Search Documents

By Raymond F. Dalton

Despite the ready availability of numerous zinc sources, the process of solvent extraction- electrowinning (SX-EW) has as yet found little favour in the zinc industry. It is suggested that this is largely due to the previous lack of availability of suitable selective reagents having the particular features required to enable them to fit in to a solvent extraction-electrowinning based process for zinc, particularly with regard to strength and selectivity for zinc over iron. This paper describes work on the development of new selective extractants for the recovery of zinc from both sulfate and chloride aqueous solutions and suggests how they might be integrated into new zinc processes.

Jan 1, 1994

By William H. Snyer, Hank Cox

A high explosive device using Linear Shaped Charge (LSC) (to rapidly cut vent and drain openings in a rail tank car) is described. In the event of damage to a tank car loaded with a pressurized flammable fluid, it may sometimes be necessary to perform controlled on-site vent, drain and burn operations. Existing techniques required refinement to achieve the desired safety and procedural reliability for use in emergency situations.

Jan 1, 1994

By E. H. Cho

Pittsburgh #8 coal cleaned by the conventional froth flotation was oxidized in a 2-liter Parr Stirred Top Bench Reactor. The oxidation time was varied up to 5 hours; the temperature, from 150 to 225°C, the oxygen pressure, from 15 to 500 psi; and coal dosage, from 15 to 60 grams in 600 ml of distilled water. The oxidation of coal was evaluated by measuring total acidic group formed on the coal surface as well as by measuring the adsorption of calcium ion from a solution under standard conditions. It was found that the oxidation increased with increasing oxygen pressure without much leveling-off effect. However, the oxidation of coal increased sharply from 150°C to 175°C and then tended to level off above 175°C. The adsorption of calcium was reached more than 3% on the coal oxidized under favorable conditions. The adsorption of calcium on coal increased sharply with increasing equilibrium pH. The BTU loss was sensitive to oxidation temperature. This study concludes that the optimum oxidation of coal should be conducted at high oxygen pressures around (e.g. 500 psi) 170°C for 3 hours. This study also concludes that the oxidation in an autoclave is far superior to that in a fluidized bed in terms of calcium adsorption, BTU loss and reaction time.

Jan 1, 1994

By Robert B. Fulton, Gill Montgomery

Fluorspar is the commercial name for fluorite, a mineral that is calcium fluoride, CaF2. The name, derived from the Latin word fluere (to flow), refers to its low melting point and its early use in metallurgy as a flux. It is the principal industrial source of the element fluorine. Two other minerals, cryolite and fluorapatite, have significant fluorine content. Cryolite, sodium aluminum fluoride, Na3AlF,, is a rare mineral that has been found in commercial quantities only in Greenland. The natural material has been supplanted by synthetic cryolite for its principal industrial use in the manufacture of aluminum. Fluorapatite, Ca5F(PO3)2, is a source of phosphate for fertilizer manufacture, containing a small percentage of fluorine. Commercially mined deposits of apatite have varying amounts of fluorine, chlorine, hydroxyl, and carbonate. HISTORY Fluorspar was used by the early Greeks and Romans for ornamental purposes as vases, drinking cups, and table tops. Various peoples, including the Chinese and the American Indians, carved ornaments and figurines from large crystals. Its usefulness as a flux was known to Agricola in 16th century Europe. Fluorspar mining began in England about 1775 and at various places in the United States between 1820 and 1840. Production grew substantially following the development of basic open hearth steelmaking, wherein it is used as a flux. Use was stimulated by growth of the steel, aluminum, chemical, and ceramic industries, particularly during World Wars I and 11. Fluorocarbons entered the picture in 1931. The use of anhydrous hydrogen fluoride (HF) as a catalyst in the manufacture of alkylate for high octane fuel began in 1942. Differential flotation for separating fluorspar from galena, sphalerite, and common gangue minerals in the 1930s and the application of heavy media concentrating methods to the treatment of low grade ores in the 1940s were outstanding technological advances that facilitated increased production. Pelletizing and briquetting of flotation concentrates for use in steel furnaces and the development of flotation schemes for beneficiating ores containing abundant dolomite and barite have been major improvements in the industry. USES OF FLUORITE Fluorspar is used to make hydrogen fluoride (HF), also called hydrofluoric acid, an intermediate for fluorocarbons, aluminum fluoride, and synthetic cryolite. It is used as a flux in the steel and ceramic industries, in iron foundry and ferroalloy practice, and has many minor specialized uses. Hydrogen fluoride is produced by reacting acid grade (97% CaF,) fluorspar with sulfuric acid in a heated kiln or retort to produce HF gas and calcium sulfate. After purification by scrubbing, condensing, and distillation; the HF is marketed as anhydrous HF, a colorless fuming liquid, or it may be absorbed in water to form the aqueous acid, usually 70% HF. Synthetic cryolite, organic and inorganic fluoride chemicals, and elemental fluorine are made from hydrofluoric acid. The acid itself is important in catalysis in the manufacture of alkylate, an ingredient in high-octane fuel for aircraft and automobiles; in steel pickling, enamel stripping, and glass etching and polishing; and in various electroplating operations. The manufacture of one ton of virgin aluminum requires about 12 to 29 kg of fluorine content in synthetic cryolite and aluminum fluoride. This quantity, through improved technology and recovery practices, is being lowered significantly in countries with the most advanced technology (i.e., Australia and Sweden), while others (i.e., Surinam and South Africa), remain at the high end. Elemental fluorine is prepared from anhydrous hydrofluoric acid by electrolysis. Gaseous at room temperature and pressure, fluorine is compressed to a liquid for shipment in cylinders or in tank trucks. Elemental fluorine is used to make uranium hexafluoride, sulfur hexafluoride, and halogen fluorides. Gaseous uranium hexafluoride is used in separating U235 from U233 by the diffusion process. Sulfur hexafluoride is a stable high dielectric gas used in coaxial cables, transformers, and radar wave guides. Halogen fluorides have important applications, mostly as substitutes for elemental fluorine, which is more difficult to handle. Emulsified perfluorochemicals, organic compounds in which all hydrogen atoms have been replaced by fluorine, are undergoing investigation as promising blood substitutes. They transport oxygen and, in conjunction with a simulated blood serum, perform many functions of whole blood. With further development, these organic compounds may ultimately, in emergencies, be useful in saving lives of animals and humans during periods of acute shortages of natural blood. Inorganic fluorides are used as insecticides, preservatives, antiseptics, ceramic additives, and fluxes and in electroplating solutions, antioxidants, and many other products. Boron trifluoride is an important catalyst. Organic fluorides are volume leaders in the fluorine chemical industry. Fluorinated chlorocarbons and fluorocarbons are prepared by the interaction of anhydrous HF with chloroform, perchlorethylene and carbon tetrachloride, and are characterized by low toxicity and notable chemical stability. They perform outstandingly as refrigerants, aerosol propellants, solvents, and cleaning agents and as intermediates for polymers such as fluorocarbon resins and elastomers. Fluorocarbon resins are inert compounds that have unusually low coefficients of friction and have found a number of applications as lubricants for parts that cannot be oiled, e.g., bearings for window raising equipment located inside of automobile doors, in small electronic equipment, for the manufacture of chem-

Jan 1, 1994

By Luis W. Pommier

The developed processes, the subject of this paper, extract the hydrocarbons, halogenated organic compounds and metal contaminants from hazardous soils, rendering them non-hazardous and ready to be placed back on the ground. The processes first segregate a non-contaminated fraction from the contaminated soil. This initial task is performed using available minerals processing technology: sizing, gravity separation, magnetic separation, froth flotation, etc. The remaining contaminated fraction, is submitted to two leaching operations for the removal of organic and metal contaminants, whenever both are present or to a single leaching operation if only one type of contaminant is present. The decontaminated soil fraction is mixed with the non-contaminated fraction and is placed back on the ground. The leaching liquors, used at neutral pH, are non- hazardous. After decontamination the liquids are processed to extract the contaminants, now valuable materials, for commercialization. Organic contaminants are removed by distillation of the solvents. The metal contaminants are precipitated in their oxide form. In both cases the regenerated solvents are recycled. The decontamination processes are economically competitive with transportation and disposal of the soils to permitted facilities for hazardous materials, and most importantly the developed processes remove the liabilities from the Responsible Parties. The law establishes that these liabilities do not disappear with either fixation nor with transportation and disposal since the environmental liabilities are of the ? cradle to grave? type.

Jan 1, 1994

By J. Z. Keating

There are close to two million tons of Industrial Minerals processed and sold in North America wherein the processor/marketer has no affiliation with the source mine. The largest quantity, about 800,000 tons, is barium sulfate, which is sourced in lump ore form mainly from China and India. The Alumina Trihydrate Industry sources several hundred thousand tons from various alumina refineries. Substantial quantities of bauxite, zircon, magnesite, and fluorspar arrive in North American ports each month. There are also rapidly growing quantities of offshore talcs and calcium carbonate ores being processed in U.S. plants. These feedstocks are usually quite pure, have unique properties, and enjoy bulk rail or waterborne freight economies that allow successful competition with locally sourced raw materials. With increasing restrictions on mining activities, and the increasing need for sophisticated functional minerals, the importation of minerals will continue to grow.

Jan 1, 1994

By J. E. Brownhill

This paper does not deal with the typical start-up issues of equipment, production capacity or work force. This is a description of the challenges faced and the changes made by the project team to bring to fruition the reconstruction of Port Inland. Many honored traditions and norms had to be overturned to find the winning combination that provided the productivity, flexibility and cost necessary to survive in today's competitive minerals environment. This paper covers the innovation in terms of machinery, operations, and management philosophy that permitted the renovation and reopening of Port Inland as a commercial limestone producer in the spring of 1992. Port Inland, constructed by Inland Steel in 1930, operated as a captive source of metallurgical grade limestone for the steel industry until its closure in 1989. Located in the Upper Peninsula of Michigan on the north edge of Lake Michigan, the operations consist of a deep water port facility with crushing, screening and stockpile storage for 500,000 tons of finished product at the port. Ninety-nine percent of the stone is shipped via lake boat to ports within the Great Lakes. The operation is unique in that both metallurgical Dolomite and Limestone are produced on site. In 1930, Port Inland was at the fore front of technological advancement. It was the first major mining operation to use roller bearings and other equipment innovations. Over the 60 years of operation, Inland Steel placed emphasis on steel making technology and iron ore mining at the detriment of the limestone operation. By the early 80's, Port Inland was no longer a leading competitor. Inland Steel, unable or unwilling to spend the capital to modernize, closed the facility in the fall of 1989.

Jan 1, 1994

By M. Karmis

The determination of the surface area which may be impacted by underground mining is an important consideration in subsidence engineering. A number of parameters have been utilized to identify this influence area, most notably the angles of draw and break. This paper discusses the implications of selecting an appropriate "damage angle" for defining a potential damage area due to mining, within which surface structures may be impacted Furthermore, the influence of both mining and geological factors, such as mining width and depth and overburden lithology, on this angle is examined, using the Surface Deformation Prediction System (S.D.P.S) software. Finally, recommendations are given for applying these concepts in subsidence control.

Jan 1, 1994

By Robert B. Fulton

Staurolite, an iron aluminum silicate mineral, is used industrially as a high value-in-use sandblasting agent, as a premium-grade foundry sand, and as the source of aluminum in portland cement manufacture in areas where the aluminum constituent is not economically available from shale or argillaceous limestone. Staurolite is produced by E. I. duPont de Nemours and Company as a coproduct of titanium mineral production in Florida, where it was first recovered on a commercial scale in 1952 from the Pleistocene sand deposit known as Trail Ridge. At this deposit it comprises about one-fifth of the heavy mineral suite, the principal other heavy minerals being ilmenite, leucoxene, rutile, zircon, kyanite, sillimanite, and tourmaline. Staurolite and other nonconductive silicate heavy minerals are separated from the conductive titanium minerals on high-tension electrostatic separators. The silicates are then separated from one another magnetically, the staurolite being relatively magnetic. In the total process, 200 t of raw sand yield 7 t of heavy mineral concentrate from which about 1 t of staurolite is recovered. The staurolite concentrates have the characteristics given in Table 1. Staurolite concentrates are sold in three grades having the size distribution of subrounded grains shown in Table 2. All three grades are used in sandblasting for cleaning metal, for paint removal, and for cleaning masonry buildings. Staurolite compares favorably with lower priced abrasives, such as boiler slags and silica sand, in applications where the abrasive is used only once and is not recovered and recycled. Because it is hard, fine, clean, and dense it can reduce blasting time, and less material is required to clean a specific area. Compared to higher priced abrasives such as aluminum oxide and garnet, which are recycled, staurolite costs significantly less per kilogram and cleans at equal or faster rates. Its breakdown factor, which is a measure of recycling performance, is intermediate between those for aluminum oxide and garnet. [ ] [Tables 3 and 4] show the blast cleaning performance of the three staurolite grades compared to other abrasives. [Table 5] compares the longevity of premium priced abrasives during recycling. [Table 6] shows a cost comparison between silica sand and staurolite. Fringe benefits claimed for staurolite's use as an abrasive are: 1. Good flow properties and freedom from the lumps or slivers found in silica sand or boiler slag abrasives. 2. Low dusting affords good visibility, permits faster working, and reduces cleanup problems. 3. Heated storage is not required during freezing conditions, because the mineral is nonhygroscopic.

Jan 1, 1994

By M. R. Yalamanchili

Recently, noequilbrium electrokinetic measurements using laser-Doppler electrophoresis were reported by Miller et al. (1992) for alkali halides and the sign of their surface charge thus determined. These results are generally as expected from simplified lattice ion hydration theory with KCI, under normal circumstances, being the most significant exception. In this regard, lattice defects (F centers and oxygen imperfections) have been found to influence the surface charge of KCI and its electrophoretic mobility. In particular, the presence of oxygen defect states in the crystal lattice has been found to be responsible for KCI's unexpected behavior. The concentration of oxygen defect states in KCI, as characterized by UV/Vis absorption, was varied in order to study their influence on the electrokinetic behavior and subsequently on the flotation response of KCl. At low oxygen contents « 60 ppm) KCI is positively charged as expected from lattice ion hydration theory. However, typically, KCI contains substantial oxygen (>300 ppm) sufficient to impart a negative surface charge which accounts for the selective flotation of KCI from NaCl by hetero-coagulation with oppositely charged alkyl amine hydrochloride collector colloids.

Jan 1, 1994

By T. J. White

Xtaltite is the trade name for a generic technology which exploits the well known insolubility of some minerals, which naturally incorporate toxic waste elements, to consolidate and immobilise a range of inorganic waste products. It is a specific case of synthetic mineral immobilisation technology (SMITE) which is already used to immobilise high level nuclear wastes (HLW. Although HLW is highly toxic, it exists in relatively small volumes, occurs in central facilities and may be stabilised at low waste loading (< 10 wt%). In contrast, heavy metal wastes are of considerable volume, therefore Xtalitite waste forms must routinely accommodate high waste loadings (usually in excess of 30 wt% for a particular toxic oxide or combination of oxides) and be suitable for fabrication in remote locations using relatively simple technology. This paper details the methodology underlying Xtaltite, with particular emphasis given to the interplay between solid state chemistry, durability and economic considerations. Specific reference is made to the treatment of arsenious and mercurial wastes.

Jan 1, 1994

By P. Ret, E. Üstiindag, R. Dieckmann, R. Subramanian, S. L. Sass

"Partial reduction reactions in the Ni-AI-O system, starting with the spinel compound NiAI20 4, are used to form metal-ceramic microstructures. By suitable choice of processing parameters, such as reduction temperature, oxygen partial pressure and time, two different morphologies of nearly pure Ni particles, equiaxed and rod-like, form within a ceramic matrix, which is either a-A12O3 or a metastable ""defect spinel"". Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis. The fracture toughness of the Ni-AI2O 3 mixture was significantly improved with respect to that of the original spinel phase. The important issues that must be addressed to form useful metal-ceramic microstructures by partial reduction reactions rue discussed. It is shown that cracking at the original spinel grain boundaries, likely due to the large volume changes associated with the reduction reaction, can be avoided by the addition of small amounts of ZrO2• Initial results illustrating effect of ZrO2 on the microsuuctures are presented.IntroductionEngineering materials used in load bearing circumstances, particularly under extreme conditions (e.g. high temperatures or stresses), generally are formulated with complex microsuuctures. Such composite-like materials can possess properties unobtainable by either of the individual constituents. With metal-ceramic composites, for example, a material can be obtained with an optimum combination of the low density and high strength of the ceramic, and the toughness of the metal. For high temperature service, where demanding conditions are often present, for example, inside jet turbine engines, a successful new material must have low density, high Young's modulus as well as good oxidation resistance, strength, fracture toughness, creep and fatigue resistance. The candidates include intermetallic compounds, and metal-ceramic, intermetallic-ceramic and ceramic-ceramic composites."

Jan 1, 1994

By Gopalakrishna B. Prabhu, David L. Bourell

"Three mol% Yttria-Stabilized Tetragonal Zirconia (YSTZ) was prepared by a sol-gel synthesis technique using zirconium tetrachloride and hydrated yttrium chloride precursors. After drying and annealing at 823K, the particle size was in the range 10 to 20 nm. The zirconia powder was sintered using a uniaxial hot press at an applied stress of 20 to 40 MPa. One hour, isothermal sintering was performed in air after initial heating at 50K/min. Theoretical density was obtained at densification temperatures above 1498K. After sintering, grain coarsening characteristics were studied using constant heating rate anneals followed by quenching, based on a model for grain coarsening in a linear heating rate cycle. The microstructural change was studied using SEM and TEM and the phases were determined using x-ray diffraction.IntroductionThe ability to sinter nanocrystalline materials to full density several hundred degrees below the normal sintering temperatures is one reason for their current interest. [1-5] Yttria Stabilized Tetragonal Zirconia (YSTZ) of grain size of about 300 nm has exhibited superplasticity, with elongations as large as 800%.[6-7] Fine grain size is critical for superplasticity. Retention of the fine grain size during sintering of nanocrystalline powder is important if a material is to exhibit superplasticity or to exhibit physical or mechanical properties associated with the ultra fine structure. This paper investigates the sintering behavior and the grain coarsening characteristics ofnanocrystalline YSTZ.Techniques for synthesizing nanocrystalline materials have been studied in great detail earlier. [8-12] The techniques used to synthesize nanocrystalline zirconia include alkoxide synthesis [9], the chloride method [11], the peroxide method [13] and the acetone-toluene method. [13] In this paper the method used in the synthesis of zirconia is the chloride technique. With this precipitation technique, either zirconium chloride or oxychloride and a corresponding yttrium salt or even pure yttria are used."

Jan 1, 1994

By T. P. Meloy

A methodology is presented for the spreadsheet solution of processing networks performing separations with the methodology developed here a spreadsheet grid is used to represent networks with and without recycle loops. In this manner, network solutions are numerically approximated by spreadsheet grid solutions. The methodology was used to explore the ramification networks developed by the Chinese for tungsten and molybdenum processing. Non-linear stage transfer functions for two-component sharp separations can be used.

Jan 1, 1994

By William E. Frazier

The presence of minute amounts of sulfur (10ppm) in nickel-base superalloys has been associated with reduced oxidation resistance and the premature spallation of protective coatings. Removal of sulfur by annealing these alloys in a hydrogen atmosphere has been successfully attempted by several researchers. This paper examines the fundamental thermodynamics and kinetics governing hydrogen desulfurization of elemental nickel. Limiting conditions for successful desulfurization are delineated. Assuming that the diffusion of sulfur is the rate limiting process of desulfurization, the effectiveness as well as time associated with hydrogen desulfurization is explored.

Jan 1, 1994

By Geoffrey D. Collins

This paper deals with the construction of the Effluent Outfall Diffusers which form part of the outfall for the Deer Island sewage project. The work was executed 15 km out to sea in Massachusetts Bay and required the drilling, installation, grouting and accurate determination of the actual position of 55 riser shafts in 33.5 m deep water. Although not strictly a "foundation", the contractor&apos;s approach to the installation of the diffusers was a logical development from many marine foundation projects executed by the Contracting companies over the last decades. The only previous application of this design of outfall had been in Australia where offshore oil drilling techniques had been adapted for use in riser installation.

Jan 1, 1994

By R. P. Viljoen, A. D. Scheglov, A. L. Sokolov

"Abstract -The distribution of mineralized provinces is analyzed on the basis of their genetic link with specific blocks of the earth&apos;s crust including ancient platforms, mobile belts and zones of tectonic­ magmatic activation. Mobile and fold belts surround the Siberian platform in Russia and the Kaapvaal craton in South Africa, with decreasing age zoning away from ancient platform margins. The main differences in the geological development of the two cratonic areas are: (1) the long period before the final stabilization of the Siberian platform (3600 Ma to 1600 Ma) and the comparatively short period of time for the stabilization of the Kaapvaal craton (3600 Ma to 3050 Ma) and (2) the intensive multiple activation of the marginal zones of the Siberian platform and the tectonically­ controlled, magmatic sedimentary, intracratonic activity, typical of the Kaapvaal craton. Mineralization of the Siberian platform is largely characterized by marginal reactivation zones of differing ages although mineralized intracratonic Cu-bearing basins of Proterozoic age are also known. Mineralization of the Kaapvaal craton is mainly related to the formation of the intracratonic basins i.e., Witwatersrand (Au, U) and Transvaal (Au). The latter is characterized by multi-age volcanic-intrusive activity including the emplacement of Bushveld Complex (Cu, Ni, Pt, Cr, Au, V). The Siberian platform is characterized by the prolonged development of inherited mineralization from Archean until the late Mesozoic. The main period of mineralization in the Kaapvaal craton is restricted to the middle Proterozoic.The Baykal-Patomskaya and Namaqua-Natal mobile zones occupy similar positions adjacent to the Siberian and Kaapvaal cratons, respectively, and demonstrate similar modes of metallogenic development: i.e., the early formation of exhalative Pb-Zn-Cu deposits during the early stage and magmatic Cu deposits during the late stage. The more remote mobile belt near the Siberian plat­ form, the Trans-Baykal, is characterized by intensive multi-age mineralization (Wo, Mo, Sn, fluorite), related to a period of tectonic-magmatic activation. The Saldania Belt occupies a similar position near the Kaapvaal craton but is known for its poor Au, and Cu rnineralization. lt does, however, have some similarities with Trans-Baykal Belt in regard to Mo-W bearing granitoids.The phenomenon of interference of geosynclinal, orogenic, platform, and tectono-magmatic activation regimes is known for the Russian section of the Pacific Ocean Volcanic Belt."

Jan 1, 1994

By Alain Dorval

"''Purification of marine sands from Les Iles-de-la-Madeleine''This paper presents the results of the work that has been done at CRM pilot plant for «Les Silices du Golfe Inc.». Essentially the purpose of this piloting was to demonstrate, on a semi-industrial scale, the process of purification of marine sands from Les Iles-de-la-Madeleine; that had been developed by CRM Process Development Service. This purification is necessary to produce silica suitable for the glass sand and the foundry sand markets.Introduction«Les Silices du Golfe Inc.» is a company who intends to dredge marine sands around the «Les Iles-de-la-Madeleine» coasts. The material will be transported to Gaspesia where electricity, water supply, and a convenient site is available to treat it. A high purity silica intended for glass sand and foundry sand markets will be produced. The objectives of this purification process are to remove organics, calcium, feldspars and iron.Material ReceivedCRM received 50 tons of sand with Si02 varying between 80,6 and 99,3 % (see Figure.1). The highest variations in impurities were the calcium and lost on ignition. We notice direct relation between% SiO2, % CaO and % L.O.I. as you can see on the following Figures 2, 3 and 4."

Jan 1, 1994

By T. C. Eisele

The separating efficiency of a flotation column is largely limited by the degree of backmixing of tailings into the froth zone, and its recovery is limited by the degree of short-circuiting of feed to the tailings. Current columns are typically made very tall, on the order of 30-40 feet, in order to limit the effects of backmixing and short-circuiting. These effects can also be reduced in a much shorter column, provided that the flow in the column approaches plug-flow. In this work, horizontal baffles were shown to improve the performance of a 6-foot tall laboratory-scale flotation column treating a difficult-to-clean, heavily oxidized coal. Tests with variation in the position of the baffles showed that for the greatest benefit, baffles are needed both above and below the feed inlet. Tracer tests with a fluorescent dye water tracer showed that the addition of the baffles reduced the amount of feed water entrained into the froth at any given coal recovery.

Jan 1, 1994

By T. R. Raponi

"The Williams Mine, Canada's largest gold mine, processes over 6,000 t/d of ore utilizing SAG/ball milling, leaching and CIP, carbon stripping, electrowinning and refining to produce gold dare bullion.Grinding accounts for over 50% of milling costs with grinding media, power and mill liners making up over 75% of grinding costs. Since 1991, several changes in these areas have been made which have significantly reduced costs, while fineness of grind and mill recovery have both been increased.This paper discusses the changes made in the grinding circuit over the past few years and assesses their impact on operating costs and mill operations.IntroductionThe Williams Mine is located in the Hemlo area of northwestern Ontario, about 40 km east of Marathon. It is operated by the Williams Operation Corporation, which is equally owned by Teck Corp. and Homestake Canada Inc. Canada's largest gold mine, the Williams Mine commenced operation in October 1985 at a rate of 3, 000 t/d. Mill throughputs have typically exceeded design, averaging 3, 397 t/d in 1986, and 3,380 t/d in 1987. In August 1988, production was increased to 6,000 t/d. Throughput averaged 4,212 t/d in 1988. Production increased over the next few years averaging 5,477 t/d in 1989, 6,248 t/d in 1990, 5,987 t/d in 1991, and 6,283 t/d in 1992. With a recovery of over 95.5%, production for the first three quarters in 1993 is averaging 6,408 t/d.GeologyThe main ore body is a steeply dipping conformable zone of microcline-quartz-muscovite rock. It occupies the contact zone between hanging wall metasedimentary rocks and foot wall felsic quartz feldspar porpyritic rocks of possible volcanic or subvolcanic intrusive origin. The ore body is enveloped by muscovite schists which are thickest on the footwall side. The schist is enriched with tourmaline, pyrite, and green mica containing vanadium and barium. The ore body contains pyrite and barite which occurs mostly in laminae and bands to veinlets and breccia fillings. The gold occurs as free (native) grains, 20 to 30 µm in size at grain junctions of the microcline and quartz. Visible gold is rare in the main zone. There are commonly two or more discernable layers of economic value which are separated by weakly gold mineralized material which usually consists of muscovite schist, barite rich zones or sulphide poor-microcline-quartz rock and in the upper and western fringes by biotite rich schist with feldspathic fragmental characteristics. Molybdenite is a common constituent as very fine disseminated grains in the microcline-quartz rock and is most prominent with gold enrichment. Stibnite and realgar are two of the more common accessory sulphides."

Jan 1, 1994