Search Documents

By John A. Herbst, William T. Pate

"Plantwide control of mineral processing operations has long been sought for its potential benefits. These benefits include minute-to-minute optimization, reacting to disturbances in ore characteristics and equipment status as they happen, and the coordination of all unit operations in pursuit of the highest performance level. However, several difficult challenges have kept us from fully realizing those benefits. One of these challenges has been to provide fairly complete quantitative descriptions of unit operations to account for critical interactions within and between unit operations. In some cases we understand the physics and chemistry very well and can incorporate that knowledge into phenomenological models. In other cases our knowledge is incomplete, so we must rely on other forms of knowledge such as fuzzy logic or neural nets. Another challenge to be met has been to simultaneously compute a large number of manipulated variables. In the past this challenge was met by optimizing only unit-by-unit, rather than on a global basis to significaritly reduce the number of variables. In this paper, a procedure that globally optimizes one or two important variables is outlined. This procedure comes much closer to true plantwide optimizing control while remaining computationally feasible. Finally, another major challenge is to choose a meaningful global objective that can be calculated with the models and can be effectively optimized. Financial goals seems to be the objectives of choice.This paper discusses recent progress in overcoming the challenges and illustrates a promising approach which is being pursued at Mexicana de Cobre's La Caridad copper ore concentrator. At M de C, advanced control strategies have been installed one at a time in the crushing, grinding and flotation sections. During this period, the throughput of La Caridad, Mexico's largest copper concentrator, increased from 76,000 tpd to 90,000 tpd. Plantwide integration is expected to gain an additional 3% improvement in profitability."

Jan 1, 1996

By Animesh Jha

"Fine ceramic powders (<500 nm) exhibit exceptional physical and mechanical properties in engineered structural ceramics. The production of fine powders, in particular the non-oxide ceramics, via a cheaper route than the organic solvent route has been rather elusive. This paper examines the physical chemistry of sub-oxide vapour-phase reduction reaction for the nucleation of non-oxide ceramic phase. Well known vapour species eg SiO and BO in the production of technical ceramic powders (SiC, BN) are particularly discussed for understanding the nucleation process of SiC and BN ceramic phases respectively. The regimes of partial pressures and temperatures are particularly 'identified. The calculated nucleation rate as a function of the temperature is compared with the experimental results on powder morphology. The production of amorphous and nanocrystalline h-BN powders is discussed in the context of substrate structure and thermodynamic parameters.IntroductionThe physical and mechanical properties of ceramic components are strongly dependent on the powder particle size and morphology used for their fabrication. For example the strength (Os) of the structural ceramic components increases with decreasing average grain-size (d) in accordance with the Hall-Petch relationship: Os = 0""0 + k/(d)1/2. Here k is an empirical constant which can be established from the graphical relationship. However as the particle size approaches submicrometer-size range, the dependence of strength on the particle size becomes more complex [1]. The design of ceramic components based on nanometer-size particles have recently become an important field which can offer ceramic materials with properties comparable to their metal counterparts. Several materials based on these concepts have been developed and reported by Niihara [2]. For example, the Al2O 3-SiC nanocomposite, having average B-SiC grain size 0.3-2um with intragranular SiC particulates of 5-10 nm has unusually high strengths (1100 MN/m2) at low and elevated temperatures combined with enhanced fracture toughness (> 4 MN-ml.5) which is an unusual combination in structural ceramics. Besides mechanical properties, as the particle size of ceramic powders approaches the nanometer-size range, the charge transport properties also improve by many times. The effect of particle size on the electrical conductivity of Si3N4-TiN composites has been well documented [3.4]. The size of ceramic particulates without doubt plays a pivotal role in determining the properties of ceramic components."

Jan 1, 1996

By Jan Tegtmeier, Horst Gerhardt

INTRODUCTION Under certain circumstances the closure of former mines which are located above a certain flood level can result in problems such as the emanation of detrimental substances after having completed filling and reclamation operations. This especially applies to uranium mines in which the radiation dose could far exceed the dose of natural background radiation. By means of an example of the uranium mining in Germany in the following it will be demonstrated how to cope with this problem. On the basis of comparative investigations in various vein deposits and using ventilation scheme calculations proposals for the optimization of the necessary forced ventilation can be submitted. REPORT ON SITUATION In the period 1946 - 1989 the former Soviet-German joint- stock company "Wismut" developed into the biggest European uranium producer with a total output of about 220.000 t of uranium. A major mineraldeposit district was the deposit of Schlemaf Alberoda in the Saxon Ore Mountains, in which 80.000 t of uranium were produced. Thus it is among the biggest uranium de- posits of the world, from which various other metals were at- tracted for many centuries. The exploitation of the Schlemal Alberoda deposit involved steep veins in regions near the surface as well as depths of 1.800 m. Until 1991 a total excavation space of 40 million m3, which is flooded at present, was produced. With the average increase in the water level of 80 cm per week the final flood level is expected to be reached in the year 2003. The shaft 373 at present still being used for ventilation will be no longer available since the second quarter of 1998 after flooding the -540 m level because it is not connected with the excavation system near the surface. As a study shows, a radiation dose far above the natural back- ground radiation has to be expected for the town of Schlema due to the extensive mining activities near the surface and due to the subsequent displacement with missing depression fo the main mine ventilating fan. An uncontrolled air flow containing radon leaves the open mine excavation due to the effect of the natural ventilating pressure and emanation caused by the barometric pressure drop with atmospheric pressure fluctuations. This mine air with its high-level radioactive equilibrium results in a high radiation dose in buildings (see Figure l). After having switched off the main ventilating fan in order to investigate the effect of the missing depression the increase in radon concentrations amounted up to 700% in various buildings of Schlema. This was partially due to the inversion state of the weather at that time. The high radon concentration has detrimental effects on the health of the population and of the miners working on the further reclamation in regions above the flood level. ANALYSIS OF THE RADON EMANATION RATE EXPECTED Considering the composition of the radon inflow from the mine workings it becomes evident that 80 % of the radon inflow originates from abandoned excavations and only 20 %from open ventilated mine excavations. This fact has to be taken into account for the ventilation after having reached the final state of flooding. After completing ventilation the radiation dose on the surface is mainly due to the radon emanation from excavations close to the surface. Investigations of the Wismut GmbH showed the in- crease in the specific radon emanation rate by a factor of 100 for abandoned excavations as compared to new drivings. One reason is the larger specific surface of abandoned galleries caused by displacements due to mining activities as well as by fall of hanging. Furthermore the radon can enter the gallery through joints, which have subsequently opened by convergences. All these effects result in a larger free surface available for radon diffusion. The large number of drivings in the deposit sections near the surface and the fact that the highest uranium contents are found near the surface as well as the high fracturing are further reasons for higher emanation rates. Considering these facts it can be expected that the radon inflow of 10.000 kBq/s, which refers to an open mine excavation of about 1.4 million m3, represents a minimum. Only by increasing the specific surface, for which a numerical value has still to be determined, this value will increase with certainty. An extensive radon emanation from the residual excavation, which cannot be flooded, can only be prevented by maintaining the ventilation system. The low pressure produced by the fan in the mine openings prevents the emanation of air containing radon due to the effect of the natural ventilating pressure. Without the controlled withdrawal of the radon the population as well as the miners working on the further reclamation in areas above the flood level would be endangered. Therefore the follow-

Jan 1, 1996

By S. A. Pirzada

A thermal plasma assisted laminar flow reactor has been used to evaluate the kinetics of converting alumina to sodium aluminate in flight. Free energy minimization calculations were used to determine experimental conditions. The experimental variables include: alumina particle size, alumina/sodium nitrate molar ratio, temperature and residence time. A mathematical model for the conversion was developed and validated. Experimental and mathematical results are presented.

Jan 1, 1996

By A. Andreas Hejja

Flow of slag and settling of matte in slag resistance electric furnaces are discussed in conjunction with furnace geometries, stirring action of the electrodes, buoyancy and electromagnetic effects. The rectangular electric furnace was regarded as a channel reactor and the mode of slag flow as a channel flow. The flow is affected both by buoyancy and electromagnetic forces, however the effect of electromagnetic forces is minimal. The flow velocity is made up of two components; (i) that developed by the action of the electrodes, and (ii) the bulk flow velocity determined by the smelting rate and the volume of the reactor. Slag samples were taken from various depths of the molten bath and were analyzed microscopically to determine the size and distribution of matte particles, The action of the electrodes was described by a simple mathematical formula indicating a balanced settling rate in the area of electrode action.

Jan 1, 1996

By S. Narasimha Rao

Significant amounts of lateral load may act on pile foundations supporting structures such as transmission line towers, tall structures, bridge abutments, offshore platforms, quay wails, harbour structures and anchorages for water front structures. There were several theoretical and experimental studies conducted on laterally loaded piles in clays to determine ultimate lateral capacity and deflections under working loads. Under a lateral load, a pile deflects in the direction of load application and the soil in front of the pile offers resistance to this movement. The ultimate lateral resistance of a pile can be estimated considering the statics of the pile for a known distribution of soil resistance with depth. In this paper, considering the contributions from both lateral shear drag and frontal passive earth pressure, a method has been proposed to estimate the ultimate lateral capacity of rigid piles in clays. The lateral shear drag has been estimated in terms of adhesion and shape factor. A few load tests were conducted on model piles subjected to lateral loading and these experimental values are used in verifying the proposed method. The reported results obtained from both model tests and field tests were used in support of the predictions made. In all the cases, there is a good agreement between the predicted and measured capacities.

Jan 1, 1996

By D. McConchie

Management of caustic red mud wastes at the QAL bauxite refinery uses an innovative approach . involving neutralising the red mud with seawater; solids settle in a Red Mud Dam and residual water (pH = 8.6) is discharged to a tidal inlet. A survey of 18 trace elements in sediment, water, mangroves and molluscs, and an ecological survey of benthic fauna in the inlet, and at near-pristine control sites, revealed no significant trends that were linked to the discharge, except for the concentration of Al which was slightly elevated within 100m of the outfall. Trace element concentrations in water samples were close to, or below, world average seawater values and oysters collected near the outfall were acceptable for human consumption. The impact of discharges is minimised by a high tidal range, >60% flushing of the inlet in each tidal cycle, and the very high trace element binding capacity of sediment in the dam (> 100meq/ 100g dry mud).

Jan 1, 1996

Blasthole deviation is a frequent, well documented and undesirable occurrence in mining operations. It is caused by the drill string mechanics, operating variables and the interaction between the drill bit and the rock mass characteristics. It is composed of three distinct components: collaring or marking error, alignment error and trajectory deviation. This study has focussed on the dependence of trajectory or natural deviation on the geological features of the rock mass being drilled.

Jan 1, 1996

By G. Van Weert

Oxygen transfer from dispersed air in agitated slurries represents an important unit operation in the minerals processing industry. Gold leaching, iron precipitation and especially bio-oxidation come readily to mind. However, little engineering information is available on the variations between impeller types on such O2 transfer. Engineering literature on the subject, i.e. information which relates slurry density and energy input to O2 transfer, is reviewed and compared to current experimental work. The latter was carried out with minus 50 micron sand/water slurries in a 64 I laboratory tank of standard proportions, equipped with a variable speed drive with torque meter. A standard Rushton turbine and a specifically sized A315 were compared. Results confirm an increasing impairment of O2 transfer with increasing slurry density for both impellers. The volumetric mass transfer coefficient, k,a, in a 10 vol. % slurry shows a decrease of 30% compared to the k,a in water. At 20 vol. % sand this decrease is near 50 %, depending somewhat on superficial gas velocities. Power efficiency, i.e. the kg O2/kWh, decreases about 25 % more rapidly for the Rushton turbine than for the A315 with the addition of sand. However, for equivalent O2 transfer the Rushton turbine was more efficient in this work. Experimental results are presented and their significance for slurry bio-oxidation discussed.

Jan 1, 1996

The Main Seam occurs in two &apos;pods&apos;, termed North and South, separated by an east-west oriented &apos;want&apos; zone (most probably a palaeo-channel). The seam on either side of the &apos;want&apos; area reaches thicknesses of over 30 metres but the North Main Seam adjacent to the &apos;want&apos; zone has been split into multiple seams of 10 to 15 m thickness. Rock types in the inter-burden of this area are characterised by inter-bedded sandstones and carbonaceous mudstones varying in thickness from 0.5 to 5 m. In the South Main Seam, an area of un-split coal exists and is characterised by few inorganic partings. Overburden in this area varies geographically from relatively thick mudstones in the south and east part of the coal deposit to inter-bedded sandstones and carbonaceous mudstones adjacent to the &apos;want&apos; area. The sandstone/mudstone overburden probably represents a splay or splay-channel complex emanating from the larger &apos;want&apos; area palaeo-channel. Modelling lithological variability is of use because it is one of the factors used in predicting cavability and roof support system design. The coal in both the north and south deposits were found to exhibit highly predictable quality and breakage parameters in relation to the coal geometry. Although ash yield and sulphur are mostly low and not variable, volatile matter and thus fixed carbon, varied in relation to seam thickness. In general, volatile matter (dat) decreased and moisture increased with decreasing seam thickness whereas moisture increased with decreasing seam thickness. In addition to these parameters it was found that the energy needed to crush the coal was lowest at the top and bottom of the seam and, on a whole seam basis, decreased with seam thickness. All of these parameters were found to vary in relation to the vitrain band content of the coal which itself was controlled by seam geometry. These parameters can therefore be modelled and inputted into mining plans and quality control operations.

Jan 1, 1996

By M. O. Lai

"Metal matrix composite (MMC) with composition of Al-4.Swt.%Cu reinforced by IOwt.%TiB2 or ISwt.%SiC particulate has been successfully fabricated using powder metallurgy technique. Disk, compression and beam specimens were prepared with (a) layered structure containing ductile Al-4.Swt.%Cu with brittle Al-4.Swt.%Cu/TiB2 or Al-4.Swt.%Cu/SiC layers, and (b) homogenous constituent with composition of Al-4.Swt.%Cu/lOwt.%TiB2' The specimens for the fracture toughness measurement were built through three ductile-brittle-ductile alternating layers. For the beam specimens, the layers were built through brittle-ductile-brittle sequence. The brittle layer consisted of Al-4.S%Cu with fixed amount of reinforcement. Fracture toughness testing revealed an increase for layered composites although the total amount of the reinforcement was the same for all disk specimens. The increase in fracture toughness is due to the existence of ductile layers which manifests a strong influence on delaying the occurrence of fracture. It acts as a barrier to resist the propagation of crack and hence increases the fracture toughness of the layered MMC specimens, Delamination in the beam specimens was observed to be due to shear stresses. Fracture surfaces of both disk, compress and beam specimens were characterized using the SEM. IntroductionMechanical and thermal properties can be achieved by the incorporation of refractory secondary phases to constrain the plastic flow of the matrix in a metal matrix composite (MMC). The size of the reinforcement particulate incorporated must be in the range larger than the dislocation cell size and strongly bonded to the matrix (I). Particulate reinforced metal matrix composites hence provide high modulus, improved wear resistance and strength (2-4). Because of the incorporation of refractory phases which are generally brittle, the major limitation in the mechanical properties of MMCs is their limited ductility in comparison to their base metals. Cracks normally initiate from the reinforcement and voids (4, 5). Due to the lack of ductility, cracks propagate rapidly with increase in load. As a result, the interactions between reinforcement particles and propagating cracks have recently been of great research interest (6). In addition, volume fraction of reinforcement and aging condition of the matrix significantly affect the mechanical behaviour of MMCs. In the case of AI-3.5%Cu reinforced with varying volume fractions of SiC particulate, it has been found that the probability of particle fracture increased with increasing volume fraction of reinforcement (7)."

Jan 1, 1996

By E. T. White, Dean Ilievski

"The population balance is one of the basic relations for analysing particulate mineral processing operations. It is an exact relation. The principles of the population balance are reviewed and applications in the minerals industry discussed.IntroductionMathematical modelling has proved to be a very successful approach for improving the design and performance of mineral processes, particularly since the availability of computers to handle the complexity usually necessary to give a useful model.Mineral processes almost invariably involve particles, as either solid fragments, liquid drops or bubbles. Process performance usually is highly dependent on the behaviour of these particles. In modelling particle behaviour, the basic relation to be used is the population balance. This paper discusses the role of the population balance and the range of its applications in minerals processing.The Population BalanceThe population balance was developed for demographic studies, ego predicting the change in the population (numbers) of, say, school children between one census and the next. The first sustained application to the processing industries appears in the 1960s for crystallization. However it was recognised almost immediately that it had application to all particulate processing."

Jan 1, 1996

By J. A. Chermak

Piles of sulfide-bearing overburden, ore, and tailings have the potential to generate acid drainage (AD) when exposed to an oxidizing environment. Laboratory column experiments were conducted using acid-generating overburden material with an added surface amendment of limestone and/or lime. Artificial rainwater was introduced and allowed to drain through the columns. Results showed that the limestone and/or lime reacted with the acidic rock, resulting in the precipitation of a hardpan layer of gypsum and amorphous iron oxy-hydroxide at the surface. The hardpan layer significantly reduced the effective permeability of the column. Based on this study, hardpan layers can be created as chemical caps to significantly reduce the infiltration of rainwater and snowmelt into acidic overburden or tailings material. Unlike traditional capping methods (for example, clay and high density polyethylene (HDPE) covers), chemical caps are self-healing.

Jan 1, 1996

By Felicia F. Peng

Using granular media for removal of soluble manganese from mine water and industry waste stream has the advantage of forming a compact surface layer of manganese oxide coating on the media. This process can avoid the step involving the separation of voluminous sludge of manganese hydroxide by the high-pH method for soluble manganese removal. The removal of soluble manganese is accomplished by adsorption and oxidation. The adsorption of Mn(II) on the manganese oxide-coated media was rapid through the specific adsorption and may be due to the ion exchange of hydroxyl ions on the manganese oxide by Mn(II). In the subsequent step, the adsorbed Mn(II) form the intermediate manganese complex on the manganese oxide product is oxidized with dissolved oxygen or other available oxidant source in the aqueous solution. This paper presents the efficiency of removal of soluble manganese from mine water by using a laboratory fluidized bed and the recovery of manganese oxide coating on the anthracite coal particles. In order to accelerate the formation of the manganese oxide layer on the surface of anthracite media, dilute potassium permanganate solution is used as an active oxidant. The effects of operation parameters on the manganese removal including pH, flow rate, concentration of feed and oxidant dosage are evaluated.

Jan 1, 1996

By S. Lin

Fan stall is a notorious phenomenon with axial-flow fans. When multiple fans of this type serve a ventilation system, their mutual impacts are very complicated and not well understood. Results from laboratory experiments indicated that the immediate consequence of a fan working across its stall zone (i.e., the pronounced trough on the fan characteristic curve) is that some branches in the system may suffer abrupt and even drastic changes in air quantity and pressure. The quantity range of the fan that causes the abrupt change is called an unstable operating range. The corresponding quantity range of a branch is called a non-achievable quantity range of the branch because any quantity within this range cannot be achieved without changing some parameters of the ventilation system (e.g., branch resistances). These concepts are introduced based on the test results from tubing networks to bring attention to these important characteristics of ventilation systems.

Jan 1, 1996

By Susumu Okabe, Etsuji Kimura

"The Mitsubishi Continuous Copper Smelting and Converting Process is the typical applications of injection metallurgy to nonferrous metallurgical operation, where the top blowing multiple lance system is employed for the continuous feeding of the raw materials and reaction gases into the molten bath. This results in an effective dispersion of the reactants into a strongly agitated bath. These are considered as the major advantage of the process with respect to the high production efficiency. On the other hand, however, the strong agitation may cause a considerable amount of refractory wear, and the melt splash generated by the lancing may also have negative effects on the productivity, i.e. the increase in the refractory wear, the metal loss, the heat loss, and the accretion growth, etc. Therefore, the optimization of the blowing condition as wen as furnace design is very important to achieve a stable and efficient operation, and fundamental understanding of the injection, agitation, and splashing is badly needed.In this paper, fundamental aspects of the Mitsubishi Process regarding injection, especially splashing phenomena, are discussed. The splashing on a vertical plane caused by the top blowing gas injection onto liquid surface was investigated through physical model study. As a result of the study, the splashing rate on the furnace wan was wen correlated with the physical properties of the bath materials, gas velocity, cavity shape, lance/wall distance and ceiling position. Obtained equations were compiled in a computer program and have been successfully applied to the evaluation of the furnace design. IntroductionInjection metallurgy is an application of gas/solid-in-liquid dispersing operation to the metallurgical processing, and has been widely adopted in various fields in order to improve their efficiency or productivity. The dispersed small particles of gas or solid materials in the liquid phase result in increased interface area, and injected momentum causes an agitation and enhanced heat and materiel transfer. Typical examples of injection metallurgy are LD converter for steel making, PS converter, Noranda process, Isasme1t for copper making, and Mitsubishi Material's continuous copper smelting and converting process, and so on."

Jan 1, 1996

By Jong-Ren Tarng, Gin-Hwa Chen, Wen-ku Chang, Ke-Ming Lin, Yuan-Haun Lee

"The majority of early studies used X-ray diffraction, but this requires a model to interpret the diffraction processes. A turbostratic model has been applied by Warren, Franklin and Bacon to a wide range of materials including both soft and hard carbons. Maire and Mering applied the same methods to the interpretation of the (001) lines of a series of graphitic carbons. In our case, graphitic carbons undergone high temperature and high pressure graphitization processes have been evaluated by the same methods. It were found that most technological XRD data were obtained by a Rietveld method with the least-squares refinements could be in the simplest way since the full correction technique is very laborious. The behavior of carbon materials as it proceeds through the graphitization process is characterized by changes in the measured interlayer spacings (d) a~ a function of temperature. A series of graphitic carbons including the transformation of diamond to graphite through the process under high temperature and high pressure have been evaluated. A simple calibration equation has been established. IntroductionRecently, in battery industry, carbon materials are used as cathode in lithium ion batteries. However, graphitization of those carbon materials is concerned as if lithium ion intercalated into those carbon cathode. Both high-graphitization and low-graphitization carbon materials are suitable for this kind of application.As for graphitization, the starling materials from which carbons may be prepared vary extensively from pure chemical compounds, to mixtures containing II wide range of molecular weights, such as pitches. So its graphitizing, perhaps the most notable feature of the process, is the very wide range of temperature over which the perfection increase, unlike the more common transformations of solid state materials which occur in a narrow temperature range. The variables involved in the conversion of the initial hydrocarbon to a carbon residue, which may vary widely in final perfection, are time, temperature, stress and impurity content"

Jan 1, 1996

By Shenbaga R. Kaniraj

The pile loading tests are generally conducted to assess the safe load on piles in compression. In the Indian practice, the safe load is determined using the pile loading test data and the two criteria specified in the Indian Standard Code, IS.2911 (Part 4) -1985. For this, the test pile should have undergone a minimum displacement equal to 10% of the pile diameter. Often, the piles are not subjected loads that are sufficient to cause a displacement of this magnitude. If the settlement is at least 12 mm, then the safe load is determined based only on the first criterion. But, if the settlement is less than 12 mm, the safe load cannot be determined using the IS Code criteria. The paper presents two procedures called hyperbolic and generalized hyperbolic methods to estimate the safe load using the IS Code criteria even when the loading test data is insufficient. The data from two initial tests have been analyzed. The predicted safe loads have been compared with the actual safe loads.

Jan 1, 1996

By D. J. Wang

Based on the thermodynamic arid kinectic aspects, the vaccum distillation processes for the separation and recovery of metals from wastes are analyzed. As to the separation criteria, The separation coefficient and equilibrium composition relation between vapor phase and liquid phase are the bases of recovery of metals by vacuum distillation, The vaporization rates and condensation mechanisms are also discussed. Some experimental results which deal with metals-containing wastes are described and the performances of a new kind of horizontal vacuum furnace are introduced, which demonstrate that , vacuum distillation may be a prospective technique for circulation and regeneration of some non-ferrous metals from industrial wastes.

Jan 1, 1996

By A. M. Raichur

Flocculation of fine coal is usually accomplished with the addition of commercially available organic flocculants. Recently it has been shown that biopolymers derived from microorganisms can be used to flocculate coal. The biopolymers flocculate coal efficiently and render the coal surface hydrophobic. The increase in hydrophobicity can be utilized either to separate the coal flocs from mineral matter. It can also be used for reducing the moisture content of fine coal. In this regard, flocculation and settling tests of fine coal with biopolymers and synthetic flocculants was undertaken and the results are discussed here. Also, a transport model was developed for the time-dependent settling tests for fine coal.

Jan 1, 1996