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By J. A. Brierley, Arpad E. Torma, Victor C. Storhok, C. L. Brierley, Batric Pesic

Chemical and electrochemical studies were performed during bioleaching of cobaltite concentrate with Thiobacillus ferrooxidans. The two principal minerals present in the concentrate were pyrite and cobaltite (CoAsS). During chemical studies, the effect of pH on dissolution rates was examined under uncontrolled and pH-controlled conditions. It was found that in the pH range 1.5-3.0 there was no pH effect if the initial pH was not controlled (maintained). When the initial pH was controlled, the leaching of Co, As, and Fe depended strongly on pH. Electrochemical studies were performed by using cyclic voltammetry and constant potential techniques. A sequential reaction mechanism was proposed for dissolution of cobaltite.

Jan 1, 1993

By Derek G. Cieplinski

Regenerative conveyors with complex conveyor profiles place unusually stringent demands on the starting drive control. Depending on the nature of the conveyor loading, the drive must either provide a positive driving force to overcome conveyor friction and gravitational forces if the belt is empty or the inclined sections are loaded, or it must provide a retarding force to resist the gravitational load of decline sections to control the acceleration rate. This paper discusses the requirements of regenerative conveyors, reviews the working principals of fluid couplings, and examines their interaction by means of a case study of a 1700 m long regenerative conveyor utilizing a fluid coupling with a proportional brake control to provide controlled starting and stopping under all load conditions.

Jan 1, 1993

By Michael J. Feltes

In mining operations, conveyors hold one of the most important keys to productivity. Sudden belt or belt-splice failures and extended repair downtimes can contribute to low material-handling system availability. Consequently, operations and maintenance personnel should have a thorough understanding of the available splicing and repair alternatives and how each method can affect the productivity and cost-effectiveness of their operation. The two primary methods of joining belt ends - vulcanization and mechanical fastening - affect the likelihood of sudden failure and repair times in different ways. The time-honored method of vulcanization remains popular in many conveyor-intensive underground and above-ground mining operations around the world. At first, vulcanization may seem attractive because, when done properly by trained and experienced craftsmen, it can match the original belting fairly closely and give the splice a smooth, continuous surface with no edges or seams to invite snagging.

Jan 1, 1993

By D. W. Mitchell

Planning today for what hopefully will never happen is one of the surest ways to decrease the chance of it happening. As Napoleon proved and Ian Mitroff wrote, "The heat and stress of battle is the worst time to make decisions of strategic importance." Mitroff also wrote, "The value of a plan is not that it will ever perfectly match reality, but going through the process of planning speeds the process of recovery. It allows the organization to emotionally work through the worst before it actually happens." This paper concentrates on things miners must consider; on the need for plans to be like a belt conveyor strong enough to carry the load, flexible enough to stretch a little; on the criticality of throwing away fax machines and telephones, and having certain officials at the scene rather than back in head-quarters; on the training of fire brigades and mine-rescue teams; on having company-controlled chromatographs; on having people who can look at trends rather than numbers. Some of the things in this paper might anger some readers; for that, I can only ask them to consider first the problem not their position.

Jan 1, 1993

By Frank E. Chase

Retreat mining is one of the most hazardous operations conducted underground. One of the keys to miner safety and an efficient recovery of the reserves is to design adequately sized production pillars to prevent pillar squeezes, excessive pillar spalling, severe floor heave, roof falls, and pillar bumps. Currently, few pillar design approaches are available which consider the abutment pressures generated by the gob. The Bureau of Mines is developing a method called Analysis of Retreat Mining Pillar Stability (ARMPS) to aid in the design of retreating sections. Back analysis of 42 case studies indicates that ARMPS can be helpful in predicting stability during retreat mining operations.

Jan 1, 1993

By John W. Conn, Harry C. Verakis

An explosion in an underground coal mine can have a devastating effect on the main fans used to provide mechanical ventilation. The Code of Federal Regulations, Title 30, Part 75.310 (CFR, 1992), specifies that each main mine fan shall be offset by at least 15 feet (4.6 m) from the nearest side of the mine opening unless an alternative method of protecting the fan is approved in the ventilation plan. Also, each main mine fan shall be protected by one or more weak walls or explosion doors. This paper presents venting and fan configuration designs which provide a comparable degree of safety for explosion protection. Design flexibility is enhanced and a means for consistency in safety judgements is afforded.

Jan 1, 1993

By Qiang Ji, Richard L. Sanford

A laboratory-scale microcomputer-based autonomous excavation system has been developed that moves a pile of fragmented rock to a designated location using a shovel attachment on a robot arm. Navigation and excavation sub- systems interactively direct a robot excavator to move the shovel to the rock pile, intelligently load its bucket using a video camera, and dump the rocks to a designated area. Although research was conducted on a laboratory scale model, the system can serve as the basis for further work on a full-scale, robust excavation system.

Jan 1, 1993

By M. H. Kotze, M. J. Virnig, G. Steinbach

Earlier work at Mintek on the development of gold-selective resins culminated in a plant-manufactured batch of the first generation of Minix resin. A subsequent pilot-plant campaign at a South African gold mine identified some problems with that resin. These included lower capacity and selectivity for gold compared with the laboratory prototype, and a slow but progressive loss in capacity as the resin was eluted and reloaded cyclically. These problems were overcome by chemical modification of the resin structure. Examples of these improvements are presented. The commercialization of a new resin for a new metallurgical application presents problems, which are exacerbated by the initial lack of demand for the resin because the process is unfamiliar to the mining industry. Progress in the commercial development of Minix is discussed in this context.

Jan 1, 1993

By J. C. Norman

The boron review did not arrive in time for publication in the June issue. The United States was the world's largest producer and consumer of boron compounds during 1992. The US Bureau of Mines estimated that boron mineral concentrate and chemical production in the United States totaled 1Mt (1.1 million st) in 1992, yielding 521 kt (574,000 st) of B203 for a total estimated value of $333 million. That was about 20% less than 1991 revised production figures, and less in value by $107 million. The United States continues to provide essentially all of its own boron supply while maintaining a strong position as a source of sodium borate products and boric acid to foreign markets. Domestic employment in the mining and beneficiation of boron products in 1992 was about 900 people, the same as in 1991. In 1988, 1250 people worked in the boron industry. The Bureau estimated that total world production of boron in 1992 was about 3 Mt (3.3 million st), or about 1.2 Mt (1.3 million st)of B2O3. World production in 1992 was about equal to revised 1991 levels. US production Mines and processing operations in southern California were the only domestic sources of boron mineral concentrates and chemicals. US producers, in order of quantity of production, included:

Jan 1, 1993

By W. L. Oliveira, J. R. Sobrinho, V. M. Hamza, S. M. Eston

The Ipueira III chrome mine is located in the northeastern part of the state of Bahia, Brazil. Extraction is actually at depths less than 300 m, but below level 200 serious environmental problems have been encountered with respect to control of air quality, toxic gas, dust and thermal comfort. At the request of the mining company the University of São Paulo started a research program to investigate the origin and occurrence of the critical problems and to propose solutions. A ventilation survey was carried out first which revealed the existence of several air leakages and short circuits that contributed to substantial reductions in the air supply to some of the main producing levels. Computer simulation of the ventilation network showed that extending the intake air shaft to deeper levels was the most convenient and economic solution to improve the air quality. The ventilation survey was followed by a mapping of the toxic gas emissions and thermal comfort levels in several parts of the mine. The air quality conditions were evaluated as a function of gas emission and heat generation associated with production and development activities. The results show that environmental conditions are already critical in most of the working levels and neither an increase in production nor deepening of the mine can be taken up without substantial changes in the ventilation system. INTRODUCTION Environmental concern is growing in Brazil and several underground mines are starting environmental engineering programs. The LACASEMIN - Laboratory of Environmental Control and Mine Safety of the Mining Engineering Department of the University of São Paulo - was contacted by Mineração Vale do Jacurici to start a research program for investigating the origin and occurrence of environmental problems that existed in the Ipueira III chrome mine. This research program involved field measurements of air quantities with gas levels monitoring, evaluation of heat stress parameters, determination of adequate flow patterns through computer simulations and training of mine technical staff. This paper presents the results of the first 4 months of this research program. The Ipueira III mine is located in the northeastern part of the state of Bahia, near the city of Senhor do Bonfim at about 400 km inland from the state capital city of Salvador. Chromite mineralization is quite widespread in this area and often associated with mafic and ultramafic rocks which cut across regional gneisses and migmatites. ROM production in 1992 varied between 25,000 to 40,000 tons per month, 25% being of lump type (38% of Cr2O3) and 75% being of fines. Lump is manually separated and fines are concentrated in a nearby plant. All the production goes directly to the group processing steel plants near Salvador. The Ipueira III mine is currently under some adverse economic situation because of imports from South Africa and Russia, which have better grades and sometimes a lower content of phosphorous. Consequently there has been little progress in the development of new mines and even in those currently under operation the extraction is becoming more difficult due to the lack of investment in improving mining methods and ventilation systems. In spite of such difficulties the company has backed up studies for initiating an environmental engineering investigation of the Ipueira III mine. MINING METHODS AND VENTILATION SCHEMES The mining methods adopted have changed as a function of extraction depth, rock mass strength and ore body geometry. Initially the orebody was found to be fairly continuous and dipping at about 55 degrees from surface

Jan 1, 1993

By Syd S. Peng

Is the laboratory sized coal specimen much stronger than underground coal pillars? The answer to this question has a profound implication to many coal operators. It will decide how much of the coal reserve can be recovered. Or, in many cases, it will determine whether it can be mined economically. Recent trends in several eastern states to establish regulations regarding coal pillar design to prevent surface subsidence long after mining heighten the debates. And, in some cases, these trends highlight the existing practices that seriously question the conventional wisdom. Currently, nearly all researchers and practitioners agree that as the size of rock specimens increases, its strength decreases. This concept has been universally adopted as the basic principle for coal pillar design in the United States. Several formulas have been derived to account for this effect. The reduction factor for underground coal pillars ranges from one-half to one-sixth of the strength obtained in the laboratory, depending on the formula selected. Recent case studies indicate that the reduction factor is not justifiable, at east in some cases. The use of a reduction factor is based on the assumption hat smaller rock specimens as tested in he laboratory contain none or fewer fractures or planes of weakness than larger specimens or underground coal pillars. In other words, the larger the rock materials, the more fractures it contains and subsequently weaker in strength. Do all underground coal pillars have more fractures than laboratory sized coal specimens? Not necessarily. All coal contains cleats. Some are con¬spicuous but others are not. In terms of cleat density (number of cleats per unit area), there is no difference between an underground coal pillar and a laboratory sized specimen, provided the specimen size is larger than the cleat spacing, which is mostly 25 to 75 mm (1 to 3 in.).

Jan 1, 1993

By A. B. Mayer

A generic task summary for design and implementation of hydrogeology programs at open-pit mine operations is presented as a guideline for management. Rigorous assessment of the local and regional hydrogeologic system is necessary to plan dewatering activities and to address environmental concerns. Dewatering activities include calculation of dewatering requirements, design of dewatering systems and evaluation of dewatering-water disposal areas. Environmental concerns include calculation of dewatering and water-disposal impacts, mitigation of soil and ground-water contamination and acquisition of water rights. Three-dimensional numerical models are commonly used to support these analyses. A thoroughly developed hydrogeology program provides an interactive basis for dewatering feasibility decisions and for support of environmental permits and regulatory compliance.

Jan 1, 1993

By A. Perelli Cippo, R. Granata, D. A. Bruce

During the last few years, significant advances continue to have been made in aspects of grouting technologies used for ground treatment in advance of tunnelling. In permeation grouting, fundamental researches have continued into improving the penetrability characteristics of cement-based grouts. The twin advantages of field regrinding normal grouts to reduce cement particle sizes, and incorporating special additives into stable grouts, are now being systematically exploited in major soft ground tunnelling projects in Europe. The methodologies of jet grouting continue to be developed with special attention being paid to qa/qc issues, reducing unit production costs, and improving predictive capabilities for subsequent settlements.

Jan 1, 1993

At present the feasibility of developing underground facilities for the storage of a number of products including toxic waste, oil, nuclear waste and low pressure gas is under investigation in e number of countries. A possible method of storage is in large excavations, Preliminary ventilation design work has identified that the climatic conditions encountered within these large excavations are a limiting ventilation pollutant within the ventilation system. This paper examines the design of a variety of sizes of excavation from a ventilation viewpoint. The main phases of an excavations lifetime can be divided into four main phases, these being construction, civil and mechanical fitting, storage, full and sealed. The paper details ventilation design options for the first two phases of e vaults lifetime, giving climatic simulations to assess the likely climatic conditions within the excavations for e number of facility depths. The options for climatic control are given and analyzed by means of climatic simulations techniques. l. INTRODUCTION The feasibility of developing underground facilities for the storage of a number of products is under investigation at present in a number of countries. This paper details a possible design for such a facility where the product is to be stored in large underground excavations. A facility layout has been designed with the aim of allowing concurrent construction and storage operations. Thus from a ventilation perspective the facility consists of two circuits , a construction ventilation circuit and a product ventilation circuit both of which are served by an intake and a return surface connection The construction and storage circuits are considered as independent of each other , any interaction in the form of leakage must be from the construction to the storage circuit. From the facility design a ventilation network was developed to assess the ventilation requirements of the facility. In analyzing the pollutant loads for the construction circuit two pollutants were recognised to be critical to the ventilation design , these being diesel exhaust fumes and heat end humidity. In this paper ventilation design options for the construction and civil and mechanical fitting phases of the excavations are analyzed by means of climatic simulation and options for climatic control within the vaults are outlined . 2. FACILITY DESIGN A schematic diagram of a facility design is illustrated in Figure 1. There would be two distinct ventilation circuits , one to service the construction operations and the second to serve the storage operations which occur concurrently with construction , the circuits are separated by ventilation bulkheads . Access to the facility for intake air is provided by two drifts, one to serve each circuit. Two shafts act as returns to surface. The facility consists of two distinct zones for the storage of two types of product. One type is to be stored in smell linear excavations. The second zone is for the storage of a second product in larger excavations. The maximum cross-sectional area and perimeter for the smell linear excavations are 456.25 m2 and 83.2 m, while for the larger excavations they are 440.1 m2 and 86.4 m. Excavation construction consists of three phases: 1. Initial pilot tunnel development between main intake and return to provide through flow ventilation. 2. Enlargement to produce the required finished cross-section. 3. Civil and mechanical engineering work to fit out the excavation ready for storage. It is proposed to excavate the excavations using drill and blest methods utilising diesel equipment. Spoil is to be transported to surface by a conveyor belt system. At any one time the maximum number of working places requiring ventilation will consist of ; 3 storage sites, 2 excavations under construction, 2 excavations undergoing civil and mechanical fitting. [ ]

Jan 1, 1993

By A. J. Jeffery

Heat transfer to a fluid flowing through a rough duct has been shown by many researchers to be a function of surface roughness. The effect of roughness asperities on the duct surface is to turbulate the fluid as it flows through the duct, increasing frictional pressure losses and convective heat transfer rates, and also increasing the surface area per unit length available for heat transfer. These factors combine to increase the total costs to the mine in terms of refrigeration and fan power requirements. A measurement system designed to automate the collection of tunnel roughness information and based on an infra-red timed pulse laser has been developed at the Royal School of Mines in London. The system allows accurate, high resolution digital recordings of tunnel surfaces to be made in two or three dimensions. Software for analysing the data has been written, and the description of a complex surface via single numerical term has been explored. A relationship between the numerically measured surface roughness and the pressure loss of the ventilating air is being investigated with a view to establishing an alternative method of describing tunnel roughness. The paper describes the roughness measuring technique developed and the analytical techniques explored so far.

Jan 1, 1993

Large deposits of eudialyte, a low grade zirconium bearing mineral, occur on the Southern Coast of Greenland in the Ilimaussaq intrusion. Various processes were tested in the laboratory to recover eudialyte from these ores, including flotation, leaching, gravity and magnetic separation. A combination of dry and wet magnetic separations has the advantage of simplicity and the least environmental impact for the location. This paper summarizes the results of laboratory testwork to develop a two-stage treatment process to recover the eudialyte by magnetic separation.

Jan 1, 1993

By M. Bai

The influence of mining on the hydro-geomechanical environment is greatly constrained by alternating mining geometries. The limiting magnitudes of surface subsidence and groundwater flow over the mining area, as a result of geometry changes, can be reasonably predicted through a coupled finite-element model introduced in this paper. Verification of the model has been tested using real and conceptual case studies which reveal that changes in strata conductivities are strongly related to the strata deformation induced by mining. The greatest modification of hydraulic conductivities occurs within the caving or severely fractured zones. The study indicates that narrowing the panel face width will substantially reduce both the intensity and extent of mining damage to the overlying strata, limit surface subsidence and constrain the change in hydraulic conductivity to a reduced scale and smaller extent, particularly as mining depth increases.

Jan 1, 1993

By Changhong Huang, Y. J. Wang

This paper describes the formulation of mine ventilation network optimization as a standard nonlinear programming problem and the solution of the problem using the generalized reduced gradient (GRG) method. In general, the GRG method is regarded as one of the most effective and efficient methods for solving large-scale nonlinear programming problems. The variables considered in the network optimization include air quantity, regulator pressure loss, and fan pressure for each branch. Each of the variables is constrained by lower and upper bounds. This facilitates proper assignments of ventilation requirements and provides a great flexibility to include various situations encountered in mine ventilation. The objective of the network optimization is to minimize the overall air power consumed by or supplied to the network; whereas the constraints are, in addition to the variable bounds, the two fundamental network laws: Kirchhoffs voltage law and Kirchhoffs current law. A computer program has been developed based on the GRG method for the network optimization. An example of network with 18 branches, 8 regulators and 3 fans is included for illustration.

Jan 1, 1993

By J. B. Hiskey, S. Chander, B. J. Scheiner

The use of selected iron complexing agents in preventing or ameliorating acid mine drainage was investigated. The experiments were conducted in weathering columns using refuse samples from a coal cleaning plant. It was observed that the treatment with iron complexing agents significantly altered the rate of oxidation. Some of the reagents tested reduced the rate of oxidation whereas the others even enhanced it. The results showed that a commercial reagent containing oleyl imidazoline was most effective in retarding the oxidation rate. In addition, a simple treatment with this reagent substantially decreased the rate of oxidation of pyrite in a column that was generating acid at a high rate. The effect of this reagent on the surface properties of pyrite was studied by cyclic voltammetry and zeta potential measurements. The decrease in the rate of oxidation resulted from suppression of both anodic and cathodic reactions at the surface of pyrite.

Jan 1, 1993

By Rajendra K. Devala, Sukumar Bandopadhyay

In order to be able to design an adequate mine ventilation system it is necessary to understand how pollutant masses disperse into turbulent ventilation air streams. The mixing of gases and dusts with ventilating air, and dispersion of these pollutants in mine airways, are important flow or transfer problems. For the solution of such problems, the finite difference technique is often used. In this paper, numerical approximation schemes for the solution of the mass transfer problem have been developed using several explicit finite difference schemes. Results from these schemes have been compared with the analytical solution for spatial and time increments using the concept of Root Mean Square error. The comparison of various schemes reveals that the explicit finite difference schemes analyzed here give more accurate results at lower velocities, though the results are dependent on the spatial and time steps considered. At higher velocities the schemes tends to oscillate about the analytical solution. INTRODUCTION In mining, most of the mine air pollutants, such as respirable dust, methane, blasting fumes and diesel exhaust, are produced at the mine face and in haulageways. Injection of any of these pollutants in the mine ventilating air causes disturbances of the equilibrium state of the pollutant concentration of the ventilating air. The mixing of these gases and dusts with the ventilating air are typical examples of mass transfer processes. Pollutants are diluted by the stream of ventilating air flow along airways and discharged into the outside atmosphere of the mine through a return shaft. The dispersions of these pollutants in mine airways are important flow or transfer problems. Knowledge about pollutant sources, emission and transport of these pollutants are essential for ventilation planning and design to ensure good engineering control over air quality, quantity, and environmental conditions. Modeling of mass transfer phenomena in mine ventilation is largely based on extensive studies of turbulent dispersion in wind tunnels and the lower atmosphere of the earth. The general approach in the formulation of models lies in the recognition that these mass transfer phenomena can be conceptualized as a flow problem that can be solved by the general application of Taylor's theory (1954) of turbulent flow and diffusion with modification appropriate static and dynamic parameters. If the face zone is initially contaminated by a pollutant over a long section (e.g. instantaneous exposure of large gas accumulation, rapid methane release etc.), the process of decontaminating the mine workings can be regarded as displacement and diffusion of the tailing edge of the cloud of contaminates in the form of a semi-infinite gas body, for which a one-dimensional mass transfer equation is represented by: [at + u • ax = Ex ex2 + f (x,t)(1.1)] In Eq. (1.1), the term [~~] is the rate of growth of the concentration in the differential element, while a [(5xx )] is the net gain of material due to convective transfer. The two terms balance the total loss of material due to turbulent dispersion that is represented by [Ex . 21] and f(x,t), the source term for the pollutant in the roadway. Several cases of mass transfer that occur in mining can be identified and modelled using the conservative volume element method. The governing equation, along with the associated boundary and initial conditions, source terms and their solutions are detailed elsewhere (Bandopadhyay and Ramani, 1988, Devala, 1989). Only one mass transfer situation is presented (Figure 1) here for the present analysis. Mixed Evolution of Pollutant (multiple pulses) Typical examples of these situations are emission of pollutants from multiple diesel vehicles in the face area, and gas emission from standing pillars as well as from broken coal seam during coal cutting with a continuous miner. The mathematical statement of the problem along with the initial and boundary conditions are given below, Governing Equation: [do+u- =E d2c(1.2) ataxx dx2] Initial conditions:

Jan 1, 1993