Search Documents

By Hans W. Schreiber

Most geologic and mining engineering consulting firms* began to experience the recession with declining billing levels, number of inquiries, and proposal requests in late 1981 or early 1982. As of today, most of them have been functioning at reduced income levels for nearly a year. And while many consulting firms have apparently reached a stabilized income level, they can see little prospect for attaining normal (pre-late 1981) billing levels and income for the remainder of 1983. A few firms have escaped being affected by the recession. Such com panies almost without exception are small (fewer than 20 personnel), offer a limited range in technical capabilities, and tend to be highly specialized in a particular niche. They include those specializing in the heap leaching of precious metals ores, in ground water testing programs, and in the derivation of computer-aided programs to monitor particular mineral processing functions. Those firms affected by the economic downturn have instituted a variety of policies and undertaken actions to cope with significantly reduced incomes to bring fixed costs in line with the depressed demand for services. These changes fall into the following broad categories: • management and management practices; • markets and market definition; • marketing and the pursuit of assignments; and • administration and personnel relationships. Not all of the perceived changes have necessarily been instituted by every consulting firm, and any one appears sporadically instituted. Management and Management Practices In favorable times the managers, and often the owners of the equity, of consulting firms tend to concentrate their attention on the part of the business they find most satisfying and enjoyable. For some, this means acting as project or assignment leaders, even undertaking a specific technical aspect of the job. For others, it means constant marketing with the associated heavy travel and entertainment schedules. In unfavorable conditions, such as the current recession, managers tend to spread themselves far more thinly, expending time and effort on all facets of the business including marketing, proposal preparation and cost estimating, budgeting, general administration, accounting and cash flow monitoring, project/assignment overview, and actual client work. The manager who in favorable times concentrated on client work is now less billable. The manager who concentrated on marketing is somewhat more billable. The manager now needs to pay attention to and expend equal effort on each facet of the business just to keep all the facets in relative balance. Falling behind schedule on a client job or carrying an unduly large percentage of accounts receivable exact a cost to the firm. Clearly the absolute cost to the firm is the same whether demand for service is good or slack. But in periods of slack demand the firm is frequently less able or even unable to bear such costs. Marketing and Market Definition Markets appear to have undergone some significant changes: • Federal and state governments have assumed a greater importance as providers of work vis-a-vis both industry and private groups. • Projects with increase-in-capacity aspects have given way to projects with maintenance or reduced operating cost aspects. • Projects searching for new deposits of minerals in generally new locations have given way to projects reviewing known mineral districts or known deposits. • Industrial mineral and mining companies have exhibited a great propensity to cut back the use of consultants and to undertake as much work as possible in-house. Further-more, a number of industrial mineral and mining companies have entered the competitive arena with consulting firms, submitting proposals (usually to the federal government) in an effort to keep their staffs intact and occupied. In response, consulting firms have reevaluated their capabilities by reviewing old work and reassessing personnel. The purpose is to broaden the services offered and the potential client base, thus redefining the available market. For example, a firm specializing in assessment of technical and cost parameters of a deposit would normally assist a prospective lender in judging the deposit's suitability for project financing. That same company could easily expand into the field of analyzing production costs for an individual operation -something that is needed in periods when lower prices reduce profit margins. Similarly, a firm that has confined such economic assistance to commercial banks could expand to provide its expertise to other lending and even equity buying in-stitutions such as insurance companies. Marketing and the Pursuit of Assignments With few exceptions, consulting firms have significantly increased their

Jan 2, 1983

By Leon Maday, Dan L. Pecha, Jeremy Johnson, Daniel N. Adams

The Brightwater conveyance system includes 26 km of tunnels, a 130 mgd pump station, 2 km of micro tunnels, and a 2.4 km outfall. The tunnels extend from Woodinville to Puget Sound through varying soils in 1 to 7 bars of hydrostatic pressure and depths to 185 m. The tunnel diameters range from 4 to 6 m and include numerous lining systems. This paper highlights major shaft and tunnel design, including dual cellshafts, multiple pipe configuration tunnels, polymer concrete segments, and the use of a one pass lining designed to convey high pressure effluent.

Jan 1, 2005

By Robert A. Bauer, Paul B. DuMontelle

In 1985, participants of the multi-year Illinois Mine Subsidence Research Program conducted surveys of subsidence effects on crop production from current high-extraction mining methods, selected a site to characterize the profile, strain, fracture development in overburden materials and changes in aquifers produced by subsidence from high-extraction mining, characterized floor materia1 s in three mines, and established bibliographic reference and data base files. The Illinois State Geological Survey, University of Illinois at Urbana-Champaign, Southern Illinois University at Carbondale, Illinois Department of Mines and Minerals and Twin Cities Research Center of the U. S. Bureau of Mines are coordinating State and Federally funded research.

Jan 1, 1986

By Verya Nasri

This paper presents analysis of damages and rehabilitation design for three major French rail-way tunnels built in mid-19th century. The La Nerthe tunnel underwent ovalization deformation with excessive displacement at the springline, and pinching and bursting of the liner bricks at the crown due to tectonic residual stresses with very high lateral earth pressure. The Saint-Louis les Aygalades tunnel invert was subjected to undulatory deformation resulting in tracks misalignment, which was caused by non-homogeneity of mechanical and hydraulic properties of the ground. The Roches de Condrieu tunnel required widening to comply with the increase in dynamic envelope of trains due to their larger cross section and higher speed. The applied rehabilitation methods and constraints of work in these busy mainline railway tunnels have been discussed in detail.

Jan 1, 2008

By Paul Hewitt, Tim Smirnoff

Design and construction of the Epping to Chatswood Rail Line tunnels in Sydney, Australia required an innovative approach to define hydrogeological properties of the Sydney Hawkesbury Sandstone and provided an insight into the hydraulic behaviour of fractured sedimentary rocks. To meet restrictive water inflow and infiltration criteria both the pre-treatment of zones of fractured or highly jointed rock, and waterproofing using an interior spray on membrane for the finished drained tunnels and stations was required. Methods typically used to address the interaction of groundwater and tunnels in the Sydney Basin are demonstrated by case histories from major design-build tunnel projects.

Jan 1, 2005

By R. E. Moore

Refractories are unique ceramic materials, which are used in large quantities in steel making furnaces, metal smelting vessels, and glass melting tanks. They are required to possess high thermal shock properties and good slag corrosion resistance as well as creep resistance at high temperatures. Therefore, they are made from very refractory minerals such as lime, periclase, corundum, spinel, and zirconia. Slags are vitreous materials produced as a residue in steel refining processes. They cover a wide range of compositions and may contain pure oxides, silicates, and sulfides as well as fluoride phases depending on the melting and smelting processes. These minerals exhibit spectacular cathodoluminescence color under electron bombardment; therefore, cathodoluminescence (CL) microscopy is found to be a superior technique for the characterization of refractory corrosion by slags. Examples included in this study are (1) reaction of fluorine containing mold slags with ZrO2-C nozzle refractories promoting crystallization of the Cuspidine, Ca4Si2O7(F,OH)2, (2) corrosion of fusion cast refractories in TV panel glassmaking furnaces and formation of glass defects, and (3) reaction of spinel based castable refractories with copper smelting slags.

Jan 1, 2001

By F. Mielli

Mine operation managers are constantly tasked with identifying new ways to produce more, while using less. Mine effectiveness and reliability is the foundation of improving operational performance. Timely decisions need to be made in order to identify production waste. Intelligent data needs to be visualized in real-time. Operational events need to be captured with impacts quantified and root causes identified. Unfortunately, complex information technology solutions often have a very poor success rate, with some reports suggesting 30 percent of complex projects are canceled before completion.

Feb 27, 2013

By B. Salopek, D. Rajkovic, D. Rumenjak

In decision making support system, that are used in various fields of environmental protection (environmental impact assessment, environmental management systems, setting environmental standards and regulation, etc.), it is often important to apply various mathematical environmental engineering models. The question of linking environmetal engineering modeling to decision making support system used in environmental protection is not yet methodically solved. The reasons for that could be manifold. Decison making support systems, used in environmental protection, because they are simply taken from bussines decision making, are not often adequate for specific problems raised in environmental protection. On the other hand, there are great number of types of models in environmental engineering, what urges the problem of finding the way of their proper linking with decision making support systems. The application of fuzzy logic in that field is estimated as one of possible solution of the problem.

Jan 1, 2005

By F. Grajales Muñoz

The Ciénega project, now under construction by Peñoles group, is located in the mountains of northwest Durango, Mexico. The gold and silver deposits are found in a 4-km (2.5mile) long system of veins. An underground operation will be built. The planned 1 kt/ d (1100 stpd) process plant will contain a countercurrent cyanide circuit for oxide ore and a flotation circuit for sulfide ore. Considerable resources have been devoted to the development of infrastructure in the isolated location, as well as for the mitigation of environmental impacts. Startup is scheduled for the third quarter of 1994. Ciénega’s ore bodies consist of quartz veins containing gold, silver, lead and zinc values. The vein thicknesses vary from 2 to 10 m (6.5 to 33 ft) with a northwest trend and nearby vertical dip. Veins are hosted in Tertiary volcanic rocks. The district has intermittently been explored since 1971 by Penoles. After the third series of diamond drilling and direct development work on vein, Peñoles decided to begin project construction.

Jan 1, 1994

By S. Bargigli, S. Ulgiati, M. Raugei, F. Cherubini

Metallic magnesium is mostly used in lightweight alloys in order to decrease fuel consumption in automotive applications. Several different production processes are currently used worldwide, and the magnesium production scenario is changing rapidly, with Chinese production increasingly dominating the world market. For the purpose of this paper, a novel approach to Life Cycle Assessment was applied, in which Material Flow Accounting and energy-based methods (Embodied Energy, Exergy and Emergy Analyses) are integrated and complemented, with a detailed description of the environmental hazards associated with emissions from all the different processes.

Jan 1, 2005

By K. Hanumantha Rao, A. Nayak, K. S. Narasimhan, S. N. Mahapatra

B.A. Hancock It is not at all surprising that causticized potato and potato derived amylopectin starch solutions performed much better than their parent starches. Some preparation is required to rupture the starch granules to effect the polymeric adsorption and interparticle bridging necessary for selective flocculation. In laboratory work comparing the deslime performance of causticized and autoclave cooked laboratory corn starch solution preparations, it was found that higher deslime weight rejections, with attendant proportionally greater iron unit losses, occurred with the causticized starch. These results may be specific to the ore involved but they do suggest that cooking and causticizing cause different starch granule rupture and/or starch breakdown, which have an effect on desliming response. I calculated from the data in the article that the slimes product grades were high - 24.3% and 20.3% Fe when 53.7% and 54.5% Fe concentrate products were obtained, respectively, in Table 4, and 21% Fe with a 62.6% Fe concentrate in Table 5 - using the natural tailings sample, which had a head of 34.3% Fe. It may be advisable for the authors to consider different starch preparations in future investigations. The combination of upgrading and selectivity results presented in Table 4 are not as good as the authors suggest. The authors' claim that a system has been developed to produce saleable concentrates from the Kudremukh tailings is quite disconcerting. There are many hurdles yet to be crossed before commercial application of selective flocculation becomes possible because differences between the very small-scale laboratory tests conducted and commercial application are rather large. Among the many differences are varying circuit feed grades that will occur from use of tailings, the apparent face that much lower tailings grades will be encountered in practice (it is much easier to achieve a high concentrate grade with reasonable recoveries using 34.3% Fe tailings as in the study rather than 25.3% Fe tailings grades that the plant apparently averages), the hydraulic nature of the thickeners used in operations compared to the static system used in laboratory tests, the different size distributions that will be obtained from a plant closed grinding-classification circuit, and differences in water used in a plant operation and the laboratory. The authors wrote that it was necessary to overgrind to be sure that the coarse gangue would not settle with the iron oxide floccules. This situation is likely to be exaggerated in commercial operations where it is assumed cyclones would be used for classification. Because cyclone classification is greatly influenced by particle densities, there will probably be an even greater difference in size between the iron and gangue particles in the plant, which would make the gangue slightly coarser still in relation to the iron. This would make the selective flocculation-desliming separations using the procedure employed by the authors even more difficult and, using the dispersant system the authors employed, greater overgrinding would be required. To grind finer to minimize the coarse gangue in the flocculated iron oxides is quite inefficient and appears not to broach the problem. The actual problem appears to be insufficient dispersion of the ground pulp. In this situation, addition of a dispersant would likely be required to attain a sufficiently high pulp dispersion level to efficiently effect a selective flocculation-desliming separation. Although the very coarse particles would still have a tendency to settle with the floccules, it probably would be found unnecessary to overgrind as much as indicated. Use of an optimum combination of dispersant and pH modifying reagents may also significantly improve the selectivity of desliming. Additionally, although it is possible that sufficient dispersion may be obtained by pH control alone in some situations, it is quite probable that added dispersity was obtained in the reported work from using distilled water. It is research experience that distilled water enhances dispersion. In commercial operations it may not be expected that sufficient dispersion will be obtained by pH control alone, unless the water used in the process is by nature quite dispersive. Overall, a change in the Kudremukh tailings dispersant scheme appears necessary where a dispersant is used in conjunction with a pH modifying reagent. With this change, different dispersion-flocculation responses will result that would have to be further evaluated. Therefore, it is still an open question whether an efficient and effective selective flocculation separation using Kudremukh tailings may be obtained that will produce saleable concentrates.

Jan 9, 1986

By D. Z. Mraz, R. S. Jones

Unlike in coal mines where caving methods are used, the subsidence over potash mines in Saskatchewan, Canada, is a function of gradual mining convergence. Because of the presence of high pressure water aquifers over the evaporite salt formations, the mines have to be designed as regionally stable and no caving is allowed. The extracted area converges gradually and the convergence is mainly a function of the extraction and the mining method employed. Consequently, the subsidence rate is very slow and the bridging of the over-lying strata is a considerably more important phenomenon than elsewhere. The paper evaluates a case history of convergence and subsidence in a deep potash mine in Saskatchewan.

Jan 1, 1986

By Jacek Paraszczak

Numerous problems encountered in the mining of narrow vein deposits challenge the productivity, competitiveness and profitability of many mines. Mechanization of mining operations is one of the most important means to ensure the healthy survival of this mining sector. Vein deposits account for nearly all the world's primary silver production, as well as a significant portion of gold, tin, copper lead and zinc. In North America, narrow vein mining constitutes an important sector of the industry. Operators exploiting such deposits are concerned with the most appropriate mining method and equipment to mine in such a way as to minimize waste rock dilution. Unfortunately, most of the equipment available does not meet the additional geological and economical restrictions typical of narrow vein mining. Thus, mining these deposits is labor intensive and can result in low productivity. Consequently, the profitability of many such mines is reduced. Increased mechanization is one of the solutions to ensure their healthy survival. This paper reviews the state-of-the art in mining equipment with reference to narrow vein mining limitations. Problems encountered Geological conditions and economical factors have a decisive impact on the choice of mining method and equipment. Many ore bodies are relatively small, usually erratically distributed, often less than 2 m (6.5 ft) wide, with dips ranging from 0° to 90°. To make things worse, ore body limits are sometimes difficult to determine and the ground is hard and abrasive.

Jan 1, 1992

By E. Sirolli

In recent times, with rare exceptions, most economically viable ore discoveries have been large, low-grade and located in remote parts of the world. Mining companies have often shown to be incapable of mitigating their social and economic impact on local communities. Sustainable development and relations can be achieved by implementing bottom-up methodologies to the top-down tools already in use by mining companies. In order to magnify the importance of enterprise facilitation as a primary method for community development, data from 25 years of community based work around the world was used. Results highlight the need for a grassroots approach to local economic and community development, which focuses on the creation of a parallel economy in communities. Using solely top-down methodologies for developing community relations is shown to be a limited resource for mining companies. There are fundamentally two dangers for mining companies: alienating the local population, resulting in militancy and lengthy legal battles to obtain a license to operate; and, being accountable for building social and economic infrastructure that are not the company?s responsibility.

Jan 1, 2012

By Yucheng Li, De Huang, Yonghong Liu

Mine frictional resistance is one of the essential parameters of mine ventilation systems, and it is of considerable significance for the prevention and control of mine risks and accident hazards. Frictional resistance requires a lot of resources and time and has errors. To reduce the errors of frictional resistance, a regression model of frictional resistance is proposed based on the correlation analysis of the affecting factors. Through the comparative test analysis of seven regression methods, it is found that the classification and regression tree method for solving the proposed regression model has better performance than other methods. The least square error criterion is used to calculate and rank the importance of the factors affecting frictional resistance. The results show that the cross-sectional area of the tunnel, the support method, and the presence or absence of devices or pedestrian ladders have the most considerable influence on the prediction accuracy of frictional resistance. The support methods and cross-sectional areas are essential input variables. Through the combination test analysis of the influencing factors, the results show that the regression model does not have predictive ability when the number of input variables is less than 3 and the best predictive performance cannot be obtained using all the influencing factors. The best prediction model of resistance is to combine the shape of the tunnel, the support method, the presence or absence of devices or pedestrian ladders, and the cross-sectional area. The method proposed in this paper does not require a lot of resources and time investment, and the frictional resistance error is small. At the same time, it solves the problem of resistance prediction with incomplete data of influencing factors and provides a compelling new method for obtaining frictional resistance parameters.

Jan 28, 2022

By MUSTAFA ERKAYAOGLU, ENVER YILMAZ

Coal is still a part of energy generation worldwide and has a significant role in the sustainable development of countries. The amount of shallow coal deposits is getting scarce, making efficient underground mining operations crucial for both local and global economies. In underground mining operations, longwall mining is a commonly utilized method to extract deep coal deposits. One of the leading engineering goals in longwall mining is increasing the efficiency of the system by investigating the effects of operational factors on equipment. This paper investigates the shearer performance for a longwall top coal caving operation by discrete event simulation that includes modeling the double-drum shearer, belt conveyors, stage loader, and armored face conveyors (AFC) to evaluate system performance by considering the amount of daily coal production of the shearer. As a result, the most influential factor on mine production is determined and a data-based framework is developed. This study suggests a framework for data collection, data analysis, and the interpretation of the operational data to evaluate the primary production unit’s performance. The models developed for the face coal extraction operations in a longwall top coal caving (LTCC) mine have a bi-directional cutting system and can be implemented in other operations readily.

Jul 2, 2021

By Congcong Chen, Bo Ma

When assessing the safety of a tailings dam, the constant weight method (CWM) is one of the most commonly used methods. However, when the evaluation indicator value suggests serious defects, the evaluation value is often inconsistent with the actual situation. To address this issue, the variable weight method (VWM) is introduced to assess the safety of the tailings dam. Initially, a three-layer indicator system for dam failure safety assessment is built, and individual indicator values are divided into four grades. Then, an appropriate state variable weight function is constructed and relevant parameters are determined. Finally, a case study is illustrated to verify the effectiveness of the model. The assessment results of the VWM more closely represent the actual situation than that of the CWM, which is more helpful for decision makers and technicians to take scientific and reasonable precautionary measures, thereby improving the safety management of the tailings pond.

Oct 8, 2022

By J. Chai, H. H. Sedarat, Gary J. E. Kramer, A. Kozak

Precast concrete segmental lining systems have been gaining widespread use in seismically active areas and a single-pass version of such a system has been developed for use on the Silicon Valley Rapid Transit (SVRT) Project in San Jose, California. The response of tunnel linings to seismic shaking is often predicted using engineering judgment, elastic closed-form solutions and numerical modeling. Such analyses generally assume a continuous structural system and hence do not explicitly model the behavior of the jointed segmental lining. A number of analyses were performed to predict radial and circumferential joint behavior during seismic ovaling and wave propagation. These analyses included a complex, three-dimensional finite element based ground-structure interaction model that incorporates inelastic constitutive soil behavior, cracked concrete properties and no-tension, frictional segment joint surfaces. The paper discusses the results of the analyses and provides guidelines for the design of precast systems in zones of high seismicity.

Jan 1, 2007

By B. Spigarelli

Carbon dioxide sequestration by conversion to carbonates has become a promising option for CO2 storage. Experiments were conducted to determine the feasibility of CO2 sequestration at ambient conditions using a Ca-rich industrial waste in a carbonate solution. The Ca-rich industrial waste used in this study was lignite fly ash. Fly ash was chosen because it is cheap, available near large CO2 point sources, already in powder form, and reactive due to amorphous properties. In the experimental set-up, CO2 absorption was inferred by monitoring feed and exhaust gas CO2 concentrations. The addition of an alkali to a fly ash-distilled water solution provided a 50% increase in CO2 absorption of the solution. Absorption time also increased by 50% compared to a fly ash-distilled water solution. TGA analysis was used to determine the extent of CO2 sequestration in the carbonate form. At a liquid to solid ratio of 20:1, the conversion of ?free? calcium to carbonates was 75%. A CO2 balance on the system concluded that at the current operating conditions 42% of the total CO2 fed to the system was sequestered in the carbonate form. SEM-EDS analysis of the fly ash particles before and after reaction with CO2 indicated that the carbonate compound being formed was calcium carbonate. The analysis identified rhomboidal structures on the surface of the fly ash particles after reaction with CO2, but not before. These rhomboids are characteristic of calcium carbonate formation and they had higher Ca, C, and O concentrations than the host spheres, suggesting calcium carbonate formation.

Jan 1, 2012

By R. Frim, S. D. Ukeles

The present U.S. production of bromine is from inland brines located in Arkansas and Michigan. The most concentrated domestic brines (up to 5,000 ppm bromide)are situated in Arkansas. Less concentrated brines(about 2,500 ppm bromide) are located in Michigan. The amount of bromine sold or used in the United States came from three companies operating in those two states. Its value was $191 million. In 2004, the estimated U.S. bromine production was 222 kt (244,000 st). That compared with 216 kt (238,000st) produced in 2003.

Jan 1, 2005