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By Sylvie C. Bouffard

The need for a better understanding of the heap biooxidation pretreatment of pyritic refractory gold ores has prompted us to develop a rigorous mathematical model of the process. The hydrological structure of the model takes the form of lateral stagnant pores in contact with a uniformly distributed gas stream and connected to vertical plug flow channels, as suggested by the results of an independent study of column hydrology. A model of pyrite oxidation kinetics was derived based on electrochemical leaching theory and the results of potentiostatic stirred tank and column tests. The growth rates of attached and planktonic iron- and sulfur-oxidizing cells are modeled with separate Monod expressions over three separate temperature ranges corresponding to mesophiles, moderate thermophiles, and extreme thermophiles. Isothermal column tests validate the model simulations. Excellent fits of several leaching indicators (potential, extent of sulfide oxidation, iron concentration, cell numbers) reveal the rate-limiting step to shift from particle kinetics to oxygen gas/liquid mass transfer with increasing temperatures and pyrite head grades. Competition for oxygen between sulfur- and iron-oxidizing microorganisms lowers potentials and slows down pyrite oxidation. This modeling tool may assist engineers in the design and operation of heaps to give more complete gold liberation in a shorter time.

Jan 1, 2003

By I. M. Santos Moraes

Achieving high current efficiencies when operating at high current densities is a goal for every refinery, whether conventional or permanent cathode technology is employed. To obtain higher current efficiency at increased current density at Caraiba's Tankhouse, the production team decided to change the cathode cycle from eleven to thirteen days, reducing cathode cycle to one per anode cycle. The idea was to reduce the anode-cathode spacing and consequently reduce the potential for short-circuiting them. With respect to current efficiency, the overall result was not much better than that obtained with the normal operating conditions. A new attempt to obtain higher current efficiency at high current density was implemented by going back to two cathode cycles per anode cycle, this time reducing cathode life to ten days. This approach yielded the highest current efficiencies. This paper presents the data generated with the three operating conditions: normal practice, a single cathode cycle per anode cycle, and two cathode cycles per anode cycle with a reduced cathode cycle time. It compares the productivity achieved with each set of operating conditions. An analysis of the main operating parameters as well as the advantages and disadvantages involved with each condition is also presented for future reference.

Jan 1, 1999

By C. Frias, M. Garcia, G. Diaz

Advances in hydrometallurgy promoted by Tecnicas Reunidas are providing increasingly simple and clean means for controlling the entire lead recycling chain. Used in parallel with pyrometallurgy, these processes allow furnace temperatures to be reduced and fumes and atmospheric pollution to be minimised. Furnace slags are digested, and residues (mainly gypsum) are non-toxic and convertible into marketable products. In addition, the global economy of the process is substantially improved by reducing the operating cost, increasing the lead recovery above 99% and obtaining a 99.99% pure lead product. These new PLACID and PLINT processes may provide the cleanest and healthiest practicable means for recycling lead from batteries.

Jan 1, 2000

By José C. Escobedo B.

A kinetic study of nitrogen dissolution in a. electromagnetically stirred Co-Cr-Mo alloy bath was made. The experiments were carried out at 1693, 1723 and 1743K of temperature, with a nitrogen pressure of 0.67 atm. The mass transfer coefficients were obtained, finding that their values increase as temperature grows. The true kinetic constants were calculated. It was found that at 1693K of temperature, the kinetics of the nitrogen dissolution process is controlled by a mixed mechanism involving both transport processes and chemical reaction, while at 1723 and 1743K of temperature, the kinetics is controlled only by transport processes mechanisms.

Jan 1, 1995

By P. Barrios

The copper refinery of Atlantic Copper was modernised and converted to the Isa permanent cathode system in 1995. The technology installed has proved to be an excellent platform for the development of operational improvements. During the years it has been working, the progressive assimilation of the new technology has been achieved and the level of operator knowledge has allowed design production to be reached and surpassed by more than 10%. At the same time, modifications to the work programmes, using existing equipment, have permitted the incorporation of new cells and the achievement of annual production levels of 250,000 tonnes and a productivity of 0.43 t/man-hour.

Jan 1, 1999

By M. D. Street

Lead and zinc production commenced in 1966 at Brunswick Smelting using the Imperial Smelting Process. In 1972 the blast furnace was modified to produce lead bullion only which was refined to corroding grade lead using conventional kettle refining techniques. Since 1972 consumption of lead concentrate and production of refined lead has doubled and this paper describes changes to operating and maintenance techniques which have contributed to this improvement. Reference is also made to improved environmental, health and hygiene practices at the smelter.

Jan 1, 1983

By James A. Warren

The phase field method has been successfully employed as both a tool to model heterogeneous materials and as numerical method for calculating the motion of interfaces and phase boundaries without explicitly tracking those interfaces. The method has been used to model a diverse suite of problems describing the microstructural evolution in materials. These models are derived from thermodynamic arguments and symmetry principles, and usually guarantee positive local entropy production for systems out of equilibrium. Descriptions of how phase field methods can be applied to the problems of solidification, grain growth, and electroplating will be presented.

Jan 1, 2001

By R. W. Lawrence

A high rate biological reduction technology has been developed to provide low cost hydrogen sulphide for various uses in water treatment and metallurgical processes. Commercial operations produce sulphide safely at a fraction of the cost of chemical sulphide. The biologically produced H2S is used for treatment of acid wastewater and selective metal recovery whereby metals present in wastewater streams are recovered in high grade metal sulphide concentrates that are sold to smelters. The combination of biological H2S production and selective metal recovery is currently marketed under the process name BioSulphide-Thiopaq. The process can be applied on a stand-alone basis or in conjunction with a conventional lime water treatment. Process advantages include: reduced lime treatment costs, reduced volume of waste sludge free of toxic metals leading to reduced long term environmental liabilities, selective recovery of metals and, in some cases, net profit from water treatment achieved through the sale of metal concentrates. Three case studies are presented to provide examples water treatment and metal recovery: the Caribou Mine, New Brunswick; the Phelps Dodge Bisbee operations, Arizona; and Falconbridge?s Raglan nickel mine in Quebec. A fourth case study is presented to highlight environmental control for treatment of ARD in the Leadville mining district of Colorado. Process flowsheets, capital and operating costs are presented for the four case studies

Jan 1, 2003

By Andreas Ludwig, Abdellah Kharicha, Menghuai Wu

"In order to demonstrate how CFD can help scientists and engineers to better understand the fundamentals of engineering processes, a number of examples are shown and discussed. The paper will cover (i) special aspects of continuous casting of steel including turbulence, motion and entrapment of non-metallic inclusions, and impact of softreduction; (ii) multiple flow phenomena and multiscale aspects during casting of large ingots including flow induced columnar-toequiaxed transition and 3D formation of channel segregation; (iii) multiphase magneto hydrodynamics during electro-slag remelting; and (iv) melt flow and solidification of thin but large centrifugal castings.IntroductionSince the Bronze and the Iron Ages, material processing, and here especially metallurgy, has got a global importance for the economic well-being of the societies. It is thus understandable that metallurgy has changed from arts and crafts into an engineering specialty, where the knowledge of centuries has lead to an enormous commercial and technical efficiency. However, increasing competition and the necessitation of energy and CO2 reduced manufacturing methods requires the improvement of existing techniques and even the development of new, alternative production technologies. On the other hand, the opacity of liquid and solid materials and the involved high temperatures makes the experimental penetration of metallurgical processes and with that the attainment of detailed process knowledge quite difficult."

Jan 1, 2012

By Ilkka V. Kojo

This paper gives an overview of the primary copper smelting business during the years of flash Smelting in the light of various projects taking into account the sustainability of copper production. Also the future challenges of copper smelting are addressed with special emphasis on the environment. Flash Smelting connected with either Peirce-Smith converting or Flash Converting offers the most economical and environmentally friendly alternatives for the smelting of normal and lean copper concentrates. For rich copper concentrates the feasibility of Outokumpu Direct Blister Flash smelting is, understandably, beyond compare. When the total investment costs for building a smelter and acid plant are considered, it is clear that Flash Smelting is the more feasible option compared to bath smelting. Reduction of equipment and operating cost is further achieved by the LUREC-process developed by Outokumpu Technology for operating plants with SO2-contents up to 25 % by volume. As an example the Kennecott-Outokumpu Flash Converting Furnace (FCF) has been in operation at Kennecott Utah Copper for 10 years and has achieved excellent results both environmentally and production vice. The FCF treats the entire output of the Kennecott Flash Smelting Furnace and has excess converting capacity. Furnace life, initially projected at two to three years, is now projected to be more than 5 years. It is likely the life will be essentially the same as a well-operated Flash Smelting furnace.

Jan 1, 2006

By R. D. MacDonald

The papers presented in this chapter cover a wide range of hydrometallurgical topics and might be considered to be unrelated to each other. All of the authors, however, utilized the basic methods of process mineralogy to characterize the reactants in their experiments and the products produced. The wide range of research topics which can be pursued successfully by the use of the methods of process mineralogy is a matter of interest in itself. One might speculate that the methods could be even more widely applied if only their utility were better recognized. These methods for characterizing reactants and products include principally x-ray diffraction, optical micros-copy, wet chemical analyses, instrumental chemical analyses, high intensity magnetic separation, micro-scale gravity separation, differential thermal analysis, micro-hardness testing, and judicious use of the sledgehammer and cold chisel. It is perhaps not by coincidence that most of the papers in this chapter were prepared not by mineralogists, but by hydrometallurgists, who are recognizing the importance of thinking in terms of mineral phases, and not just assays! It appears that the gap between process mineralogy and the mineral industry is closing, and that future AIME sessions promise to become established forums where mutual discussion of such topics as metallurgical "troubleshooting" and process design may become commonplace between plant engineer and process mineralogist.

Jan 1, 1981

By D. Maurice, W. D. Riley, J. A. Hawk

"The increased penetration of wrought aluminum into the automotive market is stimulating a need to separate wrought aluminum from cast aluminum because of: a) the additional value of scrap wrought alloys and b) the increase in the total amount of aluminum automotive scrap will outstrip the demands of secondary aluminum foundry industry. The availability of clean fractions of wrought and cast aluminum and incidentally, a clean cast magnesium fraction will allow increased recycling of aluminum used in the automotive industry.Hot crushing has been tested previously and proposed as a means to separate cast from wrought alunrinum product. The underlying concept is that when a mixture of cast and wrought aluminum is thermally processed and then subjected to crushing action, differences in toughness between wrought and cast aluminum alloys will become more pronounced. Hence, it should be possible for conditions can be established such that the cast material fragments, while the wrought material, having lost much less of its toughness, merely deforms. The two types of product could then be separated by simple sizing methods.In this paper we report on the testing of this concept. We were unable to replicate the results which originally demonstrated proof of concept. Possible reasons for this are discussed, as well as the possibility that the original results may not be as desirable as the current results for subsequent sorting."

Jan 1, 2000

By Paykan Safe

The primary source of fugitive gas emissions in most copper smelters are the Peirce Smith converter operations. The modem trend is towards installation of secondary gas collection systems which are intended to collect fugitive gases from charging, standby, and skimming operations. These have been installed with varying degrees of success. Often, the major source of emissions from the converter area is leakage of process gas from the primary hoods when the converter is blowing. This gas is typically collected by the secondary system and discharged to atmosphere or scrubbed with an alkaline agent. Those smelters considering installation of secondary hoods or scrubbing of gases from secondary systems should first address the issue of gas leakage from the primary hoods. Improving the primary hood gas collection efficiency will often be more cost effective than installing secondary hooding. In the case of secondary gas scrubbing, it will significantly reduce the reagent consumption and operating cost of the scrubbing system. This paper examines the parameters that determine whether or not a primary hood will effectively collect process gases without leakage and demonstrates, using Computational Fluid Dynamics (CFD), the effects of variations in these parameters on the overall performance of the hood. It also looks at the application of CFD techniques in the design of secondary hoods and presents a summary of measured emissions from converter buildings.

Jan 1, 2002

By Ian Masters, A. R. Khoei, D. T. Gethin

This paper describes an experimental investigation into the effects of process parameters on product quality during an aluminum recycling process. In order to build a model relating recovery to the process parameter variables and then use the model for prediction, process optimisation, or process control, a historical data analysis is employed by observing patterns in the datalogged information at IMCO Recycling Ltd. In previous work, we emphasised the importance of expressing the results of an experiment quantitatively, by implementation of a Taguchi approach, to facilitate understanding, interpretation and implementation. This research presents the technical tools that are needed to achieve quality improvement in recycling of aluminum. In this study we apply the use of historical data matching through a Taguchi orthogonal analysis, in order to control and improve the quality characteristic. For this purpose, a numerical model is developed to characterise the inputs and outputs of the process. A response surface methodology (RSM) is employed to find a suitable approximation for the true functional relationship between response and the process parameter variables. The method of least squares is used to estimate the approximating polynomials. Subsequently, Taguchi's method is used to determine the relative significance of each of the parameters. Finally, process management software (written in Visual Basic) is described, and its interface with the process modelling and optimisation routines is discussed.

Jan 1, 2000

By A. V. Tarasov

The natural resources of lead and zinc are primarily constituted by polymetallic and lead-zinc ores. Beneficiation of these types of ores to produce standard nonmetallic concentrates inevitably results in an increase in the loss of base and precious metals with tailings. An improvement in the grades of lead and zinc concentrates can be achieved by re-cleaner flotation, but it results in production of intermediate products (middlings) to which substantial amounts of lead, zinc, copper and precious metals report. Without an appropriate technology for treating such intermediate products, the recoveries of valuable constituents from lead-zinc ores would remain unsatisfactory. A process has been developed in the Gintsvetmet Institute for processing of polymetallic intermediate products produced at the ore beneficiation plants. This process is based on electrothermic smelting to produce lead bullion containing precious metals, commercial-grade copper-lead matte and high-zinc slags (up to 15-20% Zn) from which zinc can be extracted by slag-fuming or Waelz process. Tests have indicated that the recovery of lead from intermediate products into lead bullion and matte is about 83-85% and 13-14% respectively (the total recovery is 97-98%), while copper recovery into the matte and zinc recovery into the slag is 90-92% and 95-96% respectively. Precious metals (about 96-97%) report into the lead bullion.

Jan 1, 2006

By Oleg I. Platonov

The process for desulfurizing coke oven gas in a regenerative system ?scrubber-stripper?, with sour gas being fed to Sulfur Recovery Unit (SRU) and tail gas being recycled to raw coke gas scrubber, has been developed. A key problem of this process is the presence of elemental sulfur in the SRU off-gas, which may deposit on gas-blowing equipment, thus disrupting its operation. A new treatment technology for SRU off-gas that has been worked out for a Claus unit operated by «Russian Metallurgical Company» (RMC) in Magnitogorsk (Russia) is presented. It incorporates a catalytic hydrolysis/hydrogenation stage, where all sulfur-bearing species such as sulfur dioxide, carbonyl sulfide and elemental sulfur are converted to hydrogen sulfide. The SRU in Magnitogorsk comprises three main units: gas re-heater; catalytic hydrolysis reactor and waste gas cooler. Re-heater is required to increase temperature of the process gas up to a level of catalytic conversion (beyond 330-3500C). Oxygen utilized as an oxidizing agent reduces the volume of waste gas to a minimal possible value. The operational data garnered since 16.07.2004 clearly shows that the new technology allows high-level purification of Claus tail gas from elemental sulfur. Unlike SCOT ? process, this technology does not require separate stages for H2S removal and enrichment that tangibly simplifies its implementation at lower capital and operation expenditures.

Jan 1, 2006

By K. Rajani Kanth

Environmental problem is the major concern for any industry and there is a great need to that along green lines. Sangam Dairy being one of the most famous and wide spread Dairies in India, produces wide spectrum of milk products. The BOD levels of effluent water of this industry with MIF treatment were found to be around 100 ppm. Lot of research has been expended in the past to bring down the BOD levels to bare minimum. The main objective of the present study is to minimize the BOD level to the required level stipulated by environmental standards by employing various seeding materials. For this purpose microbes like Bacillus Subtiles, Pseudomonas, Aspergillas, Staphylococcus, and Pencilium have been employed and BOD levels were analyzed. Various Reagents, solutions with different dilution levels have been successfully prepared. Initial and final Dissolved Oxygen levels were determined before and after incubation. From the DO data, BOD was evaluated for all samples and comparison analysis of various seeding material was carried to suggest the efficient seeding material for the ETP plant. In the process, solutions of different dilutions have been prepared using difficult reagents. These samples are treated with above mentioned microbes and BOD levels are estimated. It has been observed that staphylococcus and Pseudomonas proved to be the best seeding materials. When there microbes have employed BOD levels fall to less than 10 and 20 ppm respectively

Jan 1, 2006

By Jay Black

In the thiosulfate gold leaching process gold is oxidized to Au+ by a copper(II) ammine catalyst and complexed by thiosulfate. Copper(I) complexes, formed during gold oxidation, are reoxidised to Cu(II) complexes by oxygen. In this study, we present the results of a spectrophotometric study of the Cu(I)-NH3-Cl system, which follows on from our recent investigations of speciation in the Cu(I)-Cl and Cu(I)-S2O3-Cl systems and is part of a detailed study of copper(I) speciation associated with the gold leaching process. Formation constants for Cu(I)-NH3-Cl complexes have been determined by modeling the systematic changes in the UV spectra that occur as the concentration of the components is varied. The analysis of the data indicates that three Cu(I)-ammonia complexes are present, i.e., [Cu(NH3)2]+, [Cu(NH3)Cl2]- and [Cu(NH3)2Cl] and their respective log Kf values are 11.13, 8.33 and 10.79 at 25°C. Investigations of the oxidation of Cu(I)-NH3-Cl solutions by oxygen in the atmosphere are also presented. These experiments indicate that the reaction of copper(I) complexes progresses through various intermediates. The presence of many copper(I) and copper(II) complexes in ammonia thiosulfate solutions complicates the task of determining optimal conditions for gold leaching. Further studies are needed to identify the complexes and chemical processes that are important in the Cu(I)-NH3-S2O3-Cl system.

Jan 1, 2003

By Peng Fan

Liquid phase tends to migrate from an aggregate of solid particles immersed in a liquid phase into another aggregate composed of the same solid particles and liquid but with smaller particle sizes and/or lower volume fraction of the liquid phase. This type of liquid migration in a two phase system can be attributed to the driving force for the system to decrease its total interfacial energy. With liquid migration pressure as a convenient measure for the total interfacial energy of a solid-liquid two-phase system, liquid migration can be attributed to the existence of liquid migration pressure gradient in the two-phase system. The kinetics of liquid migration is of great practical importance for many industrial processes, one of which is the liquid phase sintering of functionally graded WC-Co composite materials. During liquid phase sintering, WC-Co composite forms a typical solid-liquid two-phase system where solid particles of WC are immersed in liquid Co. For a sample composed of two layers of WC-Co with the same Co content but different WC particle size, Co gradient will be formed during liquid phase sintering; while for a sample composed of two layers of WC-Co with the same WC particle size but different Co content, the Co gradient will be eliminated during liquid phase sintering. The formation and elimination of Co gradient are controlled by the liquid migration pressure gradient. This paper describes a numerical simulation of the kinetic process of the formation and elimination of cobalt gradient.

Jan 1, 2006

By Wang Haibei

China is the important country in terms of Ga, Ge reserves and products. These elements usually associate with lead and zinc ores such as in Fankou, Dachang and Lanping mines. Until now these metals could not be extracted from zinc residues effectively. The main reason is that it is difficult to separate zinc and iron. BGRIMM has carried out considerable research on this subject and some hydrometallurgical processes were developed. Zinc residues were pressure leached with a reducing agent such as zinc concentrates or SO2 at 110~130C. The final concentrate of H2SO4 was 30~50g/L. The metals such as Zn, Fe, Ga and Ge were dissolved into solution. In the leaching residue Pb and Ag could reach 20% and 2000g/t. The feed of solvent extraction was prepared from the leaching solution by pre-neutralization ? precipitation of Ga, Ge and acid dissolving. Then Ga and Ge were extracted by solvent extraction through P204 and G315 produced by BGRIMM. After stripping, metallic Ga was produced by electrowinning. GeO2 was produced by precipitation. The iron in raffinate was removed by the hematite process. The solution after removal of iron came back at the zinc neutral leaching stage. In 2003-2004, pilot tests were finished in BGRIMM in cooperation with Fankou Lead and Zinc Mine Ltd. And the extraction rate of Ga and Ge in the leaching stage was 94% and 83% respectively. The total recovery rate was 90% and 80%. It is estimated that the technology has a wide commercial use in the coming five years.

Jan 1, 2006