Adding Sodium Carbonate Research Articles

Sodium carbonate-enhanced calcium carbide slag activation of sewage sludge for the preparation of green cementitious materials

The utilization of calcium carbide residue (CCR) to activate solid wastes can effectively promote sustainable development. This paper explores adding sodium carbonate (Na2CO3) to CCR activators to improve the early reactivity of alkali-activated materials (AAMs) made from sewage sludge ash (SSA). The research focuses on the effects of Na2CO3 on setting, hardening, mechanical strength, and environmental benefits. The findings indicate that Na2CO3 can shorten the paste’ hardening time and significantly enhance the early mechanical properties. The introduction of Na2CO3 accelerates the consumption of CCR during the early phases and facilitates the formation of C-(N)-A-S-H gels. Meanwhile, it can significantly reduce the porosity and refine the pore structure. When the dosage reaches 8%, the total intruded pore volume of the sample decreases to 0.15 mL/g. This activation method reduces energy consumption, CO2 emissions, and costs by 69%, 50%, and over 90%, respectively, making it an efficient, eco-friendly approach to AAM production.

Preparation of polymeric aluminum chloride from secondary aluminum dross and its water purification effect

ABSTRACT Aluminum dross is solid waste generated by the aluminum industry. Currently, a large amount of aluminum dross is produced annually year. Aluminum dross, a hazardous waste, contains harmful substances such as aluminum metal, aluminum nitride, fluoride and chlorine salts, which pose a serious threat to human health and also cause damage to the ecological environment. Thus, it is important to recycle secondary aluminum dross and realise its high-value utilisation. Polymeric aluminum chloride (PAC) is a polymer flocculant, at present, China's annual use of PAC in the field of water treatment is about 5 × 105 t, and with the continuous improvement of water purification requirements, the annual use of PAC increased year by year. Here secondary aluminum dross was used as a raw material to prepare PAC by hydrochloric acid (HCl) leaching, followed by the addition of sodium carbonate. The optimal conditions for the acid leaching of secondary aluminum dross for the preparation of PAC were as follows: HCl concentration, 18%; liquid-to-solid ratio, 4.5:1; stirring rate, 200 r/min; reaction temperature, 90 °C; and 60 min. An aluminum leaching rate of 85.5% was obtained under these conditions. The results showed that the acid leachate after adding sodium carbonate, under the conditions of polymerisation temperature of 70 °C, polymerisation time of 6 h, and polymerisation pH value of 3.0, the PAC prepared had an alumina content of 10.19%, salinity of 32.37%, density of 1.32 g/cm3, 1% aqueous solution pH 4.3. The water purification effect of the prepared PAC surpassed that of the commercially available PAC. The utilisation of secondary aluminum dross can reduce the environmental pollution caused by aluminum slag.

The role of soil dispersivity and initial moisture content in splash erosion: Findings from consecutive single-drop splash tests

Dispersive soil is commonly associated with hydraulic erosion due to its tendency to disperse when in contact with water. Nevertheless, the erosion process of dispersive soil remains poorly understood. This study aims to explore the influence of dispersivity and initial moisture content on the splash erosion of dispersive soil, which is a crucial stage of hydraulic erosion. Consecutive single-drop splash tests were conducted on artificially prepared dispersive soil (made by adding sodium carbonate to the soil) with varying dispersivity levels and moisture contents. A high-speed and a single-lens reflex (SLR) camera were employed to capture the process of erosion in exquisite detail. The results demonstrated the significant influence of dispersivity on splash erosion. At moisture content below 20%, increased dispersivity weakened the splash erosion effect, leading to reduced infiltration, splashed soil mass, crater volume, and depth. Conversely, when the initial moisture content reached 20% or saturation, intensified dispersivity exacerbated splash erosion. Dispersivity also increased the sensitivity of the soil splash process to changes in moisture content. Dispersive soil exhibited greater sensitivity compared to non-dispersive soil, affecting the mass of splashed soil, soil-water mixture droplets area, water-soil mass ratio, and particle ejection distance. Dispersivity also caused splashed particles to fragment, resulting in more soil-water mixture droplets and a greater splash distance. Furthermore, dispersivity reduced infiltration ratio and increased runoff yield after erosion events, indicating a higher risk of transporting splashed soil particles through runoff. These insights contribute to erosion models and have practical applications in managing dispersive soil.

Preparation of extra coarse-grained WC-Co cemented carbides by doping sodium in the ammonium tungstate solution during evaporation crystallization process

Coarse tungsten powders are usually used as raw material for preparing coarse grained WC-Co cemented carbides. Sodium can effectively promote the growth of tungsten powder during the reduction of tungsten oxide with hydrogen. Conventional addition of sodium salt into tungsten oxide powders by mechanical milling has the disadvantage of uneven distribution of sodium, which leads to abnormal growth of tungsten powders and affects the performance of WC-Co cemented carbides. In this study, uniform sodium doped ammonium paratungstate (APT) was prepared by adding sodium carbonate into ammonium tungstate solution during the evaporation and crystallization process based on the formation of ammonium-sodium paratungstate. Experimental results showed that sodium was uniformly distributed in the APT and promoted the growth of APT crystal. The sodium-doped APT was then used to produce coarse tungsten powders. Compared with tungsten powders obtained from tungsten trioxide with addition of sodium by mechanical milling, the coarse tungsten powders had larger average particle size and more uniform particle size distribution. The coarse tungsten powders were subsequently prepared into tungsten carbide powders and WC-Co cemented carbides by carburization and pressure sintering, respectively. Results showed that the obtained WC-Co cemented carbides had larger average WC grain size (6.8–7.2 μm), higher fracture toughness and transverse ruptures strength, and more uniform microstructure than that of WC-Co cemented carbides obtained by addition of sodium with mechanical milling. Moreover, sodium thoroughly volatilized during hydrogen reduction and carburization process, so that the purity of WC-Co cemented carbides was not reduced. Therefore, this study provided a new route for preparation of extra coarse-grained WC-Co cemented carbides.

Efficient transformation of hydroxylamine from wastewater after supplementation with sodium carbonate or calcium bicarbonate

Hydroxylamine is a highly reactive inorganic nitrogen compound that not only has a toxic effect on microorganisms, but also makes wastewater treatment more difficult, which in turn damages the environment and even endangers human health. This study reported a new method for converting of hydroxylamine by adding sodium carbonate or calcium bicarbonate to the hydroxylamine-polluted wastewater. The conversion efficiency of hydroxylamine was more than 99% in the presence of sodium carbonate or calcium bicarbonate under the reaction conditions of 25 °C, C/N ratio 15, and dissolved oxygen 7.4 mg/L. And its maximal conversion rate can reach 3.49 mg/L/h. This method overcomes various shortcomings of the reported hydroxylamine removal technologies that require a large material dosage and high cost. The technology in this report has many advantages: low cost, ‘green’ environmental protection, easy market promotion, and high economic benefits.

Resynthesis of cathode active material from heterogenous leachate composition produced by electric vehicle (EV) battery recycling stream

Massive growth of electric vehicle (EV) sales in recent years triggers the huge demands of certain elements for lithium-ion battery (LIB) production. To sustain the supply of the elements and contribute to its circularity, LIB recycling is one of the justified routes. Although hydrometallurgy is considered as the most common process in battery recycling, improvements are still required to make the recycling process cleaner by reducing the steps and minimizing the chemical use. To achieve this goal, co-precipitation method is proposed to produce cathode active metals (CAM) of Li, Ni, Mn and Co from the leach solution. As battery chemistry is evolving fast, in near future, the dominant LiNi1/3Mn1/3Co1/3O2 (LNMC 111) type will be replaced by other types with different NMC ratios. Hence, in this study, co-precipitation was tested to recover Li, Ni, Mn and Co from various leachates with different metal compositions, simulating leachates from different battery chemistries. A hydrometallurgy flowsheet comprising four precipitation steps for metal recoveries from leach solutions was developed. In the first stage, aluminium was removed as Al(OH)3 by increasing the pH of the leachate to 5.5. Cu was removed in the next stage as sulfide by adding sodium sulfide to the supernatant obtained in the first stage. In the third stage, Ni, Mn and Co were co-precipitated as hydroxide precursor by increasing pH of supernatant to 11. The results showed that >95% of Ni, >83% Co, and >42% of Mn could be precipitated from the leaching liquor. Finally, Li is recovered from the supernatant as carbonate precipitate by adding sodium carbonate. Ni,Mn,Co(OH)2 precursor was finally mixed with Li2CO3 precipitated and calcined to resynthesize CAM showing the potential of this process to close the loop of recycling.

Lithium extraction from Dieng geothermal brine using solvent extraction – A preliminary study

This preliminary study aims to obtain the lithium compounds from a geothermal brine through a solvent extraction. The brine samples were collected from PT Geodipa Energi Geothermal Power Plant in Dieng, Central Java, Indonesia. The ICP analysis was conducted to measure brine chemical composition. Brine’s lithium content was 62.73 ppm with the dominant impurities silica (Si), calcium (Ca), potassium (K), sodium (Na), and boron (B). Silica removal was conducted by centrifugation technic with the addition of flocculants, while calcium removal was achieved by adding sodium carbonate. The CYANEX® 936P was used for the extraction process and was diluted in kerosene (1:1 O/A ratio). The extraction pH was adjusted by adding 10% H2SO4 solution (acid condition) and 10% NH4OH (alkaline condition). The optimum condition for lithium extraction was observed at pH = 11, with the highest lithium recovery of 90%. The eluate from the stripping process was then precipitated by adding Na2CO3 to produce lithium carbonate powder.

Biological Synthesis and Characterisation of Silver Nanoparticles of Zingiber officinalis and Evaluation of its Biological Activity

Ginger (Zingiber officinale) belongs to Zingiberaceae family is one of the famous spices all over the world. It is a perennial creeping plant with long leaves, yellow green flowers and thick tuberous rhizome. Silver nanoparticles’ potential uses in Green Chemistry have received attention. The current study focuses on the rapid biological production of silver nanoparticles using different plant materials and characterizations using UV-visible spectrophotometry, IR, SEM, and HPLC investigations. Within 15 minutes of adding sodium carbonate, an aqueous extract of dried Zingiber officinalis rhizome reduces silver nitrate. No further reduction and stabilizing chemicals are required for the entire process, showing a green synthesis. Escherichia coli and Staphylococcus aureus use biosynthesized “Zinger-AgNps” as a competent antibacterial agent. Zinger-AgNps were evaluated as its catalytic capability to reduce the model pollutant methylene blue. Both of them are displayed 2, 2-diphenyl-1-picrylhydrazyl-specific free radical scavenging activity (DPPH). Silver biological material nanoparticles are created by utilizing less hazardous and nontoxic reduction agents, such as ascorbic acid and sodium citrate. The antioxidant and lipid peroxidation inhibition properties of ginger prevent peroxidative damage, indicating the benefits of ginger in the prevention of microbial food spoilage, free-radical-induced damage and rancidity. The sodium citrate aggregation for silver nanoparticles, firm surface contact, and synthesized silver nanoparticles are used to study antibacterial efficacy and antioxidant activity.

Pyrolysis of Denim Jeans Waste: Pyrolytic Product Modification by the Addition of Sodium Carbonate.

Quickly changing fashion trends generate tremendous amounts of textile waste globally. The inhomogeneity and complicated nature of textile waste make its recycling challenging. Hence, it is urgent to develop a feasible method to extract value from textile waste. Pyrolysis is an effective waste-to-energy option to processing waste feedstocks having an inhomogeneous and complicated nature. Herein, pyrolysis of denim jeans waste (DJW; a textile waste surrogate) was performed in a continuous flow pyrolyser. The effects of adding sodium carbonate (Na2CO3; feedstock/Na2CO3 = 10, weight basis) to the DJW pyrolysis on the yield and composition of pyrolysates were explored. For the DJW pyrolysis, using Na2CO3 as an additive increased the yields of gas and solid phase pyrolysates and decreased the yield of liquid phase pyrolysate. The highest yield of the gas phase pyrolysate was 34.1 wt% at 800 °C in the presence of Na2CO3. The addition of Na2CO3 could increase the contents of combustible gases such as H2 and CO in the gas phase pyrolysate in comparison with the DJW pyrolysis without Na2CO3. The maximum yield of the liquid phase pyrolysate obtained with Na2CO3 was 62.5 wt% at 400 °C. The composition of the liquid phase pyrolysate indicated that the Na2CO3 additive decreased the contents of organic acids, which potentially improve its fuel property by reducing acid value. The results indicated that Na2CO3 can be a potential additive to pyrolysis to enhance energy recovery from DJW.

Systemical investigation on the determination of sulfate in cement-based materials based on a promoted conductometric titrator

The concentration of sulfate ion in cement-based materials is the basic data for the design and evaluation of concrete structures exposed to sulfate lakes and saline soil areas. In this study, a conductivity titrator was developed and used to test the sulfate concentration in concrete corroded by sulfate attack based on the Internet of Things. The theories of conductivity measurement and conductivity titration were described; The main hardware composition and software design of conductometric titrator were introduced; Then, the effects of temperature, concentration, hydroxyl ion and hydrogen ion on the conductivity of solution of sodium sulfate and barium chloride were explored by the titrator; The titration parameters, the influence of hydroxyl and hydrogen ion on sodium sulfate titration were determined by test of sulfate ion titrated by barium chloride with known concentration; Finally, the titrator was used to test the sulfate concentration in cement-based materials after sulfate attack. The results show that the titrator can measure the conductivity of solution with 0.4% accuracy and the concentration of sulfate ion with 0.8% accuracy; During the titration of sulfate ion, the concentration of barium chloride should be twice that of sulfate ion, the titration rate should be less than 0.828 mL/s, and the titration volume should be at least 10 mL; It is found that the influence of hydroxyl ion can be effectively eliminated by adding nitric acid or hydrochloric acid, and the influence of hydrogen ion can be effectively eliminated by adding sodium carbonate. This conductivity meter can accurately test the sulfate concentration in the concrete after corrosion.

Experimental study on improving lithium extraction efficiency of salinity-gradient solar pond through sodium carbonate addition and agitation

The use of salinity-gradient solar ponds (SGSPs) to extract lithium from carbonate salt brine has expanded their applications beyond thermal extraction and into direct mineral exploitation. SGSPs play a significant role in lithium extraction, but the CO32- concentration will decease significantly after a cold winter, resulting in low precipitation efficiency of lithium in SGSPs. Analyzing the characteristics of the brine in the lower convective zone shows the key causative factors of this reduced extraction efficiency to be the imbalances in lithium carbonate concentration and metastability of the water at low temperatures. In this study, this problem was solved by adding sodium carbonate and agitating the LCZ. First, the proportion of sodium carbonate was determined through experiments and the practicality was further verified using SGSPs. Meanwhile, system changes caused by sodium carbonate in the LCZ were investigated and numerical simulation was carried out for thermal efficiency and salt diffusion process. This study found that the addition of sodium carbonate improved the quality of the brine and the seasonally-induced concentration imbalances between the Li+ and CO32-. By agitating the LCZ, the stable low convection state of the brine was broken, the ions were remixed evenly, and the supersaturation of lithium carbonate was increased. By adding 5 % sodium carbonate to the SGSPs and agitating the brine, the ponds’ average lithium yield was increased by 48.3 %, and the grade of the lithium carbonate was increased to over 80 %. This study enriches the application of SGSPs as an industrial tool for mineral exploitation.

Preparation, evaluation, and identification of the biological, laser, and nanoscale activity and computational chemistry of some 3,2-dihydroquinozolin-4-on compounds derived from 4-aminotetrahydropyrane

This research prepares heterocyclic compounds by the compound [G1] from the reaction of 2-chloroacetohydrazide with 4-amino-tetrahydropyrane in absolute ethanol with drops of triethylamine 3 (C2H5)N. Then the hydrozones [G7-G2] were prepared from the [G1] reactor with some substituted benzaldehyde in absolute ethanol using an acidic medium. Derivatives of 2,3-dihydroquinozoline 4-on ]G8-G13[ were prepared by the reaction of the hydrozones ]G2-G7[ with anthranlic acid using 4,2-dioxane as a solvent then adding sodium carbonate to get rid of the residual acid used. After purification of the product, the prepared compounds were characterized by some spectroscopic methods, such as infrared (IR), proton nuclear magnetic resonance (NMR) [1H and carbon NMR] 13C, as well as the study of the thermal stability of some 3,2-dihydroquinozolin 4 compounds using the laser, obtaining nanoparticles, determining their shapes and sizes, the computational chemistry of all the prepared compounds, in addition to identifying the melting and purity degrees of the prepared compounds following the course of the reactions by thin layer chromatography (TLC).

Copper recovery from copper slags through flotation enhanced by sodium carbonate synergistic mechanical activation

Flotation is one of the most important methods for recovering copper from copper slag, However, traditional grinding may be over grinding sometimes, resulting in smaller interface difference, which leads to a decrease in the selectivity of flotation. In this study, a sodium carbonate combined with mechanical activation enhanced flotation for recovering copper from copper slag was developed. Based on the phase analysis, the flotation experiment was conducted. It showed that adding sodium carbonate before wet grinding can change the surface energy of copper slag particles and increase the possibility of cracks between chalcocite particles and gangue particles, while sodium carbonate can also increase the Eh of the copper slag flotation system and improve the flotation effect. Under the optimal flotation conditions of 600 g/t sodium carbonate and 300 g/t xanthate, the recovery efficiency of copper can reach 98.07% with a concentration of 36.13%. Moreover, the flotation kinetic model of copper slag was established and the results showed that the movement of copper slag in the flotation process conforms to the first-order kinetics. The addition of sodium carbonate increased the stability of the pulp and improved the flotation kinetics greatly, resulting in a better flotation performance.

The Effect of Adding Sodium Carbonate on the Electrical Conductivity of Aluminum Paste

Base metal pastes have been widely used in the preparation of ZnO varistor electrodes, and it is important to accurately grasp the relevant mechanisms affecting the conductivity of aluminum electrodes. In this paper, the effect of adding sodium carbonate on the conductive property of aluminum paste was assessed, and the microscopic mechanism during aluminum electrode sintering explored. The results show that adding sodium carbonate can reduce the softening point of glass powder and enhance its fluidity. Sodium carbonate, glass, and aluminum oxide film react together; consequently, the aluminum oxide film is partially dissolved by reaction to produce defects, and there is tight contact at the interface between the aluminum powder particles. The sodium ions will displace the aluminum ions in the alumina, conferring the alumina film with a certain ionic conductivity. At the same time, sodium ions are doped into the aluminum lattice, which causes the aluminum lattice to swell. After sintering, the structure of aluminum electrode is compact and its electrical conductivity is significantly improved. This study is a valuable reference for the theoretical research and the potential applications of aluminum paste.

Effect of Magnesium on the Hydrophobicity of Sphalerite

The use of untreated recycled water has negative effects in the flotation of zinc sulfide ores due to the presence of dissolved species, such as magnesium and calcium. Although it has been found that magnesium is a more potent depressant than calcium, it has not been investigated in this role or for the effect of adding sodium carbonate. The results of an investigation to evaluate the effect of magnesium on the hydrophobicity of Cu-activated sphalerite conditioned with Sodium Isopropyl Xanthate (SIPX) are presented. Zeta potential of natural and Cu-activated sphalerite as a function of the conditioning pH and Cu(II) concentration, respectively, was first evaluated. Later, the effect of pH and presence of magnesium on the contact angle of Cu-activated sphalerite conditioned with SIPX was studied; it was also evaluated the effect of sodium carbonate to counteract the effect of magnesium. Cu-activation enhances the zeta potential of sphalerite up to a concentration of 5 mg/L. Contact angle tests, thermodynamic simulation, and surface analysis showed that magnesium hydroxide precipitates on the sphalerite surface at pH 9.6, decreasing its hydrophobicity. Addition of sodium carbonate as alkalinizing agent precipitates the magnesium in the form of a species that remained dispersed in the bulk solution, favoring the contact angle of Cu-activated sphalerite and, consequently, its hydrophobicity. It is concluded that the use of sodium carbonate as alkalinizing agent favors the precipitation of magnesium as hydromagnesite (Mg5(OH)2(CO3)4∙4H2O) instead of hydroxide allowing the recovery of sphalerite.

Preparation and Investigation of some Physical Properties and Photocatalytic Activity of a co-Catalyst CoO-V2O5

The current work involves preparation of neat vanadium oxide and cobalt oxide. Likewise, various percentage from their mixed forms were prepared in various ratios: 25%, 50%, 75% and 100% from CoO were precipitated with fixed weight of V2O5 2.0 g. In addition, the above percentage from V2O5 were precipitated with fixed weight of CoO, 2.0 g. The individual metal oxides and their mixtures with various ratios were prepared from the solution of sulphate and nitrate of both metals respectively by co-precipitation process by adding sodium carbonate. All metals carbonates transfer to corresponding oxides by calcification at 773 K. Spectroscopic studies for metal oxides and their mixtures with various ratios using X-rays diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Some of physical properties of these oxides and their mixtures were studies such as pore size, density, porosity and electrical conductivity. The activity of these materials were investigated by following photocatalytic oxidation of 1-octanol over a suspension of these materials. The obtained results showed that photocaatalytic oxidation of alcohol was achieved when using each of catalyst, light, air and 1-octanol.

Confirmation of unknown additives in enrofloxacin powder

应用非靶向分析技术,筛查、分析和确证恩诺沙星粉(水产用)中的非法添加物。分别制备甲酸酸化、碳酸钠碱化的恩诺沙星粉供试品溶液,经超高效液相色谱-二极管阵列检测器(UPLC-PDA)检测初筛,获取未知物色谱图。应用超高效液相色谱-飞行时间高分辨质谱(UPLC-TOF-HRMS),在正、负离子模式下对酸化、碱化样液进一步检测,获得未知物母离子和二级特征碎片的精确质荷比、同位素信息,并应用SCIEX OS软件进行分析推导。最后取疑似化合物对照品进行确证研究。UPLC-PDA初筛结果显示:酸化样液在1.870 min、5.122 min,碱化样液在5.122 min,均发现高响应未知色谱峰。对吸收波长和峰面积进行分析,推测含2个未知物,且未知物1(1.870 min)与未知物2(5.122 min)在酸性/碱性条件下可能发生转换。SCIEX OS软件分析推导结果显示:未知物2,母离子分子式拟合为C11H8O2,二级碎片结构解析含1个苯环、2个羰基和1个通过成环连接的丙烯结构,推测为甲萘醌;未知物1的分子离子峰为C11H9O5S-,二级碎片仅采集到HSO3-,丢失部分与未知物2一致,结合甲萘醌常见衍生物类型,推测为亚硫酸氢钠甲萘醌。取甲萘醌、亚硫酸氢钠甲萘醌对照品进行对比研究,UPLC-PDA检测结果显示:未知物1与亚硫酸氢钠甲萘醌、未知物2与甲萘醌,保留时间和紫外光谱一致;向供试溶液中添加对照品溶液后检测,未知物为单一峰。UPLC-TOF-HRMS检测发现:未知物1与亚硫酸氢钠甲萘醌保留时间一致,一级质谱质量偏差为1.0×10-6,二级谱库匹配度为100%;未知物2与甲萘醌保留时间一致,一级质谱质量偏差为0.6×10-6,二级谱库匹配度为99.7%。未知物1和2的结构得以确证。亚硫酸氢钠甲萘醌可止血,与恩诺沙星治疗败血症的适应证相应,佐证试验结果。随着对兽药非法添加行为的严格监管和严厉打击,非法添加物和添加手段愈发隐蔽,常规靶向分析难以满足监控需求。该文详述的使用UPLC-PDA结合UPLC-TOF-HRMS对未知物进行非靶向分析的技术,可为药品、食品、保健品、化妆品及农药等产品中非法添加物的筛查和确证提供思路和技术参考。

Calcite Precipitation at Cement–Bentonite Interface. Part 1: Effect of Carbonate Admixture in Bentonite

Calcium leaching from cementitious materials into bentonite is a key process for the long-term alteration of cement–clay interfaces of engineered barrier systems. Strong chemical gradients between cement and clay drive the precipitation of minerals such as calcium silicate hydrate (C–S–H) and calcite. To analyze the mineralogical and porosity evolution at the cement–clay interface, composite specimens consisting of cement paste and bentonite mixed with various amounts of sodium carbonate were subjected to immersion and chloride migrations tests and were investigated by electron probe micro-analysis (EPMA), thermogravimetry/differential thermal analysis (TG-DTA), and X-ray diffraction (XRD) after 4–20 months of immersion. The results show that adding sodium carbonate to the bentonite enhanced the formation of calcite in the form of a surface layer on the cement paste. This suggests pore clogging at the interface and implies the existence of a threshold amount of carbonate addition above which pore clogging occurs. This is the first of two papers; the accelerated evolution of the samples in the presence of an electrical field is discussed in the second paper.

A Combined Soda Sintering and Microwave Reductive Roasting Process of Bauxite Residue for Iron Recovery

In this study an integrated process is presented as a suitable method to transform Fe3+ oxides present in bauxite residue into magnetic oxides and metallic iron through a microwave roasting reduction, avoiding the formation of hercynite (FeAl2O4). In the first step, all the alumina phases were transformed into sodium aluminates by adding sodium carbonate as a flux to BR and then leached out through alkali-leaching to recover alumina. Subsequently, the leaching residue was mixed with carbon and roasted by using a microwave furnace at the optimum conditions. The iron oxide present in the sinter was converted into metallic iron (98%). In addition, hercynite was not detected. The produced cinder was subjected to a wet high intensity magnetic separation process to separate iron from the other elements.

Effects of hydrogen peroxide, sodium carbonate, and ethanol additives on the urea-based SNCR process

The issue of secondary pollutants represents a classic problem in the urea-based selective non-catalytic reduction (SNCR) process. Therefore, this study took to investigate the evolutions of secondary pollutants when including additives during the urea-based SNCR process. Results indicated that additives, namely hydrogen peroxide, sodium carbonate, and ethanol, clear improved denitration efficiency between 750 °C - 925 °C due to the increase of OH groups. Compared to rates without any additives, the “temperature window” width of hydrogen peroxide, sodium carbonate, and ethanol increased by 30%, 30%, and 52%, respectively. The temperature at the maximum denitration efficiency was decreased by 25 °C with the addition of ethanol. The addition of hydrogen peroxide, sodium carbonate, and ethanol decreased the amount of ammonia leakage at 725 °C - 900 °C. Besides, the emissions of HNCO and N2O were decreased by adding sodium carbonate during 725 °C - 900 °C. Therefore, the addition of sodium carbonate proved to be beneficial for reducing the secondary pollutant emissions in SNCR. This study aims to provide a deeper understanding of the urea-based SNCR process in combustion.