Roasting of a sulfide polymetallic concentrate in a fluidized bed furnace

Three series of experiments on oxidizing roasting of sulfide polymetallic concentrates in a laboratory fluidized bed furnace are performed to develop an economically efficient technology of processing the sulfide polymetallic ore concentrate of the Artem’evsk deposit (Kazakhstan). The composition of the initial concentrate and the products of its oxidizing roasting are studied. The mineral composition of the concentrate is determined, and it demonstrates that this material tends toward intense spinel formation under oxidizing roasting conditions. The main structural constituents of the cinder are found to be sulfate-spinel conglomerates and oxide and sulfide particles. The possible ways of formation of these constituents are discussed using the obtained experimental data, the existing theoretical concepts, and the results of thermodynamic analysis. The calculations are performed using the FactSage software package and database. The formation of oxide and spinel components are found to be caused by both direct oxidation of sulfide minerals (primary processes) and the interaction of primary products with sulfuric anhydride and each other (secondary processes). In turn, all sulfates in the cinder are the products of secondary processes, and primary sulfate formation does not take place in roasting under the chosen conditions. Spinels cannot be completely removed from the cinder using their sulfation because of predominant consumption of sulfuric anhydride for interaction with oxide components. The optimum roasting conditions that ensure the formation of the best cinder for subsequent hydrometallurgical processing are chosen on the basis of the obtained data. The degree of extraction of nonferrous metals achieved upon leaching of the cinder is 94–96 wt %.     

Oxidation kinetic studies of zinc sulfide in a fluidized bed reactor

Kinetic studies of the oxidation of zinc sulfide were carried out in a fluidized bed reactor over a temperature range of 740° to 1000°C with O-N gas mixtures of 20 to 40 pct O₂. A mathematical model was developed to describe the overall conversion of the solids. Application of the model to the experimental data indicated that the chemical reaction at the outer boundary of the unreacted sulfide core was the rate-limiting step for the process. The temperature dependence of the kinetic constant corresponded to an activation energy of 40,250 cal per mole. Oxygen starvation in the bed was not limiting in any of the experimental runs, but an increase in the inlet-oxygen mole fraction resulted in a substantial increase in reaction rate.     

用化学处理法从低品位辉钼矿精矿中回收钼

本文报导的研究成果涉及两种工艺:(1)苏打灰焙烧法;(2)石灰强化碳热还原法。将它们用于从低品位辉钼矿精矿中提取钼产品的试验已经获得成功。用上述两种工艺已分别产出MoO_3和钼金属半成品,所得半成品再分别用炭吸附—解吸法和熔盐电解精炼法进一步提纯,最终产品的纯度分别达到99．9%和99．8%。此外,这些工艺还提供了包括环境污染和废气治理等的有效解决办法。而它们在处理高品位MoS_2矿石(或精矿)的传统工艺中,正是两个尚未解决的主要问题。     

用化学处理法从低品位辉钼矿精矿中回收钼

本文报导的研究成果涉及两种工艺：（1）苏打灰焙烧法；（2）石灰强化碳热还原法。将它们用于从低品位辉钼矿精矿中提取钼产品的试验已经获得成功。 用上述两种工艺已分别产出MoO3和钼金属半成品，所得半成品再分别用炭吸附一解吸法和熔盐电解精炼法进一步提纯，最终产品的纯度分别达到99．9％和99、8％。此外，这些工艺还提供了包括环境污染和废气治理等的有效解决办法。而它们在处理高品位MoS2矿石（或精矿）的传统工艺中，正是两个尚未解决的主要问题。     

Oxidation of zinc sulfide in a fluidized bed

Kinetics of oxidation of ZnS particles in a batch-type fluidized bed were studied at temperatures between 800 and 910°C. A two-phase model was employed for the fluidized bed, and the partial pressure of oxygen and the gas-film mass transfer coefficient on the particle surface were separately evaluated in gas bubbles and in the emulsion phase. The calculated fractional reaction coincided well with the experimental results. The difference in O₂ partial pressure between gas bubbles and emulsion phase was found to be fairly large especially under the vigorous fluidizing condition. Furthermore, it was shown from the mathematical model that the reaction of ZnS particles in the gas bubbles is negligible because of the extremely low solid concentration and that the overall rate of reaction in the emulsion phase is virtually controlled by the rate of gas-film mass transfer at higher temperature. The resistance of interfacial reaction within the particle also becomes significant when the temperature is lowered. Y. Fukunaka and T. Monta are both former Graduate Students, Kyoto University, Kyoto, Japan.     

Thermal decomposition of limestone in a fluidized bed

Particles of limestone of 16 to 28 and 60 to 100 mesh sizes were decomposed in a fluidized bed. A mathematical model for the thermal decomposition was proposed comprising the thermal decomposition at the interface within particles and the related heat and mass transfer steps. It was assumed in this model that the particles are completely mixed within the fluidized bed and that gas is in upward plug flow. Fractional decomposition of limestone particles and the bed temperature during thermal decomposition calculated from this model coincide very well with the experimental results. It was further revealed that the overall reaction rate of 60 to 100 mesh size particles is virtually determined by the rate of heat transfer from the reactor wall to the fluidized bed, and that both rates of interfacial reaction and heat transfer from the wall to the bed contribute to the overall decomposition rate of 16 to 28 mesh size particles. Former Graduate Student at Kyoto University, is now with the Railway Technical Research Center, JNR, Tokyo, Japan.     

Iron ore reduction in a continuously operated multistage lab-scale fluidized bed reactor—Mathematical modeling and experimental results

Industrial-scale fluidized bed processes for iron ore reduction (e.g., FIOR and FINMET) are operated by continuous feeding of ore, while laboratory tests are mostly performed under batchwise operation. The reduction behavior under continuous operation is influenced by both the residence time of the iron ore particles and the reduction kinetics, which is obtained by batch tests. In a mathematical model for such a process, the effect of both phenomena has to be considered. The residence time distribution of iron ore particles in a laboratory fluidized bed reactor was obtained by measuring the response of a step input and described by mathematical models similar to a continuously stirred tank reactor. In the same reactor, reduction tests with continuous feeding of iron ore were performed. Based on batch tests in a fluidized bed reactor, a mathematical model was developed to describe the kinetics of iron ore reduction under fluidized bed conditions. This kinetic model was combined with the fluidized bed reactor model to describe continuous iron ore reduction. In this detailed model, the change of gas composition while rising in the fluidized bed was considered. The degree of reduction and the gas conversion for reactors in series were calculated. The results obtained by the mathematical model were compared with experimental data from the laboratory-scale reactor.     

Identification and activities in situ of Nitrosospira and Nitrospira spp. as dominant populations in a nitrifying fluidized bed reactor

Bacterial aggregates from a chemolithoautotrophic, nitrifying fluidized bed reactor were investigated with microsensors and rRNA-based molecular techniques. The microprofiles of O2, NH4+, NO2-, and NO3- demonstrated the occurrence of complete nitrification in the outer 125 microgram of the aggregates. The ammonia oxidizers were identified as members of the Nitrosospira group by fluorescence in situ hybridization (FISH). No ammonia- or nitrite-oxidizing bacteria of the genus Nitrosomonas or Nitrobacter, respectively, could be detected by FISH. To identify the nitrite oxidizers, a 16S ribosomal DNA clone library was constructed and screened by denaturing gradient gel electrophoresis and selected clones were sequenced. The organisms represented by these sequences formed two phylogenetically distinct clusters affiliated with the nitrite oxidizer Nitrospira moscoviensis. 16S rRNA-targeted oligonucleotide probes were designed for in situ detection of these organisms. FISH analysis showed that the dominant populations of Nitrospira spp. and Nitrosospira spp. formed separate, dense clusters which were in contact with each other and occurred throughout the aggregate. A second, smaller, morphologically and genetically different population of Nitrospira spp. was restricted to the outer nitrifying zones.     

Decreased gas consumption of a fluidized bed furnace

The feasibility of utilizing a closed circulatory system to generate gases for a fluidized bed furnace was investigated with the primary concentrations of both economizing on the raw materials used for producing furnace atmospheres and decreasing the air pollution caused by exhaust gases. Air humidified with water vapor was first introduced into a charcoal furnace for causing a reaction with hot charcoal to form a carburizing atmosphere. This atmosphere was then introduced into a fluidized bed furnace to carburize steels. The exhaust gases from the fluidized bed furnace were recycled by repassing them through the hot charcoal layer in the charcoal furnace with a gas pump. The charcoal furnace and the fluidized bed furnace formed a closed circulatory system during the carburization of steels. Experiments were performed with various parameters of this system, including content of water vapor in the humid air, temperature of the charcoal, rate of recirculation of the atmosphere,etc. The effect of each parameter on the carburizing behavior in the fluidized bed furnace was investigated on the basis of the rate of carburization and the carbon potential of the atmosphere. The feasibility of applying this system to a fluidized bed furnace was assessed from the aspects of the fluidization of A1₂O₃ powder, the result of carburizing steel, and the rate of consumption of charcoal. The closed system employed in generating atmosphere was demonstrated by the experimental results to have enabled the fluidized bed furnace to operate normally and to have significantly decreased both the consumption rate of charcoal and the environmental pollution.     

Use of a tapered fluidized bed as a continuous bioreactor

Reactor systems based on tapered fluidized beds are being developed for aqueous bioprocesses in which adhering microorganisms or immobilized active biological fractions are used. The use of a fluidized bed prevents biomass buildup, accommodates particulates in the feed stream, is compatible with gas sparging, and allows easy removal or addition of the active materials. The tapered reactor tends to stabilize the fluidized bed, thus allowing a much wider range of operating conditions. Preliminary experimental results and an empirical mathematical model of the tapered bed indicate that bed stability is associated with a decreasing velocity and void-fraction profile up the bed and the pressure drop across the bed decreases with increasing flow rates. The tapered fluidized bed bioreactor is being evaluated for use in the enzymatic production of hydrogen, microbiological denitrification, and microbiological degradation of coal conversion aqueous waste streams. The enzyme catalyzed conversion of lactose to glucose and galactose was used in the evaluation of the reactor concept.     

Fabrication of CeZrO2 on Ni/SiO2 and promoted catalysis for methane autothemal reforming in a fluidized bed reactor

The methane autothermal reforming in the present of oxygen was studied over cerium-and zirconium-promoted Ni/SiO2 catalysts in a fluidized bed reactor. The addition of CeZrO2 resulted in a significant improvement in the initial activity of the catalysis as well as an in-crease in the stability. The long-term activity of the promoted catalyst was dependent upon the rapid redox properties between the oxidative zone and the reductive zone in a fluidized bed reactor. H2 temperature-programmed reduction (H2-TPR) and temperature-progranmaed sur-face reaction (TPSR) studies demonstrated that addition of the CeZrO2 resulted in an increase in the reducibility and oxygen transfer ability of the support, Ni/Ce0.5ZrO0.5O2-SiO2 showed improved redox properties compared with Ni/SiO2 due to a low-temperature reduction. X-ray diffraction (XRD) of the fresh and spent catalysts showed that the promoter enhanced the nickel dispersion and retarded metal particle growth during reaction at high temperature, and surface Ni was gradually oxidized by remaining O2, leading to Ni deactivation.     

Fabrication of CeZrO2 on Ni/SiO2 and promoted catalysis for methane autothermal reforming in a fluidized bed reactor

The methane autothermal reforming in the present of oxygen was studied over cerium- and zirconium-promoted Ni/SiO₂ catalysts in a fluidized bed reactor. The addition of CeZrO₂ resulted in a significant improvement in the initial activity of the catalysis as well as an increase in the stability. The long-term activity of the promoted catalyst was dependent upon the rapid redox properties between the oxidative zone and the reductive zone in a fluidized bed reactor. H₂ temperature-programmed reduction (H₂-TPR) and temperature-programmed surface reaction (TPSR) studies demonstrated that addition of the CeZrO₂ resulted in an increase in the reducibility and oxygen transfer ability of the support, Ni/Ce_0.5ZrO_0.5O₂-SiO₂ showed improved redox properties compared with Ni/SiO₂ due to a low-temperature reduction. X-ray diffraction (XRD) of the fresh and spent catalysts showed that the promoter enhanced the nickel dispersion and retarded metal particle growth during reaction at high temperature, and surface Ni was gradually oxidized by remaining O₂, leading to Ni deactivation.     

Coal gasification in a system with a damped circulating fluidized bed

Experiments are conducted on the steam gasification of Borodino coal in a two-chamber gas generator. The generator is based on a circulating fluidized bed with damping of gas motion by the packing. The mean size of the coal particles is 0.2 mm. Heat from the combustion chamber is sent to the gasification chamber by the circulation of a disperse powder (electrocorundum) between the chambers. The chambers are filled with spherical packing (diameter 50 mm, porosity 0.5). The size of the electrocorundum particles is 0.3 mm. The heat of combustion of the gasification products is 8195 kJ/m³. The unburned residue is 5% in chemical terms and 2% in mechanical terms. The model proposed for the gas generator consists of one heat-balance equation each for the combustion and gasification chambers. The model is consistent with the experimental data. On the basis of the model, the optimal generator parameters are found: temperature 900°C in the gasification chamber and 1020°C in the combustion chamber; proportion of coal sent to the gasification chamber 36%; chemical efficiency 40%.     

The reduction of hematite to wustite in a laboratory fluidized bed

Particles (approximately 180 to 250 Μm across) were reduced by CO-CO₂, by H₂-H₂O, and by CO-CO₂-H₂-H₂O in a small fluidized bed, with facilities for automatic sampling of off-gas. Structural changes in the preheating period and during reduction were followed by surface area measurements and by microscopy. During reduction, surface areas increased initially and then decreased, as porosity created by chemical reaction was reduced by sintering; ‘uniform internal reduction’ was observed from magnetite to wustite. Although the bed was operated under vigorously bubbling conditions, with flow rates 7 to 15 times the minimum fluidization velocity at temperature, gas utilization was high for abstraction of about two-thirds of the maximum amount of oxygen removable by the inlet gas. The utilization fell sufficiently in the remaining stages of the reaction for approximate rate constants to be estimated. The rate increased (a) with increasing temperature, (b) with increasing gas flow, (c) with increasing reducing potential of the inlet gas, and (d) with increasing hydrogen content of inlet gas. The off-gas analyses showed the importance of the water gas shift reaction within the pores of the fluidized particles.     

循环流化床锅炉的运用

从燃烧机理、锅炉热效率、运行的稳定性、对燃煤的适应性、环境保护、锅炉启动过程、停炉过程等几个方面介绍了循环流化床锅炉的特点.同时介绍了循环流化床锅炉若干问题如床温调节、防止床层超温结焦、非金属耐磨耐火材料防磨、减少锅炉底灰、飞灰可燃物、合理选择冷渣器的处理意见.     

The fluidized bed electrowinning of silver

Fluidized bed electrowinning appears to be an alternative to the Zadra cell usually employed to deposit silver electrolytically from cyanide solutions. By using a bench scale cell it was found that when using either pure silver or silver coated copper particles such electrowinning could be carried out without operating problems and with reasonable current efficiency and cell voltage. Various anodes, for use in the cell, were examined and three found to be satisfactory. By electrolyte analysis and by EDAX analysis of the silver deposit, the silver was shown to be free of impurities down to the detection level of the analyses.     

石油焦流化床气化模拟研究

运用Aspen plus软件对石油焦气化过程进行模拟,建立流化床气化炉模型,采用RYield与RGibbs化学反应器模拟气化化学反应过程,发现模拟值与实验值具有良好的一致性.结果表明,采用Aspen plus建立的气化模型,能够准确模拟石油焦气化过程;石油焦—空气气化气体热值随ER增加而减少,CO流量先升高后减小在ER等于0.45时达到峰值;气化气体热值随气化炉内压强增大而增大,增大压强可以使CH_4流量增加;气化气体热值随汽氧比增大而增大,有效气体流量随汽氧比增大而增大.     

Extraction of rhenium from calcines of the oxidation roasting of low-grade molybdenite concentrate in a rotating tubular furnace

Consideration is given to the effect of various oxidizers used in the process of leaching on the extent of extraction of rhenium remained in the calcine as a result of incomplete sublimation upon the oxidation roasting of molybdenite concentrate in a tubular furnace. Its maximum extraction α_Re = 88%) is reached when using manganese concentrate. It has been established that for the Almalyk Metallurgical Integrated Works the most suitable oxidizer is a mixture of nitric and sulfuric acids (α_Re = 71–73%); in this case, a virtually complete purification of the calcine from copper takes place (≤0.05–0.07% Cu is retained in it). It is shown that molybdenum and rhenium that passed into solution can be separated by precipitation and ion-exchange methods.