Simultaneous removal of SO2 and NO using a novel method with red mud as absorbent combined with O3 oxidation

Enhanced NOx absorption in flue gas by wet oxidation of red mud and phosphorus sludge

The environmental problem caused by industrial emissions of NOx has been studied in the past dacades. In this study, red mud coupling with phosphorus sludge were used to enhance the solution to absorb NOx from the flue gas. Firstly, red mud reacted with the binder silicic acid in the phosphorus sludge, destroying the emulsion structure of the phosphorus sludge. Then, the P4 in the phosphorus sludge is completely released, and the P4 reacted with O2 in the flue gas to produce O3 and O. NO and NO2 contained in the flue gas reacted with the active O and O3 to produce high-valent NOx, such as NO3, N2O5. At last, the mixed slurry of red mud and phosphorus sludge absorbed the high-valent NOx, resulting in the formation of Ca5(PO4)3F along with HNO3. Using phosphorus sludge to produce O3 in the reaction process can reduce the production cost of O3 and achieve waste utilization. Meanwhile, the interaction between red mud and phosphorus sludge can promote phosphorus sludge to produce O3 and remove F- from phosphorus sludge, as well as avoid the problem of secondary pollution. This study should be helpful for red mud and phosphorus sludge utilization and flue gas denitration.

Red mud with enhanced dealkalization performance by supercritical water technology for efficient SO2 capture

The total de-alkalization treatment of industrial solid waste red mud (RM) has been a worldwide challenge. Removing the insoluble structural alkali fraction from RM is the key to enhancing the sustainable utilization of RM resources. In this paper, supercritical water (SCW) and leaching agents were used for the first time to de-alkalize the Bayer RM and to remove sulfur dioxide (SO2) from flue gas with the de-alkalized RM slurry. The results showed that the optimum alkali removal and Fe leaching rates of RM-CaO-SW slurry were 97.90 ± 0.88% and 82.70 ± 0.95%, respectively. Results confirmed that the SCW technique accelerated the disruption of (Al-O) and (Si-O) bonds and the structural disintegration of aluminosilicate minerals, facilitating the conversion of insoluble structural alkalis to soluble chemical alkalis. The exchangeable Ca2+ displaced Na+ in the remaining insoluble base, producing soluble sodium salts or alkalis. CaO consumed SiO2, which was tightly bound to Fe2O3 in RM, and released Fe2O3, which promoted Fe leaching. RM-SCW showed the best desulfurization performance, which maintained 88.99 ± 0.0020% at 450 min, followed by RM-CaO-SW (450 min, 60.75 ± 6.00%) and RM (180 min, 88.52% ± 0.00068). The neutralization of alkaline components, the redox of metal oxides, and the liquid-phase catalytic oxidation of Fe contributed to the excellent desulfurization performance of the RM-SCW slurry. A promising approach shown in this study is beneficial to RM waste use, SO2 pollution control, and sustainable growth of the aluminum industry.

Direct degradation of Bisphenol A from aqueous solution by active red mud in aerobic environment

As industrial waste from aluminum production, red mud (RM) poses a severe threat to the local environment that needs to be appropriately utilized. The activation of iron oxide, which is abundant in RM, improves its effectiveness as a catalytic material for the degradation of organic pollutants. This study developed a novel activation approach by adding dithionite citrate bicarbonate (DCB) for Bisphenol A (BPA) degradation under aeration conditions. Electrochemical experiments and reactive oxygen species (ROSs) trapping experiments showed that DCB treatment enhanced the redox cycle of Fe(II)/Fe(III), which promoted free radical generation. The optimized condition for the RM activation was achieved at 21 mmol/L dithionites, 84 mmol/L citrates, and 34 mmol/L bicarbonate, and the degradation of BPA by activated RM reached 410 µg BPA per gram of RM. This work provided a feasible way to utilize RM resources as an efficient, low-cost catalyst for organic pollutants treatment.

Red mud recycling by Fe and Al recovery through the hydrometallurgy method: a collaborative strategy for aluminum and iron industry

In this work, a collaborative strategy for the aluminum and iron industry based on red mud recycling through the hydrometallurgy method was proposed. In this method, Fe³⁺ and Al³⁺ were firstly separated from the red mud by using H₂SO₄ as a leaching agent, which was by-produced from the sintering process of an iron and steel industry. Multiple influence factors on the leaching process were investigated, with the H₂SO₄ addition amount showing the strongest influence on the leaching rates of Al and Fe. The main components of the filter residue were CaSO₄, TiO₂, and SiO₂, which could be reused as additives in the building materials. Subsequently, the final Fe recovery product was obtained through the co-precipitation, Fe/Al separation, and Fe(OH)₃ calcination. In the final product, the content of Fe₂O₃ reached 82.87%, and the iron grade was 58.01%, meeting the requirement being raw materials for sinter production.

Study on the characteristics of zeolite-promoted thermal decomposition of H2O2 for efficient NO oxidation

The H₂O₂ evaporation rate directly affected the oxidation of NO by H₂O₂. Green zeolite and synthetic mordenite were selected to promote H₂O₂ thermal decomposition and NO oxidation. The effects of different zeolites, evaporation conditions, temperatures, and reactant concentrations on the NO oxidation ratio were explored. The promotion mechanism of zeolite on NO oxidation by H₂O₂ thermal decomposition was explained. The results show that the zeolite surface can significantly accelerate the H₂O₂ evaporation rate to obtain a high NO oxidation ratio. The hydrophilicity and rich pore structure of zeolite enable the rapid diffusion and evaporation of droplets on the zeolite surface. Compared with the green zeolite with the mesoporous structure, the synthetic mordenite with the hierarchical pore structure has a more obvious promotion effect on the NO oxidation by H₂O₂ thermal decomposition. The reason is that the synthetic mordenite contains micropores, resulting in a larger specific surface area, and the mesoporous structure is conducive to the mass transfer and diffusion of H₂O₂ on its surface. The product of NO oxidation is mainly NO₂, which proves that ·OH plays a major role in the process.

Advances in air pollution control for key industries in China during the 13th five-year plan

Industrial development is an essential foundation of the national economy, but the industry is also the largest source of air pollution, of which power plants, iron and steel, building materials, and other industries emit large amounts of pollutants. Therefore, the Chinese government has promulgated a series of stringent emission regulations, and it is against this backdrop that research into air pollution control technologies for key industrial sectors is in full swing. In particular, during the 13th Five-Year Plan, breakthroughs have been made in pollution control technology for key industrial sectors. A multi-pollutant treatment technology system of desulfurization, denitrification, and dust collection, which applies to key industries such as power plants, steel, and building materials, has been developed. High-performance materials for the treatment of different pollutants, such as denitrification catalysts and desulfurization absorbers, were developed. At the same time, multi-pollutant synergistic removal technologies for flue gas in various industries have also become a hot research topic, with important breakthroughs in the synergistic removal of NO_x, SO_x, and Hg. Due to the increasingly stringent emission standards and regulations in China, there is still a need to work on the development of multi-pollutant synergistic technologies and further research and development of synergistic abatement technologies for CO₂ to meet the requirements of ultra-low emissions in industrial sectors.

Multi-process and multi-pollutant control technology for ultra-low emissions in the iron and steel industry

The iron and steel industry is not only an important foundation of the national economy, but also the largest source of industrial air pollution. Due to the current status of emissions in the iron and steel industry, ultra-low pollutant emission control technology has been researched and developed. Liquid-phase proportion control technology has been developed for magnesian fluxed pellets, and a blast furnace smelting demonstration project has been established to use a high proportion of fluxed pellets (80%) for the first time in China to realize source emission reduction of SO₂ and NO_x. Based on the characteristics of high NO_x concentrations and the coexistence of multiple pollutants in coke oven flue gas, low-NO_x combustion coupled with multi-pollutant cooperative control technology with activated carbon was developed to achieve efficient removal of multiple pollutants and resource utilization of sulfur. Based on the characteristics of co-existing multiple pollutants in pellet flue gas, selective non-catalytic reduction (SNCR) coupled with ozone oxidation and spray drying adsorption (SDA) was developed, which significantly reduces the operating cost of the system. In the light of the high humidity and high alkalinity in flue gas, filter materials with high humidity resistance and corrosion resistance were manufactured, and an integrated pre-charged bag dust collector device was developed, which realized ultra-low emission of fine particles and reduced filtration resistance and energy consumption in the system. Through source emission reduction, process control and end-treatment technologies, five demonstration projects were built, providing a full set of technical solutions for ultra-low emissions of dust, SO₂, NO_x, SO₃, mercury and other pollutants, and offering technical support for the green development of the iron and steel industry.

Effect of CO2 on the Desulfurization of Sintering Flue Gas with Hydrated Lime

The effect of carbon dioxide (CO₂) on the desulfurization of sintering flue gas with hydrate (Ca(OH)₂) as an absorbent was investigated, and the formation of calcium carbonate (CaCO₃) and its effect on the desulfurization was discussed. The competitive relationship between carbon dioxide (CO₂) and sulfur dioxide (SO₂) with the deacidification agent in sintering flue gas is discussed thermodynamically, showing that sulfates are more likely to be generated under high oxygen potential conditions and that SO₂ reacts more preferentially than CO₂ under a thermodynamic standard state. The amount of produced CaCO₃ increases under the condition that the CO₂ concentration is absolutely dominant to SO₂ in the sintering flue gas atmosphere. The effect of temperature, humidity and CO₂ concentration on the desulfurization of Ca(OH)₂ are discussed experimentally. The increasing temperature is not conducive to desulfurization, and the humidity can promote desulfurization, while excessive humidity could inhibit desulfurization. The suitable relative humidity is 20%. In situ generated calcium carbonate has a certain desulfurization effect, but the desulfurization effect is not as good as Ca(OH)₂. However, a large proportion of CaCO₃ was produced in the desulfurization ash under the condition that CO₂ concentration was absolutely dominant to SO₂ in the sintering flue gas atmosphere.

Sodium ascorbate as additive in red mud slurry for simultaneous desulfurization and denitrification: Insights into the multiple influence factors and reaction mechanism

Based on the ultra-low emission demand of SO₂ and NO_x in flue gas, a new absorption method was proposed to improve the desulfurization and denitrification efficiency and reduce the amount of ozone by using sodium ascorbate as an additive in red mud slurry. Compared with pure red mud slurry, the red mud (RM) + sodium ascorbate (SA) slurry significantly improved the denitrification efficiency from 24% to 84% and the desulfurization efficiency to 98%. Meanwhile, the effects of RM, SA concentration, reaction time and O₃/NO molar ratio on desulfurization and denitrification efficiencies were studied. The results showed that the RM + SA composite slurry maintained high efficiencies of desulfurization and denitrification for 240 min under the optimized conditions. As an antioxidant, the introduction of SA inhibited the excessive oxidation of sulfite, and itself could easily react with NO₂ through the redox reaction, greatly promoting the absorption of NO₂. In addition, the reaction mechanism of the simultaneous removal of SO₂ and NO₂ by red mud and sodium ascorbic mixed slurry combined was proposed.

A review of comprehensive utilization of red mud

Red mud (RM) is a solid waste generated during the process of alumina production. RM has already posed a serious environmental threat with the development of the alumina refining industry. The comprehensive utilization of RM has attracted much attention due to its large-scale generation and harmful nature. This paper introduces the characteristics and state of RM and summarizes the relevant research on the comprehensive utilization of RM. The results show that comprehensive utilization of RM is mainly focused on the preparation of building materials, the extraction of valuable metals, catalyst synthesis and environmental protection. Besides, the article discusses the existing problems while utilizing RM. Prospects and suggestions for different utilization methods of RM are proposed.

Buffer effect of MgO on Na2SO3 to stabilize S(IV) for the enhancement in simultaneous absorption of NOx and SO2 from non-ferrous smelting gas

Oxidation-reduction-absorption based on sulfite is a promising process for simultaneous removal of NO_x and SO₂. However, excessive oxidation of sulfite and competitive absorption between NO_x and SO₂ limit its application. A matching strategy between antioxidants and alkaline agents has been proposed to solve these problems and enhance the absorption process. The comparison results of inhibitors showed that hydroquinone exhibited long-term high-efficiency inhibition of S(IV) (SO₃^2-/HSO₃^-) oxidation. The comparison of alkaline agents showed that the Na₂SO₃ solution with heterogeneous mixture of MgO and hydroquinone exhibited better absorption performance than that with other combinations. The absorption amounts of NO_x in 0.15 mol/L Na₂SO₃ 50 mL solution added 0.1% hydroquinone (HQ) with 0.09 mol/L MgO were 2.24 mmol, which improved 5 times than that without additives. In addition, studies on the influence of pH showed that the pH of MgO mixture could be stabilized at 9-10 for a long time, while the pH of Na₂CO₃ mixture decreased faster. Further studies suggested that the hydration of MgO resulted in the solution with MgO keeping high pH. This is also the main reason why the combination of MgO and hydroquinone is superior to the combination of Na₂CO₃ and hydroquinone in desulfurization and denitration performance.

Simultaneous Removal of SO2 and NO by O3 Oxidation Combined with Seawater as Absorbent

Aiming at NOx (NO 90%, NO2 10%) and SO2 in simulated vessel emissions, denitration and desulfurization were studied through ozone oxidation combined with seawater as absorbent. Specifically, the different influencing factors of denitration and desulfurization were analyzed. The results indicated that the oxidation efficiency of NO can reach over 90% when the molar ratio of O3/NO is 1.2. Ozone oxidation and seawater washing in the same unit can decrease the temperature of ozone oxidation of NO, avoid high temperature ozone decomposition, and enhance the oxidation efficiency of NO. When NO inlet initial concentration is lower than 800 ppm, the NOx removal efficiency can be improved by increasing NO inlet concentration, and when NO inlet initial concentration is greater than 800 ppm, increasing the concentration of NO would decrease the NOx removal efficiency. Increasing the inlet concentration of SO2 has minor effect on desulfurization, but slightly reduces the absorption efficiency of NOx due to the competition of SO2 and NOx in the absorption solution. Besides, final products (NO2−, NO3−, SO32−, and SO42−) were analyzed by the ion chromatography.

Cleaning Disposal of High-Iron Bauxite Residue Using Hydrothermal Hydrogen Reduction

The hydrothermal hydrogen reduction process for treating high-iron bauxite residue (red mud) was investigated, and the optimum conditions of alumina extraction as well as the enrichment of iron minerals were verified by experiments. Results show that the surface magnetization of Al-goethite under the function of hydrogen reduction accelerates its conversion to hematite and/or magnetite. This conversion releases the substituted Al in goethite as well as the undigested gibbsite/boehmite and further enriches the iron content in residue. After hydrothermal hydrogen reduction with H₂/Red mud ratio of 0.085 mol/20 g at 270°C for 60 min, the alumina relative recovery ratio reaches 95.40% and the grade of iron (total iron in the form of iron element) in the residue can be enriched to 55.85%. Further, co-processing of the obtained iron-rich residue in the steel industry can achieve a significant reduction of red mud discharge.

Removal of SO2 from flue gas using blast furnace dust as an adsorbent

To control the SO₂ emission and achieve the target of "waste controlled by waste", a novel desulfurization method with blast furnace dust slurry was proposed. The effects of reaction temperature, oxygen concentration, and solid-liquid ratio on SO₂ removal efficiency were investigated. The optimal conditions were reaction temperature of 35 ℃, oxygen concentration of 10 vol.%, and solid-liquid ratio of 0.5 g/300 mL. Under the optimal conditions, the desulfurization efficiency reached 100% for 4 h. Response surface methodology (RSM) results showed that oxygen concentration significantly influenced the SO₂ removal efficiency. Finally, the possible desulfurization mechanism of blast furnace dust was proposed based on the EDX, XRD, SEM-EDS, ICP, and IC. The blast furnace dust (main components are CaZn₈(SO₄)₂(OH)₁₂Cl₂·(H₂O)₉, Mn_6.927Si₆O₁₅·(OH)₈, ZnO, Fe₂O₃) reacted with H⁺ to form Zn²⁺, Fe³⁺, and Mn²⁺ which shows a key effect on the SO₂ liquid catalytic oxidation. This study provides a promising, feasible, and low-cost desulfurization technology by reusing blast furnace dust.

The boosting of microwave roasting technology on the desulfurization of phosphate rock

A green and-easy to operate method, the microwave technology, was developed to promote the desulfurization process of phosphate rock, systematically investigates the strengthening effect of microwave, and uses XRD, BET, SEM, XRF, ICP, and EDS to characterize the reactants. The results show that the main reason for the desulfurization efficiency is improved by microwave heating under microwave conditions, different thermal stress phosphate rock materials lead to the destruction of each microstructure, and a specific surface area increased 40.25% phosphate rock. In addition, after microwave irradiation, the pore size of the phosphate rock at 2-5 nm is significantly increased, and the number of mesopores is significantly increased, thereby increasing the desulfurization efficiency of the phosphate rock. By investigating the effects of temperature, oxygen content, flow rate, and solid-liquid ratio on desulfurization efficiency, the paper concludes that the optimal conditions for desulfurization of phosphate rock after microwave irradiation are C(SO₂) is 2500 mg·m^-3, temperature is 40 °C, φ(O₂) is 5%, solid-liquid ratio is 3.5 g:200 ml, and flue gas flow is 500 ml·min^-1.

A novel Fe-Co double-atom catalyst with high low-temperature activity and strong water-resistant for O3 decomposition: A theoretical exploration

Developing catalysts with high activity, durability, and water resistance for ozone decomposition is crucial to regulate the pollution of ozone in the troposphere, especially in indoor air. To overcome the shortcomings of metal oxide catalysts with respect to their durability and water resistance, Fe-Co double-atom catalyst (DAC) is proposed as a novel catalyst for ozone decomposition. Here, through a systematic study using density functional theory (DFT) calculations and microkinetic modeling, the adsorption and catalytic decomposition of O₃ on Fe-Co DAC have been examined based on adsorption configuration, orbital hybridization, and electron transfer. Based on Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms, the mechanisms of ozone decomposition on Fe-Co DAC were explored by analyzing reaction paths and energy variations. To confirm the water-resistant of Fe-Co DAC, competitive adsorption behavior between O₃ and dominant environmental gases was discussed through ab initio molecular dynamic (AIMD) simulation. The dominant reaction mechanism of ozone decomposition is L-H and the rate-determining step is the desorption of the first oxygen molecule from the surface of Fe-Co DAC which has an energy barrier of 0.78 eV. Due to this relatively low energy barrier and high turnover frequency (TOF), the optimal operation window of catalytic O₃ decomposition on Fe-Co DAC is <500 K suggesting that catalytic decomposition of O₃ on Fe-Co DAC can occur at room temperature. This theoretical study provides new insights for designing novel catalysts for ozone decomposition and fundamental guidance for subsequent experimental research.

Enhanced simultaneous absorption of NOx and SO2 in oxidation-reduction-absorption process with a compounded system based on Na2SO3

Oxidation of sulfite and competitive absorption existed in Na₂SO₃ solution for simultaneous removal of NO_x and SO₂, inhibited the long-term high-efficiency when used for practical applications. A matching strategy was developed to solve these problems. Antioxidants combination was used to retard the oxidation of antioxidant and enhance inhibition of S(IV) (tetravalent sulfur) oxidation. Hydroquinone (HQ) and sodium thiosulfate (ST) showed a positive synergistic effect on inhibition of S(IV) oxidation. When SO₂ concentration was 500 and 2000 ppmV, the addition of 0.1 wt.% HQ and 1 wt.% ST decreased the percentage of S(IV) oxidized by oxygen by over 30% and 40%, respectively. Alkali (Na₂CO₃) alleviated the competitive absorption between NO_x and SO₂. Moreover, Na₂CO₃ exhibited an enhancement effect on the absorption of NO_x and SO₂ when coupled with anti-oxidants. While the increase of oxygen pressure accelerated the oxidation of S(IV), the anti-oxidants can retard the oxidation. The measurement of pH suggested the removal efficiency of NO_x highly depended on SO₃²⁻ concentration rather than pH. The further investigation of the mechanism suggested the match effect was related to the interaction between ST and the intermediate product of HQ. The match strategy holds a potential for application of SO₃²⁻ to denitration.

Simultaneous Removal of SO2 and NO x Using Steel Slag Slurry Combined with Ozone Oxidation

In this work, steel slag slurry was used in combination with O3 oxidation for the simultaneous removal of SO2 and NO x 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 NO x 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 SO3 2- promoted the absorption of NO2. However, higher SO2 concentrations strengthened the competitive absorption of SO2 and NO x . 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 SO4 2- 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.

Study on the role of copper converter slag in simultaneously removing SO2 and NOx using KMnO4/copper converter slag slurry

To achieve "waste controlled by waste", a novel wet process using KMnO₄/copper converter slag slurry for simultaneously removing SO₂ and NO_x from acid-making tail gas was proposed. Through the solid-liquid separation for copper slag slurry, the liquid-phase part has a critical influence on removing NO_x and SO₂. Also, the leached metal ions played a crucial role in the absorption of SO₂ and NO_x. Subsequently, the effects of single/multi-metal ions on NO_x removal was investigated. The results showed that the leached metal from copper converter slag (Al³⁺, Cu²⁺, and Mg²⁺) and KMnO₄ had a synergistic effect on NO_x removal, thereby improving the NO_x removal efficiency. Whereas Fe²⁺ had an inhibitory effect on the NO_x removal owing to the reaction between Fe²⁺ and KMnO₄, thereby consuming the KMnO₄. Besides, SO₂ was converted to SO₄^2- completely partly due to the liquid catalytic oxidation by metal ions. The XRD and XPS results indicated that the Fe (II) species (Fe₂SiO₄, Fe₃O₄) in copper slag can react with H⁺ ions with the generation of Fe²⁺, and further consumed the KMnO₄, thereby resulting in a decrease in the NO_x removal. The characterization of the slags and solutions before and after reaction led us to propose the possible mechanisms. The role of copper slag is as follows: (1) the alkaline substances in copper slag can absorb SO₂ and NO₂ by KMnO₄ oxidation. (2) copper slag may function as a catalyst to accelerate SO₂ conversion and improve NO_x removal by synergistic effect between leached metal ions and KMnO₄.

Study on a New Type of Composite Powder Explosion Inhibitor Used to Suppress Underground Coal Dust Explosion

At present, the world is committed to the development of environmentally friendly, sustainable and industrial safety. The effective treatment of industrial solid waste can be applied in the field of industrial safety. It is one of the ways to apply industrial solid waste to industrial safety to modify industrial solid waste and combine active powder to prepare industrial solid waste-based composite powder explosion inhibitors and apply it to underground coal dust explosion. This paper introduces the modification and preparation methods of industrial solid waste, and analyzes the good explosion suppression effect and good economic benefit of industrial solid waste-based composite powder explosion inhibitors on coal dust explosion. In this paper, four kinds of industrial solid wastes (red mud, slag, fly ash and sludge) were modified, and the modified solid waste materials with good carrier characteristics were obtained. Combined with a variety of active powders (NaHCO3, KH2PO4 and Al(OH)3), the industrial solid waste-based composite powder explosion inhibitors were obtained by solvent-crystallization (WCSC) and dry coating by ball milling (DCBM). Those kinds of explosion inhibitors can suppress the explosion of pulverized coal in 40–50% of cases. Compared with the powder explosion inhibitor commonly used in industry, it has a lower production cost and better explosion suppression effect. Those kinds of explosion inhibitors have a good industrial application prospect.

O3 oxidation combined with semi-dry method for simultaneous desulfurization and denitrification of sintering/pelletizing flue gas

With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies, the emission of pollutants such as SO₂ and NO_x has received unprecedented attention. Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process, several semi-dry desulphurization technologies such as flue gas circulating fluidized bed (CFB), dense flow absorber (DFA) and spray drying absorption (SDA) are briefly summarized. Moreover, a method for simultaneous treatment of SO₂ and NO_x in sintering/pelletizing flue gas by O₃ oxidation combined with semi-dry method is introduced. Meantime, the effects of key parameters such as O₃/NO molar ratio, CaSO₃, SO₂, reaction temperature, Ca/(S+2N) molar ratio, droplet size and approach to adiabatic saturation temperature (AAST) on denitrification and desulfurization are analyzed. Furthermore, the reaction mechanism of denitrification and desulfurization is further elucidated. Finally, the advantages and development prospects of the new technology are proposed.

Applications of red mud as an environmental remediation material: A review

Red mud is an alkaline by-product produced by alumina plants. The accumulation of red mud is becoming an increasingly serious problem with the growth of the aluminum industry. Various waste treatment methods utilizing red mud as an environmental remediation material have been developed. Red mud environmental remediation materials (RM-ERMs) are environmental remediation materials prepared by activating red mud, synergistically using red mud and other ingredients, or by extracting effective components from red mud. There are three general categories of use for RM-ERMs: for waste water purification, waste gas purification and soil remediation. As well as providing an opportunity to improve the environment through purification technologies, the highly alkaline red mud is consumed in the production of RM-ERMs. The use of RM-ERMs has been shown to be a promising strategy for the simultaneous treatment of various wastes. In this paper, the developregeneration characteristics of various red mud granularent status of RM-ERMs is described, the physical and chemical properties of red mud are introduced, and the active mechanism of RM-ERMs on target pollutants in waste water, waste gas and soil is summarized. Moreover, a discussion on the current existing problems of RM-ERMs provides important tips and suggestions for future research on RM-ERMs.

Simultaneous removal of NOx and SO2 from simulated marine ship flue gas in a novel wet scrubbing system based on divided diaphragm seawater electrolysis technology: efficiency optimization and economic assessment

This work constructed a divided diaphragm seawater electrolysis system with two tandem packed towers for the synergistic removal of NO_x and SO₂. The first tower was mainly used to oxidize NO and SO₂ by AC (active chlorine), and the second tower was used to further absorb NO_x. The factors affecting on NO removal, including ACC (active chlorine concentration), pH value, initial NO concentration and temperature in the oxidation tower were investigated. Moreover, the effect of different inlet gas concentrations and current values were explored. The results showed that with the increase of ACC, the NO and NO_x removal efficiency increased rapidly, but when the ACC was higher than 500 mg/L [Cl₂], the removal efficiency did not increase further in the oxidation tower. Low pH values in the oxidation tower were favorable for NO removal. NO removal efficiency reached a maximum at 40 °C. Higher NO and SO₂ concentrations were favorable for NO removal. The decline of pH in the anode cell was not conducive to the storage of AC in the continuous electrolysis removal process. NO_x and SO₂ were almost completely removed after being scrubbed in the oxidation and absorption towers. The relationship between current and removal efficiency of NO and SO₂ in the oxidation tower was also analyzed. Finally, the removal mechanism and the application prospects were discussed.

O3 oxidation excited by yellow phosphorus emulsion coupling with red mud absorption for denitration

Directing to unwieldiness NOx emitted by the industry, the removal of NOx was implemented using yellow phosphorus (P₄) emulsion and red mud slurry as composite absorbent. Where yellow phosphorus is considered to stimulate formation of the ecological ozone (O₃) from O₂, the oxidation of insoluble NO into water-soluble NOx species by O₃, and the red mud as a pH buffer can be used to maintain the pH of the absorption liquid in a range that better absorbs NOx. NO is finally converted into NO₂^- and NO₃^-, whereas the yellow phosphorus is mainly PO₄^3-. Single-factor influencing on the efficiency of denitration include the concentration of yellow phosphorus, reaction temperature, stirring intensity, gas flow rate, O₂ content, and red mud solid-liquid ratio were investigated. Response surface methodology (RSM) was used to optimize the process parameters. It was indicated that the removal rate of NOx can reach 99.3% under the optimal conditions. Moreover, the possible denitration reaction mechanism was also discussed.