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By Bruno Deves Flores, Guilherme Liziero Ruggio da Silva, Eduardo Osório, Anderson Azevedo Agra, Antônio Cezar Faria Vilella, Anderson Nicolodi

A microestrutura porosa do coque pode ser definida como a relação espacial entre a matriz carbonosa e seus poros. A formação da microestrutura ocorre durante o processo de carbonização dos carvões coqueificáveis. Portanto, o conhecimento das propriedades que governam a formação da microestrutura torna-se atrativa como uma ferramenta na escolha estratégica de carvões na composição de misturas para produção de coque. Neste trabalho coques laboratoriais foram produzidos por carvões com diferentes propriedades, visando a formação de coques com microestrutura com propriedades microestruturais distintas. A caracterização microestrutural foi realizada a partir de uma ferramenta de microscopia ótica associada a análise de imagens. A partir dos parâmetros obtidos na análise, foi estudado a influência das propriedades dos carvões nos parâmetros analisados. Além disso a convergência com outros modelos (MOF e CBI) foi estudada. Os resultados obtidos mostraram que carvões com estágio plástico desenvolvido e elevado teor de matéria volátil geram coques de alta porosidade e com poros de tamanho excessivo. Carvões ricos em componentes inertes apresentam microestrutura de baixa porosidade, composta de poros pequenos, no entanto, com poros de baixa circularidade. Os carvões com as melhores propriedades (critérios dos modelos MOF e CBI) resultaram nos coques com as microestruturas mais regulares, de baixa porosidade, com pequenos poros e com formatos adequado.

Oct 1, 2019

By Géssica Seara Faria

Na produção de bobinas laminadas a quente, além da força aplicada pelos cilindros de laminação sobre a tira para promover a redução de espessura, o material é também submetido a tensões avante e a ré, durante o seu bobinamento e desbobinamento, que devem ser inferiores ao limite de escoamento do material conforme sua temperatura de trabalho. Este estudo trata da caracterização das tensões de escoamento do aço elétrico de grão orientado com 3,2 % de silício em altas temperaturas. A necessidade do estudo surgiu devido a ocorrência do defeito estiramento durante processo de laminação a quente de acabamento em laminadores reversíveis tipo Steckel, defeito este que consiste no estreitamento da largura da tira em regiões localizadas. Isto acontece em função do desconhecimento do limite de escoamento real do material nas temperaturas de trabalho. Os ensaios foram realizados em máquina de tração a quente, em temperaturas previamente determinadas. Através dos resultados dos ensaios, foram determinadas as curvas tensão x deformação do aço e valores limitantes de tensão conforme variação da temperatura, para que o processo não exceda o limite de escoamento do material.

Aug 16, 2017

By Tiago Nunes Lima

Novas ligas de Ti estão sendo desenvolvidas como uma alternativa para aplicação em implantes cirúrgicos e em componentes estruturais por possuírem propriedades atraentes em comparação à liga Ti6Al4V, com destaque ao menor módulo de elasticidade, menor citotoxicidade, maior resistência à corrosão e propriedades mecânicas similares, alta resiliência e elevada formabilidade. Este estudo tem como objetivo observar as características mecânicas de ligas Ti35Nb2Sn deformadas a frio e seguidas de envelhecimento. A liga foi laminada a frio com 80% de redução e envelhecida a 400 ºC por 48 horas. Foram realizados ensaios de tração, dureza, metalografia e análise das superfícies de fratura. A liga laminada apresentou uma maior relação de resistência à tração pelo módulo de elasticidade e maior ductilidade do que a liga envelhecida.

Aug 16, 2017

By Raphael Banda

1 Initiating Systems ? a definition An initiation system is a combination of explosive devices and component accessories specifically designed to convey a signal and initiate an explosive charge from a safe distance. In the use of explosives, the initiating system performs the functions of transmission and control of the firing signal to each explosive charge. As functional groups, initiating systems may be considered as: Starters Those which provide the initial signal to start the blasting process. Surface systems Products which provide transmission of the starter signal and delay timing (if any) across the surface of the blast outside the blast hole. In-hole systems Products which provide the signal transmission, delay timing (if any) and the initial explosives energy in the blast hole.1 2 Different types of Initiating Systems The initiation systems commonly used in Sub Saharan Africa are: ? Detonating cord and detonating relay systems ? Capped fuse and igniter cord systems ? Shock tube non electric systems ? Electric systems ? Electronic detonators 3 Overview of Electronic Delay Detonator Technology Conventional detonators use pyrotechnic delay elements and the variation of the actual delay periods is at best approximately 1% the nominal delay. The lack of guaranteed precision common to all pyrotechnic systems enhances the likelihood of negative environmental blasting effects.3 For example, take a 500 ms in hole delay. In conventional detonators this means that 95 % of shots fire within 10 ms of the mean. i.e. a window of 20 ms. Taking a fixed interval between shots of 25 ms, with a range of ± 3 ms, a very ragged firing pattern could be expected which in practice would result in non uniform fragmentation.

Jan 1, 2005

By Christian Maguire

The presence of hydrogen sulphide in sewerage systems leads to severe concrete corrosion. Acid causes breakdown of the concrete matrix, and attacks reinforcement. Older sewer systems under acid attack are often found to be acutely corroded, sometimes after short operational periods. Consequently secondary liners are now almost always used. Polymer concrete is extremely acid resistant and if used in segmental linings can forgo the need for a secondary lining. Combined with fibers and/or GFRP rebar Polymer Concrete can produce a very strong acid resistant lining, saving considerable time in the installation of additional liners. This paper explains the problems and advantages of using Polymer concrete in segmentaly lined wastewater tunnels, addressing areas of design, cost, and programming.

Jan 1, 2008

By Raymond O. Dannenberg

The gas-combustion retort developed by the Federal Bureau of Mines at the Rifle Oil Shale Project near Rifle, Colo., is a continuous, gravity-feed retort. The heat required to convert the kerogen in the oil shale to liquid oil is generated by the combustion of product gas and carbonaceous residue remaining on the retorted shale after the kerogen has been converted to oil, gas, and residue. A study of the effects of the process variables on retort operation, product yields, and product properties is important to the successful solution of the problems encountered in the development of a satisfactory process. Statistical methods were used to design the experiments and analyze the effects of the rate of shale throughput, the composition of dilution gas, the height of the shale bed above the air entry, air-gas distributor design, shale size range, and the ratios of the flow rates of the various gas streams entering the retort to the rate of shale throughput.

Jan 1, 1960

By T. R. Ley

"INTRODUCTION Brutally honest mining executives will tell you that “safety is job #1 but.. dollars are also extremely important”. When economic times are tough, as they are now in mining, it can feel like you need to choose between safety and cost control. Leading edge companies know that it is excellence at both that provides the best performance. FLUID POWER SYSTEMS Fluid power systems are ubiquitous in mining – longwall systems, continuous miners, drills, haul trucks and excavators, etc. And fluid power systems are getting more powerful and using higher pressures to move greater volumes and achieve higher productivity. Average operating pressures in mobile equipment has been rising to 450 bar (6,500 psi) over the last decade. With increased system pressure comes ever increasing levels of stored energy. Stored energy that, if released in an uncontrolled fashion, can do tremendous harm to people and things.Fluid power systems are composed of pipe, flexible hoses, pumps, valves and actuators. They are filled with fluid (mineral oil or fire-resistant) to transmit power to where it’s needed for performing work. With time and use fittings can loosen, component performance diminishes and hoses wear and tear. In hostile environments, like coal mining, hydraulic hoses can fail in as little as 2 years according to DGUV (umbrella association of German Accident Insurers), maybe sooner in some particularly challenging environments. FLUID POWER SYSTEM SAFETY While appearing simple and benign on the surface, fluid power systems, particularly such systems on mobile equipment, have many potential hazards. Hazards that most workers aren’t aware of – particularly young, new hires. And those hazards that can quickly turn deadly. During the past couple of years, including at last year’s SME Conference, I talked to a wide variety of mining people about high pressure fluid injection injuries. Some people, often with little or no field experience, never heard of it. But, people with mine operations / maintenance experience were almost always aware of such injuries.Some had even seen it happen right in front of them. But most claimed it didn’t happen all that often. It just wasn’t seen as a problem!"

Jan 1, 2016

By H. T. Clark, H. K. Work

The instrument for the rapid determination of carbon in steel, described in this paper, was developed originally to facilitate the operation of the pilot-sized open-hearth furnace in the Jones & Laughlin Research and Eevelopment Laboratory. In this small furnace, with its shallow bath, the drop in carbon is accelerated, and a rapid, reliable test for carbon content is indispensable. This problem becomes rather acute when it is desired to finish heats at a carbon content higher than can be estimated with any degree of accuracy by the fracture test. Several independent methods for determining carbon were investigated, therefore, and it was found that a relatively simple magnetic device could be made to give reproducible results. A laboratory instrument was designed and set up for the use of the furnace operators. It was tested exhaustively in the laboratory and was used with considerable success for following the carbon content in the furnace bath. As soon as sufficient data had been compiled to indicate that the instrument might have a wider application, a more rugged model was constructed and placed in the mill to be tested on commercial heats. Finally, about a year ago, instruments were furnished to the plant open-hearth shops, and these have been in use since that time. As a matter of convenience, the instrument has been named the "Carbanalyzer," and will be referred to by this designation in the following pages. $ Eaklier Investigations While by far the greatest number of magnetic investigations in which the carbon content of ferromagnetic materials was considered have had to do with the evaluation of the magnetic properties of steels of known

Jan 1, 1940

By H. K. Work, H. T. Clark

The instrument for the rapid determination of carbon in steel, described in this paper, was developed originally to facilitate the operation of the pilot-sized open-hearth furnace in the Jones & Laughlin Research and Eevelopment Laboratory. In this small furnace, with its shallow bath, the drop in carbon is accelerated, and a rapid, reliable test for carbon content is indispensable. This problem becomes rather acute when it is desired to finish heats at a carbon content higher than can be estimated with any degree of accuracy by the fracture test. Several independent methods for determining carbon were investigated, therefore, and it was found that a relatively simple magnetic device could be made to give reproducible results. A laboratory instrument was designed and set up for the use of the furnace operators. It was tested exhaustively in the laboratory and was used with considerable success for following the carbon content in the furnace bath. As soon as sufficient data had been compiled to indicate that the instrument might have a wider application, a more rugged model was constructed and placed in the mill to be tested on commercial heats. Finally, about a year ago, instruments were furnished to the plant open-hearth shops, and these have been in use since that time. As a matter of convenience, the instrument has been named the "Carbanalyzer," and will be referred to by this designation in the following pages. $ Eaklier Investigations While by far the greatest number of magnetic investigations in which the carbon content of ferromagnetic materials was considered have had to do with the evaluation of the magnetic properties of steels of known

Jan 1, 1940

By N. Staroselsky

"Significant energy savings are often possible for centrifugal compressors operating in parallel by improved control strategy and improved instrumentation. Blow-off can usually be reduced by improved surge control combined with a better control strategy for loading and unloading the group of machines. More precise and stable pressure control then becomes possible. This improved control strategy will also decrease the frequency of operation near the dangerous limits of surge or overload or overspeed. A sample station of mixed centrifugal and reciprocating compressors is examined and a substantial energy saving with the recommended control strategy is projected from operating data. Present Operating Conditions of the Compressed Air StationThe Compressor StationThe compressor station described here has three centrifugal compressors and three reciprocating. It supplies a mine in New Brunswick.Compressed Air and Power ConsumptionFigure I and Figure 2 provide graphs of air consumption and pressure changes based on the owner's data.During the typical two-shift operating day (Fig . I) in the non-productive shift (midnight to 8:00 a.m.), the consumption stays at a level of 9,000 SCFM. This corresponds to a pressure of 110 PSIG. Then, after 8:00 a.m ., the air consumption starts to increase and th e pressure decreases. Around 10:00 a.m., the consumption reaches its maximum level at 97 PSIG. Around II :30 a.m., the air consumption starts to decrease because of the production drop during the lunch break of the first shift. Pressure increases again up to 109 PSIG. After the break, consumption rises to its maximum level over 16,000 SCFM andpressure drops to 97 PSIG.Around 2:30 p.m., the air consumption drops sharply to 9,000 SCFM because of the production decrease to zero level. This drop results from changing of shifts. The pressure at this time increases again up to 110 PSIG. The second shift (2:30 to II :30 p.m.) is an alogous to the first.During the three-shift operating day, the break around 4:00 . a.m . and the shift change around 6:30 a.m. cause sharp drops in air consumption. The pressure for almost the entire night shift stays near 110 PSIG because the station is working with blowing-off even under the maximum consumption. The analysis of Figures I and 2 shows that the pressure varies with the air consumption changes. During non -productive time (non-production shifts , shift changes and breaks) or during the night shift, the total station capacity is proportional to the discharge pressure. By decreasing the level of this pressure up to 97 PSIG, the flow of the station may be decreased during the non-production time as follow s:"

Jan 1, 1980

By Sharon K. Reamer, Klaus G. Hinzen

A series of controlled seismic experiments was performed in a limestone quarry in southern Germany to study seismic effects of cylindrical charges fired in both a half space (HS) (burden 63 m) and quarter space (QS) (burdens of 3 and 3.5 m) geometry. Charge columns contained from 20-32 kg of explosives and initiated from the bottom. The explosives formed a cylinder 4 m (20 kg) and 5 m (32 kg) high and 90 mm in diameter at depths from 3-8 m below ground level. Prior to each of the larger explosions, small charges of 0.12 kg seismogelit were fired at 4 m and 8 m depths in the same boreholes. Seismograms were obtained from 23 three component surface stations and up to 10 three component borehole stations (6 m depth). For each experiment, stations were located on three linear profiles of length 72 m at different azimuths from the source and one semicircular profile at a constant range of 30 m.

Jan 1, 1991

By C. K. Lee

This Bureau of Mines report presents results from experimental studies on wood fires in a laboratory-scale tunnel network. Experimental measurements include ignition delay time, flame spread rate, ventilation air and gas flow rates, wood temperature, gas temperature, pressure and composition, thermal flux, and smoke particulates. These measurements form a data base for fire-scaling studies and provide information on various fire processes, such as flow interaction between ventilation air and fire, fire throttling and reverse flow, and duct fire energetics. Results show how hazards of duct fires relate to the development of (1) asphyxiating and toxic fumes, (2) explosive gas mixtures, (3) throttling of ventilation air, and (4) high-temperature combustion products. Such fire hazards should be carefully considered when testing flammabilities of materials used in a confined underground mine environment.

Jan 1, 1980

By B. M. Larsen, T. E. Brower

Introduction and Summary By "thermochemical factors" we refer to those variables which affect the net heat which must be put into the bath in order to make a heat of steel from any given set of charge materials. This is admittedly only one phase of the production rate problem. The whole problem includes also consideration of rate of charging, flame radiation intensity, rate of optimum fuel input obtainable without undue damage to the furnace structure and any variations in conditions such as stirring, slag volume or viscosity which affect the rate at which heat can flow down and away from those exposed surfaces where the heat is first received from the flame. Because a given type of charge in a shop is often considered as being nearly constant in both physical and chemical characteristics from one heat to another, and because such a state of affairs may be thought of as resulting in a reasonably constant net heat requirement, this requirement is usually neglected as an invariable, inevitable matter, about which nothing can be done. With normally variable charge, and variable percentages of limestone and cold pig, however, the net heat requirement can be subject to very appreciable change; it may also be affected by such things as the currently popular procedure of blowing oxygen into the bath. To bring the general problem of production rate into better perspective, therefore, it seems worthwhile to try to evaluate the net bath heat requirement and the amount by which it may change through variation in different factors. Because our calculated values of net heat are admittedly uncertain, we have tried to check them in part by statistical data on actual production rates over rather large groups of commercial heats. The results of calculation of net heat requirements in a wide range of actual commercial practices may first be summarized briefly. We find a wide range between the extremes of different practices, as would be expected, with duplex practice (essentially blown metal plus hot metal) having essentially a zero net heat requirement, an all-cold charge practice somewhat over I million Btu per ton of steel and a high hot metal practice about 0.75 million Btu per ton. Over the commercial range of scrap plus hot metal practice, increasing the percentage of hot metal from 40 to 78 pct, with other factors nearly constant, decreased the net heat by only some 5-10 pct. The net heat is increased by about 1.2 pct for each I pct of the metallic charge present as cold pig. Calculated values of oxygen supplied by air varied from about 25 up to 60 lb per ton of steel, and in a 60 pct hot metal practice, an increase from 32 to 52 Ib oxygen from air decreased the calculated net heat from 0.88 to 0.74 million Btu per ton. Use of pure cold oxygen to substitute for about one half of the total charge ore (about 28 Ib oxygen replacing 145 Ib ore per ton of steel) decreased the

Jan 1, 1949

By B. M. Larsen, T. E. Brower

Introduction and Summary By "thermochemical factors" we refer to those variables which affect the net heat which must be put into the bath in order to make a heat of steel from any given set of charge materials. This is admittedly only one phase of the production rate problem. The whole problem includes also consideration of rate of charging, flame radiation intensity, rate of optimum fuel input obtainable without undue damage to the furnace structure and any variations in conditions such as stirring, slag volume or viscosity which affect the rate at which heat can flow down and away from those exposed surfaces where the heat is first received from the flame. Because a given type of charge in a shop is often considered as being nearly constant in both physical and chemical characteristics from one heat to another, and because such a state of affairs may be thought of as resulting in a reasonably constant net heat requirement, this requirement is usually neglected as an invariable, inevitable matter, about which nothing can be done. With normally variable charge, and variable percentages of limestone and cold pig, however, the net heat requirement can be subject to very appreciable change; it may also be affected by such things as the currently popular procedure of blowing oxygen into the bath. To bring the general problem of production rate into better perspective, therefore, it seems worthwhile to try to evaluate the net bath heat requirement and the amount by which it may change through variation in different factors. Because our calculated values of net heat are admittedly uncertain, we have tried to check them in part by statistical data on actual production rates over rather large groups of commercial heats. The results of calculation of net heat requirements in a wide range of actual commercial practices may first be summarized briefly. We find a wide range between the extremes of different practices, as would be expected, with duplex practice (essentially blown metal plus hot metal) having essentially a zero net heat requirement, an all-cold charge practice somewhat over I million Btu per ton of steel and a high hot metal practice about 0.75 million Btu per ton. Over the commercial range of scrap plus hot metal practice, increasing the percentage of hot metal from 40 to 78 pct, with other factors nearly constant, decreased the net heat by only some 5-10 pct. The net heat is increased by about 1.2 pct for each I pct of the metallic charge present as cold pig. Calculated values of oxygen supplied by air varied from about 25 up to 60 lb per ton of steel, and in a 60 pct hot metal practice, an increase from 32 to 52 Ib oxygen from air decreased the calculated net heat from 0.88 to 0.74 million Btu per ton. Use of pure cold oxygen to substitute for about one half of the total charge ore (about 28 Ib oxygen replacing 145 Ib ore per ton of steel) decreased the

Jan 1, 1949

By K. Terhaar, K. Prisbrey

The objective was to determine operating protocols for a lead and silver column flotation cleaner, being considered for installation at Sunshine Mining & Refining Co.’s Kellogg mill in Northern Idaho. In this column, tetrahedrite and galena were floated, and pyrite and other gangue minerals, including siderite and silica, were depressed. The procedure was to develop a dynamic simulation using a linear transfer function approach. The transfer function related cause and effect variables such as the influence of collector and depressant dosages on recovery and grades. Bench-scale flotation tests followed by pilot column testing provided the data used to develop a linear transfer function. The transfer function was derived using a spreadsheet. This model was applied to simulate how the flotation column could be made to respond to disturbances in feedgrade. The results were that xanthate, zinc sulfate, and sodium cyanide were found to be suitable controls for grade and recovery. Simulations showed the best sequence of manipulations of these reagents, and these sequences were useful for future operator training. The conclusion was that linear transfer functions were able to simulate lead and silver recovery, develop scenarios for operator training, and provide a foundation for future on-line control.

Jan 1, 1999

[Page Officers of the Institute 5 Minutes of Nineteenth Meeting 9 Coal Mine Explosions-William -Moorhead 11 "What Do You Mean-`Coal Dust'?"--K. L. Marshall 16 Discussion of Foregoing Papers 17 Shale Dusting-J. A. Smith 21 Discussion 25 Conditions That Make Coal Dust Explosive-T. T. Read 25 General Discussion 27 1-Mechanical Loading Review-Chas. Gottschalk 30 Mechanical Loading in Coal Mines-S. W. Farnham 34 Mechanical Loading Practice at Hanna, Wyo.-T. H. Butler 48 Guessing or Knowing! Which?-Eugene McAuliffe 52 Discussion of Loading Papers 54 Bumps or Squeezed Conditions in Coal Mines-Geo. A. Brown 59 Vertical Cutting-Thos. A. Stroup 62 Mine Fires-Thos. A. Foster 71 Membership List 74]

Jan 1, 1924

By Brent W. Madsen

To assist in fulfilling the Bureau of Mines goals of maintaining adequate mineral supplies to meet national economic and strategic needs, and to minimize the environmental impacts associated with mineral-processing operations, a leaching-solvent extraction-electrowinning technique was compared with a leaching-cementation technique for processing low-grade copper ores. Large-scale laboratory column leaching tests (6 to 7 tonnes) were conducted on minus 37-cm chalcocitic ore using ferric sulfate leach solutions at 25° C. Two columns contained 11 percent minus 1.27-cm fines, and two columns contained 32 percent minus 1.27-cm fines. After 416 days of leaching ore samples containing 11 percent minus 1.27-cm fines, copper extraction was 48 and 51 percent for the leach-cementation and leach-solvent extraction-electrowinning procedures, respectively. When leaching ore samples containing 32 percent minus 1.27-cm fines, the leaching-solvent extraction-electrowinning technique extracted 60 percent of the copper after 568 days, whereas the leaching-cementation technique extracted only 48 percent of the copper. In the latter test, leach solution ponded on the ore, which reflected a decrease in ore column permeability. The decreased permeability was attributed to the generation of excessive amounts of iron salts during cementation; the salts precipitated on the fine ore particles and in the interstices, thus plugging the column. This decrease also lowered the available oxygen, resulting in poor aerobic bacterial activity which slowed the oxidation rate of ferrous ions to ferric ions. Sulfuric acid required to maintain a leachant pH of 2 was nearly halved when copper was recovered by solvent extraction and electrowinning rather than by cementation.

Jan 1, 1979

By Andres M. Baquerizo, Jeremiah J. Filjones, Nicholas Feldt

The Estates at Acqualina located in Sunny Isles Beach, FL, is comprised of two, ocean-front, 50-story, luxury towers with podiums and villas. With city regulations now requesting that above-grade floors be limited to commercial or residential units, parking facilities for the tower structures were situated within two levels of underground basement parking. However, ensuring dry excavation through south Florida’s highly pervious limestone, immediately adjacent to the beach where the groundwater table is very shallow, can be extremely challenging and costly for developers. In recent years, significant advances have been made to overcome this challenge with the innovative use of deep soil mixing to create a “dry hole”, assisting in the construction of foundations and underground usable space for parking, storage, etc. The “dry hole” system includes a soil mix bottom seal, with soil mix secant pile walls in combination with auger cast deep foundation elements to support the future structure. This approach enables groundwater control to greater depths than can be achieved by conventional sheetpiling and dewatering. For the Estates at Acqualina, a successful turnkey, design-build joint venture between two foundation and geotechnical contractors resulted in a dry excavation to 34 ft (10.4 m) below grade and to a record- breaking auger cast pile depth of 182.3ft (55.6 m), all within an aggressive 26-week schedule to deliver the “dry hole” excavation for the first tower. This presentation will discuss the logistics, quality control, design, and safety for the different techniques involved. INTRODUCTION AND BACKGROUND The Estates of Acqualina is a pair of 50-story luxury towers located on Sunny Isles Beach in Florida with a two-level underground basement for parking. The project’s location just steps away from the Atlantic Ocean, geology, and high-water table created a challenging project. The owner, Trump Group, contracted the joint venture of HJ Foundation and Hayward Baker (HJ/HB) to design-assist-build a system to control the groundwater, allowing the 2-story underground parking structure to be constructed. In order to accomplish this task, the JV utilized an installation technique known as deep soil mixing. This technique mixes the in situ material with a cement slurry to create a very impermeable material called “soilcrete”.

Jan 1, 2019

By H. E. Nold

High-volatile coals are most desirable for kiln firing. Low-volatile and even anthracite coals can be used successfully. Most periodic kilns use coal and are hand fired. A few stoker installations have been economically successful. Continuous tunnel kilns reduce fuel consumption 40 to 55 per cent. They are rapidly replacing periodic kilns in the manufacture of the finer wares. They have found great favor in the refractory industry and are successfully used in firing almost all kinds of heavy clay products. Fuel oil has found rather wide application in the Southwest and West. Natural gas is a satisfactory fuel for kiln firing. It is the principal competitor of coal and has largely replaced it for firing the finer wares but cannot compete with it in firing heavy clay products except in regions where cheap gas is available. Figures are given showing the relative thermal efficiency of coal and natural gas as used for firing ceramic ware. The ceramic industry uses from 12,000,000 to 12,500,-000 tons of coal per normal year. The principal use of coal is in firing the heavy clay products. This potential market amounts to about 9,250,000 tons per year. Coal producers could increase sales by furnishing expert firing instruction.

Jan 1, 1934

By A. A. Novoselov, U. Kelm

"Large volumes of mine tailings accumulated in surroundings of porphyry copper deposits represent a growing threat to environment. They contain significant concentrations of toxic metal and metalloids which can contaminate river runoff, ground waters or can be transported by wind. Both extreme pH of fluids in tailings impoundments and high surface areas of processed mineral grains provide their increased reactivity. As a result, during only a few decades, As, Cu, and Mo can be mobilized, redistributed through the tailing column and accumulated through post-deposition leaching, evaporation and contamination with natural fluids. Those processes are reflected in the forming of secondary minerals. Gypsum, Fe oxides/hydroxides, efflorescent salts and clay minerals are typical alteration products in tailings. Here we present the results of reactive transport simulations implemented on the base of PHREEQC and SUTRA codes. The one-dimension model emulates the mass balance between rainfall, evaporation and subsurface runoff, the kinetically- and thermodynamically-driven dissolution of tailing minerals, advective and diffusive transport of tailing fluids, and precipitation of secondary phases. A typical tailing column is composed of four unequal layers with predominance of (i) evaporation, (ii) secondary mineralization above, (iii) below water table, and (iv) near the bottom of dump. Those horizons are characterized by contrasting pH, chemical composition and bulk mineralization of pore fluids, distinct accessibility of atmospheric oxygen and, as a consequence, distinct intensity of sulfide oxidation. The modeling and its verification on Chilean tailings impoundments reveal the complexity and high rates of secondary mineralization. The accumulation of toxic alteration products is controlled by fluid transport through the tailing column induced by both rainfall/evaporation and exchange with subsurface runoff. The geochemical modeling is a powerful approach which allows comparing the processes in tailing deposits produced by distinct flotation regimes and providing the long-term predictions of their environmental impact as well as identifying sectors of tailings for possible re-processing."

Jan 1, 2018