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By N. D. Policow, J. S. Orphanos

D.A. Dahlstrom In the paper, a comparison was made between flowsheets using the screen bowl centrifuge and disc filters, respectively, as the primary dewatering device. The authors very effectively show that by raising feed temperature, mechanical dewatering is enhanced through reduced viscosity of the water. When a final coal moisture of 10% is required, the net effect of heating the feed is a reduction in thermal requirements because of the lower evaporated load on the dryer. The flowsheet comparison on this, however, was not completely correct. Disc filters do not generally utilize enhanced mechanical dewatering through increased temperature. Horizontal belt filters, through the optimal use of steam heating of the filter cake, have shown significant cost reductions over disc filters where steam is not used. In addition, the authors forgot to mention that there is a certain fraction of the feed that is so fine that it cannot be recovered by the centrifuge economically. That is the function of the filtration device shown in Fig. 4. In subbituminous pipeline coals, this fraction represents more than 10% of the feed. Even after flocculation and belt pressing, the moisture content in the fine fraction is 30%-40. Recent tests on a subbituminous pipeline coal slurry, compared an Eimco-Extractor horizontal belt filter with the screen bowl centrifuge flowsheet shown in Fig. 4. Mechanical dewatering was enhanced through the use of a steam dry zone after the initial dewatering zone. Vacuum pump horsepower was reduced by more than 50% through the use of condensors, and heat recovery was utilized to minimize thermal costs. Thermal drying to 10% moisture by weight was required in both flowsheets. The 0.5 wt% fines in the filtrate were flocculated and recycled to the filter, thus eliminating the belt press and solids mixers. When the three major operating costs (which normally account for 50%-75% of the coal operating costs) of steam, electricity, and flocculants at current prices were calculated, the flowsheets utilizing the Eimco-Extractor had cost savings vs the centrifuge flowsheet of 89¢/t (81o; per st) of surface dry coal. This advantage increases with increasing thermal and electricity prices. I congratulate the authors for the strides made with the screen bowl centrifuge. However, filtration flowsheets continue to be improved and their simplicity and low thermal and electrical requirements should not be so quickly dismissed. ? Reply by N.D. Policow From a technical standpoint, a number of extensive test programs have demonstrated that by raising the feed temperature, mechanical dewatering is enhanced whether it be centrifuges or filters performing the separation. Economic constraints usually become the over-riding issue. If an inexpensive source of thermal energy is available, i.e., waste steam, etc., the approach becomes commercially acceptable. For the specific case of coal slurry pipelines, since the dewatering plants will be located close to power generation stations, the preheating approach becomes especially attractive. The cost comparison shown in Fig. 7, which was prepared by a major West Coast engineering firm, contrasted screen bowl centrifuges and disc filters. In both alternatives, a thermal dryer was specified to produce a contract moisture of the final product. Sizing of the thermal dryer on the screen bowl alternative was substantially smaller than that of the filter, since the screen bowl was credited with a four to six percentage point decrease in product moisture compared to the disc. This comparison was made at ambient temperatures and reflected solely the mechanical dewatering capabilities of the two devices. No preheating of the feed was included in this particular comparison. Early generation screen bowl centrifuges operated under the principle of maximum bulk tonnage throughput. Second and third generation machines have followed the trends dictated by the coal industry calling for higher one-pass recoveries than previously demanded. The current generation of high-speed, long-bowl centrifuges permit recoveries of ultrafine solids directly comparable to commercial filter operation. On typical coal preparation plant feeds with nominal 600 E. an X 0 (28 mesh X 0) clean coal, recovery levels in excess of 99% are now obtained. The material that does escape the centrifuge and reports to the main effluent is typically -10 µm, high ash material. We have documented substantial beneficiation effects in screen bowl centrifuge performance with the cake product containing lower ash levels than the feed. On the referenced pipeline, coal tests performed on Western subbituminous coal, we found that the percentage of -10 µm material in the feed was six to eight times greater than normally encountered on eastern Appalachian seams. Our 45-t/h (50-stph) production centrifuge was never set up to maximize recovery. It was used as part of the two-stage dewatering circuit that had been chosen by designers of the proposed pipeline. Recoveries up to 95% were recorded. With field adjustments, that performance could most certainly have been improved. In contrast, manufacturers of the horizontal belt filter provided a small pilot-scale unit that operated on a side stream at the test facility. Numerous combinations of chemical additions were evaluated to determine those that had the best impact on filter performance. Whereas the screen bowl centrifuges operated without chemical addition, producing a dry, fluffy cake, the belt filter required two stages of chemical addition to attain satisfactory performance and high recovery levels. On the two-stage circuit that incorporated a belt press as the secondary

Jan 12, 1983

By M. K. McCarter

In 1963, a major expansion program at Kennecott's Bingham Canyon mine converted rail operation in the upper portion of the pit to truck haulage. Since that time truck-haulage capacity has increased to about 272 000 Mg (300,000 tons) per day. The majority of this production is waste material which is deposited in monolithic dumps located on the eastern slopes of the Oquirrh Mountains. The largest of these dumps, referred to as Copper Notch and Keystone, measures approximately 1830 m (6000 ft) in length, from 180 to 300 m (600 to 1000 ft) in height, and contains some 430 Tg (470 mil lion tons) of waste. The height, structure, rapid rate of growth, and anticipated leaching suggested the possibility of dump failure. In order to evaluate this possibility, an outside consulting firm was retained in 1966 to investigate the stability of the growing dumps. Their investigation indicated that, other than superficial movement, the waste dumps would be stable under static loading, and that soil distribution was not continuous enough to sustain massive foundation failure. Since this investigation, however, several failure processes have been observed. Crest settlement occurs frequently in response to compaction and over-steepening in the upper portion of the dump surface. Over-steepening results from accumulation of fines near the crest caused by natural segregation. Normally, coarse material, near the base of the dump, exhibits an angle of repose near 0.65 rad (37"). The fine material, however, stands as steep as 0.75 rad (40"). Periodic equilibrium adjustments cause stepwise settlement (Figure 1) of the dump surface and occasional sloughing of the protective berm. Routine surface preparation by dozers and graders and frequent inspections by supervisory personnel have proven adequate in preventing problems associated with this form of crest instability.

Jan 1, 1976

By C. Jardine

The concept of the system is to minimize costly unscheduled breakdowns of equipment by replacing components earlier than their "life" expectancy. Periodic unit services are scheduled according to pre-set constraints. Service sheets are generated by matching a job and component master listing based on assigned cyclic component lives. The system can provide accountability of all man-hours reported and history information can be selectively retrieved. By reducing unscheduled equipment shutdowns, this system allows for better utilization of manpower and an overall improvement in equipment reliability and availability.

Jan 1, 1979

By T. Gollaher

The use of paste thickeners for mineral tailings has gained increasing acceptance by the mining industry throughout the world and in the U.S. during the last five years. Advantages of water recovery and environmental sustainability are the driving forces for paste as an alternative to conventional thickening and the slurry pond. This paper presents a summary of the differences between paste and conventional tailings thickeners, along with recent examples of full-scale paste thickener installations.

Jan 1, 2010

By M. S. Klima

Proper analysis of washability data can lead to the development of a maximum yield coal preparation plant flow sheet. Simulations, as simple as spreadsheet mass and water balancing, are important in examining yield maximization and middlings liberation. Key to such attribute tracking flow sheet simulations is the distribution model, expressing the probability of a species reporting to the product stream. There are many such models in the literature. This paper examines a functional form that can represent or fit most of the proposed distribution functions.

Jan 1, 1997

By Fabrizio Fara

The Ship Canal Water Quality Project (SCWQP) includes a 2.7-mile long, 18'-10" internal diameter tunnel which is located inWest Seattle. Tunneling in urban areas and soft ground conditions (Till and Till-like soils in Seattle) is associated with the risk of settlements, especially in presence of groundwater above the alignment. The Designer foresaw the use of soil improvement (jet grouting) outside of the launch shaft to mitigate the risk of flowing ground and to provide a redundant sealing. The Contractor proposed and ultimately successfully executed a different approach by using a “Steel Bell System” or Pressurized Can as described in this paper.

Jun 13, 2023

By Stanley M. Jarrett

Gentlemen, I am pleased to address this gathering of engineers and operation managers representing a large and important segment of the metal and nonmetallic mining industry. Since you know from the printed program that the theme of my paper is the furthering of safety in open pit mines, perhaps you will have guessed that I will also comment upon the image created in the public mind by the industry's safety record and the potential consequences thereof in national health and safety legislation. Operators of surface mines have some cause to congratulate themselves on the basis of figures issued by the national safety council which show that lost-time accidents per-million-man-hours in surface mining (11.18), is lower than that of all other mining. Moreover, the accident frequency in surface mining is only slightly above the median accident rate for all American industry (8.87). That is a good record.

Jan 1, 1972

By Francesco Chiappalone, Daniele Nebbia, Lance Waddell, Greg Colzani

As part of the 3RPORT Project, a 5-mile tunnel is being excavated underneath the three rivers of Fort Wayne using a 19-foot diameter Slurry Tunnel Boring Machine. The groundwater pressure at the tunnel axis ranges from 4.5 to 5.3 bar. The rock mass hydraulic conductivity is very high with water inflows up to 10,000gpm imposing significant challenges to the project. After excavating 1,550-feet of the TBM tunnel, major leaks between the tailskin and the segmental lining were observed, indicating the potential deterioration of the tailskin brushes and the need for inspection and eventual replacement. The first part of the paper describes the planning of the intervention, including the design of the polyurethane grouting campaign, the procedures developed for the execution and the controls established during construction to timely assess the presence of potential hazards. The second part of the paper focuses on the experience gained during execution and lesson learned to prevent future occurrences of this nature.

Jun 13, 2021

By L. Zhou, D. Bahrami

Mine ventilation is one of the most important aspects of mining operations in underground mines. It is critical to maintain and deliver required fresh air to the active areas to reduce the risk of overexposure to hazardous contaminants or explosive atmospheres. An unexpected or unknown event such as roof collapse, unexpected mine door closure/opening, a fire/explosion, or fan malfunction could adversely alter the airflow distribution within the mine ventilation network that could lead to a hazardous underground environment. Knowing the occurrence and location of such an incident is of critical importance. In this study, the authors developed a novel methodology to assist mine operators in quickly identifying the location of any abnormal airflow change within the network using the airflow changes at monitored airways. The concept is based on a direct derivative method developed by the authors. This paper provides the details of the developed method as well as numerical verification examples. The application of this method can benefit mine operators and safety personnel in making better decisions during a mine emergency response operation to mitigate hazardous conditions arising from an unexpected airflow disturbance

Mar 2, 2022

By Matthew E. Eisenmann, Gerald H. Luttrell

Performance data from phosphate plants are often untrustworthy because of difficulties associated with highly variable feeds and unstable equipment operation. In some cases, this problem is further compounded by improper sampling procedures and unreliable laboratory analyses. Questionable data often lead to misleading conclusions that result in lost productivity and profits. Data reliability may be checked using mass balances, but the mathematics associated with this procedure can be overwhelming when multiple data sets or complex circuits are evaluated. To overcome this problem, a simple spreadsheet-based mass balance program has been developed specifically for plant operators. To use this program, operators simply enter a description of their circuit and input the assay values (e.g., % BPL, % Insol, etc.) for each stream. The program then generates the best estimates of the assay values and flags values that may be unreliable. The spreadsheet is specifically designed to be easy to use and requires no knowledge of statistics or programming. This manuscript reviews the mass balance problem and describes how spreadsheet programs can be used to evaluate plant data. An example problem involving the analysis of data around a two-stage phosphate flotation circuit is presented.

Jan 1, 2002

By R. J. Sheets

In 2009 the Gold Quarry open pit mine, located 11 km northwest of Carlin, Nevada, USA, experienced multiple large-scale slope instabilities of the upper east highwall that reduced gold ore extraction for nearly 18 months. The slope instabilities occurred within a weak, consolidated sedimentary sequence that exhibits strength characteristics that are transitional between soil and rock. Instability initiated as mining exposed the lower clay-rich sub-units of the Carlin Formation (Fm.). This deformation created preferential flow paths that allowed groundwater from the upper sandy sub-units to infiltrate low permeability clay-rich sub-units, thereby enhancing deformation of the slope toe which in turn destabilized the upper portion of the highwall. The outcome was a 160 m high slope instability that had a lateral run-out of 850 m. The effort to return the pit to ore production required both the geotechnical and hydrogeological investigations and the preliminary remediation mining activity to be concurrent. This approach required the development of detailed safety procedures and a requirement to modify the remediation design as new results were obtained. An initial challenge was to mitigate a near vertical, 90 m headscarp with blast induced, localized slope failures. Back-analyses applying numerical modeling indicated that the failure surface did not coincide with initial interpretations based on field observations; drilling results eventually confirmed this alternative failure geometry. The final remediation design incorporated shallower slope geometries and an approximately 3 Mt buttress along the base of the Carlin Formation and bedrock contact to reinforce the lower clay-rich sub-units. The outcome is a stable highwall within the Carlin Fm. following nearly ten years of repeated slope instability, and an example of the necessity to conduct appropriate geotechnical and hydrogeological studies during the early stages of a new layback evaluation or new open pit development.

Feb 23, 2014

By R. Krog, S. Schatzel, H. Dougherty

Longwall coal mine operators in the U.S. are required to ventilate multipanel longwall districts, but may have little or no knowledge about what happens to the ventilation air between the inlet evaluation points (IEPs), bleeder evaluation points (BEPs) and bleeder fans. The effectiveness of bleeder performance can directly influence the ability of a ventilation system to remove and dilute coal bed methane emissions. U.S. coal mining stakeholders have acknowledged their belief that the T-junction split at the longwall face tailgate corner is very important in controlling the distribution of ventilation air. To obtain direct measurements of bleeder performance, a tracer gas, sulfur hexafluoride (SF6), was released into the ventilation air stream on active and inactive longwall panels. Testing was performed on multiple longwall panels that included various phases of longwall development and variable path lengths of ventilation air transport to bleeder fan installations. Changes in the T-junction ventilation air distribution over the life of a longwall panel, and its variable effect on panel ventilation airflow are discussed. These findings will assess the effectiveness of commonly applied ventilation strategies for improving air distribution and ventilation controls to meet statutory requirements.

Jan 1, 2011

By Thomas W. Camm

A WINDOWS-based object-oriented expert system for prefeasibility evaluation of hard rock mines is being developed at the Western Field Operations Center (WFOC) of the Bureau of Mines. Designed for use with the Bureau's Cost Estimating System (CES), this expert system assists an evaluator in choosing an underground mining method, and the related design parameters. The system provides the engineering and design guidelines necessary for an evaluator to perform a prefeasibility type cost estimate.

Jan 1, 1992

By David J. Dyet

Computer applications in the past five to seven years have become a typical and necessary practice in most modern geological offices. Manual calculations, interpretations and plotting of data can be, at times, quite tedious, inefficient and lacking in ac- curacy. The introduction of geostatistical and geological software can eliminate these problems. Computer applications in the uranium industry are not new; however, they are constantly being developed. A variety of soft- ware programs are available. Generally, these programs support most geological and geostatiscal applications in uranium mines. The Rabbit Lake Operation - Eagle Point mine in Northern Saskatchewan is a high grade mine, as one such case. Computer applications at the Eagle Point mine have been a mainstay in the geology department, since the mine's collaring in 1991. This paper presents a discussion on descriptions of programs, operations and applications of computers. It also explains and de- scribes the radiometric equipment used at Eagle Point. This pa- per will demonstrate how, by using computer systems, mine site information flows reliably with the involvement of computers.

Jan 1, 1996

By Frederick McNeill, John Harper, Mahmood Khwaja, Shawn Lavoie, Timothy Cloughert, David Polcari

City of Manchester, NH, is implementing a 20-year plan to control and significantly reduce overflow of its sewer system. The long-term control plan had called for large scale box culvert installation through downtown Manchester. The City and the project team evaluated, and eventually selected, tunneling as an alternative to mitigate construction related impacts for open trench approach. This paper provides an overview of the alternative evaluation process; discusses the development of the preliminary design for the 12,000 feet long, 12-ft internal diameter tunnel, including plan and profile selection, subsurface conditions, drop shafts and the anticipated packaging of the separation areas.

Dec 1, 2022

By Joseph Moses Botbol

The disposition of world mineral resources is such that a vital need exists for both the most efficient development of existing resources and the rapid disclosure of as-yet undiscovered resources. The technological developments described in this report are directed primarily toward the acceleration and increased efficiency of mineral-resource exploration program. In the past decade the use of computers in the mineral industry has grown exponentially. Most computer applications in mineral exploration are designed to be implemented either before or after data collection. Few, if any, computer applications are designed to be used during the collection of data. One major reason for the lack of development of computer applications in this area is that comunications links do not exist between computing systems and the remote areas that host mineral-deposit exploration programs.

Jan 1, 1975

By L. Yuan, R. A. Thomas

"Atmospheric monitoring systems (AMS) have been widely used in underground coal mines in the United States for the detection of fire in the belt entry and the monitoring of other ventilation-related parameters such as airflow velocity and methane concentration in specific mine locations. In addition to an AMS being able to detect a mine fire, the AMS data have the potential to provide fire characteristic information such as fire growth — in terms of heat release rate — and exact fire location. Such information is critical in making decisions regarding firefighting strategies, underground personnel evacuation and optimal escape routes. In this study, a methodology was developed to calculate the fire heat release rate using AMS sensor data for carbon monoxide concentration, carbon dioxide concentration and airflow velocity based on the theory of heat and species transfer in ventilation airflow. Full-scale mine fire experiments were then conducted in the Pittsburgh Mining Research Division’s Safety Research Coal Mine using an AMS with different fire sources. Sensor data collected from the experiments were used to calculate the heat release rates of the fires using this methodology. The calculated heat release rate was compared with the value determined from the mass loss rate of the combustible material using a digital load cell. The experimental results show that the heat release rate of a mine fire can be calculated using AMS sensor data with reasonable accuracy.IntroductionFires at different stages generate different gases and smoke toxicity hazards. When fires occur in underground mines, a significant amount of toxic gases and smoke enter the mine ventilation system and are carried throughout the mine ventilation network, increasing the hazard potential for personnel even if far away from the actual fire. Although fires that develop to the point of rapid flame spread pose imminent hazards, fires in their smoldering, pre-flaming stages can also contaminate the mine atmosphere with debilitating levels of smoke and toxic gases.The most important parameter for evaluating the fire hazard in mines is the heat release rate (HRR), which is directly related to the rate at which heat, smoke and toxic gases are produced and transported by the ventilation system and which provides an indication of the time available for escape or firefighting (Babrauskas and Peacock, 1992). The HRR is also an important input parameter to mine fire simulation models."

Jan 6, 2017

A comparison of gold, platinum and sulfide ion selective electrodes was made in this investigation for determination of Eh in solutions containing sulfide ions as a model system. The comparison was made in terms of the accuracy of the measured response, response time, pH dependence, and reproducibility of measurement. In addition, the sensitivity of each electrode towards changes in sulfide ion concentration was measured in terms of the change in measured Eh per decade change in concentration of sulfide ions. On the basis of a detailed investigation of the electrode processes occurring at the surface of gold and platinum electrodes, it was postulated that within the pH range investigated these electrodes respond to changes in the hydrosulfide ion, HS-, concentration in solution. In comparison, the sulfide ion selective electrode is known to respond to changes in the sulfide ion, S-, activity in solution. Although the potentials measured with gold and platinum electrodes were mixed potentials, pretreatment procedures can be used to obtain a signal suitable for process control. For control of sulfide ions in flotation pulps, the use of a gold electrode pretreated at 1.0 V with respect to a standard hydrogen electrode is recommended.

Jan 1, 1990

By G. A. Gruber

A flotation process has been developed to successfully treat ore from the Santo Domingo phosphate deposit in Baja California Sur. The ore contained less than four percent P205 with quartz, silicates, and carbonates as gangue minerals. Flotation of the low grade feed In sea water required that the conventioinal Crago Process, comprising direct anionic flotation, deolling, and inverse cationic flotation be augmented by an anionic cleaner flotation step, phosphate depression, and a calcite flotation step.

Jan 1, 1986

By Thien Sok, Yaojun Lu, Craig Gilbert, Jeremy Scott

Feedwells play a pivotal role in gravity thickeners, governing flow distribution, feed dilution, and flocculation condition during solid–liquid separation. This study presents an optimized design and digital prototyping framework for FLSmidth’s E-volute and E-Duc Feedwell systems, integrating advanced computational fluid dynamics (CFD) with quantitative criteria introduced at SME2024. Building on established FLS technologies, a series of novel configurations were developed and systematically assessed under full-scale and site-specific conditions. CFD provided quantitative insight into flow distribution, feed dilution, and flocculation efficiency, enabling iterative refinement of design parameters. The optimized feedwell demonstrated superior hydraulic performance, enhanced mixing, and improved flocculation outcomes. Beyond the specific design advances, the work highlights CFD as an effective and economical tool for digital prototyping, facilitating early identification of design limitations, reducing dependence on physical trials, and accelerating innovation. The methodology underscores the value of simulation-driven design in advancing feedwell performance and improving thickener technology.

Feb 22, 2026