Agglomeration of particles during roasting of zinc sulfide concentrates

This study was undertaken in an attempt to explain the agglomeration of zinc concentrate particles that occurs during fluid bed roasting. In order to simulate extensive particle contact, pure ZnS, FeS, and (Zn, Fe)S particles were roasted in a fixed bed at temperatures between 1223 K and 1323 K using an argon-oxygen gas mixture withP _O2 = 0.21 atm. The results were compared to the reaction products and morphology of an agglomerated commercial concentrate. The reactants were contained in MgO crucibles suspended in a thermobalance and the weight change was recorded as the reaction proceeds. The resulting data were used to identify the specific reaction that takes place for each of the reactants. Products were identified by X-ray diffraction analysis. The morphology of the products was analyzed using SEM and confirmed that the formation of a liquid phase composed of a solution of Fe-S-O causes particles to stick to each other, thus causing agglomeration. This phenomenon was observed for both the FeS and (Zn, Fe)S samples but not for the ZnS. The morphology and the X-ray diffraction pattern of the reaction products of the synthetically prepared (Zn, Fe)S showed remarkable similarity to that of the roasted industrial concentrate.     

The mechanism of ferrite formation from iron sulfides during zinc roasting

The formation of zinc ferrite (ZnFe₂O₄) during the fluidized-bed roasting of zinc concentrates presents subsequent processing difficulties both for zinc recovery and for iron separation and disposal. A major source of iron in these concentrates is from the iron sulfides — pyrite and pyrrhotite. This study examined the changes undergone by these iron minerals when roasted together with sphalerite at 1223 K in a fluidizing gas mixture of 3 pct oxygen and 97 pct nitrogen. Optical microscopy and electron microprobe analysis were employed to identify the three stages that lead to ferrite formation and to examine the processes that occur within each stage. The first stage is oxidation of the sulfides to highly vesicular, amorphous magnetite particles containing small amounts of zinc. The second stage involves both densification of these particles by sintering and counterdiffusion of iron and zinc cations to form a continuous phase of homogeneous zinc-rich spinel and a precipitate of hematite. In the third stage, continuation of cation diffusion and increasingPo ₂ results in the formation of stoichiometric zinc ferrite. These observations have been interpreted by reference to the established phase relationships that occur in the Zn-Fe-O system, and a detailed, solid state reaction mechanism for the formation of zinc ferrite has been proposed.     

The mechanism of ferrite formation from iron sulfides during zinc roasting

The formation of zinc ferrite (ZnFe₂O₄) during the fluidized-bed roasting of zinc concentrates presents subsequent processing difficulties both for zinc recovery and for iron separation and disposal. A major source of iron in these concentrates is from the iron sulfides — pyrite and pyrrhotite. This study examined the changes undergone by these iron minerals when roasted together with sphalerite at 1223 K in a fluidizing gas mixture of 3 pct oxygen and 97 pct nitrogen. Optical microscopy and electron microprobe analysis were employed to identify the three stages that lead to ferrite formation and to examine the processes that occur within each stage. The first stage is oxidation of the sulfides to highly vesicular, amorphous magnetite particles containing small amounts of zinc. The second stage involves both densification of these particles by sintering and counterdiffusion of iron and zinc cations to form a continuous phase of homogeneous zinc-rich spinel and a precipitate of hematite. In the third stage, continuation of cation diffusion and increasingPo ₂ results in the formation of stoichiometric zinc ferrite. These observations have been interpreted by reference to the established phase relationships that occur in the Zn-Fe-O system, and a detailed, solid state reaction mechanism for the formation of zinc ferrite has been proposed.     

Phase change,micro-structure and reaction mechanism during high temperature roasting of high grade rare earth concentrate

The deposit of Bayan Obo in Inner Mongolia is the world's largest rare earth element(abbreviated as REE)resource.The exploration of the theory of mineral formation of Bayan Obo is an important foundation for mineralogical research,and is the scientific basis for mining,industrial beneficiation,smelting and extraction,and processing and utilization.With the rapid development of science and technology,the demand for the utilization of rare earth elements is increasing,and the separation process between rare earth elements needs to be developed.The purpose of this paper is to provide high temperature experimental information for the formation and application of rare earth minerals.To this end,the mineral evolution of high-grade rare earth concentrates with increasing temperature and the migration of rare earths at different stages and their reaction mechanisms were studied.According to thermogravimetric analysis and differential scanning calorimetry(TG-DSC),calcination was carried out at different temperature ranges,and the calcined products were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron micro scope and energy dispers ive spectrometer(SEM-EDS)and other analytical techniques.The re sults are shown in this process,the ra re earth phase is first converted into rare earth oxide and rare earth oxyfluoride.As the temperature increases,Ca_5(PO_4)_3 F and a large number of self-shaped spherical Ca-RE-OF and Ca-RE-PO_4 particles are formed,and the separation of La and Ce elements is discovered.Acco rding to the phase diagram analysis,the production of Ca_5(PO_4)_3 F is due to the reaction of monazite and fluorite,and the phases CeF_2 and Ce F_3 are formed during the reaction.When it reaches 1500℃,barium ferrite is produced and a new substance containing Ba~(2+)is formed.     

Dearsenification of gold concentrates via microwave roasting

ABSTRACT

Arsenic can cause environmental pollution and also affect mineral processing efficiency. To determine the mechanism of separating arsenic from minerals, microwave roasting tests were conducted using Hunan arsenic sulfide gold concentrate as a raw material. The heating behaviour of gold concentrates under microwave irradiation was analysed. The effects of roasting temperature, reaction time, and oxygen content on arsenic removal were investigated. Temperature has the greatest effect on arsenic removal, followed by reaction time and oxygen content. The optimum parameters were determined experimentally. The removal rate of arsenic was 93.16% (gas supply: 4?L min^?1, reaction temperature: 650°C, duration: 15?min). Scanning electron microscopy analysis of the minerals after microwave roasting and conventional roasting showed that there are more cracks on the surface of minerals after microwave roasting, and the specific surface area is larger. The reaction mechanism of arsenic separation from gold concentrate during microwave roasting is discussed.     

Pelletizing of sulfide molybdenite concentrates

The results of a pelletizing investigation using various binding components (water, syrup, sulfite-alcohol distillery grains, and bentonite) of the flotation sulfide molybdenite concentrate (～84% MoS₂) from the Mongolian deposit are discussed. The use of syrup provides rather high-strength pellets (>3 N/pellet or >300 g/pellet) of the required size (2–3 mm) for the consumption of 1 kg binder per 100 kg concentrate. The main advantage of the use of syrup instead of bentonite is that the molybdenum cinder produced by oxidizing roasting of raw ore materials is not impoverished due to complete burning out of the syrup. This fact exerts a positive effect on the subsequent hydrometallurgical process, decreasing molybdenum losses related to dump cakes.     

烧结处理小矿山精矿的应用研究

研究小矿山精矿的性质，分析小矿山精矿对烧结过程的影响，提出了增加小矿山精矿配入量的途径及方法．     

铁铌精矿高温导热系数测定

在热平衡的基础上,根据一维稳态导热理论,测定了白云鄂博铁铌精矿在不同温度下的导热系数,回归得出了该材料在高温状态下导热系数λ与工作温度T之间的关系方程.     

连续冷却过程中铁素体相变温度的模拟

以传统的形核理论为基础,考虑了变形的影响,研究了奥氏体-铁素体相变的等温相变孕育期,采用Scheil的可加性法则计算了SS400钢在变形和未变形条件下的铁素体相变实际转变温度（Ar3）,并与实测值进行了对比,结果表明：计算的Ar3与实测的Ar3吻合良好,从而进一步表明该相变孕育期模型的准确性．     

碳质银精矿富氧-氯化焙烧试验研究

对高硫高碳型碳质银精矿进行了富氧-氯化焙烧预处理试验研究,主要考察了氯化剂质量分数、焙烧温度、空气与氧气体积比、焙烧时间等因素对碳、硫去除率及金、银浸出率的影响。试验结果表明:在氯化剂质量分数10%、焙烧温度550℃、空气与氧气体积比1∶1.5、焙烧时间6 min的最佳焙烧条件下,金、银浸出率分别为98.51%、92.20%。同时,通过对比氧化焙烧、氯化焙烧和富氧-氯化焙烧3种预处理方法表明,富氧-氯化焙烧在处理高硫高碳型复杂银精矿方面具有明显优势。     

冀东磁铁精矿球团焙烧机理的研究

研究了焙烧温度、时间等因素对冀东磁铁精矿粉球团焙烧质量的影响.当预热温度超过1 000 ℃时,颗粒表面生成液相,造成球团氧化不完全;当焙烧温度超过1 275 ℃时,球团中的脉石大量同化,产生大量硅酸盐液相,降低成品球强度.冀东磁铁精矿球团最佳焙烧工艺为:氧化温度为900～950 ℃,氧化时间不低于20 min,焙烧温度为1 250～1 275 ℃,焙烧时间不低于20 min.     

金铜硫化矿火法冶炼技术的发展

针对黄金冶炼企业的工艺技术现状,提出了造锍捕金的技术发展方向。对涉及造锍捕金的铜火法冶炼中的熔炼和吹炼工艺特点进行述评,详细介绍了底吹连续炼铜技术的进展,指出连续炼铜技术将成为新建或搬迁、升级改造金、铜冶炼项目的必然选择。     

Substructure formation and nonuniformity in strain during high temperature creep of copper single crystals

The change in substructure during high temperature creep of copper single crystals was examined to make clear the relation between the substructure and the creep rate. The structural observations by means of etch-pit technique were made in the same area of the specimen surface after successive straining by creep. Different types of substructures were formed in different localities at an early stage of transient creep. Small subgrains elongating in the direction of the deformation band were found in some regions (region A). Large subgrains containing cells within them were observed in other regions (region B). With the progress of creep, the substructures in both regions underwent gradual changes to become alike in their appearance with each other. The creep strains in regions A and B were examined at various creep stages. The ratio of creep strain to the average creep strain throughout the specimen,ε/ε _av, was a few times larger in region B than in region A at an early stage of transient creep. With the structural changes mentioned above, the difference between the ratios in the two regions came to disappear, both becoming almost unity at the later stage of creep. These results suggest the close relation between the substructure and the creep rate.     

Lime-enhanced reduction of sulfide concentrates: A thermodynamic discussion

The need to control or eliminate sulfur dioxide emissions from sulfide smelters has increased the drive to develop new processes for the extraction of metal from sulfide minerals. One such process currently gaining interest is the lime-enhanced reduction of metal sulfides. This paper discusses the thermodynamic aspects relevant to chalcopyrite, chalcocite, and pyrrhotite reduction with hydrogen, carbon monoxide, or carbon in the presence of lime. The effects of temperature and gas composition on sulfide reduction are also discussed. ΔG°vs T diagrams for lime-enhanced sulfide reductions with hydrogen, carbon monoxide, and carbon are constructed and discussed together with some experimental results produced by the authors.     

The bioleaching of different sulfide concentrates using thermophilic bacteria

The bioleaching of different mineral sulfide concentrates with thermophilic bacteria (genusSulfolobus @#@) was studied. Since the use of this type of bacteria in leaching systems involves stirring and the control of temperature, the influence of the type of stirring and the pulp density on dissolution rates was studied in order to ascertain the optimum conditions for metal recovery. At low pulp densities, the dissolution kinetic was favored by pneumatic stirring, but for higher pulp densities, orbital stirring produced the best results. A comparative study of three differential concentrates, one mixed concentrate, and one global concentrate was made. Copper and iron extraction is directly influenced by bacterial activity, while zinc dissolution is basically due to an indirect mechanism that is activated in the presence of copper ions. Galvanic interactions between the different sulfides favors the selective bioleaching of some phases (sphalerite and chalcopyrite) and leads to high metal recovery rates. However, the formation of galvanic couples depends on the type of concentrate.     

Improvement of modes and circuits of bacterial leaching of sulfide concentrates

These studies are devoted to the effect of the feed circuit of a series of chemostats on the characteristics of bacterial leaching of sulfide concentrates. The parameters and modes of the process are investigated at a laboratory installation consisting of five operating reactors, each with an active volume of 1.5 l and a conditioning tank. The initial material was a gold-bearing arsenical pyrite flotation concentrate containing Au, Ag, and As, as well as a specially adapted bacterial strain, namely, Acidithiobacillus ferrooxidans. It is established that double-flow feeding of a series of chemostats makes it possible to increase the leaching yield up to a 70% excess of the critical rate of dilution under the single-flow feeding mode at the same degree of oxidation of output sulfide minerals.     

An investigation of the dependence of roasting characteristics of sulfide nickel concentrates in fluidized bed furnaces on various factors by the method of design imitation experiment

The dependence of the roasting characteristics (fluidized bed temperature, specific productivity of the furnace, specific blasting expenditure, etc.) of nickel sulfide concentrates on various factors (blasting surplus factor, concentrate humidity, oxygen content in blasting, etc.) was studied using the method of the design simulation experiment. Software in the form of a mathematical model of roasting, which includes the material and heat balances and regression equations, is suggested. The factors are ranged by their effect on the fluidized bed temperature.