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By B. I. Pålsson, H-Å. Häggblad, J. F. Stener, P. Jonsén

"Understanding mill charge motion is important. In the charge, the center of gravity is shifted from the rotational center of the mill system, and its motion is induced by rotation of the mill. At the same time, the charge creates a torque in the mill system. Breakage of ore particles and wear of liners/ball media are closely linked to this motion. To study these phenomena in a physically correct manner, numerical models for different parts of the mill system are needed. Validations of such models are scarce, because of the difficulty of measuring inside a tumbling mill. Experimental measurements in a lab mill were done for a number of load cases: varying feed material, mill filling, mill speed and pulp liquid. The mill is set up to measure the charge-induced torque. The accuracy is good, with relative uncertainty less than ± 2% for relevant load cases. A full three-dimensional numerical model of the whole mill is used to predict induced torque. Agreement between predicted and measured torque at steady-state is good. In addition, the model can accurately predict the mill startup behavior for torque and mill power. This proves that the model is physically correct, and can be used for modeling large-scale mills.IntroductionUnderstanding of the charge motion within the mill is of importance in mill optimization. The breakage of ore particles and the wear of liners/ball media are closely linked to the charge motion. To study these phenomena in a physically correct manner, appropriate numerical models for different parts of the mill system must be used. Validation of these models is of major importance. This has led to an increased interest in obtaining an accurate and direct measurement of mill load and the behavior of the mill charge.For structural analysis, the finite element method (FEM) is the most developed and most frequently used numerical method. FEM is a numerical solution method based on continuum mechanics modeling. A constitutive relation for the actual material is described, and the governing equations are solved in Zienkiewicz and Taylor (2000). Varieties of different constitutive models for a large number of materials are implemented in modern FEM code. The computability of nonlinear problems in solid mechanics is investigated in Belytschko and Mish (2001), among others."

Jan 1, 2015

By K. Rajamani

The word adapt means "to change so that one's behavior will conform to new or changed circumstances." Applying this definition to process controllers suggests that an adaptive controller can change its behavior in response to changes in the dynamics and disturbances of the process. In the minerals industry there are many control cases where adaptive control will provide superior control as compared with more traditional PID (proportional, integral, derivative) control. A typical plant uses as many as 100 to 200 control loops for lprocess regulation. Therefore, the task of initially tuning and then periodically retuning these controllers is a formidable problem, During the time the controllers are "un-tuned", product quality may deteriorate and unstable operations may result. Adaptive controllers are capable of tuning themselves, thus avoiding this problem. The computers commonly used in distributed control systems are easily capable of implementing adaptive controllers. In addition to the possibility of using the control computer to implement adaptive controllers, many distributed control systems will offer adaptive control as a standard feature in the near future.

Jan 1, 1984

By R. Riding

Degussa Corporation's peroxide-assisted leaching (PAL) process was evaluated in the batch concentrate leach circuit at Hecla Mining Company's Republic Unit. The product leached in this batch circuit is a high grade gold-silver sulfide (predominately pyrite) flotation concentrate. The primary objectives of the test program were to determine the effects of dilute hydrogen peroxide addition on leaching kinetics, sodium cyanide consumption and precious metals recovery. The results of the testing demonstrated that using dilute hydrogen peroxide produced the following benefits: - 1. Batch leach time requirements decreased by 80%. - 2. Sodium cyanide consumption in concentrate leach reduced by 55%, which translated to an overall plant reduction of 20%. - 3. In the concentrate leach process, gold recovery was increased by 1 to 2%. Because of the excellent metallurgical results achieved with the use of dilute hydrogen peroxide, as well as an economic incentive, PAL has become standard practice in the concentrate leach circuit operation. A complete description of the Republic PAL plant evaluation and performance is provided in this paper. In addition, process chemistry considerations in regard to the role of hydrogen peroxide are discussed.

Jan 1, 1992

By Kim B. Shedd, Erin A. McCullough, Donald I. Bleiwas

"The earliest known use of cobalt was to make blue glass in Mesopotamia before 2000 B.C.E. Since then, innovations across many diverse industrial sectors transformed cobalt into an essential commodity for contemporary society. The physical and chemical properties of the element cobalt and its alloys and compounds make them indispensable for a variety of applications, including aircraft engines, hybrid electric vehicles, machine tools, missile guidance systems, petroleum refining and smartphones. As a major industrialized nation, the United States is a leading consumer of cobalt and cobalt-containing products. However, with few exceptions, U.S. cobaltcontaining ore deposits are of low cobalt grade. Historically, U.S. cobalt mine and refinery output have not met domestic cobalt demand. As a result, U.S. cobalt chemical and alloy producers need to procure most of their cobalt from the international market, which can become susceptible to supply risk.The 1978 Cobalt Crisis illustrates supply risk. At that time, the Democratic Republic of the Congo (DRC) (then known as Zaire) was the world’s leading producer of mined and refined cobalt. An insurgent invasion of the country’s copper-cobalt mining region during a period of high cobalt demand and low producer inventories caused a temporary supply shortage in the international market. The monthly average cobalt spot price increased from $18/ kg ($8/lb) before the crisis to $99/kg ($45/lb) seven months later. The high price and concern about potential disruptions in supply prompted manufacturers to reduce or substitute for cobalt where possible, and encouraged increased recovery of cobalt from scrap. The DRC has regained its position as the leading producer of mined cobalt globally and continues to be characterized by high governance risks (U.S. Central Intelligence Agency, 2015; World Bank, undated). This article will present current and historical world cobalt production trends, which can help inform discussion about the variety of international supply chain risks consequential to its trade."

Jan 12, 2017

By A. B. Holland-Batt

Following a relatively static period in the 1960s and 1970s when incremental development rather than innovation was the norm for gravity separation, the last 15 years has seen a number of new developments in this area. The paper briefly reviews the traditional gravity separation techniques and then examines the newer developments such as centrifugal separators. Particular emphasis has been placed on novel devices or improvements that offer either better control or improved performance.

Jan 1, 1998

By T. Harris

Exports of crude gypsum from Mexico currently comprise about 60% of all domestic shipments, and about 25% of the imported material consumed in the U.S. wallboard industry. However, of growing importance are the domestic markets for calcined gypsum in Mexico including building plasters and wallboard, which account for 55% of the internal demand for natural mined material. This paper will examine the current trends in the production and trade of natural mined gypsum in Mexico and North America and the opportunities and threats that are facing existing and new suppliers in this changing market.

Jan 1, 1996

By W. C. Baver

Even before the energy crisis developed in the early '70's, considerable research world-wide was being directed towards the development of schemes to both reduce the energy requirements and to reduce air pollution emissions associated with the manufacture of glass. In many cases the sought-for solutions would benefit both objectives. If, for example, the glass batch could be consolidated into such compact forms as briquettes or pellets, they could be preheated in a moving-bed heat exchanger with the high-temperature exhaust gases from the glass furnace. Lower furnace temperatures would thus be possible with a corresponding reduction in heat losses and total fuel consumption. Moreover, the lower temperatures would also reduce the amount of nitrogen oxides generated in the furnace and emitted to the atmosphere. Many tests on consolidated glass batch have been run in many countries. In some cases, extended tests on production furnaces have also been included in the programs. For various reasons, however, none of these has proved to be economically attractive. The current, but temporary lull in the rapidly rising cost of energy which has been with us in recent years, has reduced the push for research for energy saving means for melting glass. A few of the current programs will be discussed. Since raw material requirements, primarily physical in nature, are affected by some of these schemes, these will also be considered.

Jan 1, 1986

By Kadri Dagdelen

New underground coal mines have become increasingly expensive to open. A simple drift mine producing a raw coal product can cost as much as $50 million while a new shaft mine producing a washed coal product can cost up to $200 million. As a result, few if any speculative new mines are constructed. Normally, a long term coal supply agreement is needed to justify new mine projects. Negotiating a supply agreement prior to production start is difficult. Pricing must be based on estimated rather than historic costs and coal quality must be estimated from core hole samples versus actual shipments. Further in todays competitive coal markets, there is little margin for error in either price or quality.

Jan 1, 1983

By Daniel E. Collins

Massive banded Fe-Zn-Cu-Pb sulfide deposits in the Bagdad are associated with metamorphosed eugeosynclinal mafic volcanic and intrusives rocks Precambrian age. The geologic environment is very similar to that of the Jerome-Prescott area which lies 70 km. east of Bagdad. Mining of massive sulfides deposits began in 1917 on the Copper King mine in spite of its early discovery and the discovery of the Old Dick mine in 1882. The first shipments of zinc ore from the Copper King were hand sorted and averaged 46.89% Zn, 5.7 oz. Ag, 3.58% Pb and 1.68% Cu. Oxidized copper was first produced from the Old Dick mine in 1943~ In all, five deposits of massive sulfide ores have been mined in the Bagdad for a total production of nearly 2 million tons with an average grade of 12.0% Zn and 3.6% Cu. The largest deposit, the Bruce mine is currently closed because reduced metal prices and has produced a total of 823,000 tons of Zn-Cu ore to date. Mining of massive sulfide ore in the Bagdad area is presently idle. However, the potential for locating yet undiscovered ore bodies is good. Exploration for new ore bodies is difficult at best due to the complex geologic history of the area, the small size of individual ore bodies and lack of understanding as to the formation of massive sulfide deposits. The purpose of this investigation was to obtain a better understanding of the host rock formations through detailed geologic mapping, petrography and chemical analysis.

Jan 1, 1977

By S. Lee, F. Campero

"Past heap leach design has evaluated hydrodynamic parameters based on a uniform particle size of heap material, but has ignored the equal importance of the instability of fine migration within heap stack in the beginning stages of the irrigation process. The proposed probabilistic model evaluates internal fine erosion and segregation potential of well-graded crushed ores by considering the entire particle size distribution shape and site compaction degree. Using this model, unsaturated flow model parameters were successfully evaluated based on synthesized soil-water characteristic curve (SWCC). Additionally, one-dimensional unsaturated transient flow modeling with Hydrus 1D® showed that the different recovery efficiencies of heap material under unsaturated flow patterns depending on the particle size distribution and compaction degree of heap material. Agglomeration preprocess employed by most heap leach sites can reduce the potential of fine erosion within heap material significantly, but internal stability of crushed ores and hydrodynamic-based analysis of heap material’s pore structure is equally important in the prescreening stage in order to improve efficiency of the heap leach and avoid a costly agglomeration process. INTRODUCTION Accurate estimation of heap leach recovery is a difficult task due to the variety of design parameters that need to be considered - such as geochemistry, hydro-dynamics, and geotechnical design aspects, most notably particle size distribution through the process of agglomeration. After agglomeration techniques were introduced to heap leach design, the influence of particle size distribution and compaction degree in enhanced heap leach recovery has been neglected. The main purpose of agglomeration is to prevent fine segregation and internal erosion during and after heap stacking for well graded crushed ores, which will eventually diminish heap reach recovery. Recent studies show that agglomerated heap materials that had been consolidated at 10 meters below heap surface can release the fines after contact time with lixiviant to the compacted heap material and produce poor drainage performance (Milczarek et al, 2013). It must be noted that engineers and practitioners should investigate feasibility of agglomeration benefit prior to heap leach design because the agglomeration process can incur up to 20 or 30% of project costs. Internal stability of stacked heap material is mainly governed by the particle size distribution of crushed ores. Depending on this stability, segregation and internal erosion of fines can be mitigated by the application of moderate compaction effort during heap construction. Investigation of segregation and internal erosion potential therefore takes precedence for well graded crushed ore since reaction time and contact area with lixivant are greater in finer ores."

Jan 1, 2016

By R. D. Cook, J. L. Johnson

"Measuring mud bed level in a sedimentation device is an important control variable. Methods used to date for this purpose have had limited success providing continuous, consistent measurements at a reasonable price. This paper describes a new instrument for detecting the mud bed / liquor interface as well as bed density profiles. The state of the bed is measured directly with sensors located in the thickener. Data from bench-scale and full-scale tests show that the bed level is well defined and easily detected. In addition, full-scale testing revealed unprecedented information about thickener beds. Variation in bed density gave new insight into thickener bed dynamics, providing design and control opportunities never before possible. This novel instrument can significantly improve thickener control by providing reliable and consistent bed level measurements. It is also capable of measuring bed density profiles that can potentially identify significant operating problems early enough to take corrective action before experiencing costly shut downs. INTRODUCTION Numerous studies and papers have been devoted to the subject of thickener design and operation to achieve specified throughput and discharge densities. Mathematical models have been developed that present methods for sizing thickeners and predicting performance under varying process conditions. The compression effect of deeper beds on dewatering performance is a recognized phenomenon (Wilhelm and Naide 1981). This is one variable of many that are inter-related and influence thickener performance. For example in the steady-state, continuous operation of a thickener, if the solids feed rate increases and the bed level remains the same, the underflow discharge rate must increase with the result of solids concentration being lower. The interactions of these parameters are at the heart of thickener models. One such model (Burger and Narvaez 2007), predicts solids concentration profiles increasing downward and discontinuities between settling zones. This model uses sediment height (bed level) as a parameter that influences capacity calculations to achieve the specified solids concentration of the underflow. Knowing the bed depth is critical to maintaining stable thickener operation. Implicit in these modeling strategies are some basic assumptions such as homogeneous distribution of solids in the different settling zones, plug flow of solids through the settling zones and steady state operation of the thickener. The accuracy of these assumptions has not been verified because there has been little visibility inside the bed of full size operating thickeners. Testing of the instrument presented in this paper demonstrates that it provides a degree of visibility of the dynamics in a thickener not previously possible and indicates that the basic assumptions of the modeling strategies may not be completely accurate."

Jan 1, 2015

By Michael Vitale, Lee W. Abramson, Daniel McMaster, Andrew J. Thompson

"Performing risk analyses on tunnel projects has become common place and on many projects it is required from an owner or regulatory perspective. After the project is planned, designed and constructed, the data concerning identified risks, assumptions, costs, probabilities and mitigations is generally long forgotten and buried in some file somewhere. A study was performed comparing predicted risks versus actual events on four recently constructed rock tunnel projects in New York, Ohio, Georgia and California. Probabilities and costs for selectively common risks on tunnel projects have been studied and re-evaluated. Conclusions are presented that can guide future projects and the veracity of the tunnel risk analyses performed. INTRODUCTION Tunneling is a risky business. More than ever, attention is being paid to the risks associated with tunneled facilities and implications on project or program cost and schedule. Questions about why tunneling projects notoriously exceed budget numbers abound. Evaluations in retrospect and going forward have focused on the wide breadth of inherent risks associated with tunneling. More and more, these risks are being identified, studied and managed to a higher degree. As more and more scrutiny pervades the industry, little value is being obtained and leveraged on future projects. The industry seems to be headed in a direction of making the same mistakes over and over. The notion of risk evaluation has been around for decades and received wide notoriety with the U.S. Space Program and ambitious projects in the energy industry such as hydropower and nuclear power in the 1960s and 1970s (Stewart and Melcher, 1997). This led to the evolution of tunnel risk analyses with more rigorous identification of the unique risks in tunneling projects impacting cost and schedule. As tunneling risks became more readily identified, more attention has been paid to the frequency and impact of the occurrences unique to tunneling (ITIG, 2012). Currently, few tunnel projects are being planned, designed or constructed without a formal risk register that identifies the risks, mitigates the risks and quantifies the probable impacts of risks that cannot be mitigated. In hind sight on many recent projects, events that brought projects to “its knees” were not addressed in risk assessments or were not dealt with to adequately mitigate the risk of these events."

Jan 1, 2016

Cement in 1975 indeed did operate in an unfriendly environment. World recession, escalating costs, fuel crises, reduced product demand . . . . all led to market conditions detrimental to industry profit margins and investment re turns. During the year plant utilizations fell, break-even points were raised, and competitive moves introduced to move built up inventory levels. A number of cement plants were temporarily taken out of production to help alleviate specific situations. Meanwhile, under resultant financial pressure, several companies omitted dividend payments, changed their top executives, and reorganized and reduced staff overheads. It was a difficult year for cement, yet a much more ominous note was sounded in permanent plant closings. Four more cement operations were shut down in 1975; to date in 1976 we know for sure of three additional plant closings, while rumour has it that at least one more may not be in production by year-end. The somber feature is found within the descriptions of the closed facilities, and in the stated reasons for their being taken out of cement manufacture.

Jan 1, 1976

By Louis D. Murino

Compared to coal or many metals industries, talc must be considered a small, specialty market catering to niches and dependent primarily on the physical attributes of the mined and processed mineral rather than the chemical attributes with copper, lead or uranium concentrate, the primary objective is the percent metal that ultimately is refined by the smelter, as opposed to the brightness, particle size distribution, trace impurities or morphology. The latter constitute the important determinants of where, how and why talc and similar industrial minerals are used. This paper addresses the talc market-place: where it is, how much of a market there is, who the producers are, available capacity, market growth, and marketing techniques.

Jan 1, 1984

By J. R. Johanson

In recent years the procedures for functionally designing bulk storage bins and hoppers have evolved from qualitative guess and try methods to a quantative method based on theory and tests of the bulk solid to be stored. This quantative method, developed and implemented by Dr.'s A. W. Jenike and J. R. Johanson as with any new design, must prove its effectiveness and validity in the actual operation of the finished equipment. How accurate are the theoretical predictions? Is it possible to extrapolate from bench size tests on a small ample of the bulk solid to the full scale bin design? Can the theoretical designs be economically translated into working hardware? In this paper the answers to these questions are discussed in light of actual bin operations.

Jan 1, 1968

By Thomas P. Meloy

The understanding, quantification and use of locked particles. Specifically discussed is the use of Textural Transforms (Meloy, 1991) for the implementation of the Interfacial Area Conservation hypothesis (Meloy, 1984); the quantification of the locked particles as a function of fragment to inclusion size ratio; and the selection of set points.

Jan 1, 1991

By T. M. Yegulalp

A numerical model is being developed to assess the enhancement of permeability by improved fracture connectivity by micro-hydrofracturing. A generic two-dimensional percolation model has been developed to test the impact of various field conditions on permeability. Field data from Cyprus Minerals' Mineral Park Mine has been used to establish statistical properties of the observed fracture systems. Results of statistical anlyses of the field data and examples of the use of percolation model are presented.

Jan 1, 1995

Machine breakdowns and maintenance delays are large contributors to lost production and increased operating costs in the mining industry. The U.S. Bureau of Mines is investigating the applications of expert system technology to diagnostic and predictive maintenance tor mining equipment. This will help increase mining productivity and decrease operating costs, by reducing the frequency of equipment failures and repair times. The Bureau has begun this effort by applying expert system techniques to the diagnosis of hydraulic system problems on a continuous mining machine. This paper discusses the development of the hydraulic diagnostic expert system.

Jan 1, 1990

By Gary H. Higgins

The paper by Lewis and Braun l presents experimental and calculational evidence that primary chalcopyrite ores are rapidly oxidized by warm oxygen-bearing water. Resulting solutions contained copper sulfate products of the matrix rock decomposition such as magnesium sulfate and sulphuric acid. Iron was oxidized to insoluble hematite and hydrous iron sulfates. Oxygen injection near the base of a broken and permeable flooded ore deposit was calculated to cause circulation of oxidizing solutions to the entire permeable region. The rate of dissolution of copper and degree of oxygen saturation for given oxygen injection rates were presented. Their work suggests that in-situ recovery of deep, disseminate primary copper deposits is technically feasible. The actual feasibility depends on economics and environmental safety as well, and it is the purpose of this paper to address these two aspects.

Jan 1, 1972

By P. T. Bissert, L. Yan, M. D. Klein

"Federal regulations require that refuge alternatives (RAs) are located within 305-m (1000-ft) of the working face and spaced at one-hour travel distances in the outby area in underground coal mines in the event that miners cannot escape during a disaster. The Mine Safety and Health Administration mandates that RAs provide safe shelter and livable conditions for a minimum of 96 hours while maintaining the apparent temperature (AT) below 35°C (95°F). The National Institute for Occupational Safety and Health used a validated thermal simulation model to examine the mechanisms of heat loss from the RA to the ambient mine and the effect of mine strata composition on the final internal dry bulb temperature (DBT) for mobile tent-type RAs. The results of these studies show that most of the heat loss from the RA to the ambient mine is due to radiation (51%) and conduction (31%). Three mine width/height configurations and three mine strata compositions were examined. The final DBT inside the RA after 96 hours varied less than 1°C (1.8°F) for the three mine width/height configurations and less than 2°C (3.6°F) for the three mine strata compositions. INTRODUCTION Following a mine disaster, workers will try to escape the mine. If their escape is futile, they can take shelter in a refuge alternative (RA). In 2008, the Mine Safety and Health Administration (MSHA) mandated RAs in mines to ensure that a safe and livable shelter is provided for a minimum of 96 hours, and that the apparent temperature (AT) does not exceed 35°C (95°F) inside the RA [1]. An ongoing concern with RAs is the potential to exceed this limit. The temperature rise inside an RA is due to the metabolic heat released by the occupants as well as heat released by the carbon dioxide scrubbing system. The National Institute for Occupational Safety and Health (NIOSH) tested a 10-person tent-type training unit RA in its Safety Research Coal Mine (SRCM) to investigate heat buildup in RAs. The 10-person capacity for the tested RA is based on 1.4 m2 (15 ft2) of floor space per miner. NIOSH-developed simulated miners, which are heat input devices that generate both sensible and latent heat, were used to represent the metabolic heat generation of an average miner (117 W) for testing in the SRCM. It was found that the number of occupants in an RA may need to be reduced based on the ambient mine temperature, which varies from mine to mine [2]. To further research temperature rise inside an RA, ThermoAnalytics, Inc. (TAI) was contracted by NIOSH to perform thermal simulations of the tested 10-person mobile tent-type RA. TAI developed a thermal model of the SRCM using RadTherm software, which incorporates a human thermal model (HTM) to represent the equivalent metabolic heat loss of a miner within the RA’s enclosed environment. The thermal model was previously validated by comparing simulation results with test results [3]. During a mine disaster in which miners would have to take shelter in an RA, mine ventilation may not be available. As such, mine ventilation was off for both the testing in the SRCM as well as in the simulations. This paper discusses the heat loss mechanisms and the effects of mine strata composition and mine width and height associated with a ten-person tent-type RA."

Jan 1, 2016