Search Documents

By K. T. Valsaraj, L. J. Thibodeaux

Solvent sublation, the separation process for the removal of two hydrophobic compounds (penta- and trichlorophenols) from the aqueous phase, is discussed, as is a steady-state mathematical model for fire process. Solvent Sublation "'as conducted in a continuous countercurrent mode. The underlying mechanisms, theory and experimental details on the effects of process variables on removal efficiency are reported.

Jan 1, 1994

By Hans Hamrin, Bruce Kennedy

Once an ore body has been probed and outlined, and sufficient information has been collected to warrant further analysis, the important process of selecting the most appropriate method or methods for mining can begin. At this stage, the selection is preliminary only, serving as the basis for a project layout and feasibility study. Later, it may be found necessary to revise the details, but the basic principles for the ore extraction should remain a part of the final layout. With respect to the basic principles employed, relatively few mining methods are used today. For the purposes of this presentation, the principles are classified as follows: 1) For naturally supported stopes, the available methods are room-and-pillar mining and sublevel stoping. 2) For artificially supported stopes, the available methods are shrinkage stoping, cut-and-fill mining, square-set mining, and longwall mining. 3) For caving methods, the available techniques are sublevel caving and block caving. Due to the uniqueness of each ore deposit, the variations on each of these methods are nearly limitless. It is impossible to include even the major variations in this chapter; the goal of this chapter is to present the principles as a guide to the mining engineer in adapting the general methods to specific needs. The selection process described herein is intended to supply the techniques by which the candidate methods available for a given ore body can be reduced to one or two feasible approaches. The feasible approaches then can be evaluated in detail, and the particular modifications can be investigated. In describing costs and economic factors, all values herein are expressed in terms of 1978 US dollars.

Jan 1, 1982

By J. W. Merks

At mineral processing plants the accuracy and precision characteristics of assays in mill feed, tailings and concentrate largely determine the reliability of the metallurgical balance. The accuracy of measurements is ensured by selecting effective sampling methods and efficient sample preparation procedures, and by effecting each phase without introducing a systematic error while the precision of measurements is determined by the sampling regime. Sampling systems and components, sampling methods and regimes, and sample preparation procedures will be reviewed. Different techniques to determine variance components for sampling, preparation and analysis, and to detect systematic errors in assays at mineral processing plants, will be discussed.

Jan 1, 1986

By E. B. Fitch, D. A. Dahlstrom

Liquid-solids separation is common to practically all mineral and coal processing as the bulk of beneficiation plants employ water as the major processing vehicle. The growing usage of hydrometallurgy has increased the importance of liquid-solid separation as acidic and basic solutions result in greater amounts of colloidal solids, with their consequent greater difficulty of separation, the economic need for chemical recovery to minimize this operating cost, and the usual necessity of employing more costly construction materials. The three processing steps covered in this section have significant capital costs. Drying, particularly, has an important operating cost because of the obvious need for energy to evaporate the water or solvent. Several common factors influence all three liquid-solid separation steps. Particle Size and Size Distribution. In general, finer particles have slower settling and filtration rates. The specific surface area is increased, which means a lower solids concentration in the thickener underflow and discharged filter cake as well as a grater moisture content to be evaporated in the drying step. Therefore, overgrinding or excessive attrition should be avoided. Consideration should be given to optimum particle size consistent with entire plant operation performance and recovery. Solids Concentration. Increased feed solids concentration will generally minimize required equipment size and costs in all three liquid-solid separation steps. Most thickeners are designed on the basis of unit area required, expressed as square feet per short ton of dry solids per day (square meters per metric ton per day) which will usually decrease with increased feed solids concentration. Filtration rates also increase as the required flow through the capillaries of the filter cake decreases. Dryer capacity increases and less energy per ton of final product is required to evaporate the associated moisture. Particle Shape and Surface Characteristics. Generally, optimum shape is a spherical particle of zero porosity. As either of these factors degrade away from the desired state, difficulty increases. This is particularly true in drying, where porosity can decrease drying rate significantly if the moisture must first reach the particle surface by diffusion

Jan 1, 1985

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

Iron ore concentrates pellets are currently in duration heat hardened (sintered) under oxidizing conditions. Pellets produced from magnetite ore concentrate are completely oxidized during induration and finish as hematite pellets. These pellets then require a blast furnace to reduce the hematite to metallic pig iron. Partially reduced pellets would save energy and fuel during transportation and further reduction. It has been stated in the literature “the most important single factor responsible for the development of strength in fired magnetite pellets containing no additive is the oxidation of the magnetite to hematite and the subsequent recrystallization and grain growth of this constituent.” However experiments shown in this paper reveal that oxidation is not necessary to produce high-strength pellets. Magnetite concentrate pellets developed similar strength when indurated at 1350°C under either oxidizing (air) or inert (argon) atmosphere; the pellets sintered under argon remained magnetite. In addition, magnetite concentrate pellets indurated under reducing (CO) atmosphere also remained as magnetite, but required induration temperature of approximately 150°C less than the other pellets.

Jan 1, 2003

Capital budgeting and investment analysis have, to this point, been beyond the scope of this text. However, a recent conceptual development by John K. Shank and Vijay Govindarajan in the capital budgeting literature is of interest to operations managers because it (1) employs some of the cost management tools outlined earlier in this text and (2) provides a useful framework for using cost management techniques to improve the competitive position of the firm. ft Shank and Govindarajan present a method of analyzing proposed expenditures that is not based on discounted cash flow measures. Their approach employs a combination of three analytical tools: value chain analysis, strategic positioning analysis, and cost driver analysis. In each of these, cost and revenue information is used in ways normally not associated with conventional budgeting. Using this framework, capital projects are selected based on their ability to improve the firm's strategic position. Shank and Govindarajan have termed this approach "strategic cost management."

Jan 1, 1999

By P. Somasundaran

Flotation of oxide minerals is controlled by a number of factors, such as surface potential and solubility of the mineral, concentration and type of various inorganics, properties of the collector, pH, ionic strength and temperature. The role these factors play depends on the mechanisms of adsorption of the collector inorganics or polymer additives. The major mechanisms include electrostatic interactions, chemical adsorption, chain-chain interaction between adsorbed collector species and modifications of the surface by inorganics. In real systems, flotation is, however, markedly affected by various other processes, including aging of the minerals, surface precipitation of the collector on the mineral and associative interactions between various collector species leading to highly surface active, for example, ionomolecular complexes. These effects are reviewed here with selected examples.

Jan 1, 1999

By Clyde N. Garman

The Homestake-New Mexico Partners consist of Homestake Mining Company of Lead, South Dakota; Rio de Ore Uranium Mines, Inc; United Western Minerals Company; White, Weld and Company; J.H. Whitney; San Jacinto Petroleum Corporation; and Clyde Osborn, Homestake Mining Company is the general partner, the others are limited partners. The Rio de Ore Uranium Mines, Inc. has. a mine in the Ambrosia Lake area; this was the first mine to go into production in this area. The United Western Minerals Company also has a mine in the Ambrosia Lake which is operated as a "farm out" from the San Jacinto Petroleum Corporation. These mines are the principal sources of ore for the mill. This group was the first to obtain a contract with AEC to make uranium concentrate from Ambrosia Lake ores and the first to have a mill in operation specifically for these ores. With Clyde Osborn as the sparkplug and co-ordinator holding the ore suppliers of, this group together, a contract with AEC was agreed on as to its essential points by mid-summer, 1956, At that time, there was no general partner and no financing, so me formal contract could be signed. By December, 1956 when the contract was signed and the present partnership officially formed, much of the basic engineering was done and purchasing of main elements of the mill waited on the formalizing of agreements, at the specifications and sizes agreed on previously. Ground for the mill was broken in April, 1957. The sampling plant went into operation in October and ore was first fed to the ball mills on February 5, 1958, ten months after construction actually started. Filling of the circuit with sodium carbonate bicarbonate solution had begun a week before that.

Jan 1, 1959

By Allan M. Hale

The central Florida phosphate industry is not a recent development. The first phosphate mining occurred in approximately 1888 (1). Many of the original mining companies were "wildcat" operations operated with rapid phosphate extraction as the sole purpose and no long-term commitment to development. Many of the early pioneers were ill-equipped to mine phosphate at either a practical or economical level; as a result many of these early companies "folded" after only a brief period of operation. However, as these early companies went out of business, several large companies developed, expanded their mining territories bought up the folding companies and by 1903 (little more than 10 years after the first mines were started), approximately 37 of the original 60 mines were control- led by three major companies (1). In the early period, mining reclamation was nonexistent. The mined out areas were left to revegetate and reclaim "naturally" over the period of many years. Reclamation practices were only started relatively recently and the various reclamation techniques developed and used in the past have continued to be employed with varying degrees of success through the present time. The reclamation techniques used in the past and currently include land and lakes restoration, sand tailing reclamation, slime ponds reclamation and overburden fill.

Jan 1, 1980

By L. Lichty, R Bhappu, R. Rowan, G. Ramadorai

Treatment of refractory gold ores containing arsenic have always presented a major problem in their processing to recover the contained precious metal values. The major difficulties are concerned with lower recoveries, production of hazardous fumes, effluents and residues. Because of'these arsenic related problems, many otherwise economically attractive precious metal deposits and dumps all over the world are not exploited. In recent years, treatment processee for refractory gold ores and concentrates have been explored and a few commercial operations employing roasting or pressure leaching have resulted. Roasting has limitations due to environmental constraints related to off gases. Pressure leaching involving high temperatures (180% to 200%) and pressures (400 psi) is accompanied by high capital and operating costs. An alternate route to roasting for treating pyrite and arsenopyrite ores and concentrates ia the "lime-oxygen hydromet" process carried out at a moderate temperature (100%) and pressure (100 psi). A simplified process for treating such arsenic containing ores and concentrates utilizing low temperature and pressure oxidation is presented. This low cost treatment with compressed air and lime renders arsenic as an inert component in the residue, meeting all the requirements of the EPA Toxicity Test. The precious metal values are then extracted from the autoclaved residue by standard cyanidation. This paper discusses this new development.

Jan 1, 1990

By C. McDonald, S. Slottee

Deep "paste" thickeners have been used in the alumina industry for several decades to improve chemical recovery and allow “stacking” of the red mud for disposal. These paste systems have eliminated many traditional tailings ponds in addition to providing better tails washing and better water recovery. This technology is not widely used or understood in other mineral processing applications. However, there is growing worldwide recognition of the advantages of concentrating mill tailings to a “paste”, i.e. a solid suspension that does not settle or segregate. This technology offers several alternatives to the traditional tailings pond such as “stacking” or mine backfill. More water recovery is possible than with high rate thickeners. Process benefits come in the form of better chemical and metals recovery through better washing in counter current decantation (CCD) applications. Obtaining a true paste (non-segregating suspension which exhibits a yield stress) and understanding the handling characteristics for applications outside alumina, are recent developments. Achieving all of the benefits available from a paste system requires careful design that takes into account the specific requirements of the disposal application along with the peculiar difficulties in producing and handling paste. In fact, design of a paste system is markedly different from a conventional system. Project design usually requires the cooperation of experts in several interrelated specialties including geotechnical, thickener design, pumping and discharge design and controls. A successful project must coordinate all activities to ensure that the overall objectives for the project are achieved. This paper describes the properties of paste, reviews the applications, and discusses the design of a complete paste deposition system.

Jan 1, 2003

By Eric K. Albert

Computer oriented simulation techniques can be effective in the design and analysis of complex mining systems. In fact, a number of computer software products are available for mine systems simulation. However, previous models have tended toward being either data-intensive and deterministic, or data-limited and highly stochastic. The need for a fully integrated package with a simplified user interface has never been more apparent. In this paper, the design of a surface mining simulation model documented in Albert (1986) is described. The basic features of the surface mining system and their counterparts in the simulation model are discussed. The methods and algorithms used to implement these subsystems are presented. Considerations of information management and software design are illustrated, especially as they apply to the application of the package by a mining engineer. An example is provided to demonstrate the concepts embodied in the model and to show how a surface mine is simulated from mine parameters.

Jan 1, 1989

By I. Melik-Gaykazov, N. N. Melnikov, V. A. Fokin, S. P. Reshetnyak

Kola Mining Institute has been carrying out investigations of the possibility to steepen the walls of the Kovdor open pit with the design depth of 600 m. Steeping (up to 60°) wall angles is done by double height (24 and 30 m) benches with vertical slopes. One of the safety factors of mining with such walls is choosing the width of the safety berms preventing against rock falling from the slopes into the pit working area. The test on rock falling from 24 m benches has shown that vertical slopes are not more dangerous compared to the inclined(60-75°) ones.

Jan 1, 2003

By A. Wright

Gold Fields Mining Corporation is presently evaluating gold mineralization beneath thick, wet alluvium at the Chimney Creek Project, Nevada. Contamination of reverse circulation samples has been visually apparent since drilling began in the area. Tests have shown that, while contamination can affect assays, reverse circulation holes appear to define mineralized zones almost as well as the diamond drill holes. To improve reverse circulation sample integrity several techniques were tried including a stiff-mud injection system but with limited success. Diamond core drilling continues to be used in conjunction with reverse circulation drilling to further delineate the mineralization.

Jan 1, 1991

By George S. Austin

Perlite is rhyolitic glass with 2 to 5 percent by weight (wt.%) bound water held within the silicic-glass structure. It is often distinguished by vitreous, pearly luster and concentric perlitic fractures ("onionskin"). Occurrences worldwide are associated with Tertiary to middle Quaternary volcanic rocks. Perlite is in silicic domes, plugs, laccoliths, flows, vitric tephra, chill margins of dikes and sills, and welded ash-flow tuffs. It is a hydrated volcanic glass formed through secondary alteration of obsidian by the incorporation of water into the glass/silica structure. Post-emplacement hydration (weathering) of cooled glasses by meteoric water is the principal alteration process, but some hydration by magmatic or meteoric water during or shortly after emplacement, or hydration by water exsolved during cooling may occur. Commercial "perlite" is any volcanic glass that expands or "pops" when heated quickly to plasticity while evolving steam and thus forming a lightweight, frothy material. The expansion temperature typically ranges from 1,100 to 1,500°F. An expanded volume increase of 10 to 40 times the original volume yields expanded densities of 1.5 to 11 pounds per cubic foot (lbs/ft3). Perlite is mined by eight companies at 10 operations in six western states. New Mexico accounts for more than 80% of the total tonnage mined. The rest comes from Arizona, California, Colorado, Idaho, and Nevada. In 1992, domestic production was 571,000 short tons (st), domestic apparent consumption was 591,000 st, and the value of crude perlite was $15.3 million. In 1991, with about the same production and price of crude perlite, the gross value for expanded perlite was $101.7 million. Perlite exports in 1992, primarily to Canada, are estimated an 30,000 st; and imports, from Greece, are an estimated 50,000 st. In 1992, 70 plants in 33 states expanded crude perlite. Construction uses of expanded perlite accounted for 66% of total domestic sales. Expanded perlite used as filter aid accounted for 15%. All other markets, including use as a filler and in agriculture, accounted for 19%. Leading states for expanding perlite, ranked by order of sales, were Mississippi, Pennsylvania, California, Illinois, and Georgia. Domestic perlite encounters transportation disadvantages in some areas of the eastern United States compared to perlite imported from Greece. However, western U.S. perlite exports to Canada offset this in large part, and net import reliance for perlite is about 3% of domestic consumption. Perlite grab samples were tested at the New Mexico Bureau of Mines and Minerals Resources (NMBMMR) for their basic suitability in horticulture, construction, filter aids, and fillers/extenders using Perlite Institute techniques modified by the NMBMMR. Most commercial perlite ranged from 2.5 to 3.0 wt.% bound water for all major types (classical, granular, and pumiceous). Expanded density varied widely, but the lowest density of 1.9 lbs/ft3 was for granular. Average brightness of expanded perlite was 47.6 to 69.3%. Nonexpansibles, commonly obsidian or "dead" perlite, ranged from 18 wt.% to less than 1 wt.%, with granular perlte generally the lowest. Compacted density was not related to either perlite type or nonexpansibles present. Sieve analyses of the -50+100 mesh product showed that, in general, pumiceous perlite produces more fines and classical and granular perlite average 60 to 80% -30+100 mesh after expansion. Samples were tested for crystalline silica that ranged from below the detection limit of 0.5 wt.% to nearly 0.2 wt.%, but most tested below 0.5 wt.%. Although quartz content can be lowered in the expanded product by the expansion process, producers can further lower crystalline silica in the product by mixing low-quartz crude with high-quartz perlite before expansion. Chemical analysis by x-ray fluorescence confirms the rhyolitic composition of perlite, but indicates that surface weathering may increase the concentration of some elements, such as potassium and calcium, by infilling cracks or fissures developed during or after perlite emplacement.

Jan 1, 1995

By Aurel Goodwin, Diann Kraft, V. S. Znamensky

This chapter deals with the Mine Safety and Health Administrations's (MSHA] concern and obligations with regard to asbestiform minerals. Asbestiform minerals are defined as the magical group of hydrated, silicate minerals that possess a fiberlike structure capable of being woven into cloth. Their unique combination of properties, such as resistance to heat and chemical attack, high tensile strength, and flexibility was recognized centuries before Christ. Pausanias, the early Greek geographer, speaks of golden lamps, made about 430 BC, with in- combustible wicks of Carpathian flax. The Ro- mans used asbestos as cremation clothes to con- serve the ashes of deceased persons of rank. Charlemagne had an asbestos table cloth that he used to pass through fire to clean (Lanza, 19381. Early recognition of the health hazards associated with exposure to asbestos was documented in the first century by Pliny the Elder, a Roman naturalist, and Strabo, a Greek geographer. Both wrote of slaves with sickness of the lungs, whose occupation was that of weaving asbestos into cloth. This concern for the health of asbestos workers disappeared over the ages. Today, with the use of modern technology, asbestos products have been greatly exploited. The asbestos output has increased over a hundredfold in the past 70 years. World production has jumped from 454 t/y (500 stpy) in 1900 to 4.5 Mt/y (5 million stpy) in 1978. An increase in health problems for asbestos workers accompanied this increased usage. However, it was not until the modern era that the association of asbestos with chronic respiratory disease was rediscovered. Reports were published at the turn of the century documenting the effects of asbestos exposure on textile workers. One such report in 1907 by H.M. Montague Murray described the post mortem findings on a 34-year- old carding machine operator. Murray de- scribed the lungs as showing extensive diffuse pulmonary fibrosis spicules of asbestos. Subsequently, more reports of pulmonary fibrosis following inhalation of asbestos were published, including an epidemiological study of asbestos miners in 1930 (Merewether and Price, 1930), at Thetford, Que., Canada. This study took place at the mine 52 years after large-scale mining of asbestos had begun. But, the cancer- producing potential of asbestos was not established until 1949 when a report by Merewether in England described an excess of cancer of the lung and pleura [the lining of the lungs) among individuals dying from asbestosis (Merewether, 1949). In the past decade much attention has been focused on asbestosis, mesothelioma, and bronchogenic carcinoma, as the three major biological effects associated with asbestos ex- posure. Parenchymal and pleural asbestosis is a fibrosis in the substance of the lung with thickening and often calcification of the membranes lining the thoracic cavity. Mesothelioma is a malignant tumor of the membranes lining the thoracic or abdominal cavities, and bronchogenic carcinoma is a cancer of the lung tissue itself. These diseases occur in various degrees and combinations. The severity and occurrence of these biological effects are directly influenced by conditions such as dose response relationships, intensity of exposure, duration of exposure, lapse of time since initial exposure, and cigarette smoking. Numerous studies indicate that the relationship between these conditions and the incidence of disease is proportional. Congress has recently concluded (Congressional Record, 1979) that, "exposure to asbestos fibers has been identified as significantly in- creasing the incidence of cancer and other severe or fatal diseases such as abestosis." Congress conveys its concerns for the safety and health of the nation's miners through the Federal Mine Safety and Health Act of 1977 in which it gave MSHA the authority to set safe

Jan 1, 1986

By J. P. Golightly

The structure and occurrence of nickeliferous laterite profiles are described and explained in terms of mineral solubility and drainage conditions. Complete profiles, from top to bottom, include: limonite zone; nontronite or silica zone; and saprolite zone. The middle zone is present only where drainage is sufficiently slow to allow saturation conditions to build up with resulting quartz or smectite precipitation. This precipitation may occur in any climate at a water table or in tropical climates with a long dry season. The degree of serpentinization of the laterite parent rock is important in determining the nature of the saprolite zone. Unserpentinized peridotite produces saprolite ores with hard residual rock cores, nontronitic or amorphous saprolitic rims, and fracture fillings of garnierite and quartz. Ser-pentinites yield relatively homogeneous serpentine saprolite, with minimal quartz or garnierite.

Jan 1, 1979

By B. C. Paul, R. Q. Honaker, M. Huang

Froth flotation is now, the most commonly used method for cleaning fine-coal fractions in coal-preparation plants. Past research and industrial practice have demonstrated that froth flotation achieves excellent separation efficiencies for fine coals having only a small fraction of middling particles. However, the efficiency of froth flotation decreases sharply as the concentration of middling particles increases. This is due to the flotation of high-ash particles that have a small amount of hydrophobic coal present at the surface. Because gravity-based processes are much more efficient for the treatment of middlings, the application of centrifugal washing for fine-coal cleaning was studied with an emphasis on the primary cleaning of fine-circuit feed. Results are shown of a parametric study that used a semibatch Falcon centrifugal concentrator. The results of the study revealed that separation performance is a function of particle size, bowl geometry, feed solids content and feed rate.

Jan 1, 1996

By Belinda F. Arbogast

Reclaimed mine sites have been evaluated so that the public, industry, and land planners may recognize there are innovative designs available for consideration and use. People tend to see cropland, range, and road cuts as a necessary part of their everyday life, not as disturbed areas despite their high visibility. Mining also generates a disturbed landscape, unfortunately one that many consider waste until reclaimed by human beings. The development of mining provides an economic base and use of a natural resource to improve the quality of human life. Equally important is a sensitivity to the geologic origin and natural pattern of the land. Wisely shaping our environment requires a design plan and product that responds to a site's physiography, ecology, function, artistic form, and public perception. An examination of selected sites for their landscape design suggested nine approaches for mining reclamation. The oldest design approach around is nature itself. Humans may sometimes do more damage going into an area in the attempt to repair it. Given enough geologic time, a small-site area, and stable adjacent ecosystems, disturbed areas recover without mankind's input. Visual screens and buffer zones conceal the facility in a camouflage approach. Typically, earth berms, fences, and plantings are used to disguise the mining facility. Restoration approaches the best land use as restoring to its original condition. Rehabilitation targets social or economic benefits by reusing the site for public amenities, most often in urban centers with large populations. A mitigation approach attempts to protect the environment and return mined areas to use with scientific input. The reuse of cement, building rubble, and macadam meets only about 10% of the demand for aggregate. Recognizing the limited supply of mineral resources and encouraging recycling efforts are steps in a renewable resource approach. An educative design approach effectively communicates mining information through outreach, land stewardship, and community service. Mine sites used for art show a celebration of beauty and experience-abstract geology. The last design approach combines art and science in a human-nature ecosystem termed integration. With environmental concerns, an operating or reclaimed mine site can no longer be considered isolated from its surroundings. Site analysis of mine works needs to go beyond site-specific information and relate to the regional context of the greater landscape. Understanding design approach can turn undesirable features (mines and pits) into something perceived as desirable by the public.

Jan 1, 1999

By Steve Wirch, Robert Jankowski

The issue of dust control in underground coal mines has been extensively studied by both government and industry. This research work has resulted in many techniques which control the dust or help miners avoid it. Control techniques either prevent the dust from becoming airborne or cleanse the air before it can be inhaled. Avoidance measures minimize the exposure of miners to the airborne dust by blowing the dust away from work areas or making it unnecessary for a miner to occupy a dusty region. One of several successful dust control measures in continuous miner sections is the use of a machine mounted scrubber which cleanses the air and helps to prevent the contaminated air from reaching areas frequented by mine personnel. Research on the application of scrubbers on longwall shearers began in the 1970s and continued into the 1980s. The most successful projects showed only moderate improvement when a scrubber system was mounted on a longwall shearer, and the less successful projects actually increased worker dust levels. There are many reasons that scrubbers have not been successfully applied on longwalls. The most significant of these is that longwalls have across the face ventilation and generally have high face air flows. Scrubbers tend to work best when they are the primary cause of ventilation. Therefore, their capture efficiencies on longwalls tend to suffer because of the exposure of the drums to the primary airflow. Other reasons scrubbers have not been implemented on longwall s include the successful application of an excellent water spray system, effective cutting techniques, and dispersion of dust sources. These techniques can help control drum generated dust, increase production, and limit the relative effectiveness of a scrubber.

Jan 1, 1995