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By Donald P. Richards, David W. Campo, Michel Coudry

This paper presents a review of the grouting works of Line 2 of the Greater Cairo MetroSystem. The Nile River alluvial deposits underlying this ancient city provided for a challenging and sometimes difficult grouting project. Permeation grouting using state-of-the-art computerized grouting techniques, as well as extensive ground treatment by jet grout, was per-formed for soil consolidation and/or groundwater control. During the project, over 425,000m3 of ground was treated, requiring 1.4 million linear meters of drilling and PVC injection pipe, 54,000 m3 of bentonite cement and 230,000 m3 of chemical and mineral grout. In addition, over 70,000 m3 of ground was treated using the jet grout method. Relative to major international transportation projects, the grouting works for Line 2 of the Cairo Metro represent one of the largest worldwide grouting endeavors to date.

Jan 1, 1997

By J. A. Herbst, Z. Rogovin, Lo. Y. C., K. Rajamani

Knowledge of the amount of time material spends in a continuous mill in a closed grinding circuit is essential for circuit performance analysis and scale-up design. A convenient method for acquiring this information involves the use of pulse tracers in residence time distribution (RTD) experiments. In typical grinding circuit experiments, RTD measurements are done by injecting a pulse tracer into the mill inlet and detecting it in the circuit exit. In this article, an easy mathematical method for calculating mean residence time and the degree of mixing of material in a mill present in a closed grinding circuit is developed. There are no restrictions on the location of the tracer injection or detection points with this method. Any convenient location in the circuit can be chosen without affecting the residence time distribution measured. The analysis of impulse response data obtained from several commercial grinding circuits using this method is presented.

Jan 1, 1988

By James A. Commins

Accurate engineering predictions of energy needs for pollution control equipment used in surface mining operations is critically important to sound management selection of control alternatives. This paper will describe a procedure for evaluating two control alternatives with different energy needs. Three steps are involved: an analysis of the pertinent regulations, a determination of the size distribution of the particles being emitted, a calculation of the energy needs and costs of the candidate control systems as a function of these regulations and emission characteristics. The principal air pollutant to be controlled in surface mining operations is particulates, or dust, some of which is already on the material introduced into the primary crusher and other dust which is generated by the various steps in the subsequent processes. The requirement for control stems both from regulations concerning workers at the operating site, and the community surrounding the operations. In order to speak quantitatively about the need for control we will use regulations that pertain in Pennsylvania although it must be borne in mind that such regulations vary according to juristiction.

Jan 1, 1975

By Gregory E. Korbin

The effectiveness of pre-reinforcement as an immediate stabilization measure as well as its contribution to the permanent stabilization of a tunnel were studied through the use of physical (Figure 1) and numerical models (1). Physical models were designed for the investigation of two pre-reinforcement systems: first, reinforcing far ahead of the main excavation (Figure 2); second, spiling reinforcement ahead of the face (Figure 3). In both cases, the use of reinforcement was responsible for permanently stabilizing an otherwise unstable opening. Data from the physical models were used to calibrate a numerical model from which additional information on long term behavior, methods to account for the capacity of a pre-reinforcement system, and the mechanisms involved were ascertained. These studies indicated that pre-reinforcement can stabilize a rock mass effectively as it reduces deformations and thereby deterioration due to strain softening, provides rock mass confinement leading to increased available strength, and maintains rock arch continuity allowing for increased tangential stress in the immediate vicinity of the opening. Field studies verified the capacity of spiling reinforcement to restrain initial deformations.

Jan 1, 1976

By Ramarao Inguva

Feasibility studies being conducted to investigate the use of electromagnetic methods for insitu volumetric heating of oil shales will be discussed. A two dimensional numerical model which describes eletromagnetic heating of oil shales is outlines. The model includes equations for temperature, pressure, saturations, chemical reactions, mass conservation, and source terms. The gases are all assumed to form one bulk species and the oil is assumed to remain in liquid form. The chemical reactions include pryolysis of kerogen and char, release of bound water, coking, and decomposition if carbonates. Porosity and permeability are dynamic functions of the organic materials. Calibration of the model is accomplished by comparison of the model results with experimental data obtained by IITRI. Nonlinear relationships for viscosity, thermal properties, and source terms and used as inputs to the model. A finite difference approximation to the differential equations is derived and solved using Newton's iteration technique. For the cases studied the solutions are quite stable. Numerical resultes are included and a preliminary study of the optimization of the heating process is presented.

Jan 1, 1984

By Leonid Pevzner, Valerie Dmitriev, Yuri Babitchev

Performance of belt conveyors, service life of belts and mechanical elements can be radically improved if the automatic adjustment of the belt speed movement is made in such a way, that the unit load over the conveyor length be constant and close to the rated one under random input freight traffic. Such an adjustment is possible when the system of a controllable thyristor electric drive on the basis of induction squirrel cage motor is used. Computer-aided adjustment of the belt conveyor movement is effected via bicontour digital control of the main drive in order to redistribute loads when the loading of conveyor and contour of the control of tension drive are changed. The system envisages control and condition monitoring of the conveyor electromechanical system, as well as metering of electrical power and the amount of conveyor freight. The results of the simulation of speed control of the conveyor belt are given in the report. Mathematical model of the conveyor electromechanical system describes the movement of the belt with cargo and the tension drive. The input cargo traffic is assumed as stationary ergidic random process with the assigned characteristics. The solution of the problem of the synthesis of a closed-loop control system, the structure and parameters of adjustment, the conditions of asymptotic stability of the control back-up system and the condition of minimization of mean square error of shadowing are also given in the report. Microprocessor controller is used to realize the function of the adjustment unit. Under this control system standard mode of conveyor operation, different modes of start-up, operating mode with decreased speed when transporting people, service and emergency braking of a conveyor and some other modes are realized. The digital model of a conveyor as an instrument for decision making in case of emergency is used in those modes. MASTER TEXT Long-standing practice of belt conveyor operation in mines of Russia has proved their inefficient use with 40-70% capacity and 20-25% availability factor. It is associated with unreasonable power intensity and reduction of service life of mechanical components, and as a result, with the growth of total transportation costs. Low efficiency of conveyor application can be explained by the extremely irregular distribution of conveyor freight traffic. Usually, the width of a conveyor belt is identified in accordance with the possible maximum traffic value, engine power capacity for long-term operation under rated loads. However, actually a conveyor often runs without any load and its average load in most cases is lower than the rated one. The problem can be eliminated by way of the adjustment of the operational mode of a conveyor according to an actual input freight traffic via belt speed control providing for the conveyor regular linear load which is nearly equivalent to the rated one. Experimental research into freight traffic under working conditions of the operating underground and open-cast mines proves the fact that the actual freight traffic can be adequately presented through the model of stationary random function of time, for ex- ample, as a J (t) continuous random Gaussian process that is modulated with a G(t) elementary pulse flow:

Jan 1, 1996

By Kenton E. McElhattan

Financial analysts have often called National Mine Service Co. the only "pure play" company to the mining industry, meaning that an investment in NMS is an investment in the mining industry. As a leading manufacturer and supplier to the industry, National Mine Service does enjoy a close and direct relationship with mining. It is the only independent company that offers products and services that include mining machinery, health, safety, instrumentation, mine supplies, and reconditioning services for hydraulics, electronics, and machinery. But what is a positive relationship in periods of economic upturn can be eauallv as negative during the downturns. In fact, National Mine Service has felt the resounding blows of the current recession in the mining industry. Two-Fold Strategy Rising unemployment, corporate losses, bankruptcies, and mine closings in particular have directly affected NMS. But the company embarked on a strategy several years ago that included a two-fold approach to becoming less dependent upon the vagaries of the US coal industry. One strategy was to develop additional products and services for other mineral industries such as potash, trona, and salt and, where possible, apply the technology developed for the mining industry to industrial markets. The other strategy was to become a more international company. The objective was to make export sales a minimum of 10% of total corporate sales. Even today, NMS believes this is a good strategy as opposed to diversifying because its expertise is in mining, not in other areas. A review of NMS's fiscal 1982 annual report indicates that the company's strategy did begin to pay off. 1982 was a turnaround

Jan 2, 1983

By Erik Westman, Enji Sun, Xu Ma, Ben Fahrman

"Shale gas has become an increasingly important clean energy, which has been explored worldwide in recent decades. Supercritical CO2 acts as fracturing fluid for shale gas production. The safety monitoring is essential to prevent any kinds of leakage from the reservoir as the supercritical CO2 physically stored hundred kilometres underground. Seismic tomography is an imaging technique that uses induced seismic waves to create three dimensional images of the subsurface. It is an effective monitoring method to evaluate the caprock integrity in the carbon dioxide sequestration storage (CCS). In this experimental research, a simulated uniaxial compressive load is applied on a granite sample to analyze the stress redistribution for long-term in-situ caprock integrity during CO2 injection. The induced seismic waves are recorded and seismic events are traced based on the Geiger algorithm. The frequency of seismic events correlates with the caprock failure evolution. The acquired seismic data is divided into four regimes based on the frequency of seismic events and the failure process to examine the failure evolution. Furthermore, the travel time and distance is plotted to analyze the variation of velocity. Finally, the double difference tomography (TomoDD) algorithm using arrival time is adopted to recalculate the locations of seismic events and velocity structure in each regime. The results indicate that the passive seismic system can map the caprock stress distribution and allow for imaging of the caprock integrity. TomoDD exhibits sound improvements to relocate seismic events both in relative and absolute locations as well as to characterize the local velocity structure. The study further reveals that seismic monitoring along with TomoDD could evaluate the caprock failure accurately in the CCS.Introduction To reduce the CO2 concentration in the atmosphere, CO2 capture and sequestration (CCS) has been suggested to as a means of continuing to use fossil fuel resources while offsetting their negative environmental impacts (Eiken et al 2011). A positive CCS project should retain 99% of the injected supercritical CO2 (pressure is greater than 7.38 MPa and temperature is above 31.04? and a density is of about 700 kg/m3) over at least 100 years (Davidson et al 2005). As large quantities of supercritical carbon dioxide are being injected into full scale storage projects, caprock stress is redistributing and the leakage could occur anywhere over a wide storage area (Hou et al 2012). Acoustic waves are emitted from the caprock, as it fractures due to the CO2 injection, which can be detected by passive seismic sensors (Shitashima et al 2013). Tomography techniques are advantageous for imaging the integrity of the caprock in the CCS projects. Velocity tomography uses waves to model entities based on the arrival time of waves (Westman et al 2001, Westman 2004, Luxbacher et al 2008). Seismic tomography is a data inference technique that exploits information contained in seismic records to constrain 2D or 3D models of the Earth's interior. It generally requires the solution of a large inverse problem to obtain a heterogeneous seismic model that is consistent with field observations (Kudryavtsev et al 2012)."

Jan 1, 2017

By Y. Ye, J. D. Miller, E. Pacquet, S. Gopalakrishnan

From laboratory research activities during the past five years, it is now evident that effective flotation separations can be achieved with the high-capacity air-sparged hydrocyclone. The effectiveness of the equipment has been demonstrated on a pilot-scale basis (1 tph) for a number of mineral commodities including coal, copper, gold, and industrial minerals using a nominal 5-cm x 50-cm system with separation efficiencies equivalent to those achieved by conventional flotation machines. The high specific capacity of the air-sparged hydrocyclone (100 to 600 tpd per cubic foot of cell volume for a nominal 5 cm x 50 cm system compared to 1 to 2 tpd per cubic foot of cell volume for conventional columns and mechanical machines) makes it especially well-suited for the pro- cessing of low-grade ore. As a result of these pilot-scale successes, a number of plant-scale test programs are planned for larger-diameter units to establish wear characteristics and scale-up relationships for design purposes. The status of the air-sparged hydrocyclone technology is reviewed in the present paper, including a description of the system, fundamental considerations of flotation mechanisms, general discussion regarding the effect of control variables, and the significance of feed characteristics.

Jan 1, 1988

By John R. Marks

The recent trend in the ventilation of deep under- ground metal mines in the United States is to rely more and more on refrigeration for air cooling. This paper describes the layout and the economics of the refrigeration method used by Hecla Mining Company at the Star Mine. An economic analysis must compare the benefits of an engineering system against the costs. The benefits of refrigeration, for example, are increased production rates, a better safety record, improved employee moral, and generally lower airflow requirements. Air-conditioning costs include capital expenditures for equipment, labor and supply costs for maintenance, and power costs for machine operation. A study of whether or not to install refrigeration becomes academic when a mine reaches the critical ventilation depth1 (the depth at which adiabatic compression alone produces station temperatures equal to the desired stope temperatures). Ventilation planning alternatives for such mines, including the Star Mine, are limited to the different methods of refrigeration usage. In this case study of the Star Mine, the refrigeration layout is described in detail. After the system performance is discussed, air-conditioning costs are calculated. The paper then concludes with a cost- benefit analysis of the Star Mine refrigeration system.

Jan 1, 1980

By R. Mensah-Biney, M. T. Hepworth, K. J. Reid

The kinetics of gold-bromide loading onto activated carbon was investigated in a batch stirred reactor. Based on a second-order equation, the amount of gold adsorbed by the carbon was correlated with time. From a 30ºC solution containing 25 ppm Au and 0.8 g/L carbon, the rate constant for gold-bromide species onto activated carbon ranged from 0.27 x 10-3 to 1.2 x 10-3 (kg/t)-1 min-1. The equilibrium saturation capacity (Qe) was 36 ±3.0 kg/t from the same system. The rate of loading increased with increasing temperature and decreasing particle size, pH and solution gold concentration. The calculated activation energy (Ea) was 8.8 kcal/mole, significantly higher than those reported for physical adsorption. The equilibrium saturation capacity (Qe) increased with increasing concentration of gold in solution but was independent of other variables such as temperature, agitation speed, particle size and pH. These rate constants and equilibrium saturation capacity for the gold-bromide species are higher than those reported for the gold-cyanide systems.

Jan 1, 1998

By P. K. Ackerman, F. F. Aplan, G. H. Harris, R. R. Klimpel

Fourteen reagents that are potentially capable of chelating with a metal ion on the surface of the major copper sulfide minerals and pyrite were evaluated for their effectiveness in floating these sulfides. The reagents studied fall into the classes of mercaptobenzole mutations, thiouronium, thionocarbamates, thiourea, imidazole mutations, oximes, hydroxyquinoline and xanthogen formate. The best overall copper sulfide collector was an imidazoline (1-Hydoxyethyl - 2-Heptadecenyl), but it also proved to be an excellent collector for pyrite. Its potency as a pyrite collector can be reduced by structural alteration, but at some loss in its collecting power for the copper sulfides. The effectiveness of many of these potential collectors can be changed by minor alterations to the collector molecule and, to a lesser extent, by pH adjustment. The general order of mineral floatability with these reagents is chalcopyrite = chalcocite > covellite =bornite >> pyrite. The flotation of malachite is generally similar to that of the copper sulfides, indicating the special effectiveness of copper in the crystal lattice for collector attachment.

Jan 1, 2000

By G. Récoché

For the African continent promoting a sustainable utilization of its mineral resources could be considered as a key determinant to fight against poverty. Sustainable development performance indicators for measuring the economic, environmental and social impacts of mining activity are necessary for drawing up policies and sectoral actions, identifying and controlling risks, identifying and implementing sustainable development actions, negotiating between stake-holders, improving mine production, etc. To respond to this need, the SIGAfrique Network proposed to develop a joint decision support tool entitled the African Mining Observatory (AMO) and, to this end, develops a system of indicators to be integrated within the SIGAfrique database. The development of both the OMA and the indicators is based on a participatory method within the working groups, which comprise experts/participants from the 13 SIGAfrique partner and observer countries (Guinea, Burkina Faso, Mali, Tanzania, Niger, Mozambique, Kenya, Uganda, Senegal, Angola, Madagascar, Ethiopia, and Mauritania).

Jan 1, 2007

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 Louis J. Sousa, Elizabeth H. Yaremchuk, Annette P. Graham

Introduction Responding to Congressional inquiries regarding the purchase of a number of major domestic mining and metals companies by foreign firms, the US Bureau of Mines examined trends in foreign direct investment in the US. mining and mineral processing industries1. "Foreign Direct Investment in the US Minerals Industry" analyzes the extent of foreign investment in several major mineral commodity industries. It identified the countries of origin of foreign investment in US mineral assets. The study also described several reasons for the growth of foreign investment in US minerals and discussed some potential implications of this activity. Foreign investment trends in the economy and minerals For the economy as a whole, between 1977 and 1985 the number of US affiliates of foreign investors more than doubled - from 4046 to 9824 - as did employment at these affiliates - from 1.2 million workers to 2.9 million (Table 1)2. During this same time period, the total value of assets of all US affiliates throughout the economy rose from $239 billion to $736 billion (1985 constant dollars). In the domestic minerals industry, foreign investment also grew substantially during that same time as the number of US minerals-related affiliates increased by 74% - from 125 to 217 - between 1977 and 19853. During the same period, employment at all foreign-owned affiliate mineral operations in this country increased by 78% and totaled 198,000 workers at the end of 1985. Parallelling the growth in the number of and employment at foreign-owned US mineral and metal operations, the total value of US mineral assets owned by foreign firms (or individuals) has nearly doubled since 1977 and amounted to $30.9 billion at the end of 1985. The rate of increase in foreign investment in US mineral assets was slightly higher in the metals industries than in the nonmetallic groups. Foreign investment more prevalent in minerals Perhaps a more useful way of evaluating the growth in foreign investment is to analyze growth in the "intensity" of foreign investment - the proportion of total US industry assets held by foreign investors. Although insufficient data on total industry assets prevented the development of such a measure, employment data provide an indication of relative differences in the intensity of foreign investment among the mineral industries and other industries. For example, as noted in Fig. 1, the 198,000 minerals industry workers employed at US-affiliate companies in 1985 represented 12.7% of total employment in this sector of the economy. In comparison, for the mining and manufacturing sectors of the economy as a whole, 7.8% of all workers were employed at US-affiliate firms in 1985. For the total economy, 2.7% of the entire civilian employed workforce worked at US-affiliate firms that year. Using employment as an indicator, foreign investment has been more prevalent in the minerals industry than in most other industries. About one worker in eight in the minerals sector was employed at a US-affiliate firm in 1985. In comparison, for the goods producing sectors of the economy - all mining, petroleum, and manufacturing industries - about one worker in 13 was employed at a

Jan 8, 1988

By R. J. Lee

Asbestos analysis is conceptually simple. The objective, in most environmental analyses, is to determine the number of asbestos fibers per unit area or volume in a sample. The sample may be a consumer product, an ambient air sample, or a water sample. This determination is complicated by several factors: (1) sample collection and preparation, (2) counting techniques, and (3) operational definitions of asbestos in use. Three different definitions have been used in the study of environmental samples and are summarized in Table 1. The analytical procedure and detail required in the analysis vary with the definition of asbestos. Accordingly, this may be the only type of environmental analysis where the definition of a substance dictates the choice of analytical methods, and the rigor demanded of the analysis. Lead, arsenic, or beryllium are sub- stances having a constant definition and the method of analysis chosen depends on the concentration and precision required. However, the meaning of the term asbestos fiber is dependent on the eye of the beholder. Macroscopically, asbestos has certain physical properties that make it highly useful. Rockforming minerals do not display similar characteristics. Now, the question arises as to how three definitions of asbestos came into being. This is a result of two factors: (1) the definition of asbestos on any scale intrinsically involves the morphology or shape of the material, and (2) the advent of the transmission electron microscope permits detection of asbestos fibers and other mineral fragments in a size range where the physical properties of asbestos such as tensile strength, flexibility, or thermal resistance are difficult, if not impossible, to measure. There is a good deal of controversy about which definition is most appropriate for regulatory purposes because of a lack of appropriate health effects data (Cooper, 1978). Most differences of opinion center on the questions surrounding the following: 11 Morphology-Is a 3:l aspect ratio an appropriate medical or physical lower limit for the definition of an asbestos fiber? 2) Length-Are asbestos fibers shorter than some arbitrary length (5 pm) as hazardous as longer fibers? 3) Mineralogy-Is the mineralogical distinction between asbestos and nonasbestos minerals medically significant? While these questions are directly resolvable only with the biological and health effects data, ultimately such data reflects the ability of analytical procedures to fully characterize the materials used in health effects studies on animal models, and to monitor the exposure to particulates with different physical attributes in the workplace or community (Cooper, 1978). The following sections outline the analytical problems involved in distinguishing the asbestos and nonasbestos varieties of the same mineral; the analytical procedures available for identifying asbestos and measuring its concentration in environmental samples; the ability of these methods to distinguish asbestos fibers from nonasbestos particles; and their precision and reproducibility. Finally, we suggest some future directions in terms of definition and procedure that would greatly improve the quality of such analyses. ASBESTOS VS. NONASBESTOS Asbestos that is mined commercially belongs to two mineral families; amphibole and serpentine (Zoltai, 1978, Wylie, and Steel, 1978). The

Jan 1, 1986

By J. N. Eskilsson, W. P. Chen, J. L. Kaplin, V. S. Romero

The Massachusetts Water Resources Authority is currently improving its primary water supply system for the Boston Metropolitan area. The improvements planned by the Authority, which provides water for 46 communities and over 2.5 million people in eastern Massachusetts, include the MetroWest Water Supply Tunnel (MWWST) to provide redundancy in the transmission system, a large capacity water treatment plant and extensive covered storage facilities. The 28.3 km (17.6 miles) long, mostly 4.3 m (14 ft.) I.D. MetroWest Water Supply Tunnel will allow repair of the aging Hultman Aqueduct, which for 56 years has served as the transmission main from the water supply reservoirs to Boston. On completion of the tunnel, the old pipeline aqueduct will be repaired and brought back into service as a parallel, redundant transmission main. This paper describes design considerations and the design process for pressure tunnels in general and the MWWST in particular. It provides an overview of how the design of pressure tunnel and shaft components progresses.

Jan 1, 1997

By Roger Nendick

The recent developments in refractory precious metal ore processing (Bio-oxidation, Autoclaving), and the revitalization of the more traditional roasting processes have attracted great attention in recent years and are indeed the focus of todays symposium. It must always be remembered, however, that the term refractory ore by definition means that the material 'must be capable of being treated at a profit". Given the high cost of the refractory processes, the requirement to be treated at a profit requires very close scrutiny during the evaluation phase of the property development. The M.G.M. film company has the latin motto Ars Gratia Artis meaning Art for Arts Sake. Ingeniatore Gratia Ingeniatoris (a very crude attempt at saying Engineering for Engineerings Sake) should not be the motto for mining companies intent on exploiting refractory gold deposits, but rather the wittily tilted heading for this paper "Take the money and run like a thief". The following hypothetical case studies show that the high technology solution is not always the best financial solution.

Jan 1, 1990

By W. D. Gould, . W. Koren, P. Bedard, P .. B. Marchant

Ammonia and nitrate in metallurgical operations arise from several sources: (1) the use of ammonium nitrate based explosives, e.g. ANFO; (2) the use of cyanide for gold extraction which is degraded to ammonia by most cyanide destruction techniques; and (3) the use of nitrogenous reagents in the mill for neutralisation, flotation and extraction. The concentrations of ammonia and nitrate in effluents vary from 10-50 ppm and 25-300 ppm respectjvely. A number of environmental problems are associated with both ammonia and nitrate. Both of these forms of nitrogen can contribute to the eutrophication of receiving waters. Ammonia and organic nitrogen can also cause high dissolved oxygen demands in receiving waters. Ammonia is also toxic to fish, particularly at elevated pH values. Several methods are in use for the removal of ammonia and nitrate from municipal wastewater, industrial effluents and agricultural runoff. To date, no treatment systems have been developed specifically for the removal of nitrogen from mine and mill effluents. This paper will report on some removal techniques that have been tested using actual and synthetic mine effluents.

Jan 1, 1993

By Donald C. Moore

Asamera Minerals Cannan Mine has been producing a 170 g gold/tonne (5 oz gold/ton) siliciaus flotation concentrate since July 1985. Flotation concentrate is shipped to a smelter for gold recovery. Numerous processes have been investigated to economically produce bullion on site. This paper describes the laboratory and pilot plant test results of a bacterial assisted oxidation of the refractory minerals. Economic comparisons with autoclaving and roasting processes are included.

Jan 1, 1989