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By J. T. Ryan, Griffin. Wayne H.

This paper shows that if a drift has a brattice which is sufficiently leaky, changes in the operating point of the fan depend solely on the volumetric efficiency within the drift. Under this high leakage condition, an increase in the length of the drift causes very little shift in the fan operating point. For less leaky brattices, the operating point depends on both the fan characteristic curve and the volumetric efficiency. It is shown that for the fan curve and drift parameters used in this paper the fan operating point in a drift with a volumetric efficiency of 50% is essentially the same as a drift which has a zero efficiency. In this region of efficiency, an increase of 300% in the length of the drift causes only a 3% increase in fan operating pressure.

Jan 1, 1993

By J. D. Miller, P. L. Sibrell

The nature of surface sites for the adsorption of gold from alkaline cyanide solutions has been investigated using samples of synthetic, highly-oriented pyrolytic graphite (HOPG). This HOPG material offers an idealized graphite structure enabling the independent study of the graphitic basal-plane sites and the edges, or defect sites, of the graphitic planes. Radiochemical and X-ray photoelectron spectroscopic experiments independently demonstrated that gold adsorption was much higher on the edges (defects) of the graphite planes than on the planes themselves. These results suggest that site-specific adsorption is prevalent in the adsorption of gold by graphitic carbons (including activated carbon, carbon black and graphite) and that most of the favored sites are at edge defects in the graphite crystal structure.

Jan 1, 1993

By Lee W. Abramson, Mee Shing Owyang

The Lake Merced Transport tunnel is 18 feet in diameter and 1.6 miles long constructed within dune sands, beach sands, and the Colma Sand Formation. It runs beneath highway right-of-way from an existing pump station near the shore of Lake Merced to a point near the Pacific Ocean, where it will connect with the existing transport/storage tunnel. The final tunnel lining was originally designed as a cast-in-place concrete lining to be constructed within steel ribs and wooden lagging initial support. The contractor opted to use a precast concrete segmental initial lining thus requiring a redesign of the final lining. The redesigned lining incorporates composite action from the initial lining thereby eliminating the need for outer steel reinforcement. A computer model was used for analyses which included operating conditions, ground and construction loads, and possible effects of liquefaction and earthquakes.

Jan 1, 1993

By S. P. Singh

To understand the intricate nature of blast damage and counter the associated problems, small-scale blasting experiments were performed on hydrostone blocks. Tests were then conducted during a drifting operation in a quartzite quarry. Blast damage was assessed by different techniques. On the basis of the experimental results, the effects of the energy partitioning characteristics of explosives on the damage were identified.

Jan 1, 1993

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 S. Lin, Y. J. Wang

Through an example three fan ventilation network concepts of subsystem solution and characteristic curves of a multiple fan ventilation system are introduced. The major steps of defining a subsystem, working out the subsystem equations, constructing a solution curve and a characteristic curve, and determining the operating points of the reference fan and the ventilation system are systematically demonstrated through three and two-dimensional curves. Also briefly discussed are the main features of a subsystem characteristic curve.

Jan 1, 1993

By G. D. Hood, B. E. Davis

A problem that has continued to plague the Florida phosphate industry is loss of coarse phosphate in the flotation circuit. Attempts to remedy this problem such as floating the coarse material (plus 425 µm) in a separate circuit have resulted in limited success, but recovery is still not optimum. A fundamental examination of the mechanisms involved in the conditioning of the coarse phosphate has led to results that seem to supersede common paradigms. The Bureau of Mines investigated conditioning parameters such as fatty acid/fuel oil dosage, residual clay content in the feed, conditioning time, mixing intensity, and conditioner solids content. The study revealed that the effect of all these parameters was important. However, it was discovered that contrary to common beliefs, the conditioning time affected the grade of the rougher concentrate much more than the recovery. Specifically, the longer the conditioning time, the less quartz that was floated. It was also discovered that high mixing intensity conditioners could lower the conditioning time required for good grade. Many phosphate operators use low intensity drum type conditioners. Optimizing the conditioning time, mixing intensity, and other conditioning parameters resulted in a rougher concentrate grading 30 pct P.2O5, with an attendant recovery of 95 pct.

Jan 1, 1993

By J. Peck, M. J. Scoble, C. Hendricks

This paper is based on field studies in North American surface mines. The work involved the adaptation of microprocessor-based instrumentation to monitor various operating parameters on-board rotary blasthole drills and mining shovels. Following a review of instrumentation and monitoring methodology - drawing on experience gained under field conditions-the paper will focus on the application of monitoring technology within the framework of an Integrated Equipment Monitoring System. Such a system will permit real-time performance evaluation of key equipment involved in surface mine production. Drill performance monitoring has been demonstrated through work to date, to provide significant input into blast design, reserve estimation, mine planning and production control processes, through an improved facility for ground characterization. Monitoring excavation equipment has been proven valuable in assessing how effectively the input from drill monitored data has been used in the evolution of blast designs. This specifically refers to assessing blast efficiency through measuring associated levels of excavator performance in relation to muckpile characteristics. The medium-term goal of equipment instrumentation and monitoring has been to assist mines in optimizing the overall rock breakage and handling process. Based on the reported results, this has been accomplished. Long-term efforts now concern using a greater understanding of equipment performance and response to varying operating conditions as a foundation for the implementation of mining automation.

Jan 1, 1993

By Peter Sullivan, Johan van Heerden

Increased use of continuous miners and roadheaders in the underground coal mining industry in South Africa has led to improved productivity and efficiency of operations. Of major concern, however, is the increased amount of airborne dust generated during mining. Dust is a health hazard in terms of respiratory diseases, can impede productivity and is the major contributor to the potential of underground explosions. The concern of the South African coal mining industry with regard to the underground dust problem has led to the establishment of a Dust Control Section in the Coal Mining Division of COMRO. In the field of dust suppression system evaluation and design, collaborative work has been undertaken by COMRO and FLOSEP. This paper gives a review of the application of Computational Fluid Dynamics (CFD) in evaluating and improving environmental conditions in continuous miner and roadheader sections. A brief history of the development of the CFD model as well as a discussion of a typical application is included.

Jan 1, 1993

By J. A. Bleeck

A discourse on the relationship between industrial minerals and paper production, concentrating on high grade, ultra fine ground calcium carbonate (mean particle size less than 2 microns) and precipitated calcium carbonate. The scope of the paper encompasses four basic areas relevant to the topic: 1. A tutorial overview of the papermaking process with an examination of various industrial mineral components in that process; 2. A discussion of basic technological topics pertinent to the utilization of carbonate in paper with emphasis on the relative aspect. Of natural ground calcium carbonate (GCC) and synthetic precipitated calcium carbonate (PCC); 3. An overview of paper and carbonate market, in both the United State, and Europe with emphasis on (a) current status and future growth trend. Of such market., and (b) discussion of the major influences on growth and development of such market.; and 4. Identification and discussion regarding the principal producers in calcium carbonate markets serving the paper indu.try in Europe and North America.

Jan 1, 1993

By R. J. Sweigard

Many states are considering the need to establish or modify policy relating to the disposal of coal ash. One of the primary concerns is the impact of leachate from the ash disposal sites upon groundwater and nearby bodies of surface water. A detailed site investigation was conducted at a coal ash disposal facility associated with a power generation station. The disposal site is situated alongside a major river. Monitoring wells were installed and soil samples were taken for characterization. Groundwater models were used to simulate migration of leachate from the disposal site toward the river. Such models have the potential to be used to verify regulatory compliance. This paper addresses the validation and adaptability of these models to this case and their usefulness as possible tools to be used in future environmental audits.

Jan 1, 1993

By Douglas R. Malicoat, Christopher J. Pritchard

Tg Soda Ash operates an underground trona mine located In southwestern Wyoming, which utilizes continuous mining machinery to produce 2.OM tpy (2.2M stpy) by shortwall and room and pillar methods. As the mine developed, the Increasing distance from the shafts caused travel times to be a significant factor in planning for mine emergencies. It was decided to construct a barricade chamber, a modified refuge chamber, to Increase safety and to provide an additional escape option in the case of a mine emergency. Fortunately, there has been no need to use these facilities during the last 9 years, but mine emergency planning has been greatly improved.

Jan 1, 1993

By Jr. Raleigh

As part vi the development of the Coal Quality Expert (CQRN) --a computer program capable of predicting the impacts of coal quality on power plant performance, costs, and emissions control--several nationally important coals are being characterized to augment the coal quality database associated with the software. The project is sponsored by the U.S. Department of Energy and the Electric Power Research Institute (EPRI) under the Clean coal Technology Program. Since 1989, CQ Inc. (a subsidiary of EPRI) has characterized seven bituminous coals from Alabama, Illinois, Kentucky and Oklahoma and six sub-bituminous coals from the Powder River Basin (PRB) in Montana and Wyoming. Coals from the PRB region--being burned more frequently in Midwestern and southern power plants to reduce emissions of sulfur oxide compounds--can sometimes contain significant concentrations of potentially toxic elements. Although no limits were imposed on air toxics emissions from fossil-fuel fired utilities by the Clean Air Act Amendments of 1990, future regulations may be implemented at the conclusion of Federally-mandated emissions studies. One possible result is that any increased utilization of coals, including those from the PRB, may depend on the potential for removing toxic trace elements prior to combustion.

Jan 1, 1993

By LeEtta M. Shaffner, John R. Marks

INTRODUCTION In the last twelve years, underground stoping methods at the Homestake Gold Mine have evolved from open cut-and-fill with jacklegs, cribbed raises and electric slushers to ramp-based mechanized cut-and-fill (MCF) and vertical crater retreat (VCR) with dieselpowered loaders, trucks and drill jumbos. The evolution was swift. Unfortunately, ventilation practices have had trouble keeping pace. Stope ventilation is still too dependent on auxiliary fans and coolers. A single large MCF stope might contain up to eight headings, each of which requires significant ventilation resources when a diesel loader is present. Air is shortcircuited all too frequently through mined-out VCR panels. These factors and the recent rapid decent of the center of mining prompted a study to improve ventilation practices and to more accurately project future requirements. BACKGROUND In 1992, the underground portion of the Homestake Gold Mine produced 8336 kg of gold from 1407 ktons of ore (268,000 oz from 1,551,000 st). The ore is hosted in low to medium grade meta-sediments. Stoping took place from 420 to 2347 m below the surface (1400 to 7700-ft levels). The weighted center of mining was 1662 m deep (5450-ft level) in 1990 and is projected to be 1890 m (6200-ft) in 1993. The deepest level is 2440 m (8000-ft) where the virgin rock temperature (VRT) is 56.1°C (133F). The mine is ventilated by 504 m3/s (1,069,000 cfm) measured at mid-exhaust-circuit density. The air-conditioning system includes an 8.1 MWR (2300 ton) controlled recirculation plant, a 2.0 MWR (580 ton) chilled water plant, a 1.0 MWR (290 ton) exploration drift refrigeration plant, 28 spot-coolers totaling 3.4 MWR (960 tons) and 35 spray coolers totaling 1.5 MWR (420 tons). The mine employs 117 diesel units with a total nameplate rating of 7961 kW (10,672 hp). These units include twenty-four 1.5m3 (2-yd) loaders, twenty-six 2.7m3 (3.5-yd) loaders, fourteen 3.8m3 (5-yd) and two 7.6m3 (10-yd) trucks, and assorted utility vehicles and drill jumbos. THE STUDY In April 1991, the University of Nevada-Reno (Mackay School of Mines) and the South Dakota School of Mines and Technology cooperated with Homestake on an MCF study. Mackay instrumented a stope with thermocouples, air velocity meters and hygrometers (Duckworth, 1992). South Dakota Tech conducted a finite-elements computer analysis of a back-filled MCF stope with/without light-weight shotcrete insulation on the sidewalls and back (Chellam, 1992). Homestake conducted an empirical analysis of deep-level MCF stoping. This paper describes the Homestake study. Twenty-three of the forty MCF stopes deeper than 1800 m were surveyed at least once during the last quarter of 1992. The stopes not included were being cable-bolted or back-filled. Figure 1 shows the complexity of one of the ramp-based stoping areas included in the survey. This particular stope has six separate production headings. A baseline wallrock heat load was derived for each stope or heading from psychrometric calculations. Broken ore, waste rock fill and fissure water were noted when present and the effects included in the baseline heat load. Other heat sources often mentioned in the literature such as metabolic heat from workers, heat from explosives and small electric loads were neglected. Fan heat was considered part of the ramp & crosscut heat load and thus not included in the study. Diesel heat was addressed separately. RESULTS Survey results, plotted as the heat flux against VRT, are shown in Figure 2. The equation for the regression line is: W/m2 = 2.1236*VRT - 75.405 The 0.31 correlation coefficient is poor which implies that the results should be used cautiously. Previous experience strongly suggests that differences in productivity are most likely responsible for the scatter in data points. A rapidly advancing stope will have a

Jan 1, 1993

By Robert J. Wise

The mine plan for an underground longwall mine plan usually requires a longwall panel conveyor that begins operation at its maximum length and gradually shortens over the life of the panel. Current mine plans around the United States require initial panel conveyor lengths of up to 4500 m (15,000 ft) and capacities of up to 3.2 kt/h (3500 stph). Because these conveyors are constantly being moved from panel to panel, their components must be as compact and light as possible, and the design must be flexible enough to be modified as new terrain and conditions are met. In the past, when drive horsepowers or belt tensions were exceeded due to conveyor length, a new flight would be added, including additional belt storage units. In some cases, this led to as many as three flights installed in a single longwall panel. As the longwall retreated through each flight, mining was required to stop during removal of the drives and storage units. This sometimes meant several days of lost production. Intermediate drive technology was developed to eliminate this excessive downtime and still keep conveyor belts, motors, pulleys and other components as small as possible. With intermediate drives placed along the carrying side of the conveyor, belt and motor sizes are kept as small as possible, and only one storage unit is needed. Most importantly, as the longwall retreats through a booster drive station, it can generally be removed in a regular downtime slot and no additional production time is lost.

Jan 1, 1993

By J. E. Murphy, Y. Topkaya, R. E. Johnson, B. R. Palmer, D. K. Dysinger, R. B. Bhappu, A. E. Clark

The U.S. Bureau of Mines utilized a central composite experimental design to investigate leaching kinetics of pure chalcopyrite in the sulfuric acid-oxygen system. The six factors studied were oxygen pressures of 150, 300 and 450 PSI, leach temperatures of 35O, 65O, and 95O C, oxygen-to-chalcopyrite mass ratios of 0.5, 1.0 and 1.5, leach times of 8, 16 and 24 hours, initial acid strengths of 0.6, 1.2 and 1.8 g H,SO,/g chalcopyrite and pyrite to chalcopyrite mass ratios of 0, 1, and 2. Chemical analysis and oxygen consumption measurements indicatedthat leaching occurs through three consecutive reactions. Temperature was the primary determinant of leach rate and solution acidity was the primary determinant of oxygen consumption, sulfur oxidation, and activation energy.

Jan 1, 1993

By P. Holman

I would like to start this paper by looking back about twenty years to see where we have been in the mining industry. We will also look forward a bit and talk about what lies ahead. Here is what has happened to the world economy since the 1970s. Economic growth was strong in the early 70s, but slipped into a recession in the middle of the decade. Then, after a fairly decent recovery recession struck again in the early 80s and since then growth has been rather sporadic. All in all, it has been a real roller coaster ride. There will continue to be plenty of ups and downs in the world economy in the future.

Jan 1, 1993

By F. M. Doyle, K. Osseo-Asare, E. Peters

With the aid of molecular orbital theory, a discussion is presented of the relationship between the electronic structures of ions and molecules, and the elementary steps involved in homogeneous electron transfer reactions. An electronic theory of the reactivity of oxidants and the mechanism of action of oxidation catalysts is then presented, with emphasis on the oxidative decomposition of metal sulfides. For model oxidants, two molecular reagents: O2 and Cl2, and two ionic reagents: Fe3+ and CU2+ were selected; silver (1) was chosen as the model catalyst. The reactivities of these reagents are rationalized in terms of constraints on orbital overlap, the availability of unoccupied d orbitals, and the rearrangement of electronic configurations.

Jan 1, 1993

By William G. Holroyd

In January 1992, the Office of the US Trade Representative announced that the People's Republic of China had agreed to protect US intellectual property, including computer software, sound recordings, agrichemicals and pharmaceuticals. Under the agreement, China will make significant improvements in its patent, copyright and trade-secret laws. Ambassador Carla A. Hills, the US trade representative, said "this agreement should create significant opportunities for US firms interested in marketing high valued-added products to China." Principal beneficiaries will include the agrichemical and computer industries, as well as pharmaceutical, entertainment. The agreement will safeguard these industries' intellectual property, stimulating new exports to China and helping to generate additional growth in the US. Refractory grade bauxite was included in the mineral category of the $1.5 billion of Chinese products on which the US government threatened to impose an immediate 100% trade tariff. Refractory bauxite is available from Guyana and Brazil at higher cost and in different grades. However, refractory brick manufacturers would have had little choice but to pass on the costs to their consumers. Although the United States and China are separated by political ideology and internal governing structures, this agreement recognizes the importance of a $19 billion trading relationship. Consequently, the renewal of China's most favored-nation trading status in the US congress in -June 1992 was all but assured. Many US companies doing business in China and Hong Kong have been quietly increasing their investments since 1989. These companies can now concentrate on developing sales to the domestic Chinese market. This market is expected to surpass 1.2 billion people in 1995 and approach 1.3 billion by the end of the century.

Jan 1, 1993

By R. F. McFarlin, H. E. El-Shall

Since its inception, the Institute of Phosphate Research has examined every promising proposal in order to find an economical, practical and environmentally sound method of dewatering phosphatic clays. The in-house development of the FIPR/DIPR process (DIPR = Dewatering Instantaneously with Pulp Recycle) would appear to answer that quest. When small amounts of fibrous materials are mixed with clay slurries and flocculent, rapid dewatering occurs. Clay solids contents of 20 to 25% can be attained by simply rolling the clay mass down an inclined screen. Higher solids (>40%) are reached by physically pressing the cake; e.g., with a belt press. Because mechanical pressing devices are too expensive for phosphatic clay treatment, FIPR has developed the "sandwich" method of simultaneously dewatering the phosphatic clays and reclaiming the mine cut, as well as a second alternate, the "median strip" proposal. Economic projections of these bench-scale alternates suggest that the FIPR/DIPR process should be no more costly than present practice, when credit is given for the simultaneous reclamation accomplished.

Jan 1, 1993