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By B. J. Arnold, C. D. Harrison, R. A. Lohnes

More than 544 Mt (600 million st) of coal are handled annually for use by this country's coal fired power plants. Coal is transported in various ways: overland conveyors, railcars, trucks and barges. It can travel short distances or thousands of miles, picking up moisture, freezing or drying. When the coal is received at the power plant, environmental problems with fugitive dust and further handling problems can arise. To ensure that power plant availability is not jeopardized by coal handling problems, the Electric Power Research Institute's (EPRI) Coal Quality Development Center (CQDC) developed a research program aimed at addressing utility coal handling problems. The program has identified key areas, and is investigating the cost and cause of coal handling problems as well as the solutions to these problems. The ultimate goal of the program is to develop a "handleability index" that utilities can use in their coal specifications or hardware for a utility's sampling system to predict handleability and determine if a coal shipment should be accepted.

Jan 1, 1993

By Michael J. Sapko, Robert A. Cortese

A flame powered trigger device has been developed to explosively activate suppression barriers to quench gas and coal dust explosions. The important feature of the device is a silicon solar panel, which collects 0.3 p to 1.1 D wavelength radiation from the developing explosion, and generates electrical energy to initiate a detonator, which in turn causes the rapid explosive release of an extinguishing agent into the advancing flame front. Solar panels that are rated to produce 20 w of electrical power when exposed to the sun light are producing about 200 w when exposed to full-scale dust explosion propagating in the U.S. Bureau of Mines' Lake Lynn Experimental Mine. The solar panel is electrically isolated from the detonator by a pressure sensitive switch until the arrival of the precursor pressure pulse, which always precedes a deflagration. This combination of pressure arming and flame powered photo generator prevents false barrier activation and requires no external power supply.

Jan 1, 1991

By André G. Journel

As opposed to graphics applications in medical sciences and mechanical engineering, computer imaging of the subsurface faces a severe problem of data shortage. Most graphics softwares include an interpolation algorithm aimed at producing slick graphic output, irrespective of the attribute being interpolated, the quantity and quality of the data available, and what the map is intended for. It is suggested that the power of modern computers be also used in providing representations of the subsurface that accurately reflect actual spatial variability and the large variety of soft information available beyond hard data. Since any subsurface representation is uncertain, a measure of that uncertainty should be provided which can be used for risk analysis.

Jan 1, 1992

By S. K. Kawatra, T. C. Eisele

Pyrite depression is of great interest in sulfide mineral flotation, where pyrite is a common gangue mineral. Since the floatability of pyrite is a function of the pH and a variety of other chemical factors, pH control is a critical part of sulfide flotation circuits. A wide variety of pyrite-depressing chemicals have been studied and used in sulfide- mineral processing, with considerable success. However, there are certain applications where there are still no satisfactory pyrite depressants, and even when suitable depressants are available, there is always a need for less-expensive reagents. Microorganisms, such as the bacteria Thiobacillus ferrooxidans, are known to depress pyrite flotation. However, the dependence of the depression on the type of organism or on suspension pH is still being determined. In this study, the relative effectiveness of various microorganisms, and the effect of pH, has been examined. Screening tests using microflotation showed that every microorganism tested was capable of depressing naturally hydrophobic pyrite at acidic pH. Larger-scale experiments with two of the screened organisms and two different pyrites showed that microorganisms are very effective depressants at acid pH, but are largely ineffective at neutral and alkaline pH where the pyrite surface is not naturally hydrophobic.

Jan 1, 1994

By Nico Bezuidenhout, André M. van Niekerk, Jan J. G. Vermaak

This paper documents empirical evaluations of geochemical data that was recorded during a seven year pilot scale experiment. The experiment was aimed at assessing the effectiveness of natural soil covers for rehabilitation of coal discard facilities. Ten test cells were constructed using different natural soil cover materials and configurations. Results of the evaluation indicate that, although a pH breakthrough was not recorded for the single layer soil cover cells as was the case with the uncovered cells, single soil covers were not effective in preventing ARD oxidation processes. Multi layered soil covers were found to be able to create anaerobic conditions leading to a reduction in ARD oxidation processes and an improvement in leachate quality.

Jan 1, 2000

By Charles P. Lazzara, Alex C. Smith, Mark W. Ryan

The U.S. Bureau of Mines developed an experimental method to evaluate the relative effectiveness of water additives on the extinguishment of coal fires. The experiments were conducted in the fire zone of the multiple entry section of the Bruceton Experimental Mine. Chambers filled with one hundred and eighty kilograms of Pittsburgh seam coal were ignited and allowed to burn until well developed fires were achieved. Extinguishing agent-water solutions were then applied to the fires and the quantity required to extinguish the fires compared to the amount of water alone required to extinguish similar fires. A 20% diammonium phosphate-water solution required an average of 22 L to extinguish the coal fires, while two commercially available additive-water solutions required an average of 30.6 and 30.3 L, respectively. The average amount of water required to extinguish the fires was 28 L. An analysis of covariance, using the thermal energy of the coalbed, Q, to quantify the fire at the time of extinguishment, showed that the diammonium phosphate-water solution was slightly more effective at extinguishing these coal fires than water alone, while the two commercially available additive-water solutions were statistically equivalent to water alone.

Jan 1, 1992

By Terry Ritzel

Predictive maintenance technologies include vibration analysis, tribology, infrared thermography, ultrasonic detection and electrical measurements. These technologies have been applied to large electric mining shovels at the Cyprus Sierrita Mine outside of Tucson, AZ. The predictive maintenance program was initiated on the P&H models 2300 and 4100 electric shovels during August 1996. Results of these technologies have shown the potential for improving electric min- ing shovel availability and minimizing maintenance costs. Predictive technologies provide the tools to assess machinery condition. Availability is enhanced by the condition-based planning of component replacement. Maintenance costs are minimized by focusing resources through condition-based prioritization.

Jan 1, 1997

By R. L. Jones, D. D. Runnels, D. P. Dupon, D. J. Cline

To establish meaningful remediation goals and monitoring programs in areas disturbed by mining and associated industries, it is desirable to determine the natural concentrations of metals that existed in these areas prior to being disturbed. In mineralized areas, multiple natural populations of metals and associated components may be present. This paper describes a method for characterizing the natural background chemistry by means of probability distribution dia¬grams. The method can be applied to water, soil and other natural materials. In a study of a complicated hydrogeologic system at the Kennecott Utah Copper North and South Operational Areas near Salt Lake City, UT, probability distribution diagrams were used to differentiate between natural background waters and waters impacted by human activities. The probability distribution diagrams allowed a component-by-¬component interpretation of the chemistry of ground¬water and surface water over a large geographic area. Natural chemical background populations and anthro¬pogenic effects were identified Although the method is illustrated for mining-related sites, the same approach can also be used for other natural and anthropogeni¬cally impacted sites.

Jan 1, 1999

By P. E. Richardson, N. P. Finkelstein, Z. Chen

The large band gap and insulating properties of sphalerite have limited the application of standard electrochemical techniques for studying its reactions with flotation reagents. This problem has been overcome by developing electrodes that rely on the surface conductance produced when sphalerite is activated with copper or other heavy metals. A brief exposure of the mineral in copper sulfate solutions results in electrodes that exhibit significant electrochemical activity characteristic of copper sulfides. Voltammetry studies conducted on sphalerite activated in 10-4 M CuS04, solutions at pH 4.6 provide information on both the amount and the nature of the activation product(s). It is shown that copper activation is strongly dependent on the electrochemical potential applied during activation. Activation at potentials increasingly negative of the rest potential causes a progressive increase in the amount of copper on the surface; activation at potentials positive of the rest potential decreases the amount of copper on the surface. The results indicate that both the kinetics of copper uptake and, possibly, the chemical composition (stoichiometry) of the activation product are controlled by the electrochemical potential.

Jan 1, 1995

By W. J. Wuest, M. J. DeMarco, J. R. Koehler

Yield-pillar-based gate-road designs often fail to provide mine operators with adequate ground control. This is because of the unknowing m is employment of "critically" sized pillars. A "critical” pillar is one that is too large to either yield nonviolently or to yield before the roof and floor sustain permanent damage and is too small to support full abutment loads. To demonstrate the critical pillar concept, afield study of a tapering gate road was conducted by the US Bureau of Mines at the Sunnyside Coal Mines, Sunnyside, UT. Extreme pillar stresses and associated coal bumps characterize the response to first panel mining of a 16.8-m (55.1-ft) wide critical design. Significantly lower pillar stresses, early yielding of the pillar and adjacent panel rib, and an absence of coal bumps suggest that a narrower 12.2-m (40-ft) wide design more closely approaches proper yield pillar dimensions. A probe hole in several 10.6-m (34.8-ft) wide pillars revealed low stress levels and substantial pillar and panel rib yielding prior to abutment onset, indicating a properly functioning yield pillar design.

Jan 1, 1997

By D. A. Swanson, G. Danziger, G. Savci, C. Barnes

Hydrologic assessments of existing and proposed waste rock stockpiles are typically required for application of operating and closure permits at mine sites. A hydrologic assessment should include an evaluation of climatic data and prediction of the net infiltration rate through the waste rock stockpile surface. In addition, hydrologic factors such as the time required to deplete available moisture storage in the stockpiles and the time required for potential seepage to migrate to the underlying aquifer should also be predicted.

Jan 1, 2000

By R. M. Balderrama

Bench-scale laboratory flotation and gravity separation tests were conducted on tailings samples to remove the sulfidic material, mainly pyrite, the source of acid generation. A combination of xanthate collectors, promoters, and frothers were used during flotation. Pyrite recoveries were in the range of 42 to 97%, depending on the tailings being treated. Sulfide sulfur contents of 12.8 to 0.37% in the feeds were reduced to 8.68 to 0.01% in the treated tails. Flotation tests were conducted to evaluate the ARD potential as a function of percent pyrite remaining in the tails. Standard ARD predictive tests were used to evaluate the success of the treatment. In some cases, removal of only 50 to 55% of the pyritic fraction was required, thereby demonstrating the conversion of the waste material from acidic to non-acidic. A laboratory vanning table was used to evaluate the amenability of sulfide-bearing tailings samples to gravity separation. The pyrite recoveries varied from 38 to 86%. The sulfide sulfur content of 12.8 to 0.37% in the feeds was reduced to 6.0 to 0.14% in the treated tails. Predictive ARD tests performed on tailings before and after the gravity removal of pyrite showed that most samples changed from "probably" acid producing to the "uncertain" range. Data reported and analyzed in this paper demonstrate source control for ARD prevention through the removal of metal sulfides from sulfide-bearing wastes using conventional flotation and gravity separation techniques.

Jan 1, 1995

By R. J. Pugh

The surface chemical sites on several fillers (quartz, feldspar, calcite and granite) were studied by the adsorption of well defined acid and basic probe molecules (benzoic acid, benzyl alcohol, ethyl benzoate, pyridine and benzyl amine) from cyclohexane. The results provided a wide variation of adsorption data, emphasizing the extensive range of site heterogeneity on the filler surfaces. In addition, it was shown that the acidic probes were strongly adsorbed on all of the minerals, thus indicating that the basic surface sites dominate the acidic ones. Also, through FTIR studies with vapor-phase probes adsorbed on orthoclase, it was possible to identify the nature of specific sites and the type of bonding occurring between the filler surface and the probe molecule. These types of surface analytical techniques could give useful information for predicting the adsorption functional groups on dispersants, dyes, thickeners, etc. and could lead to enhanced interfacial bonding between the filler and the matrix.

Jan 1, 1993

By J. Y. Hwang, M. L. Jeong, R. C. Greenlund

Various aluminum-smelting by-products from three production sources were received and characterized. The waste materials were tested for compound identification and environmental acceptance. A coarse metallic aluminum recovery test using an Eddy Current separator (ECS) was performed using two different Circuit configurations. White dross performed equally well with either Circuit, while black dross processing shows significant difference on the separation results. It was found that ECS technology was effective for particle sizes down to 6-10 mesh.

Jan 1, 2001

By J. Y. Kim, S. L. Chryssoulis

Lead ions that originate from galena during the processing of complex sulfide ores migrate onto the surfaces of sphalerite and iron sulfide minerals. This results in poor selectivity during differential flotation. Generally, in sulfide ore processing, the lead-activated minerals float in the Cu/Pb rougher circuit. The surface lead complicates the zinc flotation circuit by lowering the concentrate grade. The effect of lead in the differential flotation of sphalerite from Cu-Pb-Zu and Pb-Zu ores is discussed. Plant and laboratory-test data are interpreted by determining the surface compositions of individual grains of sphalerite and iron sulfide particles. For the first time, surface compositions were determined by using laser-ionization mass spectrometry (LIMS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Cationic and cationic species on the surface were analyzed to elucidate the phenomena. It was proven that these new techniques are very useful in understanding the basic mechanisms of a sulfide mineral-flotation system.

Jan 1, 1997

By T. A. P. Sankar, S. Gundiah, Pradip, R. A. Kulkarni

Two modified polyacrylamide flocculants, namely polyacrylamide with glycolic acid functionality (PAMG), and a copolymer of acrylamide with N-acryloyl-[T]- aminobutyric acid (HPVP), were synthesized, characterised and evaluated for selective separation in apatite/quartz and apatite/dolomite/calcite systems, respectively. PAMG flocculant was found selective in the separation of tricalcium phosphate (TCP) from its mixtures with quartz at acidic to neutral pH range. The selectivity deteriorated at alkaline pH. In contrast, polyacrylic acid (PAA) flocculant was found most effective only in the alkaline pH range. HPVP flocculant (even though flocculating all three minerals namely apatite, dolomite and calcite) was observed to be quite selective for the separation of calcite from apatite-dolomite minerals in single mineral tests in the presence of sodium hexametaphosphate dispersant at neutral pH. There was, however, no selectivity observed during tests on synthetic mixtures. This loss in selectivity is attributed to the phenomenon of hetero-flocculation, as reported earlier, for separation in an apatite-dolomite system with polyethylene oxide.

Jan 1, 1993

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 L. W. Saperstein

In this paper, a number of novel hypotheses that provide a fresh perspective on the characterization of strata movements associated with longwall mining are developed by analyzing subsidence measurements with an influence-function-based computer program. Using an inverse application of the traditional influence-function technique, easily obtained surface displacements are used to analyze some of the complicated, expensive, and difficult-to- measure movements of the intermediate roof strata in a longwall panel. The primary hypothesis developed by this analysis proposes the existence of an area of partial roof caving near the edge of a panel called the "edge effect." A secondary hypothesis, interrelated with the first, promotes the importance of the effect of gate-entry closure on the observed strata movements. Both the primary edge-effect hypothesis and the secondary hypothesis concerning gate-entry closure are justified and quantified in an extensive analysis of surface subsidence that uses supporting information from related theories, design criteria, and in situ measurements. Next, the edge effect and the gate closure hypotheses are extended further and used to provide an explanation of the complex subsidence interaction of adjacent longwall panels in what is termed a "redisturbed" effect. Finally, the importance of accurately understanding these longwall strata movements for proper subsidence prediction or gate design is stressed.

Jan 1, 1988

By S. I. Nozhko, V. N. Guliy, A. A. Zolotarev, L. M. Luyshnia

The study of the apatite deposits of the Aldan Shield shows wide spread of the Precambrian apatite-carbonate ores and possibilities of using them for extraction of apatite. Dependency of flotation on ore minerals was studied according to the following scheme: preparation of the monomineralic samples of anhydrite, gypsum, chlorite, serpentine, phlogopite, apatite; mixing them in apatite ore of the average composition; followed by flotation. Another series of the experiments was conducted to ascertain a dependence of flotation activity of the different minerals on the different flotation reagents, which were used as collectors. It has been shown that apatite from silicate-carbonate ores is most extractable because it has the biggest size of grains and is the most free of inclusions. Beneficiation of the sulphate-containing apatite-carbonate rocks is possible when flotol - 7.9 is used as a collector. Meanwhile, the use of the tallaktam leads to an increase in the sulphate recovery. The estimation of individual technological features of the layered Mghydrosilicates and their influence on the process of beneficiation has been examined using samples of apatite-dolomite ore (P205-8%) with the addition of the phlogopite, serpentine and chlorite. The results show that there is little influence of the chlorite presence on the flotation while the serpentine presence leads to a decrease of the flotation, because of its high specific surface area.

Jan 1, 1993

By L. Shevenell

Nevada now has, or will have, 35 pit lakes resulting from open-pit mining below the water table. State regulators are requiring that the ultimate pit lake water quality be predicted as part of the permit application process. Water balances/pit lake filling rates must be esti¬mated in support of the geochemical modeling. In Nevada, analytical and numerical methods have been employed for the study of pit lakes. In the current work, analytical solutions are investigated for one pit lake, the Getchell south pit lake, which previously filled be¬tween 1968 and 1982 during a hiatus in mining. Water levels vs. time are available for this lake and these data have been fitted with a hyperbolic curve. This water-level-vs.-time curve was used in simple water-balance computations to find the net inflow rates by forcing computed water levels and volumes to match those of the known water levels and volumes through time. The model described here provides realistic volume fluxes into and out of the lake on a monthly basis as the pit lake filled.

Jan 1, 2000