Search Documents

By G. A. Hazen, S. M. Sargand

This study monitored longwall mining subsidence profiles over three panels that were mined beneath state highways in southeastern Ohio. The average maximum subsidence was 1.07 m (3.5 ft). The average maximum compressive strain recorded was 0.008 mm/mm. Three predictive methods for the determination of displacements and strains were compared: the National Coal Board (NCB) graphical method, the profile method with empirical constants determined for southeastern Ohio, and a finite element excavation program. Excellent subsidence agreement was found with the profile method, and reasonable strain agreement was determined with the finite element program.

Jan 1, 1987

By J. W. Leonard, D. A. Newman

By using physical and chemical means to increase the bulk density of newly broken coal freed from the mine face, the potential to improve coal mine productivity is significantly enhanced. It is estimated that by increasing bulk density, greater tonnages can be placed in fixed volume scoops and shuttles cars to improve production by as much as 10% to 20%. Such improved packaging to achieve new levels of volumetric efficiency might require only small and easy to implement changes to present downstream mining operations. Opportunities exist for improving broken coal bulk density from the moment of breakage, during transport across the continuous miner or loading machine, during discharge into the haulage unit, and after placement in the haulage unit. Physical/chemical methods for broken coal compaction in mobile, fixed volume units in underground operations are discussed.

Jan 1, 1990

By Feng Dingwu, Chen Jin, Sun Zhongyuan, Peng Shiying

The recent development of rare-earth permanent magnets has impacted the field of magnetic separation. The permanent magnets technology led to the advent of various magnetic separators particularly designed for application in mineral processing. In this paper, a new type of rare-earth PHGMS possessing a higher magnetic field strength in the working zone was developed using finite element analysis techniques. The NdFeB permanent magnets used had properties of 38 MGOe stored energy, and magnetic material flux levels exceed 1.2 T, The combination of scientific and engineering design and suitable matrices can offer an effective separation of industrial minerals, such as kaolin, feldspar, etc. Compared with conventional high intensity electromagnetic separators, the equipment can reduce electrical energy over 80% with lower operation and maintenance costs, and less installation space.

Jan 1, 1995

By Robert J. Guardia, James Rustvold, Robert A. Robinson, Christopher A. Robertson

In 1999, the Bonneville Power Administration (BPA) replaced approximately 730 m(2,400 ft) of damaged 42- and 36-inch concrete pipe by microtunneling Permalock pipe through sand and partly below groundwater. Microtunneling saved $3.5 to $5 million from the estimated cost of a shored excavation and avoided a railroad and contaminated valley fill. A slurry microtunnel boring machine (MTBM) was used for two segments where groundwater was present and a wheel excavator MTBM was used for one segment where groundwater was not present. This paper describes design and construction of this project that was completed within 2% of the bid and engineer’s estimate.

Jan 1, 2001

By Scott E. Broughton, Robert T. Tape

Heap leaching requires containment and storage of cyanide solutions, the volume of which may increase dramatically following an extreme storm event or extended wet periods. This paper describes a computer operated solution storage model developed to assist in the management of these requirements. It results from the accumulative efforts of various Klohn Leonoff engineers working on a number of heap leach projects throughout the western United States for the past several years.

Jan 1, 1988

By Colin C. Harris, Jie Zheng, P. Sornasundaran

Powder surface and polymer structural changes during stirred milling have been studied as a function of grinding time, solid concentration and polymer molecular weight. It was found that specific surface area of limestone particles can be increased over 100% by using polymer additives. Particle surface and polymer structure were also found to change during grinding. Powder surface and polymer properties have been determined using Surface Tension, Fluorescence, TOC and HPLC/GPC analysis, and surface and polymer properties are correlated with operating variables and the mechanisms involved are explored. Particularly, the fragmentation of the polymer molecules was found to occur during long term grinding and this was beneficial for ultrafine grinding.

Jan 1, 1998

By A. Zutshi

Production of CO2 is an inevitable consequence of burning fossil fuels, with the only CO2 sequestration technique feasible in the immediate future being its injection in various geologic media. This paper discusses the factors that influence the injection, movement, and storage of CO2 into deep coal seams, while simultaneously increasing the production of methane. The results of a laboratory-scale study to evaluate the movement of CO2 in coal, its ability to displace methane, and the capacity of coal to retain CO2 are presented. The findings are compared with observations at one of the two field-scale pilot operations practicing CO2 injection in coal. Finally, the paper summarizes the research issues that require further investigation.

Jan 1, 2006

By M. G. Hester, G. S. Adisoma

To address the problem of grade estimation in a general three-dimensional shape and the uncertainty associated with the estimate, the technique of jackknifing/ block-kriging shortcut is proposed. A new estimator called jackknife kriging is introduced first. Through the jackknife variance, a confidence limit for the reserve-grade estimate can be calculated. Unlike the kriging variance, which is more a measure of data configuration and which is independent of data values, the jackknife variance reflects the true variability of the data. This approach provides a simple way to set a confidence level for global estimation of resources.

Jan 1, 1997

By F. -U. Schneider, F. Wellenkamp

Based on previous investigations of ultrafine comminution in planetary ball mills, a new centrifugal mill has been developed which permits similar high stress conditions. Because this new type of mill is equipped with an immobile chamber, devices for measuring energy, for cooling the milling vessel, as well as, in continuous operation, for material feed and discharge can be more easily attached than to planetary ball mills. Observations of particle behaviour have shown that, in the case of dry grinding, most of the material is found on the mill walls even after short grinding times. Due to the fact that energy dissipation takes place mainly in the zone near the wall, a grinding system which reduces the amount of ball filling required is at an advantage.

Jan 1, 1995

By V. Rajaram, D. P. O’Connor, L. Sakamoto

In 1988, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) imposed a no-blasting specification (blasting is restricted to the construction shaft and shaft bottom or boot) on the Deep Tunnel project. This was prompted by numerous complaints from residents in the vicinity of the project and controversies experienced on previous projects from blasting the rock overlying the tunnel. This paper will describe the methods used by two major contractors driving 20 km (12.5 miles) of tunnel, and drilling more than 36 shafts under this restrictive specification. The impacts are detailed on design, construction, schedule, cost and the environment.

Jan 1, 1993

By Grazyna Dziurdzak, Robert C. Dunne, James H. Kyle

The pressure pre-oxidation of refractory gold concentrate from the Golden Mile has been investigated and the conditions of temperature, oxygen pressure and percent sulphide breakdown for maximum gold extraction optimised. Both tellurides and sulphides were oxidised under optimal conditions and deposited in the residue as oxides along with haematite. Under non- optimal conditions, a reactive basic ferric sulphate was formed instead on the unreactive haematite. Maximum gold recovery after cyanidation (tail < 1 ppm) is well in excess of that produced by the present roasting process (tail 3-4 ppm).

Jan 1, 1989

By C. Klauber, H. G. Linge, W. G. Jones

The carbon-in-pulp process for gold processing depends on the adsorption of dissolved Au(CN)2- from solution onto activated carbon. Our work shows that coconut and peat based carbons have the same mechanism and kinetics of adsorption. There is no contribution to the bonding from carbon-oxygen functionalities on the carbon surface, as has been invariably supposed in all previous theories for the mechanism of the reaction. It is shown that Au(CN)2- is reversibly adsorbed intact on, and parallel to, the graphitic planes of the carbon. The physiochemical basis of the measurement of carbon reactivity for gold adsorption is discussed.

Jan 1, 1989

By W. Douglas Gould, Mei-Lin K. Stichbury, Jeffrey G. Bain, Blowes David W.

The mechanisms of release of arsenic in gold mine tailings were investigated. The highest concentration of dissolved As (75 mg/L) was observed near the base of the tailings impoundment, in close association with a peat layer. Elevated concentrations of reduced iron and hydrogen sulfide were also measured at the base of the impoundment. High numbers of iron-reducing and sulfate-reducing bacteria were detected at depths within the impoundment which correlated with dissolved As, Fe and H2S. The data presented in this paper suggest that arsenic is released from the tailings by bacterially-mediated reductive dissolution of As-bearing iron minerals.

Jan 1, 2000

By B. Ni, J. D. Robertson

A new radioactive tracer method for the measurement of airflow in inaccessible airways was developed. The method can be used in situations where studies of the mine-ventilation system are not possible using conventional flowmeters (anemometers). The method was tested in the ventilation laboratory at the University of Kentucky and in the US Bureau of Mines Experimental Underground Coal Mine and was utilized in leakage, dilution and flow-velocity measurements.

Jan 1, 1998

By Louis W. Cope

The various types of placer deposits will be described as an introduction to the subject. The several methods and machines used for sample taking and processing will be discussed. The advantages and disadvantages of each will be covered. Included will be mistakes and pitfalls of placer sampling and sample reduction.

Jan 1, 1987

By M. H. Foroughi

This paper discusses the effects of seam inclination and lateral stresses on the stress distribution in pillars in inclined coal seams. The average pillar stress is a function of the overburden weight, the mine depth, the effective extraction ratio and the angle of seam inclination. Normal and shear stresses in the pillar are computed by numerical modeling. In medium dipping seams, leaving a pillar with its axis normal to the stratification causes a shearing stress concentration in the top and bottom corners of the pillar. This results in the pillar possibly becoming less stable in comparison to pillars in horizontal coal seams. Therefore, to reduce the stresses, it may be necessary to leave the pillar at an angle of b deviated from the normal axis to stratification. A mathematically approximate formula for determining b is proposed, and the results are confirmed by numerical modeling.

Jan 1, 1998

By J. Yordan, J. Zinterer

Effective removal of ink particles by froth flotation is of up-most importance in paper recycling. In this study, the potential use of talc particles as carriers of difficult-to-float fine ink particles is investigated. In order to accomplish ink particles removal, the interactions between talc and oily- ink particles in aqueous solutions containing flotation chemicals was studied by zeta potential distribution measurements and with the impinging jet apparatus. The chemical conditions under which talc-ink adhesion occurs are identified and reported.

Jan 1, 2003

By Don L. Jensen

With the successful implementation of supervisory control on the Bagdad concentrator grinding circuits, steps have been taken to expand supervisory control to the flotation circuits. This paper discusses the design and installation of the slurry delivery systems, analyzing instruments, level control devices, reagent pumps and supervisory software. Emphasis is placed on the design and installation of a reliable slurry transport system to feed the Courier 30 online analyzing instruments. Total system availability has been measured at plus 95%. Phase 1 acceptance testing of the supervisory software indicates a notable increase in copper recovery with no significant change in final copper grade.

Jan 1, 1999

By Ruth A. Maurer, Steven L. Capt. Van Drew

Coal preparation for a company having several sources of coal and several contracts for sale of coal was modeled. The objective was to minimize wash loss by selecting the quantity of coal to be supplied from each source and the appropriate washbox specific gravity setting to yield contract quality for a given shipment. constraints inposed by silo and stockpile sizes, plant and rehandling capacities, and varying coal quality specifications were included in the model. Solution is by iterative linear programming on an Apple II.

Jan 1, 1987

By R. L. Wolfrom, R. Hogg, S. Chander

A gravimetric method for measuring rates of capillary rise in powders was explored. Methods to improve reproducibility and consistency of the results were investigated. In particular, the effects of particle size and packing uniformity were addressed. Studies of the wetting behavior of both spherical glass beads and irregularly shaped synthetic graphite particles by various organic liquids were carried out. Standardized procedures for bed preparation will be described. The applicability of the Washburn equation for surface energy evaluation in such systems will be discussed. Key words: Wettability, Powders, Capillary rise, Surface chemistry

Jan 1, 2003