Kinetics of cobalt sulfide reduction in the presence of calcium oxide

Kinetic measurements have been made on the hydrogen reduction of solid cobalt sulfide in the presence of calcium oxide. The cobalt metal yield was compared with that of the direct reduction reaction over the temperature range 600 to 800°C at various hydrogen flow rates, and calcium oxde to cobalt sulfide mixing ratios. It was found that the presence of calcium oxide caused a sharp increase in the reaction rate—for example a 15 fold increase in conversion was achieved at 700°C after 24 min of reaction. Low hydrogen flow rates were found to be desirable, and an optimum mixing ratio of 3.0 established.     

The carbothermal reduction of nickel sulfide in the presence of lime

The chemical feasibility of reducing nickel sulfide with carbon and lime, without emitting sulfur-containing gases, has been investigated. A reaction mixture of nickel sulfide particles intimately mixed with carbon and lime (used as a sulfur scavenger) was prepared. The thermodynamics of reacting this mixture in an inert atmosphere, producing carbon dioxide and carbon monoxide, was examined and found favorable. The rate of this reaction was measured in the temperature range 800 to 1124 °C ( 1073 to 1397 K). The effects of particle size and relative amounts of solid reactants were determined. The possibility of recovering the product nickel by carbonylation was also investigated. Formarly Graduate Student in Metallurgy at the University of Utah,     

Carbothermic reduction of zinc sulfide in the presence of calcium carbonate

Carbothermic reduction of zinc sulfide in the presence of calcium carbonate was investigated by employing an X-ray diffractometer (XRD), a carbon and sulfur determinator, a scanning electron microscope (SEM), an energy-dispersive X-ray analysis (EDX), and a surface area analyzer. Experimental results revealed that calcium carbonate was completely decomposed to CaO in the initial stage and CaO was then involved in the carbothermic reduction of zinc sulfide to scavenge sulfur content as CaS remained in the solid. Only carbothermic reduction of zinc sulfide occurred after the initial stage. Most β-ZnS transformed to α-ZnS in the initial stage. Sintering became severe after long reaction time or at high reaction temperature. The surface area of a sample decreased drastically in the initial stage and then increased with the reaction time; the pore volume of the solid sample was also reduced more quickly initially and then kept constant; the average pore diameter, however, reduced slightly in the initial stage and then leveled off. The effect of temperature on the changes of pore surface area, pore volume, and average pore diameter was found to be similar to that of time, except in the initial stage. A reaction mechanism and a reaction model were proposed to interpret the overall reaction.     

Carbothermic reduction of nickel oxide: Effect of catalysis on kinetics

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

Thermal reduction of olivine by calcium carbide and by silicon in the presence of calcium oxide

Abstract

The vapour pressures over the reactants olivine - calcium-carbide and olivine - silicon - calcium oxide have been measured over the temperature ranges 1115 to 1190°C and 1045 to 1165°C, respectively. The equilibrium reactions do not involve olivine since this material readily decomposes in the presence of CaC₂ or CaO. In the calcium carbide reduction, the reaction mechanism depends on the ratio of olivine to calcium carbide in the charge. In the silicon reduction, the equilibrium-pressures are essentially the same as those for the corresponding reduction of dolomite. The possible role of an intermediate calcium-silicon alloy in the latter case is discussed.

Résumé

Les auteurs ont mesuré les tensions de vapeur au-dessus des réactifs olivine - carbure de calcium et olivine - silicium - oxyde de calcium à des intervalles de température de 1115 à 1190°C et de 1045 a 1165°C respectivement. Les réactions de'équilibre n'impliquent pas l'olivine car ce composé se décompose en présence du CaC₂ ou du CaO. Dans le cas de la réduction du carbure de calcium, les mécanismes de réaction dépendent de la proportion d'olivine et du carbure de calcium dans la charge. Pour la réduction du silicium, les pressions à l'equilibre sont essentiellement les mêmes que celles pour la réaction équivalente avec la dolomite. Le rôle possible d'un composé intermédiaire calcium - silicium dans le dernier cas est discuté.     

Hydrogen reduction of oxidized nickel concentrates

Thermal gravimetric analysis was used to investigate the weight change of Ni/Cu/Co calcines upon heating in an inert as well as hydrogen atmosphere. The two calcines investigated contained approximately 50 wt pct combined of hematite and magnetite in addition to sulfides of Ni, Cu, Co, and Fe. Mass spectrometry was used to analyze the gas species evolved during heating and reduction. The calcine samples are 100 pct less than 100 μm with hematite/magnetite rims around a central sulfide core. When heating the calcines at 10 °C/min in hydrogen, reduction starts at around 400 °C and is nearly complete at about 700 °C with all the reducible oxygen removed. Isothermal reduction tests show that at temperatures from 650 °C to 800 °C, half the oxygen is removed in less than 4 min. The TGA results combined with microscopic analysis show that the reduction followed a uniform internal reduction model. The reduced calcines will quickly get re-oxidized if they are allowed to contact air while they remain hot.     

Hydrogen reduction kinetics of electrometallurgical slime

The interaction of hydrogen with the zinc-containing electrometallurgical slime of the Severstal’ metallurgical works has been studied. The sequence of transformations in the slime heated to 1100°C in hydrogen or air has been established. The experimental and calculated weight losses coincide. Some of the carbonates are shown to decompose in the temperature range 300–700°C, and most iron and zinc oxides are reduced to a metal. In the temperature range 650–850°C, zinc is almost completely sublimated. At temperatures above 800°C, complex oxides are reduced and calcium and magnesium carbonates and sulfates are likely to decompose. Experimental digital data on the zinc sublimation rate are processed by the least squares method with approximating equations used in thermal analysis. The kinetics of nonisothermal zinc sublimation is comprehensively analyzed using a unique procedure developed for taking into account the background of a peak and the effect of accompanying processes. An equation for the calculation of the zinc sublimation rate under experimental conditions (fluidized bed) is given and tested.     

The study of chlorination kinetics of copper(I)sulfide by calcium chloride in the presence of oxygen

The article investigates the influence of temperature, time, quantity of calcium chloride, and oxygen flow on the chlorination degree of copper(I)sulfide by calcium chloride in the presence of oxygen. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis were used to determine morphological changes occurring with the change of temperature and time. The law of additive time and the method of stationary point were used to determine kinetic parameters, i.e., rate constant and activation energy.     

Electrochemical reduction of nickel from oxide melts

The electrochemical behavior of nickel ions in melted sodium borosilicate and calcium alumino-silicate with NiO additions (0.25–4 wt %), which cover the entire solubility region, is studied using I-V characteristics and an electrolytic method.     

The reduction of sulfide minerals by hydrogen in the presence of lime

Calcium oxide favors greatly the reduction of metal sulfides by H₂ at 800°C. Copper sulfides and copper-iron sulfides are reduced rapidly to metals: Cu₂S+H₂+CaO→2Cu+CaS+H₂O CuS+H₂+CaO→Cu+CaS+H₂O Cu₅FeS₄+4H₂+4CaO→5Cu+ Fe+4CaS+4H₂O The reduction of chalcopyrite takes place according to any of the following reactions depending on the amount of CaO added: Cu₂S·Fe₂S₃+H₂+CaO→Cu₂S·2FeS+CaS+H₂O Cu₂S·Fe₂S₃+3H₂+3CaO→Cu₂S+2Fe+3CaS+3H₂O Cu₂S·Fe₂S₃+4H₂+4CaO→2Cu+2Fe+4CaS+4H₂O Gravity and magnetic methods were not successful in separating the reaction products. However, leaching by dilute HCl was successful in eliminating CaS and iron (as FeS as well as metal) leaving behind Cu₂S concentrate or metallic copper, respectively. Reduction of molybdenite is also influenced by the presence of CaO, but that of pentlandite is not. FATHI HABASHI and RAYMOND DUGADALE, formerly with the Research Division of the Anaconda Company, Tucson, Arizona     

Kinetics and mechanism of the reduction of molten nickel sulfide by hydrogen

The kinetics and mechanism of the reduction of M₃S₂ by hydrogen have been investigated between 1133° and 1300°C. When high flow rates of hydrogen and argon or helium bubbling through the melt are maintained the rate-determining step is a chemical process which can be expressed by a rate law of the form $$\begin{gathered} r_{H_2 S} = k_{expt} (N_S - \alpha )^2 p_{H_2 }^{1/2} \hfill \\ p_{H_2 } \geqslant 0.88atm \hfill \\ \end{gathered} $$ where k_expt = 85.1 atm^-1/2 min^-1, α = 0.17 at 1250°C. The experimental activation energy for this process is 20.1 ±3.0 kcal per mole. These results are discussed in terms of possible catalysis by nickel.     

Mechanically activated reduction of nickel oxide with graphite

The reduction of nickel oxide with graphite during ball milling at both ambient and elevated temperatures was investigated using X-ray diffraction (XRD), simultaneous thermogravimetry and differential thermal analysis (TG/DTA), and electron microscopy. It was found that milling at ambient temperature did not result in the reduction of nickel oxide to nickel. However, milling significantly reduced the critical reaction temperature for the reduction, from 1350 K for the unmilled sample to ∼650 K for samples milled for 12 hours or longer. This reduction in reaction temperature is rationalized in terms of the microstructural refinement observed in the milled samples. The reduction of nickel oxide to nickel was observed to occur at elevated temperatures during milling. The thermodynamics and kinetics of the reduction reaction are discussed.     

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     

The kinetics of nickel oxide reduction by hydrogen; Measurements in a fluidized bed and in a gravimetric apparatus

The suitability of a batch fluidized bed laboratory reactor for measuring the rates of gas-solid reactions was investigated. Experiments were carried out on the reduction of Falconbridge nickel oxide by hydrogen in a batch fluidized bed reactor within the tem-perature range 550 K to 650 K using particles in the range of 60 to 100 mesh. The reactor was operated at approximately atmospheric pressure and gas flow rates were in the range of two to four times the minimum fluidization velocity at temperature. The results showed internal consistency and rough agreement with the results of previous workers. The re-sults were interpreted and correlated by means of a structural model for gas-solid reac-tions. As a check on the fluidized bed measurements, experiments were also carried out using the conventional gravimetric technique to measure the rate of reduction of compac-ted pellets of nickel oxide by hydrogen. When due allowance was made for the change of surface area of the oxide during compaction, the results were in close agreement with the fluidized bed results. Rate measurements using hydrogen-nitrogen mixtures revealed that the reaction is not first order with respect to hydrogen, as usually assumed, but is ap-proximately of order two-thirds at one atmosphere hydrogen partial pressure. Formerly Graduate Student at Berkeley     

碘量-重量法测定脱硫灰还原产物中硫化钙和亚硫酸钙

准确测定硫化钙和亚硫酸钙的含量,对于脱硫灰还原工艺的参数选择和转化进程的研究具有重要意义。用过量碘标准滴定溶液将样品中的硫化钙和亚硫酸钙氧化,磷酸(1+4)溶液溶解样品并调节pH值,硫代硫酸钠标准滴定溶液返滴定得到硫化钙和亚硫酸钙消耗的碘标准滴定溶液的量,从而得到硫化钙和亚硫酸钙的总含量;硫化钙与碘反应生成硫单质,用热氢氧化钾溶液洗脱生成的硫单质的质量得到样品中硫化钙的含量,两者之差即为亚硫酸钙的含量,从而建立了脱硫灰还原产物中硫化钙和亚硫酸钙的测定方法。将实验方法应用于不同工艺流程得到的脱硫灰还原产物测定,7次平行测定硫化钙和亚硫酸钙结果的相对标准偏差(RSD,n=7)为0.54%~1.8%。按照实验方法,对3种配制的脱硫灰还原产物中硫化钙和亚硫酸钙进行测定,测定值均和理论值相符。     

碘量-重量法测定脱硫灰还原产物中硫化钙和亚硫酸钙

准确测定硫化钙和亚硫酸钙的含量,对于脱硫灰还原工艺的参数选择和转化进程的研究具有重要意义。用过量碘标准滴定溶液将样品中的硫化钙和亚硫酸钙氧化,磷酸(1+4)溶液溶解样品并调节pH值,硫代硫酸钠标准滴定溶液返滴定得到硫化钙和亚硫酸钙消耗的碘标准滴定溶液的量,从而得到硫化钙和亚硫酸钙的总含量;硫化钙与碘反应生成硫单质,用热氢氧化钾溶液洗脱生成的硫单质的质量得到样品中硫化钙的含量,两者之差即为亚硫酸钙的含量,从而建立了脱硫灰还原产物中硫化钙和亚硫酸钙的测定方法。将实验方法应用于不同工艺流程得到的脱硫灰还原产物测定,7次平行测定硫化钙和亚硫酸钙结果的相对标准偏差(RSD,n=7)为0.54%～1.8%。按照实验方法,对3种配制的脱硫灰还原产物中硫化钙和亚硫酸钙进行测定,测定值均和理论值相符。     

铁酸钙与赤铁矿非等温还原动力学

采用非等温热重的方法,在30% CO+70% N₂(体积分数)气氛下,以10 K·min^-1升温至1123 K的过程中,比较了铁酸钙与赤铁矿的逐级还原过程及其还原动力学.结果表明:铁酸钙和赤铁矿开始还原温度分别为873 K和623 K;由反应速率与反应度的关系及分阶段X射线衍射物相分析发现,铁酸钙还原过程为两段式反应(CaO·Fe₂O₃→2CaO·Fe₂O₃→Fe),而赤铁矿还原过程为传统的三段式反应(Fe₂O₃→Fe₃O₄→FeO→Fe).通过Freeman-Carroll法计算得知铁酸钙和赤铁矿的还原平均活化能分别为49.88和43.74 kJ·mol^-1;铁酸钙还原过程符合随机成核随后生长模型,动力学模式函数为Avrami-Erofeev方程,其积分形式为[-ln (1-α)]ⁿ;而赤铁矿还原过程动力学机理分为两部分,在还原度α为0.1~0.5时,为三级化学反应模型,模式函数积分形式为1-(1-α)³;在α为0.5~0.9时,符合二维圆柱形扩散模型,动力学模式函数为Valensi方程,其积分形式为α+(1-α)ln (1-α).     

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     

Oxidation of nickel sulfide

The oxidation of nickel sulfide whose atomic fraction of sulfur,x _s, is 0.40 to 0.44 was studied in a mixed O₂-N₂ gas stream at 923, 973, and 1023 K. The oxygen partial pressure was maintained at 2.0 x 10⁴ Pa. In the oxidation of nickel sulfide ofx _s = 0.40 and 0.41, a dense NiO layer was formed on the sulfide surface without the evolution of SO₂ gas, because of the low sulfur activity. Diffusion of nickel within the inner sulfide core toward the surface controlled the oxidation rate during the first one minute of oxidation. Subsequently, the oxidation rate was controlled by the diffusion of nickel through the formed NiO layer. In the oxidation of nickel sulfide ofx _s = 0.44 at 973 and 1023 K, the reaction proceeded irregularly to the interior of the sulfide core with the evolution of SO₂ gas, and a porous oxide layer was formed, due to the high sulfur activity of nickel sulfide. For the same reason, this oxidation was also accompanied by the dissociation of nickel sulfide. Under the experimental conditions ofx _s = 0.42, 1023 K and x_s = 0.44,923 K, the oxidation started with weight increase and without the evolution of SO₂ gas, and in the subsequent stage the weight decreased and SO₂ gas was evolved. K. HAJIKA, former Graduate Student