Direct Aqueous Carbonation Research Articles

Direct aqueous mineral carbonation of secondary materials for carbon dioxide storage

Mineral carbonation of secondary materials offers an innovative way of storing carbon dioxide in materials that instead would mostly go to waste. This study investigates the carbonation efficiency (CE) of 11 different secondaries from refractory production, waste incineration, and the paper industry compared to untreated and thermally activated serpentinite. To determine the chemical and mineralogical composition of the materials, various analytical methods, like X-ray fluorescence, X-ray diffraction, scanning electron microscopy, Brunauer-Emmet-Teller and thermogravimetric analysis have been employed, both before and after the direct aqueous carbonation process. Each material was examined over reaction times of 6 & 10 hours at 180 °C and a starting pressure of 20 bar in a 0.6 L stainless steel batch reactor. The received results were then compared to the theoretical CO2 uptake, defined as the maximum carbon dioxide storage potential achievable if all Ca, Fe and Mg ions were converted to carbonates. The findings indicate carbonation efficiencies of 14–65 % for secondary materials, compared to 0.7–14 % observed in the serpentinite samples. The highest uptakes were achieved by the refractory materials, primarily due to their high metal oxide content. However, a negative impact was observed from graphite-based carbon binders in the refractories, with increased leaching of these binders leading to a decrease in carbonation efficiency. Materials with higher SiO2 content showed reduced performance, suggesting a passivation layer buildup during carbonation.

CO2 uptake of cement by-pass dust via direct aqueous carbonation: an experimental design for time and temperature optimisation

The compositional characteristics of cement by-pass dust (CBPD), specifically its alkalinity and salt content, present significant limitations to its reinsertion in cement production. Furthermore, these characteristics give rise to considerable concerns regarding its disposal. The present study investigated the potential for treating CBPD through the application of a direct aqueous carbonation technique. The aim is to assess carbon capture potential of the material and to investigate the impact of the mineralisation process on its composition. The process was conducted under atmospheric pressure, at low temperature (20–60 °C) and for short duration (20–60 min). Different CO2 quantification techniques were employed to assess experiments efficiency and replicability of the adopted quantification techniques. A Design of Experiment was developed to identify the optimum carbonation conditions in terms of time and temperature. The conditions for CO2 content maximisation resulted in a fair agreement with the prediction of the response surface methodology. High values in CO2 uptake (25.1%) and carbonation degree (82%) were achieved, outperforming previous literature studies. Moreover, the mineralisation process significantly reduces the chloride content of CBPD, paving the way for its adoption as a supplementary cementitious material in integrated industrial processes for carbon capture and utilisation.

The carbon activation of electric furnace ferronickel slag and its utilization in cement-based materials

The high annual emissions and low utilization rate of electric furnace ferronickel slag (EFS) have brought enormous impacts on environment. This work intends to propose a methodology for the carbon activation of EFS to improve its resource utilization. To this end, the exfoliation-carbonation (i.e., hybrid aqueous carbonation) was developed and compared with CO2 bubbling carbonation (i.e., direct aqueous carbonation). The carbonation process of EFS and the hydration and mechanical strength of activated EFS blended cement-based materials was evaluated. Experimental results indicated that mechanical pre-treatment could disorder forsterite crystal and promote the dissolution of Mg to form Si enriched mineral surface. The direct aqueous carbonation led to the formation of passivation layer which could be striped by hybrid aqueous carbonation to facilitate further carbon mineralization. Increase in temperature significantly improved the decomposition of forsterite and accelerated the carbon mineralization kinetics. The activated EFS could accelerate the hydration and promote the mechanical strength of cement-based materials. Carbon mineralization is an effective method to strengthening the activity of EFS.

Comparative study of direct solid-gas carbonation and direct aqueous carbonation for carbon capture and storage

Abstract Carbon dioxide (CO2) is a significant contributor to global warming and environmental issues, necessitating the development of practical storage solutions. As an alternative to CO2 storage in subsurface formations, mineral carbonation, which offers long-term CO2 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 CO2. 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 CO2 emissions. The research focuses on reaction kinetics, capture efficiency, recovery efficiency, leakage security, and cost-effectiveness. Both methods have the potential to capture CO2 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 CO2 sequestration costs, increasing the scale of captured CO2 usage in industrial processes, and developing a circular economy by transforming captured CO2 into valuable metal carbonates.

CO2 mineralization and heavy metal leaching of multi-source ashes from municipal solid waste incineration

Mineralization holds great promise in simultaneously fixing CO2 and treating ash from the municipal solid waste incineration (MSWI). However, characteristics of CO2 mineralization and heavy metal leaching largely depends on the generation process of ashes. Herein, we report a systematic evaluation on the direct aqueous carbonation of multi-source MSWI ashes and leaching behavior of heavy metals before and after mineralization. Influencing factors for CO2 mineralization are determined to follow the order of CO2 concentration > temperature > solid–liquid ratio > stirring speed. Spray tower fly ash from the semi-dry process and bag filter fly ash from the dry process exhibit better sequestration capacities of 82.3 g-CO2/kg-ash and 150.9 g-CO2/kg-ash with a maximum CO2 removal rate of 0.117 mmol/s and 0.191 mmol/s among all ashes. Moreover, leaching concentration of Pb/Cu/As/Ni/Hg in six MSWI ashes all decreases significantly after CO2 mineralization. These findings could provide guidance for the potential intensive utilization of MSWI ashes in CO2 mitigation.

A thorough assessment of mineral carbonation of steel slag and refractory waste

Escalating industrial CO2 emissions necessitate innovative carbon capture and utilization strategies. This study explores the potential of mineral-carbonation of steelmaking slags, particularly White Slag (WS) and various Refractory Wastes (RWs), to mitigate CO2 emissions and valorize industrial wastes. Experiments were performed with waste materials from the production lines at CELSA (Barcelona, Spain). We delved into direct aqueous carbonation, evaluating the performance and characteristics of these wastes under different experimental conditions. Our findings reveal that all slags can effectively sequester CO2. This process is effective not only for pure CO2 but also for diluted flue gases under mild conditions (≤ 100 ºC, ≤ 6 bar). Specifically, WS exhibited peak CO2 sequestration capacities (SC) of 359.79 gCO2/kgslag (pure CO2) and 276.65 gCO2/kgslag (diluted flue gas). In contrast, the RWs presented different kinetic, reaching a maximum SC of 311 gCO2/kgslag after prolonged times. Given the large inhomogeneity of RWs, individual analysis of distinct RW fractions revealed significant variations in carbonation performance. Tundish RW exhibited the highest CO2 sequestration capacity, emphasizing the importance of waste source and mineral composition in the carbonation. Chemical and morphological evaluations confirmed the transformation of CaO to CaCO3, with MgO remaining largely inert. Additionally, the process indicated potential environmental benefits by reducing the mobility of toxic metals, particularly Pb, suggesting an ancillary avenue for waste treatment. This study underscores the utility of CO2 mineralization as a dual-benefit approach within the circular economy framework, offering insights into its application for sustainable waste management and CO2 emission reduction in the steel industry.

Effect of NaHCO3 on the Magnesite Yield in Direct Aqueous Carbonation of Thermally-Activated Lizardite

Effect of NaHCO₃ on the Magnesite Yield in Direct Aqueous Carbonation of Thermally-Activated Lizardite

Application of ultrafine bubbles for enhanced carbonation of municipal solid waste incineration ash during direct aqueous carbonation

Municipal solid waste incineration fly ash was selected as the alkaline Ca-bearing solid waste, and a series of direct aqueous carbonation experiments using 10% CO2 gas were conducted to showcase the capability of ultrafine bubbles (UFBs) in enhancing carbonation efficiency. Results from the experiments, conducted using a one-pass water flow system, revealed that carbonation without UFBs increased the CO2 content of the ash from 59 to 200 mgCO2/g (an increase of 141 mgCO2/g), while the presence of UFBs elevated it to 237 mgCO2/g (an increase of 178 mgCO2/g). Consequently, the introduction of UFBs led to a 26% increase in CO2 content in ash [(178−141) / 141]. This improvement was primarily attributed to the enhanced carbonation efficiency for particles ≥ 46 µm. The positive impact of UFBs was more evident (62% increase in CO2 content in ash) in experiments using a water circulation system, where carbonation proceeded at a faster rate compared to the one-pass water flow system. In terms of the mechanism, X-ray diffraction and scanning electron microscopy analyses indicated that UFBs facilitated the removal of CaCO3 deposition, which inhibited Ca(OH)2 dissolution. To the best of our knowledge, this study is the first to demonstrate the favorable influence of UFBs on fly ash carbonation efficiency.

Kinetic evaluation and applicability analysis on direct aqueous carbonation of industrial/mining solid wastes

CO2 mineralization combined with goaf backfilling is an effective pathway for alkaline solid waste recycling and CO2 emission reduction. Determining the kinetics of solid waste mixtures during direct aqueous carbonation is therefore important. Here, carbonation behavior and kinetics of carbide slag and its mixes with iron tailing are examined using a kinetic model based on the two-film theory. The impact of important operation parameters is assessed through model fitting as well. Results show that there is an excellent fitting accuracy to the carbonation of carbide slag and its 50 % mixtures by the model (average R2 =0.999) although a limitation is observed when the IT blending ratio is very high. Additionally, the change of gas-liquid mass transfer flux is compatible with the theory, and the ideal parameters are determined to be a reaction temperature of 65 °C, a solid-liquid ratio of 100 g/L, and a CO2 concentration of 15 %. Difference between the experimental and predicted value is controlled within 10 %. The above results are beneficial to revealing the microscale carbonation mechanism of mixed solid waste and may offer theoretical backing for industrial applications.

Accelerated Direct Carbonation of Steel Slag and Cement Kiln Dust: An Industrial Symbiosis Strategy Applied in the Bergamo-Brescia Area.

The carbonation of alkaline industrial wastes is a pressing issue that is aimed at reducing CO2 emissions while promoting a circular economy. In this study, we explored the direct aqueous carbonation of steel slag and cement kiln dust in a newly developed pressurized reactor that operated at 15 bar. The goal was to identify the optimal reaction conditions and the most promising by-products that can be reused in their carbonated form, particularly in the construction industry. We proposed a novel, synergistic strategy for managing industrial waste and reducing the use of virgin raw materials among industries located in Lombardy, Italy, specifically Bergamo-Brescia. Our initial findings are highly promising, with argon oxygen decarburization (AOD) slag and black slag (sample 3) producing the best results (70 g CO2/kg slag and 76 g CO2/kg slag, respectively) compared with the other samples. Cement kiln dust (CKD) yielded 48 g CO2/kg CKD. We showed that the high concentration of CaO in the waste facilitated carbonation, while the presence of Fe compounds in large amounts caused the material to be less soluble in water, affecting the homogeneity of the slurry.

Direct aqueous mineral carbonation of carbide slag in a bubble column reactor under ambient conditions

The accelerated carbonation technology utilizing the alkaline minerals or alkaline wastes incurs high operation and investment costs low conversion efficiency and high energy consumption. Due to the strong alkalinity of the carbide slag, good feedstock availability and great performance of the bubble column reactor, the direct aqueous mineral carbonation of the carbide slag in a bubble column at ambient conditions is evaluated. The impact mechanism of the liquid to solid ratio (5 mL/g−50 mL/g) and gas velocity (0.0041 m/s−0.205 m/s) on the reactions are investigated. The flow patterns are identified by empirical mode decomposition (EMD) energy entropy, and carbonation efficiencies at different flow regimes are compared and illustrated. It is found that this route has a high carbonation efficiency and short reaction time. The maximum carbonation efficiency is 100% and the capture capacity is 214.05 g CO2 / kg carbide slag. The discrete bubble regime (DBR) and bubble coalescence regime (BCR) are observed, and the increase of the L/S ratio can promote the bubble coalescence. The hydrodynamics can influence the processes of the CO2 mass transfer from gas to liquid phase, Ca(OH)2 dissolution, reactant diffusion, collision and ionic reactions. At small L/S ratio, the greater carbonation efficiency is achieved in discrete bubble regime attributing to the longer gas residence time, larger gas–liquid interfacial area and better CO2 mass transfer than that in BCR. At large L/S ratio, the greater carbonation efficiencies are achieved both in DBR and BCR. It has good CO2 mass transfer in DBR and has the strong liquid turbulence intensity in BCR which is good for the reactant diffusion and collision. The enhancement factor increases when enhancing the L/S ratio in DBR. The 30 mL/g and the gas velocity operated in the discrete bubble regime are recommended considering the better three-phase contact, good carbonation conversion and low energy consumption.

Evaluation on direct aqueous carbonation of industrial/mining solid wastes for CO2 mineralization

Carbonation of industrial alkaline resources can achieve dual effects of CO2 sequestration and solid waste management, and the carbonated product may act as a potential cementitious backfill material. Based on this idea, CO2 mineralization characteristics and potential of typical industrial solid wastes, mine tailings and their mixtures are investigated by direct aqueous carbonation, and effects of reaction parameters, including particle size, reaction temperature, solid-to-liquid ratio, CO2 concentration, are systematically explored. Results show that industrial solid wastes with a high Ca content such as carbide slag have better carbonation activity with the maximum CO2 sequestration capacity of 544.6 g-CO2/kg, while the carbonation of mine tailings is very weak. The combination of coal fly ash with tailings has a potential stimulative effect during carbonation. Moreover, influences of carbonation parameters are revealed in this study, and optimal reaction parameters are determined to be particle size below 75 μm, temperature of 60 °C, solid-to-liquid ratio of 100 g/L, and CO2 concentration of 15% within mild range. These results can provide fundamental knowledge for the integrated CO2 mineralization and goaf backfilling, and accelerate carbon reduction and waste resource utilization.

Kinetic analysis on CO2 sequestration from flue gas through direct aqueous mineral carbonation of circulating fluidized bed combustion fly ash

In this work, the suitability of fly ash from 600 MW circulating fluidized bed boiler for CO2 sequestration through direct aqueous route was evaluated. The circulating fluidized bed combustion fly ash exhibited favorable carbon capture characteristics with a maximum CO2 sequestration capacity of 0.128 g CO2/g CFA and a corresponding carbonation efficiency of 78.17 %. A modified shrinking core model incorporated gaseous CO2 dissolution and time-dependent effective coefficient of internal diffusion was proposed to determine the gas–liquid-solid carbonation kinetics. The key kinetic parameters were assessed as a function of various carbonation conditions including reaction temperature, solid–liquid (S/L) ratio, energy input and superficial gas velocity. The mass diffusion through the liquid film near the gas–liquid interface was the rate-controlling step during the initial period of time, while diffusion through the expanded passivation layer constituted the controlling mechanism at the final stage. The model provides a more accurate representation of the gas–liquid-solid carbonation process and can be generalized to describe the carbonation of other solid wastes of interest.

CO2 sequestration by direct mineral carbonation of municipal solid waste incinerator fly ash in ammonium salt solution: Performance evaluation and reaction kinetics

In this study, we investigated CO2 mineral sequestration by municipal solid waste incineration fly ash (MSWI-FA) in both pure water and ammonium salt solutions [NH4Cl, (NH4)2SO4 and CH3COONH4]. The introduction of NH4+ significantly promoted the solid–liquid mass transfer of the active calcium on the MSWI-FA particles and the generation of free ammonia in the solution, which enhanced the carbonation kinetics and crystallization of the calcium carbonate product. Changes to the mineralogy, morphology, and surface properties of the MSWI-FA particles before and after carbonation confirmed the reaction mechanism. A novel kinetic model based on the two-film theory was developed to evaluate the mass transfer and chemical reaction of heterogeneous carbonation in both pure water and ammonium salt solutions. To optimize the carbonation rate and efficiency, the complex effects of various operating parameters on the CO2 sequestration characteristics were systematically investigated. Maximum carbonation kinetics was achieved at 60 °C, an ammonium salt concentration of 1.0 mol/L, and a gas flow rate of 1.0 L/min, resulting in a carbonation efficiency and CO2 sequestration capacity of 78.49 % and 0.236 g CO2/g MSWI-FA, respectively. A comparison of the present results with those of other studies suggests that direct aqueous carbonation in ammonium salt solutions is feasible owing to its higher carbonation kinetics and CO2 sequestration capacity.

Evaluation of the kinetics of direct aqueous mineral carbonation of wood combustion ash using modified shrinking core models.

The direct aqueous mineral carbonation of wood combustion ash (WCA), which is a representative high-calcium waste from combustion process, was systematically investigated by varying complex operating conditions, including reaction time, liquid-to-solid ratio (L/S), CO2 concentration, and particle size. The WCA exhibited high CO2 sequestration characteristics with an optimal carbonation efficiency of 76.4%, corresponding to a CO2 sequestration capacity of 0.314g CO2/g WCA. In addition to solid carbonates, dry residues from liquid products with high potassium contents are potential feedstocks for quality potash fertilizer. Modified shrinking core models based on diffusion-controlled mechanism were proposed to evaluate the carbonation process. The theoretical framework assumes a contracting interface mechanism where active CaO reacts with CO2 to form a product layer. The effective diffusion coefficient of CO2 through the product layer decreases over time, giving deficient carbonation efficiency. The newly proposed models corresponding to different geometrical dimensions provided more perfect fit to the experimental data when compared with the most commonly used kinetic equations. The low apparent activation energy of the carbonation reaction demonstrated the diffusion-controlled mechanism. This work is useful for improving the economics and feasibility of bioenergy carbon capture and storage (CCS) technology chain.

Direct aqueous carbonation of dephosphorization slag under mild conditions for CO2 sequestration and utilization: Exploration of new dephosphorization slag utilization

Dephosphorization slag is not effectively utilized owing to its characteristics of having high phosphorus (P) content and being rich in free CaO. In this study, direct aqueous carbonation of dephosphorization slag under mild conditions (i.e., atmospheric pressure, unconcentrated CO 2 , and room temperature) was investigated to explore the potential for CO 2 sequestration and utilization, as well as to improve its properties for further utilization. The maximum CO 2 uptake capacity of 0.06 g-CO 2 /g-slag was achieved at a solid–liquid ratio of 25 g/L with 14% introduced-CO 2 concentration. Depending on the pH value, P was fixed by crystallization with calcium (Ca), which was verified by the crystalline phases of the carbonated slag and elemental concentrations of the solution. The particle collision mechanism was confirmed by characterization of the particle-size distribution and crystalline phases of the carbonated slag, demonstrating detachment of CaCO 3 from the slag surface, which was more significant at high solid–liquid ratios. The rate-limiting step is controlled by CO 2 dissolution and CaCO 3 precipitation. The carbonated slag was determined to be stable, and it can be used for further applications. • Dephosphorization slag utilization was investigated. • A CO 2 uptake capacity of 0.06 g-CO 2 /g-slag was achieved under mild conditions. • The reaction mechanism of direct aqueous carbonation was determined. • The carbonated slags were characterized for possible further utilization.

Observation of the depassivation effect of attrition on magnesium silicates' direct aqueous carbonation products

The main obstacle to the aqueous carbonation of non-serpentinised magnesium silicates is the formation of surface passivation layers, which severely limits the reaction rate and thus the overall efficiency of the process. A technological solution to overcome this problem is to perform the carbonation process inside a stirred bead mill, which aims to continuously remove the surface by-product layers by attrition. In this work, the aqueous carbonation of ferronickel slag, a mineralogically complex mining waste composed of a Mg/Si rich amorphous phase and a crystalline ferrous forsterite, was studied at 150°C and under 10 bar of CO2 with different operating configurations: carbonation alone (C mode), attrition followed by carbonation (A-C mode) and concomitant attrition and carbonation (AC mode). By careful observation of the mineralogy and the surface of the secondary phases formed using complementary analytical techniques, the article allows a better understanding of the passivation phenomenon inherent to the carbonation of magnesium silicates, and confirms the effectiveness of continuous surface mechanical depassivation for reaching high carbonation rates with this type of material. Comparative analysis of the products obtained with the three operating modes shows that a true synergy takes place between attrition and carbonation due to the combined effect of continuous exfoliation and mechanical activation of particle surface, which goes far beyond the simple increase in surface area due to particle size reduction. While mechanical depassivation is here substantiated by several evidence, the additional mechanochemical activation effect cannot be delineated from experiment; however its beneficial contribution to carbonation is inferred from its observation in A-C mode. The work finds that the synergy between attrition and carbonation also yields very characteristic products. They consist in micrometric agglomerates formed by bound spherical particles a few tens of nanometers in size. These particles themselves contain an entanglement of nanometric grains of carbonates and amorphous silica dispersed inside a magnesium-depleted alumino-siliceous matrix. These results confirm that concomitant attrition and carbonation offers one of the most promising pathways for developing direct aqueous carbonation processes with non-thermally activatable magnesium silicates.

Carbon mineralization with concurrent critical metal recovery from olivine

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, single-step 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.

Glycine-induced synthesis of vaterite by direct aqueous mineral carbonation of desulfurization gypsum

Glycine-induced synthesis of vaterite by direct aqueous mineral carbonation of desulfurization gypsum

The effect of mineral composition on direct aqueous carbonation of ultramafic mine waste rock for CO2 sequestration, a case study of Turnagain ultramafic complex in British Columbia, Canada

ABSTRACT The heterogenous mineralogy of ultramafic mine waste rocks make their carbonation rate hard to evaluate. This study investigated the effect of mineral composition on direct aqueous carbonation, through quantitative X-ray diffraction. The results show that magnesite was the main carbonated product, which was a stoichiometric conversion of forsterite. Diopside acted as a seed for quick crystallisation of magnesite. Lizardite could enhance the carbonation conversion, which reaches the optimum value when the weight ratio of lizardite to forsterite is 0.3–0.4. Sulphide in the reactant samples has a positive influence on carbonation. Brucite, magnetite and maghemite show little influence on carbonated products.