Search Documents

By Kerry Burns

Contrary to active subsidence, which occurs concurrently with mining operations, or is completed within a few days following coal extraction, delayed subsidence may take many years to appear at the surface after coal mines are abandoned. There are two principal morphological types of delayed subsidence: troughs, which are shallow depressions, and sinks, which are steep-sided crown pits. Both types are damaging to surface structures, and a variety of methods have been introduced to deal with the problem, ranging from subsidence insurance to site restitution. In planning insurance or restitution measures, a predictive model is of value in estimating the magnitude of the problem and the size of long-term budgetary commitments. Only one model is known, which was developed for the Bureau of Mines by GAI Consultants of Monroeville (l,2,3). The GAI model is presented in qualitative terms. This report develops a formal basis for the model and tests a numerical implementation on one of the best-described study areas, Allleqheny County in Pennsylvania.

Jan 1, 1982

By D. E. Healy

In 1989 an Autogenous Grinding Task Force was formed to study potential autogenous grinding circuits to replace the existing semi-autogenous grinding at the National Steel Pellet Plant located in Keewatin, Minnesota. Pilot plant test work performed by the Hanna Research Center (HRC) indicated that fully autogenous grinding with pebble extraction and crushing could feasibly be incorporated into the existing circuits. In 1990, one of the existing ten grinding mills was converted for an in-plant test incorporating pebble crushing. The full scale test work conducted in 1990 and 1991 verified the pilot plant projections with primary mill throughputs from the fully autogenous circuit utilizing pebble crushing being greater than throughput of the existing SAG mill circuits.

Jan 1, 1992

By R. H. King

Suboleski and King (1990) analyzed the reasons for the dramatic increase in underground coal mine productivity during the last 10 years. This paper examines whether this increase can be extended. The paper forecasts whether the mix of technological, procedural and other factors that produced the increase will change in the future. The forecast is based on the base case and spreadsheet production model described in the previous paper.

Jan 1, 1991

By M. G. Rylatt

The Ekati process plant flowsheet features the common steps in diamond recovery plant design. Primary treatment and concentration is by crushing, scrubbing, high-pressure grinding rolls and heavy medium separation (Fig. 1). Secondary concentration is by an attrition mill; wet, high-intensity magnetic separation and X-ray sorting (Fig. 2). All of these are performed on site, although final sorting of the diamonds into commercial categories will be carried out elsewhere. The initial throughput rate is 9 kt/d (9,900 stpd), increasing to 18 kt/d (20,000 stpd) during the first 10 years of operation. A range of ore characteristics will be encountered that will effect the plant operating conditions during the life of the mine. The adopted design envelope is based on these expected variations. The design is based on the use of large-scale equipment, incorporating the latest and most efficient technology available. Where proven technology exists, no attempt was made to reinvent the wheel. However, where recently developed technology offers a significant advantage, this has been incorporated into the design. The Ekati run-of-mine (ROM) and coarse ore handling facilities are unheated, to take advantage of the better handling characteristics of the frozen ore in winter. The stockpile reclaim features an MMD mineral sizer (a toothed roll crusher) to minimize the problems of handling thawed, sticky kimberlite in the summer and break frozen lumps in the winter. All processing downstream from primary crushing and the coarse ore stockpile is carried out in a temperature-controlled environment in the main process plant building. Personnel involvement in the process is mini¬mized by using a Modicon Quantum series PLC with human-machine-interfaces (HMI) running Wonder-ware software on dedicated personal computers.

Jan 1, 1999

By R. Asmatulu

According to Darcy's law, the rate of filtration should increase with increasing pressure drop across a filter cake. In centrifugal filtration, the driving pressure is created by the centrifugal forces applied in the free water on the surface of a filter cake. However, the pressure drop can become negative when the free water surface disappears, which makes it difficult to achieve low cake moistures. In hyperbaric centrifugal filtration, this problem is overcome using air pressure to restore the pressure differential. In the present work, various mineral and coal fines have been subjected to hyperbaric centrifugal filtration tests. The laboratory tests show that the moistures of various mineral fines, such as copper and zinc concentrates, phosphate, talc, kaolin clay, and precipitated calcium carbonate, can be reduced substantially below that achieved by conventional centrifuges. Similar promising results have also been obtained with various coal fines in laboratory and pilot-scale test programs and in full-scale plant demonstrations.

Jan 1, 2012

By S. D. F. Rocha, A. L. A. SANTOS, E. M. A. BECHELENI, R. M. Papini, P. R. M. Viana, F. P. C. Silvas

The kinetics of atmospheric sulfuric acid leaching from a Brazilian nickel laterite ore was assessed using distinct reducing agents and ore mineralogy. This transitional ore contains 1.63% Ni distributed as 1.27% in coarse size (− 500 + 150 μm), mainly as silicates (lizardite and chlorite—28.6%), and 2.06%in the fines fraction (− 75 μm), mainly as iron oxy-hydroxides (goethite and hematite—49%). The effects of temperature, acid concentration, reducing reagent type, and concentration were evaluated. The − 75 μm fraction limited the leaching efficiency and the use of reducing media with thiosulfate improved leaching and Ni-Fe selectivity. However, at constant Eh of 626–743 mV and a pH range between 0.2 and 1.1, no substantial rise in metals extraction, except for Co and Mn, has been observed. In order to determine the process control at 95 °C, two regions in the extraction curves were used in combination with the shrinking core model. Control by porous diffusion was observed and the kinetic constant was found to be in the order kFe<kNi<kMn<kCo<kMg for atmospheric leaching without Eh control. In reducing media for the first 15 min of leaching, the kinetic constant was found to be kFe<kNi<kMg≅kCo<kMn as derived from Ni disseminated into iron oxides structures.

Oct 7, 2020

By Mahmut Altiner

In the present study, the use of horse residue as an alternative reducing agent in the roasting of a low-grade goethite ore containing 17.60% Fe was investigated. Additional roasting experiments were carried out with corn starch and without reducing agent for comparison. Each roasted product was characterized using X-ray diffraction (XRD) and magnetic hysteresis (MH) loops analyses. The optimum roasting conditions (roasting temperature [400, 500, and 600 °C], reducing agent/ore ratio [0.04, 0.08, and 0.12], and roasting time [10, 20, and 30 min]) were investigated based on the Taguchi approach. The magnetic susceptibilities of the roasted sample with the addition of reducing agents were higher compared to that of the roasted sample in the absence of reducing agent. Experimental findings indicate that the horse residue can be used as the reducing agent. Finally, an iron ore concentrate assaying a Fe grade of 62.12% with a recovery of 56.93% was prepared using wet magnetic separation at a magnetic intensity of 0.5 T from the ore roasted under the following roasting conditions: roasting temperature of 500 °C, reducing agent/ sample ratio of 0.08, and roasting time of 30 min.

Jun 3, 2020

By T. Janke

When Homestake Mining Company&apos;s Mclaughlin Gold Project was being evaluated for development, it was apparent that recovery of gold from mined ore would be difficult and relatively expensive. The ore was refractory, averaging less than 50% recovery in conventional direct cyanidation milling tests. Extensive testing narrowed the processing choices to either autoclave or roaster oxidation before cyanidation. Roasting was ruled out due to higher capital and operating costs --the Mclaughlin mill would be the first large-scale application of autoclave oxidation of a refractory gold ore.

Jan 1, 1989

By E. F. Nelson

The 1970s have witnessed the completion and successful start-up of several new non-ferrous metallurgical operations in the Western Hemisphere which utilize large semi-autogenous mills in the grinding circuits. These facilities&apos; are arranged either as single-stage circuits, or in a two-stage configuration n with ball mills. Another major concentrator, designed with an autogenous mill, ball mill, crusher (ABC circuit), is presently under construction and scheduled for start-up late this year. The large primary mills employed in these circuits have high diameter-to-length ratios and are designed to accept a very coarse feed, i.e., the product of a primary gyratory crusher, or run-of-mine ore. This characteristic obviates the need for a secondary-tertiary crushing plant or, in selected cases, even a primary crusher, which is a basic requirement in feed preparation for conventional grinding mills. This paper discusses three such grinding circuits and, presents operating data for two of them: the Island Copper Mine of Utah Mines, Ltd., near Port Hardy, British-Columbia,- and the Pueblo Viejo Cyanide Leach Plant of Rosario&apos; Dominicana, S.A. on the island of Hispaniola. The design criteria for the Cyprus Bagdad Concentrator under construction&apos; at Bagdad, Arizona, are also included. Data pertinent to these circuits are tabulated in the Summary.

Jan 1, 1977

By J. F. Colinet, W. R. Reed, J. D. Potts

Dust surveys were conducted at six underground coal mines to determine if deep-cutting practices expose face workers to higher levels of respirable dust. The surveyed mines were able to successfully mine deep cuts without significantly increasing the dust exposures of face workers. In general, all of the selected mines exercised good dust control practices by maintaining water sprays, scrubber airflows, proper curtain setback distances and providing sufficient airflow to the active faces. For exhausting face ventilation, field data indicate that scrubber airflow is the most important factor for controlling dust. Data collected for this study indicate that 20-mesh screens should be cleaned for every 12.2 m (40 ft) of advance, because 22% of the deep cuts surveyed for this study experienced a 20% to 35% decrease in scrubber airflow over the course of the cut. For blowing face ventilation, field data and past research indicate that dust control is aided by maintaining a proper curtain-to-scrubber airflow ratio of 1.0 (measured before scrubber activation), as well as a curtain setback distance that allows the miner operator to stand at the mouth of the curtain for the entire cut. Dust levels on the bolting faces did not appear to be affected by the longer cycles associated with deep-cut mining when good ventilation practices were used.

Jan 1, 2011

By Roussos Dimitrakopoulos, Liam Findlay

Semimobile in-pit crushing and conveying (IPCC) systems can help reduce truck haulage in openpit mines by bringing the crusher closer to the excavation areas. Optimizing a production schedule with semimobile IPCC requires integrating extraction sequence, destination policy, crusher relocation, conveyor layout and truck fleet investment decisions. A mining complex with multiple mines and IPCC systems should be optimized simultaneously to find an optimal schedule for the entire value chain. An integrated stochastic optimization framework is proposed to produce long-term production schedules for mining complexes using multiple semimobile IPCC systems. The optimization model has flexibility to select the crusher locations and conveyor routes from anywhere inside the pits. The framework uses simulated orebody realizations to consider multielement grade uncertainty and manage associated risk. A hybrid metaheuristic solution approach based on simulated annealing and evolutionary algorithms is implemented. The method is demonstrated using an iron ore mining complex

Nov 1, 2024

By Yi Luo, Jianwei Cheng, Mingming Li, Lei Xiao

Concealed thermal events in longwall gobs present safety hazards for underground coal miners and can significantly interrupt mining production. The probable causes for such thermal events range from coal oxidation at slightly above ambient temperature to smoldering fires due to spontaneous combustion of the broken coal left in the gobs. Locating such “hot spots” is the key step for planning and implementing mitigation measures to bring such thermal events under control. If a mine section, or even an entire mine, has to be sealed, understanding the status of the sealed mine atmosphere is important for the decisions guiding subsequent actions. The gas composition data obtained through the tube bundle mine atmospheric monitoring system is firsthand information of great value. Fire ratios proposed by various researchers and derived from gas composition data are useful in determining the fire status and even approximating the source locations (Timko and Derick, 2006). However, the applicability of each of these ratios under particular conditions should be carefully evaluated. The use of properly combined fire ratios can enhance the certainty of analysis. The explosibility of a sealed mine atmosphere deserves primary concern for safety reasons during seal construction, idle time and reopening of the sealed area.Mine atmospheric monitoring data from a longwall mine with flame fire have been analyzed. Efforts have been made to identify the possible causes, locations and statuses of these events using the obtained gas data, as well as other ventilation, geological and mining parameters. The effect of injected inert gas to control the events has also been quantified. The explosibility of the sealed atmosphere has been determined using two methods.

Jan 1, 2012

By E. E. Malouf

For centuries small amounts of copper have been recovered from acid mine-drainage waters. In recent years, the expansion of copper-bearing waste dump leaching for copper recovery has established a technological basis that is rapidly converting the art of copper leaching&apos; into a science. Leaching of copper, whether from copper-bearing ore or waste, follows well established chemical reactions. These reactions are commonly in an acid circuit, but where leaching of copper is to be made in rock that is a high acid consumer, ammonia and ammonia carbonate, as well as cyanide leach solutions, can be used effectively. Current hydrometallurgical processes are being applied at an ever increasing rate to recover the trace amounts of copper in copper mine waste by in-place leaching. Currently approximately 300, 000 tons of copper are produced annually in this manner where as recently as ten years ago, only one-eighth of this amount of precipitate copper was produced.. Where copper occurs as an oxide in higher concentrations as to be classified as an ore rather than waste, then the hydro-metallurgical processes are applied as percolation or agitation leaching in vats, pachuca tanks, or prepared heaps. This approach gives better control over the recovery of the leach solutions, particularly in the processes where ammonia or cyanide leaching agents are to be used.

Jan 1, 1972

By Richard L. Gordon

At almost no time since the end of World War I has the coal industry been free from serious threats to its competitive position. At present, the critical question is whether the industry can maintain its position in the electric power market and this paper reviews the prospects in this area. Our report is part of a study, supported by Resources for the Future Inc., dealing with coal demand in general. Like most elements of coal economics, it has received much less analysis than problems in other energy sectors--a defect we felt worth correcting. We have concentrated on electric power elements of the market. The nature of the coal market makes this the natural choice. Three markets absorb over 80 per cent of coal production and are considered in our overall work. The completely excluded sectors are largely catchall categories in which coal use is declining anyway. Comparing the three markets included in the overall study, we see: modest growth is the most optimistic forecast for metallurgical coke; export growth depends to a large extent on policies of foreign governments. Electric power use, however, has rapidly grown to absorb over half of coal output and coal&apos;s prospects depend almost entirely on continued expansion of this market. Throughout the 1960&apos;s the demand for coal used to generate electrical power in the United States grew at an average rate of 6.5 per cent annually. This growth rate will be sustained until at least 1976.

Jan 1, 1971

By Gregory Beckstrom

"During a year of challenges in the mining industry, two groups collaborated Aug. 17- 20 for a joint conference on industrial minerals of the Upper Midwest. Hosted in Minneapolis, MN, the 4th Annual SME Twin Cities technical conference and the 51st Annual Forum on the Geology of Industrial Minerals (FGIM) drew attendees from throughout the United States and Canada.Highlights of the event included a one-day field trip on Aug. 17 to a crushed stone and gravel mining and processing operations near the Twin Cities, followed by a visit to a historic mine tunnel within the St. Peter sandstone formation. The latter was used as a speakeasy during America’s prohibition era. A two-day field trip on Aug. 19-20 made stops in central and northeastern Minnesota at a granite quarry and processing plant, a peat harvesting and packaging plant, an iron mine and taconite processing plant, and a silica sand storage and loading operation. In a nod to one of Minnesota’s celebrated luminaries, the group also stopped in Hibbing to visit the boyhood home of Robert Allen Zimmerman, better known to the rest of the world as Bob Dylan.A full-day technical program featuring talks on environmental impacts of silica sand mining, regulatory updates, mine land reclamation and methods for identifying construction material failures (alkali-silica reaction) was bookended by the two field trips.According to Minnesota state geologist Harvey Thorleifson, the keynote speaker of the technical program, “This joint SME and Forum on the Geology of Industrial Minerals conference is a reflection of the important role of the mining industry in society, of the important role that partnerships play, and of the prominence of industrial minerals on the Twin Cities region and iron ore on a national scale.” He added, “While this is a tough year for the mining industry in the region, we are confident in the strength of the profession and the industry in the medium term, as we anticipate a superb SME national conference in Minneapolis in 2018.”"

Jan 1, 2015

By H. Boyd

Fluid energy grinding, or jet pulverization, refers to the process of entraining solid particles in high velocity gaseous or vaporous streams and reducing their size by impact and attrition against other particles or some sort of target. Since all desired size reduction is not achieved in one pass through the zone where energy is applied, some form of classification is necessary to return oversize particles to the grinding zone for further size reduction. Applications Fluid energy mills have normally been used to produce products where the particle size is basically finer than 325 mesh. Products having particle size distributions with a maximum size of 4 or 5 µm, and with a high percentage finer than I µm, can be produced using fluid energy mills. More recently, some fluid energy grinding units have been applied economically to produce ground products with 1 or 2% coarser than 200 mesh. It is also possible to consider usage of a jet-pulverizing zone, without the usual integrated air classi¬fier, operated either in open circuit or in conjunction with a screen. Feed sizes to be delivered to the fluid energy mill depend on the material involved, the type of jet pulverizer used, the finished product size requirement, and the upstream process. In some units feed sizes up to l in. or larger can be accepted, but practical economics usually require the starting material to be -4 mesh or smaller and some pulverizers are typically fed at 20 mesh top size. It is not unusual to find feed materials at essentially -325 mesh when extremely fine products are needed, since capacities are improved with finer feeds. Conventionally the fluid energy grinding process has been used for relatively soft and nonabrasive materials. This includes very low¬melting-point and temperature-sensitive materials or coatings, since there is no measurable temperature rise during fluid energy milling. More recently, however, jet pulverizers are being used on highly abra¬sive materials such as silica, feldspar, glass, zircon, calcined alumina, coke, boron carbide, and similar materials. Since the primary energy application is by impact of particles against themselves, there is a low rate of wear resulting in a small amount of product contamination and in low maintenance costs. Usually the fluid energy pulverizer produces a more narrow particle size distribution than other mills provide, and this is useful where such a requirement exists. It is possible, within limits, to adjust classifi¬cation and other functions of the overall fluid energy system to vary the particle size distribution curve and thereby approach the broader distribution obtained from other grinding methods. By controlling the temperature, composition, and humidity of the fluid used, it is possible to incorporate other functions with the size-reduction process. These include drying or adding moisture, coating, mixing and blend¬ing, and even oxidation or reduction and other chemical reactions or their inhibition. The finished product is discharged in the fluid stream and is conveyed pneumatically to the desired point, where a suitable dust collector must be provided. Operation and Mechanical Features One of the earliest fluid energy mills is the Micronizer now manu¬factured by the Sturtevant Mill Co. Similar units are also manufac¬tured by Jet Pulverizer Co. and others. As shown in Fig. 81, the micronizer consists of a shallow circular grinding chamber with noz¬zles arranged at the outer periphery to discharge tangentially inward. Fluid (usually compressed air or superheated steam) is provided to the nozzles from a manifold at pressures normally in the range of 100-150 psig and at temperatures up to 800°F or higher, depending on the raw material, required results, and economic factors. The com¬pressible fluid expands to high velocity through the nozzles and gener¬ates a spiral flow pattern in the grinding chamber, and discharges

Jan 1, 1985

By R. Addison

Boom, boom, boom, boom. The staccato beat rings out across the bush; the stamps are at work - slowly pulverizing gold-bearing ore for a patient, grizzled prospector. This is the State Battery near Marvel Loch - a tiny (capacity: 25 ton/day) gold plant operated by the Western Australian government. It is one of many such plants located in remote corners of Western Australia and the Northern Territory - miniature custom mills operated for the benefit of prospectors and small mine operators. These State Batteries, so called because they are operated by state governments and because the principal item of machinery in the plants are stamp batteries, are fascinating anachronisms: throwbacks to times long past, to a century ago, to the hard and heady existence of gold rush days.

Jan 1, 1986

Refractory gold concentrates often contain submicroscopic gold that is encapsulated within the crystal matrix of iron sulfide minerals, such as pyrite, pyrrhotite and arsenopyrite. To recover the gold, the host mineral must generally be broken down chemically by oxidative processes, such as roasting, pressure oxidation or bacterial leaching, which expose the gold for subsequent recovery by leaching in cyanide solution. The focus of attention in these pretreatment processes is usually the oxidation of the sulfides to elemental sulfur, sulfur dioxide gas or sulfate ions. Less attention is paid to the deportment of iron and the changes in its oxidation state, although this can have a profound effect on gold and silver liberation, as well as downstream operating costs. Iron sulfide minerals break down completely during pressure oxidation, and dissolve in the sulfuric acid solution that is gener-ated from oxidation of the sulfides. This dissolution liberates the tiny gold particles that were originally trapped in the sulfide crystals, and gold recovery during subsequent cyanidation is usually very high (>95%). Iron goes into solution in the oxidation process, initially as ferrous sulfate, but this compound is rapidly oxidized to ferric sulfate, which then hydrolyzes and reprecipitates. The form of the precipitate varies depending on the operating conditions in the autoclave and the presence of certain metal cations. When the acidity in the autoclave is quite low (<20 g/L H2SO4) and the temperature is high (>200°C), the formation of hematite is favored. When the acidity is high (>20 g/L H2SO4) and the temperature is relatively low (160 to 200°C), the formation of basic iron sulfate is favored. If the ore or the leach solution contains significant levels of certain cations (such as Na+, K+, NH4+, Ag+ or Pb2+) and the acidity is high (>20 g/L H2SO4), jarosite compounds are favored. Hematite is the desired iron product in the autoclave discharge, for both metallurgical and environmental reasons, but it is difficult to operate an autoclave under the conditions required for effective liberation of gold without converting some of the iron to basic iron sulfate and/or jarosite. These compounds fall into a category of iron compounds known generically as iron hydroxy sulfates, all of which can cause significant processing and environmental problems in the downstream gold process. This paper deals specifically with basic iron sulfate: the conditions under which it is formed in an autoclave, the problems that are caused by its presence in the feed to a cyanidation plant and possible remedial strategies that can be adopted, both in the autoclave and downstream.

Jan 1, 2010

By N. Kuyucak

Acid rock drainage (ARD) resulting from the natural oxidation of sulfide mineral wastes has become a major concern to the mining industry, both during the operational period and after mine closure. ARD is generally characterized by high acidity and high concentrations of dissolved metals and sulfates. If the generation of acid cannot be prevented or controlled, it must be treated to eliminate acidity and to reduce the concentration of heavy metals and suspended solids before release to the environment. Microorganisms play an important catalytic role in the generation of ARD. Several prevention, control and treatment technologies that are based on microbiological activities have been developed. The role of microorganisms and biotechnology in the generation of ARD and their role in the methods used for prevention, control and treatment are discussed in this paper. Recently developed passive and biological treatment processes that have been implemented at mine sites are emphasized in this paper. Benefits, limitations and design criteria for passive biological processes are also presented.

Jan 1, 2000

By Charles A. Maliszewski, James M. Galvin, Gerhard Urschitz

With obvious signs of deterioration, the double track, historically registered Bergen Tunnels as part of the commuter rail system in New Jersey waited for rehabilitation for a long time. Serious water in filtration not only caused operational and safety hazards for the electrified rail line but also deteriorated and structurally compromised the tunnel lining. An innovative rehabilitation program was developed to enlarge the tunnel and to provide a new waterproofing system and final lining. For the rock excavation and support New Austrian Tunneling Method (NATM) principles were utilized, while water tightness was achieved by installing a PVC membrane waterproofing system followed by a reinforced cast-in-place final lining. Experienced on-site supervision generated additional savings during construction by streamlining support elements based on geologic conditions encountered.

Jan 1, 2003