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By H. Roberts, C. Hassall

The opening years of the new millennium will be characterised by the closure of many lead and zinc mines because of reserve depletion. However, weak commodity prices through the second half of the 1990s have slowed project evaluation and have made it difficult to raise finances for the development of new mines required to replace lost output and to meet increasing demand for metal in the future. Growth of lead and zinc demand will be determined by the pace of global economic activity, especially in the emerging economies. How rapidly demand grows will have a key bearing on the possible shortfall in mine output and the response of prices to the implied tightening of metal supplies early in the new millennium. These issues are the focus of a discussion of the critical lead and zinc supply developments which will unfold post 2000, taking into account project lead times and the role that recycled metal plays in meeting market demand.

Jan 1, 2000

By H. Bernier

The Noranda Inc., CCR Division, copper refinery located in Montreal-East, Québec, Canada, has expanded over the years to reach a capacity of 410,000 metric tons of cathode production per year. The expansion process resulted in nine, parallel, 200 m. long bays each equipped with its overhead cranes and manually operated washing machines. Anode scrap washing and piling was done manually. The mechanization of the tank house involved the elimination of 18 cells at one end of each of the bays in order to install transfer conveyors where anode scrap and cathode loads are deposited by the bay cranes. The cathode loads are brought by new transverse cranes to new machines where cathodes are washed, piled in predetermined bundle weights, check weighed, strapped then shipped in trucks or railroad cars. Suspension bars are automatically removed, stacked in magazines and sent back to the starting sheet machines. Anode scrap loads are brought to machines located near the anode furnaces where they are washed and piled in bundles for easy charging. The mechanization has eliminated numerous hazardous jobs and has realized a reduction of 0.2 man-hours/ton. After these modifications, the refinery production capacity now stands at 370,000 metric tons per year.

Jan 1, 1987

By B. C. Tripathy

The effects of alkali metal ions Li+, Na+, K+and transition metal ions Cr3+ and Mo6+ on the cathodic current efficiency, deposit quality, crystallographic orientations, deposit morphology and polarisation behaviour of the cathode during nickel electrocrystallisation on stainless steel substrate from aqueous sulphate solutions containing boric acid were investigated. The alkali metal ions had virtually no effect on the cathodic current efficiency, deposit quality, crystallographic orientations, deposit morphology and cathodic polarisation. On the other hand, there were significant variations in the current efficiency and deposit characteristics when Cr3+or Mo6+ were present in the electrolyte. Current efficiency decreased by more than 10% even at lower concentrations (> 100 mg/L). Similarly purity of the deposits was affected by the presence of either of the metal ions. In the presence of Cr3+, there was progressive shifting of the nucleation potential of nickel towards more negative values, whereas, in the case of Mo6+the nucleation potential shifted initially towards positive values in the concentration range 2-40 mg/L, but then towards negative values when its concentration exceeded 40 mg/L.

Jan 1, 2003

Most of the world's zinc metal is produced via the roast- leach-electrowinning (RLE) process. The process is well established, but most of the sulphur in the sphalerite concentrates reports in the acid, which has to be stored and/or sold. There are significant incentives to develop a simpler process with much reduced acid generation. Ferric ion is a well known oxidant for most sulphides, in particular sphalerite, and it converts the sulphide to elemental sulphur. Based on stoichiometry, however, the amount of ferric ion needed to achieve acceptable zinc extractions is prohibitive for downstream zinc recovery from the leach solutions. The process suggested here makes use of less-than-stoichiometric ferric sulphate additions because the ferric ion is regenerated by sparging SO2/O2 mixtures. This regeneration can be effected in-situ in the leach vessel or outside the leach vessel. An example of the application of this new process is presented for a Canadian sphalerite concentrate assaying 60% Zn. The effects of temperature, ferric concentration and ferric ion regeneration are presented. Options to recover zinc from the leach solution are also briefly discussed.

Jan 1, 2000

By A. D. Besser

The world production of lead has been growing continuously and reached over 7 million tonnes in 2005. At the same time, the structure of lead consumption has changed: the use of lead compounds to liquid fuel has been virtually terminated; the proportion of lead for manufacture of lead-acid batteries has been growing and reached 76.7% of the overall world production of this metal. This has taken place against the background of increasingly stringent environmental norms and environmental legislation. This is due to the lack of an alternative for lead in manufacture of local power sources. A solution to the problem of meeting the industrial demand for lead with simultaneous reduction in the primary lead production is in recycling. A large amount of batteries manufactured worldwide and their short life cycle, as well as the positive economics and a possibility to comply with the environmental requirements encourage the development of secondary lead production. Currently, over 60% of the world demand for lead is met due to recycling. The current situation with collection, transportation, storage and processing of spent lead-acid batteries has been analyzed in this paper. Examples are given to illustrate technological and equipment solutions and trends for improvement of secondary lead production discussed.

Jan 1, 2006

By Robert W. Bartlett

Hazardous metal contaminants in liquid and solid wastes and from ground spills are important environmental problems in many metallurgical production operations. Acid rock drainage, from mines and huge quantities of permeable mine waste, is probably the most ubiquitous example. Fixing mine waste contaminants in situ has been practiced, using sulfate reducing bacteria (SRB) and organic reagents as electron donors to create anaerobic conditions and precipitate metal sulfides. Aqueous solutions of sugar and alcohol have been percolated into mine wastes with good results. However, maintaining anaerobic conditions permanently is unlikely, as these solutions are eventually washed out of solid waste and contaminated ground by inflow of either groundwater or meteoric water, allowing re-oxidation from entering air. Emulsions of inexpensive, non-aqueous organic microdroplets dispersed in water provide earth wettablility equal to aqueous solutions and easy percolation into both the ground and mine waste. Subsequent breakdown of the O/W emulsion provides permanent retention of the organic phase, attached to earth particles, that secures lasting anaerobic conditions, precipitates metals as sulfides and prevents re-oxidation of these sulfides. This process and its optimization are described, including experiments with sand-filled columns representing a vertical section through solid waste. Results of organic and metal retention in solid waste are provided from analyses of acid mine water drainage before and after waste treatment.

Jan 1, 2006

By David G. Dixon

From its first implementation for the recovery of gold from low-grade ores by cyanidation in the early 1970s, heap leaching has developed into a key hydrometallurgical technology, in conjunction with solvent extraction and electrowinning, for the recovery of base metals, including most notably copper from both oxides and secondary sulphides, and more recently, nickel and zinc. And, given recent advances in bioleaching with thermophilic microbes, the successful application of heap leaching technology to low-grade primary copper ores seems only a matter of time. However, with each new development, it becomes increasingly apparent that the successful application of heap leaching technology will ultimately depend on our having an ever more complete understanding of the fundamental processes underlying it. Much work has been done toward the development of this understanding, on many different fronts. In this paper, a critical overview of heap leach modeling work to date is presented in terms of the most important phenomena which occur during heap leaching, and potential directions for future work are discussed.

Jan 1, 2003

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 Jakub Kaczorowski

In the production of Mn-alloys, the Boudouard reaction significantly influences the mass and energy balance. The endothermic nature of this reaction requires more energy for the process, while the direct consumption of carbon is reflected in the greater demand for carbonaceous raw materials. Therefore, it is desirable to eliminate or suppress the reaction. The kinetics of the Boudouard reaction are a function of many factors, of which coke properties and the conditions around the particles (i.e. temperature, gas composition) seem to be the most important. In the present study properties of selected single source and commercial metallurgical cokes are compared with reactivity results. The single source cokes represent a single coal that has been carbonized in a laboratory scale furnace. The commercial cokes are products of carbonization of coal blends under industrial conditions. The coke properties include proximate, ultimate and ash analysis. Also, coke petrography with carbon forms is included. The reactivity tests were performed on different particle sizes at various temperatures, gas compositions and gas flow rates. The experimental parameters were chosen to simulate the conditions in an industrial furnace. The results show that highly graphitized structure of cokes, minimal surface area and a low concentration of ash retard the reactivity. Of the other factors, the temperature and the gas composition have the greatest impact on the reactivity.

Jan 1, 2006

By Kazuyuki Kakegawa

"Sintered body of lead zirconate titanate (PZT) was prepared through the spark plasma sintering (SPS) technique. When the mixture of raw materials was calcined at 800°C and sintered at 900°C for 10 min. with SPS technique, the sintered body had almost theoretical density but was a mixture of lead titanate (PT) and PZT. When a calcining temperature of 1100°C was employed, sintered body had a single PZT phase but a lower density. High dielectric constant was obtained for a sample calcined at 800°C, sintered with SPS tecbriique and fired again in the air at 1100°C.IntroductionSpark plasma sintering (SPS) is a recently developed technique for sintering metals and ceramics1. The scheme of SPS is shown in Fig. 1. Sample is put in a graphite die in a vacuum chamber. It is pressed and pulse voltage is applied. The electric current heats the die. It is said that the pulse causes a spark-plasma between particles in the sample. Because of the spark- plasma, sample can be sintered at temperatures lower than that in the ordinary sintering by several hundred degrees of Celsius. The sintering period is also very short2Low sintering temperature and short sintering period in SPS technique cause low reaction rate. It is both disadvantage and advantage. In some cases, the reaction cannot be completed under the SPS conditions. If a mixture of several compositions having different properties can be sintered without a compositional change by the diffusion during the sintering, combination of properties, and therefore a design of property will be possible3. The low reaction rate of SPS may enable such combination."

Jan 1, 2000

By H. -P. Behrendt

Muldenhiütten Recycling und Umwelttechnik GmbH is a lead smelter with a very long tradition. The first reference to the existence of smelters on this site is given by a document of inheritance dated 1318. Originally run as a primary lead smelter, which was supplied with ores from the Freiberg mining district and from overseas, it was required to change it over to secondary raw materials due the abandonment of mining in the Freiberg area in 1968. Today, Muldenhüitten Recycling und Umwelttechnik GmbH has two production lines; lead production from secondary lead and waste incineration, which are closely connected and gain advantage from each other. Installations, improved technologies, and the highly skilled personnel have contributed to satisfy all demands for a production concerning quality and environment.

Jan 1, 2000

By Tiffany Brown

In the thiosulfate gold leaching process, thiosulfate is used to complex gold following electrocatalytic oxidation of the native metal by Cu(II)-ammines. Unfortunately, Cu(II) complexes also catalyse the undesirable conversion of thiosulfate to polythionates. We have been seeking alternatives to ammonia, which fulfil the role of ammonia but minimize thiosulfate decomposition. One aspect of these studies has involved the determination of the rate of thiosulfate oxidation by the Cu(II) complexes from UV-Visible spectral changes. Various ligand classes, including pyridyls, polyamines, aminocarboxylates and picolinates, have been tested and the majority found to inhibit thiosulfate decomposition. Interesting variations in reactivity with the nature and denticity of the ligand and L/M ratio have been observed. In the case of open chain polyamine ligands with 2 to 5 nitrogen donors, the rate of thiosulfate oxidation was generally found to decrease with the denticity and the concentration of each ligand. Saturation of the Cu(II) coordination sphere appears to inhibit the oxidation of thiosulfate when excess thiosulfate is present. The Cu(II) complex of the branched polyamine ligand, tris(2-aminoethyl)amine (tren) exhibits this behaviour in excess thiosulfate. Interestingly, when the [Cu(tren)(OH2)]2+ complex is in excess oxidation of thiosulfate was observed. This unexpected finding prompted a spectrophotometric study of this reaction which has revealed that the oxidation of thiosulfate involves several processes, two of which involve the formation and decay of a tetrathionate radical.

Jan 1, 2003

By Mike Santaluce

Smelting furnace rebuild projects often require a significant capital expenditure and an extended smelter outage. Smelter operators are increasingly searching for methods and initiatives to shorten furnace rebuild schedules, maintain manageable cost levels, enhance furnace performance and achieve excellent safety results. This paper describes the ?MEPC? Model for furnace rebuilds; a project driven approach which Auburn has developed in response to the need for improving furnace rebuild project outcomes. The ?MEPC? (Management, Engineering, Procurement and Construction) approach better addresses the unique challenges presented by furnace rebuild projects when compared to the traditional EPCM (Engineering, Procurement, Construction Management) model widely in use for these projects today. One key feature of the MEPC model is that a dedicated project management team with representation from all of the major project stakeholder groups is put in place at the onset of the project. The project management team has ownership and accountability for meeting overall project goals over the entire lifecycle of the furnace rebuild project. A second key aspect of the model is emphasis on project management as a completely separate project function with its own specific skill sets, techniques, tools and best practices. These features of the MEPC model offer several advantages in terms of improved planning, coordination, communication and alignment with project goals which contribute to the overall success of furnace rebuild projects. Similar MEPC concepts have been used to deliver excellent project results in other industries and the MEPC approach has been successfully utilized on furnace rebuild projects.

Jan 1, 2006

By Zhang Jianliang, Zuo Haibin, Gao Bing, Wang Zhe

"As a result of the shortage of coking coal and the quality decrease of coke, it is important to know how to make better use of highly reactive cokes. The co-gasification behavior of highly and lowly reactive coke for blast furnace is investigated. The results show that: In the middle stage of reaction, the weight loss ratio of highly reactive coke reacted together with lowly reactive coke is higher than that of it reacted individually. However, the weight loss ratio of lowly reactive coke is lower. The weight loss ratio of highly and lowly reactive coke is almost the same as that of the weighted average. The scanning electron microscope analysis indicated that the reaction degree of surface and interior of lowly reactive coke is relatively uniform with the reaction time increased. And the reaction degree of surface of highly reactive coke is obviously higher than that of interior.IntroductionIn blast furnace iron making process, coke functions as heat supplier, reducing agent, carburizer and skeleton. With development of blast furnace iron making technology, the skeleton function of coke is becoming more and more important in requirements of large scale furnace and high pulverized coal injection. High reactivity coke is usually produced by cheap coal with bad quality, and is not good for blast furnace process. The reactivity of coke is mainly determined by the coals used, and the resource of good quality coking coal is limited and is non-renewable. In order to fulfill the need of blast furnace, a lot of research have been done to improve coal matching using new kinds of coal to enlarge resource, in which coking coal and fat coal are reduced, whereas low price coal with bad caking property are used to lower the cost, and this would inevitably increase the reactivity of coke [1-4] Blast furnace iron making would still be the main stream for a predicted future, and high reactivity coke would correspondingly be used more and more, so it has great importance to study how to use high reactivity coke in blast furnace."

Jan 1, 2013

By C. M. Iheagwara

This paper has addressed the issues that constitute major obstacles to the cost- effective and efficient operation of metallurgical vessels from the refractory standpoint. Refractories generally withstand severe conditions of high temperature reactions as well as physical loading/impingement and hence degenerate and need replacement. Scarcity of some refractory materials especially high alumina and magnesite ores in some places, the prohibitive cost and the frequency of replacement of damaged refractories threaten the continued support for metallurgical operations. Some of the causes, prevention and cure for refractory wear have been discussed and rational strategies (short and long term) have been recommended which if implemented should go a long way towards arresting the perennial problems they portend.

Jan 1, 1991

By Charles Zimmerman

The Genesis gold mine, owned and operated by Newmont Gold Co., is located in section 31, T36N, R50E within Eureka County, Nevada along the Carlin Trend of sediment-hosted disseminated gold deposits. Mining commenced in 1986 with present mineable and stockpiled reserves listed at 17,711,000 tons of ore averaging 0.073 opt Au, totalling 1.292 million ounces of gold. Ore is primarily hosted within Devonian calcareous siltstones that have been subjected to intensive argillization and silicification episodes. Additional mineralogic and geochemical features of the Genesis ores include enrichment in iron-oxides, kaolinite, arsenic and antimony; the ore zone is relatively depleted in carbonates and sulfides as a result of supergene and hypogene oxidation. Two major structural zones enhanced the permeability of the siltstones and served as the main hydrothermal conduits within the deposit. Prior to the main ore stage, the host rocks were subjected to metasomatic effects caused by emplacement of the Juro-Cretaceous Goldstrike granodiorite pluton and associated dikes and sills. Micron-size gold occurs in clays, micro-crystalline quartz, and in arsenical complexes. Non-oxidized carbonaceous and sulfidic ores and silica-locked ores result in variable preg-robbing and refractory responses during cyanide recovery. Selective mining and milling has resulted in the successful treatment of the Genesis orebody.

Jan 1, 1988

By M. E. Reed

Clyde Materials Handling (CMH) and WorleyParsons have developed a concept for a flash furnace feed system using the specialist pneumatic conveying equipment expertise of CMH and the flash furnace process experience of WorleyParsons. CMH has developed a proprietary volumetric feeder (called a Rotofeed) which is extremely accurate and overcomes many of the problems inherent with loss-in-weight screw feeders and drag chain conveyors, previously regarded as state-of-the-art. Initial indications are that the Clyde-WorleyParsons Feed System could deliver the following benefits to Flash Furnace operation: ? Accurate pulse-less delivery of feed material to the head of the burner leading to improved combustion performance and process stability; ? Highly accurate split to the individual quadrants of a conventional burner tube, or provision of a smooth hollow curtain to a burner without guide vanes; ? Decreased pressure pulsation in the furnace due to improved combustion control and performance; ? Decreased temperature fluctuations in the furnace due to improved combustion characteristics and hence reductions in refractory thermal stress and wear; Plant measurements have indicated a correlation between the discharge of concentrate from the drag chain conveyor and high speed pressure fluctuations in the flash furnace settler. Pilot scale test have been conducted to illustrate that the system delivers pulse-less feed to the burner with even feed distribution axially.

Jan 1, 2006

By Biserka Lucheva, Tzonio Tzonev

"A unique DC electric arc rotary furnace with capacity 150 kg has been designed and constructed for the recycling of low-quality scrap and aluminum dross. The main constructive feature of this furnace is that the axially positioned graphite electrodes (cathode and anode) are placed 100 mm away from the rotation axis of the furnace. A specific characteristic of the construction is the possibility one of the electrodes (the anode) apart from moving axially (parallel to the furnace axis) to move at 90° outside the working space. High recovery rate of metal aluminum from aluminum dross (92%) was realized in this furnace. This is the reason for construction of industrial DC electric arc furnace.IntroductionThe consumption of aluminum waste has been rising continuously on a world scale, which is a great stimulus for the development of the technology for aluminum recycling.To recover the aluminum in dross, the conventional recycling process uses salt rotary furnaces heated with a fuel or a gas burner. This treatment process produces a secondary dross containing alumina, salts, impurities and a small amount of aluminum. Molten aluminum is tapped from the furnace and the residue is then dumped from the furnace. It has been the practice to dispose the residue in a landfill. Improvement of this technology, known as the oxy-fuel process, uses a gas burner enriched with oxygen to increase the thermal efficiency [1]. Recent studies show that the most efficient aggregate for recycling of aluminum scrap has turned out to be the rotary tilting furnaces, heated by plasma or electric arc, for which the use of flux is not necessary [2,3].Accordingly, there is a substantial need in the industry for an improved process for recovering free aluminium. It is particularly desirable that such process be cost effective and ecologically safe."

Jan 1, 2008

By Abhishek Lahiri

Titanium dioxide is extracted from titaniferous ores by chloride and sulfate processes. These two processes produce wastes in the forms of iron chloride, iron sulfate and rare earth oxides gangue, each of which has to go through a further treatment before it can be disposed safely, which may be expensive. The shortage of high-grade ores is also making the two conventional processes less efficient. In view of the above mentioned problems, an alternate beneficiation process of roasting titaniferous ores with soda ash is discussed. The advantage of this process is that, there is no production of wastes. The impurities present in the ore can be selectively separated after the roasting process. The roasting of titaniferous ores with soda ash was carried out between temperatures of 873K and1173K for several hours. The roasting process resulted in the formation of complex alkali compounds and various sodium titanate compounds, depending on the Na2CO3to ore ratio. The phases formed after roasting were characterized using the X-ray powder diffraction (XRD), X-ray florescence (XRF) and scanning electron microscopy (SEM) techniques. The phase equilibria in the Na-Ti-O system are evaluated and compared with the phases obtained after the roasting process. The effects of temperature and the proportion of sodium carbonate on titaniferous ores are also discussed. From the experimental data, the overall reaction kinetics and phases formed were analyzed to ascertain the mechanism of overall reaction and the rate-limiting steps.

Jan 1, 2006

By Hee Dong Jang, Hong Yong Sohn, Miguel Olivas-Martinez

"Tetramethylorthosilicate (TMOS), a precursor of silica nanoparticles, is prepared from the waste silicon sludge, followed by the synthesis of silica nanoparticles from the TMOS by flame spray pyrolysis. A two-dimensional multiphase computational fluid dynamics (CFD) model for the flame spray pyrolysis process (FSP) for the synthesis of silica nanoparticles has been developed. The model incorporates the governing turbulent equations of overall continuity, momentum, energy and species mass transport to represent the gas phase and the population balance model (PBM) to account for the silica nanoparticles. The model has been validated with experimental data in terms of gas temperature and average particle size. Introduction Silica (SiO2) nanoparticles are used in various industrial applications, such as catalyst, pigments, thin film substrates, electronic and thermal insulators, and humidity sensors [1]. They are also used as additives in plastics and rubbers to improve the mechanical properties of elastomers, and in liquid systems to improve their suspension behavior. These applications rely on the particle morphology, average particle size, particle size distribution, and phase composition [2]. Silica nanoparticles can be synthesized by wet chemical processes such as sol-gel methods and high-temperature processes such as flame spray pyrolysis (FSP). The FSP process provides a unique control of particle size and crystalline structure and it can also produce high-purity, thermally stable particles continuously with minimal further treatments. The sizes of the flame- made particles range from a few to several hundred nanometers, depending on the operating conditions [1]. The synthesis of silica nanoparticles from organic compounds that contain silicon by the FSP process is of interest because it generates no harmful by-products [1, 3]. Several compounds such as tetraethylorthosilicate (TEOS) and tetramethylorthosilicate (TMOS) can be used to synthesize silica nanoparticles, but most such compounds are expensive. Thus, it is desirable to prepare the precursor compounds from waste materials. In the present study, TEOS and TMOS synthesized from silicon sludge were used as precursors of silica nanoparticles [4]."

Jan 1, 2008