Search Documents

By V. Saltas

The present work investigates whether dielectric spectroscopy can be used to detect contamination, which may appear in a natural porous material, due to the spreading of pollution. For this purpose, dielectric and conductivity measurements, in the frequency range of 10mHz to 1MHz, were carried out in sandstone samples, partially filled or saturated with solutions of leachates, at different concentrations. The experimental results suggest that although the role of water is dominant to the measured electrical conductivity, variations of two orders of magnitude are observed due to the different concentrations of leachates, in partially filled sandstone samples. Experimental data are well fitted with a Havriliak?Negami dielectric relaxation function, superimposed with a conductivity term. The parameters of the fitting function have been correlated to the concentration of leachate in the sandstone samples and considerable changes have been observed at low leachate?s concentration.

Jan 1, 2005

By Jin Kim, Jerry C. Tien

Water is still the most economical and popular means of controlling dust underground. It is a process that captures dust by bringing water droplets into intimate contact with coal particles. Wetting agents, also known as surfactants, can be added to greatly facilitate such a process since they tend to reduce the interfacial tension between the coal particles (usually hydrophobic) and the liquid. The surfactants used in the study were first chosen on the basis of their HLB (Hydrophile-Lipophile Balance) value, and later tested in order to select the right type and amount of surfactants to give the best performance. Both static and dynamic tests were later conducted using different types of surfactants to examine their respective wetting effectiveness on coal particles. Experimental results show close correlation with the theoretically calculated collection efficiency that is based on a horizontal tunnel and a solid-cone water spray.

Jan 1, 1993

By Jerry Harrington, Brad Wigglesworth, David C. Beling

Commercial operations at the open pit, heap leach Crofoot Mine commenced in April, 1988. Approximately 13,600 tonnes (15,000 st) of low grade pregnant solution are treated daily using a Merrill-Crowe circuit. Acceptable gold recoveries from these low grade solutions can be obtained by optimizing solution pre-treatment prior to zinc addition.

Jan 1, 1990

By R. Bruce Thorndycraft

Heap leaching should not be chosen for development of a property solely on the basis of paper studies. Management should be made to understand where the risks are in heap leaching, and management should be alerted to the variability of costs in heap leaching, many of which are based upon company philosophy. These concepts are complex, but easily illustrated with guided tours of existing heap leach facilities.

Jan 1, 1998

By Moudgil. B. M.

The amount of hydrophobic materials constituting the mineral froth strongly influences the froth viscosity. Higher truth viscosity, on the other hand, can retard the drainage of physically carried over, hydrophobic particles. In phosphate flotation tests, a direct correlation was observed between froth viscosity and recovery, and an inverse correlation existed between froth viscosity and grade. Phosphate flotation tests in the presence of a silica depressant indicated that higher froth viscosity is an effect rather than a cause for the presence of silica particles in the froth.

Jan 1, 1994

By L. Buckingham

Barrick Goldstrike Mines Inc. has embarked on a continuous improvement effort to ensure that Barrick Gold Corporation will retain its lead in the gold industry in years to come. The continuous improvement initiative is based on careful mapping of the key levers associated with each activity of business. The individual levers are then evaluated to determine their potential to affect the profitability and safety of the operation. The most promising are diagnosed for root causes. These root causes are then addressed to enhance benefits. Through a structured approach of mapping, brainstorming, evaluating and instigating change with follow up measurement and reporting; Barrick Goldstrike is anticipating an increase in throughput at the autoclave facility of 10% with little or no capital expenditure. The resultant approach to Continuous Improvement will be utilized throughout the Goldstrike facility and then throughout Barrick's world-wide operations.

Jan 1, 2002

By Patrick R. Taylor

This paper presents a fundamental study of the thermodynamic and kinetic effects of copper and iron on gold-cyanide leaching. It quantifies the solubilities of the impurities, complex formation, and kinetic effects. The necessity of solution recycle, to meet environmental standards, requires that fundamental information be generated to characterize behavior and allow the identification of treatment methods. Mathematical descriptions of both solubilities and kinetics will be presented

Jan 1, 1983

By R. V. Huff

An in-situ leaching technology was developed for copper oxide minerals at the Van Dyke deposit at Miami, Arizona. This paper discusses the process developed and the activities that occurred. Specifically, the activities of well installation, deposit data acquisition, leach testing and equipment development are reviewed. Installation and operation of the test facility are described.

Jan 1, 1988

By Youning Li, William J. Drury, Christopher H. Gammons

A demonstration scale, subsurface flow anaerobic wetland was built to treat zinc and other metals in surface drainage near the historic mining center of Butte, MT. Based on three years of continuous monitoring (1996-1998), copper and cadmium were effectively removed year-round, but attenuation of dissolved zinc was dependent on hydraulic residence time (HRT) and bacterial sulfate reduction (BSR) rates. BSR rates decreased in winter months, as did HRT due to the development of thick frost zones in the substrates. An additional problem was the inability of the wetland substrate to completely filter out fine-grained particles of ZnS forming in the anaerobic cells.

Jan 1, 2000

By G. D. Naugle, L. C. Atkinson

Introduction Deep open-pit mines invariably affect the local and regional hydrologic systems. Pit dewatering, occurring during mining operations, puts an obvious hydrologic stress on these hydrologic systems. However, post-mining hydrologic impacts resulting from the pit refilling with groundwater following the cessation of mining activity can also be significant. The prediction of the rate at which the post-mining pit will fill with groundwater is a critical aspect of assessing the long-term hydrologic impacts. Numerical groundwater flow modeling provides a method for predicting the groundwater refilling rate of the pit. The rate at which pit "lakes" fill depends on several factors: •the rate and duration of pit dewatering; •the depth and size of the ultimate pit and •the pre-mining hydrologic regime. These factors can be incorporated into a detailed numerical groundwater flow model that can then be used to assess the effects of dewatering and post-mining recovery on the local and regional hydrologic systems. A sufficiently detailed, numerical groundwater model provides the oportunity to: •account for complex geology near the pit; •assess the impact of active pit dewatering and •predict the long-term impacts of post-mining groundwater flow into the pit. A detailed groundwater model incorporating these items has been developed and applied at an operating open-pit mine. Developed by Durbin and O'Brien (1987), the three-dimensional, finite-element, groundwater flow model was used to represent the hydrologic system of an approximately 253-km2 (98-sq mile) area surrounding the pit. Historical groundwater elevation data, stream flows and meteorologic, geologic and geophysical data were used to establish the dimensions and initial conditions for the model. Steady-state conditions, representing the pre-mining local and regional hydrologic systems, were simulated using the initial conditions incorporated into the groundwater model. The groundwater model was then utilized to simulate various dewatering programs, to predict the filling rate and the groundwater depth in the ultimate pit once mining activities are complete and to assess the long-term impacts on the regional groundwater flow system. Development of pit lake model Groundwater modeling efforts were completed in two phases. The first focused on pit dewatering activities, while the second phase concentrated on the post-mining effects on the hydrologic system. The final estimates of groundwater elevations calculated during the pit dewatering simulations were used in predicting the post-mining recovery of the hydrologic system. The groundwater model was also modified prior to the second phase to account for the volume of rock removed during mining activities. To account for the actual volume of rock mined, the geometry of the post-dewatering model grid was modified to approximate the final pit geometry. The depth and width of the ultimate pit were divided into eight idealized stages that represented significant changes in the bench geometries. These eight stages were then introduced sequentially into the model according to the predicted water elevations within the pit. In this way, changes in the volume and depth of water within the pit were accounted for through time. Once the ultimate pit geometry was accounted for in the model, it was necessary to assign new hydraulic characteristics to those parts of the model grid (elements) that represented excavated rock. The solution of the numerical model requires that finite hydraulic conductivity values be assigned to the portion of the groundwater model that represents excavated rock. Therefore, the calculated groundwater elevations differ, somewhat, between the edges and the center of the open pit. These model-calculated water elevations at the edge and in the middle of the open pit represent the elevation of water that would occur in the pit lake. To minimize the error in the estimated level of water within the pit lake, the hydraulic conductivity was increased to a value that would: •minimize the predicted difference between the groundwater elevations across the open pit and •produce a numerically stable solution. Specific storage is the hydrologic parameter that accounts for the water produced by compaction of the aquifer matrix. To predict the groundwater volume that would flow into the ultimate pit, this parameter was assigned a value equivalent to the compressibility of water. This value of specific storage reflects the post-mining groundwater storage occurring as an open body of water. Additionally, a specific yield of 1.0 was assigned to the pit elements to represent the 100% porosity of the open pit. In

Jan 1, 1994

By H. Lyn Bourne

The is the 13th year for this column and the 12th in which the royalty data have been tabulated. There still exist some holes in the list of royalties that readers hopefully will fill. The most common mineral commodity is construction aggregates - either sand and gravel or crushed stone. In spite of their pervasive use nationwide, there are states from which the author has no information about royalties for either of these commodities. The reader can help - share information about these missing states and next year there will be fewer states without information. Severn Brown again sends helpful information from the Prospectors and Developers Association of Canada (PDAC). The PDAC Digest contained an article that distinguished between ‘net smelter return royalty' and ‘net profits royalty’ (Haase). The article also lists clauses and details that Brown suggests should be included in a net profits royalty contract.

Jan 1, 1994

By N. K. Dumakor-Dupey, K. J. Bansah

"We made site visits to determine potential environmental issues caused by artisanal and small-scale mining (ASM) in the Tarkwa Mining Area (TMA) of Ghana. Activities of the diggers were observed to degrade vegetation, land and water. Improper handling of mercury was also identified as a major threat to people and ecosystem. Large abandoned pits and trenches posed fall traps to farmers, hunters and wildlife. We argue that lack of adequate monitoring and regulatory enforcement by Ghanaian authorities, together with inappropriate mining processes, probably due to lack of technical expertise are contributing factors to the environmental issues of artisanal and small-scale mining in the TMA. INTRODUCTION Environmental degradation caused by artisanal and small-scale mining (ASM) has been a major concern to many people and governments around the world. ASM is often associated with health, safety and environmental issues in communities where it is practiced (Kitula, 2006; Asiedu, 2013; Sousa et al., 2010). Some of the environmental issues that have been reported include land degradation, mercury contamination, cyanide release, and pollution of rivers/streams. These issues have been attributed to improper mining methods, inefficient technology, lack of technical training and environmental awareness, and lack of regulatory enforcement (Serfor-Armah et al., 2005; Bansah et al., 2016a; Hentschel et al., 2002). In Ghana, ASM typically occurs in rural communities, providing jobs to many people and contributing towards socioeconomic growth of the country (Banchirigah & Hilson, 2010; Bansah et al., 2016b; Osei-Kojo & Andrews, 2016). As a result of the environmental issues, many people have called on government to develop drastic measures to control ASM operations. It is in this regard that this paper examines potential environmental issues caused by ASM in the Tarkwa Mining Area in Ghana, and suggests mitigation measures to ensure environmental sustainability. ASM in the area comprises of registered (licensed) and unregistered (unlicensed) operations that adopt surface or underground mining methods to exploit gold-bearing materials. Surface operations typically involve clearing of vegetation, removal of overburden, excavation of mineral deposit, washing/grinding of excavated gravels and processing with mercury. Except grinding, washing and mercury recovery, underground operations are conducted below ground with limited impact on the surface. Alluvial mining is also commonly practiced in streams and along river banks. These activities can have devastating impact on biodiversity of the ecosystem. To achieve the objective for this study, field visits were made to ASM sites to observe operations and interact with diggers. Visits were also made to host communities of ASM and government officials to obtain their perspectives on ASM in relation to environmental impact. The study area (Tarkwa Mining Area) is located in the Western Region of Ghana (see Figure 1). It is endowed with natural resources such as gold and manganese. Hence, mining is the major economic activity in the area. ASM is widespread, with 15 registered operations and several unregistered mines. The environmental issues observed in the study have been grouped into three main categories: vegetation and land depletion; water quality and pollution issues; and mercury contamination issues."

Jan 1, 2017

By I. Longson

Maintaining control over underground environmental conditions in the United Kingdom is increasingly dependent on the contribution of underground booster fans. Given the recent trends of higher rates of production from a fewer number of coal faces with higher levels of mechanization and higher power consumption, the effect has been to place a greater load on the mine ventilation system. This has increased the scale of potential problems that may arise should any of the main ventilation control devices not perform at the required full duty. This is particularly true for underground booster fans. Major changes occur in the main ventilation parameters on the stoppage or restart of a booster fan which results in a temporary loss of environmental control. This paper analyzes the impact of such events and details a mathematical model thar has been developed for a single-mesh circuit containing a main and a booster fan. Predictions based on this simple model are presented and discussed with particular reference to the energy changes occurring within the ventilation system immediately following a booster fan stop or restart

Jan 1, 1995

By Richard R. Klimpel

The first part of this two-part article summarizes the result of a 10-year, multimillion dollar research and plant testing program involving operating mining companies throughout the world. The program was aimed at developing a better understanding of the influence of slurry rheology on the performance of mineral/coal grinding circuits. Part 1 presents the basic concepts identified, including typical laboratory results showing the influence on grinding behavior of controlled changes in percent solids, particle size, slurry temperature, and viscosity control chemicals. Part 2, in January, will illustrate typical industrial scale test results on both open and closed circuits using the concepts presented in Part 1. Special emphasis will be placed on identifying some industrial operating implications of controlling rheology by different methods. Introduction The industrial-scale practice of wet grinding minerals and coals in tumbling media mills (ball, rod, and pebble) is well-known to operating mineral processing engineers and plant design personnel. Over the last century, considerable experience and data has been collected, correlated, and put into rules or guidelines for successful circuit design and operation. Typical factors influencing circuit throughput that have been analyzed in some depth are mill diameter and length, grinding media size and loading, feed and product particle size, mill power use, and the interaction of classifier type and efficiency with the grinding device. Until recently, knowledge of slurry rheology influence on large scale grinding circuit performance has been limited. Even today slurry rheology effects are essentially ignored in plant design. Indeed, in most plant operations only qualitative guidelines are followed. For example, too thick a slurry causes throughput losses and too thin a slurry uses excessive water or causes water handling problems such as pumping limitations. A search of published literature and numerous discussions with experienced plant operating personnel has shown an awareness that changing the percent of solids in the mill influences grinding or the response of grinding involving fine feeds versus coarse feeds. However, most the work identified relative to rheology effects in mineral/coal grinding was qualitative. Even in the few studies that were more quantitative, the scope of the work was usually too narrow to draw general conclusions. Also, the detailed rheological characterization tied to observed breakage and the combination of laboratory to industrial-scale testing that is required to develop a broad understanding of any factor influencing grinding had not been done. In this environment, this detailed program began in 1967. It had three distinct goals: • To develop a basic understanding of slurry rheology influence on breakage characteristics in the laboratory. • To test general rheology concepts developed in the lab on the industrial scale. • To develop a commercially viable chemical approach to controlling slurry rheology that would lead to the use of chemical grinding additives or grinding aids. The goals have been met, at least in part, this year. A small fraction of the extensive laboratory and plant results have been made available in published literature. Much of the research program dealt with identifying and developing chemical grinding aids, but a lot of useful and practical information on percent solids, particle size, and slurry temperature influence on grinding circuit performance also was collected. The purpose of this article is to present a clear and concise sum¬mary of the results of the entire program. The importance of rhe¬ology control in grinding circuit behavior will be demonstrated using a series of carefully per¬formed industrial scale experi¬ments (both open and closed cir¬cuits) that have not yet been reported in general literature. Mining companies participating in the test program on a proprie¬tary basis have found the informa¬tion in this article to be useful in better understanding and improv¬ing circuit performance. Viscosity Effects in Grinding Studies In this program&apos;s previous labo¬ratory studies, it was shown that there is a consistent pattern of change in specific rates of break¬age of both mineral and coal slur¬ries as slurry fluidity changes. Using the net production rate of material smaller than some spec¬ified size-for example, kg/hr of <75 µm (200 mesh)-as an index of mill production in a standard batch mill test (with a given feed material, feed size, mill, and mill conditions such as constant time of grind), the following facts were established (see Fig. 1): • The normal range of low den¬sity, low viscosity slurry (region A) gave no variation in mill produc¬tion. The measured rates of break¬age exhibited normal first order grinding. • Grinding of a somewhat higher viscosity slurry (region B) could give increased production. The higher viscosity was obtained

Oct 12, 1982

By Dennis K. Mortensen

Improvements in flotation technology are continually being made in the attempt to achieve the mineral processor&apos;s goal of maximum mineral concentrate grade and recovery at zero cost. Technology that cannot be totally proven in the laboratory must be tested under plant conditions either in a pilot plant or in the existing circuit. Problems associated with new technology can be solved effectively by the mineral processor who approaches each of the problems objectively.

Jan 1, 1989

By P. J. L. Nel

The paper describes several successful concepts used in the sinking of shafts on the Elandsrand Gold Mine. The concepts enabled the shaft sinking time to be reduced as well as the period in which development would normally take place to establish initial ore reserves.

Jan 1, 1981

By Janusz Cygankiewicz, Marian Branny, Józef Wactawik

The paper presents mathematical model of concealed fire. We consider a porous medium (goaf, coal fissures) through which air flows. The set of equations is constituted by transient, two dimensional mass, momentum and energy balance equations with sources describing oxygen loss and heat generation caused by coal oxidation. Paper presents several examples illustrating the phenomenon of spontaneous heating in goaf areas behind longwall faces.

Jan 1, 1997

By I. C. Watson, J. W. Klokow, A. F. Knoetze, R. G. B. Pickering

In the late 1970s and early 1980s there were a number of attempts to use Tunnel Boring Machines in deep level gold mines. These attempts must be regarded as unsuccessful. Since then there have been comprehensive developments in tunnel boring equipment and tunnel support technology. This paper defines the problems experienced in those early trials, reviews the technology development, and concludes that tunnel boring in deep level goldmines can be justified in today’s environment.

Jan 1, 1999

By D. Vavadakis

Abandoned bauxite surface mines in the Parnassos area may be rehabilitated using bauxite residues as filler. The objective of this study was to estimate the percentage of precipitation that may infiltrate through the bauxite residues to the lower geological formations when they are disposed off in mine open pits. Two scenarios were investigated simulating: a) available field tests, and b) a demonstration test that was planned to be performed in an abandoned open pit close to the Aluminium of Greece plant. It was indicated that the annual infiltration from bauxite residues disposed off in the demonstration test for the most probable scenario is very low, equal to 13.17mm corresponding to 3.1% of the annual precipitation. Furthermore, it was estimated that the annual percolation from the field tests is approximately 4.4%, very close to the infiltration values measured in the field tests for the same period.

Jan 1, 2006

By Robert M. Rowe

Among the increasing operating costs affecting today&apos; s processing facilities are those necessary in meeting the continually growing requirement for safe and environmentally sound materials- control and handling procedures. Of particular interest are materials listed as hazardous, the need to maintain accurate records of their acquisition, consumption and disposal, and the obligation to employees and the community to have information available regarding such materials. Some requirements affecting modern operating facilities are reviewed in this paper, and potential methods for dealing with complex handling and documentation requirements, including computer automation, are discussed.

Jan 1, 1991