Direct mineral carbonation of steelmaking slag for CO2 sequestration at room temperature

Potential of major by-products from non-ferrous metal industries for CO2 emission reduction by mineral carbonation: a review

By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can potentially sequestrate CO₂ through the mineral carbonation process. This review discusses the potential of these by-products for CO₂ reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO₂ equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO₂ emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO₂ emissions from the non-ferrous industries could be reduced by up to 9-25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries.

Carbon dioxide sequestration of iron ore mining waste under low-reaction condition of a direct mineral carbonation process

Mining waste that is rich in iron-, calcium- and magnesium-bearing minerals can be a potential feedstock for sequestering CO₂ by mineral carbonation. This study highlights the utilization of iron ore mining waste in sequestering CO₂ under low-reaction condition of a mineral carbonation process. Alkaline iron mining waste was used as feedstock for aqueous mineral carbonation and was subjected to mineralogical, chemical, and thermal analyses. A carbonation experiment was performed at ambient CO₂ pressure, temperature of 80 °C at 1-h exposure time under the influence of pH (8-12) and particle size (< 38-75 µm). The mine waste contains Fe-oxides of magnetite and hematite, Ca-silicates of anorthite and wollastonite and Ca-Mg-silicates of diopside, which corresponds to 72.62% (Fe₂O₃), 5.82% (CaO), and 2.74% (MgO). Fe and Ca carbonation efficiencies were increased when particle size was reduced to < 38 µm and pH increased to 12. Multi-stage mineral transformation was observed from thermogravimetric analysis between temperature of 30 and 1000 °C. Derivative mass losses of carbonated products were assigned to four stages between 30-150 °C (dehydration), 150-350 °C (iron dehydroxylation), 350-700 °C (Fe carbonate decomposition), and 700-1000 °C (Ca carbonate decomposition). Peaks of mass losses were attributed to ferric iron reduction to magnetite between 662 and 670 °C, siderite decarbonization between 485 and 513 °C, aragonite decarbonization between 753 and 767 °C, and calcite decarbonization between 798 and 943 °C. A 48% higher carbonation rate was observed in carbonated products compared to raw sample. Production of carbonates was evidenced from XRD analysis showing the presence of siderite, aragonite, calcite, and traces of Fe carbonates, and about 33.13-49.81 g CO₂/kg of waste has been sequestered from the process. Therefore, it has been shown that iron mining waste can be a feasible feedstock for mineral carbonation in view of waste restoration and CO₂ emission reduction.

Utilization of steelmaking slag for carbon capture and storage with flue gas

Carbon capture and storage is a necessary action for the reduction of CO₂ emissions, and thereby mitigation of climate change and its impacts. Especially, in India, with its growing fuel needs and very little attention paid towards carbon capture and storage, mineral carbonation technology is a suitable option as it is cost-effective and could be retrofitted to existing plants that emit CO₂. Given the development of carbon capture and storage technology, this study attempts direct mineral carbonation of steelmaking slag with flue gas. Response surface methodology was employed to design gas-solid and slurry phase aqueous carbonation experiments. A maximum reduction of about 36.1% was achieved through aqueous carbonation at 61.1 °C, 46.24 bar, and a liquid-to-solid ratio of 14.5, corresponding to a sequestration capacity of 127.4 g of CO₂/kg of slag. The temperature was found to be the most vital parameter in both the aqueous and gas-solid carbonation processes. Regression models used to study the carbonation process were found to be statistically significant. The carbonated slag consisted of mineral phases, namely, calcite and dolomite. The results demonstrated the sequestration potential of Indian steelmaking slag with flue gas. Carbonation of steelmaking slag with flue gas poses to be a promising option for the development of carbon capture and storage technology in the country.

CO2 Sequestration through Mineral Carbonation: Effect of Different Parameters on Carbonation of Fe-Rich Mine Waste Materials

Mineral carbonation is an increasingly popular method for carbon capture and storage that resembles the natural weathering process of alkaline-earth oxides for carbon dioxide removal into stable carbonates. This study aims to evaluate the potential of reusing Fe-rich mine waste for carbon sequestration by assessing the influence of pH condition, particle size fraction and reaction temperature on the carbonation reaction. A carbonation experiment was performed in a stainless steel reactor at ambient pressure and at a low temperature. The results indicated that the alkaline pH of waste samples was suitable for undergoing the carbonation process. Mineralogical analysis confirmed the presence of essential minerals for carbonation, i.e., magnetite, wollastonite, anorthite and diopside. The chemical composition exhibited the presence of iron and calcium oxides (39.58–62.95%) in wastes, indicating high possibilities for carbon sequestration. Analysis of the carbon uptake capacity revealed that at alkaline pH (8–12), 81.7–87.6 g CO2/kg of waste were sequestered. Furthermore, a particle size of <38 µm resulted in 83.8 g CO2/kg being sequestered from Fe-rich waste, suggesting that smaller particle sizes highly favor the carbonation process. Moreover, 56.1 g CO2/kg of uptake capacity was achieved under a low reaction temperature of 80 °C. These findings have demonstrated that Fe-rich mine waste has a high potential to be utilized as feedstock for mineral carbonation. Therefore, Fe-rich mine waste can be regarded as a valuable resource for carbon sinking while producing a value-added carbonate product. This is in line with the sustainable development goals regarding combating global climate change through a sustainable low-carbon industry and economy that can accelerate the reduction of carbon dioxide emissions.

Research status and future challenge for CO2 sequestration by mineral carbonation strategy using iron and steel slag

Mineral carbonation can simultaneously realize the effective treatment of CO₂ 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.

Influence of Hydrothermal Pretreatment Temperature on the Hydration Properties and Direct Carbonation Efficiency of Al-Rich Ladle Furnace Refining Slag

The influence of hydrothermal pretreatment temperature on the hydration products and carbonation efficiency of Al-rich LF slag was investigated. The results showed that the carbonation efficiency was strongly dependent on the morphology of hydration products and the hydration extent of the raw slag. Hydrothermal pretreatment at 20 °C or 80 °C favored the formation of flake-shaped products with a higher specific surface area and therefore resulted in a higher CO2 uptake of 20 °C and 80 °C-pretreated slags (13.66 wt% and 10.82 wt%, respectively). However, hydrothermal pretreatment at 40 °C, 60 °C or 100 °C led to the rhombohedral-shaped calcite layer surrounding the unreacted core of the raw slag and the formation of fewer flake-shaped products, resulting in a lower CO2 uptake of 40 °C, 60 °C and 100 °C-pretreated slags (9.21 wt%, 9.83 wt%, and 6.84 wt%, respectively).

Utilization of low-calcium fly ash via direct aqueous carbonation with a low-energy input: Determination of carbonation reaction and evaluation of the potential for CO2 sequestration and utilization

Environmental impacts from coal-fired power generation that produces large amounts of CO₂ and fly ash are of great interest. To reduce negative environmental impacts, fly ash utilization was investigated via a direct aqueous carbonation with a low-energy input in which the alkali calcium content in the fly ash reacted with CO₂ to form carbonate. Raw fly ash was characterized to understand the potential for direct aqueous carbonation of fly ash. The performance of the fly ash as a calcium source for direct aqueous carbonation at atmospheric pressure was investigated for different solid-liquid ratios and introduced CO₂ concentrations. Variations in fly ash elemental composition, reaction solution pH, CO₂ concentration in the reactor outlet, CO₂ uptake efficiency, CaCO₃ content and degree of carbonation were used to illustrate this process reaction. The maximum CO₂ uptake efficiency was ~0.016 g-CO₂/g-fly ash. This value was compared with previous studies, and the CO₂ uptake efficiency was comparable despite the use of a low-energy input method, i.e., direct aqueous carbonation with atmospheric pressure and unconcentrated CO₂. The calculated maximum degree of carbonation was 31.0%, which corresponds to 0.0063 g-CO₂/g-fly ash. Carbonated product characterization confirmed the carbonation reaction mechanism and safety for further utilization. A comparison of CO₂ uptake efficiency in this work with previous work, and considering the energy input and reactive species content, is provided. An assessment of the CO₂ reduction potential is provided.

Improvement of desulfurization efficiency of Al-rich ladle furnace refining slag with an aqueous carbonation method by hydrothermal or ultrasound pretreatment

Ladle furnace (LF) slag is a type of steel slag, which has limited applications due to its high S content. Aqueous carbonation is a prospective method for desulfurization of the LF slag. However, the Al-rich LF raw slag has very low desulfurization efficiency with carbonation method. This study investigated the improvement of desulfurization efficiency of the Al-rich LF slag with carbonation method by hydrothermal (HP) or ultrasound pretreatment (UP). The results showed that C3AHX was formed in pretreated slags because of C12A7 hydration, which could remove part of S. After carbonation, most of the C3AHX in pretreated slags produced crystalline CaCO3 bonded by amorphous Al(OH)3 (the other reaction product) in 10 min. In the carbonation process, S removal was mainly determined by carbonation efficiency. The S content was reduced to about 0.40% for the pretreated slags from 1.04% in the raw slag. By contrast, the S content was reduced to only 0.93% for slag without pretreatment under the same carbonation conditions. The possible reason of the improvement of desulfurization efficiency by HP or UP was the formation of thin plate-like C3AHx, which increased the surface area available for carbonation reaction. The UP slag presented slightly lower S content than the HP slag because high ultrasound energy increased the reactivity of Ca2SiO4.

Utilization of induction furnace steel slag based iron oxide nanocomposites for antibacterial studies

Metals and metal oxide-based nanocomposites play a significant role over the control of microbes. In this study, antibacterial activity of iron oxide (Fe2O3) nanocomposites based on induction furnace (IF) steel slag has been carried out. IF steel slag is an industrial by-product generated from secondary steel manufacturing process and has various metal oxides which includes Al2O3 (7.89%), MnO (5.06), CaO (1.49%) and specifically Fe2O3 (14.30%) in higher content along with metalloid SiO2 (66.42). Antibacterial activity of iron oxide nanocomposites has been revealed on bacterial species such as Micrococcus luteus, Bacillus subtilis and Staphylococcus aureus. Micrococcus luteus has undergone maximum zone of inhibition (ZOI) of 12 mm for 10 mg/mL concentration of steel slag iron oxide nanocomposite. Growth inhibitory kinetics of bacterial species has been studied using ELISA microplate reader at 660 nm by varying the concentration of steel slag iron oxide nanocomposites. The results illustrate that IF steel slag is a potential material and can be utilized in building materials to increase the resistance against biodeterioration.

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Co-treatment of Waste From Steelmaking Processes: Steel Slag-Based Carbon Capture and Storage by Mineralization

The iron and steel industry is an energy-intensive sector, and large amounts of waste/ by-products are generated during the steelmaking process, such as CO₂, metallurgical slag, and wastewater. Enhancing the development and deployment of treating waste from the steelmaking process will be environment friendly and resource-saving. Capturing CO₂ by steel slag (SS) via mineralization is regarded to be an excellent choice due to the high basicity of the slag. In this paper, recent research on the steel slag-based carbon capture and storage (SS-CCS) by mineralization was summarized. Three routes of SS-CCS are compared including, direct gas-solid carbonation, direct aqueous carbonation, and indirect carbonation, respectively. Furthermore, the challenges and prospects for further development of the SS-CCS were discussed.

Utilization of Malaysia EAF slags for effective application in direct aqueous sequestration of carbon dioxide under ambient temperature

Iron and steel industries are among the contributors of CO₂ emission in large volume into the atmosphere, causing detrimental effects to the environment and the ecosystem at large scale. These industries also generate solid wastes in the form of electric arc furnace (EAF) slag during operations which result in about 10–15% slag wastes per ton of steel produced. In this study, the EAF slags from an iron and steel-making factory in Klang, Malaysia was utilized for CO₂ sequestration through direct aqueous mineral carbonation. According to the surface area analysis, the fresh EAF slag has a mesoporous structure, its elemental composition shows the presence of 20.91 wt.% of CaO that was used for the sequestration of CO₂ through carbonation. The sequestration capacity was found to be 58.36 g CO₂/kg of slag at ambient temperature in 3 h, with the liquid/solid (L/S) ratio of 5:1 and using <63μm particle size. Moreover, the shrinking core model (SCM) was used to analyze the solid-fluid reaction in a heterogeneous phase and the CO₂ sequestration shows to be controlled by the product layer phase. The EAF slag is demonstrated to have the potential of CO₂ sequestration at ambient temperature.

Carbon Mineralization by Reaction with Steel-Making Waste: A Review

Carbon capture and sequestration (CCS) is taking the lead as a means for mitigating climate change. It is considered a crucial bridging technology, enabling carbon dioxide (CO2) emissions from fossil fuels to be reduced while the energy transition to renewable sources is taking place. CCS includes a portfolio of technologies that can possibly capture vast amounts of CO2 per year. Mineral carbonation is evolving as a possible candidate to sequester CO2 from medium-sized emissions point sources. It is the only recognized form of permanent CO2 storage with no concerns regarding CO2 leakage. It is based on the principles of natural rock weathering, where the CO2 dissolved in rainwater reacts with alkaline rocks to form carbonate minerals. The active alkaline elements (Ca/Mg) are the fundamental reactants for mineral carbonation reaction. Although the reaction is thermodynamically favored, it takes place over a large time scale. The challenge of mineral carbonation is to offset this limitation by accelerating the carbonation reaction with minimal energy and feedstock consumption. Calcium and magnesium silicates are generally selected for carbonation due to their abundance in nature. Industrial waste residues emerge as an alternative source of carbonation minerals that have higher reactivity than natural minerals; they are also inexpensive and readily available in proximity to CO2 emitters. In addition, the environmental stability of the industrial waste is often enhanced as they undergo carbonation. Recently, direct mineral carbonation has been investigated significantly due to its applicability to CO2 capture and storage. This review outlines the main research work carried out over the last few years on direct mineral carbonation process utilizing steel-making waste, with emphasis on recent research achievements and potentials for future research.

Dissolution of steel slags in aqueous media

Steel slag is a major industrial waste in steel industries, and its dissolution behavior in water needs to be characterized in the larger context of its potential use as an agent for sequestering CO₂. For this purpose, a small closed system batch reactor was used to conduct the dissolution of steel slags in an aqueous medium under various dissolution conditions. In this study, two different types of steel slags were procured from steel plants in India, having diverse structural features, mineralogical compositions, and particle sizes. The experiment was performed at different temperatures for 240 h of dissolution at atmospheric pressure. The dissolution rates of major and minor slag elements were quantified through liquid-phase elemental analysis using an inductively coupled plasma atomic emission spectroscopy at different time intervals. Advanced analytical techniques such as field emission gun-scanning electron microscope, energy-dispersive X-ray, BET, and XRD were also used to analyze mineralogical and structural changes in the slag particles. High dissolution of slags was observed irrespective of the particle size distribution, which suggests high carbonation potential. Concentrations of toxic heavy metals in the leachate were far below maximum acceptable limits. Thus, the present study investigates the dissolution behavior of different mineral ions of steel slag in aqueous media in light of its potential application in CO₂ sequestration.