Search Documents

By X. Yin

Surface force measurements based on atomic force microscopy (AFM) are used to describe the wettability of surfaces, specifically kaolinite basal plane surfaces at a high resolution. The kaolinite particles (~500 nm) were ordered with either the silica tetrahedral face exposed or the alumina octahedral face exposed, and surface force measurements were made between a hydrophobic diamond-like-carbon (DLC) tip and the kaolinite faces at pH 4, which is around the isoelectric point of the DLC tip. Under these conditions, the effect of electrostatic interaction should be eliminated and only van der Waals interactions and hydrophobic-hydrophobic interactions are expected to contribute to the surface force. The wettabilities of the surfaces were determined from the magnitude of the surface force. Wettabilities of the kaolinite basal planes thus determined were compared with the corresponding wettabilities of talc and mica surfaces, which are well-known to be naturally hydrophobic, and hydrophilic surfaces, respectively. The results reveal that the silica tetrahedral face of kaolinte has a modest level of hydrophobicity, which may be due to the lack of hydrogen bonding sites. In contrast, the alumina octahedral face showed no hydrophobicity, since a layer of surface hydroxyl groups is present at the alumina face, resulting in a relatively strong interaction between this surface and water molecules. It is expected that, with a better understanding of the surface properties of kaolinite, further improvements in flotation separations and dewatering may be achieved.

Feb 1, 2012

By G. A. Rowell, T. M. Barczak, J. C. Zelanko

The US Bureau of Mines conducted a multifaceted geomechanics research project at a bump-prone longwall coal mine in eastern Kentucky. This mine presented a unique opportunity to study coal mine bumps because the problem appeared to be confined to areas beneath a sandstone channel of limited areal extent. The Bureau's research plan sought to exploit the uniqueness of the site by monitoring strata behavior and longwall support reactions as the longwall face approached and passed beneath a sandstone channel. The study incorporated static pillar stress and strata deformation measurements, shield support leg pressure measurements and microseismic monitoring, as well as geologic mapping and the collection of observational data. Data collection was underway when a major coal bump occurred on the longwall face at the mine. Pillar behavior (load and deformation), shield loading and microseismic activity were monitored prior to, during and after the bump. Observations in the tailgate indicated that these pillars were failing prior to and following the face bump. Shield load data, evaluated in an effort to identify trends that could be used to forecast coal bumps, appear to provide a measure of the effectiveness of destressing operations conducted on the face (e.g. shot firing). Analyses of microseismic data revealed anomalous values associated with microseismic "energy" prior to the face bump. In addition, microseismic source-location data and underground observations provided some insight as to the sequence of pillar and face bumps.

Jan 1, 1992

By Edgar Urbaez

Production scheduling is one of the most important factors affecting mine planning. A program -Mine Scheduler -that aids mining engineers with the setup of an optimum open pit production scheduling algorithm has been developed. A mathematical model for open pit scheduling that optimizes the Net Present Value of the cash flows was formulated. A simulated data is formulated as a Mixed Integer Linear Programming (MILP) problem. What's Best by Lindo Systems is used as the MILP solver in Microsoft Excel. The implementation of the algorithm focuses on problem setup, allowing users to easily evaluate, simplify, and develop the model that best fits their production scheduling.

Jan 1, 1999

By Milton E. Wadsworth, Ximeng Zhu

Impurity metals can markedly influence the anodic dissolution of gold in the presence of cyanide. Several important findings related to the influence of lead are reviewed and some new observations presented. Based on the effect of pH, the scan direction, and voltage, it may be shown there are three separate voltage regimes where lead influences the anodic dissolution of gold. These are related to Pb°/ HPbO2, Au-Pb /HPbO2, and HPbO2/PbC2; oxidation-reduction reactions which provide low resistance paths for electron exchange. The gold dissolution rate was determined by direct solution analysis and is compared to the rate implied by electrochemical measurements.

Jan 1, 2005

By R. D. Hansen, R. R. Klimpel

Previous papers by these authors on slurry rheology control grinding aids have emphasized the end-use results and application methodology involved. This paper emphasizes the chemical principles and the influence of various chemical structures behind slurry rheology control chemicals. Particular examples are shown which correlate chemical structure modifications to environmental factors involved in grinding such as pH, shear, ore type, water chemistry, and particle size.

Jan 1, 1990

By Raj K. Singhal

This paper is a report on a task force study dealing with many facets of computerization. The primary mandate of the task force was to examine the software and hardware currently available for application relating to reserve estimation, mine planning, economic evaluation, equipment selection, production scheduling and composite mine simulation and to evaluate how adequately the software fulfills the user needs in surface mining of oil sands and coal. To meet its objectives the task force consulted extensively with the users, developers and suppliers of hardware and software. The paper outlines the approach taken by the task force to fulfill its mandate, summarizes its findings and presents some pointers which might be useful to others considering this type of evaluation.

Jan 1, 1986

By P. J. D. Lloyd

INTRODUCTION The mining of gold commenced on the Witwatersrand in 1884, and reached a mature state by about 1910, when nearly 20 million metric tons were mined. Mining has continued on the central Witwatersrand, the area of the first mining, at a similar rate until recent years. As a result, well over 1 billion tons of gold mining wastes have been dumped along a line over 80 km long, centred on Johannesburg and stretching from Randfontein in the west to Nigel in the east. (see Figure 1). The population of this conurbation, which straddles the line of mining, has grown to about 5 million. In 1922 uranium was first discovered as a constituent of the ore (and thus of the wastes). Investigations in the 1940's revealed that values near Johannesburg were low, but that, at the western and eastern ends of the central Witwatersrand line, and in the new areas centred on the towns of Carletonville, Klerksdorp and Welkom up to 200 km from Johannesburg, values were adequate to permit uranium recovery. Commercial production commenced in 1952, and by 1979 over 100 000 tons of uranium oxide had been produced. There thus arises on the central Witwatersrand nearly 1,3 billion tons of slimes containing an average of about 0,005% uranium and about 1,8% FeS2. The material grading is about 70%-75µm, and the primary mineral is silica (over 85%). The material is contained in dams constructed hydraulically. A typical dam has an area of about 100 hectares and there are over 6000 ha under slimes dams in the area of concern. The treatment of these dams for uranium recovery commenced in 1977. The situation has thus arisen whereby potential uranium ores have unwittingly been dumped in significant quantities within a major metropolis over a period of nearly a century. The purpose of this note is to review the experience arising from the potential hazard over a considerable time.

Jan 1, 1980

During the past decade, since the appearance of Popoff's (1966) review of grade tonnage calculations, it has become evident that defining a new method which could be followed step by step by a technician and which would improve reserve estimation was not a simple thing to do. Some concepts have emerged though, and most definitions of ore reserve now require a statement of reliability (USGS, 1975; and Zwarten-dyke, 1976). Exactly how the reliability should be computed is not a straightforward process. It also became apparent that not only was reliability a requirement but that additional questions such as how to predict mining re- serves from geological reserves were to be asked. In fact what became obvious is that specific models have to be designed for each type of mine and for each type of question which is asked. Most methods can be encased within a unique general geostatistical, model, but it takes considerable custom tailoring, and there are still questions that are left unanswered. In this chapter, before giving techniques, we intend to first review what should be required from a grade tonnage calculation done at the exploration stage. If the final objective is still to specify a tonnage and grade, with eventually a reliability, many qualifications have to be made before quoting, and of course, calculating these two numbers. Then the currently avail- able methods will be reviewed and future trends will be shown; finally a few case studies will be given and recommendations about the choice of a model will be made.

Jan 1, 1979

By Donald A. Dahlstrom

INTRODUCTION Solid-liquid separation is an important and many times a critical step (or steps) in a mineral or coal processing plant. Some examples of typical critical separations are as follows: 1. Operating a seven to eight stage CCD thickening circuit to re¬cover almost all of the caustic and alumina trihydrate values in an alumina plant. This must be accomplished with highly scaling slurries, starting temperatures of over 100°C and operate on a closed circuit system. 2. Making a filter step operate to produce a proper moisture for the balling step so that the pellet furnace can produce a proper product. Bentonite addition must be minimized and a good quality filtrate must be maintained to prevent abrasion of the internal parts of the filter. 3. Operating a closed water system in a coal washing plant so that reclaimed water containing less than one percent suspended solids is produced for reuse to maintain beneficiation ef¬ficiency. Refuse solids must also be thickened so that they can be effectively dewatered to meet state disposal requirements. 4. Recovering phosphoric acid values from a slurry containing gypsum and other gangue solids at an elevated temperature. This must be done while minimizing wash water and maximizing P2O5 re¬covery while simultaneously minimizing scale problems. While solid-liquid separations are important to overall performance in the processing plant flowsheet, it is also a significant factor in plant costs. Capital and operating costs for all the solid-liquid separation steps (includ¬ing water reclamation for reuse) in such plants are probably between 10 and 20%. Energy consumption can also be important in these separations. For example, in the copper concentrator, it is the third largest category in energy consumption, after comminution and flotation. Obviously, solid-liquid separation steps in a plant demand proper atten¬tion in design in order to achieve both optimum performance and cost. Simultaneously, knowledge of funda¬mentals are important to improve results in existing plants.

Jan 1, 1986

By A. K. Bhowmick

Size reduction is very energy intensive and is the single most power-intensive operation in mineral processing plants. Research has shown that only a small part of the energy is utilized efficiently. One of the major thrusts of all equipment manufacturers has been to improve this efficiency. Choosing the right equipment to maximize energy utilization in any comminution application has always been the utmost criteria. Due to the high energy cost and depletion of good grade minerals, it is becoming essential to optimize all the subsystems within a given comminution system for the overall economic success of such ventures. Bradley Pulverizer Company of Allentown, Pennsylvania recognized this and started offering its Feeder Controller in 1988 for automatic feed control. After its first successful operation, Bradley made this as a part of all of their grinding system standard offering. It was also recognized that the Feeder Controller was just a beginning and more automation and controls would be required for an overall, efficient grinding system.

Jan 1, 1993

By Normand Tassé

Reactive barriers, which consume oxygen, are prospective though unconventional alternatives to physical barriers for Acid Mine Drainage prevention. However, a reactive barrier implies a problem of duration. Pore gases were analysed in several wood waste piles in order to understand the factors which control wood degradation and help to determine the effective life span of such a cover. Long term efficiency seems to strongly depend on the degree of water saturation at the bottom of the pile, likely because the development of a microbial biomass in such an environment helps to keep the amounts of nutriments and readily metabolizable organic substrates at a high level, which in turn promotes oxygen consumption.

Jan 1, 2000

By K. Wangerud, B. S. Caruso

A water-balance model with deterministic and stochastic components was developed and used for the Gilt Edge Mine Superfund Site in South Dakota. The model was developed to evaluate the risks of contaminated runoff discharging to surface waters based on assumed water treatment plant (WTP) rates, for different remedial alternatives. The objectives of the modeling were to use a stochastic approach for the analysis of precipitation based on historic records and to make a probabilistic estimation of annual and monthly runoff from disturbed/mining activity areas that now require, or will need, treatment at the WTP, water storage and changes in a major pit, and risk of contaminated water bypass of the WTP to a downstream drainage. Subareas/source areas generating contaminated runoff requiring treatment were delineated. A simple water-balance model was used based on precipitation inputs and evapotranspiration and groundwater losses. Annual and monthly precipitation records for Lead, South Dakota, were used to estimate precipitation at the mine site. A lognormal distribution was estimated for monthly precipitation. The stochastic software package/ Excel add-in "@Risk" was used to generate random monthly precipitation values using a Monte Carlo method based on the distributions. The average annual and monthly distribution of pan and lake evaporation and of groundwater losses were also estimated for the site. Stochastic outputs from the model for the end of each month and year included contaminated runoff requiring treatment, water storage in mine pits and the risk of WTP bypass given different assumed WTP rates. The probability of the time required to dewater the pits was also modeled.

Jan 1, 2003

By Anthony D. Hammond, Charles A. Kliche

A slope stability study for the Annie Creek and Foley Ridge Mines was undertaken to provide Wharf Resources, Inc. with a technical assessment of the stability of the slope for an overall pit slope angle of 60°. A rock analysis of the most critical and persistent combination of discontinuities was carried out using probabilistic methods. A detailed discontinuity mapping and assessment of the rock mass provided the orientation data used in this study. The orientation data were reduced and analyzed to identify the discontinuity sets. A statistical analysis provided information about the distribution of the data. A deterministic wedge stability analysis identified the critical combination of discontinuities; those with a low factor of safety were further studied using probabilistic kinematic and kinetic stability analyses. The results from this approach were used to obtain the reliability or probability of failure of the slopes.

Jan 1, 1988

By Jerry M. Whiting, Landy A. Stinnett

The subject of this paper is broad and complex. Secondly, it is near and dear to the authors' hearts. Therefore, it doesn't seem possible to deal with every aspect of it in less space than a good size textbook. Also, if we dealt with all of the basics of feasibility studies and report preparation, we would cover a lot of material available in the literature, and would have to minimize our editorial comments. In view of these limiting realities, we have chosen to discuss selected facets of the subject, and to provide several comments which stem from our personal experiences during the past 20 years. "Think Ahead" hen someone is undergoing training to command a large ship, the following short phrase is engraved in his memory: "Think Ahead." The reason is simple enough. A battleship, aircraft carrier or oil tanker cannot change directions quickly, and if one waits to a what the other ship is going to do, there may be twisted metal and bodies scattered all over the ocean floor. The commanding officer has to use radar, forward rind aft lookouts, experience, common sense, intuition, weather forecasts, and everything else available to him to avoid trouble. Remember the USS Stark, and the fate of its captain? The fact the Stark was hit by a "friendly" missile didn't lessen the damage. How about running into a mine? Is it an excuse that no one thought about the possibility of a minefield ahead of the ship? The point is, relative to feasibility studies, that its prospective authors, and especially the commander of the efforts required to create it, must "think ahead" from the moment of their association with 4 mining activity. They must

Jan 1, 1987

By D. W. Hendrickson

Cleveland-Cliffs views the mining process as ex- tending from mine planning to cargo loading including auxiliary systems such as materials handling and plant utilities. Process automation is recognized as an area that can provide significant improvement opportunities with less capital requirement than major flowsheet modifications. This article discusses the development and results of a strategy to allow and promote implementation of process-automation improvements at individual mines based on their economic priorities, taking advantage of common systems and concepts for use at multiple mines where practical. Specific process-control upgrade projects at Hibbing Taconite Co. and the Empire Mine are reviewed.

Jan 1, 1998

By A. S. Malicsi, Vathsala Rajagopal, I. Iwasaki

Corrosion and abrasion properties of a series of chromium-containing, cast-iron balls, with Cr contents ranging from 0% to 29%, were evaluated and compared with austenitic stainless-steel and mild-steel balls. Marked ball wear tests were performed on artificial ore samples consisting of 95% quartzite, with either 5% pyrrhotite or 5% chalcopyrite, under a nitrogen or oxygen atmosphere. The electrochemical mechanism was investigated by correlating the corrosive wear with the corrosion currents obtained from potentiodynantic polarization curves under abrasion. Flotation recoveries were determined on a 95% quartzite + 5% pyrrhotite sample ground with various cast-iron ball materials under an oxygen or nitrogen atmosphere. Electrochemical results are found to be in good agreement with flotation results and with corrosive wear data obtained from marked ball wear tests.

Jan 1, 1993

By James S. Scott

Effluents discharged from gold mills, and more recently from heap leaching operations, pose significant hazards to the environment if not properly managed prior to discharge. This paper describes the nature of wastewaters which must be treated, the treatment processes being applied in Canada and the capabilities of these methods in removing cyanide and metals. As a result of past practice the most common method of reducing cyanide in gold mill effluents remains that of natural degradation in tailings ponds. This method has proven capable of producing high quality effluents where large ponds and sufficiently long water retention times can be provided, but at many mines this has not been the case. Since 1981, as a result of these limitations there has been a strong move in Canada to chemically-based effluent treatment plants, particularly as additional processes became available. Canadian gold mills have become leaders in the use of chemical processes to remove cyanide, in terms of the variety of such processes in operation (five in total), the number of plant installations and the number of processes developed in this country. The hydrogen peroxide and Inco SO2-air processes, in that order, are being applied most widely. Alkaline chlorination, the initial process to be used fairly extensively has been almost totally replaced by the two methods mentioned above. Since a number of effective methods are now available for the treatment of gold mill effluents, the selection of a process for application at a specific mill requires careful consideration of:

Jan 1, 1987

By F. F. Aplan, D. D. Xu

A novel system for the depression of pyrite and the ash-forming minerals has been developed. A metal ion, including but not restricted to Fe+2, is added to form a hydroxide coating on the pyrite or ash-forming minerals. A polymeric depressant is then added to attach to these re- surfaced minerals. Nearly 200flotation tests with I1 different coals indicate the effectiveness of this system. Many of the important process variables such as the coal source, frother- collector system. grind size and procedure, pH, metal ion, and depressant type and concentration have been studied.

Jan 1, 1995

By D. S. Cavers

INTRODUCTION This paper discusses aspects of rock engineering applicable to surface gold mines. Discussion particularly centers on areas in which rock mechanics can enhance the mine productivity or profit- ability. Methods of analysis are discussed briefly but for more detai1s the reader is referred to the appropriate references. A team approach to the overall design of the pit generally pro- duces a better result at an overall lower cost. In particular, money is wasted by asking for a "report on slopes" and then input- ting this slope angle into a pit design and economic analysis study without further reference to the geotechnical engineer. Pit slope angle depends on slope orientation, location, pit shape, pre-existing discontinuities and mining methods. Preliminary slope angles can be produced but optimization depends on ongoing inter- action between the mining engineers, geologists and geotechnical engineers. This interaction can a1 so substantially reduce overall design time which may be critical in bringing remote plays into production. Most surface gold mines in North America are in igneous or metamorphic environments. Rock mechanics aspects discussed in this paper will be discussed with reference to these environments al- though most of the principles and comments are applicable to sedimentary environments as we1 1.

Jan 1, 1987

By R. A. Pindred, M. P. Lam

Cyanide is a conventional lixiviant for gold extraction but its' toxicity is a major concern for the environmentalist. There are many alternative non-cyanide lixiviants, such as thiourea, thiosulphate, chlorine and hypochlorite etc., which may reduce environmental sensitivity. This paper will discuss the leaching characteristics of gold in hypochlorite leaching solutions. The dissolution of gold in a hypochlorite solution not only depends on the concentration of the hypochlorite but also on other variables, such as hydrochloric acid, sodium chloride and temperature. The dissolution rate of gold in hypochlorite solution is much faster than other lixiviants. Due to the interference of impurities, gold extraction from an ore under ambient conditions requires large quantities of reagents. However, refractory gold ores may be successfully pressure oxidized in an autoclave at reasonably low reagent levels. Gold extraction to the pressure oxidation leach solution is rapid and complete in one stage, thus eliminating the need for further cyanidation.

Jan 1, 1990