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By H. L. O. Huyck

A microcomputer equipped with spreadsheet, data management, and FOR- TRAN programming software is used to update and quantify a model for ranking seventeen economically important metal commodities in terms of market potential (Huyck, 1982). Weighted factors are used for the ranking: (1) demand growth trends, (2) end-use substitution vulnerability, (3) recycling trends, (4) price trends, and (5) cumulative demand versus world reserves factor. Price trends are defined using (1) price-vs.-year slopes (with prices in 1967 constant dollars) and (2) standard deviations of slopes (to indicate price volatility). Substitution vulnerability is defined as the percent of end-use which is replace- able by other commodities, and a factor indicating the likelihood of such substitution. Factors are normalized and linearly combined to produce a ranking of the seventeen metals. Microcomputer software is essential for organizing data and calculating statistical parameters and linear combinations of factors.

Jan 1, 1986

By Richardo Montoya

Radomiro Tomic, the new CODELCO division, is a copper deposit located at 3000 m a.s.l. and 40 Km from Calama in northern Chile. It has total oxide reserves of 802,000,000 tonnes with an average grade of 0.59% total Cu (using a cut-off grade of 0.4% total Cu). The copper oxide ore is mainly atacamite and chrysocolla. Startup is expected to commence in December 1997 of 150,000 t/y of Cu cathodes. Future expansion to 250,000 t/a of Cu cathodes is currently being planned. The process consists of an open-pit mine, a two-stage crushing system, agglomeration with sulphuric acid and emplacement on a heap leach pad for a 45-day leaching cycle. Solvent extraction and electrowinning will produce LME "A grade cathode. A number of significant technology innovations have been incorporated into the project.

Jan 1, 1998

By H. Yoon

Several processes involving injection of sorbent and humidification water downstream of the air preheater in a coal-fired boiler unit, are being developed as low capital cost retrofit S02 control options. Extensive laboratory work, pilot plant programs and larger scale programs have developed performance data and design information. Many of these programs were supported by the U. S. Department of Energy (DOE) as "proofs-of-concept" of three different processes proposed by Dravo, Bechtel and General Electric. Based on these project results, DOE formulated a comprehensive in-duct sorbent injection development program to fully commercialize the technology by 1992. Also, EPRI will conduct a 4 MWe pilot program to develop its HYPAS process. The Consol Coolside process is scheduled for utility demonstration in 1989 on a 104 MWe unit at the Ohio Edison Edgewater Station under partial sponsorship of the DOE Clean Coal Technology Program.

Jan 1, 1989

By E. Valdiviezo, J. F. Oliveira

Adsorption of residual flotation reagents onto equilibrium fluid cracking catalysts is a promising method of purification of flotation process water. In the present paper, adsorption of sodium dodecyl sulphate (SDS), dodecyl ammonium chloride (DAC) and sodium oleate onto a spent catalyst from petroleum industry was studied by analysing the residual concentration of the surfactant after contact with the zeolite catalyst. The adsorption of the DAC was rather low but SDS and sodium oleate presented a high affinity for the catalyst surface. The loading capacity was 4.2 kg/ton for SDS and 5.5 kg/ton for oleic acid. After the treatment of the loaded catalyst with a HCI 1 N solution these surfactants are desorbed and the catalyst may thus be regenerated. This would be an additional advantage to its low cost, not to mention its condition as a discarded product and its availability in large tonnages.

Jan 1, 1995

By R. L. Loofbourow

In addition, dewatering is seldom complete because of aquifer irregularities and an operator's natural reluctance to start a costly study program, provision of wells, and pumping long before mining begins. In some cases, water pumped from the mine is used in treatment. This use is suggested as a way to minimize effluent effects. The true objective of water supply, however, is to provide water of satisfactory quality at the rate needed and at the least cost. Pumping to permit efficient mining isn't likely to coincide strictly with that objective during much of the mine life. The history of mining is replete with efforts, some highly ingenious, to control mine water. Methods that might be used to tackle the challenge Operators of wet mines are faced with both obvious pumping costs and some unquantified water costs. It is possible to reduce both types of costs, generally by reducing inflow to the mine area-and a surprising number of methods have been used to do this. Both the obvious and unquantified costs at a wet mine are now multiplied by: •Increasing costs of power, labor, equipment, and supplies; •Work at greater depth and, in some cases, in wetter ground; •Increasing use of hydraulic fill; and •Increasing zeal in protection of surface and groundwater quality. There are many easily overlooked ways in which mine water may add to hazards and costs (Loofbourow, 1973). As to their importance, consider these examples: •Increased maintenance of equipment, tires, roads, and ditches; •Increased difficulty in supplying proper ventilation; •Increased hazards from ice and use of electric power; • Loss of friable ore minerals and fines stuck on conveyances and in chutes; •Need to use more expensive methods and explosives; and •Decrease productivity of equipment and personnel. Expressed as cost per unit of ore produced, these unquantified costs can be high. Ideally, advanced dewatering should eliminate most of them. Advanced dewatering is a highly effective water control method, but it isn't problem free. Mines in ideal ground for advanced dewatering are most unusual. To be effective, water must be pumped at a comparatively high rate for a period longer than the life of the mine, from below mining depth. Effects on both groundwater and surface water are likely to be drastic. of increasing mine water costs are listed in the accompanying table. Ten groups of possible methods are cited. Most have been demonstrated in mining; two are known from industries other than mining.

Jan 12, 1980

By S. A. Hoenig

Introduction In an earlier publication, the application of exoelectron technology to the monitoring of dry grinding in a ball mill was reported. Recently, the author has investigated the ball mill problem in more detail with the system shown in Fig.1 . Here, some of the current generated in the ore-ball-water mixture was picked up by the metal chains and served as a measure of the rate of grinding. While the mechanism of current generation has not been completely clarified, a parallel study of electrical effects associated with rock drilling indicated that the major driving force is the zeta potential*, while oxidation of the freshly fractured material provides the remainder of the current. Both of these effects are sensitive to the exposed surface area, and it might be expected that the observed currents would provide a measure of the grinding rate. This "surface area" effect allows the measurement system to be used in any type of rock or ore grinding. Some studies with sulfide copper ore indicate higher currents than those observed with silica sand, but the overall pattern of current versus grinding rate is essentially the same. Experimental Studies The experimental system was set up as shown in Fig. 1. The initial studies were done with silica sand because of its availability and for comparison with the data of reference 1. The sand was sized to an average of 425 µm (40 mesh); a typical charge consisted of 2.5 kg (5.5 lb) of sand, 0.85 L (0.22 gal) of tap water and 2.5 kg (5.5 lb) of iron grinding balls 25.5 mm (1 in.) in diameter. For a typical "run," the mill was loaded with a fresh charge of ore and operated for periods ranging from 10-60 min. During this time, the current was measured with a Keithley 417 picoammeter and a chart recorder. At the end of the grinding period, the charge was removed and sieved to recover the 425, 300, and 212 pm (40, 50, and 70 mesh) fractions which were then drained and weighed. A fresh charge was used for each test and every attempt was made to keep the draining and weighing processes uniform. *The zeta potential is the voltage developed between the surface of a solid particle and the ion solution in which it is immersed. In the case of rock/ore materials in water, the zeta potential is negative.

Jan 1, 1984

By M. E. Breitrick

Newmont Gold operates the Carlin East underground, one of four underground gold mines the company operates in northeastern Nevada. Carlin East began full production in early 1995. The mine's current rate is 900 t/d (1,000 stpd), producing about 4.6 t/a (150,000 oz/year). About 125 hourly and salaried personnel are employed at the project for its estimated six-year mine life. Two mining methods are currently used at the Carlin East Mine. Longhole stoping with cemented backfill accounts for 70% of the total mine production. Conventional underhand drift and cemented fill accounts for the balance of the daily tonnage. In December 1996. Newmont purchased an AC-Eickhoff ET-210 roadheader. The machine went into service in mid-June 1997. It is used in longhole Stope topcut development and cut-and-fill production at a rate of 225 t/d (250 stpd)

Jan 1, 1998

By David J. Collins

The emergence of activated charcoal adsorption as the most popular recovery method for precious metals, has led to numerous innovations aimed at increasing the efficiency of the process. This article describes a change in traditional charcoal transfer methods which will aid in reducing charcoal attrition losses. Studies have shown that significant charcoal attrition takes place during transfer, be it when using airlifts or centrifugal pumps. Tests conducted at Pinson Mines indicated a 4 to 8% loss to the minus 20 mesh fraction of charcoal after three (3) hours of pumping charcoal. Tests conducted while the author was at Jerritt Canyon indicated that charcoal transfer was a major contributor to charcoal losses; a decrease in the amount of coarse charcoal (plus 12 mesh) and an increase in the amount of finer charcoal (minus 16 plus 20 mesh) was noted as charcoal was moved to the head of the adsorption circuit.

Jan 1, 1998

By Atmesh K. Sinha

The market for thermal coal has recently been growing rapidly and it is projected to continue to do so in the foreseeable future. Both the national and international markets often demand high Btu low sulfur thermal coal in order to minimize the cost of utilization and meet the environmental restrictions. High quality thermal coal can be prepared to compete in the utility market by desulfurizing the high Btu midwestern coal and blending it with low sulfur western coal which is usually low in Btu content. The methods that can be used for optimizing the coal preparation plant operating parameters for physically desulfurizing coal is presented.

Jan 1, 1984

By Y. Luo, S. S. Peng

Based on the concept of slope-stability analysis, a formula for determining an important parameter required in the mathematical model for the prediction of mining subsidence in hilly terrain is proposed. The slope geometry and the physical and mechanical properties of the soil at the surface of the natural slope can all be considered in the formula. Incorporation of this new formula into an existing mathematical model provides an integrated approach for the study of ground movement in hilly regions.

Jan 1, 2000

By N. S. Dalal, V. Castranova, K. Van Dyke, V. Vallyathan, J. H. Kang

Previously we reported crushing or grinding crystalline silica results in silica-based free radicals on the particulate surface which can generate hydroxyl radicals in aqueous solution (1). Now we find that freshly ground silica is more cytotoxic to and a more potent activator of alveolar macrophages than similarly sized aged silica. Since the United States Department of Labor estimates that over 1.25 million American workers may be exposed to freshly ground crystalline silica arid nearly 60,000 may be at risk of developing some degree of silica-based occupational lung disease, then this is hardly a trivial problem. Occupations of concern include workers who come in contact with silica including miners of soft and hard minerals, stone quarry workers, glass workers and even millers who stone grind flour. Acute silicosis is manifested by inflammation, alveolar lipo-proteinosis, and the rapid development of respiratory disability that depending on the dose of silica can produce chronic silicosis which takes 20 - 40 years to develop. It is demonstrated by the appearance of concentric hyalinized nodular lesions and progressive development of dyspnea(3). Certainly the free radicals produced on the surface of freshly ground crystalline silica play a most important role in producing the acute and chronic symptoms of silicosis. When respirable-size freshly- ground silica (0.1 -- 5 microns in diameter) enters the deep alveolar spaces in the lung and contacts an aqueous environment, hydroxyl radical are generated and cellular damage is bound to occur. We have found that freshly ground silica can cause lipid peroxidation and lysis of erythrocytes(1). The objective of this investigation was to further elucidate the enhanced toxicity of freshly ground versus aged silica. It can be deduced from the data that not only is freshly ground silica more cytotoxic to alveolar macrophages but it is a more potent stimulant of these phagocytes. However the mere characterization of toxicity is not entirely helpful if there is not a useful means to detoxify the cause of the damage. We have identified an aqueously soluble substance that can be used in high dilution to detoxify the SiO(•) and Si(•) type of free radicals. This is the organosilane known as Prosil 28 (R). We have found that coating of the freshly ground silica can effectively reduce its toxicity. The importance of this observation is that such a coating could be used with water cooled drills. This may partially detoxify silica at the point of generation of the free radical, i.e., the generation of the fresh silica dust itself. Such a coating could be used in great dilution 1:103 or 1:104. The coating would be long lasting, inexpensive and should be non-toxic because of the great dilution.

Jan 1, 1991

By Peter J. Lawson, John A. Rideout, Gregory W. Dicinoski

A considerable body of literature directed towards optimising the efficiency of gold and silver extraction from cyanide leach liquors has appeared in recent years. A few examples from dissolution to solvent extraction to adsorption in carbon-in-pulp (CIP) and resin-in-pulp (RIP) operations follow. Selective leaching of gold from copper-gold ores using ammonia-cyanide mixtures extends the % copper which may be tolerated in ores (Ruane, 1991, LaBrooy et al., 1991, Costello, 1991). The removal of copper and recycling of cyanide from high copper ores is another important development (Sceresini and Staunton, 1991). Solvent extraction of alkaline cyanide liquors (Riveros, 1990, Mooiman & Miller, 1991) and solvent aided elution in CIP (Muir, et al., 1985) look promising. Recent definitive papers on the mechanism of adsorption of aurocyanide by activated carbon should lead to more efficient use of CIP (Adams and Fleming, 1989, Klauber, 1991). Strong and mixed weak-strong base resins have been applied in RIP for aurocyanide extraction in Russian Plants since the 1970's (see for example Borovskii et al., 1985, and references cited in Fleming, 1988a). Fundamental studies on applications of commercial weak and strong base resins-in-pulp (Fleming & Cromberge, 1984a, b, Fleming 1988a, Hosking 1984, Riveros and Cooper 1987) have generated much interest in RIP. Detailed comparisons of CIP vs RIP efficiencies at Mintek in South Africa (Fleming et al., 1988b), and the inefficiency of CIP in contact with clay led to the commissioning of the strong base RIP Golden Jubilee plant in 1988. Its operation and improvements have been reported (Seymore and Fleming, 1989, Fleming & Seymore, 1990). The use of anion exchange membranes for aurocyanide extraction shows some promise (Mauthoor et al., 1991). However, the development of new gold specific resins at Mintek (Green et al., 1984, 1986, 1990, Johns and Green, 1991) and elsewhere (Asker et al., 1987, Wilson et al., 1987, Harris et al., 1992) should improve the viability of RIP processes. The polydiallylamine gold specific resins (Hodgkin & Eibl, 1988, Fawell et al., 1992a, b) have high capacities for auro cyanide recovery from high concentration liquors. The use of guanidine based liquid and solid ion exchange extractants for gold was recently reported by the Henkel Corporation (Kordosky., et. al., 1993). Such specific resins tailor made for gold and/or silver cyanide extraction should lower overall cost by improving metallurgical efficiency. In the case of strong base resins this selectivity largely eliminates the problems of poor base metal elution and/or poisoning. The work reported here outlines the approach taken at the University of Central Queensland to synthesize sterically hindered strong base anion exchange resins which are designed to have high selectivity for auro- and argentocyanide complexes. It summarises selectivity tests on low grade cyanide leach liquors from several mines. It also examines an RIP vs CIP comparison, and investigates the elution properties and cycling of one such promising resin.

Jan 1, 1993

By Harry M. Castrantas, James L. Manganaro, Craig W. Rautiola, James Carmichael

Caro's acid (peroxymonosulfuric acid) was successfully field tested as a cyanide detoxification agent at a North American gold mine. An on-site FMC generator injected Caro's acid into a mill tailings slurry sump. The WAD cN-(weakly acid dissociable plus free cN-) was reduced from 40-108 ppm to below the target level of 20 ppm using a 1/1 mole ratio of CA (Caro's acid) /CN-. At an inlet CA/CN-mole ratio of 1.8/1, WAD CN­concentrations as low as 4 ppm cN-were achieved. Raw material costs for the cyanide detoxification were cut by 60% compared to using hydrogen peroxide (H202) alone. Detoxification time with Caro's acid was much faster compared to H202. This resulted in completion of detoxification before the treated slurry reached the tailings pond thereby substantially reducing the probability of wildlife fatalities.

Jan 1, 1993

By Eugene R. Palowitch

From the late 1880s to the present, the Appalachian region continues to be a dominant supplier of premium-quality coals. The region contains an estimated 93.4 Gt (102.7 billion st) of demonstrated reserves in Alabama, eastern Kentucky, Maryland, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia. Therefore, Appalachia will remain a source of quality coals for the metallurgical, export and utility markets. Figure 1 shows the annual production of coal in Appalachia and nationally from 1970 through 1993 (Energy Information Administration, 1994). During that 23-year period, annual domestic coal production almost doubled. Coal production from Appalachia increased at an average annual rate of only 0.7%. Coal production remained essentially constant at about 409 Mt/a (450 million stpy). Thus, Appalachia's market share decreased from 69.8% in 1970 to 47.2% in 1993 - a drop of almost one-third (Energy Information Administration, 1994).

Jan 1, 1995

By Donald P. Richards, David W. Campo, Michel Coudry

This paper presents a review of the grouting works of Line 2 of the Greater Cairo MetroSystem. The Nile River alluvial deposits underlying this ancient city provided for a challenging and sometimes difficult grouting project. Permeation grouting using state-of-the-art computerized grouting techniques, as well as extensive ground treatment by jet grout, was per-formed for soil consolidation and/or groundwater control. During the project, over 425,000m3 of ground was treated, requiring 1.4 million linear meters of drilling and PVC injection pipe, 54,000 m3 of bentonite cement and 230,000 m3 of chemical and mineral grout. In addition, over 70,000 m3 of ground was treated using the jet grout method. Relative to major international transportation projects, the grouting works for Line 2 of the Cairo Metro represent one of the largest worldwide grouting endeavors to date.

Jan 1, 1997

By Cherie M. Tilley

The Stillwater Mining Company has acquired a Tunnel Boring Machine to expedite the mine development operations at its Stillwater Mine. The machine purchased by Stillwater was previously owned by Melbourne Metropolitan Board of Works, Melbourne, Australia. The machine was manufactured by Robbins Co. of Kent, Washington. The Stillwater Mine has an extensive system of footwall laterals which are required by the mine development scheme. The initial mine plan called for in excess of 30,500 linear meters (100,000 linear feet) of footwall lateral drifts at a cross section of approximately 3.0 meters in width by 3.75 meters in height (10 feet x 12 feet). A Tunnel Boring Machine was selected for this work. The Robbins machine number is 146-193. This machine is approximately 4 meters (13 feet 5 inches) in diameter. The machine was modified extensively prior to commencing operation at the Stillwater Mine.

Jan 1, 1989

By Sandy Clamage

"Seeing the elephant" was a term often heard from 1849 to 1859, the period of the great California Gold Rush. The phrase was used by those who dreamed of instant wealth that was believed could be found in California's virgin earth and mighty rivers. When news of fabulous gold strikes throughout the Mother Lode reached far away places, thousands of gold seekers left home and family to join in this incredible adventure. The barren, placid state of California soon became one of the most bustling, populous areas in the West. Before the Rush Before 1848, Mexico ruled California. It was then a remote region, isolated from the urbane world of the East by 2900 km (1800 miles) of scorching desert and impassible mountains. By sea, it was 29 000 km (18,000 miles) via Cape Horn. Spaniards and Mexicans settled the coastal lands on tracts donated to them by the Mexican government. The inland area was the domain of Indians and a few settlers who also had been granted estates by the government. Among those settlers was Captain John Sutter. He had been fortunate enough to obtain about 11 leagues of land (spanning 100 km or 60 miles in length) from Governor Alvarado of Mexico. Sutter was somewhat of a visionary and possessed a gifted tongue. He managed to receive most of what he desired with minimal trouble. Enchanted with Sutter's personality, Alvarado promised him Mexican citizenship. Alvarado also commissioned him to become "representative of the government and officer of justice on the Northern frontier." With uncanny foresight, Sutter began building a fortress on his land in the Sacramento Valley. It later became known as Sutter's Fort. It was more than just a fort, however. It also became a stopping place and home for many foreigners and Americans who traveled to California, and it eventually became the mecca for overland pilgrims. Sutter engaged in many projects. These included a cattle ranch, fur trade and trapping, and the construction of an irrigation system. With the influx of immigrants over the years, the community around the fort grew rapidly. Lumber was much in demand and Captain Sutter agreed to supply the necessary capital for a community sawmill. The site chosen was some 72 km (45 miles) northeast of the fort on the south fork of the American River in the town of Coloma. During the course of its construction, Sutter's carpenter, James Marshall, discovered a problem with the tailrace on the mill. First Strike Early in the morning on Jan. 24, 1848, Marshall was checking the tailrace. He noticed an object shining in a foot of water at the bottom of a ditch. He reached down and picked it up. His heart began to thump wildly as he realized he was holding a gold nugget. Sutter planned to keep the find a secret for as long as possible. He knew very well that he could become an extremely wealthy man. The ever loyal Marshall remained faithful to his employer and the pair did their best to obtain more

Jan 3, 1985

By Robert W. Wheeler, Richard G. Ames, Robert B. Reger

Introduction The use of diesel engines as an alternate power source in US underground coal mines has been a controversial step towards more efficent mining practices. Three areas of potential benefit are foreseen. First, diesel-powered mining equipment is believed to be more efficient, resulting in less occupational risk for any given amount of production. Second, diesels are believed to pose fewer intrinsic hazards, especially those related to fires and ignition of combustibles. Finally, several other health and safety advantages are foreseen for diesel units. Each of these issues will be discussed separately. Diesel Efficiency Proponents of the use of underground diesel-powered mining equipment point to increased production efficiency due to greater maneuverability, speed, power, and payload (Bradbury, 1973; Jorgensen, 1982; Ogden, 1978; Wenberg, 1979; Olsen, 1980). Units most suitable for diesel power include LHD vehicles, shuttle cars, personnel carriers, and maintenance vehicles. Estimates of increased efficiency vary from 60%-300% and more (Wenberg, 1979). Increased diesel mining efficiency is usually viewed as making it practical to mine lower grade seams. Diesel units can also operate over a wider range of floor pitches and distances than electrically-powered units, thus allowing mining of seams with special mining problems (Olsen, 1980). Diesel application is not a universal substitute for electrical power. For example, continuous miners are unlikely diesel candidates. Reduced Intrinsic Hazards Proponents of diesel use have pointed to the increased safety potential due to a reduction in electrocutions, arcs, burns, underground cable fires, and methane ignition (Ogden, 1978). Diesel units are frequently employed in maintenance activities for lifting and moving, and for coal cleanup. Thus the case is made that diesel use, by making powered operations more conveniently available, reduces the incidence of lower back injuries and related causes for days lost due to disability (Olsen, 1980). Several other issues relating to diesel safety have also been suggested. Diesel units can continue operation even during power outages allowing, for example, personnel evacuation. The maneuverability of diesel units make them particularly attractive in difficult physical conditions, such as long haulage from the face to the belt and in areas where water is deep. The case for diesel use focuses heavily on the potential for a "per worker" reduction in accidents, or a reduction in the severity of accidents. Since accidents are a major part of the health impact of mining, a reduction in accidents and resulting injuries would make a major contribution to the health of coal miners. Opposition to Diesel Use Opposition to the use of underground diesel mining equipment in the US seems to have started with the United Mine Workers of America. Some opposition to US diesel use has been based on a widely publicized 1976 letter from NIOSH to Mine Enforcement and Safety Administration administrator Robert Barrett (NIOSH, 1982). In essence, this letter warned that while insufficient evidence existed as to diesel effects on underground coal miners, NIOSH had concerns based on prior knowledge of separate diesel exhaust constituents and the potential for interaction between these constituents and coal mine dust. Current opposition to underground diesel use has focused on respiratory health effects related to diesel emissions, particularly nitrogen dioxide (NO,), carbon monoxide (CO), and particulate content (Barrett, 1982). Through

Jan 4, 1983

By Ramon S. Pizarro, W. Joseph Schlitt

Introduction Trying to synthesize innovations occurring in gold processing is not simple. At present, this technology is exploding, brought about by the high price of gold. This price has compelled the mining industry, as a matter of survival, to produce gold. The frantic search for gold deposits continues, from glacial areas to tropical jungles. The search has been fruitful. New exploration techniques have helped to locate deposits. Some are amenable to conventional processing techniques. Others are in unusual settings that challenge the ingenuity of extractive metallurgists. Ore deposits containing traces of invisible gold, refractory mineralization, and impurities and deleterious materials that previously defied treatment are now being profitably processed. Metallurgists have developed various processing methods and equipment for gold ore treatment that reflect differences in ore characteristics, grade, mineralogy, reserves, topography, climate, and location. These processes can be categorized as: • For nonrefractory or readily leachable gold ores - vat leaching, heap leaching, and agitation leaching. • For ores containing free gold - gravity concentration methods, followed by mercury amalgamation, and • For refractory gold ores - flotation, roasting, pressure oxidation, followed by cyanidation leaching. In actual practice, a combination of these processes may be required. This is because gold mineralization, although usually simple, may be associated with other mineral species or with clays that make the ore difficult to treat. Furthermore, after the gold has been solubilized to form a cyanide complex, one of two important processes must be applied to recover the gold. These ore zinc cementation (Merrill-Crow process) and Carbon adsorption, desorption, and electrowinning. New techniques for leaching and recovery are also advancing. These will become the bases for the next generation of gold processing plants. Nonrefractory Gold Ores Nonrefractory ores with readily leachable gold are among the .easiest to treat. Even so, non-refractory ores from epithermal deposits are likely to contain too much clay. When these ores are damp, they may clog the screens and cone crushers. Depending on the type of process, scrubbing the crushed ore is very effective in overcoming clay problems. After dewatering, the slimes enter the cyanidation process and the thickener overflow is stripped of gold values and recycled. Semiautogenous (SAG) mills are also gaining popularity due to lower capital costs and ability to treat wet, sticky ores. If properly sized, the secondary crushing and screening plants, together with a secondary ball mill, can be eliminated. When the ore is of such a low grade that it can not support fine grinding, vat or heap 'teaching may be applicable. These systems are being actively applied in the US and elsewhere. Rapid construction and low capital costs are important features of these plants. Vat leaching is ideally suited for fast leaching ores and small tonnage deposits located in areas with harsh winters or wet tropical climates. For effective vat leaching, the ore is crushed to less than 25 mm (1 in.), agglomerated with lime or cement to control fines, and leached with sodium cyanide solution (upflow or downflow). The degree of size reduction is a tradeoff between increased costs of comminution and improved gold recovery from smaller particles. However, the size of material

Jan 11, 1984

By Robert R. Munro

Introduction Traditional aggregate sources - riverbeds and alluvial fans - located close to developing urban centers are being foreclosed to mining. As sand and gravel reserves are depleted, nearby production plants cannot secure additional, adjacent reserves and are being forced to close down. The sand and gravel industry, in many respects, is its own worst enemy. It promotes development, street paving, home building, and industrial and commercial centers. Economics make us favor developments close to our operations. Thus, we encourage development by our neighbors, who soon become our detractors. Current Aggregate Mining Problems Urban development is not compatible with sand and gravel mining. Neighbors dislike the view of pits and quarries, and they complain about dust, noise, and trucking. In general, the neighbors are not happy being close to an aggregate source. This is reflected in land use or zoning laws. In most localities, mining requires a special-use permit. Public hearings are required before a legislative body. If a large group of opponents show up, legislators will often deny the land use. Urban areas are seeing traditional close-in sand and gravel sites becoming no longer available for industry. A parallel situation is also developing in most urban areas. That is, the not-in-my-backyard attitude toward landfills. As urban areas mature; a significant amount of change takes place in the physical makeup of a city. Streets and parking lots deteriorate and need repaving. Curbs and gutters need to be relocated. This necessitates a place to dispose of excess, or old, paving and structural material. Since landfills have become at least as difficult to permit as sand and gravel sites, they are becoming remote from urban areas. A significant portion of the structural material that needs to be disposed of is concrete and asphalt. This material is heavier than other materials. Thus, the cost of moving a large volume of very heavy material to a landfill becomes very expensive. In California, dump truck transportation is regulated by the State Public Utilities Commission through minimum rate tariffs. A rule of thumb for estimating the cost of such transportation is once the material is loaded, the extra kilometer (mile) costs $0.09/t ($0.08 per st). Thus, to haul an 18-t (20-st) road an extra 32 km (20 miles) will cost about $32. Because of its remote location, the cost of hauling aggregates to the point of use in an urban area becomes excessive - about the same as hauling the material to a landfill. Here is a classic example for synergism. If we could save the transportation cost of heavy demolition material by disposing it relatively close to the central city (its source), and at the same time provide an aggregate source close to the central city (its point of use), two difficult economic situations can be solved. Thus, the develop¬ment of recycling concrete and asphalt. Mining Concrete and Asphalt There are two methods of mining concrete and asphalt. The first is to pick up the old pavement in pieces. Thin, cracked pavement can usually be lifted from the grade with a front-end loader. It will break up into manageable-sized pieces. With heavier pavement, it is sometimes necessary to intentionally break it up with a stomper or heavy ripper. The pieces are loaded into heavy dump trucks and shipped to the crushing site. Again, a front-end

Jan 7, 1984