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By L. Alagha, O. Molatlhegi, S. Khatibi

"In the present study, the effect of organic/inorganic (hybrid) polyacrylamide polymer on fine coal flotation was investigated. Raw coal samples contain about 37% of ash-forming mineral at a feed size of -75 + 38 um were subjected to flotation tests in the presence of in-house synthesized hybrid Al(OH)3-PAM at different polymer dosages and pH values. Results show a significant improvement in both combustible recovery and ash rejection at 1 ppm polymer dosage. Further improvement of combustible recovery was obtained when flotation was performed at pH 5. Interfacial properties of coal particles before and after flotation were examined through electrokinetic (zeta potential) measurements of coal/water slurries. Zeta potential vs. pH curve were established and compared. In the case of raw coal/water slurry, zeta potential-pH curve resembles the ash-forming minerals (silica and clays) more than coal. After Al(OH)3-PAM-assisted flotation, the zeta potential of froth/water slurry shifted to more positive values point which strongly indicates significant removal of ash-forming minerals from coal by Al(OH)3-PAM. INTRODUCTION Coal has been a major commodity in meeting the world energy demand during the past several decades (Milici et al., 2013). According to the international energy agency, global coal demand will continue to increase for the coming decades. With increasing world population, the global electricity demand would also increase as more people would get access to basic electricity especially in developing countries (Maggio & Cacciola, 2012). Due to this increase in energy consumption, operations in coal mining and beneficiation processes have been highly mechanized to meet the demands. This mechanization has increased the quantity of raw fine coal particles produced which contain high amount of ash-forming mineral matter (slimes). Aplan et al., have reported that the major constituents of ash-forming minerals in U.S.A coal are clay minerals such as kaolinite, montmorillonite and illite (Aplan, 1997). Conventional froth flotation for fine coal cleaning suffers mainly from two major problems: 1) Low recovery of ultrafine coal particles due to slime coating by ash-forming minerals, and 2) The lack of selectivity, which results in the flotation of middlings and entrainment of mineral fines in the froth (Polat et al., 2003). Slime coating on both valuable and air bubbles have been proposed to explain the observed reduction in flotation recovery especially when fine grinding is required. In this case mineral matter may be degraded to extremely fine or colloidal sizes thereby creating difficulty in the water clarification process such as flotation. Slimes inhibit bubble-particle attachment, and increases reagent consumption due to the increase in solid/liquid interfacial area, resulting in low coal recovery."

Jan 1, 2015

By B. M. Davis

Frequently ore reserve studies utilize samples from a series of drilling or other types of sampling campaigns. Sometimes there is a mix of sample types, say for instance, channel samples from underground workings and drill core from surface drilling. Since drilling, sampling, logging, and sample preparation protocols tend to change over time, there is always a question whether the samples give similar results that vary only by chance alone. The problem of comparing the various campaigns is complicated by the presence of spatial relationships among the samples. Geostatistical tests take the spatial correlation into account, but these tests may be complicated and cumbersome to implement. A comparison method based on familiar statistical graphics is presented which accounts for the spatial relationships. It allows comparisons to be made quickly by using simple statistical graphs such as scatterplots and boxplots.

Jan 1, 1996

By Remo Grandori

"INTRODUCTIONDouble Shield TBMs were introduced in the market in the early seventies with three main targets:• Increase the TBM performances in term of advance per day thanks to the ability to erect a segmental lining simultaneously with the excavation phase.• Be able to advance through unstable and disturbed rocks under the protection of the shields• Provide a finished tunnel by installing a precast lining as the TBM advance.In 2003 SELI developed the design of the Double Shield Universal (DSU) TBM as an evolution of the original Double Shield TBM design.This new TBM design was targeted to improve: the TBM capability to advance through squeezing/converging rock formations under high cover, the telescopic joint design (allowing by such to operate the machine in double shield mode in very weak rock), the capability of the TBM to investigate and treat the ground around and ahead of the tunnel face.In the same lapse of time Single Shield TBMs, originally utilized for soft ground tunnelling, extended progressively their range of application to mix rocks and finally to hard rock tunnelling with increasing performances.This also thanks to the substantial reduction in the installation time of the segmental lining ring that contributed to minimize the TBM stand by time between two consecutive boring strokes.Today the choice between the two types of TBMs needs to be carefully evaluated project by project since one type of TBM may “prevail” in certain geologies and diameters and vice versa.THE VISHNUGAD PIPALKOTI TUNNELThe Vishnugad Pipalkoti Tunnel is part of the 444 MW Vishnugad Pipalkoti Hydro Electric Project (VPHEP) on Alaknanda river in Uttarakhand (India).The Owner is the Indian electric company “Tehry Hydro Development Corporation” (THDC) and the World Bank finances the project.The Headrace Tunnel total length is 13.4 Km and a section of about 12,3km will be excavated by TBM by SELI Overseas (Italy) in subcontract to HCC (India) the General Contractor for the project. The TBM will be delivered ex workshop in March 2016 and it is foreseen to start boring in the second half of 2016.Figure 1 below shows the location of the project and the following Table 1 summarizes the geometrical characteristics of the TBM tunnel."

Jan 1, 2016

The recent mine disasters in Australian coal mines have initiated an introduction of Self-Contained Self-Rescuer (SCSR) as component in the development of new escape strategies for miners. These self-contained self-rescuers are closed circuit, demand sensitive breathing apparatus that make oxygen available to the wearer for a nominal period of time. Their operation is completely independent of the surrounding atmosphere. Once properly donned, the SCSR can assist a miner to escape from an area containing smoke, toxic gases or an oxygen deficient atmosphere. The duration of a typical SCSR is usually taken at the point of complete collapse of the breathing bag which is accompanied by an increase in breathing resistance and inhaled levels of carbon dioxide. Because the oxygen consumption (V02) and the heart rate are correlated, a prediction of V02 and consequently the duration of an SCSR can be made by monitoring the heart rate. Thirty-seven volunteers participated in field simulated escape trials at four underground coal mines. The results from the field trials suggested that oxygen consumption depends on the heart rate, the body weight and exercise rating of the miner. All the volunteers were asked to fill out the questionnaires to evaluate the performance of the units. The miners indicated that they could tolerate the inhaled temperature without any difficulty to breathing resistance. A complete statistical analysis of the field results is also presented.

Jan 1, 1997

By J. F. T. Agapito

Two flat-lying trona seams 3-to 3.5-m thick, approximately 10 m apart, and at depths of 250 m are mined by room-and-pillar at OCI's Big Island Mine in Wyoming. Continuous miners and a yielding pillar system have contributed to improvements in resource recovery and productivity. Long-term stability with minimal subsidence is needed for a large portion of the mine beneath the Green River channel. This was investigated by computer modeling in 1990. Although results of the study indicated good long-term stability, recommendations were made for stress determinations to verify the model. Stress determinations made in 1997 showed pillar stresses 10% to 20% higher than the model stresses, and barrier pillar stresses 10% to 15% lower. This implies that higher panel stresses will be transmitted from the upper to the lower seam. A stability evaluation of the lower seam is planned before two-seam mining to assess entry widths and support requirements.

Jan 1, 1999

Coal has traditionally been an integral part of life in Kentucky. Coal mining produces a large part of revenue for the Commonwealth of Kentucky and provides a significant number of jobs to the residents of eastern (less in western) Kentucky. Recently, however, the coal industry of Kentucky has had to endure many hardships. The Clean Air Act set forth sulfur dioxide emission standards which have severely affected much of the coal mining industry in Kentucky, because much of the coal mined in Kentucky has a high sulfur content. In this paper, the background around the effects of Clean Air Act on the coal industry is introduced. The economic and social effects of the Clean Air Act on the Kentucky coal mining are addressed.

Jan 1, 1993

By E. E. Maurer

Kerr-McGee has operated the Ambrosia Lake uranium mill since startup in 1958. Tonnage milled per day has varied from 3500-7000 tons. The mill capacity is currently rated at 7000 tons per day. The process consists of two parallel circuits following crushing and sampling, \\lhich include open circuit rod mill grinding, sulfuric acid leach, cyclone classification, and counter-current washing circuits of sand classifiers and slime thickeners. Pregnant solution is clarified and polished by precoat pressure leaf filters prior to amine solvent extraction. Yellowcake is precipitated from the pregnant strip solution with ammonia, filtered and dried.

Jan 1, 1972

By Richard H. Oitto

With increased interest and urgency for coal mine safety and the passage of the Federal Coal Mine Health 'and Safety Act, the Bureau's research effort in roof control has been greatly expanded. One new project, the subject of this paper, concerns improving conventional roof bolting and has been involved with the effects of different variables on the performance of roof bolt expansion anchors. These include types of expansion anchor, rock type at the anchorage horizon, borehole roughness, rate of torquing a roof bolt to set the anchor, installed tension, bolt length, and relative humidity fluctuations. For this work, two types of experiments were carried out. One was concerned with tension loss in bolt-anchor assemblies and simulated anchor performance in a static roof. The other dealt with anchor slippage as tension was increased and simulated anchor performance in an active roof. Trials were made in the laboratory under controlled conditions so that factors suspected of affecting expansion anchor performance could be selectively studied. Because of the natural variability in rock and the fact that most expansion anchor components are essentially rough castings or forgings, the experiments were designed to permit using analysis of variance techniques for analyzing data. Thus, in this paper, "significant" means statistically significant.

Jan 1, 1972

By J. Wiedenroth

Since the end of the 1970s Pipe Conveyors have become increasingly important for conveying bulk materials because they have some specific advantages over conventional troughed belt conveyors. FLSmidth KOCH Pipe Conveyor represent the marked-leading know how of the former KOCH Transporttechnik GmbH, which belongs to the FLSmidth Group since January 2007. Pipe Conveyors from FLSmidth KOCH are already being used successfully at more than 260 locations around the world. Their special properties, their extreme flexibility, the horizontal and vertical changes in direction without transfer points, the small space requirement, the low-noise running and their optimum protection of environment and material without any additional casing mean that Pipe Conveyors can provide transport solutions that are often far superior to other conveying systems. The utilization of these many advantages will be illustrated in the following example of the world?s longest Pipe Conveyor at Cementos Lima, the Peruvian cement producer.

Jan 1, 2010

By T. McCallum, C. Cooper, C. Lewis

"Following a successful solvent extraction (SX) pilot plant demonstration in 2016, CYANEX® 600 has been used commercially to recover molybdenum from concentrate leach liquor since March 2017. Consistent with the piloting results, the commercial plant has achieved expected molybdenum recovery, a significant reduction in base consumption, and a step-change improvement in physical performance. This paper highlights the optimization activities and plant performance from startup through normal operation. INTRODUCTION Historically, tertiary amines have been the most commonly used extractant for molybdenum and rhenium recovery. Tertiary amines utilize a protonation of the ligand combined with an anion exchange mechanism as proposed in equations (1-2). R3N + H+ ???R3NH + (1) 4R3NH+ + Mo8O264- ???(R3NH+)4Mo8O264- (2) In addition to the transfer of Mo and Re, the amine transfers acid and other anions to the strip liquor. The undesirable transfer of other species increases base consumption during stripping, impacting operating costs. Additionally, lower solubility of molybdenum-amine complexes create operational challenges, resulting in diminished physical performance. The presence of colloidal Si in concentrate leach liquors and the formation of Pickering Emulsions adds to the physical plant performance challenges with the amine extractant. CYANEX® 600, a phosphinic acid-based extractant, uses a cation exchange mechanism proposed by equation (3). 2(H2R2) + MoO22+ ??(HR2)2MoO2 + 2H+ (3) The cationic exchange mechanism eliminates chemical transfer of acid and other anionic impurities and avoids some of the physical challenges of the amine extractant (emulsion and 3rd phase formation). In addition, the reagent offers high selectivity for Mo over Re, which may be desirable in certain moly pressure oxidation (POX) flowsheets. Alkali base (ammonium hydroxide, sodium hydroxide, sodium carbonate, etc.) is used for molybdenum stripping. Therefore, reduction or elimination of chemical acid transfer from extract can significantly reduce base consumption in strip. Extensive laboratory and pilot plant testing was completed to evaluate the use of CYANEX® 600 for molybdenum recovery at Freeport-McMoRan’s Bagdad operation. The test work and pilot demonstration confirmed a reduction in base consumption along with improved selectivity. In addition, the evaluation highlighted a step-change improvement in physical performance over the incumbent amine extractant. The decision was made to convert the commercial operation to CYANEX® 600 in March 2017."

Jan 1, 2018

By C. F. Johnson

Nearly all of the sulphur produced in the world today is converted to sulphuric acid and 49 % is used in the manufacture of fertilizers. In the last few years we have seen the beginning of another chapter in the volatile history of sulphur as the severe shortage of 1963:-67 has been transformed into present-day surplus. Prospects for further aggravation of this situation in the years ahead seem assured. In 1970, western world production showed a rate of increase of 4 -5%, which 1S somewhat less than that of 8% for the period 1963-1967. The rate of growth of consumption dropped considerably in 1968 when the demands of the fertilizer industry fell. During the same period of time, wide-spread demands have been set in motion for a clean environment which indicates that a fundamental change in sulphur supply, demand, and even sources, is likely to result from this upheaval. The sale of sulphur by Poland to the western world has increased and for 1970 was estimated at over one million metric tons. In the next few years, increase in Canadian sulphur supply will stern from two sources;

Jan 1, 1972

By Ted H. Eyde

Nearly 17 years ago a major producer of synthetic zeolites started an extensive exploration program for natural zeolite deposits which resulted in the discovery of over 170 occurrences in the western United States. A few years later several of the other producers and consumers of synthetic zeolites also started similar exploration programs. Since then, small quantities of natural zeolite minerals have been produced from at least 12 deposits in the United States. Of these the Bowie deposit, about 13 miles north of Bowie, Arizona, is the most important,having produced over 5,000 tons of vitric tuff zeolitically altered to the mineral chabazite and minor amounts of the minerals erionite and clinoptilolite. Mining Districts and Mineral Deposits of Arizona compiled by Charles A. Mardirosian, Consulting Geologist, estimates the value of the total production from the Bowie deposit at a very conservative $2,000,000. Unfortunately, none of the companies responsible for the discovery and the initial production of natural zeolites made any effort to develop the high volume, low cost applications of this unique mineral raw material. Instead, they developed only the high unit value uses to supplement their existing synthetic molecular sieve product lines. With the producers of synthetic zeolites thinking in pounds and not in tons, further development of natural zeolite deposits stagnated for over a decade.

Jan 1, 1974

By T. S. Golosinski

Use of contractors to excavate, load and haul mined material is widespread in Australia. It is also becoming a common practice in many other countries. The paper reviews current practices in Australian contract mining. Various types of contracts are reviewed, including partnering arrangements and alliancing between the contractor and the mine owner. Applicability of various types of contracts to specific mining situations is discussed, as is their impact on overall mine performance

Jan 1, 1998

By D. S. Bird

The Kennecott Utah Copper Modernization Project, initiated in 1986, was directed to provide an expansion and modernization of mining and process facilities at the property's Bingham Canyon Mine and ore concentrators. Major components in the project included installation of an in-pit ore crusher, transfer conveying system, and construction of a new copper ore concentrator with a design capacity basis of 70,000 tonnes/day. The Copperton Concentrator was commissioned in February 1988. A principal feature of the plant is the grinding circuit, comprised of three identical lines, each consisting of a 10.37 m (diameter) by 4.57 m (length) Semi-Autogenous Grinding (SAG) mill and two 5.54 m (diameter) by 8.62 m (length) ball mills. The SAG mills are driven by two variable-speed 9,000 kW DC motors coupled through a clutch-pinion gear-ring gear assembly. The ball mills are driven by 4,125 kW synchronous motors coupled through a typical clutch-pinion gear-ring gear system. The expansion and particularly the Copperton Concentrator performance was so successful that by early 1989, management began examining options to further expand production capacity. With regards to the concentrator, numerous alternatives were considered, ranging from installation of a grinding line similar to one of the existing lines, to a "super" line consisting of a 12.8 meter (diameter) SAG mill and a 20,000 kW motor with a capacity of 50,000 tonnes per day. The technical and economic analysis of the various scenarios indicated that one "large" 11.0 meter (diameter) by 4.88 meter (length) SAG mill with a production capacity of 32,000 tonnes per day and a 12,000 kW drive would be optimum. The key question to be answered in the project was whether to continue with the pinion-ring gear combination, or install a gearless drive. The following paper outlines many of the items that were evaluated in the mill selection process followed by actual plant performance, and a discussion of ongoing plant continuous improvement projects.

Jan 1, 1995

By James J. Scott

Longwall mining has not received a great deal of attention in the United States; however, this system offers many advantages over the conventional room-and-pillar methods now being used. In order to conserve the coal resources of this country, the U. S. Bureau of Mines has investi¬gated the feasibility of adapting European longwall mining methods to American coal seams. Their studies showed longwall mining to be well suited to thinner seams and, greater depths; and, in addition, permitted almost 100 percent recovery of the coal. Most, experiments with this method resulted in higher overall production-costs than were commonly obtained with highly mechanized room-and-pillar techniques This high cost-was largely due to the excessive amount of labor required to maintain adequate roof support with conventional longwall mining techniques. With the substitution of hydraulic-powered, self-advancing roof support systems for conventional supports, this excessive labor cost has been decreased, and longwall mining costs are now competitive with those of modern room-and-pillar mining.

Jan 1, 1964

By E. W. Geist

This paper is presented from the viewpoint of the mill operator and maintenance supervisor. Its purpose is to highlight the things that have been accomplished by the mill designers to lighten the load for the maintenance superintendent and to reduce the overall costs for the plant operator. The complexity of plant design, the civil and structural engineering problems encountered when the satisfactory maintenance layout is accomplished are appreciated, and the writer is fully aware of the complexities of these problems. However, it is not the purpose of this particular paper to dwell upon these problems, nor to emphasize or de-emphasize the problems of the civil, mechanical and electrical engineers. It is simply that the paper will attempt to review what these people have accomplished in spite of the many technical problems. This paper then is prepared with the operator and maintenance people?s viewpoint. What is their definition of design for maintenance? It is the writer's interpretation that the various design concepts which mean improved maintenance are such items as (I) maintenance areas, (2) laydown space for maintenance materials in specific maintenance jobs, (3) the inclusion of bridge cranes in the plant and specific design of the craneways to accomplish flexibilities for the cranes, and (4) the location of the piece of equipment to allow maintenance people to work around the equipment - - - this specifically includes the orientation of the particular piece of equipment.

Jan 1, 1967

By J.N. Kohmuench

Teeter-bed (i.e., hindered-bed) separators are used throughout the mineral processing industry for both classification and density separation. The high capacity and sizing characteristics of these units make them ideal for feed preparation prior to coarse flotation (+0.100 mm) circuits. Teeter-bed separators are typically easy to control with two basic operating parameters, including fluidization water rate and bed level. However, data show that these two parameters greatly interact with one another. Given this finding, a high-level automatic control scheme was developed and implemented on a full-scale separator. In addition, dialogue with plant operators has led to several simple changes to an already established design that improves operational and maintenance characteristics.

Jan 1, 2010

By Michael A. Trevits

A mine fire represents one of the most dangerous and challenging safety issues facing underground mine operators. Given the right circumstances, a mine fire can occur at any location in the active or abandoned mine workings, can quickly grow beyond control, and threaten the welfare and livelihood of the entire underground workforce. The National Institute for Occupational Safety and Health (NIOSH), in partnership with the Mine Safety and Health Administration (MSHA), has been conducting an in-depth program of research addressing mine fire prevention, early and reliable fire detection, and mine fire suppression technologies. One portion of this program is focused on understanding the characteristics of mine fire combustion products and flame spread through large scale deep-seated (firmly established) fire tests and use of computational fluid dynamics (CFD) modeling. In this study, two deep-seated fire tests were conducted; one fire consisted of coal material and the other utilized the two most abundant fuel sources found in a coal mine: coal and wooden cribbing blocks. The fires were burned to completion while the combustion products were collected and analyzed. In addition, an array of thermocouples was placed within the body of the material to measure flame spread rate. The coal fire test information was then used to develop a CFD model of the fire. This paper describes the fire tests, provides insight into characteristics of flame spread, and presents the CFD modeling work results.

Jan 1, 2009

By A. K. Bakshi

Slurry rheology affects autogenous grinding performance by changing the rock's breakage characteristics. In this study pilot scale batch autogenous grinding was carried out to observe the effect of viscosity on the breakage characteristics of the rocks (the media), and on the overall specific energy consumption. Clay/fines content, and temperature of the initial charge, were varied to alter the viscosity of the slurry. Results showed that at higher slurry viscosity, rocks became more difficult to break, resulting in an overall increase in the specific energy consumption of the mill. Also, it was observed that viscosity had a significant effect on the amount of critical size material present in the grinding circuit, where the critical size material is the material which is too large to be effectively ground in the mill, and too fine to act as grinding media.

Jan 1, 1996

By P. R. Taylor

The ability to treat refractory gold concentrates that contain appreciable amounts of sulfur and arsenic, in an economic and environmentally safe manner is important to the gold mining industry. Processing alternatives include: autoclave oxidation, bacterial oxidation and roasting. Roasting may be the cheapest of all the alternatives if inexpensive methods can be found to contain the arsenic and sulfur. The research program, being reported here, has been evaluating the ability to use hydrated lime in the roaster to capture both the arsenic and the sulfur. Lime roasting is not a new idea, it was proposed for copper ores by Bartlett in the early 1970's (Bartlett and Haung 1973) and for cobaltite concentrates by Taylor in the early 1980's (Taylor et al., 1981). In addition, ores have been roasted that contained limestone and it was shown that partial capture of the sulfur was possible. Lime -sulfur containment has been proposed for the coal fired electricity industry, as well.

Jan 1, 1992