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By Evgueni Jak

Pyrometallurgy is an important sector of modern industrial society actively participating in solving current environmental, economic, materials scarcity and other challenges. Recent advances in analytical methods, experimental techniques, thermodynamic, phase equilibria and process modelling tools provide new opportunities to increase the productivity of pyrometallurgical reactors, the treatment of complex feeds and metal recoveries. Fundamental theoretical models can now be used to make a significant next step towards the development and implementation of computerised models describing real industrial processes—Virtual Reactors, and computer-aided smart-decision-making systems that may be called Pyro-GPS by analogy to GPS; these developments can facilitate knowledge-based improvement and optimisation strategies. The implementation of these improvements require ongoing collaboration between researchers, industry and government.

By Kenneth N. Ham

Hydrometallurgy covers a wide spectrum of areas and its knowledge base is enlarged and enhanced by contributions from many other fields. Dissolution of metals and alloys in aqueous media will be used to illustrate how rich the field of metal extraction can be. Comprehensive understanding of the fundamentals of metal and alloy dissolution in aqueous systems requires creative application of thermodynamic principles, solutions chemistry, ligand complexation theory, electrochemistry, transport phenomena and heterogeneous kinetics. In addition, recent developments in instrumentation in the fields of interfacial phenomena and corrosion have tremendously advanced the field of metal extraction in aqueous system. The close relationship between metal extraction in aqueous systems and various physicochemical phenomena occurring in corrosion and interfacial systems will be discussed and illustrated with examples.

Jan 1, 2002

By E. F. Vegman, Ndabezinhle Dube

"In the practice of conventional sintering, production is always afflicted with the problem of being unable to get a uniform quality of produced sinter in the bed. Invariably the top layer of the sinter cake is composed of weak but highly sinter, while the bottom layer is over-fused, forming a sinter that is very strong but less reducible. These symptoms point to a variable distribution of the heat balance in the process of sintering which results in a deficit of heat in the top layers of the sinter bed and an excess of heat in the bottom layers, due to an increasing input of regenerated heat in the heat balance down the bed. This causes losses in the productivities of the sinter machine and the blast furnace.The current work was designed to improve on the solution to the above problem through the establishment of a more accurate combustion zone heat balance of the sintering process. This development is mostly on the method of determining the regenerated heat input in the overall heat balance. Previous methods were based on the assumption that the width and the velocity of the combustion zone remain constant through out its whole life, which is not the case since tests have shown that both its width and velocity increase as the combustion zone moves down the bed. In this work, these factors have been taken into account. Tests and calculations using the model were carried out for haematite and limonitic ores. The high sensitivity of the model to changes in the sinter mix composition and sintering conditions was demonstrated.The results present the following prospects:• The minimum theoretically possible coke breeze consumption during the sintering of any type of iron ore fines, under any sintering conditions, can be established.• The model can be used to control the metallurgical quality of the sinter in any point in the sinter bed since calculation data includes desired basicity, combustion zone temperature and FeO content in the sinter produced."

Jan 1, 2001

By William Petruk

"Heap leaching is a developing technology for recovering native gold and electrum from low grade deposits and from tailings. Recovery depends on permeability of the rock and ore minerals, size of particles in the heap, and ore textures that influence exposure of gold grains to cyanide solutions. These ore textures include gold-bearing veinlets and microveinlets along fractures and microfractures, gold grains in porous minerals and rocks, and gold graim. occurring along grain boundaries of other minerals. On the other hand, small encapsulated gold grains arc not likely tote exposed even with fine grinding. Most gold grains that occtir along grain boundaries of other minerals can be exposed with a moderate to fine grind, but the. resulting material will be too fine-grained to be permeable in a heap. Such finely ground ore, as well as tailings from flotation operations, can however be prepared for heap leaching by agglomerating the material into porous briquettes. Oxidized and weathered zones above. orebodies are frequently amenable to heap leaching because the gold-bearing pyrite and arsenopyrite have become permeable by conversion to porous iron oxides and ferric oxyhydroxides. A review of ore textures in several types of gold deposits suggests that:(1) the gold in vein deposits would gtmerally be amenable to heap leaching of both oxidized ores and fresh non-refractory ores,(2) the gold in Carlin-type deposits and in volcanogenic massive sulfide deposits is not likely to be amenable to heap leaching fresh ore, but oxidized zones above the orebodies are generally amenable to cyanidation, and(3) the gold in porphyry copper-gold deposits and in Witwatersrand-type deposits would likely be amenable to heap leaching of both fresh and oxidized ores but with high cyanide consumption."

Jan 1, 1997

By Brajendra Mishra

Molten Salt electrolytic processes offer unique opportunities to extract and refine metals where gaseous or metallothermic reduction, hydro metallurgical extraction and aqueous electrolytic methods are thermodynamically constrained. Production of aluminum and magnesium by molten salt electrolysis are well known commercial processes. Several other reactive metals, such as lanthanides and actinides, as well as beryllium and calcium, make use of molten salt processing for extraction and refining. This presentation describes the science of molten salt chemistry and electrochemistry for winning and refining of several metals. In addition, recovery of metals from waste process salts by molten salt reduction as well as oxidation have been discussed. Material issues in design of molten salt reactors have been included. Various applications have been presented through case studies. Experimental data have been included to justify the suitability as well as limitations of these specific processes.

Jan 1, 2003

By Michael L. Sorokin

The behaviour of cobalt during processing of nickel raw material is analysed within the Ni-Co-Fe-S-O-SiO2 system using the computer model. For this purpose the thermodynamic parameters for "three-suffix" Margules's equations in Co-Fe-S and Co-Fe¬Ni-O-S1O2 systems were computed! Phase and iso-activity diagrams for Co-Fe-S system, and phase diagrams for the systems Co-O, Co-Fe-O, Co-Ni-O, C-oO=SiO2 and Co-Fe-O¬SiO2 are calculated using the developed computer programs and identified parameters. The diagrams are used to analyze cobalt behaviour at smelting and converting.

Jan 1, 1995

By B. L. Chulu

In the carbothermic reduction of lead sulfate to produce lead, the inclusion of soda ash (Na,CO,) in the charge provides for the control of sulfur dioxide in the effluent gas. An important mechanism in the process appears to be the carbothermic reduction of the sodium carbonate whereby sodium gas and carbon monoxide are produced. These intermediates then participate in the reduction of the lead sulfate to produce lead metal and stable sulfur species in the molten slag phase. In addition, there is some evidence that the presence of lead metal in the charge may also serve to increase the lead recovery in the process. These aspects were investigated by conducting laboratory-scale smelting tests with small charges (;3g), at 1173°K(9000C). Recovery did not exceed 74w% and the role of incipient lead metal in the charge could not be clearly assessed.

Jan 1, 1993

By Joseph Bloch

The hydriding of bulk metals and alloys is a gas-solid reaction in which a hydride product layer is initially nucleated adjacent to the gas-solid interface and continues to grow until a complete transformation of the parent (a) phase into the hydride phase. The combination of measurements of the overall hydriding kinetics of samples having defined shapes and dimensions, together with examinations of partially hydrided samples, enables the presentation of the reaction rate in terms of an appropriate reaction model. A common and important type of topochemical development of the hydride in bulk metals and alloys involves a hydride layer formed on the metallic surface. The continuity of the layer can affect the reaction rate. The rate of hydrogen absorption in a sample, in the presence of a hydride layer, is usually analyzed using a model combining several sequential steps in which the hydrogen is transferred from the gas phase into the reaction site. Coupling the flux equations across the layer under proper steady state conditions, results in a complex rate equation in which the steady state rate of hydrogen absorption (proportional to the hydride layer velocity) is expressed in terms of the pressure, temperature, the rate constants of the sequential steps and the critical concentrations of hydrogen in the hydride. Generally, the rate constants of the individual microscopic processes are comparable in magnitude, so that the overall rate is not controlled by any of the specific sequential steps. However, there are two limit cases related to the first stage, the adsorption, for which the general rate equation is much simpler, namely, the fast and the slow adsorption approximations. Using this limit cases, equations are derived for the steady state hydriding rate of a given system. These equations provide means to anticipate the pressure dependence of the steady state absorption rate under low pressures, close to Peq and under very high pressures. At the low pressure regime both the fast and slow absorption cases yield linear pressure dependence. For the very high pressure range, it is found that the rate become independent of the applied pressure. The rate is given then by a combination of the individual rate constants of the system and the critical hydrogen concentrations. The model is shown to apply in several real cases, such as ZrCo, LaNi5 and titanium.

Jan 1, 2002

By Courtney A. Young

All cyanide species are considered toxic and can be found predominantly in industrial effluents generated by metallurgical operations. For example, cyanide's strong affinity for metals makes it favorable as an agent for metal finishing and treatment and as a lixivant for metal leaching, particularly gold. These technologies are environmentally sound but require safeguards to prevent water contamination. Various methods of cyanide remediation by separation and destruction are available, but certain methods are more effective than others depending on the cyanide species being remediated. Photolytic destruction is regarded as the one technique that is independent of the cyanide species involved. The destruction of various cyanide species by several photolytic techniques has been investigated for the past few years. A literature survey suggests heterogeneous photocatalysis with anatase (TiO,) should behave similarly to homogeneous photolysis with hydrogen peroxide (H,O,) since proposed reaction mechanisms for both processes involve hydroxyl radicals. However, experimental evidence on a suite of cyanide species suggests otherwise. A new mechanism for the photocatalytic destruction of cyanides, especially SAD species, is therefore proposed.

Jan 1, 1998

By Wenxian Zhu, Patrick R. Taylor

"The small dimensions of nano-sized materials leads to novel and enhanced mechanical and physical properties. A thermal plasma reactor has been developed to study the formation of nanometer sized metal powders. A supersonic nozzle and a powder filter were designed and built. By vaporizing coarse metal powders in the plasma flame, and quenching the metal vapors through the nozzle at the rate of 107 K/sec, nanometric sized powders have been produced. The powders were collected in an airtight secondary quench-filter system. The particle size of the product power is 5 -20 nanometers, obtained through TEM analysis. The XRD analysis showed that the powder did not oxidize after the filter was handled in an inert atmosphere glove box.IntroductionNanostructured materials have been shown to exhibit improved physical and mechanical properties compared to conventional materials with larger grain sizes (1,2). There have been several methods proposed for preparing nanometer size materials. Thermally induced vapor-phase reactions have been used to produce a variety of powders. A common feature of these processes is the rapid production and cooling of condensable reaction intermediates and products, by gas-phase reactions, leading to the formation of a large number of very small particles. Thermal plasma synthesis of ultra-fine size particles has been attracting increasing interest (3,4,9-11), because it offers many advantages, especially in refractory materials processing, compared to conventional processes: (a) thermal plasma temperatures are very high(> 5000 K); (b) the rates of chemical reaction are much faster than those encountered in conventional processes; (c) high-purity materials may be obtained using fewer processing steps by collecting the product at temperatures where the by-products are in the vapor phase; ( d) the mean particle diameter can be controlled; (e) unifom sized particles may be produced with clean surfaces (these particles are particularly suitable for pressureless sintering); and, (f) high throughput per reactor volume can be achieved. In addition, the process used for generating particles determines the degree of sintering ability of the powders, since the process dictates the morphologies, the purity and its size distribution. In the future, thermal plasma synthesis nanometer size particles may play an important role in vapor phase reaction techniques and might be expected to be one of the first full scale commercial installations in the future."

Jan 1, 1998

By Alicia Esther Ares

This study was conducted to investigate the directional solidification of Zn-20%A1 and Zn20% A1-1O%Si-3o/oCu alloys under different conditions of heat transfer at the metal/mould interface. The type of structure obtained in both cases was analyzed and related to the solidification thermal parameters such as cooling rate, growth rate, thermal gradient and recalescence which were determined from the temperature versus time curves. These parameters were correlated with the structure-like length of columnar grains and size of equiaxed grains. The metallographic analyses were done performing quantitative metallography and composition analysis of the different alloying elements along the cast samples by SEM (Scanning Electron Microscopy) and EDXA (Energy Dispersive X-Ray Analysis). Correlations between properties, structures and thermal parameters were found.

Jan 1, 2008

By M. W. Kennedy

Prediction of the thermal duties of copper coolers in freeze lined furnaces is challenging. Where copper coolers are immersed in liquid slag the heat transfer is often defined by a natural convection cell immediately adjacent to the wall, in the absence of other factors producing forced convection. Slag coolers are typically not fully immersed, slag temperature, liquidus and superheat can vary, and bath levels may change significantly with batch tapping, leading to substantial variations in radiation heat fluxes. Radiation heat transfer is discussed with reference to the non-obvious impact of slag liquidus on radiation losses in the exposed cooler sections. Reference is made to literature and the results of analytical and FEM models.

By H. Deveci

Bioleaching/biooxidation is essentially a dissolution process with the involvement of acidophilic bacteria acting as the "catalyst" to accelerate the dissolution of metals from sulfide minerals. The contribution of bacteria to the metal dissolution is closely controlled by the growth of bacteria, which is itself affected by the physico-chemical conditions within the bioleaching environment. There are a number of operating parameters controlling bioleaching processes, which are required to be maintained within a certain range in the leaching environment whereby the activity of bacteria with the resultant oxidation of sulfide minerals can be optimized. In this regard temperature, acidity, oxidizing conditions, availability of nutrients, oxygen and carbon dioxide, surface area and presence of toxic ions are of prime importance for control and optimization of bioleaching of sulfide ores/concentrates. Bioleaching processes are temperature and pH dependent with optimum metal dissolution occurring in a particular range where the bacterial strain is most active e.g. mesophiles at 35-40°C and pH 1.6-2.0. Provision of nutrient salts is required to maintain the optimnm growth and hence metal dissolution with the quantity of nutrients apparently being dependent on the availability of substrate i.e. head grade/pulp density of an ore/concentrate. Oxygen transfer is one of the most critical factors since the oxygen levels below 1-2 mgll may adversely affect the oxidizing activity of bacteria. Bioleaching rate tends to improve with increasing the surface area at low pulp densities but, in practice. the pulp density is limited to -20010 w/v. Increasing concentrations of ions such as cr may also adversely affect the oxidative activity of bacteria. Keywords: Bioleaching, Biooxidation, Acidophilic bacteria

Jan 1, 2003

By J. G. Eacott

This paper reviews the role of oxygen potential and the advances that have been made in the application of tonnage oxygen in copper smelting. Brief reference is made to reaction kinetics before attention is turned to the thermodynamic considerations in copper melting to illustrate the importance of oxygen and. oxygen potential in the component parts of the overall smelting process. The chemical potential diagram for the Cu-Fe-S-O-Si02 system is used to elucidate the difference b etween the conventional matte smelting process and the modern continuous processes. A progressive oxidation scale' is constructed to show the common elements which exist, and the matte grades produced, during the smelting of concentrates to blister copper in commercially available copper smelting processes and those under development. The common route in producing blister copper from molten mattes, regardless of process, is illustrated on the Cu-Fe-S equilibrium phase diagram. The essential features of oxygen enrichment, in terms of its effect on combustion conditions (i.e. oxidation of fuel and sulphide minerals) and the heat balance are outlined. The benefits of oxygen enrichment are listed. The influence of tonnage oxygen and its effect on productivity, fuel savings, gas volume and strength in various copper melting processes are examined as a state-of-the-art review. Reference is made to the economics of tonnage oxygen utilization.

Jan 1, 1983

By Zhen Zhang, Jiang Diao, Xuan Liu, Tao Zhang, Bing Xie, Hong-Yi Li

Extracting vanadium from vanadium containing hot metal by LD process has been proven an effective solution for the utilization of vanadium-titanium magnetite ore, but the systematic analyses of vanadium extraction rate and mechanism by basic slag are seldom reported. In this study, mathematical model of vanadium transfer from metal to slag was formulated and the rates of vanadium extraction of hot metal with basic slag were investigated. The results indicated that the apparent vanadium extraction rate constant, kp, were in the range of 1.33~9.07×10-4g/(cm3·s). And the rate constant was increased with the increase of final slag basicity, reaction temperature and stirring gas flow. The apparent of mass transfer parameter decreases significantly from 0.13 cm3/ s to 0 cm3/ s in 20min, and the data changed as negative due to the decrease of slag oxidation and recovery of vanadium from slag to metal.

Jan 1, 2015

By Mingzhou Li, Lin Wu, Changren Tong, Fengli Yang, Shaohua Yang

"According to characteristics of Tm, Yb and Lu enriched oxides composition and problems in its traditional extraction separation process, the computer simulation of a optimized fuzzy extraction separation process, in which three products with high purity(>99.99%) could be obtained at same time, was carried out. Distributing Curves of every element in both organic and aqueous phases were worked out. Distribution rules of rare earth elements in every stage of the optimized extraction process were studied. The computation results of economical and technical index showed the consumption of the acid and base chemical reagents in the optimized process would be saved more than 30%.IntroductionFor the solvent extraction separation process of rare earths, countercurrent extraction process was widespread in the industrial practice. Normally, rare earth ions were extracted by the saponificated extractant and transferred into the organic phase, where the acidic extractant was saponificated by the base firstly. Then, the loaded rare earth ions were stripped from the organic phase into the aqueous phase by the acid. Therefore, the acid and the base were the main consumptions in the process, and the equilibrium acid of the stripped rare earth solution was one of the main pollution resources. Meanwhile, for the heavy rare earths, such as Tm, Yb and Lu, stripping was more difficult, and the equilibrium acidity of the stripped rare earth solution was higher, so the acid consumption increased greatly."

Jan 1, 2012

By E. Allain

Extraction of basic metals from sulfides by conventional pyrometallurgical processing leads to the emission of SO2. To avoid this inconvenient, low temperature selective chlorination of sulfide concentrates could be an alternative. However, such process generates hazardous chlorides SxCly. A part of sulfur chlorides such as SCI2 can be recycled as a chlorinating agent of metal sulfides. Hydrolysis of sulfur chlorides, using a solution containing Na2S.9H2O, led to the recovery of more than 90 pct of elemental sulfur. Reduction of SxCly by hydrogen was investigated between 300 °C and 800 °C. About 70 and 90 pct of elemental sulfur were recovered from SC12 and S2C12, respectively. A flow sheet for the chlorination of metal sulfides and the treatment of sulfur chlorides was suggested.

Jan 1, 1998

By N. A. Barcza

DC plasma-arc technology using a hollow graphite electrode (cathode) has been successfully implemented in the primary metallurgical industry in South Africa up to the 30 MW scale. Mintek has applied its expertise base, established over the past fifteen years, to testing the treatment of metallurgical wastes such as carbon- and stainless-steel plant dusts, lead- and zinc-containing slags, and residues from the base-metal industry. Favourable results have been achieved, and disposable products were produced. The evaluation of numerous wastes indicates that recovery of zinc as metal gives the best economic return from these sources. Direct recovery via a splash condenser or electrolytic zinc extraction from fume are the two preferred alternatives under review. In both instances dehalogenation is an important issue, but can be achieved by suitable treatment processes. The Enviroplas technology provides a flexible, commercially viable approach to the treatment of a wide variety of wastes. Mintek, together with its associate Pyromet CC, are installing a plasma- arc pilot-plant facility with both an ISP lead-splash condenser of about 5 t/d condensed zinc capacity and a combustion chamber to burn zinc vapour to zinc oxide. This will demonstrate the suitability of the Enviroplas technology for treating specific metallurgical wastes, so that customized industrial plants can be engineered based on large-scale testwork.

Jan 1, 1994

By N. M. Komkov

The main operation of obtaining zinc from sulfide raw materials by hydrometallurgical technologies is the oxidation roasting of zinc concentrates in fluidized bed furnaces. The technical-economic parameters are determined by the parameters of the roasting process, which depend on the composition of the initial raw materials, the temperature of the bed and on other factors. The predetermined roasting temperature is maintained due to the change of specific efficiency as well as to the quantity of the heat removed from the bed. The efficiency of caissons depends at a high degree on the composition and the thickness of the accretion formed on the surface of the caissons. Forecasting the roasting results is impossible unless we know the mechanism of the accretion formation. The aim of the present paper is the thermodynamic analyses of the behavior of the charge compositions under roasting and the determination of the potential mechanism of the accretion formation. The thermodynamic analyses show that under conditions of the oxidation roasting the thermodynamic probability of the formation of zinc sulfate is higher than the probability of the oxide formation until a temperature of873 OK is reached. The thermodynamic probability of the formation of the lead sulfate is higher than the probability of oxide formation in the entire temperature range of roasting. The probability of formation of ferrites and silicates of zinc decreases only insignificantly the sulfate stability. The results of the investigation of the accretions composItion formed under roasting of concentrates with particle sizes less than 0.02 J..lm (60%), containing 65% of sphalerite (ZnS), 12% of pyrite and chalcopyrite (FeS2 and CufeSz) each, 3% of galenite (PbS), 7% of silica and other non-ore minerals, have shown that the composition of accretion varies depending on the depth of the accretion layer. The accretions on the caissons and the thermo-siphons consist mostly of zinc sulfate (more than 50%). The accretions of forehamber consist mostly of zinc oxide. They also contain ferrites and silicates. The formation of the sulfate zinc accretion in the cold parts of the fluidized bed furnace (the caissons and thermo-siphons) may be explained by a lower temperature on the surface and probably by a catalytic influence of the present oxides in the formation of S02 and sulfates. The nature of the structure of the accretion in the hotter parts of the furnace may supposedly be explained by the formation of elemental vaporous zinc during roasting.

Jan 1, 2003

By Matthew John M. Krane, Christopher J. Vreeman, J. David Schloz

"A continuum mixture model of the direct chill casting process is used to model the transport phenomena and solidification behavior in the Direct Chill casting of an Al - 6 wt% Cu billet using Wagstaffs AirslipTM process. The model, which includes the transport of free-floating solid particles, can simulate the effect of a grain refiner on macrosegregation and fluid flow. Numerical predictions of sump profiles and composition and temperature fields are presented. Two 45 cm diameter billets were cast under production conditions with and without grain refiner. Temperature and composition measurements and sump profiles are compared to the numerical results. The comparison shows excellent agreement for the grain refined case. It is believed that an incorrect model assumption prevents good agreement in the non-grain refined billet. IntroductionDirect chill casting is a semi-continuous process in which molten aluminum enters the top of a water-cooled mold, is cooled, and forms a solid ingot drawn out below (Figure l(b)). The molten aluminum begins to solidify due to the cooling effect of the mold wall. As the ingot is withdrawn from the bottom of the mold, water jets impinge on the surface, directly cooling the billet and forming a solid layer around a liquid melt, commonly referred to as the sump.A particular defect that occurs in a wide range of casting processes, including the direct chill (DC) casting of aluminum alloys, is macrosegregation, the uncontrolled redistribution of alloying elements on the scale of the ingot during solidification. Macrosegregation in DC cast ingots can produce non-uniform mechanical properties [l], which affects the behavior of the metal during downstream forming and heat treat operations."

Jan 1, 2001