Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)format...Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.展开更多
Eggshells,a by-product of the food industry,represent a significant yet often overlooked waste stream.Given their vast production volume and inherent properties,eggshells have the potential to serve as a sustainable a...Eggshells,a by-product of the food industry,represent a significant yet often overlooked waste stream.Given their vast production volume and inherent properties,eggshells have the potential to serve as a sustainable and environmentally friendly co-fuel.Aiming to explore the co-combustion characteristics and kinetics of pulverized coal blended with eggshells and offer insights into their combined use as a renewable energy source,a systematic investigation was conducted to evaluate the physical and chemical properties of Shangwan bituminous coal,Shouyang anthracite coal,eggshell(ES)and their blends.Additionally,comprehensive experimental analyses were performed at different heating rates applying a non-isothermal thermogravimetric method.The findings revealed that the addition of ES enhanced the combustion efficiency.The combustion characteristics were significantly influenced by the ES content,with an optimal blend ratio identified for maximum combustion efficiency.To represent the thermal degradation experiments,random pore model and volume model were employed.Furthermore,activation energies and pre-exponential factors were determined.The random pore model demonstrated more superior performance compared to the volume model.The activation energies of all the samples ranged between 18.29 and 42.48 kJ/mol,with the lowest value observed for the sample containing 20 mass%ES.展开更多
Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products.In this paper,the classical segmented pyrol...Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products.In this paper,the classical segmented pyrolysis kinetics model and a new refined pyrolysis kinetics model were used to forecast the composition distribution of hydrocarbon generation products co-heated by supercritical water and medium and low maturity organic-rich shale.The prediction accuracy of the two reaction kinetics models for the composition of pyrolysis products of organic-rich shale was compared.The reaction path of hydrocarbon generation in centimeter sized organic-rich shale under the action of supercritical water was identified.The results show that the prediction accuracy of the classical segmented pyrolysis kinetics model was poor at the initial stage of the reaction,and gradually increased with increasing time.The prediction error can reach less than 25%when the reaction time was 12 h.The new refined model of reaction kinetics established is better than the classical reaction kinetics model in predicting the product distribution of pyrolysis oil and gas,and its prediction error is less than 14%in this paper.The reaction paths of hydrocarbon generation in centimeter sized organic-rich shale under supercritical water conversion mainly include organic-rich shale directly generates asphaltene and saturated hydrocarbon,asphaltene pyrolysis generates saturated hydrocarbon,aromatic hydrocarbon and resin,saturated hydrocarbon,aromatic hydrocarbon and resin polymerization generates asphaltene,and saturated hydrocarbon,resin and asphaltene generates gas.The reason for the difference of centimeter sized and millimeter sized medium and low maturity organic-rich shales hydrocarbon generation in supercritical water is that the increase of shale size promotes the reaction path of polymerization of saturated hydrocarbon and aromatic hydrocarbon to asphaltene.展开更多
This study prepared a class of RDX-based composite microspheres(RAF)containing ADN and FKM2602.The reaction kinetics of RAF composite microspheres were effectively improved by maintaining the system's high energy ...This study prepared a class of RDX-based composite microspheres(RAF)containing ADN and FKM2602.The reaction kinetics of RAF composite microspheres were effectively improved by maintaining the system's high energy and safety performance.In the close packing state,when the heating rate is rapid,the thermal stability of RAF composite microspheres is better than that of RDX;the close packing state will reduce the degree of freedom of RDX and ADN reaction but will increase the degree of freedom of RAF composite microsphere reaction.The thermal conductivity of RAF composite microspheres is close to that of RDX.In the ignition experiment,the flame of RAF composite microspheres can be maintained without the external heat source.Regarding safety,the H50of RAF composite microspheres was 274.04%higher than that of RDX.The detonation velocity of RAF composite microspheres is slightly higher than that of raw material RDX.Overall,these findings highlight the effectiveness of ADN in enhancing the reaction kinetics of RDX-based composites.展开更多
The vacuum volatilization kinetics of Pb in In-Pb solder was investigated.The results indicate a significant increase in the vacuum volatilization rates of Pb,25In-75Pb,40In-60Pb,and In with increasing temperatures fr...The vacuum volatilization kinetics of Pb in In-Pb solder was investigated.The results indicate a significant increase in the vacuum volatilization rates of Pb,25In-75Pb,40In-60Pb,and In with increasing temperatures from 923 to 1123 K,system pressure of 3 Pa and holding time of 30 min.The mass transfer coefficients and apparent activation energies of Pb and its alloys were determined at various temperatures.Additionally,a kinetics model was developed to describe Pb vacuum volatilization in high-temperature melts.It is obtained that the vapor mass transfer is the factor limiting the vacuum volatilization rates of Pb and In-Pb alloys under the above specified conditions.展开更多
Solid-state precipitation is an effective strategy for tuning the mechanical and functional properties of ad-vanced alloys.Structure design and modification necessitate good knowledge of the kinetic evolution of preci...Solid-state precipitation is an effective strategy for tuning the mechanical and functional properties of ad-vanced alloys.Structure design and modification necessitate good knowledge of the kinetic evolution of precipitates during fabrication,which is strongly correlated with defect concentration.For Fe-Ga alloys,giant magnetostriction can be induced by the precipitation of the nanoscale tetragonal L60 phase.By introducing quenched-in vacancies,we significantly enhance the magnetostriction of the aged Fe81Ga19 polycrystalline alloys to~305 ppm,which is close to the level of single crystals.Although vacancies were found to facilitate the generation of the L60 phase,their impact on the precipitation mechanism and kinetics has yet to be revealed.This study combined transmission electron microscopy(TEM)and time-resolved small-angle neutron scattering(SANS)to investigate the precipitation of the L60 phase during the isothermal aging at 350 and 400℃,respectively.The evolution of L60 nanophase in morphology and number density in as-cast(AC)and liquid nitrogen quenched(LN)Fe81Ga19 alloys with aging time were quantitatively compared.Interestingly,the nucleation of the L60 phase proceeds progressively in AC while suddenly in LN specimens,indicating the homogenous to heterogeneous mechanism switching in-duced by concentrated vacancies.Moreover,excess vacancies can change the shape of nanoprecipitates and significantly accelerate the growth and coarsening kinetics.The magnetostrictive coefficient is opti-mized when the size(long-axis)of L60 precipitates lies between 100 and 110Åwith a number density between 3.2-4.3×10-7Å-3.Insight from this study validates the feasibility of achieving high magnetoe-lastic properties through precise manipulation of the nanostructure.展开更多
Dissolution kinetics of CaO·2Al_(2)O_(3)(CA_(2))particles in a synthetic CaO-Al_(2)O_(3)-SiO_(2)steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope.Effects...Dissolution kinetics of CaO·2Al_(2)O_(3)(CA_(2))particles in a synthetic CaO-Al_(2)O_(3)-SiO_(2)steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope.Effects of temperature(i.e.,1500,1550,and 1600℃)and slag composition on the dissolution time of CA_(2)particles are investigated,along with the time dependency of the projection area of the particle during the dissolution process.It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity.Moreover,a higher ratio of CaO/Al_(2)O_(3)(C/A)leads to an increased dissolution rate of CA_(2)particle at 1600℃.Thermodynamic calculations suggested the dissolution product,i.e.,melilite,formed on the surface of the CA_(2)particle during dissolution in slag with a C/A ratio of 3.8 at 1550℃.Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA_(2)particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA_(2)particle.The formation of this layer during the dissolution process was identified as a hindrance,impeding the dissolution of CA_(2)particle.A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided,especially using calcium treatment during the secondary refining process.展开更多
Replacing solid carbon with hydrogen gas in ferromanganese production presents a forward-thinking,sustainable solution to re-ducing the ferro-alloy industry’s carbon emissions.The HAlMan process,a groundbreaking and ...Replacing solid carbon with hydrogen gas in ferromanganese production presents a forward-thinking,sustainable solution to re-ducing the ferro-alloy industry’s carbon emissions.The HAlMan process,a groundbreaking and eco-friendly method,has been meticu-lously researched and scaled up from laboratory experiments to pilot tests,aiming to drastically cut CO_(2) emissions associated with ferro-manganese production.This innovative process could potentially reduce CO_(2) emissions by about 1.5 tonnes for every tonne of ferroman-ganese produced.In this study,a lab-scale vertical thermogravimetric furnace was used to carry out the pre-reduction of Nchwaning man-ganese ore,where direct reduction occurred with H_(2) gas under controlled isothermal conditions at 700,800,and 900℃.The results indic-ated that higher pre-reduction temperatures(800 and 900℃)effectively converted Fe_(2)O_(3) to metallic iron and Mn_(2)O_(3) to MnO.By continu-ously monitoring the mass changes during the reduction,both the rate and extent of reduction were assessed.A second-order reaction model was applied to validate the experimental outcomes of H_(2) reduction at various temperatures,showing apparent activation energies of 29.79 kJ/mol for dried ore and 61.71 kJ/mol for pre-calcined ore.The reduction kinetics displayed a strong dependence on temperature,with higher temperatures leading to quicker and more complete reductions.The kinetics analysis suggested that the chemical reaction at the gas-solid interface between hydrogen and the manganese ore is likely the rate-limiting step in this process.展开更多
Selecting the embryo with the highest implantation potential is a top priority in in-vitro fertilization(IVF)centers.Few studies have explored the relationship between day 5 blastocyst morphokinetics and implantation ...Selecting the embryo with the highest implantation potential is a top priority in in-vitro fertilization(IVF)centers.Few studies have explored the relationship between day 5 blastocyst morphokinetics and implantation outcomes[1].Despite numerous time-lapse studies,the findings often conflict due to differences in patient demographics,lab conditions,and protocols,such as oxygen concentration[2].Thus,there is ongoing debate regarding which parameters are most predictive of implantation.展开更多
In this context,the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate(Sr(OH)_(2)·8H_(2)O)without introducing contaminants.Th...In this context,the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate(Sr(OH)_(2)·8H_(2)O)without introducing contaminants.This study revealed that the use of microwave irradiation to dehydrate Sr(OH)_(2)·8H_(2)O is feasible and surprisingly efficient.The effects of this approach on important parameters were investigated using response surface methodology(RSM).The results revealed that the microwave dehydration process follows a linear polynomial model.In addition,compared with the heating time and material thickness,the microwave-assisted dehydration of Sr(OH)_(2)·8H_(2)O is sensitive to the microwave power and not to the material mass.The relative dehydration percentage reached 99.99%when heated in a microwave oven at 950Wfor just 3 min.In contrast,a relative dehydration percentage of 94.6%was reached when heated in an electric furnace at 180℃for 120 min.The XRD spectra also revealed that most of the Sr(OH)_(2)·8H_(2)O transformed into Sr(OH)_(2)after dehydration via microwave irradiation,whereas a significant portion of the Sr(OH)_(2)·H_(2)O remained after conventional electric dehydration.The experimental data were fitted and analyzed via the thin-layer drying dynamics model,and the results indicated that the dehydrating behavior of Sr(OH)_(2)·8H_(2)O could be well described by the Page model.展开更多
The adsorption kinetics of polystyrene[1-butyl-3-methylimidazolium][bis(2,4,4-trimethylpentyl)phosphinate](PS[C_(4)mim][C272])towards V(V)in acidic leachate was explored under ultrasound.The effects of ultrasonic powe...The adsorption kinetics of polystyrene[1-butyl-3-methylimidazolium][bis(2,4,4-trimethylpentyl)phosphinate](PS[C_(4)mim][C272])towards V(V)in acidic leachate was explored under ultrasound.The effects of ultrasonic power and V(V)concentration on the adsorption performance of PS[C_(4)mim][C272]were investigated.The results showed that ultrasonic radiation significantly shortened the adsorption equilibrium time and improved the adsorption performance of PS[C_(4)mim][C272]compared with the conventional oscillation.At an ultrasonic power of 200 W,the equilibrium adsorption capacity of PS[C_(4)mim][C272]reached its maximum of 311.58 mg/g.The kinetic model fitting results showed that the adsorption process of PS[C_(4)mim][C272]strictly followed the pseudo-second-order kinetic model under ultrasound.Analysis using the shrinking core model and the Weber−Morris model showed that the adsorption process of PS[C_(4)mim][C272]was primarily controlled by intra-particle diffusion mechanism.The adsorption isotherm model study showed that the Langmuir isotherm model could effectively fit the adsorption process of PS[C_(4)mim][C272]under ultrasound.展开更多
The sulfation and decomposition process has proven effective in selectively extracting lithium from lepidolite.It is essential to clarify the thermochemical behavior and kinetic parameters of decomposition reactions.A...The sulfation and decomposition process has proven effective in selectively extracting lithium from lepidolite.It is essential to clarify the thermochemical behavior and kinetic parameters of decomposition reactions.Accordingly,comprehensive kinetic study by employing thermalgravimetric analysis at various heating rates was presented in this paper.Two main weight loss regions were observed during heating.The initial region corresponded to the dehydration of crystal water,whereas the subsequent region with overlapping peaks involved complex decomposition reactions.The overlapping peaks were separated into two individual reaction peaks and the activation energy of each peak was calculated using isoconversional kinetics methods.The activation energy of peak 1 exhibited a continual increase as the reaction conversion progressed,while that of peak 2 steadily decreased.The optimal kinetic models,identified as belonging to the random nucleation and subsequent growth category,provided valuable insights into the mechanism of the decomposition reactions.Furthermore,the adjustment factor was introduced to reconstruct the kinetic mechanism models,and the reconstructed models described the kinetic mechanism model more accurately for the decomposition reactions.This study enhanced the understanding of the thermochemical behavior and kinetic parameters of the lepidolite sulfation product decomposition reactions,further providing theoretical basis for promoting the selective extraction of lithium.展开更多
BACKGROUND Gastrointestinal endoscopy technology has significantly improved the diagnostic accuracy and the successful treatment of gastrointestinal diseases.However,a series of ethical issues have emerged,such as exp...BACKGROUND Gastrointestinal endoscopy technology has significantly improved the diagnostic accuracy and the successful treatment of gastrointestinal diseases.However,a series of ethical issues have emerged,such as expanding treatment indications,which affect the fair distribution of medical resources.There is limited research on ethical issues in the field of digestive endoscopy.AIM To investigate the level of ethical awareness among gastrointestinal endoscopy practitioners and analyze the ethical issues involved in gastrointestinal endoscopy technology.METHODS A questionnaire survey was performed to collect relevant data(gender,age,degree of education,professional title,personnel category,the level of understanding medical ethical principles,ethics training and its learning pathways)from gastrointestinal endoscopy practitioners at the Second Hospital of Dalian Medical University and Dalian Friendship Hospital,including licensed physicians and nurses(including trainees and graduate students).RESULTS The majority of gastrointestinal endoscopy practitioners have received training on ethics,but there is still considerable room for improvement in their ethical awareness.Different learning pathways may affect the mastery of ethical principles, and understanding of ethical principles is more easily achieved through hospital ethics institutions.CONCLUSIONTo address the ethical issues in gastrointestinal endoscopy technology, it is necessary to enhance the humanisticeducation of gastrointestinal endoscopy practitioners, incorporate ethical standards into the technology assessmentprocess, and establish a patient-centered diagnostic and treatment model to improve the ethical awareness of practitionersand achieve a balance between technology and ethics.展开更多
[Objective] The kinetic characteristics of alliinase was studied to select the optimum reaction performance. [Method] Alliinase activity was measured to analysis the influence of temperature, pH, substrate concentrati...[Objective] The kinetic characteristics of alliinase was studied to select the optimum reaction performance. [Method] Alliinase activity was measured to analysis the influence of temperature, pH, substrate concentration and metal iron. [Result] Alliinase was an enzyme with thermal instability. Its optimum reaction temperature was 29℃ and pH value was 6.1. The Vmax was 0. 439 IU/mg and Km was 0.483 mmol/L by using natural extract as substrate. Alliinase activity was activated when the K^＋ , Mg^2＋ , Na^＋ and Cd^2＋ existed and alliinase activity was inhibited when Cu^2＋ existed. [Condusion] Results showed that the kinetic characteristics of alliinase supply the academic foundation for development and application of garlic medical products.展开更多
Thermogravimetry(TG)analysis was applied for the pyrolysis of activated carbon from pistachio shell in a nitrogen atmosphere by physical activation and chemical activation using carbon dioxide and H3PO4.The kinetic st...Thermogravimetry(TG)analysis was applied for the pyrolysis of activated carbon from pistachio shell in a nitrogen atmosphere by physical activation and chemical activation using carbon dioxide and H3PO4.The kinetic study was accomplished using TG curves based on weight loss as a function of temperature.TG experiments were performed under nitrogen atmosphere(100 ML/min)and a linear heating rate of 20℃/min up to 850℃.Differential thermogravimetric(DTG)data were analyzed using an Arrhenius type reaction model assuming a first-order reaction.Kinetic parameters including activation energy,Ea,and pre-exponential factor,A,for this activated carbon was determined.The activation energy(E,,=172.25 k J/tool)and maximum rate temperature(Rt=670℃)were approximately in the ranges of Ea values from previous studies using types of activated carbon with values between 100-300 kJ/mol.The thermodynamic parameters of activation,△Gc=220.51 kJ/mol,△Hf=164.42 kJ/mol and△Sc=-59.48 J/tool K,were obtained.These quantities indicated the obtained activated carbon from pistachio shell is stable but the rate of the pyrolysis is slow at low temperatures.展开更多
The elementary reactions of propylene polymerization catalyzed by conventional Ziegler-Natta catalysts was proposed according to the comprehensive view and without considering the effect of any impurity in the materia...The elementary reactions of propylene polymerization catalyzed by conventional Ziegler-Natta catalysts was proposed according to the comprehensive view and without considering the effect of any impurity in the material on propylene polymerization. The Monte Carlo simulation technique was employed to investigate the kinetics of propylene polymerization in order to determine the validity of the stationary state assumption and the effects of the polymerization temperature on the polymerization. The simulated total amount of active species, which only increases quickly at the beginning of the polymerization, indicates that the stationary state assumption in the studied system is valid. Moreover, significant effects of polymerization temperature on the polymerization conversion, and the molecular weight and its distribution were also analyzed. The simulated results show that the consumption rate of propylene increases with the increase of polymerization temperature; the maximum values of the number-average degree of polymerization are constant at different polymerization temperatures, however, the peak appears earlier with the higher temperature; as the polymerization temperature increases, the average molecular weight decreases and the molecular weight distribution changes greatly.展开更多
Biapenem, a new parenteral carbapenem, has been widely used for treating bacterial infections. A simple, effective and accurate method based on solid-phase extraction （SPE） and HPLC was developed for the quantitativ...Biapenem, a new parenteral carbapenem, has been widely used for treating bacterial infections. A simple, effective and accurate method based on solid-phase extraction （SPE） and HPLC was developed for the quantitative determination of biapenem in human plasma. Stability and feasibility of the method was validated through a series of experiments. Using Vitamin B6 as an internal standard, analyte was separated on a Capcell Pak C18 column after SPE on Oasis hydrophilic-lipophilic balance （HLB） cartridge. The mobile phase was comprised of 0.05 mol/L NaH2PO4 （pH 5.7） and methanol （98：2, v/v） at a flow rate of 1.0 mL/min. Ultraviolet absorbance was measured at 300 nm. The calibration curve was linear in the concentration range of 0.04-50.00 μg/mL, and the lower limit of quantification was as low as 0.04 μg/mL. Recovery rates of biapenem at 0.10, 5.00, and 25.00 μg/mL were about 70%. The validated method has been successfully applied for quantifying biapenem in human samples and a pharmacokinetic study of 12 healthy volunteers who received three different doses （150, 300 and 600 mg） of biapenem by intravenous infusion. Our method has featured good accuracy and precision, and the processed sample was stable. Therefore, it can be propagated for clinical use.展开更多
The catalytic reduction of nitric oxide by carbon monoxide over cobalt tetraphenylporphyrin supported on titanium dioxide (Co-TPP/TiO2) has been investigated. Co-TPP/TiO2 pretreated by evacuation at 270℃ exhibited a ...The catalytic reduction of nitric oxide by carbon monoxide over cobalt tetraphenylporphyrin supported on titanium dioxide (Co-TPP/TiO2) has been investigated. Co-TPP/TiO2 pretreated by evacuation at 270℃ exhibited a remarkable activity. The kinetic equation for the reduction of nitric oxide by carbon monoxide in the reaction temperature ranging from 80 to 150℃ (v=kPNO 0.56Pco 0.41) suggested that the reaction can be assumed to occur via a surface reaction of the Langmuir-Hinshelwood model between nitric oxide and carbon monoxide adsorbed on the central metal ion of Co-TPP. Experimental results indicated that the reduction of nitric oxide and formation of molecular nitrogen took place simultaneously during initial stage of the reaction. The apparent activation energy was calculated to be 30.8 kJ/mol.展开更多
Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potential...Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V （vs. RHE） with the exchange current density of ca. 50 mA/cm^2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kineticor kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed （〉800 r/min） and slow potential scan rate （〈100 mV/s）. The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt（111） the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad＋H^＋＋e→←H2O.展开更多
In this study,a novel hydrometallurgical process consisting of hydrochloric acid three-stage countercurrent leaching and solvent extraction was proposed to recover rare earth oxide(REO)from the rare earth polishing po...In this study,a novel hydrometallurgical process consisting of hydrochloric acid three-stage countercurrent leaching and solvent extraction was proposed to recover rare earth oxide(REO)from the rare earth polishing powder waste(REPPW).The effects of HCl concentration,liquid-solid ratio(L/S ratio),temperature and time on the leaching yields of rare earths(in REO)and aluminum(in Al2O3)were studied.The result shows that the leaching yields of REO and Al2O3 are 90.96%and 43.89%respectively under the optimum leaching parameters of HCl concentration=8.00 mol/L,L/S ratio=4 mL/g,leaching temperature=353 K and leaching time=180 min.Meanwhile,the leaching kinetics of REO and Al2O3 were investigated in this study.The leaching behaviors of REO and Al2O3 follow a shrinking sphere/core model and the general leaching process is controlled by the surface chemical reaction.The leaching activation energies of REO and Al2O3 are 9.86 and 13.68 kJ/mol,respectively.The leaching yield of each substance in three-stage countercurrent leaching is improved substantially compared with single-stage leaching,with a change from 90.96%to 95.38%for REO and from 43.89%to 46.22%for Al2O3,respectively.Especially,the total concentration of REO in three-stage countercurrent leaching solution is greatly increased to above 300 g/L,and the acidity of which is decreased to ca.pH=2,which is conducive to subsequent solvent extraction directly.High purity REO(99.92%)is obtained by solvent extraction separation,oxalate precipitation and calcination.The total recovery yield of REO is 85.13%.展开更多
基金supported by the Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.IGGCAS-201903).
文摘Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.
基金sponsored by the Major Science and Technology Special Plan“Unveiling and Leading”Project of Shanxi Province(No.202201050201011)Major Science and Technology Projects of Anhui Province(No.202210700037)Special Funding for Science and Technology of China Minmetals Corporation(No.2021ZXD01).
文摘Eggshells,a by-product of the food industry,represent a significant yet often overlooked waste stream.Given their vast production volume and inherent properties,eggshells have the potential to serve as a sustainable and environmentally friendly co-fuel.Aiming to explore the co-combustion characteristics and kinetics of pulverized coal blended with eggshells and offer insights into their combined use as a renewable energy source,a systematic investigation was conducted to evaluate the physical and chemical properties of Shangwan bituminous coal,Shouyang anthracite coal,eggshell(ES)and their blends.Additionally,comprehensive experimental analyses were performed at different heating rates applying a non-isothermal thermogravimetric method.The findings revealed that the addition of ES enhanced the combustion efficiency.The combustion characteristics were significantly influenced by the ES content,with an optimal blend ratio identified for maximum combustion efficiency.To represent the thermal degradation experiments,random pore model and volume model were employed.Furthermore,activation energies and pre-exponential factors were determined.The random pore model demonstrated more superior performance compared to the volume model.The activation energies of all the samples ranged between 18.29 and 42.48 kJ/mol,with the lowest value observed for the sample containing 20 mass%ES.
基金support by the Basic Science Center Program of the Ordered Energy Conversion of the National Nature Science Foundation of China(NO.52488201)is gratefully acknowledged.
文摘Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products.In this paper,the classical segmented pyrolysis kinetics model and a new refined pyrolysis kinetics model were used to forecast the composition distribution of hydrocarbon generation products co-heated by supercritical water and medium and low maturity organic-rich shale.The prediction accuracy of the two reaction kinetics models for the composition of pyrolysis products of organic-rich shale was compared.The reaction path of hydrocarbon generation in centimeter sized organic-rich shale under the action of supercritical water was identified.The results show that the prediction accuracy of the classical segmented pyrolysis kinetics model was poor at the initial stage of the reaction,and gradually increased with increasing time.The prediction error can reach less than 25%when the reaction time was 12 h.The new refined model of reaction kinetics established is better than the classical reaction kinetics model in predicting the product distribution of pyrolysis oil and gas,and its prediction error is less than 14%in this paper.The reaction paths of hydrocarbon generation in centimeter sized organic-rich shale under supercritical water conversion mainly include organic-rich shale directly generates asphaltene and saturated hydrocarbon,asphaltene pyrolysis generates saturated hydrocarbon,aromatic hydrocarbon and resin,saturated hydrocarbon,aromatic hydrocarbon and resin polymerization generates asphaltene,and saturated hydrocarbon,resin and asphaltene generates gas.The reason for the difference of centimeter sized and millimeter sized medium and low maturity organic-rich shales hydrocarbon generation in supercritical water is that the increase of shale size promotes the reaction path of polymerization of saturated hydrocarbon and aromatic hydrocarbon to asphaltene.
基金supported by the Natural Science Foundation of Shanxi Province(Grant No.202203021221120)The Open Fund of MCRI-Shannxi Laboratory of Energetic Materials(Grant No.204-J-2024-2622)。
文摘This study prepared a class of RDX-based composite microspheres(RAF)containing ADN and FKM2602.The reaction kinetics of RAF composite microspheres were effectively improved by maintaining the system's high energy and safety performance.In the close packing state,when the heating rate is rapid,the thermal stability of RAF composite microspheres is better than that of RDX;the close packing state will reduce the degree of freedom of RDX and ADN reaction but will increase the degree of freedom of RAF composite microsphere reaction.The thermal conductivity of RAF composite microspheres is close to that of RDX.In the ignition experiment,the flame of RAF composite microspheres can be maintained without the external heat source.Regarding safety,the H50of RAF composite microspheres was 274.04%higher than that of RDX.The detonation velocity of RAF composite microspheres is slightly higher than that of raw material RDX.Overall,these findings highlight the effectiveness of ADN in enhancing the reaction kinetics of RDX-based composites.
基金financially supported by the Fundamental Research Project of Yunnan Province,China(Nos.202301AW070020,202201AT070229,202105AC160091,202202AB080018).
文摘The vacuum volatilization kinetics of Pb in In-Pb solder was investigated.The results indicate a significant increase in the vacuum volatilization rates of Pb,25In-75Pb,40In-60Pb,and In with increasing temperatures from 923 to 1123 K,system pressure of 3 Pa and holding time of 30 min.The mass transfer coefficients and apparent activation energies of Pb and its alloys were determined at various temperatures.Additionally,a kinetics model was developed to describe Pb vacuum volatilization in high-temperature melts.It is obtained that the vapor mass transfer is the factor limiting the vacuum volatilization rates of Pb and In-Pb alloys under the above specified conditions.
基金supported by the National Natural Science Foundation of China(Grant No.12275154)the Guangdong Basic and Applied Basic Research Foundation,China(Project No.2021B1515140028)+1 种基金the Youth Innovation Promotion Association,CAS(No.2020010)the National Key Research and Development Program of China,grant number(Nos.2021YFA1600701 and 2021YFB3501201).
文摘Solid-state precipitation is an effective strategy for tuning the mechanical and functional properties of ad-vanced alloys.Structure design and modification necessitate good knowledge of the kinetic evolution of precipitates during fabrication,which is strongly correlated with defect concentration.For Fe-Ga alloys,giant magnetostriction can be induced by the precipitation of the nanoscale tetragonal L60 phase.By introducing quenched-in vacancies,we significantly enhance the magnetostriction of the aged Fe81Ga19 polycrystalline alloys to~305 ppm,which is close to the level of single crystals.Although vacancies were found to facilitate the generation of the L60 phase,their impact on the precipitation mechanism and kinetics has yet to be revealed.This study combined transmission electron microscopy(TEM)and time-resolved small-angle neutron scattering(SANS)to investigate the precipitation of the L60 phase during the isothermal aging at 350 and 400℃,respectively.The evolution of L60 nanophase in morphology and number density in as-cast(AC)and liquid nitrogen quenched(LN)Fe81Ga19 alloys with aging time were quantitatively compared.Interestingly,the nucleation of the L60 phase proceeds progressively in AC while suddenly in LN specimens,indicating the homogenous to heterogeneous mechanism switching in-duced by concentrated vacancies.Moreover,excess vacancies can change the shape of nanoprecipitates and significantly accelerate the growth and coarsening kinetics.The magnetostrictive coefficient is opti-mized when the size(long-axis)of L60 precipitates lies between 100 and 110Åwith a number density between 3.2-4.3×10-7Å-3.Insight from this study validates the feasibility of achieving high magnetoe-lastic properties through precise manipulation of the nanostructure.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC)for funding this researchThis research used a high temperature confocal laser scanning microscope-VL2000DX-SVF17SP funded by Canada Foundation for Innovation John Evans Leaders Fund(CFI JELF,Project Number:32826),a PANalytical X’Pert diffraction instrument located at the Centre for crystal growth,Brockhouse Institute for Materials Research,and a scanning electron microscope-JEOL 6610 located at the Canadian Centre for Electron Microscopy at McMaster University.W.Mu would like to acknowledge Swedish Iron and Steel Research Office(Jernkonteret),STINT and SSF for supporting the time for international collaboration research regarding clean steel.
文摘Dissolution kinetics of CaO·2Al_(2)O_(3)(CA_(2))particles in a synthetic CaO-Al_(2)O_(3)-SiO_(2)steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope.Effects of temperature(i.e.,1500,1550,and 1600℃)and slag composition on the dissolution time of CA_(2)particles are investigated,along with the time dependency of the projection area of the particle during the dissolution process.It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity.Moreover,a higher ratio of CaO/Al_(2)O_(3)(C/A)leads to an increased dissolution rate of CA_(2)particle at 1600℃.Thermodynamic calculations suggested the dissolution product,i.e.,melilite,formed on the surface of the CA_(2)particle during dissolution in slag with a C/A ratio of 3.8 at 1550℃.Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA_(2)particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA_(2)particle.The formation of this layer during the dissolution process was identified as a hindrance,impeding the dissolution of CA_(2)particle.A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided,especially using calcium treatment during the secondary refining process.
基金the financial support from European Union’s Horizon Europe program HAlMan project (No. 101091936)
文摘Replacing solid carbon with hydrogen gas in ferromanganese production presents a forward-thinking,sustainable solution to re-ducing the ferro-alloy industry’s carbon emissions.The HAlMan process,a groundbreaking and eco-friendly method,has been meticu-lously researched and scaled up from laboratory experiments to pilot tests,aiming to drastically cut CO_(2) emissions associated with ferro-manganese production.This innovative process could potentially reduce CO_(2) emissions by about 1.5 tonnes for every tonne of ferroman-ganese produced.In this study,a lab-scale vertical thermogravimetric furnace was used to carry out the pre-reduction of Nchwaning man-ganese ore,where direct reduction occurred with H_(2) gas under controlled isothermal conditions at 700,800,and 900℃.The results indic-ated that higher pre-reduction temperatures(800 and 900℃)effectively converted Fe_(2)O_(3) to metallic iron and Mn_(2)O_(3) to MnO.By continu-ously monitoring the mass changes during the reduction,both the rate and extent of reduction were assessed.A second-order reaction model was applied to validate the experimental outcomes of H_(2) reduction at various temperatures,showing apparent activation energies of 29.79 kJ/mol for dried ore and 61.71 kJ/mol for pre-calcined ore.The reduction kinetics displayed a strong dependence on temperature,with higher temperatures leading to quicker and more complete reductions.The kinetics analysis suggested that the chemical reaction at the gas-solid interface between hydrogen and the manganese ore is likely the rate-limiting step in this process.
文摘Selecting the embryo with the highest implantation potential is a top priority in in-vitro fertilization(IVF)centers.Few studies have explored the relationship between day 5 blastocyst morphokinetics and implantation outcomes[1].Despite numerous time-lapse studies,the findings often conflict due to differences in patient demographics,lab conditions,and protocols,such as oxygen concentration[2].Thus,there is ongoing debate regarding which parameters are most predictive of implantation.
基金supported by the Research Program of the Science and Technology Department of Guizhou Province(Qiankehe Jichu[2019]1418)the Research Program of Talented Scholars of Guizhou Institute of Technology(XJGC20190965).
文摘In this context,the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate(Sr(OH)_(2)·8H_(2)O)without introducing contaminants.This study revealed that the use of microwave irradiation to dehydrate Sr(OH)_(2)·8H_(2)O is feasible and surprisingly efficient.The effects of this approach on important parameters were investigated using response surface methodology(RSM).The results revealed that the microwave dehydration process follows a linear polynomial model.In addition,compared with the heating time and material thickness,the microwave-assisted dehydration of Sr(OH)_(2)·8H_(2)O is sensitive to the microwave power and not to the material mass.The relative dehydration percentage reached 99.99%when heated in a microwave oven at 950Wfor just 3 min.In contrast,a relative dehydration percentage of 94.6%was reached when heated in an electric furnace at 180℃for 120 min.The XRD spectra also revealed that most of the Sr(OH)_(2)·8H_(2)O transformed into Sr(OH)_(2)after dehydration via microwave irradiation,whereas a significant portion of the Sr(OH)_(2)·H_(2)O remained after conventional electric dehydration.The experimental data were fitted and analyzed via the thin-layer drying dynamics model,and the results indicated that the dehydrating behavior of Sr(OH)_(2)·8H_(2)O could be well described by the Page model.
基金financially supported by the National Natural Science Foundation of China(No.52074204)Key R&D Program of Zhejiang Province,China(No.2022C03061)。
文摘The adsorption kinetics of polystyrene[1-butyl-3-methylimidazolium][bis(2,4,4-trimethylpentyl)phosphinate](PS[C_(4)mim][C272])towards V(V)in acidic leachate was explored under ultrasound.The effects of ultrasonic power and V(V)concentration on the adsorption performance of PS[C_(4)mim][C272]were investigated.The results showed that ultrasonic radiation significantly shortened the adsorption equilibrium time and improved the adsorption performance of PS[C_(4)mim][C272]compared with the conventional oscillation.At an ultrasonic power of 200 W,the equilibrium adsorption capacity of PS[C_(4)mim][C272]reached its maximum of 311.58 mg/g.The kinetic model fitting results showed that the adsorption process of PS[C_(4)mim][C272]strictly followed the pseudo-second-order kinetic model under ultrasound.Analysis using the shrinking core model and the Weber−Morris model showed that the adsorption process of PS[C_(4)mim][C272]was primarily controlled by intra-particle diffusion mechanism.The adsorption isotherm model study showed that the Langmuir isotherm model could effectively fit the adsorption process of PS[C_(4)mim][C272]under ultrasound.
基金financially supported by the National Natural Science Foundation of China(Nos.52034002 and U2202254)the Fundamental Research Funds for the Central Universities,China(No.FRF-TT-19-001)。
文摘The sulfation and decomposition process has proven effective in selectively extracting lithium from lepidolite.It is essential to clarify the thermochemical behavior and kinetic parameters of decomposition reactions.Accordingly,comprehensive kinetic study by employing thermalgravimetric analysis at various heating rates was presented in this paper.Two main weight loss regions were observed during heating.The initial region corresponded to the dehydration of crystal water,whereas the subsequent region with overlapping peaks involved complex decomposition reactions.The overlapping peaks were separated into two individual reaction peaks and the activation energy of each peak was calculated using isoconversional kinetics methods.The activation energy of peak 1 exhibited a continual increase as the reaction conversion progressed,while that of peak 2 steadily decreased.The optimal kinetic models,identified as belonging to the random nucleation and subsequent growth category,provided valuable insights into the mechanism of the decomposition reactions.Furthermore,the adjustment factor was introduced to reconstruct the kinetic mechanism models,and the reconstructed models described the kinetic mechanism model more accurately for the decomposition reactions.This study enhanced the understanding of the thermochemical behavior and kinetic parameters of the lepidolite sulfation product decomposition reactions,further providing theoretical basis for promoting the selective extraction of lithium.
文摘BACKGROUND Gastrointestinal endoscopy technology has significantly improved the diagnostic accuracy and the successful treatment of gastrointestinal diseases.However,a series of ethical issues have emerged,such as expanding treatment indications,which affect the fair distribution of medical resources.There is limited research on ethical issues in the field of digestive endoscopy.AIM To investigate the level of ethical awareness among gastrointestinal endoscopy practitioners and analyze the ethical issues involved in gastrointestinal endoscopy technology.METHODS A questionnaire survey was performed to collect relevant data(gender,age,degree of education,professional title,personnel category,the level of understanding medical ethical principles,ethics training and its learning pathways)from gastrointestinal endoscopy practitioners at the Second Hospital of Dalian Medical University and Dalian Friendship Hospital,including licensed physicians and nurses(including trainees and graduate students).RESULTS The majority of gastrointestinal endoscopy practitioners have received training on ethics,but there is still considerable room for improvement in their ethical awareness.Different learning pathways may affect the mastery of ethical principles, and understanding of ethical principles is more easily achieved through hospital ethics institutions.CONCLUSIONTo address the ethical issues in gastrointestinal endoscopy technology, it is necessary to enhance the humanisticeducation of gastrointestinal endoscopy practitioners, incorporate ethical standards into the technology assessmentprocess, and establish a patient-centered diagnostic and treatment model to improve the ethical awareness of practitionersand achieve a balance between technology and ethics.
基金Supported by the Natural Science Foundation Program of Tianjin Science Committee(043611111)the Science and Technology Develop-ment Foundation Programof Tianjin Colleges and Universities(20050901)~~
文摘[Objective] The kinetic characteristics of alliinase was studied to select the optimum reaction performance. [Method] Alliinase activity was measured to analysis the influence of temperature, pH, substrate concentration and metal iron. [Result] Alliinase was an enzyme with thermal instability. Its optimum reaction temperature was 29℃ and pH value was 6.1. The Vmax was 0. 439 IU/mg and Km was 0.483 mmol/L by using natural extract as substrate. Alliinase activity was activated when the K^＋ , Mg^2＋ , Na^＋ and Cd^2＋ existed and alliinase activity was inhibited when Cu^2＋ existed. [Condusion] Results showed that the kinetic characteristics of alliinase supply the academic foundation for development and application of garlic medical products.
文摘Thermogravimetry(TG)analysis was applied for the pyrolysis of activated carbon from pistachio shell in a nitrogen atmosphere by physical activation and chemical activation using carbon dioxide and H3PO4.The kinetic study was accomplished using TG curves based on weight loss as a function of temperature.TG experiments were performed under nitrogen atmosphere(100 ML/min)and a linear heating rate of 20℃/min up to 850℃.Differential thermogravimetric(DTG)data were analyzed using an Arrhenius type reaction model assuming a first-order reaction.Kinetic parameters including activation energy,Ea,and pre-exponential factor,A,for this activated carbon was determined.The activation energy(E,,=172.25 k J/tool)and maximum rate temperature(Rt=670℃)were approximately in the ranges of Ea values from previous studies using types of activated carbon with values between 100-300 kJ/mol.The thermodynamic parameters of activation,△Gc=220.51 kJ/mol,△Hf=164.42 kJ/mol and△Sc=-59.48 J/tool K,were obtained.These quantities indicated the obtained activated carbon from pistachio shell is stable but the rate of the pyrolysis is slow at low temperatures.
基金The National Natural Science Foundation of China(No.20406016)the Project of Fujian Petrochemical Company of SIN-OPEC (No.MS/FJ-08-JS-15-2005-01).
文摘The elementary reactions of propylene polymerization catalyzed by conventional Ziegler-Natta catalysts was proposed according to the comprehensive view and without considering the effect of any impurity in the material on propylene polymerization. The Monte Carlo simulation technique was employed to investigate the kinetics of propylene polymerization in order to determine the validity of the stationary state assumption and the effects of the polymerization temperature on the polymerization. The simulated total amount of active species, which only increases quickly at the beginning of the polymerization, indicates that the stationary state assumption in the studied system is valid. Moreover, significant effects of polymerization temperature on the polymerization conversion, and the molecular weight and its distribution were also analyzed. The simulated results show that the consumption rate of propylene increases with the increase of polymerization temperature; the maximum values of the number-average degree of polymerization are constant at different polymerization temperatures, however, the peak appears earlier with the higher temperature; as the polymerization temperature increases, the average molecular weight decreases and the molecular weight distribution changes greatly.
基金National Natural Science Foundation of China (Grant No.30973597)
文摘Biapenem, a new parenteral carbapenem, has been widely used for treating bacterial infections. A simple, effective and accurate method based on solid-phase extraction （SPE） and HPLC was developed for the quantitative determination of biapenem in human plasma. Stability and feasibility of the method was validated through a series of experiments. Using Vitamin B6 as an internal standard, analyte was separated on a Capcell Pak C18 column after SPE on Oasis hydrophilic-lipophilic balance （HLB） cartridge. The mobile phase was comprised of 0.05 mol/L NaH2PO4 （pH 5.7） and methanol （98：2, v/v） at a flow rate of 1.0 mL/min. Ultraviolet absorbance was measured at 300 nm. The calibration curve was linear in the concentration range of 0.04-50.00 μg/mL, and the lower limit of quantification was as low as 0.04 μg/mL. Recovery rates of biapenem at 0.10, 5.00, and 25.00 μg/mL were about 70%. The validated method has been successfully applied for quantifying biapenem in human samples and a pharmacokinetic study of 12 healthy volunteers who received three different doses （150, 300 and 600 mg） of biapenem by intravenous infusion. Our method has featured good accuracy and precision, and the processed sample was stable. Therefore, it can be propagated for clinical use.
基金This work was supported by National Science Foundation of China.
文摘The catalytic reduction of nitric oxide by carbon monoxide over cobalt tetraphenylporphyrin supported on titanium dioxide (Co-TPP/TiO2) has been investigated. Co-TPP/TiO2 pretreated by evacuation at 270℃ exhibited a remarkable activity. The kinetic equation for the reduction of nitric oxide by carbon monoxide in the reaction temperature ranging from 80 to 150℃ (v=kPNO 0.56Pco 0.41) suggested that the reaction can be assumed to occur via a surface reaction of the Langmuir-Hinshelwood model between nitric oxide and carbon monoxide adsorbed on the central metal ion of Co-TPP. Experimental results indicated that the reduction of nitric oxide and formation of molecular nitrogen took place simultaneously during initial stage of the reaction. The apparent activation energy was calculated to be 30.8 kJ/mol.
基金V. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.20773116）, the National Instrumentation Program （No.2011YQ03012416）, and 973 Program from the Ministry of Science and Technology of China （No.2010CB923302）.
文摘Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V （vs. RHE） with the exchange current density of ca. 50 mA/cm^2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kineticor kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed （〉800 r/min） and slow potential scan rate （〈100 mV/s）. The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt（111） the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad＋H^＋＋e→←H2O.
基金Project supported by National High-tech Research and Development Program(2017AA031002)。
文摘In this study,a novel hydrometallurgical process consisting of hydrochloric acid three-stage countercurrent leaching and solvent extraction was proposed to recover rare earth oxide(REO)from the rare earth polishing powder waste(REPPW).The effects of HCl concentration,liquid-solid ratio(L/S ratio),temperature and time on the leaching yields of rare earths(in REO)and aluminum(in Al2O3)were studied.The result shows that the leaching yields of REO and Al2O3 are 90.96%and 43.89%respectively under the optimum leaching parameters of HCl concentration=8.00 mol/L,L/S ratio=4 mL/g,leaching temperature=353 K and leaching time=180 min.Meanwhile,the leaching kinetics of REO and Al2O3 were investigated in this study.The leaching behaviors of REO and Al2O3 follow a shrinking sphere/core model and the general leaching process is controlled by the surface chemical reaction.The leaching activation energies of REO and Al2O3 are 9.86 and 13.68 kJ/mol,respectively.The leaching yield of each substance in three-stage countercurrent leaching is improved substantially compared with single-stage leaching,with a change from 90.96%to 95.38%for REO and from 43.89%to 46.22%for Al2O3,respectively.Especially,the total concentration of REO in three-stage countercurrent leaching solution is greatly increased to above 300 g/L,and the acidity of which is decreased to ca.pH=2,which is conducive to subsequent solvent extraction directly.High purity REO(99.92%)is obtained by solvent extraction separation,oxalate precipitation and calcination.The total recovery yield of REO is 85.13%.
