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By F. Habashi

Chile is at present the largest copper and rhenium producer and was before World War I the largest nitrate producer. She is also an important producer of lithium carbonate and molybdenum oxide. An important event in the history of the country is the Pacific War of 1879-1883 in which she acquired the northern provinces initially belonged to Bolivia and Peru. In 1888 Chile annexed Easter Island. The Chilean mineral and cultural history is briefly reviewed together with the people who contributed to her development. The present report is the result of a number of academic and industrial visits to Chile during the period 1992 to 2009.

Jan 1, 2011

By G. Chi, M. C. Fuerstenau, R. C. Bradt, A. Ghosh

Technical Papers, Mining Engineering Vol. 49, No. 12, pp. 70-75, Discussion by McIvor, R. and Fink, R. P. We must challenge what we consider to be dubious statements in the above-mentioned article. Much of what is reported was published elsewhere over a year ago (i.e., in their reference: Chi, G., Fuerstenau, M.C., Brandt, R.C. and Ghosh, A., 1996, "Improved comminution efficiency through controlled blasting during mining," International Journal of Min¬eral Processing, Vol. 47, p. 93). There is nothing unusual or significant about a 10% or more difference in grindability between two materials of apparently similar origin and other attributes (such as chemical assays, hardness and specific gravity). Consider also that: • the materials came from different locations in the pit; • only two sets of four blastholes were considered per blast: • spatial orientation with respect to the face and other blastholes was also altered; • only two pairs of data were collected; • the impact of sampling error and bias, • both of which could be significant in this case; and • normal experimental error in parameter measurement and calculation. It is clearly inappropriate to draw any conclusions with regard to cause-and-effect relationships without first presenting a thorough error analysis. A substantial number of randomly selected test and control areas might provide meaningful statistical evidence of the claimed effect of the variables being studied. Even that appears doubtful, however, because Figures 3 and 4 show about as much variation in crushing energy for the two "regular" conditions vs. regular and altered conditions. On a separate, but also important issue, broad experience with autogenous/semiautogenous milling has shown that smaller or weaker feed material results in reduced tonnage. ? Reply Thank you for the opportunity to respond to the comments of Messrs. Mclvor ant Fink. The points raised are addressed in the order of presentation. As the commenters noted, there are parallels between this article and a previous manuscript. The reason for these complementary articles is that the audiences for the two publications are different, although there is obviously some overlap. We believe that the different audiences each profit from the technical aspects of the two manuscripts. We are not in agreement that a grindability difference of 10% is insignificant. The laboratory work is corroborated by data obtained at plant scale, which confirms that an increase in throughput of the same magnitude (between 5% and 10%) is achieved when the blasting pattern is modified, i.e., reduced from 9 to 8 m (29.5 to 26.2 ft). This increase in throughput translates into substantial power savings for ore grinding. No differences in appearance in the rock were noted between the two adjacent areas. Rock in both areas belonged to the same rock mass/block, which was quite homogeneous and without geological features in between that could create drastic differences in comminution characteristics. Given the resources, we would have sampled from all of the holes. Additional data would certainly have been desirable, as would have been additional funding to expand the study. Their comment, "spatial orientation with respect to the face and other blastholes was also altered," is not clear. Figure 1 does not show the initiation sequence. Without the initiation sequence, we do not understand how the commenters concluded that spatial orientation with respect to the face and other blastholes was altered. The commenters may be trying to make the point that the four-hole configurations with respect to the original bench face are not exactly the same. In fragmenting the

Jan 1, 1999

By V. Herman, B. Knorr, D. Whalen

"Edge effect is a condition widely observed in High Pressure Grinding Roll (HPGR) operations that gives rise to reduced comminution at the edges of the roll surfaces. This effect is caused by a reduction in the local crushing pressure at the edges of the rolls resulting from the sliding friction between the static cheek plates and HPGR feed material. Practically, this has an impact on equipment sizing, as the edge effect leads to coarser particles reporting to downstream equipment in open-circuit operations and increased circulating load and diminished HPGR circuit capacity in closed-circuit operations.To address this, Metso's HRC™ HPGR incorporates an Arch-frame to maintain a parallel relationship between the rolls and allow for the use of a flanged roll design. We conducted a series of pilot-plant tests with a 750 mm by 400 mm HRC HPGR to compare the performance of the flanged roll design against that of a traditional cheek plate arrangement under similar operating conditions. The edge effect was found to be significantly reduced with the flanged roll design. Based on the pilot-plant results, the implications for circuit design, energy efficiency and overall plant performance in a full-scale application were investigated and discussed.IntroductionGlobal trends such as lower ore grades and rising operating costs are driving the market toward more energy-efficient mineral processing solutions, most notably in comminution circuit design. High pressure grinding rolls (HPGRs) have been recognized as an energy-efficient solution relative to more conventional circuit designs. The basic operating principle of HPGRs, in which a fairly uniform pressure is applied to a bed of material in the compression zone, lends itself to this improved energy efficiency (Morley, 2006). Studies have estimated that savings of 10-15 percent are possible when comparing an HPGR circuit with a traditional SABC circuit (Rosario and Hall, 2008). While HPGRs offer a more energy-efficient solution than tumbling mills, there is still room for improvement in many aspects of the design. Edge effect, in particular, is one such aspect that limits the effectiveness of the machines. Edge effect is the impaired performance at the edge of the rolls due to a reduction in crushing pressure (Morley, 2010; van der Meer, 2010). As described in our prior work (Knorr, Herman and Whalen, 2013), edge effect is caused by the interaction between the ore entering the crusher and the relatively static cheek plates positioned at the edges of the rolls. As the material is drawn into the crushing zone, the sliding friction between the ore and the cheek plates inhibits the ability of material to be effectively drawn into the compression zone at the edges of the rolls. This reduces the crushing force in those edge regions relative to the center of the roll where material is being drawn into the compression zone at a higher rate. In addition, the cheek plates of a traditional HPGR design are held in place by spring-loaded brackets that are adjustable to manage the clearance. This spring-loaded cheek plate design prevents full compression of the material in the edge regions of the roll as there is relief at the outer edges."

Jan 1, 2016

By Clinton Birch

The multiple-criteria decision analysis is a technique that helps to find an optimal solution by evaluating conflicting criteria. In this study, an approach to perform multiple-criteria decision analysis for cut-off grade optimization, which considers the diverse stakeholder groups prevalent in the mining industry, is presented. The optimization model developed in this approach links the resource block model to the financial model, enabling the process to either maximize profit, net present value, revenue to the State, or extend the mine's life. To identify the optimal cut-off grade in each case, the Excel Solver function is utilized. Although it has limitations, the Solver function can still be modified to handle models with thousands of block values for determining input variables based on the target value. Following stakeholder engagement and dialogue, a single weighted average cut-off grade can then be determined. This approach is demonstrated for nine South African Witwatersrand gold mines.

Jun 25, 2023

The mineral sands industry is oriented primarily toward the supply of titanium (Ti) raw materials (titanium feedstocks) for the production of titanium dioxide (TiO2) pigment and titanium metal. Titanium minerals ilmenite, rutile and leucoxene, and titanium slag and synthetic rutile are all used principally as feedstocks for the production of white TiO2 pigment. It accounts for almost 90 percent of the world?s consumption of titanium minerals. The remainder is used for the production of titanium metal, fluxes for welding rods and as a metallurgical flux in iron and steel making. Titanium dioxide pigment is produced by two alternative process routes, the sulfate process or chloride process. The bulk of the world?s titanium dioxide is derived from the mineral ilmenite, which also contains iron oxide and other minor impurities. At some mining operations, the iron present in ilmenite is removed (ilmenite beneficiation) to produce a high TiO2 feedstock (slag or synthetic rutile) typically containing between 80 percent and 95 percent TiO2. Pigment producers then further process it to produce pigment.

Jan 1, 2011

By Fitzhugh T. Lee

Results from the first part of a two-part investigation of the stability of highwalls in open-pit coal mines in the Paleocene Fort Union Formation of the western Powder River Basin of Wyoming and Montana indicate that these highwalls are subject to time-dependent deformation. Field investigations and laboratory physical properties tests of coal and overburden rocks suggest that several factors influence highwall stability. Some of these factors are rebound of overconsolidated rocks, desiccation, water, orientation and spacing of fractures, and strength and deformation properties. Factors of safety for a typical highwall in the study area (calculated by the finite element method) may be less than 1.0 when open fractures are present and the highwall has degraded. Although it is concluded that most open-pit highwalls in the Fort Union Formation within the study area have adequate short-term stability, these highwalls do deteriorate and become progressively less stable. Because of this, postmining failures are common and stability conditions could become critical if mining were delayed and then resumed after a period of several months. The second part of the investigation will utilize field measurements of rock-mass properties and instrumentation of actively mined highwalls to obtain data for comparison with the results of the initial investigation. Because the height of highwalls will increase as the more shallow coal is exhausted, these data will also be used to predict the behavior of slopes higher than those presently found in the western Powder River Basin.

Jan 1, 1977

By Jean-Michel Rendu

That you are giving the Daniel C. Jackling award to me is a great personal honor. But more significantly, it is a recognition that geostatistics has come of age. And since I am considered by many as belonging to an older generation of geostatisticians, I thought that it would be fitting that I reflect on where geostatistics came from and where it might be going. First, though, let me propose a definition of geostatistics. Etymologically, paraphrasing Webster's definitions of "geo" and "statistics," it is "a branch of mathematics dealing with the collection, analysis, interpretation and presentation of masses of numerical data taken from the earth." This definition is most appropriate in the context of mining geostatistics. It includes both classical and spatial statistics. It emphasizes the earth aspect, or the analysis of geologic features. And it should remind the practitioner that geologic input is a critical part of all geostatistical applications. In the 1910s, statistical methods were already used to analyze geological data. However, the origin of geostatistics, as we know it today, is best set in the late 1940s, when H.S. Sichel recognized the lognormal distribution of sample values in the South African gold mines. In 1951, Daniel Krige observed that "it can be expected that the gold values in a whole mine will be subject to a larger relative variation than those in a portion of the mine." In other words, samples taken close to each other are more likely to have similar values than if taken farther apart. This observation is the foundation on which spatial statistics, which characterizes values defined in a multidimensional space, is built. However, the 1950s were marked by studies based on classical, as opposed to spatial, statistics. It was only in the 1960s that the need was recognized to model the similarity between sample values as a function of the distance between samples and that the semivariogram was defined. A theoretical framework was developed by Matheron that supplied an elegant mathematical explanation to the empirical observations made by Krige. Matheron coined the term "kriging" in recognition of Krige's pioneering work on the geostatistical evaluation of mineral deposits. As soon as this theoretical framework was developed, it was possible to bring geostatistics to the academic world. The "Centre de Geostatistiques" was founded in Fontainebleau. Numerous students were trained there, disciples eager not only to improve the theory and develop more sophisticated mathematical tools, but also to spread the new faith throughout the world. Expansion of geostatistics exploded in the 1970s, arguably the most fertile decade if it is judged by the frequency of theoretical breakthroughs, the number of original publica-

Jan 1, 1995

By Florence Ntsiful, Eric Stemn

Exposure to whole-body vibration has been recognised as an occupational hazard in the mining industry, especially in the operations of earthmoving equipment. Managing whole-body vibration exposures requires periodic measurement of exposure levels to identify priority areas for implementing controls. However, due to different approaches to collecting exposure values, significant variabilities lie in the results. This systematic review is the first attempt to analyse whole-body assessment methods in the mining industry. The aim was to identify how whole-body vibration has been assessed, including the sources of variabilities to improve future research. The PRISMA methodology was adopted for the review and a total of 152 peer-reviewed journal articles were identified. However, only 24 were included in the review, following the application of some inclusion criteria. Descriptive and thematic analyses were performed on the 24 selected articles. Results indicate that whole-body vibration has been assessed as a function of either equipment characteristics, activity undertaken, operator characteristics, measurement approach or the assessment standards. Due to the multifactorial and dynamic nature of wholebody vibration exposures, the variabilities in results are due to the interrelationships between the risk factors of whole-body vibration and the differences in the sample sizes. To identify the sources of variabilities, a comprehensive assessment of all the risk factors, including equipment characteristics, road conditions, operator characteristics, and activity undertaken, is highly warranted. Finally, research gaps and directions for future research have also been discussed.

Dec 21, 2022

A digital computer program has been developed to mathematically simulate the effect of limited changes in feed rate on the grinding circuit of an operating mill. The data on which the program is based was supplied by the staff of the mill in question. Samples taken around the complete grinding circuit were analyzed for solids content and particle size distribution for two feed rates. Matrix models were used to represent the grinding units: rod mill and pebble mills. Parameters for these models were computed using a method developed by Mular(l). Classifier parameters were computed by the Powell search method(2) for the Plitt model (3) . The simulation program, which permits the computing of the size distributions in the circuit resulting from the changes in feed rate between the two measured values, assumes that a linear relationship exists between the corresponding parameter coefficients. The program uses an iteration method to bring the simulated grinding circuit to a steady-state material balance for any specified' feed rate between those measured. The program is, in addition, extremely fast and economic in computing time. The results show that the simulations are not everywhere consistent with practice. For example, higher feed rates on simulation predict finer products. These errors are shown to be attributable to anomalies in data gathering techniques. An improved sampling procedure for grinding-circuit data gathering is suggested for future simulations of this type. It is concluded that the

Jan 1, 1971

By M. S. Moats, A. Luyima, W. Cui

"Organic smoothing additives are used to produce dense, thick, high-quality cathodes in copper electrowinning. Glue had been used traditionally and is still used in operations that do not employ solvent extraction to produce the electrowinning electrolyte. With the advent of solvent extraction–electrowinning, guar started to be used and remained in use for many years as it does not affect the phase disengagement in solvent extraction. Recently, however, guar has been replaced by less-expensive saccharide- and polyacrylamide-based additives. This paper is the first of a series of four papers that examine saccharides and polyacrylamides as new additives for copper electrowinning. A review of previous research related to copper electrowinning additives is presented here, along with a selected review of additives in other copper electrodeposition systems.IntroductionThe recovery of copper from solution by electrowinning was first practiced in the early 1900s, but it was the combination of solvent extraction with electrowinning (SX-EW) in March 1968 at the Ranchers Bluebird Mine (Kordosky, 1992) that changed the landscape for the electrowinning process. Most copper electrowinning capacity is now associated with solvent extraction, though some copper is still won directly from leach solutions (Robinson et al., 2013). The ability to produce high-purity copper cathodes from SX-EW has taken the continued improvement of SX-EW technology over the past more than 40 years.One of the technologies that has seen improvement is that of the organic smoothing agents used during the electrodeposition of copper in the tankhouse. These organic additives are added to the acidic copper sulfate electrolyte during electrowinning to improve the smoothness, brightness and density of the copper cathodes. The organic additives that are presently in use are different from those used in 1999 (Jenkins et al., 1999). Over the past decade, many tankhouses have replaced the use of guar-based organic additives with those derived from other saccharides. Until now, there has been no comprehensive publication in the open literature on the behavior of these additives during copper electrowinning."

Jan 1, 2016

By Kendall Y. Keuhey

The Mercur Mine, developed and operated by Getty Mining Company, is designed to process 3,000 tons/day of gold ore from the historical Mercur Hill mining district. The mill process involves crushing, grinding, and cyanide carbon in leach for recovery of gold ores ranging from 0.08 to 0.10 oz/ton. During the mining of normal grade ore, a substantial tonnage of material containing 0.02 to 0.05 oz/ton is mined and would be available for heap leaching. Also, Getty Mining is developing methods to test and prepare lower grade material for heap leaching by rejecting a course rock fraction from the grinding circuit SAG mill. This lower grade fraction is suitable for heap leaching, and its removal will upgrade the regular mill feed. Other test methods are directed toward leaching techniques on some 4.0 million tons of tailings that resulted from roasting and/or cyanide leaching Mercur ores in the early 1900s. The natural carbons associated with the Mercur deposits require special treatment to reduce their gold adsorption effects when leached with cyanide.

Jan 1, 1983

By R. S. Datta

In the article "Concentration of Oil Shale,"(1) Dr. N. Arbiter stated, "One of the major factors in the delayed utilization of oil shale as an energy raw material is the low grade or content of hydrocarbon (kerogen) in oil shale as compared with coal and even more so to the liquid and gaseous fuels. " When the availability of high-grade deposits decreased, mineral industries started adopting prebeneficiation procedures for the low-grade deposits. This practice, which is becoming standard in these other industries, has been largely overlooked by the oil shale industry in its drive to produce oil from oil shale. If a major portion of this mineral matter can be removed, there can be potentially large savings in the capital and operating costs of oil shale retorts. Moreover, the environmental impact, associated with recovering the shale oil, could be reduced considerably. In 1980 Roberts & Schaefer Resource Service (RSRS) completed successfully the first set of demonstration runs with a 20-ton oil shale sample from Cathedral Bluffs (C-b tract), Colorado. This relatively low grade (~12 gpt oil content) oil shale was beneficiated applying the Dutch State Mines Heavy Medium Cyclone process. (2)

Jan 1, 1985

By Baolin Qu, Jingxin Wang, Cuncang Xu, Bing Wu, Mingyu Zhong

With the development of the coal mine regulation regime, the situation of coal mine safety production in China has continued to improve. However, coal mine accidents have not been fundamentally eliminated; constantly learning from historical accidents can make mining work safer. Therefore, to better understand the coal mine accident characteristics, this study analyzes the tendency of coal mine safety accidents from multiple perspectives, among which all accidents after the establishment of the State Administration of Coal Mine Safety in 1999 are the top priority. The results show that strict national policy, technological progress, and reasonable coal prices are conducive to the safe development of mines. On the contrary, high-intensity centralized production will lead to frequent accidents in the peak season of coal production. In addition, the type of coal mine ownership will have an indirect impact on the occurrence of coal mine accidents. The research results not only play a positive role in the prevention and control of coal mine accidents in China but also have reference meanings for the safety production of coal mines in other countries in the world.

Dec 28, 2022

By B. Barry, M. S. Klima

"Testing was conducted to evaluate the effects of hydroacoustic cavitation (HAC) treatment on two bituminous coal slurries and the subsequent separation of each slurry in a classifying hydrocyclone. HAC treatment was performed using a pilot-scale circuit fabricated by Furness-Newburge Inc. The circuit was designed to induce cavitation by means of flow through an ultrasonic resonator chamber or enhanced cavitation by initial flow through a cavitation chamber followed by flow through the ultrasonic chamber. The test materials were nominal -1,500-micron and -150-micron Illinois-basin bituminous coal slurries, which were obtained from an operating coal preparation facility. After 5 sec of HAC treatment, the median size of the -1,500-micron material was reduced, with ash values for certain size fractions decreasing more than 5 percent compared with untreated samples. Extending treatment time led to greater degradation of the +1,180-micron material and an increase in the -25-micron material, with ash reductions occurring for material in the -850+150-micron size range. Size degradation was less for the -150-micron material. Subsequent separation of the treated slurries was carried out in a hydrocyclone with diameter of 102 mm. HAC treatment led to a decrease in the ash value and an increase in the heating value of the underflow stream compared with the feed material. For example, the ash value was reduced by about 16 percent for the -1,500-micron material and 25 percent for the -150-micron material with heating value increases of 7 and 33 percent, respectively, after HAC treatment. Overall, HAC treatment appeared to have a slight effect on the size selectivity curves.IntroductionUltrasound in the range of 20 to 1,000 kHz, referred to as power ultrasound, consists of high energy waves that can create zones of compression and expansion when used to irradiate liquids (Frederick, 1965; Leighton, 1994; Mason and Lorimer, 1988). This action generates varying pressure regions leading to cavitation or the formation, growth and near-immediate collapse of microscopic voids or bubbles (Frederick 1965; Leighton 1994; Mason and Lorimer 1988). Collapse occurs when the bubble reaches critical size and cannot absorb additional sound field energy, and the critical size is governed by the ultrasound frequency (Shchukin et al., 2011)."

Jan 1, 2015

By P. Moran

A promising and increasingly popular tailings management strategy is to place cemented tailings underground as backfill. The placement of cemented tailings results in enhanced geotechnical stability and a purportedly more geochemically stable tailings form with lower leaching potential. Conventional subaerial tailings management can negatively affect water quality if weathering causes acid rock drainage and metal leaching (ARD/ML) to occur, whereas cemented tailings can limit leaching via porosity and permeability reductions and contribute alkalinity to limit the potential for ARD/ML. Cemented tailings backfill appears to be better, but how can this advantage be proven? Currently, cemented tailings backfill is utilized at mining operations internationally, but there is limited guidance on performing geochemical characterization and associated evaluation of the potential impacts to water quality. As a result, various approaches to simulating the leaching behavior of cemented backfill have been utilized, including some methods that are unlikely to represent weathering under site-relevant conditions. American Society for Testing and Materials (ASTM) Standard Test Method C1308-08 is a diffusion testing method initially developed to assess constituent release rates from solid nuclear waste forms. ASTM C1308-08 uses intact cylinders that more closely represent actual backfill than methods that require crushing or size reduction. It is widely believed that leaching from actual cemented tailings is controlled by diffusion through small pores that exhibit limited exposed surface area, making diffusion testing particularly applicable to cemented tailings placement.

Feb 27, 2013

By R. J. Roman

The "mass balance" is unquestionably the most common class of problems for the process engineer'. Closely related, mathematically, is the "heat balance". Every laboratory test requires a mass balance to describe the results. Mass balance calculations can be subdivided into several sub-categories based on whether the results are time dependant or not and depending on whether the input data are measurements that contain errors or are hypothetical values with no errors. Time dependent mass balances are dynamic process simulations and in addition to the conservation of mass constraints require kinetic data input. They are one step beyond simple mass balances.

Jan 1, 1992

By D. J. Englund, R. A. Davis

"A three-dimensional CFD model of a straight grate furnace for indurating iron-oxide pellets was developed for exploring conditions of furnace operation for fluid flow, heat transfer and reactions. The model includes reactions for natural gas combustion in the gas phase and calcination and magnetite oxidation as well as drying in the pellet bed. The performance of the model was investigated with a series of pellet production rates that included adjustments to the fuel rates to achieve proper induration temperatures in the pellet bed. The model may be used to discover opportunities for process improvement.IntroductionIron oxide pellets are a feedstock to blast furnaces for iron making. Pellets require physical strength characteristics needed to maintain their integrity during storage, handling, transportation and smelting. Pellets are produced from iron ore in a series of mineral processing operations that form wet green balls from slurries of iron-ore concentrate with binders, such as bentonite, and possibly fluxing-agents such as limestone and dolomite. The green balls are dried, fired at high temperature, and then cooled in an induration furnace to achieve the strength and chemical composition required for efficient reduction and slag separation in blast furnaces. Induration furnaces are generally straight grates or grate-kilncooler configurations. These furnaces operate with pellet beds passing through a series of temperature zones to control drying and chemical reactions in the bed.Process air passes through the zones in an overall counter flow direction to the pellets for efficient heat transfer and energy recovery from the cooling stage. Consequently, the zone conditions and the overall furnace performance are highly coupled. Thus, it becomes challenging to predict how changes to any single zone may affect the rest of the furnace. To gain a better understanding of machine performance and coupling, a three-dimensional, steady-state model of a complete straight grate induration furnace was created using computational fluid dynamics (CFD)."

Jan 1, 2015

By J. A. Meech

An analysis of screen design options on the operating efficiency of secondary crushing plants has been conducted using a dynamic computer model. The model allows for the simulation of a wide variety of crushing circuits and can be run on either a microcomputer (IBM PC/XT) or a large time-sharing mainframe computer. Size reduction and separation characteristics of crushers and screens are based on standard manufacturer design and performance data. Input/output routines are available in tabular, alarm or strip chart recorder modes to facilitate operation of the program. A number of alternate circuit designs are compared to show the influence of surge capacity, screen size and area, screen deck location, and closed side crusher settings on the operation of a 10,000 ton per day plant. The program is currently in use at Queen's University to teach plant operations and control. It has potential to be a valuable tool for operator training.

Jan 1, 1985

By Wilson Blake

The occurrence of rock bursts in some deep mines throughout the world constitutes a severe operational hazard. In addition to endangering the safety of the miners, the rock-burst problem is a major factor in mining economically in deep mines because of the loss of production and expense owing to cleanup and repairs following a burst. Developing means of controlling or eliminating rock bursts has been the subject of intensive research for over 50 years. While much has been learned about the effects of rock bursts, little is known about their basic causes; hence, control measures have been at best only partially effective--attested to by the number and severity of bursts that continue to occur throughout the world each year. In the Coeur d'Alene mining district of north Idaho, the rock-burst problem continues as the silver and lead veins persist at depth. These veins are presently being mined at greater than 7,000 feet below the surface and will be mined to some 10,000 feet in the future. The majority of rock bursts in this district occur in pillars. While pillar bursting has been essentially eliminated in some deep-mining districts by longwall techniques, modification or application of this technique to the thin, irregular, and near vertically dipping veins of the Coeur d'Alene district has not been found to be practical. The creation of pillars is a consequence of the horizontal cut and fill mining method used. Figure 1 shows a vertical longitudinal projection of the silver vein at the Galena mine, illustrating the mining method. Stoping progresses between raises and is carried upward between levels. A horizontal pillar is created as a stope approaches a mined-out level. Recent broad-band micro seismic monitoring of rock-burst-prone stopes by the Bureau of Mines has shown that potential burst zones could be delineated weeks in advance of a burst and that a definite sequence of events took place prior to the occurrence of a pillar burst (1). Hence, time was available for control measures to be effected when a stope pillar reached a critical burst geometry.

Jan 1, 1971

By Caibin Wu, Bin Xie, Jiaqi Tong, Ningning Liao, Chong Zeng

Understanding the energy-size reduction relationship is vital to grinding process; therefore, this paper aims to show the energy-size reduction of magnetite-calcite binary mixture in a laboratory wet conical ball mill. Single magnetite, single calcite, and blended magnetite-calcite mixture at three weight ratios in four particle sizes were ground in a laboratory wet conical ball mill at four grinding time periods. The results showed that the particle size distribution of both fine particles and coarse particles of single and mixture ground product fitted well with the PSD computed by Rosin–Rammler-Benne function. The larger mass percentage of calcite is, the higher t10 of binary mixture ground product is. On the contrary, t10 in the mixture decreases as the percentage of magnetite in the mixture increases. The different breakage behaviors in blended samples are due to the hardness and particle size. The results of calculated ratio of energy absorption factor showed that the calcite consumed more energy in the breakage process of binary mixture than ground alone. The JK size-dependent breakage model based on the t10 method fits all the experiment data, be it generated from pure minerals, mixtures at different weight ratios, or each component separated from the mixture.

Jun 4, 2022