Search Documents

By H. Suharyono

The results of an experimental study of polymer-induced flocculation of clay suspensions in continuous, stirred-tank reactors are presented. The effects of polymer dosage, mixing time and mixing intensity are shown to be generally similar to those observed for equivalent batch systems, but flocculation appears to be generally less effective in the continuous process. Settling rates are lower and supernatant turbidities are higher for the continuous system. It is postulated that non-equilibrium effects due to simultaneous polymer adsorption and floc growth can be exploited so as to enhance flocculation in batch systems. The nature of the continuous process, however, offers less opportunity for taking advantage of such effects. Conditions in a continuous flocculation system inherently lead to a closer approach to equilibrium.

Jan 1, 1994

By Eugene C. Robertson

INTRODUCTION A direct proportionality between the observed displacement of a fault and its thickness of breccia and gouge has been proposed recently (Robertson, in press). To validate this finding, an explanation of the mechanics of continuous breccia formation is needed and is offered in this paper. A summary of evidence for the finding will show why an explanation is needed. The correlation between fault displacement [d] and accompanying breccia- plus-gouge thickness [t] seems to be linear and reasonably well established over 6 orders of magnitude, with a range in [d] from 1 mm to 1 km, on a trend of [d/t]= 100, shown in Figure 1. Most of the points are for faults observed underground in mines. The [d] – [t] relation is limited to normal and reverse faults, that have a flat to steep dip and a displacement less than 5 km. It is not applied to large strike-slip and low-angle overthrust faults, whose displacements and breccia thicknesses are widely variable and uncertain. Undisplaced jointed rock is not included in the thickness measurement. A complete description of sources and analysis of the data is given in Robertson (in press). One would intuitively expect that continued movement on a fault would grind up the previously formed breccia and gouge and not produce any more, but the evidence (Fig. 1) indicates otherwise. A physical model to explain continuous formation of gouge and breccia from the wall rocks can be obtained from laboratory experiments on friction.

Jan 1, 1982

By G. G. Richards

"The slag fuming process has operated for close to 70 years to recover zinc from lead blast furnace slag. The process is normally carried out through the batch treatment of slag by submerged injection of coal and air. Within the bath the coal acts as both a reductant, to reduce Zno to zinc vapour, and a fuel, to maintain bath temperature during the endothermic reduction process. The partition of coal between the slag, combustion and bypass is dependent on factors such as bath depth and injection pressure. The option of continuous fuming has been pursued at the D. Blagoev smelter in Bulgaria using heavy fuel oil as reductant/fuel. There has, however, been little attempt at commercial continuous fuming with coal. This paper presents an analysis of a coal-based continuous slag fuming furnace. The data on the Plovdiv fumer is used as a reference point. Critical design criteria for continuous fuming include the slag feed rate, degree of coal combustion and furnace size. Mathematical modelling analysis suggests that continuous fuming with coal can achieve respectable zinc/coal ratios.IntroductionThe slag fuming process was developed in the early part of this century to recover zinc from non-ferrous smelting slags [1-3]. The majority of installed furnaces were put in place to fume zinc from lead blast furnace slag on a batch basis. In most cases coal is used to effect reduction of zinc oxide, but one furnace uses natural gas [4] and, in a curious twist, a continuous fumer was developed based on fuel oil [5].Given the general nature of blast furnace lead smelting, it is not surprising that slag fuming has remained a batch process, in spite of the advantages that could be gained by moving to continuous fuming. Blast furnaces are usually operated as relatively independent units, and tapping has traditionally been done into ladles. The presence of a crane aisle makes direct coupling of the blast furnace to a slag fumer difficult, especially in a retrofit situation. Furthermore, steady-state blast furnace operation is not easy to achieve. The size of these furnaces and the nature of their feed make it difficult to guarantee constant operation."

Jan 1, 1996

By L. Magne, M. Maldonado, R. Varela

Real-time optimization of flotation circuits demands for accurate and reliable measurements to support the decision making process. The collection zone gas holdup is an important variable in this context as integrates the effect of machine and chemical factors on the bubble size and velocity distributions. It has been demonstrated that gas holdup not only correlates with bubble surface area flux, which defines the particle collection rate and recovery in the collection zone, but also with water overflow, a variable which has been related to the froth zone recovery. Therefore, on-line gas holdup measurements provide a reliable alternative to judge efforts leading to the optimization of flotation cells and columns. Estimation of gas holdup in flotation from electrical conductivity measurements has been proposed and extensively used in lab and industrial installations. The approach is based on the application of Maxwell's model, which relates the concentration of a dispersed phase in a continuous medium to measurements of the conductivity of the liquid medium and of the mineral pulp with and without air bubbles included. These measurements require a conductivity cell which covers a representative volume of the flotation cell, and creates a homogeneous electric field throughout this volume that ideally is not affected by the conductivity of the medium. The development of such a cell in the limiting space and geometry of a laboratory flotation cell has been problematic, but a multi-electrode arrangement offers a promising alternative. Electrodes were installed in the flotation cell of a Denver unit; the results of preliminary testing are discussed with a focus on its performance in the measurement of two- and three-phase dispersion conductivity.

Jan 1, 2015

By R. Pérez, James A. Finch, F. Tavera, Cesar O. Gomez

"Gas holdup is a variable which affects the operation of flotation columns. On one hand, gas holdup is a function of bubble size (a function of sparger type, frother characteristics and concentration, and air flowrate), tailings flowrate, solids content, and mixing patterns in the collection zone. On the other, gas holdup defines flotation kinetics and carrying capacity. Therefore, gas holdup is a useful variable to control and diagnose the operation of a flotation column, but the lack of a reliable sensor for on-line gas holdup monitoring has prevented its use in industry.This work describes the principle and the practical difficulties associated with the development of a gas holdup sensor based on the measurement of the electrical conductivity of dispersions. Two different approaches have been devised. These approaches will be described and test results presented of prototypes in laboratory and industrial columns.Background.Several years ago, a research program was initiated at McGill to use electrical conductivity as the basis for developing sensors for process measurements in mineral processing. Electrical conductivity is an intensive property which is a function of the concentration of the different phases present in a dispersion. The initial focus was on the detection of the interface between two dispersions with different characteristics (i.e., that between the collection and froth zones in flotation columns or that between clear water and sedimented solids in thickeners). The technique works in this case by searching for the location at which a sudden change in specific conductivity occurs, as a consequence of different gas holdup or solids content, and absolute values of the specific conductivity of the dispersions involved are not necessary1,2."

Jan 1, 1995

By L. E. Dalverny

This Bureau of Mines report describes the deployment, 5-month operation, and lessons gained from a continuous gas monitoring system using sampling-tube bundles at an underground mine fire in West Virginia. Research information gained indicates the utility of relating certain gas concentration ratios to events during fire development, mine reventilation, and mine recovery. In addition to monitoring the quality of remote fly ash seals, the system provided timely warning of dangerous gas concentrations which developed during surface and underground recovery activities. An evaluation of system components is supplemented by recommendations for improvements.

Jan 1, 1975

By C. M. Sliepcevich

This paper is a brief status summary of investigations by the authors over the past decade to develop a continuous process for recovering' high purity metal powder from pregnant solutions by gaseous reduction at elevated temperatures and pressures. Although these studies included extraction of other metals such as nickel, silver, and gold, this presentation will be confined to the hydrogen reduction of acidic and ammoniacal solutions of copper. The continuous hydrogen reduction process (CHR) described herein enjoys the environmental advantages of other hydrometallurgical processes but, in addition, provides a substantial benefit in fuel economy over competing processes. As was recognized by Schaufelberger in 1956, for a given amount of fuel a continuous hydrogen reduction process has the potential for producing four to six times as much metal as an electrolysis process (1). Although hydrogen reduction of metal salt solutions has been known for more than a century, extensive development work leading to commercialization was not initiated until the 1950's. Since then, commercial applications relative to other extractive techniques have been minor and have been confined to batch or to continuous, completely-mixed autoclaves. By contrast, the process described herein utilizes a continuous, tubular reactor which is operated in modified plug flow so that only limited and localized backmixing occurs. Thus, gradients in concentration, temperature, and pressure exist over the length of the reactor, the presence of which can be utilized to advantage for achieving high conversions and product quality (2, 3).

Jan 1, 1975

By Jouko L. Lehtonen

Sheet pile walls can be sealed watertightly using various methods. The objective of this paper is to introduce a new innovation comprising the use of continuous cement grouting during embedding. The method has been tested on a field test site and installation and permeability features have been observed and analyzed. Installation can be carried out using traditional sheet piling machinery, merely some additional grouting equipment is needed. Installation speed of grouted sheet piles corresponds to that of conventional embedding. The permeability of the tested method is satisfactory in applications where e.g. polluted soil or water has to be isolated from the surrounding environment. In addition, this method can be used for conventional retaining walls where very low permeability is required or for reduction of soil vibration, e.g. close to a railway embankment. The new method to grout simultaneously and continuously during embedding has been developed based on respective innovations on impact driven steel piles.

Jan 1, 2006

By N. G. W. Cook

The conventional cyclic system of deep-level mining by drilling and blasting gives rise to an inadequate degree of stope sorting when mining thin reefs. This results in poor utilization of the capital facilities of a mine in the form of shafts, haulages, airways and associated equipment. Continuous and controlled removal of the thin gold-bearing portion of the reefs would permit better stope sorting and hence greater utilization of capital facilities. Results of experiments to develop hard rock cutting machines for mining are reported and the benefits which could be derived from their use are discussed.

Jan 1, 1969

Detailed observations were made for two existing continuous miner and shuttlecar systems. A simple model for the shift average cycle consisted of three time components - delays, mining and transport. Cycle improvement and productivity improvement factors are derived and used to predict the theoretical improvement which the observed cycles could achieve. Various strategies of action ranging from short-term optimisation through to long-term planning for continuous haulage systems are evaluated. High potential for improvement is shown for a wide range of operating conditions. An overview is presented for systems, currently available or under active development, which can accept coal directly from continuous miners and offer continuous haulage to the surface. Systems are broadly classified as mechanical-roof mounted, mechanical-floor mounted and hydraulic transportation.

Jan 1, 1982

By S. K. Bhatt

This paper reviews major developments in continuous haulage technology for underground coal mines. Haulage systems in use and development are investigated through a comprehensive literature search and visits to mines and manufacturers. The systems include flexible conveyor train, mobile conveyor, multiple- unit continuous haulage, extensible and belt turning systems. Strengths and weaknesses of the systems are assessed in light of their operating under remote control and their application to the computer-assisted continuous mining machine being developed by the US Bureau of Mines. Through mining scenarios, candidate haulage systems are conceptualized to be consistent with the capabilities of the mining machine.

Jan 1, 1991

By S. K. Bhatt

This paper reviews major developments in continuous haulage technology for underground coal mines. Haulage systems, both in use and development, are investigated through a comprehensive literature search and visits to mines and manufacturers. The systems include flexible conveyor train, mobile conveyor, multiple-unit continuous haulage, extensible, and belt turning systems. Strengths and weaknesses of the systems are assessed in light of their operating under remote control and their application to the computer-assisted continuous mining machine being developed by the U.S. Bureau of mines. Through mining scenarios, candidate haulage systems are conceptualized to be consistent with the capabilities of the mining machine.

Jan 1, 1990

By Lennox A

In an attempt to increase underground productivity Coal and Allied has introduced a continuous haulage unit into it's Moonee colliery. A second unit is planned for Nallarah colliery in the near future. Both systems will be roof mounted or monorail type and manufactured by Joy Manufacturing Pty Ltd. The introduction of these machines is seen as a logical step in improving the efficiency of mining with continuous miners. This could be in conjunction with longwall mining in the rapid development of gate roads or, as in the case with these machines, as conventional development and extraction units. The advantages of the continuous haulage system are; Relatively low cost. 2 Ability to obtain high productivity in irregular or disturbed coal reserves not suitable for longwall mining. 3 Increased worker safety with the elimination of shuttle cars and the majority of trailing cables. 4 Increased productivity independent of soft or difficult floor conditions. At the time of writing the Moonee installation is 6 months old. The Nallarah machine is due for delivery March 1988.

Jan 1, 1988

By William D. Mayercheck

Beginning in 1974, the Bureau of Mines, U.S. Department of the Interior, sponsored R & D efforts related to further development and use of continuous face haulage in underground coal mines (Cowan, 1975). The U.S. Department of Energy continued this effort as of October 1977. This paper represents an update of an article previously published in Mining Engineering magazine (Mayercheck, 1979). Development progress is summarized for a variety of prototype systems or components now being built, surface tested, or tried underground.

Jan 1, 1981

By W. D. Mayercheck

Beginning in 1974, the Bureau of Mines, US Department of Interior, sponsored research and development efforts related to further development and use of continuous face haulage in underground coal mines (Cowan, 1975). The Department of Energy continued this effort as of Oct. 1977. This paper represents an update of an article previously published in Mining Engineering magazine (Mayercheck, 1979). Development progress is summarized for a variety of prototype systems for components now being built, surface tested, or tried underground.

Jan 1, 1984

By T. A. McAfoose

As one of the major suppliers of the chestnut Ridge energy center, Rochester and Pittsburgh Coal Company continues the search for more efficient haulage systems. This search is one that is essential in providing coal to the Keystone and Homer City power plants at the most economical cost. These two electrical generating plants located in west central Pennsylvania are part of the energy center which consists of four generating stations. Prior to the time the two stations were put on line, August, 1967 for Keystone and August, 1969 for Homer City, our company made the decision to rely on belt conveyors from the section to the surface to provide for continuous main line haulage. The proximity of these generating stations to proven reserves allow for minimal truck haulage and minemouth setups. With the addition of seven new mines, in the past ten years, revisions have been made on the original setup to interconnect the haulage of several mines to deliver the product by belt to the power plants.

Jan 1, 1979

By Bo Arvidson

SALA MAGNETICS, INC. is now operating a 15 tph continuous high gradient magnetic separator, the SALA-HGMS® Mark III Carousel, as part of a complete mineral processing pilot plant installed at Sala's Cambridge headquarters. The Mark III can generate a maximum magnetic field of 18 kG making it possible to process even weakly magnetic, finely ground ores and ore tailings on a continuous basis at the performance level achieved in Sala's cyclic high gradient magnetic separators. Test results on iron ores, clay, and decoppering of molybdenum concentrate will be discussed. Bench scale tests have been performed on all of these materials using the SALA-HGMS® Model 10-15-20 Cyclic Magnetic Separator. A direct correlation may be made between cyclic and carousel results. Sala's Mark III Carousel high gradient magnetic separator is designed to permit scale-up to machines capable of processing two hundred (200) tons of ore per hour and more.

Jan 1, 1976

By Klaus Schönert, Martin Botsch

In common high intensity magnetic separators, the magnetic particles are deposited on ferromagnetic matrices, such as expanded metals, steel balls or grooved plates, inserted into a strong magnetic field. The nonmagnetic material is flushed through the matrix chamber. Discharging the magnetic particles is only possible if the magnetic field is reduced to zero (e.g. high gradient magnetic filtration for the purifying of kaolin) or the matrix chamber is moved out of the field by a rotor (e.g. the Jones Separator). Therefore, these separators perform only in a batch or semicontinuous mode. A real continuous operation requirs transport of the deposited magnetic material to an outlet where it can leave the separation chamber inside the field. One possibility for accomplishing such separation and transport is through the use of a rotating induction body with a certain shape, such as a spiral.

Jan 1, 1995

By Tadafumi Adschiri

"Supercritical water can provide an unique reaction atmosphere for synthesizing metal oxide nanoparticles. Due to the drastic change of properties of water around the critical point, including density, dielectric constant and ionic product, the reaction phase with O 2 or H2 gas and the reaction rate and equilibrium can be varied to synthesize new materials or define particle morphologies. In this work, hydrothermal crystallization experiments are performed with several types of flow apparatus that allow convenient manipulation of variables such as temperature, pressure, and residence time. Key features in the flow modes and material preparation are discussed. The proposed supercritical hydrothermal synthesis method has the following desirable features: i) nanoparticles can be produced, ii) morphology of the produced particles can be controlled with small changes in pressure or temperature, and iii) a reducing or oxidizing atmosphere can be applied by introducing oxygen or hydrogen or other gases. An overview of this method is given for functional material synthesis of significant industrial interest including barium hexaferrite magnetic particles, YAO/Tb phosphor fine particles and lithium cobalt fine crystals.IntroductionHydrothermal crystallization, a method of metal oxide formation from metal salt solutions, is typically used at temperatures ranging from 373 K to 473 K. We are developing a new process for hydrothermal crystallizations that uses temperatures in the range of 673 K to 723 K, which is just above the critical temperature of water1 • 8 • In this work, we refer to this process as supercritical hydrothermal synthesis. The supercritical state of water allows one to vary reaction rate and reaction equilibrium by shifting the dielectric constant and solvent density with pressure and temperature. From of our research on material production in supercritical water, we have identified the following specific features of the supercritical hydrothermal synthesis method: (i) ultrafine particles can be produced, (ii) morphology of the produced particles can be controlled to some extent with pressure and/or temperature, and (iii) a homogeneous reducing or oxidizing atmospheres can be provided by introducing gases, such as O 2, H2, H2O 2• and so on.1"

Jan 1, 2000

By Ehlert G, Steinlechner E

The paper describes a new process for filtration which combines the continuous operation of conventional vacuum filters with the low final moisture contents hitherto only achievable with plate and frame presses. The increasingly high portion of fine particles causes several problems in the filtration of copper concentrates. One drawback is that remarkable quantities of liquid are attached to the very fine particles because of their specific surface area. Furthermore, fine particles also reduce the size of the capillaries in the filter cake, thus increasing the critical pressure which any filtration system has to exceed to achieve the desired final cake moisture. The maximum filtration pressure of conventional vacuum filters is limited by nature itself and by practical aspects to approximately 0.75 bar. The hyperbaric filter combines the continuous operating principle with an increase in filtration pressure of up to 6 bar simply by placing the entire disc or drum filter inside a pressure vessel. The major machine components and process features are explained in the details of the paper. After extensive research and field testing, 23 ANDRITZ hyperbaric filters, with a total filtration area of 1968 m2 have now been sold. Seventeen of these units (1440 m2) are in commercial use and more units are, on order. Performance data on copper concentrates from plants in Australia, South America, Poland, Africa and North America are outlined in detail. Compared to vacuum filters, generally hyperbaric filters will reduce the final cake moisture of concentrates with 75 per cent

Jan 1, 1993