Intrinsic Kinetics of Chlorination of WO<Subscript>3</Subscript> Particles With Cl<Subscript>2</Subscript> Gas Between 973 K and 1223 K (700 °C and 950 °C)

Chlorination is one of the methods applied in extractive metallurgy for the treatment of minerals to obtain valuable metals, such as titanium and zirconium. The possibility of applying chlorination metallurgy to other metals such as tungsten was the major aim of this study. The kinetics of the chlorination of tungsten oxide (WO₃) particles has been investigated by thermogravimetry between 973 K and 1223 K (700 °C and 950 °C) and for partial pressures of chlorine ranging from 15 to 70 kPa. The starting temperature for the reaction of WO₃ with chlorine is determined to be about 920 K (647 °C). The influence of chlorine diffusion through the bulk gas phase and through the particle interstices in the overall rate was analyzed. In the absence of these two mass-transfer steps, a reaction order of 0.5 with respect to chlorine partial pressure, and an activation energy of 183 kJ/mol were determined. For tungsten oxide particles of less than 50-μm size, a complete rate expression has been obtained.     

Chlorination kinetics of ZnO with Ar-Cl2-O2 gas and the effect of oxychloride formation

The chlorination rate of ZnO with Ar-Cl₂-O₂ gas was measured from 1023 K to 1273 K and the effects of temperature and partial pressures of chlorine and oxygen were investigated. The rate-determining step of chlorination was considered to be the dissociation of intermediate between ZnO and Cl₂ from linear relationship between reciprocal values of reaction rate and partial pressure of chlorine. The activation energy of chlorination was 58.2±2.5 kJ/mol. This comparatively low activation energy as a chemically controlled reaction was consistent with estimated rate-determining step of the dissociation of unstable compound. Increasing the partial pressure of oxygen slightly increased the chlorination rate, and this effect is considered to be caused by the increase in the formation rate of zinc oxychloride. To clarify the formation of zinc oxychloride, the equilibrium between Ar-Cl₂-O₂ gas and ZnO was investigated by the transpiration method at 1073 K. Calculated partial pressures of ZnOCl from experimental results were in the same order with or one order of magnitude larger than those estimated from reported Gibbs energy of formation of ZnOCl. Zinc oxychloride formation in ZnO chlorination must be taken into consideration as well as ZnCl₂ and Zn₂Cl₄ formation.     

High temperature chlorination kinetics of a niobium pyrochlore

The chlorination kinetics of a niobium (Cb) pyrochlore has been studied between 1873 and 2223 K, the chlorine concentration in helium varying between 0 and 20 pct. The pyrochlore was subjected to a preliminary thermal treatment at 1473 K in order to remove fluorine which escaped under the form of niobium oxyfluorides. This left NaNbO₃, CaNb₂O₆ and residual refractory oxides. The large chlorination reaction rate difference between NaNbO₃ and CaNb₂O₆ made possible the definition of distinct chlorination reaction rates for these constituents. It was found that the decomposition of CaNb₂O₆ is the controlling step in the chlorination of this constituent, while Nb₂O₅ (NbO₂ + NbO₂ at the prevailing temperatures) chlorination is very fast. The reaction is second order with respect to CaNb₂O₆ concentration and first order with respect to chlorine partial pressure between 1873 and 2023 K, a distinct reaction rate equation being obtained at 2223 K. Reaction rate constants have been calculated and vary between 3 and 10 moleJ.kg ·min for the temperature range considered. The NaNbO₃ reaction rate is first order with respect to total Nb₂O₅ concentration and 2.5 order with respect to chlorine partial pressure for the temperature range covered (1973 to 2223 K). Reaction rate constants are much higher than in the former case, being respectively 148 (1873 K), 214 (2023 K) and 518 (2223 K) mole/kg-min. Reaction orders may be affected by an error varying between 16 and 40 pct. The reaction rate constants are found accurate within 40 pct for CaNb₂O₆ and 25 pct for NaNbO₃.     

Kinetics of Iron Chlorination of Roasted Illmenite Ore,Fe2TiO5 in a Fluidized-Bed Reactor

The preferential chlorination reaction of iron constituents in roasted ilmenite ore was studied in an experimental fluidized bed reactor. The influence of the roasting temperature on the selectivity of chlorination reactions was also examined. It was found that preferential iron chlorination is dependent on roasted product morphology. Effects of chemical and process variables in the fluidized bed reactor, such as chlorination temperature, chlorine gas partial pressure, gas-solid contact time and the quantity of coke added, were investigated in order to study the kinetics of the preferential chlorination reaction. A modified bubble assemblage model was applied to analyze behavior of gases and solids in the reactor. The chlorination reaction rate constant was found to be a function of temperature and coke quantity present.     

The selective carbochlorination of iron from titanlferous magnetite ore in a fluidized bed

The selective chlorination of iron from titaniferous magnetite ore using solid carbon as a reducing agent was studied in a fluidized bed. The effects of chlorination temperature, chlorine gas partial pressure, ratio of ore to carbon particle sizes, and the amount of added carbon were determined. Experimental results indicate that temperatures between 900 and 1000 K were favorable for the selective chlorination of iron. The rate was found to be first order with respect to chlorine concentration, and the observed effects of particle size, temperature, and the amount of carbon added were expressed quantitatively by using a mixed-control model. Formerly Graduate Student with the Department of Metallurgical Engineering, University of Utah     

Kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys with chlorine gas

This report deals with the kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys (containing 1.25 pct Cr-0.5 pct Mo, 5 pct Cr-0.5 pct Mo, and 12 pct Cr) with low partial pressure chlorine gas in the temperature range 270 to 550 °C. The rate of reaction generally decreases with exposure time and, in the case of alloys containing five pct Cr and higher chromium content, the kinetics follows a parabolic rate law. The reaction kinetics is influenced by surface films containing FeCl₂ and CrCl₃ which have very low vapor pressure in the temperature range studied. The effect of molybdenum on the reaction is negligible. In the case of alloys containing five pct Cr-0.5 pct Mo and 12 pct Cr, the reaction product film consists essentially of CrCl₃ (outer layer) and much smaller concentration of FeCl₂ (inner layer). For these alloys, the observed parabolic kinetics is attributed to kinetic control of the overall reaction by solid-state diffusion through the reaction product surface film. In the case of the 1.25 pct Cr-0.5 pct Mo alloy, the film consists essentially of a mixture of FeCl₂ and CrCl₃. In this case, an outer CrCl₃ film layer is not formed and the overall kinetics is influenced by the rate of formation of volatile FeCl₃ speciesvia the reaction 2 FeCl₂ + Cl₂ (FeCl₃)₂.     

Equilibria between ferrous and ferric chlorides in molten chloride salts

Equilibria between ferrous and ferric chlorides in molten salts have been studied for improving magnesium electrolysis and molten salt chlorination. The apparent equilibrium constants,K, of reaction FeCl_2(melt)+0.5Cl_2(gas)=FeCl_3(melt) were obtained. Measured values ofK were in good agreement with computed ones from regression equations. The composition of the melts, the partial pressure of chlorine, and the temperature were found to have important effects onK, and the effect of dissolved iron was smaller than that of other factors. At identical other conditions, the largest values ofK were observed in system 3, which suggested that the current efficiency for electrolysis of MgCl₂ should be lower when carnallite was used as electrolyte and that catalysis of iron species in molten salt chlorination would be better when molten salt systems containing high potassium chloride were used.     

Kinetics of chlorination of tantalum pentoxide in mixture with sucrose carbon by chlorine gas

The mechanism and kinetics of β-Ta₂O₅ chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method, and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is 144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable mechanism for the carbochlorination of β-Ta₂O₅ is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta₂O₅, (3) oxidation of carbon, and (4) recrystallization of β-Ta₂O₅.     

The selective chlorination of iron from llmenite ore by CO-Cl2 mixtures: Part I. intrinsic kinetics

The intrinsic kinetics of the selective chlorination of iron from ilmenite ore using carbon monoxide as the reducing agent were studied in a shallow fluidized bed. Experiments on the effects of chlorination temperature, carbon monoxide and chlorine gas partial pressures, and particle size were conducted in the absence of mass- and heat-transfer influences. Results indicate that the kinetics in the temperature range 923 to 1123 K are represented by the following pore-blocking rate law: λ[ exp (X_Fe/λ) − 1 ] = 33.7 exp (− E/RT)p _co ^0.52 ₂ ^0.32 t where E is 37.2 kJ/mol and p and t are in atm (=101.3 kPa) and minutes, respectively. The partial pressure of carbon monoxide was found to affect the chlorination rate more strongly than that of chlorine. A reaction mechanism in which iron in ilmenite reacts with chlorine before the liberated oxygen is removed by carbon monoxide is proposed. Formerly Graduate Student at the Department of Metallurgical Engineering, University of Utah     

Kinetics of decarburization of iron-chromium melts in highly oxidizing atmosphere

The kinetics of decarburization in Fe-Cr-C melts were studied to determine the rate con-trolling step for the process. The experiments were carried out under nitrogen-oxygen at-mosphere in a resistance-heated vertical-tube furnace. The liquid melt was held in a freshly prepared magnesite crucible. Sampling and chemical analysis of the metal phase led to time-carbon concentration curves for the system. An iron oxide layer just below the impinging are a and a general boil were observed. Results obtained by varying param-eters such as temperature, partial pressure of oxygen, flowrate of the oxidizing gas and amount of melt determined the limiting reaction mechanism. The rate has been found to be almost independent of flow rate and partial pressure of oxygen (between 1.0 to 2.0 l/min. and 0.5 to 1.0 atm of oxygen). The amount of melt and temperature have a marked effect on the reaction rate. The apparent activation energy has been found to be 48.0 ± 5.4 K cal/mol. The carbon oxidation reaction has been proposed to occur predominantly at CO bubble/metal interface. On the basis of the experimental results and discussions reaction involving reduction of oxides by carbon has been proposed to be the rate controlling step. Formerly a graduate student of IIT, Kharagpur     

A kinetic study of the leaching of chalcopyrite at elevated temperatures

A study of the rate of dissolution of chalcopyrite (CuFeS₂) in acidic solutions under oxygen overpressures was carried out by measuring the rate of formation of cupric ions in solution. Effects of temperature, oxygen partial pressure, surface area, and concentration of sulfuric acid were evaluated. A sized batch of chalcopyrite was leached in the temperature range of 125 to 175° and in the pressure range of 75 to 400 psi of oxygen. In 0.5N H₂SO₄ all products of reaction went into solution except for trace amounts of elemental sulfur. The dissolution of chalcopyrite followed linear kinetics and was essentially independent of hydrogen ion concentration for H₂SO₄ concentrations between 0.2 and 0.5 JV. The oxygen dependence indicated adsorption approaching limiting values with increasing oxygen pressure. The linear mechanism was explained in terms of steady-state adsorption of oxygen at the chalcopyrite surface followed by a surface reaction. The enthalpy of activation for adsorption of oxygen was found to be approximately 33 kcal per mole. An activation enthalpy of approximately 9 kcal per mole was observed for the surface reaction. Charge transfer reaction are not rate controlling in the process.     

High Temperature Corrosion of Fe-25Cr and Fe-17Cr-1.5Si-0.5Al Alloys in Oxidizing and Sulfidizing Enviornments

The simultaneous oxidation and sulfidation of Fe 25Cr and Fe-17Cr-l.5Si-0.5Al alloys was studied at 1023K and 1223K in H₂-H₂O-H₂S gas mixtures. The kinetic boundary which indicates the transition from oxide to sulfide has heen found in these two alloys. The critical oxygen partial pressures of Fel7Crl.5SiO.5Al alloys were systematically lower than those of Fe-25Cr alloy. The reaction kinetics were measured by the stainless steel spring balance, and the reaction products were characterized by X-ray diffraction and scanning electron microscopy. The reaction rate usually decreased with the increase of the oxygen partial pressure at the constant sulfur partial pressure. The exista-nce of silicon plays an important role to suppress the sulfidation of Fel7Cr alloy.     

A novel cyclic process using CaSO4/CaS pellets for converting sulfur dioxide to elemental sulfur without generating secondary pollutants: Part II. Hydrogen reduction of calcium-sulfate pellets to calcium sulfide

The reduction of calcium sulfate to produce calcium sulfide is a part of the cyclic process for converting sulfur dioxide to elemental sulfur that is described in Part I. The kinetics of the hydrogen reduction of nickel-catalyzed calcium-sulfate pellets were investigated using a thermogravimetric analysis (TGA) technique at reaction temperatures between 1023 and 1088 K and hydrogen partial pressures between 12.9 and 86.1 kPa. The reactivity of nickel-catalyzed calcium-sulfate pellets was demonstrated by the conversion of 70 pct fresh nickel-catalyzed calcium sulfate to calcium sulfide in 20 minutes at 1073 K under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after ten cycles of reactions and regenerations. This observed characteristic of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants. The nucleation and growth rate expression was found to be useful in describing the kinetics of the reaction, which had an activation energy of about 167 kJ/mol (∼40 kcal/mol) in all reaction cycles except for the first regenerated samples that were lower at 146 kJ/mol (35 kcal/mol). The reaction order with respect to hydrogen partial pressure was 0.22 in all cycles with the exception of the first regenerated sample for which it was 0.37.     

转炉生产低磷钢的脱磷反应热力学

 为实现磷质量分数小于0.010%的低磷钢批量生产,系统研究了转炉脱磷反应热力学。分析了影响转炉渣-金间磷分配比LP的主要因素,研究了P2O5活度系数和脱磷反应氧分压的定量确定方式,以及碳、磷选择性氧化问题。研究结果表明：LP主要受氧分压、P2O5活度系数和温度的影响;P2O5活度系数采用修正的柯热乌罗夫规则离子溶液模型计算较为准确;脱磷反应氧分压受炉渣氧分压控制,炉渣氧分压主要取决于钢中碳含量、炉渣碱度和温度。对传统复吹转炉生产磷质量分数小于0.010%低磷钢的工艺条件是：终渣碱度w(CaO)/w(SiO2)≥3.0,终渣w(MgO)≤9.0%,终点碳w(［C］)≤0.065%,终点温度控制在1873～1923K范围。     

Separation of copper from steel

Abstract

Copper has been separated from iron and steel by chlorine–air mixtures at 800°C. It was found that, contrary to predictions based upon thermodynamics, cupric chloride was the favoured copper product rather than cuprous chloride. This was due to the high vapour pressure of cupric chloride. It was found that in order to prevent the reaction between iron and cupric chloride it was necessary to preoxidise the iron to form an impervious oxide film. Copper contents lower than 0·05 wt-% were readily obtained after 10 min exposure to the gas, even when starting with several per cent of copper mixed with the iron or steel.     

高炉中氯的危害及行为分析

阐述了高炉中氯的影响和危害,并分析了高炉中氯的来源及反应行为。结果表明,高炉中氯的主要来源是由于烧结矿喷洒氯化物,此外通过热力学分析明确了氯化物与碱金属盐类化合物的反应机制,据此探讨了烧结矿喷洒氯化物的利弊关系,并针对高炉中氯的危害控制提出了相关措施。     

Kinetics of pyrite oxidation in sodium hydroxide solutions

The kinetics of pyrite oxidation in sodium hydroxide solution were investigated in a stirred reactor, under temperatures ranging from 50 °C to 85 °C, oxygen partial pressures of up to 1 atm, particle size fractions from -150 + 106 to -38 + 10μm (-100 + 150 mesh to -400 mesh + 10 μ), and pH values of up to 12.5. The surface reaction is represented by the rate equation:-dN/dt = Sbk″pO^0.5 ₂[oH^{- 0.25}/(1 +k‴ pO₂ ^0.5) where N represents moles of pyrite, S is the surface area of the solid particles,k″ andk″ are constants,b is a stoichiometric factor, pO₂ is the oxygen partial pressure, and [OH^-] is the hydroxyl ion concentration. The corresponding fractional conversion (X) vs time behavior follows the shrinking particle model for chemical reaction control: 1 - (1 -X)^1/3 =k _ct The rate increases with the reciprocal of particle size and has an activation energy of 55.6 kJ/mol (13.6 kcal/mol). The relationship between reaction rate and oxygen partial pressure resembles a Langmuir-type equation and thus suggests that the reaction involves adsorption or desorption of oxygen at the interface. The square-root rate law may be due to the adsorption of a dissociated oxygen molecule. The observed apparent reaction order with respect to the hydroxyl ion concentration is a result of a complex combination of processes involving the oxidation and nydrolysis of iron, oxidation and hydrolysis of sulfur, and the oxygen reduction. Formerly Graduate Student, Department of Mineral Engineering, Pennsylvania State University