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By Carl Erickson, James Hislop

INTRODUCTION As practiced today, longwall mining is a mechanical version of an established mining system. The equipment for longwall mining consists of four basic units: roof supports, face conveyor, winning or mineral-getting ma¬chine, and stage-loader conveyor. The system mines relatively thin slices of mineral across a predetermined face length in a virtually continuous sequence. As the winning machine cuts, the mineral is loaded automatically onto the face conveyor. In turn, the face conveyor is pushed over into the newly cut track by hydraulic rams attached to the conveyor and the roof supports. The roof supports then are lowered individu¬ally from the roof, advanced to the repositioned con¬veyor, and reset to the roof. At the end of the pass, the longwall cutter is pushed over, and a slice is taken in the opposite direction, so the system repeats itself. Fig. I illustrates a typical longwall mining system. The principle behind the longwall mining system is that the roof is supported only immediately adjacent to the worked seam, keeping the blocks of immediate roof clamped securely from the face to the rear of the sup¬ports. At the rear of the supports, the roof is allowed to fall and break up, with the swell of the broken material eventually establishing an equilibrium in the strata be¬hind the mined area. Fig. 2 illustrates the principle of longwall support. There are two distinct types of longwall mining. The longwall retreating system is the most common in the United States, South Africa, and Australia. The longwall advancing system is the most common in the re¬maining industrialized countries such as Britain, Ger¬many, Poland, and the Soviet Union. The longwall retreating system comprises a mining panel, where the roadways that form the head entry (end at which mineral is delivered from the face con¬veyor to a stage-loader conveyor) and the tail entry are predriven before the longwall units starts production. In the longwall advancing system, the longwall unit makes the head and tail entries as the face advances, utilizing various techniques to prevent the entries from being destroyed as they are left in a consolidating gob area. Fig. 3 illustrates the comparative approaches of the longwall retreating and advancing operations. As with most other underground mining systems, there are many variations on these two basic systems, using combinations of the systems that are dictated by

Jan 1, 1982

By Keith A. Heasley

At this point in time, approximately 800 M tonnes (880 M tons) of coal are mined each year in the United States. Forty percent of this coal or approximately 320 M tonnes (350 M tons) is taken from underground coal mines, and from this subtotal 16% or 50 M tonnes (55 M tons) is from longwall panels (1). If, for the sake of argument, an aver- age extraction thickness of 1.5 m (5 ft), an aver- age extraction ratio of 50 percent and an in situ density of 1360 kg/ms (85 lb/ft3) for this coal are assumed, then the 320 M tonnes (350 M tons) of underground coal translates to over 310 km2 (76,000 acres) that is undermined each year. Con- sidering that the total U.S. production of under- ground longwall coal to date is approximately 345 M tonnes (380 M tons), then a total of approximately 165 km2 (41,000 acres) (considering 100% extraction) has been directly undermined by longwall coal production in the United States. If the angle-of- draw is considered, the total area affected by longwall subsidence in the United States is probably twice the above value or 330 km2 (82,000 acres) . In the future, a number of other miscellaneous factors seem likely to multiply the number of potentially damaging situations that occur due to longwall coal mining. First, the overall production of coal in the United States is expected to gradually increase. This factor is further com- pounded by both the fact that the percentage of the overall production due to underground mining is bound to increase, since the vast majority of U.S. reserves (68%) are only recoverable by underground methods, and the fact that the percentage of the underground production of coal that is recovered by longwall mining is drastically increasing (1). Finally, as the nicest underground reserves are depleted, the remaining reserves will tend to be deeper, which increases the affected surface area, and under denser population concentrations, which increases the likelihood and severity of possible damages. Overall, considering the number of factor which are biased towards increasing the amount of undermined acreage, it appears that there must certainly be a corresponding increase in the number of possible damaging situations due to longwall-induced, ground subsidence.

Jan 1, 1986

China’s vibrant economic growth is built on coal, the source of two thirds of the country’s electricity. Over 95 percent of China’s coal is mined underground with the average mining depth at 410 m and in-creasing at 10 m per year; today, the deepest Chinese coal mines have exceeded 1,000 m. With increasing mining depths, there are greater challenges including increased methane emissions and spontaneous combustion. According to the government, nearly half of China’s coal mines are classified as gassy (with specific gas content at least 10 m3/mt). Coalbed methane (CBM) is a clean energy source. However, only a small percentage of the methane is captured, and the rest is vented directly to the atmosphere. This paper describes China’s CBM resource, its production and utilization.

Jan 1, 2006

By J. M. Mutmansky, Y. J. Wang

The usual method employed to determine the direction of flow in a connecting airway in advance is to conduct a survey between the two existing nodes being connected by means of the new airway. It is then assumed that airflow will take place from the node with higher pressure to the node with lower pressure. The purpose of this paper is to examine this direction-of-flow problem -- using properties of the system characteristic curve for a two-terminal network -- and specify some conditions that ensure that flow will take from the higher-pressure node to the lower-pressure node. It is concluded that the only requirement is that all characteristic curves of fans in the network should be strictly decreasing. Five numerical examples illustrate some important properties of the direction-of-flow problem.

Jan 1, 1999

By X. M. Yuan

In the flotation of Zn-Pb ores, sphalerite is floated following copper sulfide activation. In this type of sulfide ore, pyrite is commonly treated as a gangue, and poor selectivity between sphalerite and pyrite/quartz is often reported. But pyrite may also appear in association with gold, and flotation of such auriferous sulfides is of great importance in many countries (e.g. South Africa, Australia). In the cationic flotation of sulfide ores with dodecyl amine, sphalerite can be floated while depressing quartz and pyrite. While in a well-aerated pulp in the presence of lime (especially after oxidation with H2O2) the cationic flotation of pyrite is depressed, oxidation of pyrite in the presence of Na2S makes it floatable with amines even in very alkaline environment.

Jan 1, 2002

By Erich U. Petersen, J. B. Hiskey, William J. Tafuri, Donald M. Hausen, X. H. Jiang, Douglas N. Halbe, G. Ramadorai

The extraction of gold from chloride solutions with activated carbon is examined. It is shown that the uptake of gold by activated carbon from chloride solution follows a mechanism whereby gold is reduced to the metallic state. Metallic gold appears as deposits both on the carbon surface and in pore space within the carbon particle. The deposition rate is dependant on the carbon particle size and pH. At low initial gold concentrations, the initial rate is insensitive to gold concentration. Sodium hypochlorite exhibits an adverse effect on the reduction reaction. The overall loading and initial rate of reduction are both decreased in the presence of NaC10. The effect of iodide on the loading of gold was also examined in an attempt to overcome the superficial deposition of gold on carbon.

Jan 1, 1990

The molecular form of aliphatic amines precipitates in alkaline solutions when the amine solubility limit is exceeded and forms a typical colloidal system. The zones of mines precipitation and micellization are defined and it is shown that the appearance of a colloidal system in a certain pH range is a unique feature that makes weak electrolyte type surfactants differ from strong electrolytes. The formation of iono-molecular complexes reported in the literature is shown to be a pre-precipitation phenomenon. The zeta potential - pH curves for minerals and bubbles in the presence of amines in the pH range where the amine forms a colloidal precipitate are entirely determined by the precipitate. The pH dependence of the flotation of certain minerals using amines is discussed in the light of these findings.

Jan 1, 1989

By William J. Douglas

Defining Productivity Productivity is a principal concern to all organizations - industrial, commercial, government, and academic. As a ratio of output to input, productivity measures the efficiency of an industrial process, much as thermodynamic efficiency measures the useful work obtained from the available energy consumed. However, there is one important difference. Whereas thermodynamic efficiency is a dimensionless a ratio of energies, productivity output and input are usually measured in different physical units. Nevertheless, the resulting ratio is a normalized expression for unit of output per unit of input to the process. In the early days of coal, mining was essentially a hand loading operation. There was little expenditure of alternative forms of energy within the process. Loading required expenditures of human energy on the order of 1.2 MJ/t (1,000 Btu per st). And if we accept the conventional value "you load 16 tons," the output to input ratio is 14.5 t (16 st) per manshift. In energy terms, it is on the order of 116 MJ/t (100,000 Btu per st) produced per labor Btu expended. However, the latter measure of efficiency was not meaningful in economic terms, while the 14.5 t (16 st) per manshift was significant. Since labor was the principal component of cost, it represented a direct relationship to the cost of production: [ ] Furthermore, when workers were paid directly on the basis of tons produced, the labor cost per ton was specified directly by this rate. With the introduction of mechanized loading, significant increases in productivity occurred, when measured on the basis of tons per manshift. Electric power consumed about 11.6-116 MJ/t (10,000-100,000 Btu per st). This makes the 29-GJ/t (25 million Btu per st) coal output/input ratio between 100 and 1,000. That is one or two orders of magnitude lower than hand loading. However, electric energy was quite inexpensive compared to labor, which made the mechanization economically efficient. The accepted productivity measure continued to be tons per manshift. This measure includes some of the effects of mechanization: namely, the additional manpower needed to maintain the machines and support the equipment that uses electrical energy. However, it does not consider the capital and operating costs that relate to mechanized equipment. As a result, the concept of tons per machine-shift has emerged as an accepted measure of shift productivity. The only appropriate measure that encorporates the productivity of men and machines is an economic one. The output is the tonnage per shift and the impact is the cost per shift. [ ] This is simply the inverse of the cost per ton. In addition, much flexibility is available in allo¬cating costs to the three categories. This adds a level of intangibility to the measure. The amount of information needed to obtain all of the required costs is appreciable compared to the simple matter of counting tons and workers. Furthermore, financial information relating to production costs is closely held by mining companies, so historical statistics on economic productivity are not publicly available. To extend the concept further, consider the value of the tonnage produced, to obtain a dimensionless ($/$) measure of economic productivity.

Jan 11, 1983

By D. D. Carda, S. Dunn, W. E. Dunn, T. Storbeck

Gold chlorination which will be presented in this paper is limited entirely to the use of gaseous chlorine in a fluidized bed reactor at elevated temperatures in the absence of aqueous water. The only water used in this process is that which is used in scrubbing the effluents. Low temperatures are defined as those below 500°C. All experimentation for this paper was carried out on a laboratory scale, with all calculations extrapolated frpm this. Some of the data is drawn from work with other projects which have been operated at pilot and larger scale.

Jan 1, 1998

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

3.1 INTRODUCTION The final subsidence basin discussed so far is that developed long after mining has stopped. In a supercritical final subsidence basin, the central portion subsides uniformly. Thus any structures located there are not subjected to any final permanent surface deformation. But this statement is only true for the final subsidence basin. When the face is moving, the structures are subjected to dynamic deformations associated with the dynamic subsidence basin. For instance the house in front of a moving face (location 1 in Fig. 3.1) is subjected to the maximum tensile strain and the maximum positive curvahue. When it falls behind the face in location 2, it is subjected to the maximum compressive strain and the maximum negative curvature. When the house is far behind the face in location 3, it returns to its original condition with only uniform subsidence. However, the magnitude of the dynamic deformations may be sufficiently large to damage a structure in locations 1 and 2 before it reaches location 3. Therefore it is very important to study the characteristics of the dynamic subsidence basin. Under normal conditions, when the face has advanced for a distance approximately one-sixth to one-third of the seam depth from the setup entry, depending on the seam depth and the physical properties of the overburden strata, the movement of the over- burden strata reaches the surface, whereupon the surface also be- gins to deform. Thereafter, the surface point where the movement initiates is always located at a fixed distance ahead of the face. The angle between the vertical line at the faceline and the line connecting the movement initiation point on the surface and the face- line is the angle of advance influence, w. The angle of advance influence can be used to determine the distance, [ 1], which is the influence zone ahead of the face. w is approximately 20O to 35 O for the northern Appalachian coalfield (Peng and Geng, 1984). The movement of each surface point is a relatively complicated process both in time and in space, because the relative position between the faceline and each surface point varies continuously, so that the direction and rate of movement for each surface point differ. In the following sections, the movements of each surface point on the major cross section are illustrated. 3.2 DYNAMIC SURFACE MOVEMENTS Dynamic surface movements include dynamic subsidence and displacement. The movement of each point on the subsidence basin is different as the face advances from 1 to 6 (Fig. 3.2). Surface points A and B, being far in front of the moving face, subside and displace toward the face (i.e., from A to A' and from B to B'). Point C, which is quite near but in front of the moving face, subsides continuously but displaces initially toward the face and then turns to pure subsidence ending up at C'. Point D, which is behind the face above the gob, subsides continuously, but displaces initially toward the face when it is in front of the face and reverses to follow the moving face when it is behind the face, with the amount of displacement toward the face being larger than that following the face. As a result the net displacement is toward the center of the gob (i.e., from point D to D'). The same statement is true for point E. For point F, the net displacement is zero, i.e it appears to have dropped down vertically to F'. For points G to I, the net displacements are in the direction of face advance except the magnitudes are increasing in sequential order. Point 1, has reached the final dynamic position of 1'. In other words, the face has passed sufficiently away such that it does not affect the movement at point I. All other points (A to H) are still within the face influenced area. 3.3 DEVELOPMENT OF DYNAMIC SUBSIDENCE PROFILES When the face has moved for a distance of h/6-h/3 from the setup entry, surface subsidence reaches the surface. At this time the surface subsidence basin is very mild (S, in Fig. 3.3), and it is symmetrical about the center. As the face continues to advance, the maximum subsidence continues to increase, and its location moves with, but falls farther behind the face. When the face has advanced a sufficient distance, e.g., (0.9-2.2)h, away from the setup entry, the maximum subsidence reaches the maximum possible value (curve S,). At this time, the dynamic subsidence profile is fully developed. Thereafter both sides of the dynamic subsidence profile become stabilized. The subsidence profile on the face side moves with the advancing face in an orderly manner (curves S, and S,). When the face stops, the face side of the profile continues to subside and becomes stabilized (curves;) sometime after. Curve S; is the final subsidence profile (see Fig. 2.22). 3.4 DEVELOPMENT OF DYNAMIC DISPLACEMENT AND SLOPE PROFILES The dynamic displacement profile moves with the advancing face (Fig. 3.4), but changes according to some specific rules. When the face has advanced to A, the surface begins to move and its dynamic displacement profile has two maximum values (curve Ua): one positive near the setup entry moving toward the face advancing direction and the other negative on the face side also moving toward the face advancing direction. As the face continues to advance, the positive maximum displacement on the setup entry side increases and moves toward the face continuously. The same statement is true for the negative maximum displacement on the face side. When the opening increases to the critical size, both the maximum positive and negative displacements reach the peak values and remain constant thereafter. Notice that when the opening becomes critical in size, the point of zero displacement no longer moves with the advancing face. Rather it spreads into an area of zero displacement (curve Ue) and expands as the face advances. When the face stops, the displacement on the face side continues until it becomes stabilized (curve Úe). Curve Úe is the final displacement profile. The ratio of maximum dynamic to final displacement ranges from 60 to 75%. The dynamic slope profile follows the same patterns of change. The ratio of maximum dynamic to maximum final slope ranges from 50 to 80%. The maximum slope decreases with in- creasing rate of face advance (Peng and Geng, 1984). It must be pointed out that except for those near both sides of the profiles, each point on the displacement and slope profiles is subjected to a cycle of positive and negative displacements and slopes depending on its relative position with respect to the face.

Jan 1, 1992

By Sun Guangzhong, Liang Jinhuo

Adverse geological condition is a major factor which makes construction difficulty in tunneling. But if it is predicted and tunnel support is made efficiently in time, the above difficulty can be reduced. It is necessary to develop one or several effective and economical geological methods for prediction of tunnel geology while expensive and time-consuming instruments are used. This paper reviews and proposes several geological methods for prediction of fault, seam, contact zone, and groundwater inrush. These methods have been proved to be effective and economical in tunneling practice in China.

Jan 1, 1987

By S. Meng, R. Jin, W. Hu

In alkaline pulp, galena is depressed by sodium carboxymethyl cellulose (NaCMC), while Cu(II) -activated sphalerite exhibits a high floatability so that satisfactory separation can be achieved. In addition to hydrogen bonding, chemical bonding of NaCMC with galena is confirmed by infrared (IR) spectra; only hydrogen bonding is involved between NaCMC and Cu(II)-activated sphalerite. It is also found that the greater the degree of substitution and polymerimtion of NaCMC, the stronger the depressive effect of NaCMC and that lower stirring speed favors the depression.

Jan 1, 1988

By John R. Turney

MARY KORPI: Harry Hinds will be filling in for John Turney today. Harry is an exception to the industry these days, in more ways than one. He has worked for the same mining company for 33 years. That is something very few of us can claim. He is currently metallurgical superintendent for Homestake Mining Company in Lead, South Dakota. Harry is also the envy of many of us as he will be retiring this year and working on lowering that handicap! Harry will be discussing the "Role of Consultants."

Jan 1, 1998

By C. O. Hamilton

Poor plant start-up performance is usually blamed on poor design and unsatisfactory equipment. But, in most cases, the real cause of poor performance is inadequate preparation for operations and maintenance. Inadequate maintenance preparation, unlike inadequate operations preparation, will not immediately manifest itself in a new plant. However, not taking advantage of the window of opportunity afforded a new plant to organize the maintenance operation ensures that the new equipment honeymoon is unexpectedly short. Also, once a plant has entered a “breakdown mode,” it is extremely difficult to turn around.

Jan 1, 1991

By G. A. Dawe, E. G. Kelly

Because of the nature of the breakage in the Barmac vertical spindle impactor, the 80% reduction ratio is very small, so that when an energy efficiency is calculated from Bond's method, it appears to be very low. However, the product size distribution contains a high proportion of fines. It is argued that the production of these fines accounts for the high energy consumption, and Bond's method is modified to account for this, by considering the crusher to be, effectively, a number of smaller crushers in parallel, each having a different reduction ratio.

Jan 1, 1990

By G. X. Wang, J. O. Marsden, M. C. Fuerstenau

Zinc cementation of high-temperature carbon eluates is now used extensively in gold processing to replace electrowinning. Under these conditions, zinc consumption is high. In this paper, zinc solubility is press rated us functions of temperature, cyanide concentration and pH in the presence of gold, silver and mercury cyanides (both individually and in combined solutions). Based on the experimental results, cementation of these metals is characterized and discussed. The importance of cyanide concentration in cementation efficiency and the effect of mercury and its co-precipitation onto zinc are also discussed.

Jan 1, 1997

By Greg Barfoot, K. Payne

Condition monitoring of conveyor belting has become an established tool for maintenance programming, replacement strategies and quality assurance for belt conveyor systems. What is less well known is that the condition of the conveyor belting is usually a symptom of problems in other areas rather than the problem source. This paper presents an overview of the state of the art in belt monitoring and the move towards on-line NDT systems. The use of belt monitoring data as an indicator for overall system design, maintenance and operation is also discussed.

Jan 1, 1996

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

Under normal conditions, a significant amount of pyrite is recovered in the froth during flotation of high-sulfur coal. To reduce this pyrite recovery, it is first necessary to determine the primary recovery mechanism, because different measures are required for reducing entrainment, locked particle flotation or true hydrophobic flotation. In this paper, evidence is presented that suggests that hydrophobic flotation is not the major mechanism for recovery of liberated pyrite; instead, the bulk of the recovered pyrite results either from simple entrainment or from being physically locked with floatable coal particles.

Jan 1, 1993

By S. A. Allison, N. P. Finkelstein

After a brief consideration of the properties of zinc sulfide minerals, their flotation characteristics, and their reactions with thiol collectors, the literature on the activation of the minerals by cupric ion, their deactivation by cyanide, and their depression is reviewed in detail. The distinction between deactivation and depression is stressed. The contradictions in the published results and theories are discussed and attempts are made to resolve them. It is concluded that, whereas all aspects of the subject require further investigation, the study of depression is most likely to yield benefits in practice.

Jan 1, 1976

By Steve Rule, Jose Roberto Vago, Walter de Moura

Cerro Vangaurdia Gold Mine is a joint venture between AngloGold (the operator), Perez Companc and Formicruz and is situated in the southern province of Santa Cruz, in Argentina, approximately 2,150 km south of the capital, Buenos Aires. The mine is located in a severe, semi-arid environment with very cold winters and little annual rainfall (200mm). It is an open-pit operation, mining several narrow, shallow epithermal quartz veins with . gold and silver mineralisation. Commissioning of the plant commenced in September 1998 and the first dore bar was poured towards the end of the same month. The nominal capacity of the plant is 55,000 tonnes per month, with a design capacity of 60,000 tonnes per month. Prior to finalising the design, an extensive testwork programme was undertaken at Nova Lima, in Brazil, in which all parts of the process were evaluated together on a pilot-plant scale. The process flowsheet selected at Ce1rn Vanguardia is quite novel, in that it includes milling in cyanide, as well as a cyanide recovery and recycling plant on the tailings section of the treatment plant is included. The cyanide recovery process selected was a version of the acidification - volatilization - reabsorption (AVR) process, known as Cyanisorb™. The selection of the Cyanisorb™ process in the plant design was as a direct consequence of two factors:

Jan 1, 2000