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By Qing Wang, Xiaochuan Xu, Jianping Liu, Xiaowei Gu, Qingyu Zhu

"The ecological costs related to the various optimized production schemes were calculated based on the designed ultimate pit. Moreover, the influence of the ecological costs on the selection of production schemes was discussed. In one designed pit, a series of geologically optimum pushbacks with sufficiently small increment were produced using the floating cone method founded on the principle of the highest metal content. Then all the pushbacks were reordered by the dynamic network diagram. The production scheme with the maximum NPV route was considered as the optimum one. The ecological impacts produced by mining were quantified and the ecological cost calculation models, which contain the direct eco-value loss, the indirect eco-value loss, the eco-restoration cost and the carbon emission cost were proposed. In one big open pit mine case, various production schemes were optimized and the one with maximum NPV was selected without taking into account the eco-costs. The scheme with the maximum comprehensive profit was obtained by calculating the eco-cost of each scheme. The results showed that the best scheme considered with the eco-cost was not the scheme with the maximum NPV. Therefore, the eco-cost presents the effect on the selection of the best production scheme.Introduction Optimizing production scheme is to determine the mining quantities of ore and rock, the pushing position of stope each year, and maximize the NPV of mine. In the theory, production scheming optimization has gone through trial and error (Pana and Carlson 1966), linear programming method (Johnson 1968), mixed integer programming (Gershon 1983), integer mapping (Kim and Cai 1990), dynamic programming et al (Gu et al 2014). In recent years, the study on production scheduling optimization has been focused on two aspects. On the one hand, the study is to solve the investment risk caused by the uncertainties of economic and geological environment (Ramazan and Dimitrakopoulos 2013, Marcotte and Caron 2010, Lamghari and Dimitrakopoulos 2012, Godoy and Dimitrakopoulos 2004, Benndorf and Shishvan 2014). On the other hand, the emphasis of the study was on reducing the problems for the optimization algorithm, to make it more efficient and practical (Cullenbine et al 2011, Shishvan and Sattarvand 2015, Askari-Nasab et al 2011, Nasab et al 2010). However, different production schemes cause different damage of mine land and pollutant emission, thus triggering environment problem. With the improvement of people’s consciousness of environment protection, the environmental issue of mining has been attracting more and more attention."

Jan 1, 2017

By Martin F. Grier

The Mt Todd Gold Project is located 300km to the south of Darwin in the Northern Territory of Australia. The identified resource comprises 46 million tonnes at 1. 65g/t using a 1. 0g/t cut-off ( 50 million short tonnes at 0.05oz/st). The resource is open to the north and at depth. Mineralisation comprises easterly dipping sheeted quartz/sulphide veins, typically 10 to 20 millimetres in thickness, hosted by hornsfelled greywackes. The majority of the ore body is primary ore with only 10% classified as oxide ore. Early testwork showed that the ore was not suitable for heap leaching, giving only 50% recovery at a -3mm crush size. Acceptable recoveries were obtained at a P80 of 75 micron. However, the ore is extremely hard.

Jan 1, 1992

By R. J. Rice, K. F. Denning

Effect of iron on the removal of arsenic, mercury and selenium from gold mining effluents. Arsenic, mercury and selenium are common trace elements in gold tailing effluents that require removal before the water is either recycled or returned to a receiving body. One of the better methods of removal of these elements is the use of iron salts whereby, the metal is trapped on the freshly precipitated hydrolyzed iron oxides either by adsorption or enmeshment of the fine particulate and hence, removed from solution. The metal removal is effected by iron to metal ratio, pH, temperature etc. Pilot plant tests have shown that mercury can be reduced to < 5 ppb Hg, while full scale tests on arsenic and selenium have achieved levels of < 50 ppb As and < 10 ppb Se in well controlled systems.

Jan 1, 1993

By Thomas H. Koenning, William E. Bruce

The importance and complexity of the ventilation systems in many underground coal mines necessitates the use of digital computers to model the ventilation networks. The modeling procedures used by the Mine Safety and Health Administration (MSHA) utilize the MSHA-modified Penn State computer program. The basic techniques used by MSHA have been described in detail in NESA (now MSHA) Informational Reports 1066 and 1183 (1. 2). Two basic methods are utilized for modeling underground mine ventilation systems. The first modeling method is the use of actual air-flow, pressure, and fan-performance data acquired during a full air-pressure, air-quantity ventilation survey to develop a mathematical model of the ventilation system. The second modeling method is the design of a ventilation system using data obtained from calculation, from past experience, or from technical literature. The latter method would typically be used to design a ventilation network prior to developing a new mine. Regardless of which method is used for modeling, there is a need to know, or to calculate, appropriate resistance values to be used for airways and for the various ventilation control structures. Such data is typically difficult to obtain and this report is an attempt to summarize typical resistance values which may be used in designing ventilation networks for new mines or in simulating proposed system changes in existing mines. Illustrations are presented to show where some of the resistances typically are located and how they are modeled in mine ventilation net- works.

Jan 1, 1987

By Peng Yu-mei, Cao Zhi-yun, Fan Qing-en

In China, an enormous amount of Au-Ag bering calcines, residues and tailings are produced each year from various sources in mining, metallurgical and chemical industries. For a long time, these materials have been either stored up in dumps or disposed of into rivers, resulting in not only waste of resources but also severe environmental pollution. It is therefore of great significance, both from economical and public welfare points of view, to recover efficiently and make full use of the metallic values from these miscellaneous materials. In this paper the physical and chemical properties of these Au-Ag bearing calcines, leached residues and tailings are described and the current status of their utilization are briefly outlined, followed by a more detailed description of some innovative processes now in practice. Lastly, the potential prospects of gold and silver recovery from these materials in China, particularly in the Hunan province, are envisaged.

Jan 1, 1998

By George McArthur

GEOLOGY One of the largest copper resources in North America occurs in the Bingham mining district, located 40 km (25 miles) southwest of Salt Lake City, UT. Anaconda&apos;s present contribution to the development of this resource is the Carr Fork mine. (Fig. 1, Bingham district plan map.) The Carr Fork story began about 300 million years ago when a thick sequence of sedimentary quartzite and limestone was deposited in the Oquirrh Basin. Subsequent earth stresses formed a series of west-northwest-trending overturned anticlines and synclines that were later offset by northwest-striking thrust faults and northeast-trending normal faults. (Fig. 2, Bingham district cross section.) About 38 million years ago the Bingham stock was intruded into some of the folds, resulting in the formation of porphyry ore in the intrusive, and fissure, replacement, and skarn ore deposits in the sediments. The Carr Fork skarns were formed preferentially in two limestone units, called the Yampa and Highland Boy, which average about 46 m (150 ft) in thickness, separated by about 76 m (250 ft) of quartzite. Copper mineralization consists almost entirely of chalcopyrite associated with pyrite and molybdenite in a gangue of garnet, diopside, magnetite, quartz, and carbonate. Molybdenum, gold, and silver are economic byproducts. (Figs. 3 and 4, indicated ore in plan and section.) EXPLORATION HISTORY The West Mountain mining district, of which Carr Fork is a part, was organized in 1863, after leaf-silver ore was discovered in the Carr Fork of Bingham Canyon. However, it was not until 1873, when the Bingham and Camp Floyd railroad to the town of Bingham was completed, that the mining camp flourished. Many small mining companies in the district were reduced, often through consolidation. By 1937 only the National Tunnel and Mines Co. was active in the Carr Fork area. In 1948 it declared bankruptcy, and was later purchased by The Anaconda Co. Anaconda conducted geologic investigations in the Bingham district until 1968, when a concerted diamond drilling program was initiated to fully evaluate the geologic potential of the Carr Fork area. The exploration program commenced with one diamond drill, but was enlarged to three drills following discovery of the first major ore intercept. Near completion of the exploration effort, large oil well rotary drills were used to drill to depths of 762 to 914 m (2500 to 3000 ft), after which the holes were completed by standard diamond drilling techniques. All holes were collared vertically, but considerable deviation occurred because of structure and rock conditions. Wedging and directional drilling were used to keep the holes on target and to provide multiple ore intercepts in the deeper holes. Geophysical surveys, in-

Jan 1, 1982

By Graham J. Morgan

The following material is excerpted from a presentation Mr. Morgan gave recently to representatives of the financial community. Introduction 1982 was a period of challenge for United States Gypsum Company because of reduced market opportunity. Housing starts for the first 10 months averaged a seasonally adjusted annual rate of 1 million units, 9% below the comparable 1981 period when housing starts were the lowest in 35 years. Industry gypsum board shipments declined 9% from the already low levels of the same period in 1981. US Gypsum met the challenge with stringent cost reduction programs and aggressive action in the marketplace. In late 1981, anticipating market deterioration, the company&apos;s management adopted strategies to focus on two shortterm objectives: • Adjust operations to perform profitably in view of limited opportunities through more efficient operations and asset management. • Continue to strengthen U.S.G.&apos;s resources and ability to take advantage of important market opportunities as the economy improves through selective expansion of production capacity in key growth markets. Concentration on these two objectives resulted in a nine month performance in 1982 that, while certainly not satisfactory by company standards, compared very favorably with that of principal competitors in terms of net earnings, margin on sales, and return on average stockholders&apos; equity. To counteract limited market opportunities, U.S.G. focused on productivity improvement, cost reduction, expense control, and maximization of market penetration. Energy Use Improving performance encompassed all segments of operations. For example, efficient use of energy was a significant factor despite lower operating rates at most plants. Overall, in the third quarter of 1982 versus 1972, the company used 27% less energy per unit of production, a savings of $15 million in that quarter alone. These continuing improvements helped to partially offset constantly rising energy costs. A number of operations achieved superior results in the first nine months of the year compared with the same period in 1981. For example, gypsum board plants in Jacksonville, FL, and Sweetwater, TX, recorded 8% and 7% reductions, respectively, in energy use per unit of production. Paper mills in Oakfield, NY, Galena Park, TX, and Kansas City, MO, each reduced energy use more than 12%, while the Greenville, MS, ceiling products facility achieved a 16%o reduction. Safety Safety is another important element that received increased attention. U.S.G.&apos;s safety performance over the past five years has consistently improved. In 1981 it was five times better than that of the gypsum industry; nearly 10 times better than all industry as measured by the National Safety Council; and almost 20 times better than all US manufacturing as recorded by the Bureau of Labor Statistics. In addition to human concerns, this excellent record results in significant dollar savings that directly affect company results. In 1981, U.S.G.&apos;s pre-tax savings in claims, premiums, and related expenses were about $20 million compared to the industries in which it competes. For the first half of 1982 performance improved further, with a cumulative lost workday incidence rate per 200,000 man-hours worked of only 0.27, an all-time record. Expense Control Careful control of inventories and receivables also received special attention. As of Sept. 30, 1982, inventories were 29%, or $44 million, below the level of Sept. 30,

Jan 2, 1983

By Victor F. Hollister

Introduction Trends of successful discovery technology and psychology emerge from a thoughtful study of various companies&apos; exploration programs. These subjective patterns can be generalized into groups of factors for discussion. Here, for convenience, factors that influence exploration success are separated into management and geologic concerns. Most successful discoveries have a demonstrably favorable management combined with a technically competent geologic input. Both are required. But the management input is decisive. Management factors include the correct definition of management&apos;s role; cost of exploration; time needed for exploration; commodity selection; and the fostering of autonomy, creativity, and confidence in the geology department. Geologic factors include imaginative technical competence (field as well as academic), correct development and use of empirical exploration or prospecting models, and dedication. Success comes to those entities that are properly managed and have technological competence. A management team that directs a company&apos;s business has been compared to a dynasty. The dynasty lays out policy and follows up with appropriate action. In that management&apos;s power is pervasive, the term is appropriate. Management&apos;s role is, however, more important. Many examples can be cited where the geologic input was impeccable. But management somehow snatched defeat from the jaws of victory, and the exploration success was turned to a third party&apos;s profit. Management Factors Management&apos;s role can be broadly generalized to four parts. These are to identify the commodities it seeks, define its part in the exploration process, develop a functioning exploration department, and have the desire to succeed. It must have confidence in its geologists and delegate to them the authority and responsibility they need to operate successfully. Head office management cannot do the thinking for a field staff thousands of kilometers away. There is no substitute for confidence and delegation of authority. Successes came to those who had the freedom to act. Motivation is a management requisite. Management&apos;s role is to prevent destructive, internecine political battles within the corporate structure. Most large US mining corporations have well known histories of political strife that have damaged their exploration efforts. Management&apos;s role must, above all, include the desire to succeed. There are cases where management has been confronted with a commercial exploration success, but their reaction is to request additional study or exploration. Perhaps the problem of bringing a commercial find into production is beyond their capabilities. But a bona fide discovery sent back for additional work commonly is lost due to that management. The cost of exploration is a factor that management must accept. A variety of studies made during the past 40 years shows the cost per discovery to be $25 million, $38 million, $200 million, or even $290 million. These figures are derived by dividing the total exploration expenditure by the number of discoveries. However, successful management dynasties have a much lower cost per discovery during their management regime. Asarco, from 1948 through 1963, had one of the lowest cost discovery rates in the world. Duval Corp., from 1948 through 1968, had comparably low discovery costs. Placer Development, from 1955, was equally successful. Western Mining in Australia has had one of the longest lived dynasties associated with exploration success. Time is vital in exploration success. Most successful exploration case histories stress sufficient time in project exploration so that the target is well tested. A large target cannot always be adequately evaluated by a few holes (strat or concept testing). Serendipity helps in exploring large targets, but it best operates in a lengthy program. Numerous case histories include pleasant surprises. But these came mostly after the 10th hole. Commodity markets are important factors governing exploration success. Management&apos;s decision to explore for a specific commodity can doom its effort if that product suffers from severe oversupply. Unquestionably, progressive copper price increases from 1948 through 1968 helped convert marginal porphyry copper discoveries

Jan 8, 1985

By L. M. Cenegy

Introduction The formation of scale is common in gold ore processing plants. A working definition of such scale is: "A hard, tightly adhering deposit formed in place by the precipitation of calcium-bearing mineral compounds from water." The most common scale found in gold processing plants is calcium carbonate (CaCO3) although calcium sulfate (CaSO4) is occasionally a problem. The problem of scale in carbon strip circuits Carbon strip circuits present a particularly challenging scale inhibition problem. Many of the factors that tend to promote scaling are present in these systems. For example, carbon strip circuits are run at high temperatures and high pH levels and require long batch cycle times. Tortuous paths are encountered by the strip solution circulating through heat exchangers, pipes and elbows, causing transient pressure drops throughout the system. Severe conditions such as these cause the water to possess a high scaling potential and may lead to the breakdown of some of common types of scale inhibitors. Formation of scale Natural waters contain dissolved minerals and gases that promote scaling. One of the contained gases, carbon dioxide (CO2), is an important factor in scale deposition. Carbon dioxide dissolves in water to yield carbonic acid according to the following reaction: [CO2 + H2O - H2CO3 (carbonic acid)] Carbonic acid rapidly dissociates to yield bicarbonate and carbonate ions depending on the pH of the system: [H2CO3 -s H+ + HCO-3 (pH range 6-10) HCO3 -a H+ + COO (pH range > 9)] In gold cyanidation processes, lime is added to raise the pH of the mill solution to 10 or above to promote cyanidation of the gold and to eliminate the possibility of hydrogen cyanide (HCN) formation. Lime contributes both hydroxyl ions (OH--) and calcium ions (Ca++) to the solution. The normal scale forming reactions in mill water systems were described by Beasley (1973) as: [HCO-3 + OH -s C03 + H2O Ca++ + C03 -a CaCO3] Factor affecting scale deposition According to Linke&apos;s (1958) solubility tables, the solubility of calcium carbonate in carbon-dioxide free water is only 13 mg/dm3 (13 mg/L) at 25° C (77° F). Scale deposition occurs when the concentration of calcium and carbonate ions in the solution exceeds the solubility of calcium carbonate. This occurs, in most cases, when the water has undergone some chemical or physical change. Some typical changes that might occur that lead to scale deposition are discussed below. Temperature An increase in temperature can greatly increase the tendency to form calcium carbonate scale. Studies by Miller (1952) have indicated that calcium carbonate is less soluble at higher temperatures. Hence, high temperatures promote scaling. For this reason, scale is often noticed on heat exchangers, autoclaves and other high temperature surfaces. Pressure A decrease in pressure may lead to an increase in the tendency to form calcium carbonate scale. Fulford&apos;s (1967) work has shown that scale is more soluble at high pressures. Hence, scale is likely to be prevalent in pump suction lines, elbows, baffles and other areas that produce turbulence and subsequent pressure drops. Change in pH Calcium carbonate scale is pH dependent and tends to form more readily at high pH. Any event that causes an increase in pH, such as the introduction of lime or caustic, would tend to initiate scale formation. Since most gold recovery operations are run at a pH above 10, the tendency to form calcium carbonate scale is always great. The use of scale inhibitors to prevent calcium carbonate scale Many products are commercially available to inhibit the formation of calcium carbonate scale. Some of the more effective types include phosphonates, as well as acrylate and maleate-based polymers and copolymers. Many of these products function by means of threshold

Jan 1, 1992

By Justus B. Deen, Randy Peterson

INTRODUCTION The General Chemical Soda Ash Operation located near Green River, Wyoming produces about 4.5 Mt of trona per year. In July 1989, Mine Ventilation Services Inc. performed a ventilation survey of this complex trona mine which had thirteen active panels spread over 36 square kilometers. The ventilation survey and subsequent study showed that the intake shaft air velocities were at their practical limits (Wallace and Rogers, 1987). The need for additional intake capacity was immediate. The ventilation network modeling delineated the best location for this new intake shaft as it applied to the 5 year ventilation plan. Unfortunately, this location, 6.5 kilometers from the soda ash processing plant, would make heating this intake air very costly. Presently, the intake air is heated by heat exchangers which use waste heat from the plant. Air heating during the winter months is necessary for miner comfort and to prevent potential freezing of water lines in the mine. It was decided to examine the feasibility of heating the air geothermally by coursing it through an old production panel. This method of air heating has been used in this region with good results at the Stauffer Chemical Operation (now Rhone-Poulenc) (Moore, 1985). In 1990, a geothermal heating study examined four different production shaft/panel configurations and a workable design was found. The operators at the General Chemical Soda Ash Operations acted on this design and began raise boring a ventilation shaft in the Spring of 1991. This paper describes the ventilation system, briefly, and the geothermal heating studies performed. Findings of the 1990 geothermal studies are then compared to field data acquired in the Winter of 1992. THE VENTILATION SYSTEM The ventilation system at General Chemical had four shafts serving the mining horizon in July 1989; three of these shafts are located at the Northwest end of the mine. The active work areas had progressed to the South over the past years and supplying ventilation has become increasingly difficult. The 6.1 meter diameter #3 Production shaft and the men and materials compartment of the 6.1 meter diameter #2 Split Shaft had reached their air velocity limits. Conversely, the 4.6 meter diameter #5 Exhaust Shaft was under utilized. Ventilation studies showed the conversion of the 3.7 meter diameter #1 Exhaust Shaft to an intake would provide adequate intake capacity for two years. The next option to improve ventilation was the addition of an intake shaft at the southeast part of the mine at the intersection of H Mains South(H-M-S)and J Mains East(J-M-E) (See Figure 1). A service shaft has been planned for the extreme Southeast end in the late 1990&apos;s. Ventilation network analyses showed this interim intake shaft would have to be at least 2.5 meters in diameter to postpone the service shaft construction beyond 1995. The greater the size of the borehole, the further the construction could be postponed. In October 1991, General Chemical commissioned the 4.57 meter diameter #4 Ventilation Shaft near the junction of H-M-S and J-M-E as shown in Figure 1. The L95 panel would be used for air heating as described in the geothermal heating section to follow. GEOTHERMAL STUDIES Geothermal heating studies were performed by MVS Inc. in May 1990. Using a modified code of CLIMSIM, an underground mine climatic simulation model, several different shaft/panel configurations were examined to see which would provide adequate air heating during the winter months. CLIMSIM simulates heat flow into a single underground airway. The program was used to evaluate the heat flow to and from the airway surface and to calculate the resulting change in dry bulb temperature of the ventilating air. CLIMSIM uses inlet air conditions, airway characteristics, and rock thermal properties input by the user to predict the variation of psychrometric and thermodynamic parameters along an underground airway.

Jan 1, 1993

By Steve Kral

The power industry throughout the world is in the midst of a significant transition that will result in a major restructuring. Deregulation of utilities in the United States is continuing, resulting in increased competition among power providers. The traditional ways that electric power is globally bought, sold and delivered will also change. However, according to the Department of Energy&apos;s (DOE) Pat Godley, one thing is clear: "Those who provide the power during the 21 st century will be those who are willing to change - those who are willing to accept new ways of doing business and willing to employ new technologies." Godley is assistant secretary of fossil energy with DOE. Her comments came during the opening remarks at the Fourth Annual Clean Coal Technology Conference, held in Denver, CO, Sept. 5-8, 1995. The conference was sponsored by DOE and the Center of Energy and Economic Development. Under the theme "Global Opportunity," more than 300 coal and utility executives spent three days discussing the new face of the electric-power industry throughout the world and the new, mostly clean coal technologies (CCT) that will be available to power providers.

Jan 1, 1995

By Zhuang Jianming, Liu Qinxia, Yuan Mingliang, Mei Xiangong, Chen Jin

Up to now, the leaching of manganese carbonate ore is usually performed at high temperature of 363K and the leaching rate is lower than 90%. Although in laboratory test, the leaching rate is only 90%. This paper introduced an improved method for leaching of manganese carbonate ore. Certain ammonium salt was added to the pulp to raise the solubility of Mn2+ and reduce the adsorption quantity of Mn2+ on the ore surface. Experimental results show that a leaching rate over 95% can be obtained at the temperature >273K. The activation energy is calculated to be 7.15 KJ/mol and is lower than that of normal leaching technique. The effects of the parameters, such as particle size, pulp density and initial acid concentration on the process results are investigated. A leaching rate higher than 95% can be obtained under the following conditions: particle size below 0.25mm, leaching time 60 min, stirring speed higher than 960 r.pm. H2SO4:MnCO3>1 .2, pulp density 105-205 g.L-l. A kinetic model was deduced, verifying with actual experiments. It showed that the model can describe the leaching process successfully.

Jan 1, 1995

By T. B. Jarboe, H. Wen

Introduction The 150 MW circulating fluidized bed (CFB) power plant described in this article is the product of recent Bechtel experience in the industrial power and steam market, where the economic feasibility of fluidized bed projects has been proven. The ability of CFB boilers to burn low grade fuels makes it possible to burn low ranking coals or coal wastes. These include anthracite culm, coal mine rejects, and coal wash-plant-waste slurries. This article also addresses the impact of fuel characteristics on plant design. This includes solids handling, steam generation, sulfur capture, and auxiliary load requirements. The uncertain economic environment in which utilities must now operate has shifted the industry&apos;s interest away from large, base-loaded generating units to small, more versatile installations. Utilities now consider purchasing new generating capacity in smaller increments and staging its deployment to correspond with demand increases. In this way, they lower their risk in the increasingly hazardous art of long-range load forecasting. This strategy has many advantages. Multiple, smaller units have inherently greater turndown capability and better availability than a single larger unit of the same size. In addition, the smaller units will each have better cycling capability. And, with CFB combustion, the smaller units will have greater fuel flexibility. General plant description The 150 MW powerplant described here is a grassroots CFB unit. Fluidized bed technology differs from conventional combustion techniques. With CFB, solid fuel, together with inert material such as sand, gypsum, limestone, or ash from the fuel, is kept suspended in the combustion chamber. This is done by using the action of the fluidizing air distributed below the bed. Fluidization promotes the turbulent mixing conditions required for good combustion. The turbulence causes the entire mass of solids to behave like a liquid. The result is improved mixing. This allows heat to be generated at a lower and more uniformly distributed temperature that is below the ash fusion temperature of most coals. The fluidizing mechanism offers several other advantages over conventional combustion. There is less volatilization of alkali compounds, which cause deposits on boiler tube surfaces. And there is less sensitivity to the quantity and nature of the ash in the fuel. The low combustion temperatures prevent vitrification of the ash particles and minimize problems associated with furnace slagging. The ability to select from many fuels is one of the major advantages of CFB combustor technology. Fuels that can be burned in CFB plants to produce steam and electricity include: low grade coals with high ash or sulfur, lignite, peat, wood and pulp products, biomass, refuse, anthracite culm, petroleum coke, and oil shales. The plant&apos;s turbine cycle uses superheated steam at 12.4 MPa (1800 psi) and 538°C (1000°F), with single reheat to 538°C (1000°F). Two high pressure and three low pressure, closed, feedwater heaters are furnished. So is a deaerator, which is an open, direct-contact heater. The CFB plant exceeds EPA&apos;s New Source Performance Standards (NSPS) for air emissions. The design limits sulfur dioxide (SO,) emissions to 0.25 kg/GJ (0.6 lb per million Btu). SO2 reduction occurs in the combustor by reac-

Jan 11, 1988

By Richard Stahura

The longtime rule-of-thumb for conveyors was that only one cleaner was needed to solve carryback problems and help keep belt replacement costs under control. That is now being rethought. Belt-cleaning systems manufacturers, designers, and users are shifting to the view that multiple cleaners, placed at key locations on the conveyor and properly maintained, are necessary to solve today&apos;s material build-up (carryback) problems. There are still not many statistics on conveyor belt cleaning. But some recent studies support this belief. One study contends that the plant maintenance engineer&apos;s biggest problem is keeping the conveyor system running efficiently. The study also said the conveyor itself is responsible for most plant shutdowns. An unscheduled conveyor shutdown can cost more than $100,000/hr and run into millions in lost production in a given year. Other studies pointed out that belt replacement is the greatest single cost of the conveyor system. These studies allude to an important fact: cleaner belts lead to reliability and longer belt life. They showed that a critical relationship exists between characteristics of material being moved and the design of all major conveyor components. In practically all situations this relationship is keyed to belt cleaners, which have long been considered "add-ons" or "accessories." At the Fifth International Coal Utilization Exhibition and Conference, the Sammis Station-Ohio Edison Co. said it installed four belt cleaners on each problem belt. The company found that under certain conditions, when the coal is wet and sticky, carryback can be so heavy that it will flow over two cleaners. Before installing the cleaners, it was necessary to schedule a cleanup crew of four men each day and rent a large vacuum truck for an eight-hour shift. In addition, the company dredged the harbor three times a year, to remove coal spillage. Once the cleaners became operational, however, cleanup costs were reduced to a few days labor every third month. Renting the vacuum truck crew was also eliminated, and harbor dredging became necessary only once each year. In addition, the Mechanical Handling Engineers&apos; Association (MHEA) in London pointed out that standards for cleaners are sorely lacking in the industry. MHEA called for instituting such standards in the future. They also reaffirm using multiple belt cleaners for increased efficiency. MHEA pointed out that some conveyor belts can be cleaned by one device, provided that it is correctly installed and adequately maintained. But MHEA recommended that a system approach be adopted, since this has proved more effective in practice. There are two main reasons why one belt cleaner fails to solve most carryback problems. First, management often reasons that the design of the current cleaner has probably been around for years, so it "must be good." This logic leads to a continued investment in keeping the current model operating, which includes pouring substantial sums of money in "housekeeping" manpower hours because the cleaner does not clean. Second, most single-belt cleaners are specified too late in the design process (indeed, some after the system is operational). This complicates matters since cleaning efficiency is directly proportional to when they are specified: the later the specification, the less efficiency. Cleaning equipment should be taken into consideration before the conveyor&apos;s structure is designed and fabricated. Otherwise the space available to install adequate cleaning equipment at the head pulley may be inadequate. Instead of matching conveyor with proper cleaner (as would occur during the design of the conveyor itself), designing a cleaning system "after-the-fact" becomes a matter of matching cleaner to conveyor. This limits choices in cleaners and, therefore, overall cleaning effectiveness. This is why after-the-fact designs of single belt cleaners are costly and rarely successful. While it is always best to specify belt cleaners during early design stages, the multiple-cleaner systems approach makes the timing of cleaner installation less critical. Because of flexible mounting hardware, a well-designed system can lead to 99% efficiency in cleaning and put an end to carryback even after a system is operational. Multiple-Cleaner Systems Approach In a multiple-cleaner system approach, the first step is to achieve a thorough understanding of the material to be moved under the worst conditions. With such un-

Jan 4, 1984

By W. Kemp Wait

Electronic ore sorting is a coarse particle beneliciating process which performs a function which in the past was primarily achieved through the use of hand picking belts. Photometric ore sorting is capable of separating waste from mineral bearing rock having a distinct difference in surface light reflectance levels. This type of ore sorter can be applied to gold and silver ores which are contained in quartz veining. Photometric ore sorting has been used at gold mines in South Africa as well as the Black Pinc silver mine in Montana. A new ore sorter has recently been developed with precious metal ores in mind. This ore sorter is capable of sorting ores on both photometric and conductivity sensing parameters. The first production machine has been installed at a gold mine near Beardmore, Ontario and currently is being used to process low grade waste dumps.

Jan 1, 1998

By Trent Temple, Curtis Johnson, John Mudge

Newmont Gold Company uses centralized carbon handling facilities to strip loaded carbon from five mills and four leach facilities located along a 38 mile stretch of the Carlin Trend in Nevada. Both Zadra and AARL elution processes are employed at this centralized facility which is located near the company's Gold Quarry operations. The Zadra elution circuit was commissioned in 1985 and later expanded in 1987. This circuit can strip carbon at a rate of 24 tons per day. The AARL elution circuit, commissioned in 1988, also has the capacity to strip 24 tons of carbon per day. Two horizontal, rotating, regeneration kilns are used to reactivate approximately 60% of the stripped carbon before it is returned to the mills or leach facilities. One kiln is located in the Zadra plant, while the other is located in the AARL plant.

Jan 1, 1990

By Paul A. Lahti

Independence Mining Company, Inc. (IMC) has for the past several years processed refractory gold ores at its Jerritt Canyon operation near Elko, Nevada. The ore is typical of those of the Carlin Trend and is refractory due to physical encapsulation of gold in carbon, pyrite, and arsenopyrite. It is also "preg robbing" due to the contained organic carbon that acts as a gold adsorber. Refractory ores require some form of pretreatment before cyanidation to enable economical recovery of gold. The metallurgical facility at Jerritt Canyon is unique in that it consists of two distinct pretreatment methods for the recovery of gold: a chemical process utilizing chlorine and a pyro-metal­lurgical process employing oxidative roasting. This paper pro­vides a comparison of the two methods highlighting flow sheets, pretreatment operation detail, performance comparisons, and pertinent environmental data.

Jan 1, 1996

By V. Fred Swanson, J. Patrick Glynn

The environment for process engineers today is very different from 20 years ago. The ideas and mathematical description of models for a multitude of different unit operations is an ongoing development. The computer tools to deal with the mathematics are readily available and specialist companies have developed, tested and verified their models. The challenge for the process engineer is to know which package to use and to know whether a particular application is the most accurate for the specific process. Metallurgical simulation programs today are well known and proven. Certain programs are specialized while others are broader based. The needs of each user are dependent on the application. Typically, most users require the following operations: • Comminution • Flotation • Hydrometallurgy • Pyrometallurgy • Additional requirements could be defined as: • Thermodynamic capabilities for solids, phases, and gases • Dynamic simulation • Data analysis tools • Coal oriented operations • Diamond oriented operations

Jan 1, 1997

By I. K. Gilmore

PCS Phosphate operates an open-pit phosphate mine in the central coastal plane of North Carolina. The company has mining and refining facilities located on the south shore of the Pamlico River. Phosphate ore is recovered at the Aurora facility by open-cast mining techniques. Walking draglines and bucketwheel excavators remove the overburden and mine the phosphate ore. The mined ore is slurried about 8 km (5 miles) to the processing plant. At the plant, the phosphate ore slurry is passed through screens to remove material coarser than 2 mm (10 mesh) and then pumped through hydrocyclones to remove material finer than 75 mm (200 mesh). The resulting phosphate and sand mixture is treated with various reagents and subjected to an anionic flotation process. A cationic flotation process removes the sand from the final phosphate concentrate.

Jan 1, 1995

By G. Piegols, J. A. Lombardi

Substantial volumes of cyanide are consumed in precious metals mining due to the purposeful destruction of base metal cyanide complexes and free cyanide to meet surface discharge regulations. This destruction of cyanide resource runs counter to the prevailing social ethic of resource conservation wherein cyanide recovery-and-reuse is considered a more socially responsible cyanide use pattern than systematic cyanide destruction. HW Process Technologies, Inc. (HWPT) has developed membrane based methods for the recovery of cyanide from barren solution as a means to reduce cyanide waste. The HWPT Engineered Membrane Separation (EMS™) system uses state-of-the-art spiral wound membrane elements that are engineered specifically for the treatment of high pH cyanide process solutions. The membranes fully reject WAD CN, SAD CN and most minor metals, and partially reject SCN, Free CN and precious metal cyanide from a high clarity barren solution feed to a small volume EMS™ “concentrate” stream. The EMS™ “concentrate” stream is returned to the process. The large percentage of the EMS™ process feed exits the system as cyanide lean EMS™ “permeate.” The EMS™ permeate, after residual cyanide destruction, polishing, and pH adjustment, is, thereafter, typically suitable for discharge. Separately, the HWPT EMS™-PLS method of cyanide recycling is an internal plant cyanide recovery step that removes base metal cyanides from a pregnant leach solution to a small volume EMSTM concentrate stream. The concentrate stream is then typically processed further for the recovery of metals and recovery-recycling of cyanide. The method makes it economically practical to recover gold from Merrill-Crowe or car-bon plant “fouling” solutions, e.g., those with greater than 400 ppm Cu, as might result from the use of the EMS™ method wherein EMS™ concentrate is constantly thrown back into the mine leach solution pool as part of the free cyanide recycle process, or as might result from the single-pass leach treatment of high copper content ores or concentrates. The EMS™ cyanide recovery method for barren solution treatment is shown to be “economic” for the treatment of clear solutions at the approximately 200 ppm total cyanide level (CNT), and for slurries at the approximately 400 ppm total cyanide level, where economic is defined as a 2 year EMS™ plant payback. The EMS™ plant payback calculation includes the beneficial monetary impacts of gold and free cyanide recycling and the avoided operating cost of cyanide destruction.• The cyanide recovery plant payback period is reduced further when the avoided capital costs for cyanide destruction (EMS™ permeate “clear solution CN destruction polish” only required) and/or metals precipitation are considered.

Jan 1, 2004