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By 1980, the US mining community had reached a broad consensus regarding coal pillar design. The pillar load could be estimated from tributary area theory, and the pillar strength could be estimated from empirical formulas and laboratory coal strength testing. Then the growth of longwall mining required new thinking. Recently, powerful design methods have emerged from analysis of large databases of real-world pillar successes and failures. These include the analysis of retreat mining pillar stability (ARMPS), the analysis of longwall pillar stability (ALPS), the Mark-Bieniawski rectan¬gular pillar strength formula and guidelines for preventing massive pillar collapses. Sophisticated numerical models have also helped transform the pillar design landscape. In the process, the understanding of pillar mechanics has been greatly enriched. A new paradigm identifies three categories of pillars according to the types of failure that are associated with them. These categories are slender pillars (w/h < 3.0), which are subject to sudden collapse; intermediate pillars, in which pillar squeezes seem to be the most common failure mode; and squat pillars (w/h > 10), which are dominated by entry failure (rib, roof or floor) and coal bumps.

Jan 1, 2000

By D. R. Spears, D. A. Stanley

The US Bureau of Mines investigated the fundamental aspects of shear-flocculation using a rapid, in-situ particle size analyzer. Silica was stirred in the presence of an aliphatic amine to determine the effects of collector coverage, stirring speed and solids concentration on the kinetics of shear-flocculation. The results showed that shear flocculation is a two-stage process. In the first stage, which occurs during the first 1-2 min. of the reaction, the mean particle size increases rapidly, and in the second stage, an equilibrium is set up between the rates of floc growth and floc decay. Collector dosage affected the position of the equilibrium by altering the number of surface sites for particle-particle attachment. A minimum stirring speed was necessary for shear flocculation, which was dependent on solids concentration and collector dosage. This stirring speed was the minimum necessary for particles to overcome the electrostatic energy barrier, and that results in keeping the conditioned particles dispersed. Larger particles flocculated more rapidly. At very high stirring speeds, large flocs became unstable, resulting in a narrowed particle size distribution in the slurry.

Jan 1, 1995

By L. G. Austin

Using an instrumented laboratory high-pressure grinding rolls mill, the grinding force, gap dimension, mass flow rate and net mill power were measured for six coals and a crystalline quartz. A technique was developed to estimate the compressive stress-strain curves for compression of the materials in the mill plus the effects of elastic decompression. To reconcile the mill power and grinding pressure results, it was necessary to allow for the energy recovery on decompression. No clear correlation was obtained between the form of the stress-strain curves or the variation of specific mill power factor with the Hardgrove grindability index (HGI), although coals with the lowest and highest HGIs (i.e., 44 and 106) gave results significantly different from the other coals. Feeds below 140 mesh (105 µm) flowed more rapidly than coarser feeds and would not build up high grinding pressures. This indicated shearing and fluidlike properties rather than compression as a locked bed.

Jan 1, 1998

By P. Somasundaran, S. E. El-Mofty

A comparison of the IMC Anionic Process and the CLDRI Process, based on pilot plant testing of waste pebble by Jacobs Engineering is presented. Estimated costs for constructing and operating a beneficiation plant utilizing dolomite flotation are given. Research to develop practical flotation processes for removing dolomite from low-grade phosphate rock has been a high priority for the Florida Institute of Phosphate Research. The Institute funded the above pilot plant programs in 1998 and 2000. The Florida Phosphate industry currently deals with the increasing dolomite content of ore reserves by practicing selective mining. Heavy media separation plants installed at two mines to remove dolomite from pebble are not being operated. The flotation separation of dolomite from waste pebble requires that the flotation feed be ground. Grinding liberates the mineral species and produces particle sizes small enough to be floated. Only two dolomite flotation processes, the IMC Anionic Process and the CLDRI Process, have been successfully demonstrated on flotation feed that has not been deslimed after grinding. Deslimed flotation feed, relative to undeslimed feed, has improved flotation performance and reduced reagent consumption. However, for the above mention processes, undeslimed ground feed increases the yield of concentrate because the phosphate desliming losses are avoided.

Jan 1, 2002

By J. Hanna

The University of Alabama Mineral Resources Institute (MRI) has developed a unique process for selective fatty acid flotation of carbonate gangue from sedimentary apatites (francolite) in the pH range of 4-6 without collector conditioning of the pulp. The process, which does not require an apatite depressant, was modified to benepciate a high- MgO siliceous phosphate matrix from south Florida. The modified process includes two flotation stages, one for car- bonate removal and the other for phosphate recovery from the siliceous gangue. The selective flotation separation of the carbonate and phosphate from siliceous constituents of the matrix at various pH levels and collector dosages are discussed. In the carbonate flotation stage, about 70% of the MgO was rejected in the froth. The phosphate flotation stage produced concentrates analyzing about 31% P2O5 0.7% ? 5 MgO, and 4% insol. The overall P2O5 recovery In the two stages was about 85%

Jan 1, 1991

By Kenneth J. Leib, Laurie Wirt, M. Alisa Mast

Chemical-constituent loads were determined for an alpine stream in southwestern Colorado that is affected by natural acid drainage from weathering of hydrothermally-altered rock and from acidic metal-rich discharge from abandoned mines. Base-flow loads were compared to storm-related loads using a tracer-dilution approach. A rainstom occurred during the tracer injection, providing the opportunity to measure metal loads before, during, and after storm runoff. Chemical-constituent loads during the storm increased by 1 to 2 orders of magnitude relative to base-flow conditions. The increase in loads was related to two distinct periods; (1) a flush of higher concentrations that occurred soon after rainfall began, and (2) the peak of storm runoff. The initial flush-having no measurable change in discharge--contained the highest loads of trace metals and dissolved iron. The chemical character of peak runoff was distinctly different, as evidenced by the highest loads of total and dissolved major elements and total iron.

Jan 1, 2000

By Steven Atkin, Rens Verburg, Bryony Hansen, David McWharter

The use of paste tailings as underground backfill and for surface disposal is rapidly expanding, and with it comes the requirement to understand and predict its long-term environmental stability. This paper presents the results from a kinetic testing study performed on cemented tailings paste mixtures under both subaqueous and subaerial conditions. In addition, the effects of grainsize reduction are investigated. It will be demonstrated that the long-term weathering behavior of tailings paste is controlled by its physical and chemical characteristics, as well as its placement conditions. The testing indicates that subaqueous disposal of paste inhibits acid generation, whereas the exposed samples produced acidic leachate despite the presence of cement added to meet geotechnical requirements.

Jan 1, 2000

By L. Piga, G. Belardi, V. Alesse, N. Shehu, J. Freund

The physico-chemical interactions among minerals such as olivine, chromite and serpentine; the most commonly present ions in solution such as Ca and Mg; and flotation reagents such as EDTA and oleic acid were investigated. The study was conducted via release tests, electrophoretic measurements and microflotation of selected minerals coming from the Kukes deposit in Albania. The results were confirmed in beneficiation tests on two ores, one from the Kukes (Kalimash) deposit and the other from the Rizo deposit in Greece. It was demonstrated that, when Na-oleate is used as collector, chromite, olivine and serpentine can be separated at pH 2.5 and/or pH 5.5 when employing ethylenediamine tetraacetate (EDTA) on previously deslimed material. This approach ensures flotation concentrates with a Cr203 content better than 50% with a recovery of more than 75%.

Jan 1, 1998

By M. Karmis

Surface subsidence has been recognized as an inevitable consequence of underground coal mining for several centuries. The damage resulting from this phenomenon has been witnessed in rural as well as in urban areas and ranges from simple land settlement to severe structural damage to buildings. Subsidence prevention is not feasible, at least under the existing technological and economic constraints of underground coal mining. Using a rational method of subsidence prediction, it has been demonstrated in many coalfields that subsidence control can be successfully practiced in order to reduce and accommodate subsidence within environmentally acceptable levels. This paper presents the development and testing of a subsidence model, based on the zone area method. This technique is a refined development of the influence functions and it is capable of investigating a mining plan of any shape, thus facilitating both longwall and room-and-pillar mining systems. More specifically, this study can be divided into two major efforts: (a) The development of the zone area model. This formulation was designed to accommodate the analysis of an optimum number of zones, over the area of interest, both accurately and efficiently. (b) The testing of the computer techniques with appropriate field measurements. In order to accomplish this, published as well as unpublished information was collected and analyzed according to a regionalized scheme. This procedure minimized differences in subsidence characteristics between the various coalfields and allowed a regional validation of the predictive capabilities of the model.

Jan 1, 1982

By H. Barry Holt, Charles A. Bischoff

On November 15, 1990, President Bush signed the Clean Air Act Amendments of 1990. The new legislation is sweeping in its demands for cuts in smog, acid deposition, toxic air pollutants and ozone-depleting chemicals. The Amendments will siqnificantly alter air quality permitting and compliance and are estimted to cost billions of dollars to implement. This article provides an overview and summary of each of the eleven titles of the Amendments. It also addresses how the Amendments will be implemented.

Jan 1, 1991

By Tzou-Shin Ueng

Rock reinforcement of rock anchors and rock bolts are commonly used for the support of large rock caverns. The rocks at the location of most large underground openings are usually under very high initial stresses prior to excavation. Hence, the stress redistribution caused by excavation will induce considerable rebound deformations of rocks surrounding the caverns. Since the pressures exerted by the reinforcement are generally far below the initial rock stresses, the reinforcement will be stretched along with the rock deformations, and the stresses in the reinforcement increase accordingly. It is not uncommon for the stress in the reinforcement to reach the yield strength, and in some cases the reinforcement may even have failed. Therefore, the increase of stresses caused by the rebound deformations of rocks should be taken into account in addition to the force required to stabilize the caverns. It was found that the measured stress increases of the prestressed tendons after installation were in good agreement with those computed based on the measured rock deformations between surface and the anchoring point of the reinforcement. The rebound rock deformations and the stress increases in the reinforcement can be estimated based on the results of the finite element analysis and experiences in previous field measurements incorporated with considerations of the geologic conditions, rock properties, rock reinforcement and construction procedures.

Jan 1, 1986

By B. (Manas) Das

Rock characterization for geotechnical purposes using the microhardness technique is discussed in this paper. The concept of rock characterization and its steps are logically developed. The geotechnical properties should be functionally tethered to the technological problems for characterization. The overriding geotechnical concern is rock mass stability. The important factors in this respect are rock properties, structural discontinuities, ground water, field stress, temperature and technological factors. The rock properties are the primary factors and the other factors generally affect rock properties. Of the rock properties the strength and elastic properties can form a basis for rock characterization. The microhardness technique can provide these two properties. Study on coal shows that the microhardness impressions can be used for this purpose. On the basis of this study coals of all ranks can be divided into distinct geotechnical groups. The details of these are discussed in this paper.

Jan 1, 1986

By P. Bevilacqua, G. Ferrara, M. C. Williams, T. P. Meloy

Tabling is an old environmentally friendly separation unit operation. This paper models shaking tables and explores the action and design of riffles on shaking tables. By reassessing riffle shape and riffle patterns, significant improvements in tabling performance appear feasible. While table sales appear at their nadir, a high-tech environmentally friendly table may have a significant market in the coming decade. Riffles on a shaking table impact particle separation. Particles are affected by riffles and their exit position on the table is dramatically changed, Riffle shape determines how much the riffle will influence a given material. Moreover, riffle patterns influence the concentration of a given material and its exit points on a table. This effect of riffle placement and design is modeled in a spreadsheet. Major performance and separation improvements may he expected by improved table design. Two physical laws of tabling have been derived. These laws aid in the design of sophisticated high-tech tables.

Jan 1, 1995

By F. C. Schwerer, C. R. McKee, J. C. Seccombe

Production of methane from coal seams requires hydrofracturing, and the length of a hydraulic fracture determines we11 spacing. Since the volume of fluid injected is known, the fracture length is the volume divided by average width and height. If the fracture is contained in the known height of the seam, then fracture width becomes the major factor con- trolling length. Width is proportional to coal compressibility; bulk compressibility is known to be larger than intrinsic compressibility. A method is given here to measure in-situ compressibility (a) from transient pressure testing. Theory linking flow in porous media with rock mechanical properties is reviewed. A consistent derivation of the porous flow equation is given incorporating 3-D deformation and the effective stress parameter "st&apos; linking changes in effective stress and pore pressure. The relations for "st&apos; in terms of a and intrinsic compressibility (ai) are substituted into the field measured porosity-compressibility product (net) and solved for a, the constrained matrix compressibility. In a field example, using 4 wells with an anisotropic analysis, the ratio of major to minor permeability was 17 for the Pratt A seam. a was found to be 6x10-5/psi as opposed to the laboratory value of 1.4x10-6/psi.

Jan 1, 1986

By M. A. Ackerson, R. E. Griffin, W. H. Pomroy

Two automated fire detection system configurations have been used successfully in underground mines: the pneumatic "tube bundle" approach and the electronic telemetry approach. The electronic telemetry approach is more widely used, owing to its greater speed, flexibility, and capacity to both monitor other underground conditions, and remotely control underground equipment. However, depending on specific mine conditions and layouts, pneumatic detection, or a combined pneumatic/telemetered system may offer significant advantages over the telemetered approach alone. This paper describes research by the U.S. Bureau of Mines to design and in- mine test a rapid response pneumatic fire detection system tailored to the unique requirements of multilevel metal mines. The relative merits of pneumatic detection are discussed in the context of typical multilevel mine layouts and environments. A Bureau developed proto- type system is described with emphasis on design features which counter commonly perceived and/or experienced pneumatic detection system operating problems. Finally, the results of a 3-yr in-mine performance evaluation of the prototype hardware are discussed. Included are descriptions of system layout and coverage, response time, tube leakage, sample dilution, elimination of accumulated water from sample lines, and system maintenance and reliability.

Jan 1, 1989

By F. Forbes

For many years, the Machinery Division of Dravo Corporation has been designing and constructing bins and hunkers as part of overall plant facilities. We have designed bins to handle a variety of materials including coal, coke, iron ores and concentrates, sintered and pelletized ores, calcined and raw limestone, bentonite, alloys for BOF shops, and even cast iron chips from machining operations. We, along with everyone else in this business, have had our bin problems. The bins either plug, rathole, segregate, wear out, flood the discharge device, or overload it. Surprisingly, sometimes they have worked. As engineers, it has long concerned us that something as important as bin design should be so imprecise and that it has been so conspicuously avoided in research and in literature. In past years, rule-of-thumb design criteria had been to keep the sides of the bins as steep as possible and the outlets of the bin as large as possible. This criteria led to the design of bins with 600 to 700 side slopes and table feeders which were very large. Unfortunately, this meant trying to fit tall, skinny bins into a layout where minimum building height was required for obvious economic reasons. Like everyone else in the industry, we found that this design procedure was expensive and ineffective.

Jan 1, 1968

By Gerald H. Luttrell, Rick Q. Honaker

A coal preparation plant incorporates a variety of solid-solid separation processes that operate in relatively independent parallel circuits. Studies have shown that total plant performance can be optimized by selecting circuit cutpoints that maximize total clean coal yield irrespective of the performance of individual circuits. Although the optimum cutpoints can be determined using simulation programs, these mathematical routines require detailed washability data and empirical partition information that is not often available to plant operators. In addition, routine fluctuations in the washability characteristics of the plant feed make this approach impractical to implement in industrial facilities. As an alternative, practical optimization criteria can be developed for plant operators through a fundamental understanding of scientific principles involved in coal cleaning operations. This article provides an overview of the most important optimization criteria and presents several industrial case studies that illustrate the financial benefits of this practical approach m plant optimization.

Jan 1, 2005

During 1997-2001, an EC funded project investigated the environmental consequences of the use of industrial waste and sewage sludge based artificial top soils (ATS) in rehabilitating large coalmine waste dumps in the Saar region of Germany. Both the laboratory leaching tests and field lysimeter data analysis carried out by the research partners have shown that the amount of dissolved heavy metals in the leachate was low, and generally below the regulatory limits. However, the dissolved amount of nutrients, especially mineral nitrogen, was found to be relatively high. The hydrological properties of waste rocks and ATS mixtures were established through history matching of the laboratory column tests and the field measurements. 1D column models and 3D field models were used to numerically simulate pollutant transport at the ATS rehabilitated waste dumps. This paper presents the findings of the numerical modelling research carried out for the characterisation of hydrological and pollutant transport properties of rehabilitated coalmine waste dumps in the Saar coalfield.

Jan 1, 2003

By K. N. Han, P. B. Queneau, A. Stojsic, M. J. Collins, V. J. Ketcham, R. M. G. S. Berezowsky, W. D. Vardill

The bulk of the ore found in the Lihir Island deposit is refractory in nature, with the gold contained in auriferous pyrite. In support of an evaluation of the development of this deposit by Kennecott (a wholly owned subsidiary of RTZ) and Niugini Mining Ltd., testwork has been carried out at the Sherritt Research Centre to demonstrate the amenability of the Lihir ore to pressure oxidation pretreatment to liberate the refractory gold. The results of pilot plant treatment of the Lihir ore in a continuous circuit with a feed rate of between 10 and 30 kg/h ore are described. The integrated circuit comprised pressure oxidation, residue washing, and gold recovery from the washed residue by carbon in leach or carbon in pulp cyanide leaching. Significant factors affecting gold recovery included temperature and retention time in the pressure oxidation step, and the concentration of soluble chloride in the feed. Gold extraction from well washed ore, after oxidation at 210°C for 66 minutes in the autoclave, was typically between 94 and 96%, compared with less than 30% by direct cyanidation.

Jan 1, 1993

By M. C. Williams

The dynamic behavior of batch mill, CSTR mill, and a closed grinding network consisting of a mill, sump, and cyclone was analyzed using the dynamic population balance model (PBM). The dynamic solution of the PBM of a batch, CSTR and a closed grinding network consisting of a mill, sump, and cyclone forms the basis of the dynamic analysis presented here. Two numerical dynamic solution approaches were used. These are: 1) providing additional constraints on breakage selection functions or 2) performing the Arbiter-Bhrany (or other) normalization of the selection functions. Actual experimental anthracite batch grinding data was used to obtain the functionality of the batch dynamic mill selection and breakage functions for a real physical system. The Levenberg-Marquardt algorithm for systems of constrained non-linear equations is used to solve the batch dynamic PBM grinding equations to obtain the grinding selection and breakage rate functions. The mill, sump and hydrocyclone were modeled as a CSTR operating at various retention times. Batch dynamic PBM data was used to provide the mill kinetic and breakage selection function data. Different dynamic solutions were obtained depending on the numerical approach used. Each solution approach to a dynamic PBM with transport, while giving the same prediction for a single batch grinding time, gives different solutions or predictions for mill composition for other grinding times. This fact makes dynamic nodal analysis and control problematic. The fact that the constraint solution approach gives a solution may suggest that normalization for closed networks is not necessary. Differences in solutions to the PBM cannot be excused away by inaccuracies in the data used to model the grinding phenomenon.

Jan 1, 1995