ce- and Nd-bearing solutions at temperatures ranging from ambient to low hydrothermal (30-90 °C). The synthetic fluocerites were then placed in contact with Na2CO3 solutions at temperatures up to 200 °C. A combined approach using powder X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy was used to determine the nature and quantify the crystallising solids. Our findings reveal a temperature-dependent fluorite-fluocerite transformation, with completion observed within 1 hour at 90 °C and extending to around 30 days at 30 °C. The rate of crystallisation decreases proportionally with the atomic number of the rare earth elements. On the other hand, the carbonation reaction of fluocerite exhibits a significantly slower rate, by ∼3 orders of magnitude, in comparison to the fluorite-fluocerite transformation, regardless of temperature conditions. The synthetic La, Ce and Nd fluocerites transformed into bastnäsite at all temperatures, also forming cerianite (CeO2) in the Ce-bearing experiments and metastable kozoite, NdCO3OH(orth), in the Nd-bearing experiments. Activation energies of fluocerite nucleation increase proportionally with the ionic radii of the REE (81 ± 6 (La); 84 ± 5 (Ce), 96 ± 10 (Nd) kJ mol-1), while the activation energies associated with fluocerite crystallisation are slightly higher for La (90 ± 12 kJ mol-1) and similar for Ce and Nd (76 ± 12 and 72 ± 8 kJ mol-1, respectively).

Nanoscale control over water-film thickness using temperature modulation: tuning mineral carbonation reactivity

Temperature modulation was demonstrated as a novel way to control water partitioning during the reaction of silicate minerals with water-saturated supercritical carbon dioxide.

Development of green cement from solid wastes

In this study, a green cement (GC) was prepared primarily using incineration bottom ash (IBA) and recycled concrete fine (RCF) at a low clinkering temperature of 1200ºC. This clinker mainly consisted of belite (C2S) and rankinite (C3S2) and demonstrated the versatility of strong carbonation reactivity and latent hydraulicity. Compared to the commercial benchmark - ordinary Portland cement - after being subjected to carbonation curing, GC exhibited superior macro- and micro-mechanical performance due to the densified microstructure. In addition to rapid strength gain at an early age, the carbonated GC also exhibited a substantial increase in strength at later ages and eventually recorded a high strength of 86.4 MPa. Furthermore, the leaching behaviour assessment on commonly regulated heavy metals validated the environmental stability of this waste-derived binder. The development of this sustainable cement has good potential to divert solid wastes otherwise destined for landfill sites to high-value-added construction products.

Unveiling the Carbonation Behavior and Microstructural Changes of Magnesium Slag at 0 ℃

Magnesium slag (MS) is an industrial byproduct with high CO2 sequestration potential. This study investigates the carbonation behavior and microstructural changes of MS during wet carbonation at 0 °C. XRD, TG, FTIR, SEM, and BET techniques were used to characterize the phase composition, microstructure, and porosity of MS samples carbonated for different durations. The results showed that the main carbonation products were calcite, vaterite, and highly polymerized silica gel, with particle sizes around 1 μm. The low-temperature environment retarded the carbonation reaction rate and affected the morphology and crystallization of calcium carbonate. After 480 min of carbonation, the specific surface area and porosity of MS increased substantially by 740% and 144.6%, respectively, indicating improved reactivity. The microstructure of carbonated MS became denser with calcite particles surrounded by silica gel. This study demonstrates that wet carbonation of MS at 0 °C significantly enhances its properties, creating an ultrafine supplementary cementitious material with considerable CO2 sequestration capacity.

Enhancing CO2-Cured cementitious binder with Mg-doped γ-C2S from high-Mg limestone

This study explores the use of Mg-doped γ-C2S, an alternative to conventional Portland cement, to address the environmental impact of the cement industry. γ-C2S, known for low hydration activity, shows promise as a CO2-cured binder. The research investigates Mg substitution in γ-C2S synthesis, utilizing high-Mg limestone resources. Varying Mg/Ca ratios in γ-C2S synthesis promoted bredigite and merwinite phases during calcination, enhancing specific surface area by over 40%. Optimal Mg doping significantly increased carbonation reactivity, resulting in a 20% strength boost (115 MPa) after 24h of CO2 curing. This improvement is attributed to enhanced crystallinity in carbonation products, namely hydromagnesite, nesquehonite, aragonite, and magnesite, leading to microstructure densification. The findings highlight Mg-doping as a promising strategy to enhance the carbonation performance of γ-C2S from high-Mg limestone, offering prospects for sustainable construction materials with reduced CO2 emissions.

Mechanochemical formation of highly stable amorphous calcium carbonate in calcium silicates: Potential long-term storage of CO2 in cement

We have investigated mechanochemical reactions with the calcium silicate wollastonite to probe potential mechanisms of sequestration and long-term storage of CO2 as mineral carbonates in cement pastes. Wollastonite, CaSiO3, was milled under ambient and 13C enriched CO2 atmospheres. Milling induced a structure change from monoclinic wollastonite−2M to triclinic−1T, consistent with high pressure treatment. The results from solid-state 13C nuclear magnetic resonance (NMR) spectroscopy shows this process forms an extraordinarily stable amorphous calcium carbonate (ACC) phase that remains despite a high temperature dehydration treatment (130 °C) and persists in the same form after 3 yrs. of storage at ambient conditions. Thermogravimetric analysis (TGA) of these samples indicates that ACC is produced at the similar solid concentrations in both CO2-enriched and ambient atmospheres. The observation of meta-stable ACC due to wollastonite carbonation may play an important role in further exploration and optimization of mineral carbonation reactions for CO2 capturing cement formulations.