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. 2021 Oct 22;6(43):28804–28812. doi: 10.1021/acsomega.1c03572

Simultaneous Removal of SO2 and NOx Using Steel Slag Slurry Combined with Ozone Oxidation

Xiaolong Liu †,*, Yang Zou †, Ran Geng †,§, Tingyu Zhu †,‡,*, Bin Li §
PMCID: PMC8567348  PMID: 34746573

Abstract

graphic file with name ao1c03572_0013.jpg

In this work, steel slag slurry was used in combination with O3 oxidation for the simultaneous removal of SO2 and NOx in a laboratory-scale wet flue gas desulfurization process. The effects of the oxidation temperature, steel slag concentration, initial SO2 concentration, and pH value on the desulfurization and denitrification efficiencies were studied. The results showed that the highest NOx removal efficiency occurred at an oxidation temperature of 90 °C. With an increase of the oxidation temperature above 90 °C, the denitrification efficiency decreased due to the decomposition of N2O5. The effect of the SO2 concentration on denitrification was complicated. When the concentration of SO2 was 500 ppm, generation of SO32– promoted the absorption of NO2. However, higher SO2 concentrations strengthened the competitive absorption of SO2 and NOx. In the pH range of 8.5–4.5, the denitrification efficiency was maintained at about 96%. The component analyses of the aqueous solution and the solid residue were conducted to investigate the compositions of the absorption products. The results showed that NO3– and SO42– were the major anions in the aqueous solution. The nitrogen balance was analyzed to be 95.8%, clearly illustrating the migration and transformation path of nitrogen. In the solid residue, most alkaline substances were consumed, and the final products were mainly CaSO4 and FeO. Accordingly, the reaction mechanism of simultaneous desulfurization and denitrification using steel slag combined with ozone oxidation was proposed.

1. Introduction

According to China Statistical Yearbook on Environment 2018, the industrial emissions of SO2 and NOx were 15.57 million tons and 11.81 million tons, respectively, accounting for a great proportion of the national total emissions. Many efforts have been devoted to the development of desulfurization and denitrification technologies.1−3 At present, the wet flue gas desulfurization (WFGD) method has been widely used for SO2 removal due to its advantages of high efficiency and technical maturity.4 The denitrification technologies mainly include selective catalytic reduction (SCR)5−8 and selective non-catalytic reduction (SNCR)9−11 methods, converting NOx into N2 by using NH3 or other reducing agents. However, these purifications methods have strict requirements on the flue gas temperature, which is usually inconsistent with the industrial flue gas. Recently, the oxidation–absorption denitrification method has been developed, and it can be easily combined with the WFGD facility. In the oxidation process, NO is oxidized into species with higher nitrogen valence states such as NO2 and N2O5,12 which are more soluble than NO in water. Then, SO2 and NOx can be simultaneously removed in the absorption device.3,13

Numerous oxidants have been investigated for NO oxidation, such as NaClO2,14−17 NaClO,18,19 ClO2,20 and so forth. However, the environment-unfriendly Cl element is introduced into the aqueous system, showing great harm to the metallic pipe and scrubber. H2O2 is also employed as an oxidant, whereas the ultraviolet light or some other chemical agents are commonly needed for radical generation, limiting its industrial applications.21,22

In comparison to other oxidants, ozone shows apparent advantages of high-oxidation efficiency, high selectivity, no secondary pollution, and application convenience. With the continuous maturity of commercial ozone generators, O3 has been widely used in practical oxidation denitrification applications.23−30

Besides, various alkaline compounds have been investigated for simultaneous desulfurization and denitrification, such as Ca(OH)2,31−34 Mg(OH)2,35 NaHCO3,36 NH3,37,38 and so forth. The emission amounts of SO2 and NOx in the practical flue gas are very high and abundant absorbents are used. Therefore, it is meaningful to explore a method to reduce the absorbent cost.

Metallurgical slag is the solid waste generated from the metallurgical industry including steel slag, red mud, copper slag, and so forth. These metallurgical slags commonly contain the alkaline components such as CaO, MgO, and other species with high contents.3,39 It is applicable to use the slurry of metallurgical slag as absorbent for desulfurization and denitrification, realizing the objective of “waste control by waste”. Sun et al.40 used pyrolusite slurry as an absorbent combined with O3 oxidation for simultaneous desulfurization and denitrification and found that MnO2 in the slurry could promote the oxidation of SO2 and NOx into MnSO4 and Mn(NO3)2, respectively. Li et al.3 used red mud slurry as an absorbent combined with O3 oxidation and found that alkaline components in red mud play important roles in the desulfurization and denitrification process.

Steel slag is the byproduct generated from the steel production process with a much higher production amount than other metallurgical slags. In China in 2018, 120 million tons of steel slag was produced, whereas its utilization rate was only 22%.41 It contains a large number of alkaline components, such as CaO and MgO,42 and it has been used as a desulfurization agent in previous reports.43,44 It was found that the liquid–gas ratio, solid–liquid ratio, and inlet SO2 concentration showed obvious influences on the desulfurization performance. Considering the ultralow emission standard published for the iron and steel industry in China, it will show great appropriacy and conveniency by using the alkaline components of steel slag for the simultaneous removal of SO2 and NOx from the iron ore sintering/pelletizing flue gas.

It is noteworthy that simultaneous removal of SO2 and NOx using steel slag combined with ozone oxidation was rarely reported.39 In a few studies, NO2 was selected as the only oxidation product when the O3/NO molar ratio was below 1.0. Considering the higher solubility and reactivity of N2O5 than that of NO2, it is meaningful to further investigate the denitrification performance with N2O5 as the final oxidation product in the combination of steel slag with ozone oxidation. Besides, the effect of the alkaline components in the steel slag on the purification efficiencies and the reaction mechanism are still unclear.

Hence, it is of great interest to investigate the simultaneous desulfurization and denitrification using steel slag slurry combined with O3 oxidation. This method can achieve the purification of flue gas and the reuse of steel slag. Herein, the factors affecting the removal efficiency of SO2 and NOx were systematically studied, and the reaction mechanism was proposed.

2. Results and Discussion

2.1. Chemical Composition of Steel Slag

Four kinds of steel slag samples were collected from different steelmaking converters, and their compositions were obtained using an X-ray fluorescence (XRF) analyzer. As shown in Figure 1, the highest component content is CaO within the range of 35–40%. It is reasonable to use the steel slag for SO2 and NOx removal. The contents of the components decreased in the sequence of CaO, FeOx, SiO2, and MgO. In addition, the samples also contained Al2O3, P2O5, MnO, TiO2, and other substances. The specific values of each component are demonstrated in Table S1. It could be seen that sample 3 had the highest (CaO + MgO) content with the value of 46%, which was responsible for SO2 and NOx removal as useful components.

Figure 1.

Figure 1

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Chemical composition proportions of different steel slag samples.

In order to further investigate the specific structures of the steel slag samples, X-ray diffraction (XRD) patterns were collected for the four samples. As shown in Figure 2, the main compositions of sample 1 were Ca(Mg)–Fe-based oxides and Fe0.925O. It is noteworthy that Ca14.92(PO4)2.35(SiO4)5.65 and Fe0.925O were observed in the samples 2–4, showing that most calcium oxides existed as a phosphatic calcium silicate phase. The XRD results were consistent with the conclusion that CaO and FeOx contents were high in the XRF analysis.

Figure 2.

Figure 2

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XRD patterns of (a) sample 1, (b) sample 2, (c) sample 3, and (d) sample 4.

2.2. Factors Affecting Absorption Performance of Steel Slag

2.2.1. Absorption Performance of Different Steel Slags

In order to test the absorption performance of different steel slags as additives to the absorbing solution, the oxidation denitrification experiments were carried out with the O3/NO molar ratio of 1:1. The results in Figure 3 revealed that sample 3 contributed the highest NOx removal efficiency (up to 42%). Combined with the analysis of XRD and XRF results, it might be due to the highest total content of CaO (41.1%) and MgO (4.6%) of sample 3. It has been reported that CaO and MgO are responsible for NO2 removal.13 Therefore, sample 3 was selected in the following research.

Figure 3.

Figure 3

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NOx removal efficiencies of different steel slags ([NO], 200 ppm; [SO2], 500 ppm; [O3], 200 ppm; [O2], 16%; oxidation time, 1.2 s; oxidation temperature, 130 °C; the concentration of steel slag, 20 g/L; slurry velocity, 270 mL/min; gas–liquid contact time, 10 s).

2.2.2. Influence of Oxidation Temperature and O3/NO Molar Ratio on Denitrification

In the ozone oxidation–absorption method, the denitrification efficiency highly relies on the oxidation product distributions (the solubility of NOx in water: NO, 0.032 g/dm3; NO2, 213 g/dm3; N2O5, 500 g/dm3).13 The oxidation temperature and the molar ratio of O3/NO have a crucial influence on the oxidation product compositions.45 Hence, it is of importance to investigate the influence of oxidation temperature and the molar ratio of O3/NO on the denitrification efficiency.

As shown in Figure 4, when the molar ratio of O3/NO was below 1.0, the oxidation temperature showed little influence on the denitrification efficiency. The reason is that the oxidation of NO gives NO2 as the only product with basically chemical equivalent yield under these conditions. NO2 is stable at high temperatures, and the oxidation temperature has little influence on NOx removal. However, when the molar ratio of O3/NO was above 1.0, the removal efficiency of NOx first increased with the improvement of the oxidation temperature from 70 to 90 °C and then decreased from 90 to 150 °C. N2O5 is generated with the O3/NO molar ratio above 1.0. When the temperature is ≤90 °C, increase of the temperature leads to a faster reaction rate and higher N2O5 yield. However, N2O5 is unstable and easily decomposes at high temperatures, leading to the decrease of denitrification efficiency. Sun et al.27 found that the best temperature range for the formation of N2O5 is 80–100 °C. In our previous report, it has been proved that the oxidation temperature at 90 °C resulted in the highest N2O5 yield,45 which is considered to be the main reason for the highest denitrification efficiency at 90 °C. However, the temperatures of the practical flue gases are commonly above 110 °C before the wet scrubbing device to avoid the acid corrosion of the flue pipe. Hence, the oxidation temperature was set at 110 °C in the following research.

Figure 4.

Figure 4

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Effect of oxidation temperature and the O3/NO molar ratio on denitrification. ([NO], 200 ppm; [SO2], 500 ppm; [O2], 16%; oxidation time, 1.2 s; oxidation temperature, 70–150 °C; the concentration of steel slag, 20 g/L; slurry velocity, 270 mL/min; gas–liquid contact time, 10 s).

Besides, the effect of different solid–liquid ratios on the NOx removal efficiency was explored by adjusting the amount of steel slag in slurry (Figure S1). The result revealed that the steel slag concentration in the range of 5–30 g/L had little effect on the denitrification efficiency, but it could be observed that denitrification efficiency increased with the increase of the O3/NO molar ratio. In order to maintain the pH value of each experimental slurry, 20 g/L of steel slag slurry was used in the following studies.

2.2.3. Influence of pH on Desulfurization and Denitrification

The pH value reflects the H+ concentration in the slurry, and it has an obvious impact on the removal efficiencies of NOx and SO2. As shown in Figure 5, the initial pH value of the slurry was 9.1, and it gradually decreased to 3.6 over time. The removal efficiency of SO2 remained at 100% in the first 4.5 h with the pH value of 9.1–7.0, and then it gradually decreased. It was noteworthy that the desulfurization efficiency began to decrease sharply after 8.5 h mainly due to the low pH value and the acidity of the slurry. In the absorption of SO2, SO2 and H2O firstly reacted to form SO32– (eq 1) and HSO3– (eq 2), which were subsequently oxidized into SO42– (eqs 3 and 4). Besides, abundant FeOx components existed in the steel slag accounting for 25–35% (Figure 1). More Fe3+ cations were constantly released during the acidification of the absorption solution, and it has been reported that Fe3+/Fe2+ redox plays an important role in SO2 absorption process (eqs 5 and 6).3 SO2 was oxidized into SO42- by Fe3+ (eq 5), and Fe2+ was easily oxidized into Fe3+ in the O2-rich environment (eq 6), realizing the catalytic desulfurization. Finally, CaSO4 was accordingly generated from CaO in the steel slag (eq 7), which has been verified in the following XRD patterns.

2.2.3. 1
2.2.3. 2
2.2.3. 3
2.2.3. 4
2.2.3. 5
2.2.3. 6
2.2.3. 7
Figure 5.

Figure 5

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Desulfurization and denitrification efficiency and pH value of slurry over time ([NO], 200 ppm; [SO2], 500 ppm; [O3], 360 ppm; [O2], 16%; oxidation time, 1.2 s; oxidation temperature, 110 °C; the concentration of steel slag, 20 g/L; slurry velocity, 270 mL/min; gas–liquid contact time, 10 s).

In the absorption of NOx, the reactivity of N2O5 is much higher than that of NO2. Absorption of N2O5 by the basic solution gave NO3– as the product (eq 8). Meantime, absorption of NO2 by the basic solution gave NO3– and NO2– with poorer efficiency (eq 9). Noteworthy, the NOx removal efficiency increased obviously from 90 to 95% in the first 3 h. The main reason is that the soluble SO32– and HSO3– could easily react with NO2 to form SO42– and NO2– (eqs 10 and 11), promoting the absorption of NO2. While the pH value was between 8.5 and 4.5, the denitrification efficiency was consistently about 96%. As time extended, the pH value decreased below 4.5, and the denitrification efficiency showed an obviously decreasing tendency. It was mainly due to the fact that most alkaline oxides in the steel slag (such as CaO and MgO) have reacted, resulting in an obvious decrease in the alkalinity of the slurry.

2.2.3. 8
2.2.3. 9
2.2.3. 10
2.2.3. 11

2.2.4. Influence of SO2 Concentration on Desulfurization and Denitrification

The influence of SO2 concentration on the desulfurization and denitrification was investigated within the range of 0–2000 ppm. As shown in Figure 6a, the removal efficiency of SO2 was basically 100% when SO2 concentration is 500 ppm. Increase of SO2 concentration led to the decrease of SO2 removal efficiency. When the initial concentration of SO2 increased to 2000 ppm, the desulfurization efficiency decreased to about 89%. This is because excessive SO2 dissolves in water, leading to the generation of abundant H2SO3 and the decrease of pH value. After 60 min, the desulfurization efficiency declined to about 65%, which is also because too much H+ inhibits the absorption process.

Figure 6.

Figure 6

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Influence of SO2 concentrations on (a) SO2 removal efficiency with time extension, (b) NOx removal efficiency with time extension ([NO], 200 ppm; [SO2], 0–2000 ppm; [O3], 360 ppm; [O2], 16%; oxidation time, 1.2 s; oxidation temperature, 110 °C; the concentration of steel slag, 20 g/L; slurry velocity, 270 mL/min; gas–liquid contact time, 10 s).

Figure 6b revealed that the effect of SO2 concentration on denitrification was complicated. In the first 40 min, the experiment without SO2 gave the highest denitrification efficiency, and the presence of SO2 led to the decrease of the denitrification efficiency, illustrating that the competition absorption existed between SO2 and NOx. However, over time, the experiment with 500 ppm SO2 gave the highest denitrification efficiency, which gradually increased due to the reaction of SO32– and HSO3– with NO2. Within the time range of 40–120 min, the experiment with 500 ppm SO2 resulted in higher denitrification efficiency than those with 1000 and 2000 ppm SO2, mainly due to the competitive absorption between SO2 and NOx.

2.2.5. Liquid- and Solid-Phase Analysis before and after Reaction

In order to investigate the compositions of the absorption products, the component analyses of the aqueous solution and the solid residue were conducted. An ion chromatography (IC) method was employed for anion detection in the aqueous solution. As shown in Figure 7 and Table S3, NO3–, NO2–, and SO42– were analyzed, whereas SO32– was basically not observed, possibly because it was too easily oxidized in the experimental and analytical processes. The concentration of NO2– was much lower than those of NO3– and SO42–. It can be seen that the concentration of SO42– increased in the first 250 min due to the absorption of SO2. Then, the concentration of SO42– was basically stabilized due to the formation of CaSO4 and the dissolution balance. The concentration of NO3– increased with time due to the formation of nitrate after N2O5 absorption. The concentration of NO3– was far higher than that of NO2– possibly due to two reasons: (1) N2O5 is formed as the major oxidation product, which reacts to form NO3– in the absorption process. (2) NO2– is oxidized by O3 or O2 in the absorption or waiting for detection. Besides, the nitrogen balance calculation was performed to investigate the nitrogen distributions. The total outlet nitrogen (total N) content was the sum of NO3–, NO2–, and non-absorbed NOx. In the experiments, the non-absorbed NOx mainly existed in the form of NO2. When the pH was 3.5, the nitrogen balance rate was 95.8%, illustrating a clear and accurate nitrogen migration and transformation path.

Figure 7.

Figure 7

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Anion concentration over time.

In order to analyze the mechanism of simultaneous desulfurization and denitrification using steel slag combined with O3 oxidation, XRD, XRF, and scanning electron microscopy (SEM) tests were performed for the original steel slag, the steel slag after a period of exposure in the experimental apparatus, and the solid residue of steel slag after the end of the experiment. As shown in Figure 8, it was found that the main components in the original steel slag were CaO, FeOx, SiO2, Al2O3, MgO, and so forth. After 90 min of absorption (pH = 8.0), the XRD patterns were similar to the original sample. In the solid residue of reacted steel slag, the main product was bassanite (CaSO4·0.5H2O) and Fe0.925O, revealing that the most alkaline substances were consumed, while the recycling of Fe species will be considered in the future study.

Figure 8.

Figure 8

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XRD patterns of (a) original steel slag (pH = 9.1), (b) steel slag in the absorption process (pH = 8.0, 90 min), and (c) steel slag after absorption (pH = 4.5, 450 min).

Figure 9a–c shows the SEM images of steel slag. It can be seen that the microstructure of steel slag has significantly changed after desulfurization and denitrification. The original steel slag showed a smooth surface structure (Figure 9a). With the progress of the reaction, the steel slag was slowly corroded during the desulfurization and denitrification process, and the generated CaSO4 spattered on the surface as particles (Figure 9b). Finally, many fine particles appeared on the reacted steel slag with a porous structure (Figure 9c).

Figure 9.

Figure 9

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8K magnification SEM images of (a) original steel slag (pH = 9.1), (b) steel slag in the absorption process (pH = 8.0, 90 min), and (c) steel slag after absorption (pH = 4.5, 450 min).

Based on the results mentioned above, the reaction mechanism of simultaneous removal of SO2 and NOx using steel slag combined with O3 oxidation was proposed. As illustrated in Figure 10, in the gas phase, NO is oxidized into NO2 and N2O5 with higher solubility, which is convenient for slurry absorption. NO2– and NO3– are formed after NO2 absorption. Part of NO2– is oxidized to NO3– by O3 and dissolved in the slurry. N2O5 is absorbed by dissolved species of steel slag to generate stable NO3–. Absorption of SO2 generates SO32– and HSO32– species, which were subsequently oxidized into SO42– by O2 or O3. In addition, SO32– and HSO32– also react with dissolved NO2 to form SO42– and NO2–, achieving the synergistic absorption. In the solid phase, the alkaline substances were consumed during the absorption, generating CaSO4 and Ca(NO3)2 as the major products.

Figure 10.

Figure 10

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Reaction mechanism of simultaneous desulfurization and denitrification using steel slag.

3. Conclusions

In this study, the effects of different factors on the removal of SO2 and NOx with steel slag combined with O3 oxidation were investigated, including the oxidation temperature, the concentration of steel slag, initial concentration of SO2, and pH value. The oxidation temperature at 90 °C gave the highest removal efficiency of NOx. When the oxidation temperature was further increased, high temperature led to the decomposition of N2O5, and the denitrification efficiency decreased. When the concentration of SO2 was 500 ppm, generation of SO32– promoted the absorption of NO2. However, further increase of the SO2 concentration would strengthen the competitive absorption of SO2 and NOx. The denitrification efficiency was maintained at about 96% in the range of pH 8.5–4.5, whereas further decrease of pH value would induce the decrease of the denitrification efficiency. Besides, the compositions of the absorption products were systematically studied. In the aqueous solution, NO3– and SO42– were the major anions. In the solid residue, CaSO4 and FeO were obtained as main components. It showed that most alkaline substances were consumed, whereas FeO still existed, which might be recycled in the future study.

4. Experimental Section

4.1. Experimental System

The schematic diagram of the experimental device for ozone oxidation combined with steel slag is shown in Figure 11. The simulated flue gas mixture is composed of NO [1%, balanced with N2 (99.999%)], SO2 [2%, balanced with N2 (99.999%)], and O2 (99.999%). In the industrial flue gas, CO2 commonly exists with percentage levels. However, SO2 and N2O5/NO2 commonly show far higher reactivity than CO2 in the absorption process due to their acidity and electronic properties. Hence, the influence of CO2 was not studied in this work, and CO2 was not included in the simulated flue gas. All gases were purchased from Beijing Hua Yuan Gas Chemical Co., Ltd. The mass flow controller was purchased from Beijing Seven star Electronics Co., Ltd. to control the mixing of gases. The total flow rate of the gas mixture was 6 L/min. Ozone was generated from the Ozonia Lab2B generator with high purity oxygen (over 99.999%) based on the principle of high voltage discharge. The steel slag samples used in the work were from different steelmaking converters of HBIS GROUP CO., LTD.

Figure 11.

Figure 11

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Schematic diagram of the experimental apparatus: (1) high purity O2 cylinder; (2) high purity O2 cylinder; (3) N2–NO cylinder; (4) N2–SO2 cylinder; (5) high purity N2 cylinder; (6) mass flowmeter; (7) ozone generator; (8) gas pre-heating furnace; (9) oxidation reactor; (10) heat-collecting magnetic stirrer; (11) pH meter; (12) peristaltic pump; (13) spraying tower; (14) cooling device; and (15) infrared gas analyzer.

The simulated flue gas was first heated to the oxidation temperature (70–150 °C) by the gas pre-heating furnace and then mixed with ozone entering the oxidation reaction furnace. The oxidation residence time was set at 1.2 s according to general applications for the industrial flue gas. The steel slag slurry was stored in a 2 L three-necked flask and heated and stirred by a heat-collecting magnetic heating (DF-101S, Jiangsu Jinyi Instrument Technology Co., Ltd.). The steel slag slurry was injected into a self-made spraying tower (400 mm in height and 72 mm in diameter) through a spraying nozzle (1/4 internal thread, 1.0 mm aperture) by a peristaltic pump (BT100-2 J, Longer Precision Pump Co., Ltd.) at a flow rate of 270 mL/min. The simulated flue gas flowed from the bottom to the top of the spray tower to achieve the absorption of the flue gas by steel slag slurry. In the reaction vessel, the experiments were conducted under continuous flow conditions other than steady-state conditions. The pH value of the slurry and the concentrations of gas components (SO2, NOx, and O3) were consecutively recorded every 32 s to ensure the data accuracy.

The concentrations of SO2, NOx, and O3 in the simulated flue gas were detected using a Fourier transform infrared spectroscopy gas analyzer (Tensor II, Bruker Co., Ltd.). The concentrations of SO42–, NO2–, and NO3– in the aqueous solution were analyzed by an IC instrument (ICS-2100, Dionex Co., Ltd.). XRD patterns of the samples were recorded on a powder diffractometer (Rigaku D/Max-RA). XRF data were collected using an XRF analyzer (AXIOs, PANalytical B.V.). SEM images were performed on an S-4600electron microscope (Hitachi instruments Co., Ltd.). The pH value was recorded on a laboratory pH meter (FE20, Mettler Toledo Co., Ltd.).

4.2. Removal Efficiency

The removal efficiencies of SO2 and NOx were calculated by formulas (12) and (13) to illustrate the denitrification and desulfurization performance of steel slag. NOx in this article includes NO, NO2, and N2O5.

4.2. 12
4.2. 13

where, CinletSO2 and CinletNOx represent the concentration of SO2 and NOx before entering the spray tower, respectively. CoutletSO2 and CoutletNOx represent the concentration of SO2 and NOx discharged after entering the spray tower, respectively.

4.3. Nitrogen Balance Rate

The nitrogen balance rate was calculated by the following formula to illustrate the nitrogen migration and transformation path. NOx in this article includes NO, NO2, and N2O5.

4.3. 14

where MinletNOx and MoutletNOx represent the total molar amount of substance of NOx before and after entering the spray tower during a certain time, respectively. MliquidNO2– and MliquidNO3– represent the total molar amount of anion of NO2– and NO3– in the liquid phase of the spray tower during a certain time, respectively.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (51978644) and the National Key Research and Development Program of China (2018YFC0213400).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c03572.

  • Effect of steel slag concentration and molar ratio of O3/NO on denitrification; chemical compositions of steel slags; and anion concentrations in the aqueous solution over time (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao1c03572_si_001.pdf (92.8KB, pdf)

References

  1. Skalska K.; Miller J. S.; Ledakowicz S. Trends in NOx abatement: A review. Sci. Total Environ. 2010, 408, 3976–3989. 10.1016/j.scitotenv.2010.06.001. [DOI] [PubMed] [Google Scholar]
  2. Hao R.; Mao X.; Qian Z.; Zhao Y.; Wang L.; Yuan B.; Wang K.; Liu Z.; Qi M.; Crittenden J. Simultaneous removal of SO2 and NO using a novel method of ultraviolet irradiating Chlorite-Ammonia complex. Environ. Sci. Technol. 2019, 53, 9014–9023. 10.1021/acs.est.8b06950. [DOI] [PubMed] [Google Scholar]
  3. Li B.; Wu H.; Liu X.; Zhu T.; Liu F.; Zhao X. Simultaneous removal of SO2 and NO using a novel method with red mud as absorbent combined with O3 oxidation. J. Hazard. Mater. 2020, 392, 122270. 10.1016/j.jhazmat.2020.122270. [DOI] [PubMed] [Google Scholar]
  4. Wang D.; Lu Y.; Li Z.; Wang X.; Xu H. Integrated electrochemical-aerating oxidation in recovery system of seawater flue gas desulfurization. Chem. Eng. J. 2018, 338, 184–190. 10.1016/j.cej.2017.12.151. [DOI] [Google Scholar]
  5. Xiong J.; Li Y.; Lin Y.; Zhu T. Formation of sulfur trioxide during the SCR of NO with NH3 over a V2O5/TiO2 catalyst. RSC Adv. 2019, 9, 38952–38961. 10.1039/c9ra08191g. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Qi G.; Yang R. T. Performance and kinetics study for low-temperature SCR of NO with NH3 over MnOx-CeO2 catalyst. J. Catal. 2003, 217, 434–441. 10.1016/s0021-9517(03)00081-2. [DOI] [Google Scholar]
  7. Qi G.; Yang R. T.; Chang R. MnOx-CeO2 mixed oxides prepared by co-precipitation for selective catalytic reduction of NO with NH3 at low temperatures. Appl. Catal., B 2004, 51, 93–106. 10.1016/j.apcatb.2004.01.023. [DOI] [Google Scholar]
  8. Liu X.; Zhao Z.; Ning R.; Qin Y.; Zhu T.; Liu F. Ce-doped V2O5-WO3/TiO2 with low vanadium loadings as SCR catalysts and the resistance of H2O and SO2. Catal. Lett. 2020, 150, 375–383. 10.1007/s10562-019-03077-y. [DOI] [Google Scholar]
  9. Bae S. W.; Roh S. A.; Kim S. D. NO removal by reducing agents and additives in the selective non-catalytic reduction (SNCR) process. Chemosphere 2006, 65, 170–175. 10.1016/j.chemosphere.2006.02.040. [DOI] [PubMed] [Google Scholar]
  10. Chen H.; Chen D. Z.; Fan S.; Hong L.; Wang D. SNCR De-NOx within a moderate temperature range using urea-spiked hydrazine hydrate as reductant. Chemosphere 2016, 161, 208–218. 10.1016/j.chemosphere.2016.07.010. [DOI] [PubMed] [Google Scholar]
  11. Fu S.-L.; Song Q.; Yao Q. Mechanism study on the adsorption and reactions of NH3, NO, and O2 on the CaO surface in the SNCR de-NOx process. Chem. Eng. J. 2016, 285, 137–143. 10.1016/j.cej.2015.09.116. [DOI] [Google Scholar]
  12. Skalska K.; Miller J. S.; Ledakowicz S. A. Kinetics of nitric oxide oxidation. Chemurg. Pap. 2010, 64, 269–272. 10.2478/s11696-009-0105-8. [DOI] [Google Scholar]
  13. Zou Y.; Liu X.; Zhu T.; Tian M.; Cai M.; Zhao Z.; Wu H. Simultaneous removal of NOx and SO2 by MgO combined with O3 oxidation: The influencing factors and O3 consumption distributions. ACS Omega 2019, 4, 21091–21099. 10.1021/acsomega.9b02502. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Chien T. W.; Chu H.; Hsueh H. T. Kinetic study on absorption of SO2 and NOx with acidic NaClO2 solutions using the spraying column. J. Environ. Eng. 2003, 129, 967–974. 10.1061/(asce)0733-9372(2003)129:11(967). [DOI] [Google Scholar]
  15. Zheng C.-H.; Xu C.-R.; Gao X.; Zhang Y. X.; Zhang J.; Luo Z. Y.; Cen K. F. Simultaneous absorption of NOx and SO2 in oxidant-enhanced limestone slurry. Environ. Prog. Sustainable Energy 2014, 33, 1171–1179. 10.1002/ep.11903. [DOI] [Google Scholar]
  16. Hao R.; Luo Y.; Qian Z.; Ma Z.; Ding Y.; Gong Y.; Wang Z.; Zhao Y. Simultaneous removal of SO2, NO and Hg0 using an enhanced gas phase UV-AOP method. Sci. Total Environ. 2020, 734, 139266. 10.1016/j.scitotenv.2020.139266. [DOI] [PubMed] [Google Scholar]
  17. Hao R.; Mao X.; Wang Z.; Zhao Y.; Wang T.; Sun Z.; Yuan B.; Li Y. A novel method of ultraviolet/NaClO2-NH4OH for NO removal: Mechanism and kinetics. J. Hazard. Mater. 2019, 368, 234–242. 10.1016/j.jhazmat.2019.01.042. [DOI] [PubMed] [Google Scholar]
  18. Li Y.; Zhong W.; Ju J.; Wang T.; Liu F. Experiment on simultaneous absorption of NO and SO2 from sintering flue gas by oxidizing agents of KMnO4/NaClO. Int. J. Chem. React. Eng. 2014, 12, 539. 10.1515/ijcre-2014-0066. [DOI] [Google Scholar]
  19. Raghunath C. V.; Mondal M. K. Reactive absorption of NO and SO2 into aqueous NaClO in a counter-current spray column. Asia-Pac. J. Chem. Eng. 2016, 11, 88–97. 10.1002/apj.1946. [DOI] [Google Scholar]
  20. Jin D.; Deshwal B.; Park Y.; Lee H. Simultaneous removal of SO2 and NO by wet scrubbing using aqueous chlorine dioxide solution. J. Hazard. Mater. 2006, 135, 412–417. 10.1016/j.jhazmat.2005.12.001. [DOI] [PubMed] [Google Scholar]
  21. Liu Y.; Zhang J.; Sheng C.; Zhang Y.; Zhao L. Simultaneous removal of NO and SO2 from coal-fired flue gas by UV/H2O2 advanced oxidation process. Chem. Eng. J. 2010, 162, 1006–1011. 10.1016/j.cej.2010.07.009. [DOI] [Google Scholar]
  22. Qi Y.; Ge P.; Wang M.; Shan X.; Wu J. Experimental investigation and numerical simulation of simultaneous desulfurization and denitrification by H2O2 solution assisted with microwave and additive. Chem. Eng. J. 2019, 391, 123559. 10.1016/j.cej.2019.123559. [DOI] [Google Scholar]
  23. Mok Y. S.; Lee H.-J. Removal of sulfur dioxide and nitrogen oxides by using ozone injection and absorption-reduction technique. Fuel Process. Technol. 2006, 87, 591–597. 10.1016/j.fuproc.2005.10.007. [DOI] [Google Scholar]
  24. Wang Z.; Zhou J.; Zhu Y.; Wen Z.; Liu J.; Cen K. Simultaneous removal of NOx, SO2 and Hg in nitrogen flow in a narrow reactor by ozone injection: Experimental results. Fuel Process. Technol. 2007, 88, 817–823. 10.1016/j.fuproc.2007.04.001. [DOI] [Google Scholar]
  25. Skalska K.; Miller J. S.; Ledakowicz S. Kinetic model of NOx ozonation and its experimental verification. Chem. Eng. Sci. 2011, 66, 3386–3391. 10.1016/j.ces.2011.01.028. [DOI] [Google Scholar]
  26. Skalska K.; Miller J. S.; Ledakowicz S. Intensification of NOx absorption process by means of ozone injection into exhaust gas stream. Chem. Eng. Process. 2012, 61, 69–74. 10.1016/j.cep.2012.06.007. [DOI] [Google Scholar]
  27. Sun C.; Zhao N.; Zhuang Z.; Wang H.; Liu Y.; Weng X.; Wu Z. Mechanisms and reaction pathways for simultaneous oxidation of NOx and SO2 by ozone determined by in situ IR measurements. J. Hazard. Mater. 2014, 274, 376–383. 10.1016/j.jhazmat.2014.04.027. [DOI] [PubMed] [Google Scholar]
  28. Sun C.; Zhao N.; Wang H.; Wu Z. Simultaneous absorption of NOx and SO2 using magnesia slurry combined with ozone oxidation. Energy Fuels 2015, 29, 3276–3283. 10.1021/acs.energyfuels.5b00229. [DOI] [Google Scholar]
  29. Ma Q.; Wang Z.; Lin F.; Kuang M.; Whiddon R.; He Y.; Liu J. Characteristics of O3 oxidation for simultaneous desulfurization and denitration with Limestone-Gypsum wet scrubbing: Application in a carbon black drying kiln furnace. Energy Fuels 2016, 30, 2302–2308. 10.1021/acs.energyfuels.5b02717. [DOI] [Google Scholar]
  30. Shao J.; Ma Q.; Wang Z.; Tang H.; He Y.; Zhu Y.; Cen K. A superior liquid phase catalyst for enhanced absorption of NO2 together with SO2 after low temperature ozone oxidation for flue gas treatment. Fuel 2019, 247, 1–9. 10.1016/j.fuel.2019.02.120. [DOI] [Google Scholar]
  31. Fernández J.; Renedo M. J.; Pesquera A.; Irabien J. A. Effect of CaSO4 on the structure and use of Ca(OH)2/fly ash sorbents for SO2 removal. Powder Technol. 2001, 119, 201–205. 10.1016/s0032-5910(01)00263-7. [DOI] [Google Scholar]
  32. Renedo M. J.; Fernández J. Preparation, characterization, and calcium utilization of fly ash/Ca(OH)2 sorbents for dry desulfurization at low temperature. Ind. Eng. Chem. Res. 2002, 41, 2412–2417. 10.1021/ie010938g. [DOI] [Google Scholar]
  33. Lee K. T.; Bhatia S.; Mohamed A. R. Removal of sulfur dioxide using absorbent synthesized from coal fly ash: Role of oxygen and nitrogen oxide in the desulfurization reaction. Chem. Eng. Sci. 2005, 60, 3419–3423. 10.1016/j.ces.2005.01.002. [DOI] [Google Scholar]
  34. Fernández J.; Rico J. L.; García H.; Renedo M. J. Development of sorbents for SO2 capture prepared by hydration of fly ash and hydrated lime in seawater. Ind. Eng. Chem. Res. 2006, 45, 856–862. 10.1021/ie0508435. [DOI] [Google Scholar]
  35. Sada E.; Kumazawa H.; Sawada Y.; Kondo T. Simultaneous absorption of dilute NO and SO2 into aqueous slurries of Mg(OH)2 with added FeII-EDTA chelate. Ind. Eng. Chem. Process Des. Dev. 1982, 21, 771–774. 10.1021/i200019a037. [DOI] [Google Scholar]
  36. Ebrahimi S.; Picioreanu C.; Kleerebezem R.; Heijnen J. J.; van Loosdrecht M. C. M. Rate-based modelling of SO2 absorption into aqueous NaHCO3/Na2CO3 solutions accompanied by the desorption of CO2. Chem. Eng. Sci. 2003, 58, 3589–3600. 10.1016/s0009-2509(03)00231-8. [DOI] [Google Scholar]
  37. He B.; Zheng X.; Wen Y.; Tong H.; Chen M.; Chen C. Temperature impact on SO2 removal efficiency by ammonia gas scrubbing. Energy Convers. Manage. 2003, 44, 2175–2188. 10.1016/s0196-8904(02)00230-3. [DOI] [Google Scholar]
  38. Hao R.; Mao Y.; Mao X.; Wang Z.; Gong Y.; Zhang Z.; Zhao Y. Cooperative removal of SO2 and NO by using a method of UV-heat/H2O2 oxidation combined with NH4OH-(NH4)2SO3 dual-area absorption. Chem. Eng. J. 2019, 365, 282–290. 10.1016/j.cej.2019.02.059. [DOI] [Google Scholar]
  39. Meng Z.; Wang C.; Wang X.; Chen Y.; Li H. Simultaneous removal of SO2 and NOx from coal-fired flue gas using steel slag slurry. Energy Fuels 2018, 32, 2028–2036. 10.1021/acs.energyfuels.7b03385. [DOI] [Google Scholar]
  40. Sun W. Y.; Ding S. L.; Zeng S. S.; Su S. J.; Jiang W. J. Simultaneous absorption of NOx and SO2 from flue gas with pyrolusite slurry combined with gas-phase oxidation of NO using ozone. J. Hazard. Mater. 2011, 192, 124–130. 10.1016/j.jhazmat.2011.04.104. [DOI] [PubMed] [Google Scholar]
  41. Yi H.; Xu G.; Cheng H.; Wang J.; Wan Y.; Chen H. An overview of utilization of steel slag. Procedia Environ. Sci. 2012, 16, 791–801. 10.1016/j.proenv.2012.10.108. [DOI] [Google Scholar]
  42. Pang B.; Zhou Z.; Xu H. Utilization of carbonated and granulated steel slag aggregate in concrete. Constr. Build. Mater. 2015, 84, 454–467. 10.1016/j.conbuildmat.2015.03.008. [DOI] [Google Scholar]
  43. Zhu J. W.; Wang F.; Ren H. Y.; Zhang F.; Wang H. M. Experimental study on steel slag used as wet flue gas desulfurization absorbent. J. Environ. Eng. Technol. 2011, 89, 611–622. [Google Scholar]
  44. Zhou J. A.; Zhong S. J.; Dang J. X.; Li X. Experimental investigation of sintering flue gas desulfurization with steel slag using dry CFB method. Appl. Mech. Mater. 2011, 71–78, 2547–2550. 10.4028/www.scientific.net/amm.71-78.2547. [DOI] [Google Scholar]
  45. Ji R.; Wang J.; Xu W.; Liu X.; Zhu T.; Yan C.; Song J. Study on the key factors of NO oxidation using O3: The oxidation product composition and oxidation selectivity. Ind. Eng. Chem. Res. 2018, 57, 14440–14447. 10.1021/acs.iecr.8b03597. [DOI] [Google Scholar]

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