Direct Conversion of Desiliconization Slag to a CaO-Mesoporous Silica Composite for CO₂ Capture: Effect of Acid Dissolution Agent

Abstract

Calcium looping (CaL) utilizing CaO-based adsorbent has been studied to reduce carbon dioxide emissions (CO₂). Synthesis of the CaO-based adsorbents from waste slags has captured the interest of the iron and steel industry, which is dealing with intensive amounts of waste slag produced. The drawback of using CaO-based adsorbents is their low regenerative ability during cyclic CO₂ adsorption. In this study, aiming to synthesize a CaO-based adsorbent with better cyclic stability, we used desiliconization slag as a raw material, which is produced during the steel purification process by minimizing the silicon concentration. We synthesized a CaO and mesoporous silica (CaO-MS) composite from desiliconization slag using P123 as an organic template and several organic acids, including formic acid (FA), acetic acid (AA), and citric acid (CA) as dissolution agents. The structure and performance of the adsorbents were investigated using X-ray diffraction analysis (XRD), N₂ adsorption-desorption, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and thermogravimetric analysis (TG). Compared to the samples synthesized with other organic acids, the slag-derived adsorbent synthesized with acetic acid (DSslag-CaO-MS(AA)) displayed the optimum CO₂ adsorption capacity with 21.0 wt% per mass of adsorbent and the highest stability. The findings demonstrated that the mesoporous structure enhanced the CO₂ adsorption and acetic acid is the best dissolution agent in synthesizing CaO-MS adsorbent by separating the crystalline CaO phase and SiO₂ phase. Environmentally benign and economically viable CaO-based adsorbents synthesized from desiliconization slag can be used for CO₂ capture, particularly in the iron and steel industry.

1. Introduction

Anthropogenic carbon dioxide emissions contribute significantly to global warming and climate change, prompting significant international efforts to investigate and develop effective materials for CO₂ capture.^1,2,3,4,5,6) The iron and steel industry contributed approximately 5–7% of global CO₂ emissions, which is the largest consumer of energy.^7,8,9,10) As a result, it is critical to significantly reduce global CO₂ emissions in the future. It is commonly acknowledged that CO₂ capture and storage (CCS) is a promising solution for reducing CO₂ emissions in the short to medium term.^11,12) To this end, there has been a wide range of studies on CCS. CaL, which is based on the carbonation-calcination cycles of CaO, is regarded as one of the most promising technologies for large-scale CO₂ capture due to several advantages; high reactivity with CO₂, high theoretical CO₂ adsorption capacity (0.78 gram of CO₂ per gram of CaO), and low material cost.^13,14,15) Calcium looping appears to be particularly ideal for CO₂ capture in the iron and steel industry because the CaO-based adsorbent can be utilized as a feedstock for clinker manufacture after its use.¹⁴⁾ The reversible reaction between CaO and CO₂, as expressed in Eq. (1), has a high potential for lowering CO₂ emissions from various renewable energy systems.   

$$\mathrm{C}\mathrm{a}{\mathrm{O}}_{(\mathrm{s})}+\mathrm{C}{\mathrm{O}}_{2(\mathrm{g})}\rightleftharpoons \mathrm{C}\mathrm{a}\mathrm{C}{\mathrm{O}}_{3(\mathrm{s})},\mathrm{\Delta }{H}_{r,\mathrm{\hspace{0.17em} }298\mathrm{K}}=-178\mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$$(1)

During the CaL operations, the CaO-based adsorbent is usually heated in the temperature range of 973 K or higher to allow the above reaction to proceed.¹³⁾ The reactivity of CaO is very crucial and related to its pore structure, surface area, and porosity.¹⁶⁾ Previous literature reported that most of the CaO-based adsorbents are suffered from a loss of adsorption uptake during the repeated cycle of the adsorption-desorption process because of the sintering.^17,18,19) The surface area and porosity of the adsorbent are continuously reduced during sintering, resulting in a lower CO₂ adsorption uptake. This phenomenon has sparked the interest of researchers striving to enhance the regenerating capabilities of CaO-based adsorbents.

Concerns about climate change have rekindled interest in exploring the potential of waste slags as a means of sequestering and utilizing the CO₂ created during the iron and steel manufacturing process.²⁰⁾ Waste slag materials with high concentrations of CaO and SiO₂, such as blast furnace slag^21,22) and converter slag,²³⁾ have the potential to be utilized as raw materials for CO₂ adsorbent synthesis. In addition, the rate of waste slag recycling in Asian countries remains quite low. Experts estimate that the total accumulation of steel slags since 1980 has surpassed 2.5 billion tonnes and has been growing at a pace of approximately 3–4% per year at the present consumption rate.²⁴⁾ Currently, most of the iron and steel-making slag has been utilized in cement, concrete, roadbed materials, and fertilizer. With the increasing production and limited disposal site, new solutions to reuse the waste slags have been required. Nevertheless, slag production cannot be prevented entirely, and finding other uses for these slags, especially steel-making slags with various complex compositions, continues to be a priority for the sustainable development of the iron and steel sectors.

In iron and steel production, desiliconization is a significant parameter in increasing product effectiveness throughout the basic oxygen furnace process. Depending on the desired steel quality, carbon, phosphorous, sulfur, and silicon could be eliminated during the refining process of the hot metal.⁷⁾ In order to compensate for the energy produced during the combustion of silicon, the utilization of scrap increases as the silicon content in steel increases. Utilizing a large quantity of scrap in the manufacturing of steel may be expensive and inefficient because it contributes to the production of steel with high impurity levels. For a reliable, efficient, and high-quality steel production process, it is essential for controlling the silicon content of the produced steel. Desiliconization slag, thus produced, typically comprises 40–50% CaO and 11–15% SiO₂, which may be suitable for use as a raw material in the synthesis of a CaO-based adsorbent.

Previously, our group utilized blast furnace slag,²¹⁾ converter slag²³⁾ and dephosphorization slag⁷⁾ as the raw materials for the synthesis of CaO-based CO₂ adsorbents. As discussed above, it is crucial to synthesize and develop a stable CaO adsorbent to improve its CO₂ adsorption capacity and long-term stability. In this study, we utilized desiliconization slag as a raw material for the synthesis of CaO-based CO₂ adsorbent and examined its CO₂-capturing performance and regenerative ability. In the previous studies, we determined that formic acid is the most effective dissolution agent for the synthesis of CaO-based adsorbent; however, the scope of other organic acids has not been explored extensively. Herein, we synthesized CaO and mesoporous silica composites using a feasible chemical process by utilizing three types of organic acids, including formic acid, acetic acid, and citric acid, as dissolution reagents. Intriguingly, the type of organic acid had a substantial impact on the crystallinity of CaO, the mesoporous structure of the adsorbent, and consequently the CO₂ adsorption performance.

2. Experimental

2.1. Materials

Desiliconization slag (DSslag) employed as a raw material was kindly supplied from JFE Steel Corporation, Japan, and Pluronic P123^® triblock polymer (M_w = 5800) used as an organic template was purchased from Sigma-Aldrich Co., Ltd.. The organic acid employed were all purchased from Nacalai Tesque, Inc., such as acetic acid (AA, 99.7%), citric acid (CA, anhydrous), and formic acid (FA, 98%), which were all used without further purification.

2.2. Synthesis Method

The CaO and mesoporous silica composite from DSslag (DSslag-CaO-MS) was synthesized through a ball-milling process (PULVERISETTE7), acid dissolution, and hydrothermal treatment according to a previously described method.²¹⁾ Figure 1 represents a schematic diagram of the composite synthesis procedure. At room temperature, to depolymerize the metal components in the DSslag into metal ions, 3.0 g of DSslag (consisting of 16.6 wt% of SiO₂) was mixed with 33 mL of a 3.0 mol/L acid solution (step 1 in Fig. 1). This preliminary step required the application of one of three kinds of acids, either FA, AA, or CA. Then, 33 mL of deionized water containing 0.82 g of P123 (P123 : Si = 0.017 : 1, equivalent to 0.14 mmol) was added dropwise to the aforementioned solutions (step 2). This solution was agitated in a water bath at 313 K for one day (step 3) to produce mesoporous silicate phase and was transferred to a Teflon container and placed in an oven at 373 K for one day (step 4). The resulting solution was evaporated to remove the water, followed by calcination in an electric oven at 873 K for 4 hours in air to eliminate the organic components, during which the dissolved Ca²⁺ ions transformed into CaO crystals (step 5). Hence, a solid product consisting of CaO and mesoporous silica (MS) was obtained using DSslag as a sole metal precursor. The samples were designated as DSslag-CaO-MS(FA), DSslag-CaO-MS(AA), and DSslag-CaO-MS(CA) based on the dissolving acid used.

Fig. 1.

The synthetic procedure of CaO and mesoporous silica composite from desiliconization slag. (Online version in color.)

2.3. Characterizations

X-ray diffraction (XRD) measurement was carried out on a Rigaku Ultima IV diffractometer using Cu K_α radiation (λ = 1.54056 Å) at 40 kV and 40 mA. N₂ adsorption-desorption isotherms were obtained at 77 K using a BELSORP-max (MicrotracBEL Corp.). Before the measurement, samples were outgassed at 573 K for 3 hours under vacuum to remove physisorbed water molecules. From the N₂ adsorption isotherm data, the Brunauer-Emmett-Teller (BET) specific surface areas, pore diameter, and total pore volumes were determined. To determine the pore size distribution, the Barrett-Joyner-Halenda (BJH) method was employed. To quantify the elements in the samples, SEM in a JEOL JSM-5600 equipped with an energy-dispersive X-ray (EDX) spectrometer and inductive coupled plasma atomic emission spectroscopy (ICP-AES) analysis with a Nippon Jarrell-Ash ICAP-575 Mark II were utilized. To observe the morphology of the samples, transmission electron microscopy (TEM) images were measured using Hitachi H-800 operating at 200 kV. Scanning transmission electron microscopy (STEM) images, EDX spectra, and selected area electron diffraction (SAED) images were obtained by JEOL ARM200F equipped with a JED-2300T EDX detector.

2.4. CO₂ Adsorption Study of DSslag-CaO-MS

CO₂ adsorption experiments were carried out using thermogravimetric (TG) instrument (Rigaku Thermo plus EVO2). First, the DSslag-CaO-MS adsorbents were pre-treated for 60 mins at 1023 K with a flow of dry N₂ (50 mL/min) to eliminate any impurities that could adhere to the samples. The CO₂ adsorption (carbonation) was begun by exposing the sample to 10% CO₂/N₂ (50 mL/min) for 150 min at 973 K and CO₂ desorption (decarbonation) was done by exposing to dry N₂ (50 mL/min) at 1023 K for 60 min. To observe the regenerative capability of the adsorbent over time, the preceding adsorption/desorption cycles were repeated ten times.

3. Result and Discussion

3.1. Synthesis of DSslag-CaO-MS from Desiliconization Slag

XRD measurement was carried out to see the crystalline structure of the adsorbents. Figure 2 shows the crystallinity phase of the DSslag-CaO-MS adsorbents. In all adsorbents, CaO and CaCO₃ phases were observed. The existence of the crystalline CaCO₃ phase proved that this adsorbent has CO₂ adsorption capability. Similar crystalline phases were observed in all samples, however, the peak intensities of the adsorbents vary depending on the type of the organic acid used.²⁵⁾ The DSslag-CaO-MS(FA) showed higher intensity peaks of CaCO₃ compared to the samples synthesized with acetic and citric acid. It is assumable that, during calcination at 873 K, the organic component of the sample synthesized with formic acid was easily eliminated, hence contributing to a higher crystallinity of CaO, which resulted in a higher intensity of CaCO₃ phase in XRD.

Fig. 2.

XRD patterns of DSslag-CaO-MS samples.

ICP analysis was employed to determine the chemical compositions of the DSslag-CaO-MS adsorbents synthesized utilizing the three kinds of acid. As shown in Table 1, the chemical composition of CaO in all samples was between 40–48 wt%, while that of SiO₂ was between 15–20 wt%. The calculations for each metal revealed that practically all of the raw DSslag’s constituent metals had been recycled. The remaining components may include Na₂O and water.

Table 1. Chemical compositions of DSslag-CaO-MS adsorbents and raw DSslag determined by ICP-AES.

Sample	Composition (wt%)
	CaO	T–FeO	SiO2	Al2O3	MgO	TiO2	P2O5	MnO	Others
DSslag-CaO-MS(AA)	47.3	12.0	18.5	2.4	1.8	0.6	1.6	2.8	13.0
DSslag-CaO-MS(FA)	44.1	13.3	17.2	3.3	1.6	1.0	2.2	3.9	13.4
DSslag-CaO-MS(CA)	41.3	14.5	16.1	4.0	2.0	1.2	2.5	4.5	13.9
Raw DSslag	42.5	14.4	16.6	3.9	1.7	1.3	2.4	4.4	12.8

The N₂ adsorption-desorption isotherms and the corresponding BJH pore size distributions for the DSslag-CaO-MS slag samples are shown in Fig. 3, and the textural properties determined from N₂ adsorption isotherms are shown in Table 2. N₂ physisorption isotherms of type IV with type H2 loop were observed for all samples at partial pressure greater than 0.7 (P/P₀ > 0.7), indicating the presence of mesoporous structure. The presence of hysteresis loops between adsorption-desorption branches may explain the presence of relatively uniform channel-like pores.^26,27) The DSslag-CaO-MS(FA) showed relatively sharp uptakes at P/P₀ = 0.8–0.9, indicating that the adsorbent contained uniform and well-defined large mesopores. From the BJH plot in Fig. 3(b), DSslag-CaO-MS(FA) exhibited a pore size of 12.2 nm, which is similar to DSslag-CaO-MS(AA), with a higher pore volume (V_total = 0.39 cm³/g) compared to the sample synthesized with acetic acid (V_total = 0.29 cm³/g). On the other hand, DSslag-CaO-MS(CA) sample showed less porosity compared to the other sample with a pore volume of V_total = 0.15 cm³/g and with an average pore size of 9.44 nm. The apparent surface areas calculated from the BET model are 85.8, 80.4, and 59.5 m²g⁻¹ for DSslag-CaO-MS(FA), DSslag-CaO-MS(CA), and DSslag-CaO-MS(AA), respectively.

Fig. 3.

(a) N₂ adsorption-desorption isotherms and (b) corresponding BJH pore size distribution curves of DSslag-CaO-MS samples.

Table 2. Physisorption data obtained from N₂ adsorption-desorption measurement and CO₂ adsorption results.

Sample	SBETa (m2/g)	Vtotalb (cm3/g)	Dpeakc (nm)	CO2 adsorption
				CO2 uptake (g-CO2/g-adsorbent)	CO2 uptake (g-CO2/g-CaO)
DSslag-CaO-MS(AA)	59.5	0.29	12.2	0.21	0.37
DSslag-CaO-MS(FA)	85.8	0.39	12.2	0.20	0.35
DSslag-CaO-MS(CA)	80.4	0.15	9.44	0.16	0.32

^a Specific surface area calculated by BET method. ^b Total pore volume reported at P/P₀ = 0.99. ^c Peak pore diameter determined by BJH method.

The TEM measurement of CaO-MS adsorbents was carried out to observe the morphology of the three samples (Fig. 4). The dark solid grains depict the CaO while the low-contrast area depicts the SiO₂. It can be observed that the SiO₂ structure is mesoporous in all DSslag-CaO-MS samples. The SiO₂ phase appears to have the morphology of fumed silica, indicating that a well-defined hexagonal arrangement of pores similar to SBA-15 was not developed despite the addition of P123. This is likely because impurity metal ions impeded the formation of micelles and the growth of SBA-15 silica crystals.²¹⁾ The structure of mesoporous silica and CaO for DSslag-CaO-MS(AA) sample was well separated and defined. However, the mesoporous structure of SiO₂ and CaO particles was partly mixed for DSslag-CaO-MS(FA) sample. In contrast, the CaO particles and amorphous silica grains were poorly observed for DSslag-CaO-MS(CA) sample. Considering the XRD and N₂ isotherm, the DSslag-CaO-MS(CA) sample is less porous compared with other samples because of the formation of mixed oxide phases, such as merwinite (Ca₃Mg(SiO₄)₂). STEM measurement and mapping analysis were performed to confirm the elemental distrubutions in the DSslag-CaO-MS(AA). Figures 5(b)–5(i) depicts the elemental maps for Ca, Si, Mg, Fe, Al, O, Mn, and P, respectively. The elemental mapping revealed that the main phases of CaO and SiO₂ were well separated, as confirmed by TEM. The CaO phase was composed of Ca and O, with a trace of Mg, Al, and Mn in some areas. The crystalline phase of SiO₂ was made up of Si, O, Mg, Al, Mn, and Fe. In the SiO₂ phase, P was locally enriched. The SAED image in Fig. 5(j) shows that the interplanar spacings are 0.393 nm and 0.173 nm, confirming the formation of a crystalline CaCO₃ structure which is derived from CaO, while the SAED image for SiO₂ particle region (Fig. 5(k)) shows electron diffraction with weak periodicity, indicating the amorphous nature of SiO₂.

Fig. 4.

TEM images of (a) DSslag-CaO-MS(AA), (b) DSslag-CaO-MS(FA), and (c) DSslag-CaO-MS(CA) samples.

Fig. 5.

(a) STEM image, elemental maps of (b) Ca, (c) Si, (d) Mg, (e) Fe, (f) Al, (g) O, (h) Mn, (i) P and SAED patterns for (j) CaCO₃ particle region and (k) SiO₂ particle region of DSslag-CaO-MS(AA) sample.

All organic acids employed are polar protic solvents that are capable of releasing H⁺ and dissolving DSslag in water. Dielectric constant (k) is one of the good indicators to determine the polarity of the solvent. The DSslag-CaO-MS(AA) showed a well-separation of CaO and SiO₂ particles. This may be because acetic acid has a lower dielectric constant (k = 6.2 at 293 K) than formic acid and citric acid, which have dielectric constant values of k = 51.1 (at 298 K) and k = 35.5–58.5, respectively. In an acetic acid medium, acetate anion binds with Ca²⁺ ions to form calcium acetate (Ca(C₂H₃O₂)₂) (for the formation of calcium acetate in the sample before calcination at 873 K, see Fig. S1), thereby permitting Si⁴⁺ to interact with P123 micelles to form a mesoporous SiO₂ phase. The remaining Ca(C₂H₃O₂)₂ will transform into crystalline CaO during the evaporation and calcination steps. However, formic acid and citric acid are more polar and therefore more soluble in water, allowing the dissolved Ca²⁺ and Si⁴⁺ ions to mix and accordingly result in poorly-separated CaO and SiO₂ phases. These results demonstrated that acetic acid is the most suitable dissolution agent for synthesizing DSslag-CaO-MS sample with well-separated CaO and SiO₂ particles.

3.2. CO₂ Capture Performance

The CO₂ adsorption capacity of the sorbents was evaluated using TG measurements at 973 K for 150 min adsorption process under a flow of simulated gas (10% CO₂ balanced with N₂) and another 60 min at 1023 K for desorption with 100% N₂ gas. According to Fig. 6, DSslag-CaO-MS(AA) and DSslag-CaO-MS(FA) exhibited initial CO₂ adsorption of around 21 and 20 wt%, respectively, whereas DSslag-CaO-MS(CA) exhibited a 16 wt% CO₂ adsorption capacity. The high CO₂ adsorption capacities for the former two samples are due to the formation of the crystalline CaO phase, which serves as CO₂ adsorption site during the CO₂ uptake cycles. Despite having almost similar CO₂ uptake as DSslag-CaO-MS(FA), the adsorption rate of DSslag-CaO-MS(AA) was slower. It is well-known that the initial adsorption process is controlled by carbonation kinetics on the surface of CaO particles, and the latter stage is governed by the diffusion of CO₂.²⁸⁾ The slower adsorption rate of DSslag-CaO-MS(AA) is probably due to the lower porosity and surface area as confirmed by the N₂ adsorption measurements, which may hinder the diffusion of CO₂ molecules at the solid-gas interface. On the other hand, the CO₂ uptake of DSslag-CaO-MS(CA) was the lowest among the samples due to a lower crystallinity of CaCO₃ as confirmed by XRD and a lower content of CaO as shown in Table 1, because the CO₂ uptake generally increases as the crystalline CaCO₃/CaO content of the adsorbent increases.

Fig. 6.

CO₂ adsorption-desorption tests for 10 repeated cycles for DSslag-CaO-MS adsorbents synthesized using various acids from desiliconization slag. Adsorption: 10% CO₂/N₂ at 973 K for 150 min, desorption: 100% N₂ at 1023 K for 60 min.

During the repeated cycles, DSslag-CaO-MS(AA) surprisingly exhibited better stability than the other adsorbents, retaining 95% of its initial CO₂ adsorption. Figure 7 shows the XRD crystalline phase of the samples after 3 repeated cycles of the CO₂ uptake. All DSslag-CaO-MS samples showed crystalline phases of CaO and Ca₃Mg(SiO₄)₂. DSslag-CaO-MS(AA) and DSslag-CaO-MS(CA) showed more intense peaks for CaO crystalline phase compared to DSslag-CaO-MS(FA) sample. In the DSlag-CaO-MS(AA) sample, CaO and SiO₂ particles are spatially well-separated, thereby suppressing the formation of Ca₃Mg(SiO₄)₂ and retaining a higher ratio of crystalline CaO. This explains why the sample synthesized with acetic acid had greater regenerative stability over the course of 10 CO₂ adsorption-desorption cycles. Despite the fact that DSslag-CaO-MS(CA) sample had the lowest CO₂ uptake, it remained stable from the third to tenth cycle in terms of regenerative stability. The CO₂ adsorption performance of DSslag-CaO-MS(FA), on the other hand, decreased continuously, preserving 85% of the original CO₂ adsorption after 10 repeated cycles. DSslag-CaO-MS(FA) exhibited the lowest intensity peak for CaO crystal after its use (Fig. 7), although it exhibited the highest intensity peak in its original form (Fig. 2). This is probably due to the high-temperature sintering of the adsorbent because of a tight contact between CaO and SiO₂ particles, leading to the loss of porosity and surface area.^29,30,31) The mixture phase of CaO and mesoporous silica in DSslag-CaO-MS(FA) and DSslag-CaO-MS(CA) samples also contributed to the interaction between these two phases to form calcium silicate phases such as Ca₃Mg(SiO₄)₂, which are inactive for CO₂ adsorption, resulting in a continuous decrease of CO₂ uptake.

Fig. 7.

XRD patterns of DSslag-CaO-MS samples after 3 cycles of CO₂ adsorption-desorption.

In the previous studies, blast furnace slag (BFS),²¹⁾ converter slag²³⁾ and dephosphorization slag⁷⁾ were used as feedstocks to synthesize CaO-based adsorbents. In evaluating their regenerative ability, the CO₂ uptake during the cyclic activity was decreased due to the sintering through the formation of undesirable calcium silicate phases. When BFS was employed as the raw material,²¹⁾ the higher SiO₂ content in the adsorbent (approximately 37 wt%) led to sintering via the formation of a calcium silicate, thereby resulting in a lower CO₂ uptake in repeated CO₂ adsorption-desorption cycles (55% of the initial CO₂ uptake after 10 cycles at 973 K). A pure CaO sample showed a continuous decrease in CO₂ uptake over the 10 cycles, keeping around 80% of the initial CO₂ uptake. This is due to the agglomeration of CaO particles, hindering the adsorption of CO₂.⁷⁾ The DSslag-CaO-MS(AA), on the other hand, could retain almost 95% of its initial CO₂ uptake even at 973 K, albeit possessing 18.5 wt% of SiO₂ content and other slag-derived impurity elements. Thus, we demonstrated that a more effective and durable adsorbent for CO₂ capture can be synthesized from DSslag by choosing a proper dissolution agent.

4. Conclusion

In this study, a CaO-mesoporous silica composite adsorbent with CO₂ adsorption capability was synthesized via a simple dissolution-hydrothermal process using desiliconization slag as the sole metal source and by using acetic acid (AA) as the dissolution agent. Crystalline structures and porosity of the DSslag-CaO-MS adsorbents, in addition to CO₂ capture performances, were significantly influenced by the acid used. The use of acetic acid facilitated the separation of CaO and mesoporous silica particles due to the lower solubility of calcium acetate in an aqueous solution. This resulted in superior CO₂ adsorption uptake and regenerative ability of the adsorbent compared with the samples synthesized with formic acid and citric acid. Due to substantial regenerative capability and stability, an accumulated volume of CO₂ can be recovered, which will contribute to an increase in net CO₂ capture efficiency and will aid in reducing CO₂ emissions in an economically viable manner. This synthetic strategy would help the steel and iron industries address the current issue by offering a new recycling method of desiliconization slag and by reducing CO₂ emissions through CO₂ capture.

Supporting Information

XRD patterns of DSslag-CaO-MS(AA) before and after calcination at 873 K.

This material is available on the Journal website at https://doi.org/10.2355/isijinternational.ISIJINT-2022-435.

Acknowledgements

This study is supported by the Grant-in-Aid for Scientific Research(C) (KAKENHI) from Japan Society for the Promotion of Science (JSPS) (no. 21K05147), and the ISIJ Research Promotion Grant (Tekkou Kenkyu Shinko Josei) from the Iron and Steel Institute of Japan. Z. H. H. wishes to thank the NSK Scholarship Foundation for funding her studies in Japan, as well as the Malaysian Research University Network (MRUN) (grant no. 304/PJKIMIA/656501/K145) of the Malaysian Ministry of Higher Education. Y. K. sincerely acknowledges financial support from JST, PRESTO (no. JPMJPR19T3), Japan.

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