Kinetics analysis of decomposition of vanadium slag by KOH sub-molten salt method

A novel process was developed for the decomposition of vanadium slag using KOH sub-molten salt under ambient pressure, and the effects of reaction temperature, alkali-to-ore mass ratios, particle size, and stirring speed on vanadium and chromium extraction were studied. The results suggest that the reaction temperature and KOH-to-ore mass ratio are more influential factors for the extraction of vanadium and chromium. Under the optimal reaction conditions （temperature 180 °C, initial KOH-to-ore mass ratio 4：1, stirring speed 700 r/min, gas flow 1 L/min, and reaction time 300 min）, vanadium and chromium extraction rates can reach up to 95% and 90%, respectively. Kinetics analysis results show that the decomposing process of vanadium slag in KOH sub-molten salt can be well interpreted by the shrinking core model under internal diffusion control. The apparent activation energies for vanadium and chromium are 40.54 and 50.27 kJ/mol, respectively.

Non-isothermal thermal decomposition kinetics of high iron gibbsite ore based on Popescu method

The thermal decomposition kinetics of high iron gibbsite ore was investigated under non-isothermal conditions.Popescu method was applied to analyzing the thermal decomposition mechanism.The results show that the most probable thermal decomposition mechanism is the three-dimensional diffusion model of Jander equation,and the mechanism code is D3.The activation energy and pre-exponential factor for thermal decomposition of high iron gibbsite ore calculated by the Popescu method are 75.36 kJ/mol and 1.51×10-5 s-（-1）,respectively.The correctness of the obtained mechanism function is validated by the activation energy acquired by the iso-conversional method.Popescu method is a rational and reliable method for the analysis of the thermal decomposition mechanism of high iron gibbsite ore.

Kinetic method for enzymatic analysis by predicting background with uricase reaction as model

Objective：To investigate the reliability for kinetic assay of substance with background predicted by the integrated method using uricase reaction as model. Methods： Absorbance before uricase action （Δ0） was estimated by extrapolation with given lag time of steady-state reaction. With Km fixed at 12.5μmol/L, background absorbance （Δb） was predicted by nonlinearly fitting integrated Michaelis-Menten equation to Candida utilis uricase reaction curve. Uric acid in reaction solution was determined by the difference （ΔA） between Δ0 and Δb. Results .Ab usually showed deviation 〈3% from direct assay with residual substrate done fifth of initial substrate for analysis. ΔA showed CV 〈5% with resistance to common interferences except xanthine, and it linearly responded to uric acid with slope consistent to the absorptivity of uric acid. The lower limit was 2.0 μmol/L and upper limit reached 30 μmol/L in reaction solution with data monitored within 8 min reaction at 0. 015 U/ml uricase. Preliminary application to serum and urine gave better precision than the direct equilibrium method without the removal of proteins before analysis. Conclusion .This kinetic method with background predicted by the integrated method was reliable for enzymatic analysis, and it showed resistance to common interferences and enhanced efficiency at much lower cost.

Science Letters:Evaluation of a kinetic uricase method for serum uric acid assay by predicting background absorbance of uricase reaction solution with an integrated method

A patented kinetic uricase method was evaluated for serum uric acid assay. Initial absorbance of the reaction mixture before uricase action （A0） was obtained by correcting the absorbance at 293 nm measured before the addition of uricase solution, and background absorbance （Ab） was predicted by an integrated method. Uric acid concentration in reaction solution was calculated from AA, the difference between A0 and Ab, using the absorptivity preset for uric acid. This kinetic uricase method exhibited CV〈4.3% and recovery of 100%. Lipids, bilirubin, hemoglobin, ascorbic acid, reduced glutathione and xanthine 〈0.32 mmol/L in serum had no significant effects. △A linearly responded to 1.2 to 37.5 μmol/L uric acid in reaction solution containing 15 μl serum. The slope of linear response was consistent with the absorptivity preset for uric acid while the intercept was consistent with that for serum alone. Uric acid concentrations in clinic sera by different uricase methods positively correlated to each other. By Bland-Altman analysis, this kinetic uricase method accorded with that by quantifying the total change of UV absorbance on the completion of uricase reaction. These results demonstrated that this kinetic uricase method is reliable for serum uric acid assay with enhanced resistance to both xanthine and other common errors, wider range of linear response and much lower cost.

Effective point kinetic parameters calculation in Tehran research reactor using deterministic and probabilistic methods

The exact calculation of point kinetic parameters is very important in nuclear reactor safety assessment, and most sophisticated safety codes such as RELAP5, PARCS,DYN3D, and PARET are using these parameters in their dynamic models. These parameters include effective delayed neutron fractions as well as mean generation time.These parameters are adjoint-weighted, and adjoint flux is employed as a weighting function in their evaluation.Adjoint flux calculation is an easy task for most of deterministic codes, but its evaluation is cumbersome for Monte Carlo codes. However, in recent years, some sophisticated techniques have been proposed for Monte Carlo-based point kinetic parameters calculation without any need of adjoint flux. The most straightforward scheme is known as the ‘‘prompt method'' and has been used widely in literature. The main objective of this article is dedicated to point kinetic parameters calculation in Tehran research reactor(TRR) using deterministic as well as probabilistic techniques. WIMS-D5B and CITATION codes have been used in deterministic calculation of forward and adjoint fluxes in the TRR core. On the other hand, the MCNP Monte Carlo code has been employed in the ‘‘prompt method''scheme for effective delayed neutron fraction evaluation.Deterministic results have been cross-checked with probabilistic ones and validated with SAR and experimental data. In comparison with experimental results, the relativedifferences of deterministic as well as probabilistic methods are 7.6 and 3.2%, respectively. These quantities are10.7 and 6.4%, respectively, in comparison with SAR report.

Kinetics and Mechanism of Hydration of Acrylic Acid over Ion-exchanged Resin:Experimental Exploration and DFT Calculation

Liquid-phase acrylic acid hydration over solid-phase catalysts is a key reaction for the industrial productionof 3-hydroxypropionic acid. However, the relevant literature primarily focuses on the experimental aspects of catalystscreening and exploring reaction conditions, with few accurate descriptions of the reaction kinetics and determination ofthe reaction mechanism. Here, we combined kinetics experiments and theoretical calculations to elucidate the kinetics andmechanism of acrylic acid hydration on a resin catalyst. The pseudo-homogeneous model, and Langmuir-Hinshelwood-Haugen-Watson and Elie-Riedel (ER) heterogeneous models were used to explain the experimental kinetics data. TheER model can explain the experimental data very well, suggesting strong adsorption of acrylic acid on the surface of theresin catalyst. Furthermore, density functional theory calculations show that the hydration follows a stepwise, rather than aconcerted, reaction pathway. The present study provides theoretical insights into the reaction mechanism and kinetics, fillingthe gap in our understanding of the reaction on a fundamental level.

An Arbitrarily High Order and Asymptotic Preserving Kinetic Scheme in Compressible Fluid Dynamic

We present a class of arbitrarily high order fully explicit kinetic numerical methods in compressible fluid dynamics,both in time and space,which include the relaxation schemes by Jin and Xin.These methods can use the CFL number larger or equal to unity on regular Cartesian meshes for the multi-dimensional case.These kinetic models depend on a small parameter that can be seen as a"Knudsen"number.The method is asymptotic preserving in this Knudsen number.Also,the computational costs of the method are of the same order of a fully explicit scheme.This work is the extension of Abgrall et al.(2022)[3]to multidimensional systems.We have assessed our method on several problems for two-dimensional scalar problems and Euler equations and the scheme has proven to be robust and to achieve the theoretically predicted high order of accuracy on smooth solutions.

Mechanistic Study and Kinetic Determination of Cu(Ⅱ) by the Catalytic Kinetic Spectrophotometric Method

A highly sensitive and selective catalytic kinetic spectrophotometric method for the determination of Cu(Ⅱ) is proposed. It is based on the catalytic effect of Cu(Ⅱ) on the oxidation of glutathione(GSH) by potassium hexacyanoferrate(Ⅲ) in acidic medium at 25.0℃. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of oxidant at 420 nm using the fix-time method. Under the optimum conditions, the proposed method allows the determination of Cu(Ⅱ) in a range of 0-35.0 ng m L^(-1) with good precision and accuracy and the limit of detection is down to 0.04 ng m L^(-1). The relative standard deviation(RSD) is 1.02%. The reaction orders with respect to each reagent are found to be 1, 1/2, and 1/2 for potassium hexacyanoferrate(Ⅲ), glutathione and Cu(Ⅱ) respectively. On the basis of these values, the rate equation is obtained and the possible mechanism is established. Moreover, few anions and cations can interfere with the determination of Cu(Ⅱ). The new proposed method can be successfully used to the determination of Cu(Ⅱ) in fresh water samples and seawater samples. It is found that the proposed method has fairly good selectivity, high sensitivity, good repeatability, simplicity and rapidity.

Sub-Criticality Measurement with Source Term for Research Reactor in Inverse Kinetics Method

In reactor physics tests, it is important to monitor sub-criticality continuously during criticality approach. Reactivity measurements by the inverse kinetics method are widely used during the operation of a nuclear reactor. This technique is successfully applied at sufficiently high power level or to a core without an external neutron source where the neutron source term in point reactor kinetics equations may be neglected. For operation at low power levels or in the sub-critical domain, the increase in the fluctuation of the neutron signal may cause difficulties in the evaluation of reactivity and the effect of direct emission from the external neutron source may not be neglected. Therefore, contribution of the neutron source must be taken into account and this implies knowledge of a quantity proportional to the source strength, which calls the source term and then it should be determined. The research work has been conducted to measure reactivity with source term using a dedicated reactivity measurement system by the Least Square Inverse Kinetics Method (LSIKM). Application to a simulator of HANARO research reactor, Korea Atomic Energy Research Institute (KAERI), with known source strength and reactivity worth has showed consistent and satisfactory agreement.

Diffusion-controlled Adsorption Kinetics at Air/Solution Surface Studied by Maximum Bubble Pressure Method

In studying the diffusion-controlled adsorption kinetics of aqueous surfactant solutions at the air/solution surface by means of the maximal bubble pressure method, Fick's diffusion equation for a sphere should be used. In this paper the equation was solved by means of Laplace transformation under different initial and boundary conditions. The dynamic surface adsorption F(t) for a surfactant solution, which was used to describe the diffusion-controlled adsorption kinetics at the solution surface, was derived. Different from the planar surface adsorption, the dynamic surface adsorption F(t) for the short time consists of two terms: one is the same as Ward-Tordai equation and the other reflects the geometric effect caused by the spherical bubble surface. This effect should not be neglected for the very small radius of the capillary. The equilibrium surface tension γeq and the dynamic surface tension γ(t) of aqueous C10E6 [CH3(CH2)9(OCH2CH2)6OH] solution at temperature 25℃ were measuredby means of Wilhelmy plate method and maximal bubble pressure method respectively. As t→ 0, the theoreticalanalysis is in good agreement with experimental results and the dependence of γ(t) on is linear.

A Kinetic Study of Anaerobic Biodegradation of Food and Fruit Residues during Biogas Generation Using Initial Rate Method

A kinetic study of biogas production from Urban Solid Waste (USW) generated in Dar es Salaam city (Tanzania) is presented. An experimental bioreactor simulating mesophilic conditions of most USW landfills was developed. The goal of the study was to generate the kinetic order of reaction with respect to biodegradable organic waste and use it to model biogas production from food residues mixed with fruit waste. Anaerobic biodegradation was employed under temperature range of 28℃ - 38℃. The main controls were leachate recirculation and pH adjustments to minimize acid inhibitory effects and accelerate waste biodegradation. The experimental setup comprised of three sets of bioreactors. A biodegradation rate law in differential form was proposed and the numerical values of kinetic order and rate constant were determined using initial rate method as 0.994 and 0.3093 mol0.006·day-1, respectively. Results obtained were consistent with that found in literature and model predictions were in reasonable agreement with experimental data.

Design and Analysis of Terminal Guidance Law for Kinetic Interceptors based on Pulse Engine

A new terminal guidance law is proposed based on a solid propellant pulse engine and an improved proportional navigation method to address the terminal guidance issue for kinetic interceptors.On this basis,the start-stop curve of the pulse motor during the terminal guidance process is designed,along with its start-up logic.The effectiveness of the proposed guidance strategy is verified through simulation.

Preliminary analysis of reactivity reconstruction capability based on inverse kinetics method under different initial reactivity states

Online reactivity monitoring plays an important role in operation and safety analyses of fission reactor systems. The inverse kinetics method, which is based on a point kinetics model, is the most widely used method for reactivity reconstruction of critical water reactors. However, this method is seldom applied to the reactivity reconstruction of subcritical reactors. In this study, an inverse kinetics method was employed for the reactivity reconstruction of a lead-based reactor under different initial reactivity states(ρ_0= 0,-2786,-5486,-8367, and-12,371 pcm). The results showed that the deviation in the reactivity of the lead-based subcritical reactor was greater when ρ_0 became smaller. The reactivity reconstructed using the inverse kinetics method was globally underestimated. At a given reactivity perturbation, the relative and absolute errors increased with the decrease in the initial reactivity. At a given initial reactivity, with the increase in the reactivity perturbation, the absolute error increased, whereas the relative error remained the same.This deviation is due to the variation in the external neutron source, spatial-spectral effects, and sub-diffusive effects, which require further study.

ABSORPTION KINETICS OF HYDROGEN SULPHIDE USING ISOTHERMAL AND ISOVOLUMETRIC METHOD

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Grain Growth Kinetics of SnO_2 Nanocrystals Synthesized by Precipitation Method

Monodispersed spheroidal SnO2 nanocrystals with the grain size of 8-30 nm were synthesized by the precipitation method using SnCl4·5H2O （stannic chloride hydrate） as raw materials.Differential scanning calorimetry/thermogravimetry （DSC/TG）,X-ray diffraction （XRD） and transmission electron microscope （TEM） were used to characterize the structure of SnO2 nanocrystals.The influences of the calcination temperature and time on the lattice constant,the lattice distortion and the grain size of SnO2 nanocrystals were discussed based on the XRD results.The grain growth kinetics of SnO2 nanocrystals during calcination process was simulated with a conventional grain growth model which only took into account of diffusion and with a new isothermal model proposed by our group,which took into account of both diffusion and surface reactions.Using conventional model,the grain growth rate constant of SnO2 crystals is 1.55×104nm5/min with a pre-exponential factor of 5 and an activation energy of 108.62 kJ/mol.Compared with the convention model,the new isothermal model is more realistic in reflecting the grain growth behavior of SnO2 nanocrystals during the calcination process.This indicates that the grain growth of SnO2 nanocrystals is controlled by both diffusion and reaction factors,and the effect of surface reactivity on the grain growth of SnO2 nanocrystals could not be ignored.A combined activation energy estimated with the new isothermal model is 53.46 kJ/mol.

KINETIC STUDY OF SPINEL LiMn_2O_4 SYNTHESIZED BY SOLID REACTION WITH SOFT-CHEMICAL METHOD

The differential thermal analysis （DTA） curves were measured at different heating rates in flowing air for studying the synthesis of the spinel LiMn2O3 with Li2CO3 and MnO2, The reaction began at about 503K, and finished at about 873K. The apparent activation energy of Kissinger method was about 122.77kJ.mol^-1, the reaction orderwas 1.67, the frequency factor was 7.81×10^9, and therefore the dinetic epuation was dδ/dt=A·exp（- E/RT）·（1-δ）^n=7.81×10^9, exp（-122770/RT）·（l-δ）^1.67 . Coats-Redfem integral method was used to analyze the DTA curves of the samples at different heating rates, and the calculated apparent activation energy and frequency factor were 112. 13kJ· mol^-1 and 1.18 × 10^9, respectively, rather close to that of Kissinger method. X-ray diffraction （XRD） and scanning electron microscope （SEM） results shown that the synthesized LiMn2O3 possesses pure phase, regular shape and normal particle distribution.

Reaction pathway and kinetics of CdO nanoparticles prepared from CdCO_3 precursor using thermal decomposition method

The non-isothermal kinetics of CdO nanoparticles prepared from CdCO3 precursor using thermal decomposition method was investigated. A model-fitting Malek approach and a model-free advanced isoconversional method of Vyazovkin were applied to the analysis of the DSC and TGA data. The results showed that CdO nanoparticles prepared from CdCO3 followed an autocatalytic reaction. Sestak–Berggren model could favorably describe the studied reaction process. Moreover, the apparent activation energy of CdCO3 decomposition was calculated to be (119.19±9.97) kJ/mol and the explicit rate equation form of CdCO3 decomposition was established.

HOMOGENEOUS ENZYME IMMUNOASSAY OF SERUM AFP BY FLUORIMETRIC KINETIC METHOD

The activity of the Ab-bound enzyme(HRP)changed after immunochemical reaction,and can be indicated by a sensitive fluorimetric kinetic method.The finding set the stage for developing sensitive homogeneous immunoassay.AFP was measured as an example.

STUDY OF KINETIC ANALYTICAL METHOD BASED ON CATALYTIC REACTIONS

In this thesis a reviwe is presented for the advances of catalytic spec trophotometric method, three new catalytic reaction systems were presented, and its rela live catalytic spectrophotometric methods have been established by flow injection tech nique. Particulary the relative chemometric methods and theories were used in the field of kinetic - catalytic analysis, in order to solve the problems of multicomponents analysis.

Precipitation kinetics of NZ30K-Mg alloys based on electrical resistivity measurement

The electrical resistivity of NZ30K-Mg alloy was measured at different heating rates during continuous heating to stud the precipitation kinetics.Two kinds of metastable phases,β＂ and β＇,formed during the heating.Kissinger method and differentia isoconversional method were employed to assess the precipitation kinetic parameters of NZ30K-Mg alloy,activation energy Eα an pre-exponential factor A＇α.The fraction of transformation（α） and the precipitation sequence in NZ30K-Mg alloy were determinec Continuous heating transformation（CHT） and isothermal heating transformation（IHT） diagrams were further obtained for guidin the aging of NZ30K-Mg alloy.The analysis shows that the precipitation kinetic parameters of NZ30K-Mg alloy can be obtaine accurately using isoconversional method.