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,     

Successive gas-solid reaction model for the hydrogen reduction of cuprous sulfide in the presence of lime

As an alternative to conventional smelting processes for producing metals from sulfide ores, which suffer from SO₂ emission problems, direct reduction in the presence of lime has in recent years attracted much attention. In this work, a mathematical model of successive gas-solid reactions in a porous pellet has been applied to the hydrogen reduction of cuprous sulfide (Cu₂S) in the presence of lime. The model has been formulated by incorporating the intrinsic kinetics of the individual reactions obtained from separate experiments, and compared with the experimental results on the hydrogen reduction of chalcocite mixed with lime particles. The model predictions were in good agreement with experimental measurements of the overall rate of reaction and the degree of sulfur fixation over a wide range of experimental conditions. The mathematical model not only can predict the performance of a given system but also enables one to design the optimum pellet properties and reaction conditions in terms of the reaction rate and sulfur fixation. Formerly Graduate Student in the Department of Metallurgy and Metallurgical Engineering, University of Utah.     

Pentlandite: Preparation,hydrogen reduction in the presence of lime to yield an iron-nickel alloy

Metallurgical and Materials Transactions B - The present paper describes the hydrogen reduction of synthetic pentlandite and pentlandite concentrate in the presence and the absence of added calcium...     

Pentlandite: Preparation, hydrogen reduction in the presence of lime to yield an iron-nickel alloy

The present paper describes the hydrogen reduction of synthetic pentlandite and pentlandite concentrate in the presence and the absence of added calcium hydroxide. Synthetic pentlandite was prepared by heating a stoichiometric mixture of an iron-nickel alloy and sulfur for about 10 days at 473 to 723 K. Differential thermal analysis (DTA) apparatus was used to study the thermal decomposition of the synthetic pentlandite. Hydrogen reduction of synthetic pentlandite in the presence and the absence of added Ca(OH)₂ was studied at 673 to 1023 K in a thermogravimetric apparatus. Additions of Ca(OH)₂ to penlandite accelerated the reduction rates. An acetic acid leach of a product obtained by H₂ reduction of a mixture of pentlandite and Ca(OH)₂ yielded a leach residue containing mainly an iron-nickel alloy. The iron and nickel content in the leach residue averaged about 44 pct iron and 52 pct nickel with recoveries of about 82 pct iron and 94 pct nickel.     

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     

Kinetics of zinc oxide formation from zinc sulfide by reaction with lime in the presence of water vapor

A novel reaction scheme for transforming certain metal sulfides to the corresponding oxides has been developed. In this process, steam oxidizes the sulfide into the oxide, and the hydrogen sulfide produced reacts with lime to form calcium sulfide and regenerate steam. There is no net consumption or generation of gaseous species. Thus, the overall reaction can be carried out in a closed system as far as the gas phase is concerned. This eliminates the possibility of emitting hydrogen sulfide out of the reactor. Only certain metal sulfides are thermodynamically amenable to this treatment. In this paper, the reaction of ZnS to ZnO by this scheme is described, together with a detailed formulation of the rate equation for the overall reaction based on the kinetics of the component gas-solid reactions. Although the present work was done with CaO, other suitable oxides may be used in its place. A further potential application of this process is to the selective oxidation of certain sulfide(s) from complex sulfide ores as a treatment prior to the separation of minerals.     

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.     

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.     

Hydrogen reduction kinetics of nickel sulfide in the presence of calcium oxide

Recovery of pure nickel from nickel sulfide (Ni₃S₂) was studied by following to completion the hydrogen reduction reaction in the presence of calcium oxide. The effects of reaction temperature, molar ratio of calcium oxide to nickel sulfide, bed depth, and particle size of the nickel sulfide powder on the reaction were experimentally investigated. A simple empirical integrated rate equation describing the relationship among these variables over the temperature range 773 to 973 K was derived. The activation energy for the scavenged reaction was found to be 101.9 kJ from the experimental data. Over the range of experimental conditions, both globular and fibrous forms of metallic nickel were observed.     

Fuzzy logic model of lime enhanced hydrogen reduction of cuprous sulphide

Traditional methods for metal extraction from sulphide minerals cause environmental pollutions. In recent decades, direct hydrogen reduction in the presence of lime has attracted an increasing attention among metal-sulphide separation methods. This study aimed to represent an alternative technique for the modelling lime enhanced direct hydrogen reduction process with a fuzzy logic model. The focus of this paper is to find a well defined relationship among the vital variables including bulk temperature, ratio of molar quantities of the solid reactants, pellet diameter, porosity, sulphide particle size, weight loss of the pellet, sulphur fixation in the pellet, and reaction completion time using a fuzzy logic model scheme. Finally, the results predicted by the fuzzy logic model were evaluated and validated against a mathematical model and experimental data.

Les méthodes traditionnelles d’extraction du métal à partir de minéraux sulfureux engendrent une pollution environnementale. Dans les dernières décennies, on a porté une plus grande attention à la réduction directe de l’hydrogène en présence de chaux, parmi les méthodes de séparation du métal-sulfure. Cette étude avait pour but de représenter une technique de rechange pour la modélisation du procédé de réduction directe de l’hydrogène, augmentée par la chaux, au moyen d’un modèle de logique floue. Le point central de cet article est de trouver une relation bien définie parmi les variables vitales, incluant la température globale, le rapport des quantités molaires des réactants solides, le diamètre des boulettes, la porosité, la taille de particule du sulfure, la perte de poids de la boulette, la fixation du soufre dans la boulette et le temps d’exécution de la réaction en utilisant un schéma de modèle de logique floue. Finalement, on a évalué et validé les résultats prédits par le modèle de logique floue contre un modèle mathématique et des données expérimentales.     

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     

Direct reduction of lead sulfide with carbon and lime; Effect of catalysts:Part i. experimental

The direct reduction of lead sulfide with carbon in the presence of lime was investigated in the temperature range 795 to 989 ‡C. Samples of PbS : 4CaO : 4C mixtures prepared from pure constituents were reacted isothermally under a nitrogen atmosphere. The kinetics of reduction were determined for both the uncatalyzed and the catalyzed reduction processes by thermogravimetry. The catalysts used included K₂CO₃, Li₂CO₃, Na₂CO₃, Rb₂CO₃, NaF, Na₂SO₄, and the ternary (K, Li, Na)₂CO₃ eutectic. The extent of catalysis was strong and the rate increase, in some instances, was as large as 10-fold. The following ranking was developed for the various catalysts studied: Li₂CO₃ > Rb₂CO₃ > ternary = NaF = K₂CO₃ > Na₂CO₃ > Na₂SO₄. A detailed study of the effect of temperature on catalyzed reaction kinetics was made with PbS:4CaO:4C mixtures doped with 2.5 wt pet ternary (K, Li, Na)₂CO₃ catalyst. Different catalysts seem to act through different mechanisms. The gas phase emanating from a reacting PbS : 4CaO : 4C was found to contain little or no SO₂ and other sulfur-bearing gaseous species. Independent chemical analysis confirmed that virtually all of the sulfur in the charge is retained as CaS(s) in the final reacted solid product.     

Reduction of molybdenite with carbon in the presence of lime

The thermodynamics of the MoS₂-C-CaO system has been studied in order to understand the carbothermic reduction of molybdenite in the presence of CaO. Kinetic studies were also conducted with mixtures of MoS₂+C+CaO in the temperature range of 900 °C 1200 °C. The reduction of MoS₂ with carbon in the presence of lime proceeds through the direct oxidation of MoS₂ by CaO to form intermediate molybdenum oxidized species, MoO₂ and CaMoO₄, which subsequently undergo reduction by CO to yield mixtures of Mo, Mo₂C, and CaS. Complete conversion of MoS₂ can be obtained at 1200 °C in less than 20 minutes for molar concentrations of MoS₂:C:CaO=1:2:2. The kinetic model ln (1−X)=kt was used to determine the rate constants. The activation energy found for the temperature range studied was 218.8 kJ/mol.     

Thermochemical decomposition of hydrogen sulfide with nickel sulfide

In this research, the two-step thermochemical cycle shown below is proposed and experimental studies were made on the cycle. $$\frac{\begin{gathered} {\text{Ni}}_{\text{3}} {\text{S}}_{\text{2}} + {\text{H}}_{\text{2}} {\text{S}} = {\text{3NiS + H}}_{\text{2}} \hfill \\ {\text{3NiS = Ni}}_{\text{3}} {\text{S}}_{\text{2}} {\text{ + 0}}{\text{.5S}}_{\text{2}} {\text{(g)}} \hfill \\ \end{gathered} }{{{\text{H}}_{\text{2}} {\text{S = H}}_{\text{2}} {\text{ + 0}}{\text{.5S}}_{\text{2}} {\text{(g)}}}}$$ In the case where Ni₃S₂ alone was used without inert additions, nickel sulfide sintered or partly fused due to the melting point depression resulting from the thermal decomposition of formed NiS. Such sintering could be prevented by mixing the nickel sulfide powders with Al₂O₃ or MoS₂. The cyclic reactions were thereby shown to provide a stationary high decomposition rate of H₂S. Polysulfides, such as MS₂, have previously been employed in this kind of cycle. This research showed that the use of lower sulfides such as Ni₃S₂ may be regarded as rather promising based on the thermodynamic investigation of the respective reactions composing the cycle. The comparison between the sulfurization reactions of NiS to NiS₂ and of Ni₃S₂ to NiS further showed that the latter was superior to the former with respect to the kinetics and thermodynamical properties of the reaction.     

The reaction of titanium powder with hydrogen sulfide

Summary A study was made of the reaction of titanium powder with hydrogen sulfide. It was shown that, beginning from 600°C, titanium sulfides are formed with combined titanium and sulfur contents approaching 100%. The compositions of the products formed at 900 and 1200°C are similar to those of the monosulfide and the sesquisulfide, respectively.     

Direct reduction of lead sulfide with carbon and lime; Effect of catalysts:Part ii. analytical model

The experimental data presented in the Part I of this series are interpreted by means of an analytical model. The model is derived on the premise that the Boudouard reaction controls the overall rate of the reduction process in the PbS:4CaO:4C mixtures. The presence of the catalyst is considered to enhance the density of reaction sites on the carbon surface. For the uncatalyzed reduction under nitrogen, the model gives logI ₁ ^u = 4.988 (± 0.408) - 10216 (± 477)T⁻¹. A similar analysis conducted with the catalyzed reduction experiments provided the following relation: logI ₁ ^c = 4.032 (± 0.280) - 7976 (± 329)T ^-1. It is clear that the addition of the (K, Li, Na)₂CO₃ catalyst, in the amount of 2.5 wt pet, causes definite enhancement in the value of the intrinsic rate constant /,. The latter is expressed in mole · (g · C)⁻¹ · atm⁻¹ · s⁻¹. The magnitude of rate enhancement ranges from 13.6 at 800 ‡C to 6.4 at 1000 ‡C.     

Kinetics of the direct synthesis of molycarbide by reduction-carburization of molybdenite in the presence of lime

Kinetic studies were conducted on the carbon monoxide reduction of molybdenite in the presence of lime. Contrary to the expectation that the MoS₂ (s)+CaO (s)+CO (g) reaction will result in metal formation, molycarbide was found to form and no Mo was detected in the product. This is explained on the basis of thermochemical considerations, which indicate that the Mo₂C formation is more feasible by eight orders of magnitude. The effects of quantity of lime in the charge, CO flow rate, temperature (1123 to 1298 K), and time of reduction have been studied. Kinetic analysis reveals that the results on the MoS₂ (s) conversion to Mo₂C (s) fit into a modified parabolic rate law. Based on the thermochemical calculations and experimental findings, the probable reaction scheme has been identified. Molycarbide appears to form by a three-successive solid-gas reaction path consisting of (1) metal formation by the MoS₂ (s)+CO (g) reaction followed by (2) in-situ carburization of Mo metal by CO (g), and finally (3) the scavenging of the COS (g) by lime, resulting in CaS (s). The latter two reactions drive the overall reaction forward. Further, out of these three consecutive reactions, progress of the overall MoS₂+CaO+CO reaction seems to be governed by the intrinsic kinetics of the first one. Calcium molybdate, which forms as a transitory phase, plays a significant role by modifying the linear kinetics of the MoS₂ (s)+CO (g) to one of parabolic nature.     

Stresses induced in iron-ore pellets by hydrogen reduction

The objectives of this investigation were (a) to determine the effect of reduction temperature on the strength of iron ore agglomerates and (b) to develop enhanced understanding for the cracking associ-ated with reduction. Iron-ore agglomerates from two sources (Samarco Mineração and Bethlehem Steel) were reduced in a hydrogen atmosphere at temperatures varying from 873 K to 1373 K at intervals of 100 K and times varying from 30 to 300 minutes. The compressive strength at the ambient temperature of the pellets was determined after the various reduction treatments by using a piston-and-cylinder testing technique and computing the energy required in crushing them. The highest strength, at a specific level of reduction, was found after reduction at 1073 K, for both the Samarco and Bethlehem pellets. Profuse cracking of the pellets was observed after reduction. These cracks led to a weakening of the pellets. A mechanism for reduction-induced cracking, based on internal stresses due to volume changes produced by the chemical reactions, is presented.