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By M. G. Irish, E. E. Vidal, M. J. Jahraus, P. R. Taylor

An experimental system has been designed to monitor on-line variations of leaching parameters in a closed circuit of cyanide leaching solutions and gold bearing ores. Experiments performed to deter-mine variations in some important leaching parameters of the solution: pH, dissolved oxygen, free cyanide, oxidation/reduction potential, gold content, temperature, pressure and solution chemistry. By comparing results obtained when the leaching solution is allowed to become acid or kept basic, it was possible to infer the chemical reactions that occurred between the solution and the ores.

Jan 1, 2004

It is crucial to reestablish a domestic rare earths minerals production industry to help secure the Nation's clean energy future, reduce the U.S. vulnerability to material shortages related to national defense, and to maintain our global technical and economic competitiveness. Given that the Chinese dominance of the rare earths market has adversely impacted supply stability and endangers the United States and its allies' assured access to key materials, rare earths should qualify as materials either strategic or critical to national security. Further, the U.S. government should facilitate the reintroduction of a globally competitive rare earth industry in the U.S. Realization of this objective requires: ? Developing domestic processing capability so that the U.S. is not primarily dependent on China as a source of rare earth ore, and almost exclusively dependent of China for processing of the ores. ? Providing a mechanism where access to Federal lands for rare earth exploration and extraction is possible, and ? Training engineers to design and operate rare earth ore processing facilities

Jan 1, 2011

By A. Sand

A 2-dimensional computational model based on the discrete element method (DEM) is utilized for modeling of stamp-charged coke making. In this process, a large volume of coal is compacted to one single coal cake before entering the coke oven. Cake densification and mechanical strength development are key factors for the subsequent production of a high-quality coke. An approach is introduced for model calibration utilizing multiple control parameters obtained from a laboratory-scale stamping device. Experimental data on stamper rebound amplitude, attenuation and peak force are compared with simulation output in a pairwise manner by constructing a criteria space, which allows identification of model settings best satisfying the control parameters. The calibration procedure carried out by multiple criteria comparison aided model parameter selection for reproducing stamper behavior in response to the properties of the cake subjected to compaction. This modeling and calibration procedure offers possibilities for numerically studying the densification and mechanical strength development of coal cakes. However, the approach is also more widely applicable to other compaction processes.

Feb 27, 2013

By S. Janisko

Studies have linked long-term inhalation of diesel exhaust with adverse health effects such as cardiovascular disease, cardiopulmonary disease, and lung cancer. Diesel exhaust levels in underground mines can approach 100 times the environmental level and are therefore monitored closely in the mining industry. Elemental carbon (EC) (a product of diesel combustion commonly referred to as ?soot?) has proven to be a good indicator of diesel exhaust levels. The current procedure for measuring EC levels involves taking personal samples from a mine worker?s breathing zone and/or stationary samples in various parts of the mine and subsequently sending these samples to a lab for analysis by NIOSH 5040 method. Unfortunately, the whole process can take up to several weeks to complete. To address the problem of waiting weeks for results, NIOSH?s Pittsburgh Research Laboratory is developing a portable device for measuring levels of elemental carbon. This optical device takes a continuous sample of air in the surrounding environment and measures the absorbance of light passing through a filter that collects diesel exhaust particulates within the instrument. This technology can provide a near real time measurement of EC with accuracy within 10% error. The ability to take near real time measurements, combined with the instrument?s portability (currently small enough to be worn on a miner?s belt), makes this device extremely useful in the mining industry.

Jan 1, 2009

By H. J. Haselhuhn

Selective flocculation and dispersion processes for the concentration of hematite ore are strongly dependent on the ionic content of the process water. It has been noticed that magnesium ions are more detrimental to iron recoveries during desliming and flotation processes than calcium. This phenomenon was studied by measuring the zeta potential of hematite ore at various concentrations of magnesium, calcium, strontium and barium at a pH of 11. Results show that zeta potential inverts from negative to positive at very low concentrations of magnesium ions in the solution. It takes a significantly higher concentration of calcium, ions to achieve the same effect. This difference may be attributed to the ability of magnesium ions to adsorb to all surface hydroxyl groups, whereas calcium, due to their larger size, can only adsorb to every other hydroxyl group. This hypothesis was confirmed by results similar to those seen with calcium when this test was repeated with strontium and barium ions. The tendency for calcium ions to adsorb to every other surface hydroxyl group causes higher concentrations of calcium to be less detrimental to hematite concentration processes than magnesium.

Feb 27, 2013

By Y. Wang, K. S. E. Forssberg, A. Johansson, X. Lu

This paper presents the desulphurisation of a fine graphite powder below 80 µm by high gradient magnetic separation. The removal of pyrite (FeS2) and pyrrhotite (Fe1-xS) from the fine graphite powder was carried out with a modified version of the Sala dry HGMS with vibration assistance. In addition, a comparative study with dry and wet HGMS systems has also been performed. In order to establish the performance of the desulphurisation, a test series of varying parameters such as magnetic induction, matrix type/configuration and vibration were performed. As an equipment/process for removing sulphurous impurities from the fine graphite powder, the dry HGMS is deemed useful and comparative with the wet HGMS.

Jan 1, 2002

By David Van Horsen

Big Creek Tunnel 2, constructed in 1912, is located in the Sierra Nevada Mountains of California, east of Fresno. It is horseshoe and circular shaped with a 3.6m (12ft) diameter and extends 6.6km (4.1mi). Historically, tunnel performance suffers from highly jointed rock and low cover. In 2003, leaks were observed surfacing through outcrops of highly jointed graniodiorite, and subsequently investigated by visual inspection, joint mapping, ground penetrating radar, and a water-tracing survey. Several grouting targets were identified as a result of these investigations. Cement grouting was used to fill void spaces, broken rock and open joints expected to exist behind the concrete and steel liners. Project work consisted of grout hole drilling through the existing concrete liners, and grout placement through squeeze packers supplied by standard grout hose and portable grout plants. Grout pressures were typically 20?30 psi. Grouting was completed in 16 days with a total of 1,550 sacks of Type II/III grout placed at the three likely leak source areas. No grout was observed exiting the tunnel and the leak was stopped.

Jan 1, 2008

By Colin P. Pigott

The paper describes a variety of existing techniques and equipment which when combined together permit faster and cheaper drilling of shafts in soft to medium strength formations. Drilling fluid circulation, methods of hole stabilisation and bit design, including the advantages of flat bottomed and conical bits, shrouds and skirts, tungsten carbide, long tooth and disc cutters are considered. The principles of rock chip transportation and bottom hole cleaning are described together with a new and very efficient fluid circulation system which was invented by the author.

Jan 1, 1985

By Gary Jackson

Preliminary engineering for the Waller Creek Tunnel was completed in 2001, but the project was held in abeyance until the summer of 2007. This paper describes several features of the revised design, which required significant changes from the original concept. Most notable is the expected replacement of a tunnel boring machine (TBM) by conventional tunneling. The considerable influence of geological conditions on the tunnel vertical alignment is discussed, in particular the impact of the zones of Eagle Ford Shale with swelling potential. Other features which are described include the wide span tunnels and large diameter shaft requirements.

By Liming Yuan

To reduce fire hazards from spontaneous combustion of coal in longwall gob areas, a series of computational fluid dynamics (CFD) simulations were conducted by the National Institute for Occupational Safety and Health (NIOSH) to model the spontaneous heating of coal in longwall gob areas. The previous modeling results demonstrate that spontaneous heating of coal usually occurred behind the longwall shields and along the face with a bleeder ventilation system. Assuming a stationary longwall face, the spontaneous heating could turn to a spontaneous fire in several days for the most reactive coal under favorable conditions. When the longwall face advances, the spontaneous heating process will be significantly affected. In this study, the effect of longwall face advance on the spontaneous heating in the gob area is investigated using the CFD model developed in previous studies. One longwall panel with a bleeder ventilation system is simulated. The width of the panel is 300 m (984 ft), while the length of the panel is changed between 1,000 to 2,000 m (3,280 to 6,560 ft). The same permeability and porosity profiles are used for gobs with different lengths. The spontaneous heating first develops in the gob when the longwall face is stationary. Then, the face advances at a certain rate. The face advance is simulated as a series of discrete movements, and the effect of the face advance on the maximum temperature developed during the face stoppage is examined.

Jan 3, 2010

By Leonel Lopez

Throughout Mexican history, mining has been an important, traditional activity. Before the "Discovery of America," native miners worked a variety of deposits throughout the country, including Mixtec gold and gem mines in Oaxaca State and Aztec gold, silver and copper from mines in Michoacán. The 500th anniversary of Mining in Mexico after the "Discovery of America" was initiated by the Mexican mining sector on April 15, 1991. As early as 1548, when the Guanajuato mining district was discovered, Mexico had become a leading world producer of precious metals. Since then, Mexican mineral production has developed in cycles, responding to changing technological, economic and political conditions. During the 20th century, Mexican mine output reached its peak in the decades of the 1930s and 1940s, when it was producing about 40% of the world's silver, 15% of its lead, 10% of its zinc, 4% of its copper and 3.5% of its gold. In 1990, by way of contrast, these percentages of world output stood at 13.5% for silver, 4.7% for lead, 4.1% for zinc, 3.2% for copper, and 0.43% for gold. The lowest production levels were recorded during the 1960s and 1970s, when Mexicanization of the industry and increasing state controls weakened mineral economics to a point that mineral exploration budgets were sharply reduced or eliminated, along with the industry's future. Only the noble old mining districts continued to supply production, with occasional eruptions of "bonanzas" and new extensions in established mining districts.

Jan 1, 1994

By Tim O’Neil

What prompted the merger of the two long-established American Mining Congress/National Coal Association (AMC/NCA) groups that combine the coal, hard-rock, industrial- and agricultural-minerals sectors of mining? Both associations have been facing similar stresses for several years - structural changes in their respective industries, the changing personality and role of government and well-financed and organized opposition groups. In 1993, the AMC board of directors undertook efforts at reorganizing the association. One board member, who serves on both boards, suggested it might be time to give serious consideration to merging the organizations. This is an idea that had been discussed more or less informally at least three times during my tenure at NCA. Negotiations toward a merger began after that and were consummated in February of this year.

Jan 1, 1995

By J. Barrett

State-of-the-art wireless communication and location-tracking technologies will dramatically change the face of mine worker safety. The MineTracer System developed by a Liberty Lake Washington company is a broad capability wireless sensor network based on a new breed of technologies known as wireless mesh systems. In this paper, R&D Manager Jim Barrett summarizes the balance of engineering tradeoffs that result in a system that (1) performs well, (2) is survivable against many types of mine accidents, (3) operates for many hours post-accident on battery power, (4) meets stringent MSHA requirements for intrinsic safety, and (5) is economically affordable for the mines.

Jan 1, 2009

By J. Darlington, A. K. SenGupta

Water-swellable layered silicates, namely, the smectite clays can remove suspended materials (called herein as debris) and metal ions from aqueous streams. The present study shows that the flocculating and metal extracting abilities of smectite clay-based flocculants can be enhanced when these clays are used in conjunction with a specific anionic polymer. Such performance enhancement is attributed to the following: i) the clay-dispersing ability of the polymeric additive, that would translate into an increase in the clay-surface area available for the attachment of the debris particles onto the clay particles; ii) the possibility of dispersant-to-coagulant transition of the polymer during the later instants of the treatment process, as a result of reduction in solvency of the wastewater for the polymer due to the release of cationic species from the clay-based flocculant solids; iii) metal-complexing ability and adsorption properties of the polymer.

Jan 1, 2002

The OptiPit® software program is developed based on expertise gained at the Colorado School of Mines (CSM) using Mixed Integer Linear Programming (MILP) techniques. This program has been developed to satisfy the need in the mining industry for a multi-time period schedule and cutoff grade optimization tool that handles large scale open pit and underground mining operations involving many dumps, stockpiles, complex processing options and blending requirements. The current software (or earlier development versions) has been beta tested and used on various large scale projects within Placer Dome Inc., Newmont Mining Corporation, and Phelps Dodge Corporation since 2003. Through the use of this software, these companies experienced additional value creation by optimizing mine sequences, cutoff grades, material process flows and stockpiles under complex operational and processing constraints. This paper will present simple case study results to demonstrate the power of OptiPit® when used as a cutoff grade optimization tool. Furthermore, the paper will show, by example, how significant the difference in the Net Present Value (NPV) of a given project can be, depending on whether results are obtained by way of cutoff grade optimization using OptiPit®, or by using traditional breakeven cutoff grade approach.

Jan 1, 2007

By Byron T. Darnton

Gravity concentration at the Pegasus Gold/Montana Tunnels Mine, near Helena, MT, began in June 1991 when a coarse-gold-scalping circuit was commissioned. It processes a small portion of the ball-mill circulating load to reduce the risk of gold particles that are too coarse to float from advancing to flotation. The circuit also cost-effectively enhances overall gold recovery and payable gold ounces. This gravity circuit has been a major success. Since the circuit was commissioned, throughput has increased 30%. Several modifications and improvements were made during the last three years that allowed the gravity circuit to keep pace with the higher tonnage. The overall approach to gravity concentration at Montana Tunnels has always been to optimize production rather than maximize the gold ounces produced. This philosophy has now yielded a circuit expansion and relocation project. It will allow for an estimated 50% increase in gravity gold production, while significantly reducing the unit costs of production.

Jan 1, 1995

Effective tools are not only essential for the design of practical and efficient underground mine ventilation systems but must also play an integral part in the operation of the mine. One such tool is VUMA-coal ventilation simulation software. VUMA-coal is Windows-based and has been specially designed for the simulation of underground coal mines and includes user-friendly coal specific interfaces and three-dimensional graphics designed to facilitate in the construction and analysis of networks. VUMA-coal can be utilised during the design phase of new collieries, be used to conduct ?what-if? and optimisation studies, and be integrated into the ?day-to-day? ventilation related operations. In addition, VUMA-coal can be used to simulate dust and gas distribution in a ventilation network, as well as predict the impact of control measures. This paper describes the interactive VUMA-coal ventilation simulation software and its underlying design features and outlines a case study of how VUMA-coal has been integrated into Anglo Coal?s Ventilation and Occupational Hygiene Engineering [VOHE] department as part of the standard planning and evaluation process in their operational mines as well as long term planning and future mining operations.

Jan 1, 2009

The stability of surfactant-free foam films was studied using the thin film pressure balance (TFPB) technique. In pure water, it was not possible to produce foam films due to weak film elasticity and strong hydrophobic force. In the presence of NaCl, however, the hydrophobic force was sufficiently dampened to allow metastable films to form. At 10-5 M NaCl, the equilibrium film thickness reached a maximum of approximately 130 nm at pH 6.0-7.3. The thinner films obtained on either side of this pH range was due to the increased ionic strengths associated with the HCl and NaOH additions for pH control.

Jan 1, 2009

By J. F. Lupo

Heap and valley leach operations rely on solution collection piping placed within the heap to enhance both solution recovery and to assist overall solution management. The most common piping used in leaching operations is solid or perforated High Density Polyethylene (HDPE) pipe and Corrugated Polyethylene pipe (CPE). These pipes are widely used because of their low cost, ease of installation, durability, and flexibility. The typical recommended maximum design depth of burial for HDPE and CPE pipes is on the order of 30 meters (100 feet). However, ore heap heights at many facilities exceed 30 meters and some are now approaching 180 meters (600 feet) in height. At very high ore heap heights, the stability and performance of HDPE and CPE pipes becomes a critical issue for leaching facility design and operation. Failure of solution collection piping can lead to poor solution recovery, high hydraulic heads on the liner system, and in some cases, unstable ore slopes due to high solution pressures near slopes. This paper presents a review of methods that have traditionally been used to evaluate pipe stability under high normal loads. A common shortcoming of these methods is the inability to account for beneficial effects of ore arching around pipes and the time-dependent creep (stress relief) behavior of polyethylene (PE) materials. A new analytical approach is developed and presented which includes the effects of ore arching around pipes and creep of PE materials. The results of the new approach show that PE pipes will deform under high heap loads, but can remain stable and functional. Pipe stability is shown to be dependent on the type of pipe backfill and initial backfill compaction. The new approach represents a useful tool for designing applications for PE pipe under high normal loads.

Jan 1, 2001

By Delon Hampton, Francis K. Mensah-Dwumah

INTRODUCTION The state-of-the art in the area of soil-structure interaction is not sufficiently developed that one can accurately predict the earth load distribution on buried structures. This lack of knowledge has led to the use of high factors of safety in their design and conservative assumptions for the loading diagrams. As a step towards the improvement of the design methodology for buried structures, it is important to be able to apply new analytical techniques and monitor the performance data obtained on full-size buried structures. The performance data should preferably include: 1) the actual stress distribution on the buried structure, 2) stress distribution in the buried structure and surrounding soil media, 3) vertical and lateral movements in the soil adjacent to the buried structure, and 4) deflection of the buried structure. Brown (1967), Davis (1972), Krizek, et al (1974), Krizek and MacQuade (1978), and some few others have compared the performance of full-size culverts with finite element results. Despite all these efforts, a complete understanding of the soil-structure interaction problem has not yet been fully achieved. In an effort to make improvements in the existing design procedures for buried structures constructed in an open-cut, the Department of Environmental Services (DES), Washington, D.C., in conjunction with Howard University, undertook a detailed study of Section II of the Capitol Hill Relief Sewer (CHRS). Inclinometers were used to measure lateral movements of the excavation wall and the total normal interface stresses acting on the concrete sewer were obtained using glotzl total pressure cells. This paper describes the results of the field instrumentation program for acquisition of data, their comparison with the design assumptions, and the results of a series of post-construction finite element analyses of the CHRS project.

Jan 1, 1979