A novel cyclic process using CaSO<Subscript>4</Subscript>/CaS pellets for converting sulfur dioxide to elemental sulfur without generating secondary pollutants: Part I. Feasibility and kinetics of the reduction of sulfur dioxide with calcium-sulfide pellets

Certain new sulfide-smelting processes and coal-gasification processes generate high-strength sulfur dioxide streams, for which a new process for converting sulfur dioxide to elemental sulfur needs to be developed because no process exists that is generally and economically applicable to the treatment of such streams. A thermodynamic and experimental investigation to develop a new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and calcium sulfate without generating secondary pollutants was carried out. In this process, the starting raw material, calcium sulfate, is reduced by a suitable reducing agent, such as hydrogen, to produce calcium sulfide, which is used to reduce sulfur dioxide to elemental sulfur vapor and calcium sulfate. The latter is, in turn, reduced to regenerate calcium sulfide. In this Part I, detailed experimental results are presented on the kinetics of the reaction between sulfur dioxide and calcium-sulfide pellets, which produces elemental sulfur and calcium sulfate. The experiments were carried out at temperatures between 1023 and 1088 K and sulfur-dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis (TGA) technique. The rate of this reaction was demonstrated by the conversion of 40 pct calcium-sulfide pellets obtained from the hydrogen reduction of fresh calcium sulfate in 10 minutes at 1073 K under a sulfur-dioxide partial pressure of 43 kPa. The reactivity decreased somewhat during the first three cycles but remained largely unchanged thereafter up to the tenth cycle. This characteristic of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants. A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur-dioxide partial pressure and has an activation energy of 101 to 134 kJ/mol (24 to 32 kcal/mol) for calcium-sulfide pellets reacted and regenerated several different times. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated-gasification, combined-cycle, desulfurization unit and new sulfide-smelting plants, contain much higher partial pressures of SO₂. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported in this article. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part II.     

Intrinsic kinetics of the hydrogen reduction of Cu2S

Intrinsic kinetics of the hydrogen reduction of cuprous sulfide (Cu₂S) have been measured. Experiments were carried out in the temperature range 823 to 1023 K using a thermogravimetric analysis method. The reaction was studied in detail using both thin pellets and powder samples. The reaction followed first-order kinetics with respect to the solid reactant concentration as well as the hydrogen concentration. An activation energy of 92.0 kJ/mol (22.0 kcal/g-mole) was obtained for the reaction. Copper produced from the reaction formed filaments which sintered above about 1000 K. Is now Senior Metallurgist with Cyprus Metallurgical Process Corporation     

Kinetics of the reaction between hydrogen sulfide and lime particles

The reaction between hydrogen sulfide and lime is important, among others, as a component reaction of the hydrogen reduction of metal sulfides in the presence of lime, and in the desulfurization of fossil fuels. The results of experiments on the kinetics of this reaction are presented in this paper. The experiments were carried out in the temperature range 873 to 1073 K, using a thermogravimetric analysis technique. A “pore blocking” model was found to fit the reaction rate, which was initially rapid and leveled off at less than the complete conversion. An activation energy of 76.1 kJ/mol (18.2 kcal/g-mole) was obtained. The reaction was first order with respect to hydrogen sulfide concentration in a gaseous mixture with hydrogen. A higher initial moisture content in the calcium oxide particles resulted in a considerably higher reaction rate. Formerly Graduate Student in the Department of Metallurgy and Metallurgical Engineering, University of Utah     

间接碘量法测定稀土硫化物中硫

试验提出了一种用间接碘量法测定稀土硫化物中硫含量的方法:稀土硫化物易与盐酸反应生成硫化氢,而硫化氢气体易和碘反应,故用已知浓度和用量的碘标准溶液完全吸收硫化氢气体,再用已知浓度的硫代硫酸钠标准溶液滴定出未反应的碘标准溶液,从而间接计算出稀土硫化物中硫含量。通过溶剂的选择、碘标准溶液用量及反应摇动时间的研究,确定了适宜的反应条件。结果表明,在稀土硫化物中硫质量分数为10%～25%时的最佳反应条件是:用盐酸作为反应溶剂,0.1 mol/L碘标准溶液用量为35 mL,反应开始至滴定前的剧烈摇动时间为2 min。采用实验方法对稀土硫化物中具有代表性的Ce₂S₃、Sm₂S₃及La₂S₃这3种样品中的硫进行了测定,结果的相对标准偏差(RSD,n=11)小于1%。测定结果与高频红外吸收法及硫酸钡重量法的测定值基本相符。     

Reaction mechanism for the acid ferric sulfate leaching of chalcopyrite

The acid ferric sulfate leaching of chalcopyrite, CuFeS₂ + 4Fe⁺³ = Cu⁺² + 5Fe⁺² + 2S⁰ was studied using monosize particles in a well stirred reactor at ambient pressure and dilute solid phase concentration in order to obtain fundamental details of the reaction kinetics. The principal rate limiting step for this electrochemical reaction appears to be a transport process through the elemental sulfur reaction product. This conclusion has been reached in other investigations and is supported by data from this investigation in which the reaction rate was found to have an inverse second order dependence on the initial particle diameter. Furthermore, the reaction kinetics were found to be independent of Fe⁺³, Fe⁺², Cu⁺² and H₂SO₄ in the range of additions studied. The unique aspect of this particular research effort is that data analysis, using the Wagner theory of oxidation, suggests that the rate limiting process may be the transport of electrons through the elemental sulfur layer. Predicted reaction rates calculated from first principles using the physicochemical properties of the system (conductivity of elemental sulfur and the free energy change for the reaction) agree satisfactorily with experimentally determined rates. Further evidence which supports this analysis includes an experimental activation energy of 20 kcal/mol (83.7 kJ/mol) which is approximately the same as the apparent activation energy for the transfer of electrons through elemental sulfur, 23 kcal/ mol (96.3 kJ/mol) calculated from both conductivity and electron mobility measurements reported in the literature. formerly Metallurgy Graduate Student, University of Utah.     

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.     

Pressure oxidation kinetics of orpiment (As2S3) in sulfuric acid

Pressure oxidation kinetics of a massive orpiment (As₂S₃) sample in sulfuric acid solution were systematically investigated. The effects of temperature (170 to 230 °C), mean particle size (48 to 125 μm diameter) and oxygen partial pressure (345 to 1035 kPa) were evaluated. Oxidation rates were found to be affected significantly by changes in temperature and particle size, but were relatively insensitive to changes in oxygen partial pressure. Kinetics appear to be controlled by product layer diffusion over the temperature range of 170 to 210 °C, due to the formation of elemental sulfur on particle surfaces. However, Arrhenius activation energies over this range are large (> 40 kJ/mol) and increase with decreasing temperature, perhaps reflecting the kinetics of sulfur oxidation rather than diffusion. Above 210 °C the rate-controlling step is a surface reaction with an activation energy of approximately 33.8 kJ/mol. The reaction order at 210 °C is approximately 0.2 with respect to oxygen partial pressure.     

Rate controlling processes for crack growth in hydrogen sulfide for an alsl 4340 steel

Parallel fracture mechanics and surface chemistry studies were carried out to develop further understanding of environment assisted subcritical crack growth in high strength steels. The kinetics of crack growth for an AISI 4340 steel (tempered at 477 K) in high purity hydrogen sulfide have been determined as a function of pressure at room temperature and as a function of temperature at hydrogen sulfide pressures of 0.133 and 2.66 kPa. The kinetics for the reactions of hydrogen sulfide with this steel and the extent of reactions were also determined. Two rate controlling processes have been identified. At the lower pressure, the rate of crack growth varies according to T^1/2 and is controlled by the rate of transport of hydrogen sulfide to the crack tip. At the higher pressure, crack growth is controlled by the rate of diffusion of hydrogen into the steel ahead of the crack tip and exhibits an apparent activation energy of about 5 kJ/mol. Embrittlement results from hydrogen that is produced by the reactions of hydrogen sulfide with the steel. These reactions are extremely rapid and are limited in extent, leading to the formation of one to two layers of “sulfide” on the fracture surfaces. The crack growth results are discussed in terms of measured reaction kinetics and published data on diffusion, and in relation to models for transport- and diffusion-controlled crack growth. Formerly with Lehigh University, Bethlehem, PA     

高磷铁矿石含碳球团等温还原动力学

 为了研究高磷铁矿石含碳球团等温还原动力学在温度为1 173、1 273、1 323、1 373、1 423和1 473 K时,采用界面化学反应模型、Jander方程、Ginstling-Broushtein方程、G Valensi-R E Carter方程等固-固/气反应机理函数对反应过程进行拟合,并采用XRD、SEM、EDX等对样品的物相组成、微观形貌和元素分布进行表征分析。研究结果表明,随着还原程度提高,反应速率由0迅速增至最大值,随后逐渐减小并趋于平缓;当温度为1 173～1 373 K时,反应过程符合界面化学反应,表观活化能为70.02 kJ/mol,线性相关系数为0.948 1;当温度为1 373～1 473 K时,反应过程符合Jander方程,限制步骤为铁离子固相扩散,表观活化能为215.36 kJ/mol,线性相关系数为0.991 2。     

铁矿-生物质复合球团还原行为及还原动力学

通过分析生物质合成气气氛下,不同组分复合球团（添加和未添加生物质）的还原速率、还原度、表面微观结构和失重变化规律．对球团中添加生物质的作用机理以及含生物质球团还原过程的限制性环节展开研究．添加生物质的复合球团表面结构比无生物质球团疏松,孔隙率高,有利于后续还原的热质传递,增加产物还原度,降低反应活化能;复合球团的还原以收缩核方式进行,在1123~1323K温度范围内,界面化学反应是两种球团还原反应的主要控速环节;添加生物质后,有利于界面化学反应的进行．使得球团的还原表观活化能由95．448kJ·mol-1降低到68．131kJ·mol-1．      

硫化铜精矿加碳酸钙焙烧表观动力学研究

通过DTA和TG结合X 射线衍射分析的方法,将硫化铜精矿加碳酸钙焙烧与硫化铜精矿焙烧的反应机理进行了对比研究。结果表明:加碳酸钙的硫化铜精矿焙烧在673～857K时铜的硫化物被氧化成硫酸盐;在857～1073K时生成的硫酸盐会发生分解。由数据分析可知它的两个阶段都受化学反应控制,其表观活化能和频率因子分别为E1=121.1kJ/mol,E2=182.9kJ/mol,A1=1.155×107s-1,A2=2.115×107s-1,其非等温动力学方程的表达式为:dαRT(1-α)2dT=Aβe-E     

Intrinsic kinetics of the chlorination of hematite powder between 898 and 1023 K

The kinetics of the chlorination of hematite powder was investigated between 898 and 1023 K by isothermal thermogravimetry. The influence of the chlorine partial pressure and sample size on the reaction rate was studied between 15 and 70 kPa and between 0.5 and about 50 mg, respectively. The reaction occurs under mixed control; pore diffusion and chemical reaction are the rate-controlling steps. An apparent reaction order of 0.5 with respect to chlorine partial pressure (that implies a zero intrinsic order) and a value of activation energy of 451 kJ/mol were found.     

不锈钢尘泥球团煤基直接还原动力学

摘要：研究了不锈钢尘泥球团在温度分别为1100、1150、1200、1250℃时的煤基直接还原反应动力学。采用随机成核和随后生长、化学反应控制、相界面反应和n（n=1、2、3、4）维扩散模型及其相应动力学机制函数对反应过程进行拟合,并结合X-射线衍射（XRD）、扫描电镜（SEM）、能谱分析（EDS）等手段对不锈钢尘泥球团煤基直接还原过程的物相组成、显微结构及元素分布进行表征和分析。研究结果表明：反应初期铁氧化物还原速率较快,随后逐渐减慢,当反应至40min后,反应趋向于平衡。在1100~1250℃温度范围内反应遵从随机成核和随后生长及A1(α)=-ln(1-α)机制函数,碳的气化反应和界面化学反应是尘泥球团煤基直接还原反应的限制性环节,该反应活化能E为47.423kJ/mol,线性相关系数为0996。     

Kinetics of dissolution of sulfur in tetrachloroethylene

The kinetic regularities of the dissolution of sulfur in tetrachloroethylene (TCE), which depend on the temperature, hydrodynamic conditions, and TCE concentration, are presented. Using the rotating disc method, it is revealed that this process occurs in a mixed mode; its diffusion and kinetic components are revealed. The reaction order of the kinetic component of the dissolution rate of sulfur by TCE is 1.5, while the experimental activation energy of the process is 39.2 ± 2.0 kJ/mol. The activation energy of the diffusion component of the convective mass transfer during the dissolution of sulfur in TCE is 28.0 ± 2 kJ/mol.     

The dissolution of galena in ferric chloride media

The dissolution of galena (PbS) in ferric chloride-hydrochloric acid media has been investigated over the temperature range 28 to 95 °C and for alkali chloride concentrations from 0 to 4.0 M. Rapid parabolic kinetics were observed under all conditions, together with predominantly (>95 pet) elemental sulfur formation. The leaching rate decreased slightly with increasing FeCl₃ concentrations in the range 0.1 to 2.0 M, and was essentially independent of the concentration of the FeCl₂ reaction product. The rate was relatively insensitive to HCl concentrations <3.0 M, but increased systematically with increasing concentrations of alkali or alkaline earth chlorides. Most significantly, the leaching rate decreased sharply and linearly with increasing initial concentrations of PbCl₂ in the ferric chloride leaching media containing either 0.0 or 3.0 M NaCl. Although the apparent activation energy was in the range 40 to 45 kJ/mol (∼10 kcal/mol), this value was reduced to 16 kJ/mol (3.5 kcal/mol) when the influence of the solubility of lead chloride on the reaction rate was taken into consideration. The experimental results are consistent with rate control by the outward diffusion of the PbCl₂ reaction product through the solution trapped in pores in the constantly thickening elemental sulfur layer formed on the surface of the galena.     

Kinetics of manganous oxide sulfidization in carbonyl sulfide (COS) contaminated atmospheres

To contribute to the mitigation of man-made emission of sulfurous compounds, the susceptibility of manganous oxide for carbonyl sulfide under reducing atmospheres (C-O-S system) has been investigated over the temperature range 700 to 1010 °C (973 to 1283 K). The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the topochemical reaction of spherical MnO pellets under various experimental conditions. The apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C-O-S system, was determined to be 12.06 (±1.5) kcal/mol (52.33 (±6.28) kJ/mol). Overall sulfidization appeared to proceed by mixed control involving convective mass transfer of COS across the boundary layer and diffusion through the product layer. Formerly with the Department of Theoretical Metallurgy, Royal Institute of Technology, Stockholm     

Kinetics of manganous oxide sulfidization in carbonyl sulfide (COS) contaminated atmospheres

To contribute to the mitigation of man-made emission of sulfurous compounds, the susceptibility of manganous oxide for carbonyl sulfide under reducing atmospheres (C-O-S system) has been investigated over the temperature range 700 to 1010 °C (973 to 1283 K). The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the topochemical reaction of spherical MnO pellets under various experimental conditions. The apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C-O-S system, was determined to be 12.06 (±1.5) kcal/mol (52.33 (±6.28) kJ/mol). Overall sulfidization appeared to proceed by mixed control involving convective mass transfer of COS across the boundary layer and diffusion through the product layer. Formerly with the Department of Theoretical Metallurgy, Royal Institute of Technology, Stockholm     

Fe3O4内配石墨球团的还原动力学

开展了Fe3O4内配石墨球团还原试验,以考察球团的中温还原性。设定温度950～1 100℃,时间低于35min。并采用新建立的还原动力学方程(PKV方程)计算球团的动力学参数。结果表明,球团的还原能力随时间、温度的提高而增加,初始时间段及较低温度下增加幅度相对较大;温度对球团的还原影响很大。球团在19min前后的活化能分别为102.046kJ/mol和86.872kJ/mol。控制环节为界面化学反应,前19min为碳的气化反应,后19min为CO还原Fe3O4。     

Oxygen pressure leaching of white metal

Sulfuric acid–oxygen pressure leaching of white metal was investigated at laboratory scale as an alternative to the pyrometallurgical Peirce–Smith converting to produce metallic copper. The main variables studied were temperature, concentration of sulfuric acid, partial pressure of oxygen, and time of leaching. The results indicated that most of the sulfur in the white metal is oxidized to sulfate in the range 105 °C to 150 °C. The concentration of sulfuric acid over 0.05 M, and oxygen partial pressure over 608 kPa had little effect on the dissolution of copper. The temperature was the most significant variable; below 130 °C copper dissolution was incomplete after 5 h of leaching while at 150 °C the dissolution was complete in 90 min. The dissolution of white metal proceeded in two stages through the formation of CuS as an intermediate compound and the kinetics of copper dissolution was analyzed by considering two consecutive reactions controlled by chemical reaction. The activation energies for the first and second stages were determined as 55 and 88 kJ/mol, respectively.     

钒钛磁铁矿含碳球团的还原历程

 为实现钒钛磁铁矿资源的高效合理利用,对钒钛磁铁矿含碳球团的还原过程进行了解析,初步建立了动力学控制方程;利用差热分析方法对钒钛磁铁矿的还原熔分历程进行了分析与讨论,认为钒钛磁铁矿的还原可分为煤的氧化、钒钛磁铁矿的直接还原、借助碳的气化反应的直接还原和还原结束4个部分;以攀枝花钒钛磁铁矿为原料,煤为还原剂,考察了反应时间和温度对含碳球团还原度的影响,确定固体产物层内扩散是钒钛磁铁矿含碳球团直接还原反应的控制性环节,计算出其表观活化能为112.13 kJ/mol。