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By L. L. Gagné

The Churchill Falls Development will eventually be the largest source of hydroelectric power in North America. Churchill Falls was discovered in 1839, but until recent years it was not practical to begin development of this site to tap the 7 million horsepower available. This $1 billion project is located in Labrador, 700 miles northeast of Montreal and 650 miles northwest of St. Johns, Nfld. The construction will divert the Churchill River 5 miles upstream from the 245 foot Churchill Falls. Rapids above and below the Falls, together with the Falls proper, give a natural head of 1,040 feet. In contrast to the basic simplicity of the surface installations, the powerhouse labyrinth is astounding in size and complexity. The largest in the world, it consists of three major chambers - the powerhouse, 972 feet long by 81 feet wide and 154 feet high; the surge chamber, 763 feet long, 40 feet to 64 feet wide and 148 feet high; and the transformer gallery, 856 feet long by 50 feet wide and 39 feet high. Other major features include eleven inclined penstocks, each 1200 feet long and 20 feet in finished diameter; eleven draft tubes averaging 37 feet in finished diameter and 162 feet long; six vertical cable shafts each an average of 865 feet in length; a series of eleven short bus tunnels linking the powerhouse and the transformer gallery; a vertical power-

Jan 1, 1997

By C. E. Seaman, H. Jiang, S. Klima, T. W. Beck, Y. Zheng

Respirable coal dust has been long recognized as a leading cause of multiple lung diseases. Efforts aimed at reducing dust concentration in underground mines have been made, but increases in coal workers’ pneumoconiosis incidence rates over the last 20 years among U.S. miners are concerning. Dust deposition and water spray suppression are two types of dust removal mechanisms in underground mining activities. In this study, laboratory tests were conducted to investigate the respirable dust decay characteristics during deposition and suppression processes in a confined dust chamber. Dust concentration and size distribution were monitored continuously throughout each 60-minute test. A number-basis particle size distribution was used for analysis to capture the changes of smaller size fractions within the investigated dust sample. This study found that around 62.1% of respirable dust particles were deposited at the end of the deposition test. In addition, the final deposition rate for very fine particles can be less than 20%. The results from the suppression test indicate that larger particles were removed quickly; however, sub-micron particles remain suspended through the 60- minute water spray, and particles under 0.5 µm can be considered irremovable dust under single-spray operation conditions. This study also observed the resuspension of a significant amount of sub-micron particles by the water spray. The results of this study provide basic information for improving dust control strategies and can be utilized to improve the water spray performance for reducing airborne dust levels.

Mar 2, 2022

By Christophe Bragard, Rebecca Reeve

The Regional Connector Transit Corridor (RCTC) Project is a 1.9-mile-long metro light-rail extension project that traverses the historical core of downtown Los Angeles, California. This project aims to improve mobility throughout downtown LA with fewer transfers for riders. It is designed to connect two existing rail lines for a more seamless travel. The project consists of twin bore tunnels, three new stations, and is scheduled to be completed in 2022. The design-build contract was awarded to the Regional Connector Constructors (RCC) in 2014, a joint venture of Skanska and Traylor Bros, Inc. with Hatch Mott MacDonald as the designer. One of the challenging aspects of the project was the construction of a crossover cavern in a narrow public right-of-way surrounded by historical structures. RCC used Sequential Excavation Method (SEM) to construct the crossover cavern measuring 287 ft long by 58 ft wide by 36 ft tall. The initial lining of the cavern featured a 12 in. fiber reinforced shotcrete lining. The initial lining was separated from the final lining by a hydrocarbon resistant membrane, as specified by the standard requirements of Metro. The cavern features a cast-in-place final lining with a thickness of 5 ft 9 inches in the invert and 18 inches in the crown and walls. The structure also features a nonload bearing plenum slab and interior walls for ventilation.

Jun 13, 2021

By Prof. Dr. T. R. Boulos

The Egyptian marine phosphorite of Sebaiya West, the Nile Valley, consisting of both non-oxidized hard siliceous and oxidized leached friable ore types, is subjected to a roughing-cleaning silica flotation circuit for production of wet-process phosphoric acid concentrate. Operating at its maximum capacity of 268 t/hr, the following were the main problems encountered during the early stages of running the plant: 1. The tremendous amount of slimes generated by scrubbing the crushed ore causing turbidity in the plant thickener after a short time of operation, regardless of the added flocculant. 2. Rod mill choking leading to inefficient performance of all other equipment and poor flotation results. 3. The drastic increase in imported oleic acid price. Pulp density and slurry flowrate measurements at different points of the plant as well as ore microscopy, size distribution analysis, chemical analysis and x-ray diffraction analysis of representative ore samples coupled with Work Index measurements of feed samples showed that the wide variation in the ore's hardness was responsible for such problems. Application of the locally produced non-edible rice bran oil as a substitute to imported oleic acid in flotation resulted in total saving of U.S.$2 million in 1990. The total unsaturated fatty acid content of the oil is high, ranging from 75.2 to 81.5 mole % of which the C18-unsaturated fatty acid content ranges from 72 to 79 mole %.

Jan 1, 1993

By Harold Bloom

The Mount Pleasant Mines, or Mount Pleasant Joint Venture as it is presently known, is located approximately 59.5 km (37 miles) south of Fredericton, NB, Canada. Earliest indications of mineralization were found in 1954, during a regional reconnaissance geochemical stream sediment survey carried out over large parts of New Brunswick and the Gaspé Peninsula. The regional geology of New Brunswick is shown in Fig. 1. This program, sponsored by Selco Exploration Co. Ltd. of Toronto was conducted by H. Bloom, H.E. Hawkes, J.E. Riddell, and J.S. Webb. At its conclusion in 1955, 30 significant anomalous drainages were identified for follow-up evaluation. A total of 4937 sample sites were occupied. Geochemical reconnaissance using stream sediment sampling was a new technique which had only been field tested the previous year in the Gaspé and the northern coastal area of New Brunswick. Sediments collected from known mineralized drainages were found to leave a train of anomalous heavy metals from 1.6 to 9.7 km (1 to 6 miles) in length. When the exercise was extended to a reconnaissance survey, the previously unknown mineralized prospect at Nash Creek, New Brunswick, was discovered, staked, and later drilled (Hawkes and Bloom, 1956). Although it did not come into production, the discovery left little doubt as to the viability of the method and led to the Selco sponsorship of the program for the following two years.

Jan 1, 1991

By F. Soumis

This paper describes an integrated procedure for the very short term production planning of an open pit and the execution of this plan: the truck dispatching. Integration of plan and dispatch means that the plan is realistic so that its objectives can be realized by the dispatch. This realism is obtained by supplying the plan optimization, which involves mixed integer programming, linear programming and non-linear programming, with experimental O.R. models of waiting and blending. The arrangement of these models in the computer programm has made it possible to obtain very short computing time for the planning in spite of the width of the optimisation. The dispatching of a truck is made by solving a classical assignment problem for each dispatch over a horizon of the expected*next 10-15 trucks to request dispatches. This deep-reaching dispatch procedure uses the continuously arriving information about trucks' positions and shovels situations and models by probability functions the expected waiting time of shovels and trucks. In this manner trucks and shovels are synchronized and last moments' opportunities for productivity gains can be obtained. The dispatch procedure takes .5 second on PDP11. This integrated planning and dispatch procedure gives high productivity while ensuring good blending. Results from the Mount Wright mine of the Quebec-Cartier Mining Co., where the integrated procedure has been installed on the existing computer equipment PDP11, are included.

Jan 1, 1989

By Lynne Chastain

The Eastern Shoshone and Northern Arapaho tribes of the Wind River Indian Reservation, Wyoming are interested in developing their industrial mineral resources. The U.S. Bureau of Indian Affairs (BIA), Division of Energy and Mineral Resources (DEMR) is assisting the tribes in evaluating the potential of their industrial mineral prospects for development. Gypsum occurs on both sides of the Owl Creek Mountains in the basal portion of the Jurassic Gypsum Springs Formation. The gypsum resources that are being evaluated crop out along the northern flank of the Owl Creek Mountains in the Sweetwater basin, a small topographic sub-basin of the Big Horn Basin. From October 1998, to April 1999, DEMR personnel mapped, sampled, and drilled the southcentral butte within the Sweetwater basin. Samples were analyzed for free and combined water, and major mineral oxides to determine gypsum purity. Gypsum purity averaged 93.6 percent for surface samples and 95.1 percent for drill core samples. The basal portion of the Gypsum Springs Formation is comprised of several beds of gypsum up to 9 feet (2.7 m) thick separated by 0.5 to 2.0 foot (0.15 to 0.61 m) thick lenses of siltstone and limestone. Overall gypsum in the formation ranges from 35 to 90 feet (11 to 27 m) in thickness. A resource of approximately 7 million short tons (st) (6.4 million metric tons [mt]) has been identified.

Jan 1, 2001

By Kostas Fytas

Canada still remains today a strong resource nation with a huge geological potential. Canada ranks among the top five leading countries in the production of 15 major minerals. Acid mine drainage (AMD) is a serious environmental problem that preoccupies the Canadian Mining Industry. Considerable amounts of money are spent every year in an effort to prevent or reduce the acid mine drainage production. It is estimated that across Canada there are a few thousand abandoned mine sites as a result of the last fifty years of mining. Most of these sites are acid producing presenting a serious threat to the environment. It has been estimated that the cost of stabilizing and reclaiming these sites across Canada will be over $5 billion over the next twenty years. Current practices for decommissioning acid producing sites are water covers (flooding), dry covers, revegetation and treatment of the acid effluents. This paper presents the technical and legal issues of mine closure and reclamation in Canada. The methods used in the revegetation of acid producing mine sites is also presented This paper also reviews the financial guarantee requirements for mine closure by the provincial legislations in Canada. A case study of stabilizing and reclaiming a sulphide tailings area in the Sudbury region is presented. It illustrates the challenges facing the Canadian Government and the mining companies in restoring and revegetating the closed and abandoned mine sites across Canada.

Jan 1, 2002

By R. D. Grove

The control of Florida phosphate flotation plants is largely based on the visual observations of experienced operators, both in recognizing good and bad froth conditions and in making judgments about the composition of feed, concentrate and tailing streams. Chemical analyses lag the process by at least two hours and, therefore, only assist in recalibrating the operators' vision when major deviations occur. An image analysis system was developed by IMC Fertilizer to improve the accuracy and precision of the composition estimation process. It still relies on the operator taking a representative sample, but provides a measurement in about 15 minutes after that sample is obtained. Background The search for a quick and inexpensive technique for estimating phosphate flotation stream composition continues. There have been attempts at using "wet chemistry," nuclearmagnetic resonance, neutron activation, X-ray diffraction and other techniques reported on in the past several years. None of these have yet found its permanent place in the flotation plants of the Florida phosphate industry. IMC attempted to use wet chemistry to provide 7.5-minute estimates of final concentrate insol and tailings BPL. This was aborted after 36 months of plant operation due to the high operating costs for chemicals and an operator. There was also no significant economic improvement in the plant's operation. Another factor was the necessity to limit these crude analyses to only a few process streams, which were insufficient to achieve improved plant operation.

Jan 1, 1993

By S. K. Kawatra, S. J. Ripke

Iron ore pellets use bentonite clay as binder at dosages from 0.5to 1.0% (10 to 20 pounds per ton) of moist iron ore concentrate. Bentonite is typically shipped hundreds of miles from Wyoming to the Lake Superior iron ore district. It is therefore best to know how effective a bentonite will be before it is shipped and used to bind concentrate into pellets. Current tests of bentonite effectiveness include: plate water absorption, methylene blue uptake, free swell, exchangeable cations, and glycolated layer expansion. However, these tests have many disadvantages: First, they only measure the ability of a bentonite to expand, disperse, or absorb, not how well it will bond. Second, most of the tests require up to 20 hours to perform. Bentonite only has a few minutes to interact within the concentrate before it is indurated (sintered). These long-term tests may not reflect the true behavior of bentonite. Third, the tests are tedious and often results are inconsistent between different iron ore concentrates, labs, and technicians. Fourth, some of the testing equipment is difficult to procure. Fifth, procedures are often difficult to standardize. In this paper, the Binder Effectiveness Strength (BESt) test to evaluate binders for iron ore pellets is presented that: measures the ability of bentonite to bond, requires only about two hours to complete, is simple and reproducible, and utilizes readily available equipment that has been standardized for decades.

Jan 1, 2003

Coal fly ash and flue gas desulfurization (FGD) sludges can be returned to mine pits, fills and revegetation zones in Virginia by regulation if (and only if) a positive beneficial use can be shown. Utilization of alkaline fly ash for control of acid drainage from pyritic coal processing waste piles, and use as a soil amendment for revegetation, are the two dominant beneficial uses proposed over time. Both applications must be controlled by the basic chemical properties of the ash proposed for utilization. Currently, public concerns over long-term As and Se leaching from various applications are increasingly driving regulatory options for mine site utilization. Many fly ash materials are relatively low in inherent alkalinity or neutralizing ability, and certain ashes are actually acidic. Failure to add sufficient total alkalinity will result in strong acidification of the ash utilization zones, stripping heavy metals like Mn, Zn and Cu from the fly ash matrix. Similarly, if alkaline ash is loaded into non-acid forming coal wastes at high rates such that leachate pH is > 9.5, significant leaching of As and Se has been documented in large scale laboratory leaching columns. Utilization of fly ash and FGD as a mine soil amendment for revegetation is based upon combined liming and water holding capacity benefits, however, levels of soluble salts (primarily sulfate and borates) limit one-time application rates to 100 Mg/ha or less.

Jan 1, 2006

By Joaquin Ruiz

Although Mexico is known for its important base-and precious-metal deposits, and lately oil, some industrial minerals play an important role in the Mexican economy. Sulfur, the most important industrial mineral produced, accounts for approximately 7.5 percent of the total value of mineral production. This commodity is followed by fluorspar, which accounts for 6.4 percent. Predominantly, the fluorspar deposits are very high grade (75 percent CaF) and are contained in lower Cretaceous limestone in the states of Coahuila and San Luis Potosi. Base-metal deposits in the area of Parral (notably San Francisco del Oro), however, have become important fluorite producers in their own right. (San Francisco del Oro has 12 percent fluorite gangue.) Salt from the Guerrero Negro solar-evaporation ponds in Baja California account for 6 percent of the total shares; phosphate from Baja California also accounts for 6 percent. Barite from man to deposits in Lower Cretaceous limestone in Coahuila and exhalative deposits in the Paleozoic section of Sonora account for 1.0 percent. In addition, Mexico is an important producer of gypsum, graphite, and celestite. Although graphite and celestite are not large-scale operations and thus do not contribute much to the Mexican economy, the Mexican graphite and celestite deposits are among the most important in the world; Mexico is one of the world's few sources of celestite. The celestite is in the form of large, high-grade mantos in Cretaceous limestones in northern Mexico.

Jan 1, 1987

By G. Deschenes, P. J. H. Prud'homme

A laboratory study was carried out to evaluate the effect of oxygen and lead nitrate on the recovery of gold by cyanidation of a free milling gold ore, which contains 0.4 % copper as chalcopyrite. Efficient gold extraction is achieved only under specific conditions. The recovery of gold was increased from less than 90% to up to 98% by addition of lead nitrate. In the pre-leaching, the kinetics of oxidation of soluble sulphides are not an accurate indication for the length of the treatment. Even though the consumption of cyanide was reduced due to the inhibition of the dissolution of chalcopyrite by increasing additions of lead nitrate, cyanide consumption had to the held above 1.85 kg/t to maintain good recovery of gold. The continued addition of lead nitrate above 300 git had no impact on the recovery of gold. It was also found that the addition of lead nitrate at the start of cyanidation gave the same performance as when added during pre-leaching. The addition of oxygen increased the recovery of gold by 1.5%. The concentration ofNaCN had to be maintained in the range of700 mg/L because of the high concentration of copper in solution. The recovery of gold dropped significantly when the average NaCN concentration fell below 640 mg/L. Application of the findings of the laboratory study at the industrial scale led to improved plant performance.

Jan 1, 1997

By Dale A. Bivens

INTRODUCTION The Waste Isolation Pilot Plant (WIPP) is currently being constructed for the United States Department of Energy in SE New Mexico. The purpose of the project is to store low level transuranic waste in an underground environment which will ensure a safe atmosphere for the life of the stored waste. Ohbayashi was contracted by the DOE to sink two shafts and underground drift development which will be used to conduct a series of long term experiments in order to finalize the suitability of the geology and the environment for the transuranic waste storage. The two shafts sunk at the WIPP site were excavated around a borehole by conventional methods. The excavation around a borehole eliminates some of the established blind bottom sinking techniques, but creates unusual problems which must be pre-planned and scrutinized closely. An analysis of the slashing to the borehole technique will be given. WASTE SHAFT The waste shaft (w/s) is 5.8 meters (19 feet) in diameter and will be used primarily to transport the radioactive waste to the underground storage area. A pre-existing 1.83 meter (6 feet) diam borehole was taken to a depth of 655 meters (2150 feet) to the existing drift; at this level, a 38 meter (125 feet) sump was installed using blind bottom sinking techniques. Geology The primary geology for the w/s excavation is redbeds, anhydrites, dolomite, mudstone and

Jan 1, 1985

By H. T. Mikkelsen

Mineral production implies emissions of particulate matter (dust), noise and vibration that may cause conflicts with neighbors living nearby. In Norway a few conflicts has been brought to court, the latest in 2006. This paper discusses dust emissions and dust depositions (dustfall). The pollution authorities have accepted monitoring of dustfall instead of suspended dust as the first step in conflict cases concerning small and medium sized enterprises. In the case of exceeded limit values, the second step is to require monitoring of suspended dust and next the implementation of control actions to reduce dust emissions. Dustfall monitoring programmes carried out at six mineral production plants in Norway, show that the mineralogical rates of dustfall are rather low a few hundred meters away from the plants or the tailings disposal. They are mostly considerable lower than the limit value of 5 g/m²/30days accepted by the authorities. Seasonal variations between mineralogical and organic dust fractions can be observed in Norway, with higher content of mineral dust during winter time. Other sources to mineralogical dust can be recognized. During winter time wear of road pavement and sand on icy roads can give high emissions of mineralogical dust to the ambient air. Parallel monitoring of suspended dust and rates of dustfall indicate that dustfall can be used to estimate the level of suspended dust. A model for estimating suspended dust based on records of dustfall is presented.

Jan 1, 2007

The Chinese city of Shanghai is one of the fastest growing in the world. To keep up with the growth, two tunnels, three-lanes each, are being built beneath the Yangtze River to connect Shanghai with the Changxing River Island. To complete such a large project, Herrenknecht Tunneling Systems was brought in to construct the largest tunnel boring machine (TBM) in the world. The first Herrenknecht S-317 Mixshield has a diameter of 15.43 m (50.62 ft). It was built to construct one of the two 7.2-km (4.5-mile) tunnels. The tunnels are part of the Changjiang Under River Tunnel Project and will be at depths of up to 65 m (213 ft) beneath the Yangtze River in Shanghai-Pudong. These two tunnels are to be opened to traffic in April 2010, in time for Shanghai to host the World Expo. More than 20 million people live in the Shanghai area. The area itself has been growing at an extremely rapid pace for more than a decade and is in need of more space. The search extended beyond the natural limits of the Yangtze River Delta. As part of its incredible growth, 500 new vehicles are registered every day. The new tunnels will connect the Changxing River Island, with a population of approximately 600,000 people to the road traffic network. A bridge construction will also provide a traffic link between Changxing Island and the large island of Chongming.

Jan 1, 2007

By David T. Swanson

The term "pressure tunnel" in the broad sense includes all hollow spaces, aligned along an axis and surrounded by rock, which are suitable for pressurization. In particular, this category includes: • horizontal or slightly inclined water pressure tunnels; • vertical or inclined pressure shafts; • pressure chambers or shafts of surge chambers; and, • compressed air storage tunnels. The main problems in the design and construction of pressure tunnels result less from their length or size than from the requirement for watertightness and, dependent upon this, reliability in operation and economy in construction. Where the lack of sufficient overburden does not permit the rock to accept the internal pressure in the tunnel, or where this pressure is so high that the watertightness is in doubt although the stability of the tunnel shell is not in question, a pressure tunnel must nevertheless be reinforced. Surge chambers, pressure tunnels and tailraces which are subjected to relatively low internal pressure, usually not much in excess of 1.5 MN/m2, are eminently suitable for construction in post-tensioned concrete. Pressure shafts, which as a consequence of the high water head are subject to a considerable maximum service pressure, are usually lined with a steel tube, a considerable proportion of the internal pressure being transmitted to the rock by backing concrete. TYPES OF LINING FOR PRESSURE TUNNELS In general, the type of lining will depend upon the nature of the rock. As a result, pressure tunnels usually are not uniform in con-

Jan 1, 1981

By Dietrich F. C. Hudewentz, Alfred H. F. Lücker

For centuries tunnellers have made use of the experience of miners. In West German coalmining tunnellers have returned the impulses in recent years by giving the miners valuable stimuli with the result that a technology has evolved which benefits drill and blast heading, opens the door to TBM heading and has developed special measures for difficult strata conditions in deep coal mines. WHAT DO THESE ROCK HEADINGS LOOK LIKE? The main roadways dealt with in this paper have crosssections of 20 to 40 m2, big enough to allow the massive airflows needed to aircondition the mines. Because of the difficult strata conditions they have to be supported: in shotfired headings mainly with multi-element arches, in TBM headings with rings of 6 to 6.5 m diameter. In West German coalmining the majority of rock headings are blasted. The proportion of rock headings driven by TBM was 11 % in 1980 and 16 % in 1981, a rising trend expected to continue. Drill and blast headings Drill and blast headings are normally equipped with two or three-boom electro-hydraulic jumbos, electro-hydraulic crawler-mounted loaders with 1.2 m3 shovel capacity, a movable working platform and both chain and belt conveyors for dirt clearance to the minecar loading point. Fans and air-condition plant complete the equipment. Spacing between arches is usually 0.8 m. Investment for this type of mechanisation works out at around 1.3 m DM.

Jan 1, 1983

By Bond. F. C.

Introduction Although autogenous grinding applications date back to the early years of mineral processing when tumbling-type mills were first used, there has been a renewed interest in this type of grinding over the past few decades. A review of the historical aspects of autogenous grinding is provided which follows the development of the various types of mills and processes. Wet and dry grinding operations using either autogenous or semiautogenous mills, including the Aerofall mill, are described. Em¬phasis has been placed on the test work required to evaluate the feasibility of using autogenous or semiautogenous grinding for a spe¬cific application. The factors which must be considered to establish the appropriate design criteria for these types of grinding circuits are discussed in detail. Successful application of these grinding circuits results from a thorough test program, a careful analysis of the test results, and a practical engineering approach to the design of the process flowsheet and milling equipment. Certain pebble milling applications, where the pebbles consist of the ore or rock itself, can be classified as autogenous pebble mill grinding, or better known as ore-pebble mill grinding. In the generic sense, pebble milling includes those grinding operations using a tum¬bling mill in which the grinding media consists of various types of pebbles, either ore or other pebbles, instead of metal balls. Conse¬quently, this subject is covered separately in Chapter 5, Pebble Mills. Operating data from many of the installations located throughout the world are included in this chapter. Our appreciation is extended to those companies who contributed this important information. History of Autogenous Grinding F. C. BOND Autogenous grinding, the grinding of ore by itself rather than by special metallic or nonmetallic grinding bodies distinct from the ore, has an old and honorable place in the art of mineral processing. It antedates the use of the rod mill and is only a few years younger than the development of the continuously fed rotating tumbling mill in which it is accomplished. Its history71, 72 is inextricably bound up with that of gold mining. Every important early development of autogenous grinding took place on ores of gold, except in one case of silver ore. In common with many other features of modern mineral processing, autogenous grinding would have been greatly retarded if the winning of gold had been so small a part of mining in the past as it is today. Gold unlocked the secrets of rock-on-rock grinding. In years past gold ores were crushed in stamp batteries and then flowed over copper plates covered with mercury which amalgamated the gold. The McArthur Forrest cyanide process for the dissolution of gold in a dilute alkaline cyanide solution appeared in 1890. With finer grinding it recovered more gold than could be won by amalgama¬tion alone. The first response was to stamp in cyanide solution and finer mesh screens guarding the stamp discharge. However, the fine screens greatly restricted the tonnage stamped, and they wore out rapidly. Rotating tumbling mills70, 73 were the obvious choice to grind the coarse product from stamps. Many of these were Gates tube mills; more than 1,000 of these were sold between 1907 and 1913. They were made in 6, 51h, and 5 ft diam, with lengths of 20 and 22 ft. The 5 x 22-ft size was the most popular. The term tube mill did not refer to the mill shape, but included all tumbling mills using grinding pebbles. The flint or chert rocks found along the coasts of Denmark and Normandy are probably the most durable and resistant to abrasive and tumbling wear of any on earth. They were much used in the early tube mills. The early linings were all silex or Danish flint blocks, cemented into place with portland cement. Local hard stones or cast iron blocks were also used later. The cast iron liners carried lifters and were not bolted to the shell, but were held in a tight circle against it by steel wedges hammered home between them. The first ribbed metal liners designed to hold grinding pebbles pounded into them by the mill action were developed at El Oro, Mexico, about 1905. These and the Forbes, Komata, and Tonopah types, as well as the Osborne type developed in South Africa within about five years, were very successful in reducing liner wear. They sometimes lasted two years or more, and equalled or exceeded the life of silex lining at a lower cost. Some of the types were patented. The pioneer name recorded in the history of autogenous grinding is that of Kenneth L. Graham. In 1907 at the Geldenhuis Deep Ltd. mine near Johannesburg, he ran a comparative test on two tube mills. One mill used pieces of the common gold ore, or banket, and the other used the customary imported Danish pebbles as grinding media. He published the first account of autogenous grinding.'' In a test lasting 81 days the ore pebbles showed a definite saving over the Danish pebbles. Graham's historic paper also describes the invention of B. Chew of the Crown Deep Mines of the first trammel to be attached to a grinding mill discharge. The first known account of autogenous grind¬ing printed outside of South Africa was the description of the Graham test in Mining and Scientific Press's The use of grate- vs. overflow¬discharge was also described at this time." The news of this successful test appears to have had immediate effect, for by the end of 1908 the number of tube mills on the Rand had increased from 72 to 120.76 Presumably, most of these mills were now using autogenous grinding. The ore was principally a hard conglomerate of quartz peb¬bles cemented by silica, and was eminently suitable for use as a grind¬ing media. It is unfortunate that in South Africa the new autogenous process continued to be called by its old name of pebble milling, since the name does not distinguish between grinding with ore and grinding with extraneous pebbles. For increased clarity the former is called rock pebble milling. The first historical stage in the development was what is now designated as secondary autogenous grinding, or rock pebble milling. It consists of grinding a feed all passing 'A in. or finer with ore pebbles about 2 to 4 in. in diameter. The next stage to develop was that now called intermediate autogenous grinding, where larger amounts of larger pebbles about 5 in. in size were used to grind ore which had been crushed to about rod mill feed size or somewhat finer. It was developed on the Rand and in other places where coarse stamp screens were used to increase mill tonnage. In many cases the early secondary and intermediate autogenous mills have now been replaced by conventional ball mills and rod mill-ball mill circuits, with the object of further increasing grinding capacity. The third stage to develop is designated as wet primary autogenous grinding, in which run-of-mine ore or a primary crusher product is all fed to the autogenous mill together. It developed many years later indepen¬dently in the United States and in South Africa. The fourth and most recent stage is that of dry primary autogenous grinding, which developed in the United States and Canada. All four stages originated in gold mining. The first use of commercial autogenous grinding outside of the Rand apparently took place five years later in 1912 at the Santa Gertrudis gold mine at Pachuca, 55 miles northeast of Mexico City. This was followed closely by an installation at Goldfields, Nevada, in 1914-1915. The first name associated with autogenous grinding

Jan 1, 1985

By R. B. Hoy, Stanley J. LeFond, Unni H. Rowell, K. Reckling, Derek G. Fullerton

In 1989 natural industrial diamonds counted for 55% of the world's natural diamond production. Australia is currently the leading producer (35%). Zaire is the second largest producer (19%). of what is primarily industrial grade rather than gem grade. Botswana (17%) is third, with the former USSR (15%) fourth, and the Republic of South Africa (8%) fifth. Diamonds are also mined in Angola, Namibia, the Ivory Coast, the Central African Republic, Ghana, Tanzania, Guinea, and other African countries. In the Western Hemisphere, Brazil is the principal producer, with some production from Venezuela and Guyana [(Fig. 1)]. A very small output of diamonds is mined today in India, which was the first source of commercial production. In the United States, efforts at commercial diamond mining have been confined to a small area near Murfreesboro, AR. The first diamond was found in a pipe there in 1906. Small scale trial mining has not, however, proved economical. Since diamonds were first discovered more than 2,000 years ago, only about 380 t have been mined. In order to obtain 1 g (5 metric carats) of diamonds, it is necessary to remove and process approximately 25 t of rock. Recovering this small percentage involves a combination of highly developed techniques in mining and extremely sophisticated processes in diamond recovery. END USES Diamonds are used for two unrelated end uses: gem diamonds are jewels of great beauty, while industrial diamonds are essential materials of modem industry. Although imitation stones are substituted for the gem diamond, none of these matches its properties sufficiently well to offer real competition. Synthetic industrial diamonds are now of a quality and size that permit them to be substituted for natural diamonds in numerous industrial applications. For example, synthetic diamonds are available today in sizes up to 100 stones per carat (1.2 to 1.4 mm). In addition, polycrystalline synthetic diamond inserts, such as De Beers Syndite", General Electric's Compaxa and Stratapax", and Megadiamond's Megapax" have replaced natural diamonds in turning tools, mining and oil drilling bits, and dressing tool applications. Industrial Diamonds The diamond is by far the most important industrial abrasive. As recently as 50 years ago, consumption of industrial diamonds was less than that of gem diamonds, but since that time, industrial use has grown to a position of great dominance. During the six-year period 1929 to 1934, the material produced for industrial use amounted to about 74% by weight of the world's total output of diamonds. In 1989 the percentage of natural industrial diamonds mined in the world was 55%. When synthetic industrial diamonds are added to the natural industrial diamond figures, this percentage becomes 87% of total world diamond production including gems, near gems, industrial, and synthetic stones. The many uses responsible for these significant increases are dependent on the properties of the diamond, including hardness, cleavage, and parting, optical characteristics, presence of sharp points and edges, and capacity for taking and maintaining a high polish. The utilitarian role of the diamond was confined primarily to lapidary products until the industrial revolution, which created the first demand for diamond as an industrial tool. In 1777, a British inventor and instrument maker, Jesse Ramsden, used a diamond to cut a precision screw for an engine that he had invented. The first authentic description of industrial diamonds being set in a saw was recorded in 1854 by a Frenchman, Durnain. Eight years later a Swiss watchmaker, Jean Leschot, developed the first diamond drill bit for use in a hand operated machine, which was employed to drill blastholes in rock. In 1864, diamond bits were put to their severest test up to that time in the construction of the Mont Cenis Tunnel in the Alps. A few years later a steam-powered diamond drill with a speed of 30 rpm was able to penetrate rock at the modest rate of 0.3 m/hr. As the industrial revolution gained momentum on both sides of the Atlantic, metal replaced wood and machines replaced people. Thus the foundation was laid for precision engineering and the recognition of diamonds as an indispensable tool of industry. The next major demand for industrial diamonds came after World War I with the development of cemented carbide cutting tools. Diamond was found to be the most effective medium for finishing and grinding the new ultrahard metal. This discovery rapidly increased the demand for industrial diamonds. The availability of inexpensive diamond material inspired tremendous research into applications. By 1935, the first successful phenol-resin grinding wheel containing diamond had been marketed. Soon afterward, the metal-bonded and vitrified diamond wheels were produced, and, as the matrices and bonds that held the diamond grit in place began to improve, the popularity of diamond grinding wheels grew. The outbreak of World War II, and the accompanying increase in use of hard-metal tools in the munitions industry, increased the demand for industrial diamonds. Since about 1950, the development of ultrahard ceramics, semi- conductor materials, plastics, and exotic metal alloys has further consolidated the diamond's position as an indispensable tool of industry. Only diamond is hard enough to cut these superhard materials with the precision, speed, and economy that industry demands today. Special machines equipped with industrial diamonds are used to remove bumps from concrete runways and highways and to modify highway surfaces in order to prevent skid accidents. Many skids are caused by hydroplaning, a phenomenon that occurs when the roadway is wet. Tires mount a film of water and virtually lose contact with the road surface. Diamond machines cut neat, narrow

Jan 1, 1994