Optimization of the Wet Mechanochemical Process Conditions of SrSO4 to SrCO3 and (NH4)2SO4 by Using Response Surface Methodology

The wet mechanochemical process was optimized for insoluble SrCO₃ and soluble (NH₄)₂SO₄ formation from celestite (SrSO₄)-(NH₄)₂CO₃-H₂O mixtures in a planetary ball mill by Box-Behnken design (BBD). The products formed during wet milling were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. For converting to SrCO₃ of celestite (SrSO₄) and to (NH₄)₂SO₄ of (NH₄)₂CO₃, a hydrometallurgical process optimization via the wet mechanochemical conversion using (NH₄)₂CO₃ was developed the first time in this work using response surface methodology. The wet mechanochemical conversion was carried out by varying ball to grinding material mass ratio, (NH₄)₂CO₃ to SrSO₄ mole ratio and the rotational speed of mill in a planetary mill. Under the optimum experimental conditions (9.24 of ball to grinding material mass ratio, 1.86 of (NH₄)₂CO₃ to SrSO₄ mole ratio and 400 rpm of the rotational speed of mill), the conversion of SrCO₃ was 99.08 pct. The (NH₄)₂SO₄ obtained as byproduct was crystallized.     

Revealing active species of CePO4 catalyst for selective catalytic reduction of NOx with NH3

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst.Herein,we tried to demonstrate the roles of amorphous and crystalline structures on CePO₄ catalyst during selective catalytic reduction(SCR) of NO_x by NH₃.Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO₄.Both amorphous and crystalline CePO₄ species on CePO-X samples can...     

The kinetics of gold cyanide adsorption on activated charcoal

Adsorption rates of gold cyanide on activated carbon were determined as a function of temperature, free cyanide concentration and charcoal concentration. The experimental rate data is explained by use of a diffusion controlled model developed by Crank. The adsorption rates were determined to be controlled by pore diffusion with the effective diffusion coefficient having an activation energy of 3.3 kcal/mol. Good agreement between experimental rate data and predicted rate curves by the diffusion model was obtained. Formerly with the Department of Metallurgy,University of Utah.     

氢含量对氧化亚铁粉体还原动力学的影响

采用热重法获得了873~1 173 K氧化亚铁在不同氢含量H2-Ar还原气中的等温还原动力学曲线,发现在973~1 023 K温度范围,随着氢气含量(体积分数)的增加,反应达到的还原程度降低.结合产物的显微结构分析,在该温度范围,随着氢气含量(体积分数)增加,氧化亚铁还原的化学反应速率加快,新生成的铁相黏结加剧,阻碍反应气体的扩散,最终影响整个反应进程.同时发现,反应速率与氢含量不符合线性规律.     

Study on the adsorption of lanthanum(III) from aqueous solution by bamboo charcoal

The adsorption behaviors of La(III) ion on bamboo charcoal were investigated with various chemical methods and IR spectrometry. Parameters studied include the effects of pH, average particle size, initial ion concentration, contact time and temperature by batch method. The results showed that bamboo charcoal could remove La(III) ions effectively from aqueous solution. The loading of La(III) ions was strongly dependent on pH of the medium and the optimal adsorption condition was in HNO₃-TEA medium with pH value of 7.20. In the batch system, the modified bamboo charcoal exhibited the highest La(III) ion uptake as 120 mg/g at 298 K, at an initial pH value of 7.20. The adsorption kinetics were tested with Lagergren-first-order model and pseudo-second-order model. The adsorption data were conformed to the Langmuir and Freundlich isotherms, and the correlation coefficients had been evaluated. Thermodynamic parameters such as free energy (ΔG), which were all negative, indicated that the adsorption of La(III) ion onto bamboo charcoal was spontaneous and the positive value of enthalpy (ΔH) showed that the adsorption was endothermic in nature. Thomas model was applied to experimental column data to determine the characteristic parameters of column useful for process design. The characterization of both before and after adsorption of La(III) ion on bamboo charcoal was undertaken using IR spectroscopic technique. The results revealed that bamboo charcoal was a good choice as a biosorbent for the recovery of lanthanum from aqueous solution.     

Carbothermic reduction of nickel oxide: Effect of catalysis on kinetics

Formerly Senior Research Fellow, Chemical Engineering Division, National Chemical Laboratory.     

金属Cu还原MoO42-的动力学研究

本文对铜还原钼酸盐动力学进行了初步研究.通过还原反应的动力学模型,绘制出其氧化-还原反应机理示意图.同时为了进一步明确其反应机理及动力学过程,采用初始速率法研究还原反应的级数,计算还原反应的活化能,并研究了温度对速率系数的影响.     

Effect of Pd, Cu, and Ni additions on the kinetics of NiCl2 reduction by hydrogen

Differnetial thermal analysis (DTA) and thermal gravimetric analysis (TGA), at a heating rate of 10 °C/min, revealed a complete reduction of NiCl₂ by hydrogen in a temperature interval of 375 °C to 450 °C. However, addition of 0.1 mass pct of Pd, Cu, or Ni to the sample caused the reduction to occur at considerably lower temperatures, in the rather narrow range of 315 °C to 370 °C. The activation energy of NiCl₂ reduction by hydrogen (between 300 °C and 550 °C) without additives is 54 kJ/mol, and with Pd and Cu or Ni added, under isothermal conditions (from 260 °C to 380 °C), is 33 and 50 kJ/mol, respectively. These values confirm a positive effect of additives on the reduction kinetics. The positive effect of Pd is a consequence of the dissociation and spillover of hydrogen, whereas in the case of Cu and Ni(HCOO)₂, it is manifested in a decrease in bonds energy in the nickel lattice because of good Cu solubility, and in the formation of artificial nickel nuclei that intensify the reduction, respectively. Scanning electron microscopy (SEM) analysis of nickel powders obtained under isothermal conditions shows relatively rounded spherical particles (0.321 to 0.780 μm in size) of powder samples with additives, and particles of irregular shape (2.085 μm mean size) of the sample without additives. This illustrates the positive effect of Pd, Cu, or Ni added in the reduction process, in decreasing the size of nickel particles and in the production of a more uniform particle shape.     

A study on the kinetics of iron oxide reduction by solid carbon

Rate of reduction of ferric oxide in the presence of solid carbon was measured in the laboratory using a thermogravimetry setup. Iron oxide in the form of powder and micropellets were used. Coconut char of high reactivity was employed as carbonaceous material. Product gas analysis was carried out to calculate the rate of carbon loss during reduction. Ferric oxide reduction was found to take place in a stage-wise manner. For the powder system, the overall reaction was found to be exclusively controlled by the gasification process. Gasification rates of coconut char in carbon dioxide were utilized to predict the rates of carbon loss during reduction. The predicted and experimental rates of carbon loss during reduction of ferric oxide by carbon were compared and possible explanations were given for the observed trends.     

Effect of magnesium and aluminum oxide additions on the reduction kinetics of the system Fe-Co-O

Translated from Poroshkovaya Metallurgiya, No. 10(334), pp. 102–104, October, 1990.     

The kinetics of the reduction of chromium oxide by hydrogen

The reduction kinetics has been studied as function of hydrogen partial pressures,pH₂O/pH₂ ratio, gas flow rate, and temperature. The reduction follows a linear time law and is dependent on the gas flow rate below a value of approximately 10 cm · s^-1, since the rate is determined by the removal of the water vapor being formed. In this range the reduction rate may be calculated from gas dynamical data. At sufficiently high flow rates the phase boundary reaction is rate determining. The activation energy is 123 kJ · mol^-1. The reduction rate is proportional to the square root of hydrogen pressure and decreases with increasing water vapor content. Formerly Research Associate with Dechema-Institut     

The kinetics of reduction of hematite by carbon

Reduction kinetics of mixtures of hematite and carbon powders were investigated in the temperature range of 850° to 1087°C. Experiments were carried out under argon atmosphere and the isothermal weight loss of the samples was determined as a function of time. The effects of carbon particle size, hematite/carbon ratio of the mixture, and addition of promotive or inhibitive reagents were also investigated. The results were summarized in the form of fractional reaction vs time plots. A kinetic model developed on the basis of carbon solution-loss reaction as rate-controlling represented the results fairly well. An enthalpy of activation of 72 kcal/per mole was calculated, within the range of 957° to 1087°C. The observed effects of Li₂O and FeS on the reduction kinetics are consistent with the influence these reagents are known to exercise on the solution-loss reaction.     

Postprandial bile-duct kinetics under the influence of 4-methylumbelliferone (hymecromone)

The physiological correlate of biliary colic is a rapid increase in pressure in the presence of biliary obstruction. The relaxing action of hymecromone on the biliary tract provides a pharmacotherapeutic approach. As the symptoms usually occur postprandially we used ultrasonography to examine whether hymecromone was able to reverse the contraction of the common bile duct (CBD) after ingestion of a standardized test meal. The study was designed as prospective, double-blind randomized crossover study versus placebo in 20 healthy volunteers. The width of the CBD was measured ultrasonographically in the fasting subjects and at 1, 3, 5, 10, 15 and 20 minutes after ingestion of a test meal. Then the subjects were given either 400 mg of hymecromone or placebo and the measurement series was repeated. After ingestion of the test meal the width of the CBD decreased by a maximum of 20% after 15 minutes. While there was only a slight increase in the width of the CBD after subsequent administration of placebo, a maximum increase of 36% was measured 10 minutes after administration of hymecromone. The postprandial contraction of the CBD can be reversed within a short time by i.v. administration of hymecromone.     

Ca3(PO4)2对Al粉氮化制备AlN粉末动力学的影响

利用DSC、TGA等方法研究了稀释剂Ca3(PO4)2对Al粉氮化制备AlN粉末动力学的影响.结果表明,在Al粉中添加Ca3(PO4)2能显著加快氮化速率和提高氮化率.尽管稀释剂对氮化温度没有明显的影响,但添加稀释剂能降低Al熔化后的液滴尺寸,且Al液滴尺寸对氮化的动力学有重要影响,即小尺寸的熔融Al液滴有利于加快氮化速率和提高氮化率.     

Nonisothermal gravimetric investigation on kinetics of reduction of magnesia by aluminum

An investigation of the reduction of magnesia by aluminum was carried out using a nonisothermal gravimetric technique under an argon atmosphere, in the temperature range from 1273 to 1873 K. The mixture of magnesia and aluminum powders was formed into a pellet under various isostatic pressures. It was found that magnesia is reduced by aluminum to form magnesium and spinel at first, and then the excess aluminum reacts with spinel slowly. The temperature at which the reaction starts increases with an increasing heating rate. The reaction rate is also affected by pellet-forming conditions. A kinetic model is proposed to explain the experimental results. The activation energy of the reduction of magnesia by aluminum is 151.2 kJ/mol. Good agreement between calculated and experimental results is obtained.     

Investigation of the kinetics of reduction of nickel tungstate by hydrogen

In the present work, the kinetics of reduction of nickel tungstate, NiWO₄, by hydrogen was investigated by a thermogravimetric method in the temperature range 891 to 1141 K. The experiments were conducted under both isothermal and nonisothermal conditions. The products were examined by X-ray diffraction analysis. The results indicate that the reduction reaction proceeds in two steps; first, reduction of NiWO₄ to nickel as well as WO₂ and then WO₂ to tungsten. From the isothermal experiments, the activation energies of the two reaction steps were calculated to be 95.3 ± 4.9 and 80.8 ± 6.4 kJ · mol⁻¹, respectively. The activation energy value obtained from nonisothermal experiments for the first step is in agreement with the isothermal experiments. The values are compared with the activation energies reported in other literature for the individual oxides. Formerly with Royal Institute of Technology, Stockholm, Sweden     

Intrinsic kinetics of the hydrogen reduction of copper sulfate: Determination by a nonisothermal technique

The direct hydrogen reduction of metal sulfates may provide an attractive method for producing high-purity metals. In this work the intrinsic kinetics, unaffected by diffusional and mass transfer effects, of the hydrogen reduction of copper sulfate particles have been determined using a nonisothermal technique. The reduction rate shows a first-order dependence on the hydrogen partial pressure and the amount of unreacted copper sulfate. The activation energy of the reaction was determined to be 63.7 kJ/mol. SUN K. KIM, formerly Graduate Student in the Department of Metallurgy and Metallurgical Engineering, University of Utah.