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By J. J. Moore, B. Mishra, D. L. Olson

The production of radioactive and reactive metals, such as plutonium, uses various pyrometallurgical techniques that generate significant quantities of waste salts contaminated with hazardous, reactive or radioactive materials. Health concerns, environmental regulations and economic considerations require proper mitigation processes to recover the valuable components and for recycling or unrestricted release of these salts. The Oxygen Sparging Process converts soluble metal halides, such as chromium-, plutonium-, cerium chlorides, into insoluble oxides and/or oxychlorides which can be consolidated and separated for long-term storage or further processing. The matrix salt phase, viz. calcium and/or alkali chlorides, are clean after oxygen sparging and fit for recycling. This method has been described and its optimized parameters discussed to show that RCRA regulated elements, such as, chromium, lead, cadmium, etc. report to the consolidated phase making the salt recyclable. Salt Scrub Reduction Process for the recovery of radioactive and RCRA metals from the waste salts has been developed. The process uses a Ca-Ga intermetallic alloy which recovers over 98 percent of the reactive metals. The matrix salt phase in this process, viz. calcium or alkali metal chlorides, are clean after salt scrub reduction.

Jan 1, 1995

By Dao De Xu, Heechan Cho, Mark S. Klima

A study was conducted to determine the feasibility of using dense-medium centrifugation for separating fine (-150 µm) coal. A centrifuge provides the capability of varying the rotational speed and retention time independently, which offers the potential for a higher degree of control as compared to a dense-medium cyclone. Tests were conducted with a 140-mm diameter by 76-mm long Plexiglas separator, which was fitted with appropriate feed and discharge pipes to allow continuous separations to be made. A suspension of ultrafine (-10 µm) magnetite and water was used as the dense medium. The effects of operating conditions, including the magnitude of the 'g"-force and retention time, on centrifuge performance were investigated.

Jan 1, 1995

By C. K. Nworu, L. O. Asuquo, C. O. Nebo

Selective flocculation studies of Agbaja iron ore with starch-type and nonionic polyacrylamide-type flocculants has been conducted to determine the effect of flocculant type. The results indicate that corn starch was slightly better than cassava starch in selectivity performance. Cassava starch was in turn better than Superfloc 16, while the poorest results were obtained with commercial starch. Sodium humate shows better dispersive capability, and thus enhanced flocculation results, than sodium silicate. Pulp pH affects the zeta potential, polymer chain configuration and hence selective flocculation. Overall results indicate that recovery and separation of this very fine grained iron oxide by selective flocculation is feasible.

Jan 1, 1995

By P. E. Richardson, N. P. Finkelstein, Z. Chen

The large band gap and insulating properties of sphalerite have limited the application of standard electrochemical techniques for studying its reactions with flotation reagents. This problem has been overcome by developing electrodes that rely on the surface conductance produced when sphalerite is activated with copper or other heavy metals. A brief exposure of the mineral in copper sulfate solutions results in electrodes that exhibit significant electrochemical activity characteristic of copper sulfides. Voltammetry studies conducted on sphalerite activated in 10-4 M CuS04, solutions at pH 4.6 provide information on both the amount and the nature of the activation product(s). It is shown that copper activation is strongly dependent on the electrochemical potential applied during activation. Activation at potentials increasingly negative of the rest potential causes a progressive increase in the amount of copper on the surface; activation at potentials positive of the rest potential decreases the amount of copper on the surface. The results indicate that both the kinetics of copper uptake and, possibly, the chemical composition (stoichiometry) of the activation product are controlled by the electrochemical potential.

Jan 1, 1995

By Brian Flintoff

Basic process control is an integral part of most mineral processing plants. It is widely acknowledged to have helped many operations reduce costs and increase productivity and performance. The research community is very active in the development and evaluation of both model based and Al techniques for advanced control applications. Vendors and specialist consulting or engineering firms are in business to help deliver these solutions to the plant floor. It would seem that there is a good balance between business needs and technology, and that the industry should be moving steadily forward in an aggressive pursuit of plant-wide automation. However on closer examination one sees some systemic problems which are sewing to inhibit progress. One of the mist obvious manifestations is the gap which exists between the available technology and current This paper explores the control of mineral processing systems, with a particular emphasis on some of these problem areas.

Jan 1, 1995

By Richard A. Williams

The design, modelling and simulation of solid-liquid mixers remains one of the least advanced aspects of minerals processing, due to difficulties in quantifying complex slurry hydrodynamics from first principles, and in acquiring reliable experimental data for model verification and development. This contribution describes the application of electrical resistance tomography (ERT) for three dimensional imaging of the concentration of mineral particulates in a slurry mixer as a function of key process variables (particle size, impeller type, agitation speed). It is demonstrated how ERT can provide a wealth of detailed data to allow model development, which ultimately will lead to much improved design capabilities and the generation of mixing models which could reside within Particle Process Simulators. This principle is illustrated using descriptions of mixer behaviour based on an empirical approach, although the measurement methodology described is equally suited to development of computational fluid dynamics models, cellular models or design approaches based on artificial intelligence. The experimental data can be built into a visualisation data bank, which acts as a "process toolkit" by allowing a library of process responses to be catalogued. Hence these data can be accessed for the purposes of model development, equipment selection, optimisation of operating conditions or testing on-line control strategies.

Jan 1, 1995

By Anthony J. Peach

With the new generation of so called "Super TBM", we would all expect to witness the implied super-performance. In some instances this is occurring, but one must ask why is it not occurring in the majority of applications? For hard rock TBM related projects, we are observing a decrease in the volume of projects in the previously traditional areas such as North America and Western Europe and an increase in Asia (Hong Kong, Indonesia, China, Korea etc). As a consequence less experienced contractors are acquiring the latest ultra high power equipment, without the knowledge necessary to achieve optimum performance. The interdependence of TBM and muck removal systems has been assessed with emphasis on the emergence of the continuously extending conveyor technology, as a means of achieving dramatic productivity increases. The Australian system assessed here at the time of drafting this paper holds the world record tunnel excavation production of 2,166 metres. A little considered aspect of the adoption of conveyors is the associated improvement in safety.

Jan 1, 1995

By Krystyna Raszka, Jerzy Iskra

The paper presents results of spectrophotometric investigations concerning the adsorption of sodium oleate on silicon carbide in the presence of the cations of multivalent metals, applying the ATR IR technique with computer-aidedprocessing of the spectrum. The analysis of these spectra indicates the occurance of distinct OH and COOH bands in the pH range in which the hydroxy complexes of metals of the type MeOH+ and MeOH++ reach in the respective cases the highest concentration in the solution. The correlation of these results with those of flotation, measurements of the zeta potential confirms the proposed mechanism of activation of the flotation of silicon carbide, applying sodium oleate as a collector, the collection taking place over the adsorption of hydroxy complexes of the type MeOH+ and MeOH++

Jan 1, 1995

By P. J. Brown, R. W. Nice

The Thalanga Copper-Lead-Zinc Concentrator in Northern Queensland was commissioned in early 1990. The design of a flotation process for the sequential production of separate copper, lead, and zinc concentrates has always been a most formidable mineral processing challenge. In 1988-1989 during the process design phase, sized fractions of various samples were subjected to quantitative and qualitative mineral analyses. These analytical techniques are collectively known as modal analysis. Modal analysis aided in the selection of key process treatment parameters for the initial laboratory testwork on the Thalanga ore. The work also guided the flowsheet development and quantified the mineralogically imposed limitations on the separation process. This paper describes in general terms how these modal techniques were used to guide the program of laboratory flotation testwork which constituted the flowsheet design phase of this project. During these design studies, the primary grind and regrind requirements were deduced and the basic flowsheet configuration selected. Recent operating plant performance data are to illustrate the value of modal methods in addressing complex metallurgical separation problems.

Jan 1, 1995

By Jim Truman

Appalachian coal mines include operations in eastern Kentucky, Maryland, Pennsylvania, Virginia and West Virginia. During 1994, they produced a total of about 342.5 Mt (377.6 million st) of bituminous coal. This figure represents 37% of the total production from the United States. This region contains nearly all of the nation's coking coal reserves and high-quality compliance steam coal that will be in demand after the turn of the century as utilities comply with phase two of the 1990 Clean Air Act Amendment. Figure 1 shows the location of the study area and the general regions that supply various coal types. Data for the study reviewed here were compiled and interpreted from Mine Safety and Health Administration (MSHA) production reports, Federal Energy Regulatory Commission 423 reports, King's Export database and additional data from the US Department of Energy's (DOE) Energy Information Administration (EIA). Table I is an overview of the total production from Appalachia and the delivered tonnage to various sales categories.

Jan 1, 1995

By James J. Gusek

Passive-treatment systems that mitigate acid-rock drainage (ARD) from coal mines have operating since the mid-1980s. Large systems at metal mines are being contemplated. A 95L/sec (1500-gpm) capacity system is planned this year at an underground lead mine in Missouri. Mine, process and environmental managers need to understand how and why passive-treatment systems work. They must understand what operational limitations to expect, as well as the economics of construction and operation compared to the alternatives, like lime precipitation. Wetlands have been recognized as nature's method of improving water quality. Contaminant reductions can occur through the precipitation of metal hydroxides, sulfides and carbonates and pH adjustments. Local conditions, oxidation state and water and soil chemistries dictate whether these natural reactions will occur under oxidizing (aerobic) or reducing (anaerobic) conditions.

Jan 1, 1995

By E. Topuz, M. J. McPherson, J. Banik

This paper summarizes the analyses of ventilation layouts for mines that experience both spontaneous combustion. The major focus is placed on the longwall coal mine layouts used in several countries. Each of the different layouts is modeled in the form of a ventilation network. The gob of a longwall panel is the most critical location for the occurrence of spontaneous combustion. Airflow leakage paths inside the gob are simulated by using a simplified grid-like network. Computer simulations with this model indicates that the W-system of ventilation is most effective in minimizing air leakage into the gob. Homer, the U-system of ventilation, with pressure balancing behind the face support line, is also found promising for longwall panels. The magnitude of air leakage into the gob is observed to change with the advance or retreat of bee, thus requiring appropriate balancing of pressure to maintain the leakage at a minimum.

Jan 1, 1995

By L. C. Atkinson, E. A. Azrag, T. M. Hanna

The results of using a simple analytical solution and a relatively complex numerical model to estimate ground water inflow to an open pit mine are compared. The analytical solution assumes lateral, radial flow to a fully penetrating pit in an idealized confined aquifer, whereas the numerical model simulates fully three-dimensional flow to a partially penetrating pit from a water table aquifer. The latter is a more realistic simulation of the problem, but the former method is significantly easier to use. Comparison of the results obtained with the two methods for some typical hydrogeologic conditions encountered in mining yields ratios between them in the range of 0.2 to 0.6. These values can be used as a coefficient in the Pit Flow analytical solution to produce reasonable estimates of in-flow even when there are significant differences from the idealized conditions implicit in its application.

Jan 1, 1995

By M. D. Carter

The availability of environmentally acceptable and reliable energy sources is an important issue for Federal, State, and local planners. A cooperative program by the U.S. Geological Survey, State geological surveys, and the U.S. Bureau of Mines has developed a national GIS-based systematic effort to collect, analyze, and depict data characterizing the relationship between restrictions to mining and the potential development of the Nation's coal resources. Land use/environmental and technologic/geologic restrictions are identified within selected 1:24,000-scale, 130-to 150-sq-km 7.5-min quadrangles and applied as overlays to maps of coal-bed thickness, depth, and mined-out areas. Tonnages of original, mined and lost-in-mining, remaining, restricted, and available resources are calculated. Resultant data files are transferred to the Bureau of Mines for recoverability and cost analysis.

Jan 1, 1995

By O. Guyot, A. Broussaud, J. Björkman, P. Söderman, P. O. Samskog

Model-Based Expert Control systems (MBEC) are on-line supervisory dynamic optimization systems which combine the ability of a phenomenological model to generate a large amount of information about the state of the process and predict its evolution, with the flexibility of a rules-based approach to take plant constraints into account and apply a complex control strategy. For its new concentrator started in 1995 in Kiruna (Sweden), LKAB has implemented a progressive grinding flowsheet with closed-circuit autogenous grinding followed by closed-circuit pebble grinding with ore pebbles. The standard for instrumentation in this new plant is very high. The control hardware consists of a Distributed Control System (DCS) through which the operators interact with the plant, supplemented by a site-level Management Information System (MIS). A state-of-the-art MBEC system was imbedded in the MIS by the authors before plant start-up. It consists of several modeling and expertise software modules: a phenomenological process model and a Kalman filter estimate continuously the state of the process, an optimizer calculates an optimum feedrate, while rules-based modules establish production targets and key process set-points. The decision to install the MBEC system as an integral part of the new plant before start-up illustrates the current maturity of the technology, i.e., enough know-how was accumulated through former projects to design and develop the system to a large extent without accessing the plant. The feasibility and the power of dynamic optimization systems were previously demonstrated in Kiruna pre-existing concentrator by the authors. First, a MBEC system was installed on the three existing pebble mill circuits, providing both an increase in quality (stabilised size distribution) and a 10% increase in capacity. An on-line expert control system with limited modeling capabilities was also installed in the existing flotation plant, with the aim of stabilizing phosphorous content in the concentrate and optimizing collector additions. Both objectives have been achieved.

Jan 1, 1995

By Tim Avery, Steve Klein, Mark Schmoll

Tunnel boring machine (TBM) performance in hard rock is highly dependent on the geologic conditions, including the type of rock and hysical properties like the rock strength, hardness, and the spacing of the fractures. This paper examines TBM performance relative to the geologic conditions and rock mass properties at four recent TBM-bored tunnels in California.

Jan 1, 1995

By Dean J. Soderstrom

Soil and sands were contaminated with depleted uranium from weapons testing. This resulted in the formation of a complex mixture of uranium compounds. Characterization studies of the soil indicated the uranium was present as uranium metal, uranium oxides, silicon-bearing metallic uranium, and uranium silicates. A process was developed to selectively remove dense uranium compounds using gravity separation and a chemical extraction system to remove uranium which was not available for separation by gravity methods. Results from characterization studies and pilot scale testing are presented for background information. The primary purpose of this presentation is the report of the results achieved in the field application of the processes.

Jan 1, 1995

By Robert C. Dunne, Maurice E. Freeman, Denis S. Yan

A laboratory tower mill was used to investigate the effect of some variables on the power requirements of a plant mill. The grinding laws were tested for fine grinding and Charles' law and Rittinger's law found to be most closely satisfy the experimental data. The effects of ball size, ball charge mass and media type were investigated. The screw speed was altered to control the power input as required. The results indicate that changes in these variables will change the grinding kinetics but in terms of the grinding efficiency they have no effect on the size-energy relationship. The main factor in the specific energy efficiency is the transfer of the input energy to the charge by variation of the agitation mechanism. The efficiency of a tumbling ball mill and a pin stirred mill were tested for comparison.

Jan 1, 1995

By David Logan, Sigurdur Finnsson

This project, which is intended to provide effective sewerage services to the Blue Mountains community, is located in the Blue Mountains National Park, about 60 km west of Sydney, Australia. The sewerage scheme consists of about 40 km of tunnels, out of which approximately 22 km have been completed. This paper describes the last major tunnelling operation on this project, the Hazelbrook to Katoomba tunnels. These tunnels, which mainly traverse the Hawkesbury Sandstone formation, are being excavated by a new 3.4 meter diameter Jarva Mk12C TBM. The mucking system consists of a continuous conveyor, which has allowed for some very impressive advance rates. The paper will consist of three main sections; the general geological conditions expected along the tunnel will be described in the first section. The second section will discuss the design and main features of the TBM, back-up system and continuous conveyor. The third section of the paper will describe the operational aspects and various performance data of the machine.

Jan 1, 1995

By Downing Terry L.

Dry mineral beneficiation methods have been developed for separation of borate minerals from montmorillonite claystone gangue. The methods include the use of newly developed dry high intensity magnetic separators. The application of these methods has the potential for economic benefit at U.S. Borax Inc. in three areas: ? Processing surface impoundments (ponds) material. ? Pre concentrating ore to be fed to primary refinery. ? Concentrating borate minerals to produce potential products.

Jan 1, 1995