Search Documents

By Meisam Ghiasi, Mohammadreza Khalesi, Mahmoud Abdollahy

In the current research, isothermal experiments of kinetic analysis were performed at different temperatures (800–1050 °C) and particle sizes (885 to 10,763 μm) to investigate the calcination kinetics of high-purity limestone. Thermal analyses were carried out in a zirconia crucible, 1 cm in height, for different temperatures and particle sizes. The reaction rate coefficients were varied in the 2.2 × 10−5-1.62 × 10−3-m0.6.s−1 range. Moreover, various isothermal kinetic analysis methods were applied to assess the decomposition mechanism and the calcination function governing the process. The modified shrinking core model was found as the best representation of the high-purity limestone kinetic data. The activation energy was evaluated using the Arrhenius curve, and an average value of 86 kJ.mol−1 was obtained.

Sep 15, 2020

By M. J. Ross, D. A. Norrgran, J. A. Wernham, J. N. Orlich

INTRODUCTION Laboratory testing for magnetic concentration circuit design is a requirement, just as it is for most other types of concentration. Natural variations in raw materials allow on1 y the broadest of generalities to be made regarding magnetic separation. Further, magnetic fields are geometry dependent, leaving fundamental models of a separator overly dependent upon the exact conditions for which the models were derived. Despite this, an understanding of the basics of magnetic separation and of the problem to be attacked can result in rapid progress towards the final circuit design with a relatively simple testing program. Magnetic Separation Basic Principles A magnetic field can readily be understood in terms of lines of flux. A familiar demonstration of these lines of flux is the pattern of iron filings on a sheet of paper when a magnet is placed underneath. Lines of flux2 are measured in Gauss (1 line/cm2) or Tesla (10000 gauss). Regions of high field strength have a greater number of lines. Field direction is indicated by a convergence of lines. When a particle is placed in a magnetic field it cuts the lines of flux and alters them in one of three basic patterns. These patterns are referred to as diamagnetic, paramagnetic and ferromagnetic. Diamagnetic materials have electronic structures which react to oppose an applied magnetic field. This opposition acts to locally reduce the applied field slightly. The visualization is that lines of flux diverge and go around the particle. Because of this divergence or opposition, a diamagnetic particle will tend to move towards regions of lower flux density. That is to say that the particle will be repelled by a magnetic field. Aluminum oxide and napthalene are examples of diamagnetic materials. Paramagnetic materials have an electronic structure which increases an applied magnetic field. Although these materials also exhibit diamagnetism, they have randomly oriented impaired electrons which align with the magnetic field. The resultant local field enhancement is significantly larger than the diamagnetic opposition. The visual-

Jan 1, 1986

By David B. McWhorter

Conventional analyses of seepage through saturated media do not apply when tailings impoundments are located above a partially saturated zone. Three stages of seepage are identified and methods for estimating the seepage rates and duration of each stage, based upon flow in partially saturated and saturated porous media, are demonstrated. The effectiveness of earthen liners is discussed and procedures for estimating the required properties of the porous media are provided.

Jan 1, 1978

By John Barakso

The Sam Goosly or Equity silver deposit is fundamental- ly a discovery based on the analysis and interpretation of reconnaissance geochemical samples. The discovery was made by Kennco in an area of heavy forestation and wide- spread cover by thin glacial debris. No major mines had been discovered in the vicinity of the discovery prior to the geochemical reconnaissance, and the interpretation of the geochemical results therefore was based on data available through geologic mapping and the sample collection process. In the period 1959-1961, PE. Hirst and his crew, in 1962- 1965 P.T. Blackand his crew, and in 1966-1967 C.S. Ney and P.T. Black and their crew collected geochemical samples from the area of what is now the ore body. Several of these samples were compiled and reanalyzed in the winter of 1966- 1967 for various trace elements, including fluorine. A strong, almost 16-sq-km (10-sq-mile) fluorine anomaly was projected along with a very weak heavy metal anomaly. On the basis of this anomaly, a chalcopyrite-bearing quartz monzonite was discovered in 1967. This was a misleading, noneconomic discovery not associated with the Sam Goosly discovery. The interpretation of the geochemical data by Barakso that summer indicated that another source was responsible for the fluorine anomaly. The conclusion was based on the assemblage of trace elements. Therefore C.S. Ney recommended further regional soil sampling to check the original data. The early results of this follow-up sampling found over 33 ppm silver. First float, then ore outcrop was found in the area of the silver anomaly. The attached reprints complete the development of the property after the discovery of the outcrop of ore.

Jan 1, 1990

By Aline Tatom

This paper presents numerical and experimen¬tal results dealing with the application of ferric ion oxidation of uranium in acidic media. Conclusions are derived from matching numerical results to experimental data taken on one-dimensional laboratory leaches using ore from a South Texas Coastal plain deposit. Since the numerical results can be made quite general, we are able to extract and quantify the effects of oxidant concentration, flow velocity, mass transfer, chemical kinetics, and competitive oxidant consumers (pyrite and molybdenite) on the experimental results. Our results suggest that the leaching of uranium is a mass transfer controlled while that of pyrite is kinetically controlled.

Jan 1, 1981

By Verya Nasri, Mehdi Bakhshi

"Fiber reinforcement has emerged as an alternative to steel bars in precast concrete segments due to advantages such as saving cost and reducing production time while developing a more robust product with improved handling and long-term durability. ACI recently drafted a new report as the first design guideline on FRC tunnel segments to provide specific guidance for this emerging technology. ACI document offers general information on the history of FRC precast segments from tunneling projects throughout the world; a procedure for structural analysis and design based on governing load cases, and a description of the material parameters, tests and analyses required to complete the design. This paper summarizes the design considerations in this ACI guideline prepared by the authors of this paper as the main contributors. Application of this guideline to design of a tunnel with an internal diameter of 5.5 m (18 ft) results in elimination of steel bars.INTRODUCTIONPrecast concrete segments are installed to support the tunnel excavation behind the Tunnel Boring Machine (TBM) in soft ground and weak rock applications. The TBM advances by thrusting off the completed rings of precast concrete segments that provide both the initial and final ground support as part of a one-pass lining system. These segments are typically designed to resist the permanent loads from the ground and groundwater as well as the temporary loads from production, transportation and construction. Tunnel segments are generally reinforced to resist the tensile stresses at both the Serviceability (SLS) and the Ultimate Limit States (ULS). With traditional rebar, a significant amount of labor is needed to assemble the cages and place the rebar, which results in higher production costs.Fiber Reinforced Concrete (FRC) can be used to enhance the production, handling, and placement of precast concrete segments. This is because of the uniform dispersion of fibers throughout the segment to include the concrete cover, which is very advantageous for resisting the bursting and spalling stresses. These stresses develop as a result of the high loads induced on the segments during the TBM jacking process. The presence of fiber in the concrete matrix helps mitigate against unintentional impact loads during segment handling and tunnel construction operations."

Jan 1, 2016

By Josef Arnold, Norbert Fuegenschuh

The “Eggequerung” is an important part of the German Railway’s (Deutsche BahnAG) modernized Dortmund—Kassel line. The heart of this 13-km-long (8 miles)construction lot is the double-track Egge Tunnel with a total length of 2,880 m(9,450 ft.). The tunnel was driven using the New Austrian Tunnelling Method (NATM).The construction contract also called for a reinforced concrete secondary lining, guaranteed for a full water pressure of 30 m (100 ft.) water column. Preliminary geological study already showed that very problematic geological-hydrological conditions would have to be expected. This talk describes the chosen NATM driving concept that was adapted to the prevailing geological and hydrological conditions, the special driving method applied in geologically difficult zones as well as the water control concept used during driving. The flexibility and the limits of the NATM under exceptional hydrological conditions are illustrated. Also described are reinforced concrete lining works for the watertight secondary vault (reinforced concrete secondary lining without water-proofing membrane).

Jan 1, 2003

By K. V. K. Prasad

Stochastic simulation has been routinely used for performing risk and sensitivity analyses in a variety of fields. The commonly used means of generating the simulations has been the Monte Carlo approach which usually employs a Simple Random Sampling (SRS) scheme of the variable distributions. This method is prone to sample clustering and requires a large number of samples to represent the distribution faith-fully. This can become problematic for simulating complex processes where it is impossible to run an arbitrarily large number of replicate simulations. The Latin Hypercube Sampling (LHS) method uses a stratified sampling approach which assures representation of the input distributions for any given number of samples. In this paper the LHS and SRS approaches are compared using a petroleum resource estimation example.

Jan 1, 1993

By Zhiguo Chang, QINGXIANG CAI, Ebelia Manda, IZHAR MITHAL JISKANI, XIANG LU, Wei Zhou, Saleem Raza Chalgri

The concept of mine safety is highlighted in the literature of sustainable mining but not extensively discussed. This study analyzes various aspects of underground and surface mine safety and emphasizes its importance in the context of sustainable mining. More specifically, this research attempts to find the relationship between mine hazards and demographic characteristics, examine and compare the perceptual difference among miners, and determine the impact of mine hazards on workplace safety and safety climate. Descriptive analysis, chi-square test, independent samples t test, and linear regression modeling were conducted to achieve study objectives. Results confirmed that mine hazards were significantly associated with age and experience. Miners perceived lower levels of management safety practices, followed by supervisor safety, coworker safety, and job safety. The analysis showed that underground miners reported lower safety scores than surface miners. There was a statistically significant difference between miners’ perception of safety climate (p < 0.05). The results showed that the higher prevalence of mine hazards predicts poor workplace safety and a low safety climate. The regression models revealed that mine hazards have a significant effect on workplace safety (p < 0.05) and safety climate (p < 0.05). In conclusion, the distinctive model of mine safety presented here contributes to the monitoring and design of comprehensive safety interventions and helps to better understand how certain factors interact on multiple levels to influence the overall safety of the industry. In this study, some suggestions are put forward to provide directions to develop a sustainable mine safety system.

Mar 27, 2020

By Hemant Agrawal, Arvind Kumar Mishra

Rock breakage using blasting is one of the important operations of the mining industry. The delay timing decides the initiation sequence of holes in the blasts and is a crucial factor to improve the overall blast performance. Blast-induced ground vibration is an undesired yet unavoidable outcome of blasting. Peak particle velocity (PPV) is commonly used to measure the magnitude of blast-induced ground vibration. Channelization and better utilization of explosive energy delay are provided between blast holes using initiating systems. The use of different initiation systems even on the same site results in a very significant difference in the values of PPV generated. Due to scattered delay timings of pyrotechnic detonators, the scaled distance predictor equations obtained become unreliable. The error/scatter in delay timing leads to overlapping of holes and hence increases in maximum charge per delay. In this paper, an analytical approach has been discussed to measure the overlapping of holes during blasting with initiation systems having inherent cap scatter. The analytical approach will be calculating the probable overlapping of holes due to scatter in delay timing and will help blasting engineers to understand the variation in maximum charge per delay due to pyrotechnic based initiating systems. In this study, a total number of 102 blasts were conducted using different initiation systems at two different opencast coal mine and 221 corresponding blast vibrations events were recorded.

Nov 10, 2020

By Thomas E. Finch

Engineering mine design encompasses a range of situations, and each situation has its own range of detail and fineness. The most time consuming, and perhaps repetitive design situation involves evaluation of new or alternate mining methods. Many man years are consumed examing alternatives conjured up at all levels of the design team, from the number crunching engineer to the engineering manager. Many alternatives are intuitively disregarded, some are briefly evaluated and thrown out, and many others are started but not completed due to time constraints. All alternatives have similar input characteristics and evaluation procedures. In the design process, production requirements are known and equipment production capabilities are generated to determine the numbers and costs of an equipment type required to match a given situation. The end result is some comparative figure, typically cost per ton or yard upon which a decision is built. The similarity of input data and problem solving techniques lends design to computer solution. Computer aided equipment evaluation is not new to the mining industry. An existing and accepted technique is exemplified with the programs used by truck manufacturers. Given a haulage profile and production requirements, the number of anyone capacity, horsepower, tire size, gear ratio or similar characteristically identified truck can be determined. This information can be outputted in varying degrees of complexity and the results used with equally varying percentages of credibility by design or production engineers. Most engineers are willing to accept-the computer&apos;s effort with relief and a desire for belief. Although inherently more complex, the ultimate end of computer manipulation should be total mine design. This is an extremely large step in the evolution of mine design, and not many engineers, including the authors, believe the results would be directly applicable or necessarily correct. As with computer simulations of an operation, total computer design of mines requires such complex and lengthy input that each mine might be manually designed more quickly and cheaply. The existence of computer programs which initially evaluate a mining system or part of the system is upon us, however.

Jan 1, 1978

By Hongqiang Wang, Qingliang Wang, Eming Hu, Zhiwu Lei, Fang Hu, Rui Zhang, Wei Hou

Pyrite, a mineral associated with uranium ore, is closely related to uranium leaching. In this study, Ozone micro-nano bubbles (OMNBs), as an environmentally friendly advanced oxidation technology, were used for the first time to oxidize pyrite under experimental conditions to improve the leaching rate of uranium. A laboratory-scale agitation leaching experiment of pyrite was carried out with a pH of 1.0–3.0, gas flow of 1–3 L/min, ozone generation rate of 0.55–2.22 mg/s, and pyrite concentration of 0.1–5.0 g/L for 1 h. By adding three different co-oxidant: Mn(II), Mn(IV), and Fe(III), it was found that only Mn(IV) increased the oxidation rate of pyrite by 21.7%. The results of the scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) show that the formation of Fe(III)-O film on the surface of the ore suppresses the oxidation rate of pyrite to a certain extent. Pyrite can be rapidly oxidized up to 57.6% by OMNBs, which is beneficial to uranium leaching. This method is expected to be used for in situ acid leaching of uranium with OMNBs injected into the ground.

Jan 3, 2022

By Mahamuda Abu, John Kalimenze, Benatus Norbert Mvile

The central Dodoma region of Tanzania is one of the regions defined by the Tanzania Craton (TC). Although the Craton gold mineralization has been well explored and hosts most of the gold deposits in the country, the understanding of the mineralization potential of the Dodoma region is still an enigma. This study using trace elements geochemistry of soil samples aims basically at providing information for future exploration works in the region by delineating the possible mineralized zones, the pathfinder elements, and the lithological facies to target. Generally, there is an anomalous spatial distribution of a probable Cu-Au deposit in the N, NE, S, and SE parts of the region and are prospective areas worth exploring for gold from the Gaussian variogram models. The multivariate statistics shows that Cu, Pb, Zn, and Fe are the main pathfinder elements while searching for Au mineralization in the region. The gold deposit is most probably a Cu-Au porphyry type, although VMS type of Au deposit cannot be precluded in the area. The mineralization in the area is largely associated with tonalitic orthogenesis, tonalities, granodiorite, and granitic rocks with Cr-Ni-Co-V forming elemental association. This elemental association is similar to other gold bearing greenstone belts. The style of mineralization in the Dodoma region is similar to other gold deposits within the TC; hence, successful exploration methods in these ancient gold deposits like Geita and Kahama gold deposits can be adopted in the event of any further exploration exercise in the central Dodoma region.

Jul 12, 2021

By A. L. Hinde

The recovery of heavy minerals by gravity concentration during grinding is practised widely in the minerals industry. Studies have shown that the grade and recovery of the concentrate depends not only on the performance of the concentrator but also on the degree of liberation achieved in the mills and the scavenging action of the hydrocyclones closing the grinding circuit. In the current study, consideration is given to the development of mathematical models to quantify and unify the operations of comminution, liberation, classification and concentration. The models are based on test work done at production scale with gold ore.

Jan 1, 1985

By James C. Hower, B. K. Parekh

Introduction The purpose of coal preparation is to improve the quality of coal to make it suitable for a specific purpose by (1) cleaning to remove inorganic impurities; (2) sizing-crushing or screening, or both; and (3) special treatment, such as dedusting. The properties and quantities of impurities in coal are of major importance in the design and operation of steam generating equipment. Although boilers are often designed and equipped to use a wide range of coals, no boiler will perform equally well with all types of coals. All coals have certain properties that place limitations on their most advantageous use. These limitations are especially stringent for many of the older installations. Because of a general lowering of quality of raw coal in recent years, the need for coal cleaning has significantly increased. Among the factors contributing to the need for increased coal preparation are (1) increased demand for quality brought on by market and environmental requirements; (2) increased extraneous dilution caused by mine, health, and safety laws; and (3) depletion of the higher-quality coal seams. The major characteristics of coal and impurities from the standpoint of mechanical cleaning are particle size composition, generally called size consist; density differences; the relative friability of the coal and its associated impurities; hardness; and strength. Some of the other factors related to preparation are petrographic composition and rank. RANK CLASSIFICATION Coal is a general designation for a great number of solid organic minerals with different compositions and properties; all are rather rich in carbon and have a dark color, generally black. Next to mineral oil and kerogen, coal is the most important reservoir of carbon in the world. Carbon is an indispensable necessity of life as well as the main source of energy. Coals are found in stratified deposits, sometimes at great depths. All coals owe their origins to slow decomposition and chemical conversion of immense masses of organic material. As found in seams, coal is a heterogeneous mixture of organic and inorganic materials. Not only are there large differences in the properties of coal originating from different seams, but also in coal removed from different locations in a single seam. A genetic relationship exists between peats, brown coals, lignites, biturninous coals, and anthracites. As a whole, the process of coal formation, or coalification, proceeds as a continuous transformation of plant material, each phase characterized by a degree of coalification, or rank. As a measure of this rank, the carbon content or some related parameter can be used.

Jan 1, 1991

By Y. Gonzalez

The reaction kinetics of sulfuric acid leaching of brass foundry flue dusts were studied. As received flue dusts were separated into two size fractions, a coarse fraction (median size 103.5 microns) and a fine fraction (median size 3.4 microns). Experiments were performed on both fractions al-though most results are reported for the coarse fraction. Leaching experiments were conducted in a stirred reactor to determine those factors which govern the kinetic response of the sys-tem. The kinetics were followed by determining the increase in the concentration of dissolved copper with time. The effects of temperature, concentration and oxygen partial pressure on the rate of copper dissolution were examined. In addition, reaction residues were examined by SEM, EDAX and X-ray analysis. An activation energy of 4.8 kcal/mole (20.08 kJ/mole) was calculated. The rate was found to be significantly dependent on oxygen partial pressure and acid concentration. The order of the reaction with respect to oxygen partial pressure and hydrogen ion concentration was approximately 1.50 and 0.37, respectively. Results indicate that the dissolution reaction is limited by diffusion and can be described by the following mathematical expression where ~ is fraction of copper extracted in time t

Jan 1, 1988

By J. K. Horbaczewski

The reclamation of an open dragline pit (Pond A3P-2) at the Gibbons Creek lignite mine in east-central Texas required neutralization of acid mine pit water. At the start of treatment with hydrated lime (Ca(OH)2) on March 28, 2000, the pond had partially filled with 913,000 m3 (740 acre ft) of pH 4.9 water. Another 666,600 m3 (540 acre ft) of pH 3.3 water was pumped in from an adjacent pit (PitA3P- 1). By the end of the project (July 5, 2000), a combined volume of 1,579,000m3(1,280ac-ft or 417milliongal) in PondA3P-2 had been successfully treated to pH 8.2 with 431 t (475 st) of lime. This was two to three times more neutralizer than laboratory trials and detailed chemical titration had predicted. The main reasons for the difference are thought to be the inadequate representation in a laboratory setting of some of the chemical reactions that occurred in the field, including incomplete mixing of reactants, reactions with clay minerals in the pit walls, the kinetics of biologically-mediated reactions and the kinetics of aluminum oxyhydroxide polymerization (aging).

Jan 1, 2002

By David B. Brooks, Roger L. Williams

Control of the environment is as old as mining. Engineers have always had to consider how best to deal with the surface, and the character of the surface environment always affects mining method in some way. However, if the relationship of the mine to the environment is old, today&apos;s approach is new. For one thing, land, air and water formerly could be viewed simply as obstacles to be overcome or resources to be utilized to win ore at the lowest possible cost. Now we have come to realize that these nonmineral components of the environment also are highly valuable. For another thing, environ- mental protection has become a public policy issue. Again, a special public interest in land and land use is old. From the firs(, the crown claimed extra rights in valuable minerals, and to this day a multitude of laws and regulations control-and tax-land use in every country. What is new is the detailed public attention bring given to waste management practices, whether these wastes be in the form of solids, liquids or gases, and regardless of where in the environment they appear. (It is convenient to lump all mining environmental problems, including hank fires and subsidence, together under the term "waste management," for in effect that is what they are.) As a result of these changes, the mining engineer must consider that lie is dealing with two productive resources the minerals and the remainder of the environment-and he must expect that lie will be judged not only on his efficiency in recovering the one but also on his effectiveness in protecting the other. Further, in seeking to protect the environment, the modern mining-environmental engineer has a dual role. First, there is the obvious task of finding better ways for industry to cope with waste-management problems in actual operations. Second, there is the less obvious but equally important task of helping formulate appropriate public policy objectives for the environment. Throughout; the section it is assumed that mining is an acceptable land use for the tracts under consideration. The question of whether mining will be permitted at all on these tracts is a further public-policy issue, ultimately to be resolved politically and thus, since it is beyond the scope of engineering, is not a subject that can be usefully discussed in a mining handbook. Finally, none of the statements in the section are predicated on the assumption that required waste-management measures will be privately profitable in the conventional sense. Indeed, the reverse is more likely to be the case-at least if accounts are kept so as to include all appreciable costs and a normal rate of return on investment in waste-disposal and reclamation equipment.&apos;,&apos;,&apos; However, it is clear that improved waste management will be required of mining firms and that, to a considerable although undetermined degree, this expenditure is in the best long-run interest of both public and industry. The several studies that have attempted to quantify the impact of mining on the environment are admittedly rough but still provide enough information to indicate that there is a big job to be done. For example, something approaching 7,000 mi of stream in Appalachia alone are continuously or significantly affected

Jan 1, 1973

By Young C. Kim

Introduction and Objective of This Paper Computerized open pit mine models* are more and more used today for feasi¬bility studies as well as for long range mine planning. In fact, using these models is becoming an enforced practice due to various reasons. One main reason is its capacity to evaluate several designs in a fraction of time required by manual effort. Another reason is the necessity to evaluate several. pit designs due to ever decreasing grade of the orebody and increasing financial risk due to smaller profitability margin. In spite of today&apos;s accepted use of computer models, very little guidelines are available which the average practitioner can follow either to choose or to build the type of model best suited for his need. Consequently, the objectives of this paper are: 1. To review the current state of the art in the computerized open pit mine models. 2. To provide some suggestions for model selection. 3. To share our experiences in developing a model for a highly irregular copper ore deposit (see Appendix).

Jan 1, 1977

By S. Hamm

Elevated total dissolved solids (TDS) content in waters downstream from surface coal mines in Central Appalachia is an increasing concern, as unnaturally high TDS and/or associated specific conductivity (SC) may contribute to deteriorated stream ecosystem health. The aim of this preliminary study was to explore the efficacy of accelerated leaching as a means of minimizing long-term TDS/SC generation by problematic overburden materials. Five spoil samples were collected and leached using simulated rainwater solutions under ambient and acidified pH conditions. SC and pH were monitored during each leach cycle, and ICP-MS was used to determine how leaching conditions affected release of specific ions. This paper highlights the results of both jar and column leaching tests. Among the most significant findings was that, for certain spoil materials, SC in leach column effluent was effectively reduced when spoil was leached first with acidic rainwater followed by ambient rainwater (vs. ambient rainwater leaching alone). This suggests that accelerated leaching might aid in long-term stabilization of some materials.

Feb 23, 2014