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By J. L. González-Chávez, A. Ballester, M. L. Blázquez, F. González

In recent years, the bioleaching of sulfidic raw materials has been of great interest. However, the application of this biotechnology is now very limited for many different complex reasons. The mechanism of the chemical and electrochemical reactions taking part in the process is not well understood. The application of electrochemical techniques is useful in its elucidation. Among the common sulfides, galena has been studied very little with respect to its behavior during bioleaching. Therefore, the electrochemical evolution of massive electrodes of lead sulfide in the presence and absence of' a mixed culture of mesophilic microorganisms was investi¬gated by the application of potentiometry, anodic and ca¬thodic polarization and cyclic voltammetry. The agitation rate, the use of pH control and the composition of the nutrient mediums did not have any significant affects on the oxidation of galena. However, the temperature (25 'to 45 °C), the scan rate (4 to 100 mV/s) and the acid used to adjust the pH were significant variables that influenced sulfide oxidation. There¬fore, the peak (600 to 1,000 mV) corresponding to the oxida¬tion of sulfide ions from the mineral was only detected in the presence of a complexing anion of lead. In the presence of bacteria, the peaks corresponding to galena oxidation de¬creased and, at the same time, new peaks appeared both during the oxidation at -300 mV and during the reduction of the mineral surface at 150 and -300 mV. These signals were more important when the attack time increased. The rest potential of bioleached mineral increased with an increase in leaching time, which was related to the electrochemical transformation of the galena surface.

Jan 1, 2000

By Daniel Hodouin, Antoine Berton

Mineral processing plants are monitored and controlled using measurements that are usually processed by on-line material balance calculation techniques. However, gross errors, due to sensor biases or failures, may corrupt all the process variable estimates. On-line gross error detection methods are required to ensure efficient mass balance evaluation. In the proposed approach, material imbalances and raw measurement corrections are tested by statistical techniques designed to detect and isolate sensor problems.

Jan 1, 2000

By Jerry Demchuk, Allan Flemming, Stephan Day

Luscar Ltd. is currently developing open pit mining plans for the Telkwa Coal Project. Most waste rock is predicted to be non-acid generating but a proportion (less than 20%) is potentially acid generating. The waste management plan includes in-pit and ex-pit disposal of blended and till-capped waste rock, segregation and in-pit encapsulation of strongly potentially acid generating materials, and in-pit underwater disposal of coarse and fine tailings. The paper will present the steps used to design the waste management plan including the development of geochemical design criteria using various tests and theoretical and practical knowledge of waste behaviour.

Jan 1, 2000

By V. B. Achanti, A. W. Khair

This paper deals with the effects of various bit geometric parameters on the failure characteristics of rock material. Improving the rock-cutting efficiency of continuous mining machines has proven to be an interesting research topic during the last few decades. In the current study, an automated rotary rock-cutting simulator, duplicating a continuous miner, was used to study these parameters in the laboratory. The improvement of bit performance in terms of its life, cutting efficiency, dust production and energy consumption has drawn widespread attention. Research has demonstrated that optimizing bit parameters can result in efficient fragmentation of rock. Indiana limestone rock material was used in this study. The bit tip angle, bit tip size, bit spacing, depth of cut and cutting velocity of the rotary drum were varied to investigate the failure characteristics. The cutting pressure, penetrating pressure and the depth of cut were monitored on the simulator during the cutting process. Airborne dust and settled dust were measured for each experiment. Then, the specific airborne dust and specific energy were determined for each type of bit. Triaxial tests were carried out to correlate the failure angle of the rock in the static case to the dynamic cutting process failure. The physical and mechanical properties of the rock were also determined to assess their influence on the wear characteristics of each bit.

Jan 1, 2000

Environmental conflict management approaches and procedures have been used to successfully address and resolve a variety of issues, problems, and conflicts related to the extraction of natural resources. Companies in the mining industry have been involved in a range of controversies over planning, siting, permitting, environmental, and enforcement issues. Through the use of conflict resolution case studies, this paper will present approaches and procedures that can help companies and other involved parties to successfully manage and resolve differences in a mutually acceptable manner.

Jan 1, 2000

By Osvaldo Bascur, Laurent Garrigues, Nouna Kettaneh, Svante Wold

The chemical, oil, semiconductor, mining, and paper and pulp industries, as well as most other modern industries, are rapidly expanding the range of measurements used to characterize raw materials, process steps, intermediates, and final products. In addition, process variables such as temperature, pressure, and flow become more and more numerous, providing extra information on the state of the process. However, no matter how many sensors are added, the underlying sources of variations that drive the process behavior remain constant. On the other hand, the measuring frequency of these data has increased from once a day or once an hour to once, ten, or even hundred times a minute. This gives masses of data that are swelling in both directions (more variables and more observations). These data need to be properly stored, managed, and analyzed to provide diagnostics about the state of the process as well as an understanding of the relationships between different parts of the process and the product properties. Projection methods such as PCA (principal components analysis) and PLS (projection to latent structures) compress process data to informative summaries of the original variables. These can be shown on line, providing an efficient, graphically oriented suite of diagnostics regarding the "health" and performance of the process. The power of these methods is illustrated by two examples of industrial data in the mining industry.

Jan 1, 2000

By N. Parra, M. N. Herrera, T. Vargas, B. Escobar, C. Gonzalez

originally published May 1998, Vol. 15, No. 2, pp. 15-1 9 Discussion by G. Rossi, University of Cagliari Reply by T. Vargas, University of Chili

Jan 1, 2000

By B. R. Reddy, Y. V. Swamy, B. V. R. Murthy

Chromitiferous overburden containing nickel in oxide form is reduced with CO-CO2-N2 gas mixtures. This converts the nickel oxide to metallic nickel and restricts the iron oxide to the magnetite state to extract the nickel. Reduction experiments were carried out on 500-g samples in a bench-scale vertical reactor. The tests were run to establish the process parameters, including the optimum partial pressure of CO, the reducing gas flow rate, granule size and roasting time. The reduced calcine is then subjected to an ammonia-ammoniacal carbonate leach to extract nickel selectively as its amine complex. More than 90% of the nickel could be extracted with a volumetric CO/(CO+CO2) ratio of 0.57 at 750°C and a roasting time of 90 min. The addition of 2.5% (by weight) charcoal to the granules improved nickel extraction by 11 % to 19%. Nickel leaching efficiency with ammoniacal solution is compared to the bromine-methanol method.

Jan 1, 2000

By Barnaby J. Watten, Sibrell. Philip L., Brian J. Vinci, Andrew E. Friedrich

We evaluated a new process for remediation of acid rock drainage (ARD). The process treats ARD with intermittently fluidized beds of granular limestone maintained within a continuous flow reactor pressurized with CO2. Tests were performed over a thirty day period at the Toby Creek mine drainage treatment plant, Elk County, Pennsylvania in cooperation with the Pennsylvania Department of Environmental Protection. Equipment performance was established at operating pressures of 0,34,82, and 117 kPa using an ARD flow of 227 L/min. The ARD had the following characteristics: pH, 3.1; temperature, 10 OC; dissolved oxygen, 6.4 mg/L; acidity, 260 mg/5; total iron, 21 mg/L; aluminum, 22 mg/L; manganese, 7.5 mg/L; and conductivity, 1400 uS/cm. In all cases tested, processed ARD was net alkaline with mean pH and alkalinities of 6.7 and 59 mg/L at a CO2 pressure of 0 kPa, 6.6 and 158 mg/L at 34 kPa, 7.4 and 240 mg/L at 82 kPa, and 7.4 and 290 mg/L at 117 kPa Processed ARD alkalinities were correlated to the settled bed depth (p<0.001) and CO2 pressure (p<0.001). Iron, aluminum, and manganese removal efficiencies of 96%, 99%, and 5%, respectively, were achieved with filtration following treatment. No indications of metal hydroxide precipitation or armoring of the limestone were observed. The surplus alkalinity established at 82 kPa was successful in treating an equivalent of 1136 L/min (fivefold dilution) of the combined three ARD streams entering the Toby Creek Plant. This side-stream capability provides savings in treatment unit scale as well as flexibility in treatment effect. The capability of the system to handle higher influent acidity was tested by elevating the acidity to 5000 mg/L with sulfuric acid. Net alkaline effluent was produced, indicating applicability of the process to highly acidic ARD.

Jan 1, 2000

By Todd A. Duex

The Richmond Hill Mine has recently completed a reclamation plan to mitigate Acid Rock Drainage (ARD) which was identified at the toe of the former waste rock pile in 1992. Reclamation activities began in 1994 with the removal of ARD material from the waste rock pile and placement of this material in the former pit. This material was then isolated from the near surface environment by a low permeability capping system designed to minimize water and oxygen flow into the material. The capping system consists of, from bottom to top, six inches of limestone, 18 inches of low permeability clay liner, 4 and one-half feet of thermal barrier/drain layer, and six inches of topsoil. This capping system was completed in 1995. An extensive program is in place to monitor the effectiveness of the reclamation plan, and includes measurements on moisture content movement, temperature, oxygen content, and groundwater impacts. Monitoring has been ongoing since the completion of reclamation. This monitoring plan is demonstrating the success in isolating the material from the near surface environment and minimizing the impacts to the surrounding environment.

Jan 1, 2000

By D. R. East

Recent experiences within certain sectors of the international mining industry suggest an underestimation of the environmental risks associated with the design of mine waste-management facilities. These experiences show that the technical and managerial challenges of responsible mine waste management is not always fully appreciated. Unfortunately, the image of the mining industry&apos;s environmental performance is negatively impacted by a relatively few number of failures. This negative view overrides the many positive contributions made by the majority of mining companies. The fact that these failures continue to occur in developed and developing countries is indeed re¬markable and indicates a degree of risk-taking approaching unacceptable levels. The design requirements for tailings storage facilities are, in many cases, more demanding than those of conventional water dams because seepage of fluids that contain dissolved metals may pose a greater threat than the mere loss of water.

Jan 1, 2000

By Osvaldo Bascur

Large metallurgical complexes have more data than a small city and much of it is "real time," changing rapidly as internal and external conditions evolve. As corporations buy and sell assets and reengineer their staff, the structures and tools that were used to understand these data are lost. This results in significant deterioration in the ability to maintain a "smart" operation. The solution is to use the sophisticated new tools built for the Internet so as to leverage information in a familiar browser format that people can use and understand. This paper describes the use of Internet technologies with plant data. Examples are drawn from existing industrial sites. Users must project where this technology will lead - standing still is the most dangerous philosophy and the only one guaranteed to be obsolete. These examples show the way to leverage existing workers with information technology.

Jan 1, 2000

By J. S. Y. Wang, R. C. Trautz

A 9-meter-long drift was constructed in the unsaturated-fractured tuff at Yucca Mountain to evaluate the potential for water seeping into an underground opening. Forty seepage tests were performed by releasing a finite volume of water at a constant rate into short test intervals located in boreholes positioned above the drift. The seepage threshold flux, defined as the liquid-release flux at and below which water will not drip into the opening, was determined for 10 test intervals. The seepage data, observations, and model results indicate that a seepage threshold exists because a capillary barrier diverts water around the opening.

Jan 1, 2000

By Jean-François Boucher, Ernest K. Yanful, Mei Lin Shelp, Lionel J. J. Catalan

Shallow water covers for preventing acid production in tailings are based on the principle of minimizing oxygen availability. Resuspension of material from the tailings bed may result in increased oxidation and metal releases since dissolved oxygen is at near saturation levels in the water cover. Resuspension can be caused by waves and currents strong enough to mobilize the surface of the tailings bed. Tailings resuspension was measured with sediment traps in the Upper Cell of the Heath Steele site near Mirarnichi, New Brunswick Canada. Although significant amounts of resuspended tailings were collected in all traps, analysis of resuspended solids and bed tailings suggests that for the observed wind conditions resuspension did not occur at locations where the water cover depth was greater or equal to 1.0 m. Currents were likely responsible for the transport of resuspended tailings from shallower areas to locations where the water cover was deeper than 1.0 m.

Jan 1, 2000

By Michael L. Nave

Mining belt conveyor elements are becoming larger and more expensive. Conveyor reliability requirements are rising. Conveyor condition monitoring can aid maintenance, reliability, and risk management in conveyor system operation. This paper examines the application of condition monitoring in coal mining belt conveyor systems. Types and form factors of condition sensors are described. Example costs are included. Suggestions for OEM developments are examined. Application problems are discussed. Two simple cost case studies are presented.

Jan 1, 2000

By J. Changsheng, Z. Youdi

Based on the criteria of maximum net present value per ton of reserves and on the optimum matching of some other essential parameters, a comprehensive optimization model of surface-mine production rate is developed using system- engineering approaches and using the theory of economy of scale. A mine is then selected to demonstrate the application of the model.

Jan 1, 2000

By Robert Seal, James J. Rytuba, Michael P. Hunerlach, Roger Ashley, Dean Enderlin

Cessation of open pit mining in 1996 at the McLaughlin hot-spring type gold deposit has resulted in the development of two pit lakes that will be managed as permanent lakes with a total storage capacity of 10,000 acre-feet. The south pit lake developed from alkaline ground water infiltration and had an initial pH of 7.2. It contained high concentrations of boron and chloride, indicating that it consisted of a mix of meteoric and evolved connate waters. Numerous carbon dioxide gas vents were present initially in the shallow south pit lake, but as the pit lake increased in depth, gas venting ceased and carbon dioxide is retained in the lower layer of the chemically stratified lake. Continued increase of dissolved carbon dioxide in the lower layer increases the potential for a limnic eruption. A chemocliie occurs at a depth of 47 m. The upper layer of the lake has lower pH, temperature, and conductivity than the lower layer. Effluent from ore and waste rock piles directed into the south pit lake has contributed to high levels of antimony, arsenic, cobalt, copper, mercury, nickel, and zinc. Iron oxyhydroxide is abundant in mine effluent that enters the pit lake and adsorption onto this phase has lowered the arsenic and antimony concentrations. The north pit lake formed primarily from winter surface runoff. The acidic water, pH 4.56, initially had high concentrations of cobalt, mercury, and nickel derived from weathering products of pyritized serpentinite and shales. Buffering by wall rocks has established a slightly alkaline pH of 7.62. The concentrations of trace metals in the north pit lake have substantially decreased due to continued dilution of the lake by surface runoff and remediation of parts of the pit walls that have been covered by backfill.

Jan 1, 2000

By F. M. Doyle, C. V. Diniz, A. H. Martins

A proposed process for the direct production of battery¬grade Mn02 leaches manganese ore with HCl to remove heavy metals selectively. The acidic manganese chloride solution produced is contaminated with Cu, Ni, Co, Pb and Fe at levels that preclude immediate utilization. This paper reports on screening tests to measure the uptake of Cu, Ni, Co, Pb, Fe and Mn from acidic chloride solutions onto different chelating ion exchange resins. Dow M-4195, which contains the bis-picolylamine,functional group, showed promise for detoxifying manganese chloride process solutions. Column ion-exchange tests demonstrated the ability of this resin to produce pure manganese chloride solution from an acidic manganese chloride leach solution contaminated by Cu, Ni, Co, Pb and Fe.

Jan 1, 2000

By Andrew Neale, Ari Supomo, Mike Mular, Rob Perry

A method is presented to measure and correct the performance of regulatory control loops. Freeport Indonesia treats over 220,000 dmtpd of copper-gold ore in a complex of four concentrators. More than 400 regulatory control loops are implemented throughout the operation. The performance of each loop is quantified by an index based on its time in automatic, the deviation of the measurement from the setpoint and a metallurgical assessment of its impact on overall plant operation. Index values are recorded in a plant-wide data acquisition system and analyzed to produce a report of loops requiring attention. Loop statistics are analyzed to show if the problems can be corrected with tuning. The practical application, benefits, management and staffing requirements of this method are discussed.

Jan 1, 2000

By L. I. Gyrskia, Y. V. Andreev, T. N. Greiver, G. V. Petrov

Traditionally, chromite ores are regarded exclusively as a monomineral raw material for extraction of chromium. The results of the investigations indicate a wide range of PGM in the Ray-Iz chromites, amounting to 1-3 ppm PGM. The study of products of primary gravity concentration from heavily and lightly disseminated ores (Tsentralnoe deposit, Ray-Iz block), showed that the platinum-group minerals are concentrated in the tails and slimes of the processed products, containing 10-30 ppm total PGM. Preliminary data make it possible to conclude that an in-depth study of the platinum mineralogy of the Ray-Iz block chromite ores is necessary to develop a process that will produce both chromium and the PGM.

Jan 1, 2000