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By Cynthia K. Belt

Improved energy efficiency has grown in importance within industry as energy costs have escalated. The analysis of trends and changes to a process is critical in making the best business decision in energy management. Frequently, energy use per day (Kilowatt-Hour or British Thermal Units) is used to track energy efficiency. Sometimes, the somewhat more complex method of energy per processed weight (Kilowatt-Hour per Metric Ton or BTU per Pound) is used to make this evaluation. Yet both methods ignore the effects due to throughput and weather. In this paper, different thermal processes and systems will be evaluated using statistical methods to highlight alternative methods to evaluate energy efficiency. Examples and potential problems will be discussed for both a single process and a collection of processes within a plant or corporation.

Jan 1, 2008

By Adam Powell, David Dussault

"Electric Field-Enhanced Smelting and Refining is a process for driving the reaction between carbon in hot metal and iron oxide in slag, for example, in a steelmaking reactor. This process involves inserting electrodes into the slag and metal phases, such that the overall reaction FeO + C -> Fe + CO is separated into two half-cell reactions: Fe2+ + 2e· -> Fe at the cathode in the slag, and C + O 2 • -> CO + 2e· at the anodic slag-metal interface. Without the electrodes, the reaction is very slow, but with electrodes, the additional surface area available to the ferrous ions for reduction accelerates the reaction even without any applied bias. When a bias is applied to the electrodes, the electric field across the slag further accelerates the overall reaction.With or without applied bias, the process is first-order in the ferrous ion concentration, and limited by ferrous ion transport to the cathode. To complicate matters, as the liquid iron is reduced at the cathode, the Mullins-Sekerka instability leads to formation of dendrite-like liquid iron fingers which grow into the slag. Because of this, the design of the cathode can have a significant effect on the overall process kinetics, and understanding of the dynamics of these fingers and of their effect on mass transfer is necessary for the intelligent design of the overall process and the cathode in particular.Toward this end, a detailed mesoscopic two-phase slag-metal model is presented here which describes multi component diffusion in the slag and fluid flow in both phases in the vicinity of the cathode. Diffusion in the slag is driven by chemical and electrical potentials. The phase boundary is modeled as a diffuse interface using a phase field approach. Because this electrochemical reaction occurs at high-temperature, the kinetics of charge transfer and adsorption through the double layer are fast relative to transport, permitting the use of simple linear reaction kinetics. This also eliminates the need to discretize the double layer, with the result that charge neutrality may be assumed everywhere in the domain. Introducing electric field dependence of the gradient potential and well height coefficients in the free energy function allows the model to capture electrocapillarity at the interface."

Jan 1, 2001

By F. Nava-Alonso, O. Alonso-González, A. Uribe-Salas, R. Pérez-Garibay

"Cyanidation is the most used method to recover gold and silver from their ores. In this process, other metals besides gold and silver may sometimes dissolve and interfere with the efficiency of extraction. Copper is one of those metals, reaching concentrations as high as 1000 mg/L in some cyanidation plants, making difficult the extraction and purification processes, and increasing the operating costs.This preliminary work was intended to study the feasibility of using amines to form a precipitate and to eliminate copper from a synthetic solution containing high copper and cyanide concentrations, as is the case of some cyanidation effluents. The solid formed is removed from the solution using conventional filtration techniques. Seven amines were evaluated at different pH values and amine additions. Up to 90% of copper present may be removed at the natural pH of the effluent (alkaline). The remaining copper would permit to recycle the solution back to the cyanidation process. IntroductionCopper is generally considered the most problematic metal in gold leaching due to the rapid formation of copper cyanide complexes when some readily-soluble minerals are processed (e.g., azurite, malaquite, cuprite, chalcocite and bornite). The copper solubilization as cuprous cyanide complexes leads to a significant economic penalty in terms of excessive cyanide consumption and high cost for cyanide elimination. When activated carbon is used to recover gold and silver, the copper-cyanide complexes decrease the efficiency of the process because of the competition of the cuprocyanides with the aurocyanide for the adsorptive sites on the activated carbon (Rees and Deventer, 1999).Several techniques have been developed to attempt to overcome the problems caused by the copper presence in cyanidation solutions, notably: acidification-volatilization-regeneration (AVR), ion exchange-electrolysis or solvent extraction-electrowinning (Lu et al., 2002). In this work the use of some amines is proposed to remove the copper-cyanide complexes by precipitation of a copper-cyanide-amine solid. The process was evaluated for different amine additions and pH values, using copper-cyanide synthetic solutions of composition similar to that presented by some cyanidation plants with high copper."

Jan 1, 2008

By P. A. Metz

The Fairbanks mining district has produced in excess of 7.5 million troy ounces of placer gold and 250,000 troy ounces of lode gold since gold was discovered in the area in 1902. The Fairbanks mining district is in the northwestern part of the Yukon-Tanana Upland Schist Terrane, an area of approximately 240,000 square km that has produced in excess of 21 million troy ounces of placer gold. All lode gold production from the terrane has been from the Fairbanks mining district, and all of this production has come from high-grade gold-quartz polymetallic sulfide veins. Gold grains in the vein systems range in size from several microns to several millimeters. The veins are localized in a complex metamorphic rock assemblage which includes greenstones and felsic metavolcanic and volcaniclastic rocks, meta-exhalatives and metasediments. Gold occurs in the metamorphic host rocks in association with arsenopyrite and arsenic-antimony sulfides which occur in lenses and disseminations within the host rock. Gold grains occurring in the metamorphic host rocks range. in size from sub-micron to a few microns in diameter.

Jan 1, 1987

By Gaifeng Xue, Jingxuan Zhou, Shangchao Liu

"Both COD and TOC can characterize organic pollution of coking wastewater. In theory, there is a linear correlation between these two indicators. After continuous monitoring TOC and COD of coking waste water, linear regression relationship between of these to indicators was studied with the use of mathematical statistics. And conversion equation between these two indicators was established, and using t-test method for significance testing. The results showed that the linear relationship of COD and TOC was significant. Also interval estimation of equation slope and intercept were given in the condition of 95% confidence level. A linear regression equation established can be used to indirectly convert TOC to COD with high precision and accuracy.IntroductionBoth chemical oxygen demand (COD) and total organic carbon (TOC) are measure of the degree of characterization for organic pollution of water bodies. The current COD standard analytical methods is Potassium dichromate titration method [1] . there are some disadvantages in this method, such as only part of organic matter in the water bodies being oxidated, the refluxed steps, a long time needed for each measurement, high cost. It is the most important that sulfuric acid silver and mercury sulfate reagents used in the measurement may easily lead to secondary pollution. In contrast, the measurement of TOC is by the method of combustion or Photocatalytic Oxidation. The result could be easily got from the instrument. There are some advantages in this way, such as easy operation, short time and little expenses for each measurement and no secondary pollution 121• In addition, the measurement of TOC has higher degree of precision and accuracy than the measurement of COD both in the determination of calibration standards and actual samples. The meaning and contrast of TOC and COD are listed in the table 1."

Jan 1, 2013

By Hyun Kyu Shin, Byeong Deok Lee, Young Eun Lee

The reduction of Mn oxides at pre-smelting steps is an integral part of smelting processes for Mn alloys, and an understanding of its reaction mechanism is expected to contribute to the improvement of processing efficiency for Mn alloys smelting. The phase diagram shows that five Mn carbides are operative in the Mn-C system. Although they are expected to participate in the reduction of Mn oxides, no specific information is available yet to clarify their roles in presmelting carbothermic reaction of Mn oxides. Experiments with composite pellets prepared with Mn oxides and graphite powders show that Mn3O4 is reduced initially to MnO at about 1130oC and, subsequently, to Mn7C3 carbide as temperature increases further. At 1331oC, Mn7C3 carbide dissociates to Mn alloy and carbon. The degree of reducing reaction increases with increasing carbon balance in composite pellets and increasing temperatures.

Jan 1, 2014

By Marcelo Jimenez Bustos

The Chagres Smelter was the first in Chile to follow environmental regulations to control sulfur dioxide emissions. Because of this, the operation and development plans have had to incorporate environmental planning as part of its policies for almost three decades. The present article shows the development of the environmental standards applied to its operations, investments and operational improvements carried out to meet the regulations and improve competitiveness. Results to-date and future plans are outlined, as well as their impact on operations and the environment.

Jan 1, 1993

By Michael P. Meisel

Solinox is a physical scrubbing process capable of removing a number of noxious materials from off-gasses, especially SO2, hydrocarbons, halo¬gens, heavy metals such as dust, etc. As these materials are dissolved physically, (not chemically bound), the solvent is absolutely stable and no by-products are formed in the scrubbing cycle. The process has been installed in three plants up to now, treating from approximately 30 MMSCFD to approximately 100 MMSCFD. These installations are in a non ferrous metal smelting operation, in a cellulose factory, and in a roasting process.

Jan 1, 1992

By Oleksandr Liaskovskiy, Sergey Beringov, Sergiy Yatsuk, Timur Vlasenko, Iryna Buchovska

"Working with solar-grade silicon for solar cells application usually meets some difficulties in comparison to polysilicon produced by Siemens method: higher impurities content leads to lower yield, worse electro-physical parameters and poor performance in solar cells application. However some adjustments in ingot production can show significant improvements in quality of final product: crystalline wafers and cells.Recent investigations have shown that solar-grade silicon is suitable for high effective production process such as mono-like multicrystalline wafer production. Production-scale lots made at Pillar show promising results for solar-grade silicon application: high-quality wafers with significantly big crystalline grains of <100> orientation.IntroductionThe standard technology of producing multicrystalline silicon ingots by directional solidification method in quartz crucibles has a number of disadvantages resulting in limited efficiency of solar cells made of multicrystalline material: crystallites of multicrystalline ingot are relatively small (down to 5 mm size), grain borders of crystallites contain parasitic impurities such as metals, silicon nitride etc., crystallographic orientation of crystallites is random. The listed deficiencies are an integral characteristic of the technology which affects the efficiency of solar cells, such as presence of solar cells with low efficiency even at a high level of average efficiency, problems with shunted cells, silicon nitride inclusions, which adversely affect cell efficiency and are centres for silicon carbide formation, impossibility of application of high effective alkaline texturing etc. Also with regard to the targets set by photovoltaic to reduce the cost per Wp in the nearest future, standard technology of multicrystalline silicon ingots production by directional solidification faces certain challenges some of which are hard to overcome due to rather low efficiency of solar cells made of multicrystalline wafers. Therefore alternative methods of multicrystalline silicon production for photovoltaic application having a number of advantages in comparison to traditional technology are developing rapidly."

Jan 1, 2012

By J. H. Huang

In this investigation, the selective precipitation of cobalt and molybdenum from Co-Mo aqueous solutions was studied in order to recover efficiently valuable elements from industrial effluents generated from a novel electrodeposition of nanocrystalline Co-based alloys process and reduce the effluent impact on environment. It was found that the behavior of cobalt in aqueous solutions was substantially affected by the presence of molybdenum. When adding 11.6 to 46.6g/L molybdenum to a 50g/L cobalt solution, the co-precipitation of molybdenum and cobalt started to occur at pH value of 3-4. However, without the presence of molybdenum, cobalt could only be precipitated out of the solution at about pH 6. Most of the molybdenum was found in the solid phase when the solution pH reached 5. After further increasing pH to greater than 7, the molybdenum dissolved back into the solution. Cobalt kept precipitating as the pH increased. When the pH was greater than 7, most of the cobalt was present in the solid phase. The chemical and physical characteristics of the precipitated materials were investigated by SEM, XRD, AAS and EDX. It was revealed that the precipitate was initially present as cobalt molybdate oxide hydrate and subsequently transformed as sodium cobalt molybdenum oxide. With further increasing the solution pH, the precipitate was transformed into cobalt hydroxide. Further investigation implied that most of molybdenum was chemically tied to the precipitate produced at the low pH, yet at the same time, physically entrapped at the high pH. The paper also presents the influence of reaction temperature and time on the precipitation process and kinetics.

Jan 1, 2003

By David Dreisinger

The pressure oxidation of pyrite is an important hydrometallurgical technology, especially in the total oxidation of refractory gold ores and concentrates (gold is locked in the pyrite structure preventing direct cyanide recovery). It has been noticed in some commercial applications and benchscale studies that the leaching of pyrite may be slow and apparently can be inhibited by the presence of molten elemental sulfur in the leach pulp. The purpose of this study was to determine whether Ortho-Phenylene-Diamine (OPD) could be used as a surfactant or dispersant for sulfur in the pressure oxidation of pyrite. OPD has previously been shown to be useful for pressure leaching of zinc and copper sulfides at 150 C.In this work, the interfacial chemistry of sulfur was studied at temperatures of up to 190 C in the presence and absence of OPD and other surfactants. The contact angle between molten sulfur and pyrite was also measured. Finally, the impact of OPD on the kinetics of pyrite oxidation was measured in bench-scale pressure oxidation experiments. The essential finding of this study was that OPD lowers the interfacial tension between molten sulfur and acid solutions and increases the contact angle (reduces wetting) between molten sulfur and pyrite. The work of adhesion between sulfur and pyrite was reduced by more than an order of magnitude in the presence of OPD. In bench scale tests, addition of OPD was found to significantly accelerate the rate of oxidation of pyrite. Conveniently, it was found that OPD was also fully degraded during high temperature oxidation processes. No residual OPD was detected in solution or solid samples from the leach testing. OPD is recommended as a sulfur dispersant in the pressure oxidation of pyrite and/or elemental sulfur containing feeds.

Jan 1, 2003

By Yanping Xiao

In submerged-arc furnace (SAF) for smelting chromite ores into ferrochrome, there exist large temperature gradients and wide distributions of mineralogy and compositions in the furnace, due to the complexity of feed structure and electrical-thermal-chemical interactions. This leads to various zones in the furnace and thus different reaction mechanisms. In the present paper, the behaviour of chromium in the submerged arc furnace is discussed in various reaction zones, including solid state chromite reduction in the packed bed zone, chromite dissolution and reactions in the smelting and coke bed zone, and recovering chromium from slag to metal. In the gas-solid reaction zone, the reaction mechanism is discussed based on the experimental observations and analysis. In the smelting zone, the behaviour of partially reduced chromite and slag formation are analyzed based on the information in literature. The slag in FeCr process contains mainly Al2O3, MgO, SiO2, CaO and CrOx, featured by chromium with both divalent and trivalent oxidation state, which plays an important role for chromium recovery into metal. The factors influencing the slag and metal interfacial reactions and the chromium recovery are addressed.

Jan 1, 2006

By Nexhmedin Lohja

The production of high-carbon ferrochromium in a submerged electric furnace based on double-level technology has some advantages compared to close-type furnaces with one tap hole. These advantages include the reduction of the specific energy consumption for the overall process, good separation of ferrochromium from slag, an effective treatment of raw materials including lean chrome ores (low percentage of Cr2O3) etc. An outline of the operation of this furnace along with the production line of briquettes from fines of chrome ore by using organic and inorganic binders, will be followed by a description of the recent work carried out to improve the energy consumption in this furnace through a pre reduction process of Cr2O3 ores by the off-gas energy recuperated from the furnace and the use of SiC in the feed. A short theoretical analysis of the new work will also be given.

Jan 1, 2006

By P. P. Knight

The Parkes Process is an important step in the pyrometallurgical refining of lead bullion and it is estimated that more than 50% of the Free world&apos;s primary silver production is processed by this route. The metallurgical efficiency of the process can have a significant impact on the overall refining costs, particularly with regard to zinc consumption and the costs of working up the silver-rich crusts?. Several authors have used mathematical or graphical methods in order to calculate the minimum required zinc additions and to study the merits. of alternative. operating procedures, but these methods are of necessity very cumbersome and are only able to deal with relatively simple systems. The paper explains how a computer model was developed which simulates the Parkes Process accurately and can predict the effects of changes made in operating methods. Examples are given of some of the findings and their relevance to the practical conduct of the process is? discussed.

Jan 1, 1990

By Gerhard Bayer

X-ray and thermoanalytical studies were carried out on the formation and stability of Ca-, Mg-and Mn-tungstate, and of the corresponding minerals scheelite and wolframite. The tungstates were synthesized by different methods: precipitation from solution, solid state reactions, displacement reactions with solutions and in the solid state. The reactivity of natural scheelite and wolframite with different salt solutions and in mixtures with other minerals was investigated.

Jan 1, 1989

By T. T. Chen, J. E. Dutrizac

Noranda Inc., CEZinc presently employs a cement-stabilization (jarofix) process to stabilize its jarosite residues for direct disposal. In this process, Portland cement partly decomposes Na-jarosite to form Ca6Fe2(SC>4)3(OH)i2.nH20, ferric hydroxide and sodium sulphate which further reacts to form gypsum; approximately one-third of the Na-jarosite reacts in the current commercial product. The cured jarofix products also contain minor amounts of various Ca-Al-Fe silicate-sulphate-hydrate phases and traces of calcite. Together with gypsum and a Ca-Fe sulphate phase, these species bond the various particles together, imparting mechanical strength and reducing the permeability. Water-soluble Zn and Mg are stabilized in the Ca-Al-Fe silicate-sulphate-hydrate phases. The freshly cured products usually contain small amounts of moisture and traces of residual Portland cement, which provides additional alkalinity for the neutralization of any residual acid species. Jarofix products stored for more than six years in the laboratory, after curing, are usually dry and exhibit the same micro-textures as those of the freshly cured products. However, the stored products are depleted in the Ca6Fe2(S04)3(OH)i2.nH20 and Portland cement phases, and are enriched in gypsum and calcite which reflects the highly alkaline environment of the jarofix products. The aged products also have increased amounts of the Ca-Al-Fe silicate-sulphate-hydrate phases which have elevated Zn and Mg contents. This implies a further immobilization of residual water-soluble Zn and Mg during stora

Jan 1, 2000

By M. F. Chambers

Neodymium metal was electrowon from a molten-chloride electrolyte at 650° C using a molten-metal cathode. A 50 mol pct NdC13-50 mol pct KC1 mixture served as the electrolyte. Binary metal alloys of &apos;Mg with Zn and Mg with Cd were used as molten cathodes. Under the best conditions, current efficiencies were 90 pct with a Mg-Zn cathode and 80 pct with a Mg-Cd cathode. Vacuum distillation was performed at 1,100° C for 30 min under a vacuum of 10-3 to separate the cathode metals from the neodymium. Neodymium metal of 99.9+ pct purity was recovered from the Mg-Cd alloy cathode. Almost 2 pct zinc remained in the neodymium recovered from the Mg-Zn alloy.

Jan 1, 1989

The concepts of capacity and basicity have proved extremely useful in dealing with a wide range of solute species in metallurgical slags, and as a result have been widely applied. These two concepts are reviewed, and it is suggested that the Lewis approach to basicity has much to commend it. In some cases, it appears that the term capacity has been used without due consideration being given to the nature of the solution being formed, or even to whether a true solution was being formed at all. This paper proposes a rigorous definition of capacity, based on the true nature of the solution process in slags and glasses, and briefly reviews the repercussions of this approach on data available in the literature and the limitations which it may impose on future investigations in this area.

Jan 1, 1994

By KNona C. Liddell

The time and spatial dependence of component and species concentrations during in situ uraninite leaching have been modeled using a reactive transport model based on partial equilibrium between reactive minerals and the solution. The flow field is represented by mixing cells in series. The effects of the H2O2, (NH4)2CO3, and NH4HCO3 component concentrations have been simulated, and results are presented for a one-dimensional flow field.

Jan 1, 1995

By Jeff M. Kuhn

A new solvent extraction process for the removal of halides from zinc sulphate solution was tested in pilot plants at both a 0.1-L/min scale and at a 3-L/min scale. Teck Cominco?s process is called the HalogonTM process, for which patents are pending. Mixer-settlers were used for the 0.1-L/min pilot scale and two BATEMAN pulsed columns for the higher rates. Pilot testing was performed with commercial zinc sulphate solutions containing variable amounts of chloride and fluoride. Sulphate extraction was also controlled and deleterious halides were loaded and stripped into a form suitable for disposal. The engineering aspects and economics of this solvent extraction process for halide removal are also reported.

Jan 1, 2003