A thermodynamic view on the in-situ carbon dioxide reduction by biomass-derived hydrogen during calcium carbonate decomposition

In the carbonate industry,deep decarbonization strategies are necessary to effectively remediate CO_(2).These strategies mainly include both sustainable energy supplies and the conversion of CO_(2)in downstream processes.This study developed a coupled process of biomass chemical looping H2 production and reductive calcination of CaCO_(3).Firstly,a mass and energy balance of the coupled process was established in Aspen Plus.Following this,process optimization and energy integration were implemented to provide optimized operation conditions.Lastly,a life cycle assessment was carried out to assess the carbon footprint of the coupled process.Results reveal that the decomposition temperature of CaCO_(3)in an H_(2)atmosphere can be reduced to 780℃(generally around 900℃),and the conversion of CO_(2)from CaCO_(3)decomposition reached 81.33%with an H2:CO ratio of 2.49 in gaseous products.By optimizing systemic energy through heat integration,an energy efficiency of 86.30%was achieved.Additionally,the carbon footprint analysis revealed that the process with energy integration had a low global warming potential(GWP)of-2.624 kg·kg^(-1)(CO_(2)/CaO).Conclusively,this work performed a systematic analysis of introducing biomass-derived H_(2)into CaCO_(3)calcination and demonstrated the positive role of reductive calcination using green H_(2)in mitigating CO_(2)emissions within the carbonate industry.

A Review of the Application of Process Evaluation in Junior High School English Teaching under “Double Reduction”

The “Double Reduction” policy is not only to reduce the excessive learning burden of students, but also to improve the quality of students’ learning and to promote their overall development. In order to achieve the goal of the “Double Reduction” policy, it is necessary to focus on the implementation of measures to strengthen process evaluation as proposed in the “General Plan for Deepening Education Evaluation Reform in a New Era”. Therefore, the article will analyze the current situation of the research from three aspects: the connotation of “Double Reduction” and process evaluation, process evaluation under “Double Reduction” and process evaluation in English teaching, and look forward to the future development trend, with the aim of implementing the “Double Reduction” policy and giving full play to process evaluation. The aim is to implement the policy of “Double Reduction” and give full play to the role of process evaluation, so as to effectively guide the practice of English teaching.

Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process

Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.

Electrochemical reduction process of Co(Ⅱ) in citrate solution

Effects of citrate concentration and pH on the electrochemical reduction process of Co（Ⅱ） were investigated by cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. The results show that Co（Ⅱ） is reduced into two species which are free Co2＋ and [Co（C6H607）] in the solution composed of 0.05 mol/L CoS04·5H2O, 0.20 mol/L Na2SO4 and 0-0.40 mol/L C6H5O7Na3·2H2O in the pH range of 3-9. The reduction behavior depends on the pH of the solution. Co（H） is mainly reduced into the form of free Co^2＋ at pH 3 and into the form of [Co（C6H6O7）] at the pH range of 4-6 in citrate solution. The [Co（C6H6O7）] is first reduced to an intermediate state and then to Co°. Adsorption of the intermediate state exists on the surface of the electrode. Co（Ⅱ） is difficult to be reduced in the solution with the pH above 7, because the existing Co（Ⅱ）-citrate complex species [Co（C6H5O7）]- and [Co（C6H4O7）]2- are more difficult to be reduced than the hydrogen ion.

Activation of Transition Metal(Fe,Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO_(2) Reduction Reaction

The electrochemical carbon dioxide reduction reaction(CO_(2)RR),which can produce value-added chemical feedstocks,is a proton-coupled-electron process with sluggish kinetics.Thus,highly efficient,cheap catalysts are urgently required.Transition metal oxides such as CoO_(x),FeO_(x),and NiO_(x)are low-cost,low toxicity,and abundant materials for a wide range of electrochemical reactions,but are almost inert for CO_(2)RR.Here,we report for the first time that nitrogen doped carbon nanotubes(N-CNT)have a surprising activation effect on the activity and selectivity of transition metal-oxide(MO_(x)where M=Fe,Ni,and Co)nanoclusters for CO_(2)RR.MO_(x)supported on N-CNT,MO_(x)/N-CNT,achieves a CO yield of 2.6–2.8 mmol cm−2 min−1 at an overpotential of−0.55 V,which is two orders of magnitude higher than MO_(x)supported on acid treated CNTs(MO_(x)/O-CNT)and four times higher than pristine N-CNT.The faraday efficiency for electrochemical CO_(2)-to-CO conversion is as high as 90.3%at overpotential of 0.44 V.Both in-situ XAS measurements and DFT calculations disclose that MO_(x)nanoclusters can be hydrated in CO_(2)saturated KHCO_(3),and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions,which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

Electrochemical reduction characteristics and mechanism of nitrobenzene compounds in the catalyzed Fe-Cu process

The reduction of the nitrobenzene compounds （NBCs） by the catalyzed Fe-Cu process and the relationship between the electrochemical reduction characteristics of NBCs at copper electrode and reduction rate were studied in alkaline medium（pH=11）. The catalyzed Fe-Cu process was found more effective on degradation of NBCs compared to Master Builder＇s iron. The reduction rate by the catalyzed Fe-Cu process decreased in the following order： nitrobenzene 〉4-chloro-nitrobenzene ≥m-dinitrobenzene ：〉 4-nitrophenol ≥2,4-dinitrotoluene 〉2-nitrophenol. The reduction rate by Master Builder＇s iron decreased in the following order： m-dinitrobenzene ≥4-chloro-nitrobenzene 〉4-nitrophenol 〉2,4-dinitrotoluene ≈nitrobenzene 〉2-nitrophenol. NBCs were reduced directly on the surface of copper rather than by the hydrogen produced at cathode in the catalyzed Fe-Cu process. The reduction was realized by the hydrogen produced at cathode and Fe（OH）2 in Master Builder＇s iron, It is an essential difference in reaction mechanisms between these two technologies. For this reason, the reduction by the catalyzed Fe-Cu depended greatly on NBC＇s electron withdrawing ability.

Toxicity Reduction of Municipal Wastewater by Anaerobic-anoxic-oxic Process

Objective This study was conducted to optimize the operational parameters of anaerobic-anoxic-oxic （A^2/O） processes to reduce the toxicity of municipal wastewater and evaluate its ability to reduce toxicity. Methods A luminescent bacterium toxicity bioassay was employed to assess the toxicity of influent and effluent of each reactor in the A2/O system. Results The optimum operational parameters for toxicity reduction were as follows： anaerobic hydraulic retention time （HRT） = 2.8 h, anoxic HRT = 2.8 h, aerobic HRT = 6.9 h, sludge retention time （SRT） = 15 days and internal recycle ratio （IRR） = 100%. An important toxicity reduction （%） was observed in the optimized A2/O process, even when the toluene concentration of the influent was 120.7 mg·L^-1. Conclusions The toxicity of municipal wastewater was reduced significantly during the A^2/O process. A^2/O process can be used for toxicity reduction of municipal wastewater under toxic-shock loading.

Microwave enhanced chemical reduction process for nitrite-containing wastewater treatment using sulfaminic acid

High-concentration nitrite-containing wastewater that presents extreme toxicity to human health and organisms is difficult to be treated using traditional biological process. In this study, a novel microwave-enhanced chemical reduction process （MECRP） using sulfarninic acid （SA） was proposed as a new manner to treat such type of wastewater. Based on lab-scale experiments, it was shown that 75%-80% nitrite （NO2-） could be removed within time as short as 4 min under 50 W microwave irradiation in pH range 5-10 when molar ratio of SA to nitrite （SA/NO2-） was 0.8. Pilot-scale investigations demonstrated that MECRP was able to achieve nitrite and chemical oxygen demand （COD） removal with efficiency up to 80% and 20%, respectively under operating conditions of SA concentration 80 kg/m3, SA/NO2- ratio 0.8, microwave power 3.4 kW, and stirring time 3 min. Five-day biological oxygen demand （BODs）/COD value of treated effluent after MECRP was increased from 0.05 to 0.36 （by 620%）, which clearly suggested a considerable improvement of biodegradability for subsequent biological treatment. This study provided a demonstration of using microwave irradiation to enhance reaction between SA and nitrite in a short time, in which nitrite in wastewater was completely converted into nitrogen gas without leaving any sludge and secondary pollutants.

Recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation: process optimization and mineralogical study

Currently, the majority of copper tailings are not effectively developed. Worldwide, large amounts of copper tailings generated from copper production are continuously dumped, posing a potential environmental threat. Herein, the recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation was conducted; process optimization was carried out, and the corresponding mineralogy was investigated. The reduction time, reduction temperature, reducing agent (coal), calcium chloride additive, grinding time, and magnetic field intensity were examined for process optimization. Mineralogical analyses of the sample, reduced pellets, and magnetic concentrate under various conditions were performed by X-ray diffraction, optical microscopy, and scanning electron microscopy-energy-dispersive X-ray spectrometry to elucidate the iron reduction and growth mechanisms. The results indicated that the optimum parameters of iron recovery include a reduction temperature of 1150A degrees C, a reduction time of 120 min, a coal dosage of 25%, a calcium chloride dosage of 2.5%, a magnetic field intensity of 100 mT, and a grinding time of 1 min. Under these conditions, the iron grade in the magnetic concentrate was greater than 90%, with an iron recovery ratio greater than 95%.

Research on Development of Dolomite-Ferrosilicon Thermal Reduction Process of Magnesium Production

Up to now, the Pedgion magnesium reduction process is the dominating magnesium production process. In 2004, about 98% of raw magnesium is produced by Pedgion magnesium reduction process in China which equals to 60% of the global output. It shows that the dolomite-ferrosilicon thermal reduction process is the most important method to produce magnesium in the world. Limited by the disadvantage of dolomite-ferrosilicon thermal reduction process, the magnesium producing process always followed by relatively severe pollution, while the resource utilizing efficiency keeps very low. With the rapid development of dolomite-ferrosilicon thermal reduction process in China, many research works have been done aiming at the process technology and the reduction theory, and the magnesium producing process has got great evolution. The history of dolomite-ferrosilicon thermal reduction process was introduced; the process character, the merits and which defects were also discussed. Defects in dolomite-ferrosilicon thermal reduction process were expatiated, and feasible method and idea to upgrade the process was put forward. The main problems and the potential troubles hindering the development of magnesium industry were analyzed. Finally, the probability to further improve the thermal reduction process and the effective approaches to develop Chinese magnesium industry were discussed.

Mathematical simulation of direct reduction process in zinc-bearing pellets

A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.

Effect of Mn addition and refining process on Fe reduction of Mg−Mn alloys made from magnesium scrap

The Fe reduction,microstructure evolution and corrosion susceptibility of Mg−Mn alloys made from magnesium scrap refining with Mn addition were investigated.The results show that significant Fe content change occurs during near-solid-melt treatment(NSMT)process even in the absence of Mn,because of the high saturation of Fe in the melt.Furthermore,in the NSMT process,even a small amount of Mn addition can lead to a sharp deposition of Mn atoms.The NSMT process can increase the growth rate of the Fe-rich particles,and then accelerate their sinking movement.Nevertheless,the addition of Mn hinders the coarsening process of Fe-rich particles.Besides,the corrosion susceptibility of the alloys is mainly affected by the solubility of Fe,which can be significantly reduced by Mn addition.Moreover,the presence of more Fe-rich particles does not necessarily increase the corrosion susceptibility of the alloy.Consequently,in the refining process of Mg−Mn alloys made from magnesium scrap,on the basis of NSMT process and adding an appropriate Mn content(about 0.5 wt.%),the purity of the melt can be improved,thereby obtaining an alloy with excellent corrosion resistance.

Industrial application prospects and key issues of the pure-hydrogen reduction process

The industrial application prospect and key issues in basic theory and application are discussed by the methods of theoretical analysis and calculation to promote the development of the pure-hydrogen reduction process.According to the discussion of thermodynamics and kinetics of pure-hydrogen reduction reaction,the reduction reaction of iron oxide by pure hydrogen is an endothermic reaction,and the reaction rate of hydrogen reduction is significantly faster than that of carbon reduction.To explore the feasibility of the industrial applications of pure-hydrogen reduction,we design the hydrogen reduction reactor and process with reference to the industrialized hydrogen-rich reduction process and put forward the methods of appropriately increasing the reduction temperature,pressure,and temperature of iron ore into the furnace to accelerate the reaction rate and promote the reduction of iron oxide.The key technical parameters in engineering applications,such as hydrogen consumption,circulating gas volume,and heat balance,are discussed by theoretical calculations,and the optimized parameter values are proposed.The process parameters,cost,advantages,and disadvantages of various current hydrogen production methods are compared,and the results show that hydrogen production by natural gas reforming has a good development prospect.Through the discussion of the corrosion mechanism of high-temperature and high-pressure hydrogen on heat-resistant steel materials and the corrosion mechanism of H_2S in the hydrogen gas on steel,the technical ideas of developing new metal temperature-resistant materials,metal coating materials,and controlling gas composition are put forward to provide guidance for the selection of heater and reactor materials.Finally,the key factors affecting the smooth operation of the hydrogen reduction process in engineering applications are analyzed,offering a reference for the industrial application of the purehydrogen reduction process.

Comparative evaluation of energy and resource consumption for vacuum carbothermal reduction and Pidgeon process used in magnesium production

With the fast development of the application of magnesium based alloys,the demand for primary magnesium is increasing dramatically all over the world.The Pidgeon process is the most widely used process for producing magnesium in China,but suffers from problems such as high energy,resource consumption and environmental pollution.While the process of vacuum carbothermal reduction to produce magnesium(VCTRM)has attracted more and more attention as its advantages,but it has not been well-practiced in industrial applications and there also is no comprehensive and quantitative analysis of this process.This study quantified the flows of resource and energy for the Pidgeon process and the VCTRM process,then compared and analyzed these two processes with each other from three aspects.The VCTRM process results in 63.14%and 69.16%lower of non-renewable mineral resources and energy consumptions when compared to the Pidgeon process,respectively.Moreover,the low energy consumption(2.675 tce vs.8.681 tce)and material to magnesium ratio(2.953:1 vs.6.429:1)of the VCTRM process,which lead to lower greenhouse gas(GHG)emissions(8.777 t vs.26.337 t)and solid waste generation(0.522 t vs.5.465 t)with a decrease of 66.67%and 90.45%,respectively.Results indicate that the VCTRM process is a more environmentally friendly process for magnesium production with high efficiency but low cost and low pollution,and it shows a good potential to be industrialized in the future after solving the bottleneck problem of the reverse reaction.

Methanol oxidation in acidic and alkaline electrolytes using PtRuIn/C electrocatalysts prepared by borohydride reduction process

PtRuIn/C electrocatalysts( 20% metal loading by weight) were prepared by sodium borohydride reduction process using H_2PtCl6·6H_2O,RuCl_3·xH_2O and InCl_3·xH_2O as metal sources,borohydride as reducing agent and Carbon Vulcan XC72 as support. The synthetized PtRuIn/C electrocatalysts were characterized by X-ray diffraction( XRD),energy dispersive analysis( EDX),transmission electron microscopy( TEM),cyclic voltammetry( CV),chronoamperommetry( CA) and polarization curves in alkaline and acidic electrolytes( single cell experiments). The XRD patterns showPtpeaks are attributed to the face-centered cubic( fcc) structure,and a shift of Pt( fcc) peaks indicates that Ru or In is incorporated into Ptlattice. TEMmicrographs showmetal nanoparticles with an average nanoparticle size between 2.7 and 3.5 nm. Methanol oxidation in acidic and alkaline electrolytes was investigated at room temperature,by CV and CA. PtRu/C( 50 ∶ 50) shows the highest activity among all electrocatalysts in study considering methanol oxidation for acidic and alkaline electrolyte. Polarization curves at 80 ℃ showPtRuIn/C( 50 ∶ 25 ∶ 25)with superior performance for methanol oxidation,when compared to Pt/C,PtIn/C and PtRu/C for both electrolytes. The best performance obtained by PtRuIn/C( 50 ∶ 25 ∶ 25) in real conditions could be associated with the increased kinetics reaction and/or with the occurrence simultaneously of the bifunctional mechanism and electronic effect resulting from the presence of Ptalloy.

Direct oxidation of methane at low temperature using Pt/C,Pd/C,Pt/C-ATO and Pd/C-ATO electrocatalysts prepared by sodium borohydride reduction process

The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25 ℃ and in a direct methane proton exchange membrane fuel cell at 80 ℃. The electrocatalysts prepared also were characterized by X-ray diffraction( XRD) and transmission electron microscopy( TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic( fcc) structure,and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic( fcc) structure. For Pt/C-ATO and Pd/C-ATO,characteristic peaks of cassiterite( SnO_2) phase are observed,which are associated with Sb-doped SnO_2( ATO) used as supports for electrocatalysts. Cyclic voltammograms( CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However,this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism,where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR( Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed,which indicates the production of carbon dioxide. Polarization curves at 80 ℃in a direct methane fuel cell( DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.

N₂O Formation in Selective Non-catalytic NO_xReduction Processes

Nitrous oxide is not an environmentally regulated species in the U.S., but it does participate in the stratospheric ozone chemistry and contributes to the greenhouse effect. Nitrous oxide has been found to be a by-product of the selective non-catalytic reduction process. Chemical kinetic calculations demonstrated that the formation of nitrous oxide in the urea-based selective non-catalytic reduction process is linked to the conversion of NO by cyano species released from the process parent compounds. This conversion occurs within in temperature window between 850 and 1050℃. With urea injection, nitrous oxide emissions represent up to 20 percent conversion of the NOx reduced. The amount of nitrous oxide formed depends primarily on the process temperature, the amount of chemical injected, the initial NOx level, and the carbon monoxide level in the gas stream. These observations, which were based on the chemical kinetics of the process, should be considered in designing selective non-catalytic reduction systems to minimize nitrous oxide by- product formation.

Application of coal-water slurry on the rotary calcining kiln of pedgion magnesium reduction process

Energy saving has been an important concept in modern industry especially to the countries and regions with energy shortage such as China and Japan. Utilization of Coal-Water Slurry （CWS） can improve the burning efficiency of coal and reduce the pollutions of soot, sulfide and the nitride by burning lump coal directly. The CWS is a promising energy saving technique and the effectual substitute of oil. The study on the preparation and application of the CWS has made progresses in many aspects. The present paper studied the basal problems for applying the CWS on the rotary kilns during the calcining-dolomite process in the magnesium factory, summarized the key points for the application process of the CWS and gave the corresponding solutions.

CFD simulation of effect of anode configuration on gas–liquid flow and alumina transport process in an aluminum reduction cell

Numerical simulations of gas–liquid two-phase flow and alumina transport process in an aluminum reduction cell were conducted to investigate the effects of anode configurations on the bath flow, gas volume fraction and alumina content distributions. An Euler–Euler two-fluid model was employed coupled with a species transport equation for alumina content. Three different anode configurations such as anode without a slot, anode with a longitudinal slot and anode with a transversal slot were studied in the simulation. The simulation results clearly show that the slots can reduce the bath velocity and promote the releasing of the anode gas, but can not contribute to the uniformity of the alumina content. Comparisons of the effects between the longitudinal and transversal slots indicate that the longitudinal slot is better in terms of gas–liquid flow but is disadvantageous for alumina mixing and transport process due to a decrease of anode gas under the anode bottom surface. It is demonstrated from the simulations that the mixing and transfer characteristics of alumina are controlled to great extent by the anode gas forces while the electromagnetic forces(EMFs) play the second role.

Preparation of primary Al-Si alloy from bauxite tailings by carbothermal reduction process

Effects of various reaction parameters such as atmospheric pressure, treating temperature, sintering time and bituminite content on the preparation of primary Al-Si alloy by carbothermal reduction of bauxite tailings were investigated by XRD,XRF, infrared absorption carbon-sulfur analysis unit and SEM coupled with EDS. Meanwhile, the mechanism of carbothermal reduction of Al2O3 and SiO2 was discussed. It is found that pressure and temperature are major factors that influence the carbothermal reduction of bauxite tailings. The appropriate conditions for preparation of primary Al-Si alloy are as follows: atmospheric pressure of 0.1 MPa, heating temperature of 1 900 ℃,bituminite content of 95% (mass fraction) of theoretic bituminite content and sintering time of 1 h. Among four mechanisms of carbothermal reduction of Al2O3 and SiO2, the theory of the formation and decomposition of carbides might be the best one to interpret the reaction process.