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By Y. Zimmels, C. Feldman

Closed-circuit grinding processes are considered in the context of a reactor-separator circuit that involves multifraction streams and products. Because grinding circuits are low-efficiency, capital-intensive operations, modeling to maximize their economic return is appropriate. An attempt to develop and test such a model is presented in this work. The model relies on process simulation for both the mill and the separator, in conjunction with constraints imposed by product specifications. The grinding process was simulated using breakage functions, which provided complete data on the feed and product of the mill. A cyclone bank used as the separator was also simulated using known models. The overall process model provided a complete simulation of the multistream grinding and separation process. The process model was then incorporated into an economic model that predicts grinding cost, subject to process constraints, for a given set of operating variables. The model facilitates economic optimization of the grinding process as it relates to process variables and process hardware.

Jan 1, 1993

By A. Alfantazi, M. Mahon

The current efficiency in zinc electrowinning is a key indicator of the performance in a cell house. This is typically measured by comparing the weight of the cathode to the electric current applied over the deposition period. This calculation can be cumbersome because the deposition history of each pulled set of cathodes will be unique. It will depend on the applied current and electrolyte conditions from onset of deposition until the cathode is removed and stripped. Not accounting for these can introduce errors to the calculated current efficiency. To track this history and reconcile the current efficiency, a time based computer process simulation was made of an industrial cell house. Two months of hourly recorded measurements from the cell house were input to the simulation, including current to the cell houses, concentrations, flow rate, and temperature of the purified leach solution. The simulation’s predictions of the concentration of zinc in the circulated, spent, and returned electrolyte all showed good agreement with the industrial data over the two months giving a validated zinc balance. The simulation was then tuned to predict the instantaneous current efficiency for all times, as well as the expected masses for the deposits given their deposition history.

Jan 1, 2014

By P. E. Queneau

This study confines itself to an examination of the two million square miles of the northern hemisphere which the geographer defines as the terrestrial Arctic, a land region in which the mean temperature of the warmest month is below 50°F-in effect, the area lying north of the tree line. The engineering and human problems there are of a different order of magnitude than is generally true of the sub-Arctic. Whether in Dawson Creek or Matanuska, in Mo i Rana or Skelleftea such problems are of the same general order as in Hibbing or Noranda. The same is not true in Kong Oscar's Fjord or Lancaster Sound.

Jan 7, 1961

By F. D. Rosenthal, F. J. Dunkerley, G. J. Mills

Activities, free energies, and heats and entropies of mixing of liquid Pb-Zn alloys have been obtained by the electrode-potential method between 400° and 650°C. The large positive deviations observed from Raoult's law are in agreement with the phase diagram, which indicates a wide immiscibility field. A vapor-pressure method was used to extend the activity measurements to 900°C, allowing the maximum of the immiscibility gap to be estimated by thermodynamic calculation. Data on the mono-tectic and eutectic points compare favorably with previously existing work. SEVERAL long-standing methods have been in use for the study of phase diagrams from measurement of the activities of the component metals.' The use of thermodynamic analysis for interpreting equilibria data is comparatively recent, however. Such analysis is usually undertaken by first evaluating the principal thermodynamic functions as, for example, the enthalpy, entropy, and free energy of the alloy constituents. These, in turn, quite often can be correlated with the interatomic potential energies and atomistics of the system, from which a clearer understanding of the causes leading to deviations from ideal behavior is gained. The present study of liquid Pb-Zn alloys is concerned with a determination of these quantities by electrode-potential and vapor-pressure measurements, using these values in calculations involving phase equilibria and to obtain a theoretical insight into an alloy system exhibiting strong positive deviations from ideal metallic solution. A considerable portion of the previously reported work is based on thermal analysis. Supplemented by optical studies of solid alloys, these techniques have revealed the essential nature of the immiscible mixtures that are formed. It is difficult, however, using the phase-

Jan 1, 1959

By Bianka Nani Venturelli

Estudou-se o efeito do tamanho de grão austenítico nas propriedades de tração do aço Hadfield refinado com Hf. Estas propriedades foram comparadas com as de um aço Hadfield sem refino, ambos com a composição química de acordo com a norma ASTM A128 – grau B2. Adicionalmente, foram usadas técnicas de caracterização macroestrutural, microestrutural e fractográfica. A caracterização macroestrutural mostrou que o aço Hadfield com adição de Hf apresentou tamanho do grão austenítico (600 ?m) aproximadamente cinco vezes menor do que o do aço Hadfield sem refino (3000 ?m). Os resultados do ensaio de tração mostraram um pequeno aumento (~6%) no valor do limite de escoamento com o refino do grão, em acordo com a Equação de Hall-Petch para materiais austeníticos. No entanto, os resultados dos ensaios de tração do aço Hadfield refinado mostraram aumentos que não foram previstos para as propriedades de resistência à tração (~37%), alongamento (~53%) e tenacidade (~88%). O exame fractográfico dos corpos de prova de tração indicou predominância do mecanismo de fratura dúctil para o aço Hadfield sem refino, enquanto que o aço Hadfield refinado apresentou predominância do mecanismo de fratura intergranular dúctil.

Oct 30, 2017

By G. M. Gordon, J. W. Spretnak, R. Speiser

AT present, considerable research is being directed toward the development of high-temperature, oxidation-resistant columbium alloys. Columbium. along with molybdenum and tungsten, exhibits good high-temperature strength. Unlike molybdenum and tungsten. however. columbium does not form a volatig oxide below 1375°c.l Although the outermost oxide formed on pure columbium, Cb2O3 is stable in air at elevated temperatures, it is not of a protective nature. It is porous and voluminous, and

Jan 1, 1959

By A. J. Smethurst, S. B. Hearn, S. Boskovic

"The problem of crud in solvent extraction is well known and can be a major handicap and operational issue. Colloidal silica can cause a number of problems including interfering with flocculation, initiating crud formation in solvent extraction (SX), decreasing SX extraction kinetics and increasing SX phase disengagement times. Flocculation can be utilized to remove some of the troublesome particulates but colloidal silica does not flocculate well and presents a different problem requiring innovative chemistry to solve. Coagulants can assist by facilitating the removal of this colloidal silica by promoting the agglomeration of the particles to a size which can be more readily settled or flocculated in solid/liquid separations. This is achieved when the coagulants bind to the surfaces, displacing water and destabilizing the colloids, whereupon they bind to each other which facilitate their amenability to conventional flocculation.INTRODUCTIONSilicate minerals are abundant in the upper layers of the Earth’s crust, and there are few mineral deposits without significant levels of gangue silicates. Silicate minerals include the pure silicas, such as quartz and other silicate containing minerals such as clays, chlorites, feldspars, as well a vast number of less common silicates.During the acid leaching of ores, two types of fine silica particles are released in solution from the dissolution of the host mineral. The first consists of partly depleted silicates, and the second is colloidal silica, which forms in solution. It is this second type which has the potential to cause crud formation as well as poor solution clarities, slow filter rates and excessive flocculant usage (Figure1)."

Jan 1, 2016

By S. P. Sandoval

Several researchers have shown that the surface of chalcopyrite becomes hydrophobic under oxidizing conditions. Because dissolution of copper from chalcopyrite in dump leaching occurs under oxidizing conditions, the U.S. Bureau of Mines studied the effect of surfactants on chalcopyrite leaching under dump chemical conditions. Surfactants were selected for study because they can lower interfacial tension. The tests were conducted in shaking water baths using 250-mL Erlenmeyer flasks in statistical experimental design formats. The addition of nonionic surfactants increased copper extraction in the fernc sulfate leaching of chalcopyrite when sufficient Fe3+ was present. A positive interaction between Fe3l+ concentration and surfactant concentration was demonstrated. Copper concentration in the leachhing solutions was increased by as much as 100 pct at 25° and 50° C by adding nonionic surfactants. ionic surfactants decreased leaching. The structure of the nonionic surfactants and their hydrophile-lipophile balance (HLB) influenced surfactant performance. The branched hydrophile of an ethoxypolyol was beneficial to surfactant performance. The ethoxypolyol was the superior surfactant at 25° C, but became unstable at 50° C. Four surfactants, an ethoxyalchohol and three block copolymers, performed best at 50° C.

Jan 1, 1990

By Dale S. Preece, J Paul Tidman, Stephen H. Chung

A discrete element computer program named DMC_BLAST (Distinct Motion Code) has been under development since 1987 for modeling rock blasting (Preece & Taylor, 1989). This program employs explicit time integration and uses spherical or cylindrical elements that are represented as circles in 2-D. DMC_BLAST calculations compare favorably with data from actual bench blasts (Preece et al, 1993).

Jan 1, 1997

Jan 1, 1929

By H. M. Howe

Page 1. Introduction............................514 2. Definitions.............................517 3. Brevity of the Heating........................517 I. THE HARDENING OF THE BORE..............517 4. The Hardening of the Bore.....................517 5. The Thickness of the Hardened Layer.................517 6. Martensitization..........................518 7. The Hardening Repetitive ......................519 8. The Temperature Cycle.......................519 9. The Hardened Layer is the Merged Layer............... 521 10. The Progressiveness of Merging....................521 11. The Progressive Thickening of the Hardened Layer from Round to Round. 523 12. Merging and Hardening are Cumulative................523 13. Three Additional Causes of the Progressive Thickening of the Hardened Layer 525 14. Progressive Roughening of the Bore..................525 15. Avoidance of an Endothermic Transformation.............525 16. Asymptotic Retardation of the Thickening of the Hardened Layer.....527 17. The Troostitic Layer........................ 529 18. The Usual Lack of Martensitic Markings................529 19. The Thickness of the Hardened Layer Should Increase with the Quantity of Heat Taken up by the Walls of the Bore.................530 20. The Decrease of the Thickness of the Hardened Layer from Breech to Muzsle 531 21. Phstic Deformation as a Contributory aCause of Hardening........531 22. In What Way May Plastic Deformation Hasten Hardening?....... 535 23. Possible Need of Coarsening.....................535 24. Carburization as a Cause of Hardening..........:.....536 25. Does Hardening Increase Erosion?..................-538 11. THE CRACKING OF THE BORE ...............539 26. Appearance of the Bore and Cracks in Elevation............539 27. The Cracks in Elevation in the Rear Ring...............539 28. The Cracks in Elevation in the Forward Ring.............540 29. The Copper Network in the Grooves.................540 30. The Cracking of the Lands......................541

Jan 1, 1918

By Gui Hua Wang, Xin Chang, Zhong Ying Han, Yuan Fang Cheng

"According to the geometrical characteristics of triangular meshes, Triangular Mesh Split Model (TMSM) based on a finite element method is proposed to simulate cracks propagation of fractured rock. With TMSM, stress intensity factors at the tip of cracks are obtained by far-field contour integral. Meanwhile, vector cross multiplication is adopted to fix the cracking unit, and maximum circumferential stress criterion is used to determine the crack propagation angle. Then crack dynamic propagation simulation is realized through local mesh split or node movement at crack tip. With this method, the crack can split apart a unit or extend along the mesh boundary, so the crack could extend along an arbitrary path and is not restricted by the initial mesh. The applicability of the mesh split algorithm is verified by the crack propagation examples of wing crack and multi-fractured rock mass with holes. The results show that this method not only has higher accuracy of fracture parameters calculation, but also can accurately simulate the crack initiation and propagation of rock under complex stress state such as tension, compression and shear. In addition, the far contour integral is introduced to determine the crack tip stress intensity factor and there is no need to reconstruct a singular element at the crack tip or to intensify the meshes. Compared with the existing mesh reconstruction algorithm, this method significantly improves the computational efficiency.INTRODUCTIONGenerally, rock is neither the full continuum, nor entirely discrete body, but rich in geological defects, such as joints and cracks. A large amount of geotechnical engineering practice shows that most fracture of rock is closely related to the internal joints, cracks and crack expansion (Horii et al., 1985; Wong et al., 1998). Although the classical theory of fracture mechanics established the theoretical foundation of crack initiation, propagation, so far it is still extremely difficult to characterize the propagation of airfoil-typed crack and the interference problem of multiple cracks. Up to now, the micromechanics mechanism research of crack propagation of fractured rocks has still been a hot research topic of rock fracture mechanics."

Jan 1, 2015

By C. P. Manning

This paper reports recent progress in the development of a unique metal extraction technology utilizing zirconia-based inert anodes for the electrolytic reduction of metals from their oxides. In this process, the target metal oxide is dissolved in an ionically conducting liquid solvent phase. An extended anode consisting of an oxygen-ion-conducting stabilized zirconia membrane in intimate contact with a catalytically active electronic phase and an inert electronically conducting cathode are inserted into the molten flux containing the oxide. When the appropriate electric potential is applied between the electrodes the target metal is reduced at the cathode and oxygen ions are selectively transported across the stabilized zirconia membrane and oxidized at the anode. When the process is conducted at temperatures between 1200-1400°C, the ohmic resistance drop across the stabilized zirconia membrane is low, and high current densities on the order of I A/cm2 or greater can be obtained. In addition, the process efficiency can be increased further by directly reforming hydrocarbon fuel over the anode. Laboratory experiments at Boston University have demonstrated the technical viability of employing zirconia-based inert anodes for environmentally sound production of metals such as magnesium, tantalum, aluminum, etc., directly from their oxides. Significant progress has been made in the application of this concept to the electrolytic reduction of magnesium at 1300°C. The research topics covered include stability of the zirconia membrane in the selected molten solvent (flux), volatility of the flux, electrochemical characterization of the electrolytic cell, and analysis of the metals produced.

Jan 1, 2003

By R. Bouzaiene

In the paper presented by F.W. Brackebusch on the “Basics of paste backfill systems,” paste fill was presented as a backfill process that offers many advantages over other alternatives such as hydraulic fill and rockfill. It was observed, however, that the mechanics of paste-fill transportation in pipelines is not fully understood and that the success of its implementation in practice depends on the precise control of the proportions of fines, aggregates and water in the mixture. The author emphasized the necessity for laboratory and full-scale testing to determine the suitability of a material to be used as paste fill. Although experimental testing is definitely an important operation in the design of a reliable paste fill, advances in the understanding of the fundamental laws that govern paste flow in pipelines are equally relevant. Ideally, the results of such efforts would provide predictive models for the rheology of the paste and the corresponding pumping-energy requirements. In an attempt to achieve this objective, an ongoing research program has been active at McGill University’s Department of Mining and Metallurgical Engineering.

Jan 1, 1995

By J. F. Butler

The degree and type of carbide dispersion resulting from changes in the cooling rate from austenite determine the amount of carbon remaining in solution after slow cooling- from a subsequent subcritical annealing treatment. A difjusion model has been proposecl to explain the effect of carbide dispersion on the amount of carbon retained in solution and the amount of carbon in solution has been related to the degree of carbon strain aging. COTTRELL and Leak' have shown that the rate of strain aging in low-carbon steels is dependent upon the amount of carbon and nitrogen in solution. Carbon can be effectively removed from solution as Fe , C by quench aging at temperatures of 200" C or lower; however, the relatively higher solubility of nitrogen at these temperatures prevents sufficient removal of nitrogen as iron nitrides. For this reason, nitrogen in solution has been considered the major cause of strain aging in rimming grades of commercial low-carbon steels. Nitrogen can be effectively removed from solution and nonaging steel produced through the addition of aluminum to form the stable nitride, AlN; however, the aluminum also causes deoxidation resulting in a killed steel. III an attempt to produce a rimmed steel which was also nonaging, Morgan and Shyne 2 investigated tile strain-aging properties of low-carban steels containing boron and found that strain aging was suplx-essed in steels containing as little as 0.007 pet B. The original purpose of this investigation was to determine the mechanism of strain-aging suppression by boron. Early in the study, the function of boron was discovered to be much like that of aluminum in that the formation of a nitride, BN, removed the nitrogen from solution.' However, during the course of the investigation, an effect of heat treatment upon the strain-aging properties and the amount of carbon in solution was found which could be related to the microstructure of the steel. The purpose of this paper is to examine these relationships among heat treatment, microstructure, carbon in solution, and strain aging in steels where nondetectable amounts of nitrogen are present in solution. EXPERIMENTAL PROCEDURE The investigation was carried out using 0.030 in. by 12. in wire specimens which had been cold swaged and drawn to the final diameter. Table I lists the compositions of the low-carbon steels used. Those with 'V' designations were vacuum melted and cast; the alloys designated 'AISI' were prepared from high-purity iron obtained from the American

Jan 1, 1962

Jan 1, 1939

By H. L. Willett

The self heating of coal, or spontaneous combustion, has been a problem for centuries. This symposium addresses the issue.

May 23, 1905

By M. J. Scoble, N. Rowlands, L. Piciacchia

Pronounced non-linear behaviour of mine backfill arises from the influence of confining pressure, cementing agent content, curing time, void ratio and water content. Past research into backfill behaviour under stress is reviewed and related to the needs for constitutive laws which can be integrated into numerical modelling for mine design where structures employ backfill support. A method for representing non-linear backfill behaviour is proposed, which is based upon numerical regression treatment of triaxial laboratory data. The non-linear behaviour observed from a program of laboratory triaxial testing of cemented hydraulic backfill is presented. The particular influence of confining stress and curing duration is high- lighted. The paper concludes by considering the alternative means of accounting for such behaviour in mine design.

Jan 1, 1984

By R. G. Bowman

Discussions of processes for the manufacture of white lead generally open with the statement that white lead is the oldest chemical pigment known to man. This fact is of more than historical interest; in the light of the present extensive use of white lead, it indicates that the compound possesses characteristics that make it unique among white pigments, and superior to all in its particular field. A greater variety of processes have been proposed for manufacturing white lend than for any other one chemical compound. Only a few of these processes have come into commercial use, however, and a large part of the present production here and abroad is made by the process used in ancient times. The outstanding disadvantages of the old process are that it is slow and laborious, affords no control of the product, and yields at best an impure material lacking in uniformity. Improved processes, sometimes classed all together as "quick processes," have had as their main object the shortening of the time required. Most of them accomplish this and some have yielded a superior product as well, but only two or three are now in use commercially. For centuries the manufacture and mixing of paints have been treated as an art, and the practice has been much influenced by tradition and precedent. There is a reluctance to abandon old materials for this purpose, and as few new uses for white lead have been developed, the adoption of the quick processes has been slow. The electrolytic production of white lead is not new, a large number of processes and forms of apparatus have been proposed and patented within the past 25 years, all directed toward the production of white lead, wholly or in part, by electrolysis. One or two of these processes were tried commercially but proved unsuccessful. Process The Sperry process, used by the Anaconda Lead Products Co., is the invention of Elmer A. Sperry, and was worked out to a commercial basis at the East Chicago plant. It resembles, in a general way, earlier methods, but embodies the features that make it possible to operate

Jan 1, 1926

By John Wulff, Richard P. Seelig

THE importance of the pressing operation in the forming of articles by powder metallurgy depends to a great extent on the type of product to be made. While in some few cases the pressing is merely a means of compacting loose powder particles into a solid mass preliminary to a sintering treatment in most applications it constitutes a molding operation with the purpose of shaping the raw material in powder form into a certain predetermined, accurately defined part not altered in shape by sub- sequent sintering. In still other cases, no pressing at all but sintering in molds gives useful articles. A limited number of products are made by the simultaneous application of pressure and heat. The factors that control the product of the pressing operation are raw material, lubricant, type, size and shape of die and compact, magnitude and time of application of pressure, as well as temperature of pressing. All such factors need to be con- trolled; yet, depending on the function of the pressing operation, greater emphasis may be placed on processing factors other than the pressing operation. In any complete discussion of pressing, subsequent sintering cannot be disregarded. For the sake of brevity, the present paper has been limited to the mechanics of pressing and only occasionally refers to sintering. For the same reason, hot-pressing has been omitted as beyond the scope of this paper. In any survey of the literature on the pressing of metal powders, the 1938 paper of Balshin1 on the theory of the process of pressing deserves mention. The first attempts at an interpretation of pressing phenomena were made by Balshin1 and Rakovski.2 The experimental results of both are of great interest. Since the experimental results are not described, the work was repeated, using our own interpretation of the possible techniques, and is reported in the following pages. The basic theory of Balshin,1 based on a hydro- dynamic analogy, however, leads to but another way of plotting density and pres- sure against height of a pressed compact. Since it does not give any new insight into the phenomena, nor account for the influence of side-wall friction, a discussion of the theory has been omitted from this paper. DENSITY GRADIENTS IN COMPACTS The process of pressing metal powders in a die (disregarding for this consideration the powder filling and ejection operations) may be divided into three phases: (I) packing, (2) elastic and plastic deformation, (3) cold-working with or without fragmentation. It must be emphasized that these three steps do not follow each other in sequence; on the contrary, in practice

Jan 1, 1946