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By Frank B. Amon

Highland Valley Copper had to make some significant changes in the way it was working in order to counter the effects of ever-increasing costs and decreasing metal prices. A mine/mill optimization plan started in 1997 introduced new technologies and management approaches that resulted in a dramatic drop in cash breakeven costs. The changes involved employee training, added authority and responsibility for staff, better communications, and a consistent approach to setting and achieving property-wide goals. The net effect was to change the culture of the organization from one that was fragmented and focussed on local objectives to one that is cohesive and has common goals. These changes have allowed the mine to remain in business during a protracted period of low metal prices, and have positioned the mine favourably to benefit even more from any future increase in prices.

May 1, 2004

By L. Salnais

"Aluminum alloy structural components f or aircraft designed prior to the early 1970s, were machined from 2024, 7075 and 7079 plate, bar and forgings in either the T3xxx of the T6xxx tempers. Protective treatments for these parts consisted of chromic acid anodizing and alkyd zinc chromate primer, plus a nitrocellulose lacquer for exterior parts.The major service problem with these parts was the frequent occurrence of exfoliation corrosion and stress corrosion cracking (S. C. C.). Therefore, 2024 and 7079 alloys, with min or exceptions, were not used in aircraft designed after the early 1970s. Replacement materials were 7075 and 7050 alloys in the overaged, exfoliation corrosion and S. C. C. resistant, T73xxx tempers.The use of improved materials together with the upgrading to chromated epoxy primers, polyurethane enamels and the introduction of water displacing corrosion inhibiting compounds have significantly reduced corrosion in aircraft. IntroductionThe prevention of corrosion in aircraft has been a challenge to aircraft designers for many decades. With the design of the first all-metal aircraft, the designer and builder were thrust into the relatively new field of protective treatments as corrosion started to become more prevalent. This resulted from the continually increasing importance and wider utilization of aircraft, and their exposure to a wider variety of ho stile environments such as urban industrial pollution, high humidity tropical areas and salt ladened marine environments.Corrosion advanced another significant step when, after World War II, designs of new and larger aircraft utilized larger and thicker metal sections in the manufacture of structural components. With thicker mill products came higher residual heat treat, fabrication and assembly stresses resulting in an increased number of stress corrosion and exfoliation corrosion problems.Apart from the exterior environment, aircraft interior s can be exposed to a number of fluids which are either directly or indirectly responsible for corrosion. The most common of the fluids is water which is usually introduced as a result of condensation, especially in pressurized fuselages, and spillage from lavatories, galley s and electrolytes from batteries. These fluid s have a degrading effect on protective treatments and are also corrosive to the substrate metal. Fluids such as phosphate ester hydraulic fluids and ester based turbine engine lubricating oil s are not corrosive to the substrate metal, albeit they do contribute to corrosion by the degrading effect on protective treatments."

Jan 1, 1988

By Ting Lu, Gerard Laman

"This document compares the systems of coal classification described under ASTM standards used in Canada to GB standards used in China. A preliminary connection of metallurgical coal classes was set up between the two classifications. In GB classification system, there are nine metallurgical coal groups, namely PS, SM, JM, FM, ½ ZN, RN, 1/3 JM, and QM used in coal blending for coke production. PS coal is almost equivalent to the Low Volatile Bituminous coal; SM, JM, and FM coal groups fall into Low to Medium Volatile Bituminous range; ½ ZN, RN, 1/3 JM, and QM are equivalent to bituminous coal with medium to high volatile matters; QF contains higher volatile bituminous coal compared with High Volatile Bituminous coal. The caking properties commonly used in respective country are also compared in this document. These properties include free swelling index (FSI) and maximum fluidity used in Canada, as well as caking index (GR.I.), and the maximum plastic layer thickness (Y) mainly employed in China. It has been observed that the log of the maximum fluidity has a stronger correlation with the caking index than the Y values. Metallurgical coal processing strategy and typical coking coal product qualities are briefly discussed in the last section of this paper. Currently there is a trend to use heavy medium cyclone in both countries. In Canada the conventional two-product cyclone technology is the preferred practice; whereas in China the three-product heavy medium cyclone arrangement is widely used.INTRODUCTION Coal can be simply classified by applications into two categories: i) thermal coal used to provide heat energy in combustion, and ii) metallurgical coal which is converted to coke, in a carbonization process, and used mainly in the iron and steel industry. Metallurgical coal contains even higher heating values than thermal coal. In addition, it presents unique plastic properties during carbonization which in turn produces a porous solid, high in carbon referred to as coke. Coke is one of the most important raw materials in the iron and steel industry."

Jan 1, 2012

By Adam Powell, Matthew Earlam

INFINIUM, Inc. is scaling up a new molten salt electrolysis process for producing rare earth metals. Instead of conventional carbon anodes, this process uses Pure Oxygen Anodes™ which employ a stabilized zirconia solid electrolyte between the molten salt and anode. This eliminates two problems with today's rare earth metal production technology. First, it eliminates carbon anodes and contamination of the product by carbon and its impurities, enabling 10-100 times larger batch size than current practice, and lower labor costs. Second, it eliminates emissions of perfluorocarbons (PFC) such as CF4 and C2F6, which are very problematic greenhouse gases with 6000+ times the global warming potential of CO2. The zirconia also enables a sealed vessel with no LiF emissions, creates a reducing environment enabling use of low-cost welded steel vessels, and either produces a high-purity oxygen by-product or can use natural gas to reduce the necessary electrical energy with no HF production. This paper will describe the technology and its current status for rare earth metal production.

Jan 1, 2014

By W. Roy Dunbar

"The Porcupine area is in northern Ontario at the intersection of N. Lat. 48° 30' and 81° W. Long. It is 125 miles due north of the Sudbury nickel range. Practically all the mineral production of this area has come from the townships of Tisdale, Deloro, Whitney, and Ogden, in order of importance. The accompanying map of the Porcupine area and its extensions to the east and west (Fig. 4) has been included to show what I consider to be an essential objective of this paper, a perspective for exploration.The discovery of gold ore in the Porcupine area at such an early date resulted from the extension of the Temiskaming and Northern Ontario railway and exploratory survey lines north into unexplored territory, for the early history of Porcupine is inextricably tied to the exploration along Niven's survey lines and the extension of the railway north from Cobalt to Nellie Lake. The following are the more significant events leading to the discovery of gold in Porcupine.1896-E. M. Burwash, employed by the Ontario Bureau of Mines, examined the country along Niven's base line and noted quartz veins that carried traces of gold. He was attached to Niven's survey party.1899-The late W. A. Parks reported on the geology of the portage route from Mattagami river to Night Hawk lake, for the Ontario Bureau of Mines. He noted the occurrence of gold in quartz veins and reported “I regard the region south of the trail to Porcupine lake as giving promise to the prospector"". He also was attached to Niven's survey party.1901-Charles Camsell, while prospecting for the Algoma Central railway, did some work on a vein occurrence carrying low gold on ground now known to be part of the Hollinger mine (3).1907- Extension of the Temiskaming and Northern Ontario railway to Nellie Lake.1909- Bannerman followed up Indian story about occurrence of coal, and found iron formation. He remained to prospect and found the gold-bearing vein of the Scottish Ontario property."

Jan 1, 1954

By C. Xiao, F. Mohamm, A. Borsoi

"Nitrogen compounds produced by cyanide destruction and/or blasting are often a cause of concern for environmental compliance and at times, for water re-use in metallurgical circuits. Natural attenuation in tailings ponds and wetlands is not always sufficient to ensure compliance and/or achievement of overall water management objectives. This paper provides a general overview of active treatment methods for nitrogen management followed by an investigation of selective adsorption combined with electro-oxidation as the potential treatment method for thiocyanate. Results from bench scale treatability study are presented. The concept of holistic assessment of nitrogen management at mine sites using Risk Adjusted Life Cycle Cost is introduced and discussed in the context of gold mining operations using sodium cyanide.INTRODUCTION Unlike metals, nitrogen compounds present in mine waters originate entirely from anthropogenic sources rather than mineral deposits. Table 1 summarizes the main sources of nitrogen compounds reporting to mine wastewater.The best management practice related to the use of ANFO involves minimizing contact between ANFO and water, control and monitoring of blasting to reduce the occurrence of misfires, and reducing the consumption of blasting reagents for a given ore body. The most common practice for the management of NaCN is the incorporation of cyanide destruction in the metallurgical flowsheet and the use of tailings impoundments and holding ponds for natural attenuation of cyanide destruction residues such as NH4-N and CNO. At most mine sites there is no active management of NO3-N and SCN in wastewater. While current practices have produced satisfactory results, new enhanced methods to manage nitrogen compounds at mines are needed due to: 1) Increased scrutiny over the adverse effects of nitrogen compounds released into the environment; 2) New effluent standards; and 3) The shift away from wet tailings towards dry stack systems resulting in diminished natural attenuation and dilution of nitrogen residues prior to effluent discharge or water re-use in mineral processing."

Jan 1, 2017

By I. O. Ojala

Detailed knowledge of velocity-depth trends is essential for constructing well-to seismic ties, determining background velocity and generating synthetic seismic traces for interpreting seismic amplitudes in terms of porosity, lithology and pore fluid type. The acoustic properties of shales are of particular importance in the exploration setting as shales constitute more than 80% of sediments and rocks in siliclastic environments. Seismic and sonic log data may be used for estimating overpressure in shales in order to maintain borehole stability during drilling. In addition, velocities in shales can be used for predicting its mechanical properties and hence, borehole collapse. Despite of the apparent importance of understanding shale acoustics, sonic logs in shales are frequently unavailable or unreliable especially for older wells. Hence, it is essential to compute pseudo-velocity logs from other available information. This can be accomplished by using empirical relationships or rock physics transforms. In this study we have compared the predictive power of resistivity (Faust 1951, Hubert 2008) and porosity based models (Wyllie 1956, Holt & Fjær 2003) for computing synthetic P-wave velocity logs using wireline log data from mudstone intervals at three North Sea wells. The wells 6507/2-1, 6507/2-2 and 6507/2-1 are located at the Haltenbanken area at the Norwegian Sea. The wells targeted hydrocarbon potential at the upper Cretaceous and lower Tertiary sandstone sequences. The sandstone beds are overlain by thick Tertiary and Cretaceous sequences of mudstones. Since our primary goal is to model acoustic velocities in shale, we used wireline data from the Nordland (NL), Rogaland (RL) and Hordaland (HL) groups that are mainly composed of mudstone. The mudstone beds were identified from the well log data by using natural gamma log, sonic and resistivity data as well as information from the Norwegian Petroleum Directorate website. The volume of shale was estimated from the natural gamma log and the data points with values higher than 0.65 were discarded. Similarly, the data points with shale volume less than 40 % were discarded. Furthermore, exceptionally high resistivity values amounting to more than 6 Ohm m were not included in the analysis. Porosities were determined from the density log assuming 2.7 and 1.05 g/cm3 for matrix and fluid densities, respectively. The depth that was used for calculating Vp from Faust (1953) was the depth below mudline in order to the compare of well data from wells that have been drilled at different depths (Hubert 2008).

May 1, 2009

By N. Morrison, I. Holl, R. Welyhorsky, A. Hempstock

ABSTRACT: The Victor diamond mine is located in the James Bay lowlands, 90 km west of the First Nations village of Attawapiskat. The project was the first of its kind in northern Ontario. The process plant was designed to produce a 95 to 98% by weight diamond concentrate through three stages of comminution, dense medium separation, and proprietary X-ray technology for final recovery. The plant was commissioned over a period of six months, commencing prior to substantial completion of construction. Through effective planning of the commissioning phase, the Victor mine start-up was safely completed nine months ahead of schedule.

Jan 1, 2011

By Andrew G. Patton

The Alimak mining method was introduced at the David Bell mine in 1998 to extract an otherwise uneconomic and inaccessible reserve. The success associated with the extraction of these reserves led to major expansion of the method. To date, results have been extremely positive in terms of grade control, reduced dilution, stope recoveries, productivities and mining costs. It is hoped that through further development of the method at David Bell mine we will continue to see positive results in these areas and be able to increase mineable reserves to include proven resources that do not currently meet the criteria of our current stoping plan.

Oct 1, 2001

By M. Drozd, A. Ibrado, P. Butcher

While effective in treating refractory sulfide ores, pressure oxidation leaves carbonaceous matter unscathed and able to adsorb gold from cyanide solutions. Barrick Goldstrike's strategy to mitigate this problem is to minimize contact between dissolved gold and native carbon in advance of the carbon-in-leach (CIL) process. Measures currently in use include limiting carbonaceous matter in the plant feed by meticulous blending of ore, controlling the degree of oxidation in the autoclaves and blinding native carbon surfaces with lauryl sulfate. The presence of residual cyanide and thiocyanate in the process water remains to be a cause of premature gold dissolution and loss of gold by adsorption on carbonaceous matter. This cyanide is introduced by water that is recycled from the tailing pond. Of several treatment options considered, oxidation by peroxymonosulfuric acid, also known as Caro's acid, is deemed to be the most effective. Laboratory and pilot plant tests show that Caro's acid can oxidize free cyanide, weak¬acid-dissociable (WAD) cyanide and thiocyanate, resulting in significant improvements in gold recovery downstream. The process requires Caro's acid at 125 % of the stoichiometric requirement and pH in the range of 9.5 to 10 to accomplish the desired destruction in about twenty minutes. A cyanide destruction plant is currently being designed and construction should be completed by the end of 2005.

Jan 1, 2005

By Nicolae Dobritoiu

The literature in this field and the practical activity record that a method, respectively the technology used for an underground mining work have many components which, in order to be applied, demand that for each of the parameters that describe the environment of the mining work and that influence the chosing of that method and that technology of execution, must have values in an interval well determined. There are situations when one or many parameters of the set of parameters that describe the environment of the mining work, can modify its values, and, as a result, one or more components of the methods or technology cannot be applied anymore, making necessary a replacement of their values. The information offered by this graphical-analytical model allow the determination of optimum solutions for the process of digging of the underground mining work and thus it will result the incresing of the technical-economical efficiency of the digging process and, also the increasing of the quality of the underground mining work.

Oct 1, 2009

By R. Bashir, J. F. Hatley

ABSTRACT Northern Saskatchewan boasts some of the world’s largest known high-grade uranium deposits. The successful mining of these deposits cannot be accomplished without overcoming technical challenges, however, which include high grade of the uranium ore, specialized mining methods to deal with groundwater at high pressures, and poor ground conditions. This paper discusses the various mechanisms of inflows at three of Cameco Corporation’s sites in northern Saskatchewan. The risk of inflows is quantified in terms of unique challenges due to hydrogeological conditions, rock mass integrity, and uncertainty in geological conditions. Strategies in the case of an inflow are also briefly described.

Jan 1, 2013

By Jean M. Richardson, Steven R. Williams

"Geometallurgical mapping is a new team-based approach that documents variability within an orebody and quantifies the impact of geology (host rocks, alteration and structure) and mineralogy on grinding, metallurgical response and metal recovery processes. The quantitative, spatially constrained database that results can be readily integrated into 3-D block models and mine planning activities. Thus it is an important tool to reduce the technical risk associated with new mine developments or expansions.Normally undertaken during pre-feasibility or feasibility planning stages, the first step of geometallurgical mapping is to review the geology, mineralogy and other critical parameters and construct a geometallurgical matrix. This matrix provides an objective base to then guide sampling and/or compositing activity for physical property and metallurgical testing. Depending on the project, an array of testing techniques can be used to characterize the ore and feed data into the geometallurgical model.While the range and number of tests needed is project-dependant, the geometallurgical mapping approach allows the development of empirical models or interdependent relationships, grounded by spatially-constrained real data. Extensive data sets collected using less expensive testing methods can be meaningfully correlated with results from complex specialty tests to yield realistic metallurgical recovery data.With geometallurgical mapping completed, the resulting database can be integrated into an overall 3-D block mine model. This means that metallurgical response can be used to realistically forecast the recoveries of specific blocks, perhaps sampled only by drilling. Mine planning can then incorporate the forecasted metallurgical response and generate future project cash-flows; opening the door to economic optimization of the mine exploitation."

Jan 1, 2004

By R. England

"This paper describes the objectives and design parameters for the operation of a computerized In-The-Hole (I. T.H.) Drill. The principal objective is to add computer control to an Inco 00-60 I. T.H. (CMS-CD-90) drill in order to drill holes with greater accuracy. The computer provides control of the angle of the hole by maintaining the orientation of the drill head, and optimizes the straightness of the hole by maintaining a constant force on the drill bit.The second objective is to provide the greatest degree of operational automation, so the objective outlined above can be accomplished with a minimum of operator intervention.In order to provide full operational automation it was necessary to also provide the capability for the computer to add and remove drill rods. To accomplish this, a rod-handling mechanism consisting of a rod storage rack and rod manipulator arms was used.IntroductionMining machinery that lacks automatic control has been found to show a high degree of variation in work output and performance quality when operated by different personnel. Differences in operator attitude, judgment, and skill are reflected directly by production statistics. The addition of automated control has the potential for considerable improvement in machine life and performance. Even with a more acceptable mine environment and much safer conditions than ever before, situations still exist where it is preferable to remove personnel for reasons of safety as well as productivity. Typical advantages of such situations are automated skip loading and hoisting, and the use of remote control load-haul-dump units exposed to open stopes.Other cases arise where heavy work is required under conditions where lighting is poor, floors are slippery, noise levels are high and dust and oil mist exist in the atmosphere. I.T.H. drilling is carried out under such conditions and is one operation where automation can easily be justified."

Jan 1, 1987

By M. H. Attia

The concept of sustainable development has been evolved into a working framework for sustainable manufacturing, in which the environmental requirements are introduced into product development at the design stage. This keynote paper is discussing a number of issues pertaining to the impact of manufacturing on the environment. The conflicting requirements of sustainable development, sustainable manufacturing (SM) and economical growth are presented in the light of successful case studies that were able to convert conflicts into opportunities. Integration of SM into the product life cycle is also presented. A number of concepts that are related to Ecoefficiency, e.g., inverse manufacturing, demanufacturing and re-manufacturing are also discussed. The paper underlines the fact that the positive impact of this new philosophy is equally applicable and beneficial to both; developed and developing countries. The paper concludes with an overview of Global trends in environmentally benign manufacturing (EBM); e.g., product-take back and emerging material and processing technologies. The state-of-the-art approach to Life Cycle Impact Assessment and integration of design for the environment DfE principles are demonstrated through some case study.

Jan 1, 2006

By Stephen L. Chryssoulis, Stamen Dimov

"Preg-robbing has been known for many years, where increased losses are suffered because dissolved gold is removed from solution by adsorption onto carbonaceous matter. In direct cyanidation circuits it is reasonable to conclude that the preg-robbed gold is either in a gold cyanide [Au(CN) - 2, AuCN] or metallic [Au°] form. However, in circuits with a pre-oxidation step possibilities increase and multiply even further because of water recycle streams containing apparent and not-so-apparent gold ligands. It is in these circuits where speciation of sorbed gold, i.e. the identification of the gold compound, is useful. The importance arises from the fact that proper identification of the sorbed gold species can be used to determine how, when, where and why gold was removed from solution, thereby identifying the exact cause of the problem and providing clues as to how it may be rectified.INTRODUCTIONTo the best of our knowledge, this is the first attempt ever to speciate gold preg-robbed by carbonaceous matter using a surface sensitive microbeam technique. This approach enables the direct determination of gold species sorbed on carbonaceous particulates, opening an entirely new field in the understanding of the chemistry of gold sorption on carbon. The reasoning behind this effort was to add to the current knowledge of the detrimental effect chloride ions have on gold recovery by the pressure oxidation and in particular why in the ensuing CIL step, gold is not being desorbed from the surface of the carbonaceous particles (Table 1)."

Jan 1, 2004

By C. Cornejo, C. Schuffeneger, J. Rosas

"At the end of 2010 the AMSA Esperanza Concentrator started commissioning. Located in the Atacama Desert this project is the first of several large size concentrators developed recently to operate in Northern Chile. In addition to the new operations to be implemented in the short term, many existing installations are planning expansions. The use of large size equipment is one of the common characteristics of the new concentrators, but also new technologies are being considered and innovation is present in most cases. Sea water or desalinated water will be required to process large tonnages of sulphide copper ores as well as gold bearing ores, since process water supply from the Andes will no longer be available. The high cost of sea water or desalinated water supply and the high cost of energy are not a limitation as the current metal market scenario allows obtaining an attractive NPV even from installations designed to process relatively low grade ores. A review of the current concentrators being developed in Chile is presented, including a description of the main design issues related to technology and innovation. An analysis of the Chilean mining industry is also presented, detailing mine and plant capacities as well as expected final products.INTRODUCTION The mining sector in Chile has become a reference when analysing the large concentrator plants projected or currently in operation all over the world. At present and as a consequence of the high price of metal commodities, most South American countries have an active mining sector. Chile is known as a major producer of metals. First records of copper production exported to Spain are dated to the early XVII century. Since then Chile has produced over 13% of the total copper ever produced in the world. After 1990 Chilean mining and the associated cluster of activities has substantially grown to levels never reached before, especially in the production of copper, gold and other non-metallic minerals. This dramatic increase is the result of an economic policy based on delivering comparative advantages and incentives for the admission of foreign capital to offset the weak domestic investment in previous decades. Massive mining of its huge mineral resources has allowed Chile to be a world leader in the production of copper and other base metals and mineral products."

Jan 1, 2012

By Terry A. Lee

The grade of mineral resource estimates underpin all major economic considerations of mining prospects. While there are reporting requirements to satisfy when stating a mineral resource estimate, an examination of NI 43-101 style reports suggests that authors believe that there are a number of ways of addressing these requirements. As a reader of these reports, some processes are helpful and others are not so in getting a real appreciation of how realistic is the mineral resource estimate. Critical to the quality of the mineral resource estimate is how realistic is the economic mineral concentration component. In many cases, this parameter is called grade. The industry experiences increased difficulty in achieving realistic grade estimates as the sample grade variability increases. The level of transparency in a mineral resource estimate is very much a function of the competence of the author. An objective presentation of the critical data, such as grade sampling variability can assist a reader in determining if the geology of the mineral concentration is adequately understood and how realistic is mineral resource grade estimate. This paper has considered 75 NI 43-101 style reports released in the past 2 years. The review demonstrates features that were helpful in determining how realistic the mineral resource grade estimate is. If there is insufficient transparency in a report, there is a high probability that the mineral resource grade estimate will not be realistic.

Apr 1, 2005

By Raphaël Mermillod-Blondin, Claude Bazin

"Sampling is an important step for ore body evaluation and daily plant material balances. The Gy’s equation is regularly used to assess the size of the samples to be collected and to estimate the reproducibility of the collected samples. The equation works well for iron and base metal ores but seems to produce pessimistic estimates of the gold content reproducibility for gold ores. A model is proposed to simulate the division of samples using a standard splitter and discrepancies are observed between the Gy’s equation predictions and simulated samples reproducibility for crushed gold ore. Results of the simulation show that sampling a pile of ore crushed to -2 mm should lead to more reproducible gold content than it is observed in practice and predicted by the Gy’s equation.INTRODUCTION With current gold prices above $1400 per troy ounce operators seek for new economical ore bodies. The metallurgical evaluation of an ore body is one of the numerous steps required to justify the investment for the development of a gold mine. Metallurgical testing requires to sample the ore body and to prepare the ore sample for the grinding and separation tests. The preparation implies crushing the ore usually to less than 2mm and its division into batches of a given weight for subsequent processing. For gold ore testing a batch of crushed ore is ground in a laboratory mill and leached using cyanide. Gold recovered in the solution is used as an indicator of the ore processing amenability. One difficulty associated with ore testing is due to the reproducibility of gold content measurements of the feed sample. According to the Gy’s equation (Gy, 1979; Morisson, 2009) the division of a 20 kg batch of -2 mm ore containing 5 g/t of gold into batches of 1 kg may lead to batches containing 5 ± 5 g/t of gold. For this reason the gold content of a feed sample is usually back calculated from the assays of the solution and solids residues of the leaching process. However, these two assays may contain measurement errors that can propagate through the calculation of the gold recovery. The use of the feed assays as a redundant information could add robustness in the evaluation of ore amenability to processing. This paper discusses the problem of sampling reproducibility for a gold ore. The analysis is carried out with reference to the Gy’s equation for the sampling of particular materials."

Jan 1, 2012

By J. E. Dutrizac

"The end of an era in zinc metallurgy took place on July 31, 1976 when the horizontal retort furnaces of the National Zinc Company in Bartlesville, Oklahoma were permanently shut down (1) . For more than a century, horizontal retorting had been the most common method of producing zinc in the United States; it was a thriving industry in many parts of that country, especially in the natural gas belts of Oklahoma and Texas. With the Bartlesville closure, yet another metallurgical process has become an object of historical interest for North American metallurgists. Although shrouded in controversy, the origins of zinc metallurgy seem to date back at least 2000 years. Pyrometallurgical methods with carbon reductants are capable of producing zinc from oxidic zinc ores, but only above the boiling point of the metal. Although slow cooling results in re-oxidation of the zinc vapour by air or carbon monoxide, quenching yields liquid zinc; some form of rapid cooling, either accidental or intentional, was likely used by ancient metallurgists to liquify the metal. Zinc metal found in Athenian objects of the Roman era was likely of accidental origin. The Romans employed brass extensively for coins and ornaments(2) , and this was intentionally produced by the calamine process whereby oxidic zinc ores were added to molten copper under strongly reducing conditions. Zinc appears to have been known in China and India as early as 1000-1300 A.D., and was probably smelted commercially in those countries from the 14th century. Although the early metallurgical procedures were probably inefficient, they were able to produce zinc metal in significant amounts. The large heaps of zinc residues with clay retorts bear testimony to an early smelting industry of impressive magnitude. It is estimated that the heaps at Zawar, India alone represent the extraction of 100 000 tons of metallic zinc(2) In the 1730s the smelting of oxidic zinc ores was developed in England using a vertical retort method. In 1788 a British patent was granted for making zinc from zinc blends (ZnS) by roasting the ore in a coalfired reverberatory furnace, mixing the calcine with charcoal and smelting the mixture with suitable zinc condensation. The English process was very energy intensive, however, and early in the 19th century the Belgians developed a horizontal retort process for the reductiondistillation of zinc that was more fuel efficient. This technique was gradually developed into what came to be known as the Belgian process, the forerunner of the ""modern"" horizontal retort furnace."

Jan 1, 1999