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By G. Hu, P. Chang

"As hydraulic fracturing is forbidden in some countries due to its accompanying environmental pollutions, microwave fracturing was proposed as a substitute technology to enhance coal seam permeability. Its mechanism includes: on the one hand, thermal stress caused by non-uniform microwave heating leads to fracture development in coal body, which increases coal seam permeability for gas; on the other hand, moisture within the coal body that hinders gas desorption and diffusion is removed during this process. To study the effect of moisture content on fracture development under microwave irradiation, high resolution photographs were taken before and after microwave treatment. These photographs were then binarized and skeletonized. Based on the processed photographs, the total area were calculated using ImageJ. The results showed that coal samples with 0% and 25% water saturation have more variation in fracture development as compared to that of samples with 50%, 75% and 100% water saturation. This study can be very useful in gas drainage and gas control in coal mines. INTRODUCTION Coalbed methane (CBM) is a clean energy source as well as a natural hazard to underground mining (Kurnia, Sasmito, & Mujumdar, 2014; Ranathunga, Perera, & Ranjith, 2014). One of the main goals of mine ventilation is diluting methane and removing underground contaminants (Xu, Huang, Nie, Chalmers, & Yang, 2017). Coalbed methane (CBM) has to be extracted prior and during underground mining to avoid methane outburst and explosion accidents. However, with the increase of mining depth, the coal permeability decreases significantly, which makes it hard to extract the methane (Huang, Xu, Hu, Kizil, & Chen, 2018). To enhance the coal seam permeability, many CBM recovery methods have been applied on-site, such as hydraulic fracturing and enhanced coalbed methane (ECBM). However, hydraulic fracturing is restricted due to environmental concerns and ECBM is only suitable for the coal seam with relative large permeability (Bustin, Bustin, Chikatamarla, Downey, & Mansoori, 2016; Huang, Xu, Chen, & Chen, 2018; Huang, Xu, Hu, et al., 2018)."

Jan 1, 2019

By Xuemei Zheng, Aiyuan Ma, Yonggang Zuo, Jinhui Peng, Shiwei Li, Libo Zhang

The effect of moisture content on the dielectric properties and microwave drying behavior of zirconium hydroxide was studied by using an open-ended sensor dielectric measurement system at the frequency of 2.45 GHz. The experimental results showed that moisture content can significantly influence the variation of dielectric properties. Dielectric constant, loss factor and loss tangent all increase with the increasing moisture content. Compared with the conventional drying method, the microwave-assisted drying method resulted in a substantial decrease (81.8%) in the drying time, and the drying effect was better at the lower power level of 600 W. This study offers the useful information on dielectric properties of zirconium hydroxide, which can be used for developing microwave drying applications in mineral processing and designing better microwave sensors for measuring zirconium hydroxide moisture content.

Jan 1, 2015

By Edgar Stansfield

ONE of the most striking features of the coal series passing from peat through brown coal, lignite, etc., up to anthracite is the gradual reduction of moisture content with the increased coalification of the original plant material. Thus drained peat from a bog may contain 90 per cent water, brown coal contain 50 per cent, lignite 30 per cent, while a bituminous coal may contain only 1 per cent moisture. Moisture, therefore, is one of the important factors to be considered in coal classification, especially with the lower rank coals. With bituminous and higher rank coals the moisture content is less satisfactory for classification; it may even pass a minimum value and then increase with increasing rank to anthracite and superanthracite. Coal in an undisturbed seam contains moisture which is an integral part of the coal, but it may also be wet with free, underground water percolating through the seam. Only the former must be considered in evaluating the moisture content of the coal for classification purposes; this will be called the "true moisture" of the coal. When the seam is mined and sampled the sample taken may show the true moisture; on the contrary, it may contain in addition free mine water or, especially in dry, well ventilated mines, it may contain less than the true moisture. Coal contains unstable organic compounds which may decompose, with the production of moisture, when the coal is exposed to air at ordinary temperatures, or is heated with or without exposure to air. The potential moisture of a coal therefore is higher than its actual moisture. The lower the rank of the coal, the greater its instability, as a rule, and the greater the care necessary to avoid oxidation or decomposition in any investigation of moisture content. The majority of coal workers have preferred, on account of the difficulty in evaluating the true moisture of a coal, and for other reasons, to classify coals by analyses calculated to the dry-coal basis. A number of workers familiar with lower rank coals have recently insisted that the classification of such coals can be satisfactory only if analyses on the moist-coal basis are employed. The moisture-holding capacity of coal is therefore intimately connected with coal classification, and in this paper a procedure is outlined for determining the true moisture of a coal.

Jan 1, 1932

By Membrey W. B, Partridge A. C

Lower transportation costs, improved handling and better utilization efficiency are some of the reasons that make low moisture coal product desirable. There has been considerable interest in the development of effective coal dewatering techniques to achieve this result. One avenue of considerable merit for enhancing dewatering processes is by modification of the surface chemistry of the coalwater slurry system by chemical means, resulting in better performance of existing equipment. This paper reports the results of an investigation of the utility of surface active agents in the enhancement of fine coal dewatering. A large variety of proprietary dewatering agents have been studied in relation to their efficiency in enhancing the dewatering of a number of Australian coals. Properties of particular coals that make them amenable to improved dewatering by particular chemical agents have been identified. Surface studies, including surface tension and zeta potential measurements as a function of surfactant concentration, as well as dewatering assessments, were used. Particular attention was paid to filtration, but the results could be applied to other dewatering systems.

Jan 1, 1989

By D. A. Dahlstrom

With today's high energy costs per million BTU's, far greater emphasis is placed on increasing thermodynamic efficiency in the use of energy. America has long since discarded its previous golden age of "low cost energy" in the past ten years. Energy costs are now a very significant percentage of operating expense in industrial operations. Public utilities have felt the same influences of increasing costs in energy for the generation of electricity. Not only has the input energy expense increased seriously, but as pointed out by Blackmore in a paper, fuel costs were 53.4% of the total operating costs for American Electric Power Company.

Jan 1, 1983

By Marco Le Roux, Quentin Campbell

"Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 x 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2 - 3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent."

Jan 1, 2014

By M. L. Harris

Explosions in underground mines and surface facilities such as processing plants are caused by confined accumulations of combustible dust and/or flammable gas mixed with air in the presence of an ignition source. Underground explosions can be prevented by minimizing methane concentrations through methane drainage and ventilation, by adding sufficient rock dust to inert the coal dust, and by eliminating ignition sources. The effectiveness of rock dust in arresting explosion propagation was proven by experiment and practice (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11). The precise mechanism by which rock dust (generally pulverized limestone dust) quenches flame has not been fully explained, but is believed to be absorption of thermal energy from the heated gases and absorption of radiant energy, which reduces the preheating of unburned coal particles ahead of the flame front. One measurable aspect of explosibility is incombustible content. In order to determine whether enough rock dust is applied, 30 CFR1 § 75.403, Maintenance of Incombustible Content of Rock Dust, requires at least 80% incombustible content on the roof, ribs, and floor of underground coal mines. 30 CFR § 75.403-1 further defines the incombustible content as follows: ?Moisture contained in the combined coal dust, rock dust and other dusts shall be considered as a part of the incombustible content of such mixture.? In order to determine the incombustible content of the mine dust, samples of deposited dust from specified areas in a mine must be collected, analyzed, and then compared with the minimum standard of 80%. The traditional low temperature ashing (LTA) approach to determine if a coal and rock dust mixture is compliant with the inerting requirement consumes the coal dust and considers the remaining material to be inert. Compliance with the law is then determined by comparing the measured percentage of inert material of the representative band sample with the pre-established requirement of 80%. The incombustible content of the sample includes rock dust, the amount of moisture as received at the lab, and the inherent ash in the coal. The LTA method is not itself a direct measure of explosibility but is a surrogate that calculates a single parameter associated with large-scale Bruceton Experimental Mine (BEM) explosion test results conducted with dry rock dust. This method assumes a homogenous mixture with no layering of rock dust and coal dust. Float coal dust is a serious explosion hazard if it accumulates on top of the rock dust and is not mixed with the rock dust (12). Mitchell and Nagy (13) studied the effectiveness of water as an inerting agent for the coal dust explosion hazard. The study emphasized that surface water evaporates readily from dusts. Thus, in a passageway where the dust is wet, changes in weather or the ventilation system could dry the dust and make it unsafe in a relatively short period of time. Where adequate rock dust has been applied, this drying effect is not a factor. However, if the mine depends upon the moisture content as part of the incombustible content, fluctuations in the dust surface moisture within a mine can render moisture content an ineffective and inconsistent measure of safety. Additionally, if sufficient moisture is absorbed and subsequently relinquished by rock dust, a cake can form and render the rock dust ineffectual. The trend has long been recognized that mine explosions occur primarily during the winter season when the humidity is low for long periods of time (14, 15, 16). In light of this trend and due to the potential variability of the moisture content of the dust, it may not be prudent to include variable surface moisture in the total incombustible content of the sample. Instead, surface moisture should be viewed as an additional safety measure as long as the rock dust is dispersible. However, moisture limits the ability of the rock dust to disperse and can significantly reduce its capacity to effectively inert propagating explosions (2, 13, 17, 18, 19, 20, 21, 22). Given the methods by which the as-received moisture and incombustible content are determined, dust samples from the 2010 MSHA database were assessed to determine the variability of the moisture content throughout a year and how often the measured as-received moisture might have affected the dust explosibility determination if removed. The findings were then verified by observation in laboratory studies and within the NIOSH OMSHR Safety Research Coal Mine (SRCM).

Feb 23, 2014

By M. L. Harris

Coal dust produced during the mining process is a prime explosion hazard in underground coal mines. To inert the coal dust and prevent a catastrophic propagating dust explosion, rock dust is applied to the roof, ribs, and floor surfaces of mine entries. Currently, one determination of whether a mine is adequately protected from the coal dust explosion hazard is made by analyzing collected mine dust samples for percent total incombustible content (% TIC). A minimum of 80% TIC is required per 30 CFR 75.403. The as-received moisture of the dust sample is included in the % TIC. Moisture and humidity within a coal mine vary greatly with the seasons, with explosions occurring more frequently during dry winter months. This paper will discuss the fluctuations of the as-received moisture content of the mine dust samples collected by U.S. Mine Safety and Health Administration inspectors in 2010 and the observed fluctuations of the moisture content of rock dust within the U.S. National Institute for Occupational Safety and Health Office of Mining Safety and Health Research Bruceton Experimental Mine and the Safety Research Coal Mine over a one-year period.

By K Williams, A Lavrinec, V Gurung, D Ilic

The moisture content of iron ore during handling can range from the dust extinction moisture at the point of arrival at the port to the transportable moisture limit at the point of loading ships for maritime transport. Moisture content and ore composition, specifically fines content, have a large influence on ore flowability. Typically, elevated moisture can result in bottlenecks, downtime and lost productivity due to build-up, conveyor carry-back and blockages, increasing maintenance costs. On the other hand, low moisture can result in increased dust emissions influencing the environmental footprint and product losses. Managing the use of water across the supply chain is therefore critical for service life of equipment, productivity, but also has environmental and social impacts, affecting the social license to operate. Previously, experiments have shown that oscillations induced in iron ore during handling and transport can result in movement of moisture through the ore. This kind of moisture migration depends on the nature of these oscillations, such as the undulation of idlers during conveying, the inherent ore properties and the initial moisture content. Moisture has been observed to move either upwards and/or towards the bottom of the burden. These effects can be exploited to remove excess water from the ore influencing handleability and operation, however, the actual mechanisms of moisture migration are currently poorly understood. The study presented herein involves the use of simulation to examine moisture and ore interactions. Simulations using discrete element method (DEM) and coupled with smoothed particle hydrodynamics (SPH) are implemented to investigate the behaviour of moisture in wet ore in the presence of oscillation. This is conducted at a fundamental level first using glass beads and water which is then compared to iron ore at high moisture content. The results of the modelling are discussed in view of experiments conducted.

Sep 18, 2023

By Long Fan, Shimin Liu, Guijie Sang

"Weak shale roof falls have long been the main cause for fatalities in underground coal mines. Moisture-induced swelling is one of the root causes for the degradation of roof shales. In this study, slake durability tests are conducted on shale samples collected from Illinois basin coal mines, and different levels of durability are analyzed according to Gamble slake durability classification. There are two main mechanisms influencing the shape of retained fragments after two cycles of wetting and drying: mechanical abrasion and swelling pressure. A prototype optically based shale swelling apparatus is designed and manufactured for the shale free-swelling measurement. The experimental results suggest that swelling pressure tends to deteriorate shale laminations. Moisture-induced swelling of the No. 6 roof shale from Bear Run Mine was measured under 100% relative humidity condition. The measured swelling strain normal to beddings is ~5 to 7 times greater than the swelling strain parallel to beddings. This suggests that interlayer expansion plays a key role in moisture-induced swelling. Cracks induced by swelling pressure tend to occur along the bedding plane and lead to shale deterioration. INTRODUCTION Background Ground falls have long been the cause for nearly 50% of all fatalities in underground coal mines and continue to be one of the greatest safety hazards in underground spaces. Among the various ground fall hazards, roof failure takes up 23% of total fatalities in underground coal mines, of which 13% are due to skin failure and 10% are due to massive roof falls (Mark, Pappas, and Barczak, 2011). Roof failures associated with weak shales are summarized in previous studies (Molinda and Mark, 2010; Aughenbaugh and Bruzewski, 1973; Bajpayee, Pappas, and Ellenberger, 2014; Murphy, 2016). For mine roof instability and failure, two aspects can explain the failure mechanism of weak roofs. One is the elevated stress concentration in lateral direction due to the mining-induced excavation and its stress redistribution around the mine opening (Song and Stankus, 1997; Fan and Liu, 2017; Hill, 1986). The other mechanism is the passive stress-relief due to the strength weakening induced by the ambient moisture and temperature fluctuations during a period of time. Shale is moisture sensitive and presents a lower durability if it is exposed to a highly humid environment for a long time, thus leading to roof deterioration and instability in underground coal mines (Aughenbaugh and Bruzewski, 1976; Stateham and Radcliffe, 1978; Chugh and Missavage, 1981; Klemetti, Oyler, and Molinda, 2009). It is well known that shale is a clay-bearing sedimentary rock and that clay minerals are water sensitive. The moisture uptake for shale will induce the micro-deformation of a shale matrix, thus the structure and strength of shale is a function of time and intensity of moisture exposure. All mine engineers notice moisture-induced shale deterioration; however, the underlying mechanism(s) are still not fully understood due to the complexity of geophysical-chemical water-shale interactions (Huang, Aughenbaugh, and Rockaway, 1986; Hensen and Smit, 2002; Diaz-Perez, Cortés-Monroy, and Roegiers, 2007). The coal mining industry is still in the process of finding a technically sound, cost-effective technology to prevent this unexpected and unpredictable shale roof failure. Therefore, understanding how the moisture-sensitive shale responses to various ambient moisture and what role exposure duration plays in shale roof failure is key to prevent unexpected roof incidents, which will lay the foundation for the long-term roof support design and ground control management."

Jan 1, 2017

By Neville Slade, Doug Shumway, Dayan Anderson, Joe Siefke, Curtis James

The Mojave Desert is a particularly fragile ecosystem that faces several significant impacts. These include rapid housing development, overdrafted water supplies and loss of wildlife habitat — all a result of mining, industrial activity and urban sprawl. During the past three years, a diverse group of educators, natural resource managers and business leaders was assembled under the auspices of a local community college. This group’s goal was to provide unique natural resource education opportunities for the region.

Jan 1, 2005

By CHARLES M. A. STINE

IN fighting a war the all-absorbing intent is to win. There is little time to analyze the rush of events or to appraise their consequences beyond the war's end. The united objective is, rightly, success for our arms. Yet under the pressures of a great war there may be compressed scientific, economic and social developments that might have taken many decades to achieve under less urgent conditions. Their effects on our lives and all civilization may be more wide-reaching and lasting than any military conquest. They constitute one of the must imperative incentives to victory. No American, least of all any scientist worthy the name, conceivably could endorse war as a justifiable means to progress. The destruction of life and property wrought by the present war far exceeds the havocs of a century's earthquakes. Most of mankind is burning itself on an altar of paganism. Nonetheless, one fact is inescapable Despite the recurrent malady of war history's overall course is forward. Mankind has the habit of rising phoenix-like from its own ashes to attain greater heights. Progress is immortal.

Jan 1, 1942

THERE is probably no phase of basic open-hearth steelmaking that is more of an art and less of a science than mold and pouring practice. It varies widely from plant to plant; consequently it is obviously impossible to set down in detail in this chapter the many ramifications of practice that are now used. The discussion that follows therefore attempts only to give an outline of the more common methods, with examples sufficient to indicate some of the variations in procedure, and to emphasize a few of the many underlying problems that face the open-hearth operator at the pouring platform. MOLD DESIGN Ingot molds are hollow castings of considerable wall thickness. Despite this, non-uniformity in wall thickness should be strictly avoided to prevent the setting up of unnecessary stresses. Molds are cast in various forms, sizes, and shapes depending on the type of steel, and on whether the ingot is to be withdrawn from the mold or the mold from the ingot. The selection of ingot-mold material, which is usually cupola or blast-furnace iron containing approximately 3.5 per cent carbon, 1 per cent silicon, 0.9 per cent manganese, 0.2 per cent phosphorus, and 0.07 per cent sulphur, is governed by numerous considerations that affect mold life. (1) Factors in addition to wall thickness that should be given primary consideration at the foundry are casting skin, shrinkage stresses, and casting temperature. Factors in Mold Design. In use, mold thickness is of greatest importance, for it must be heavy enough to freeze the molten metal rising in the mold and to reduce the temperature of the steel below that of the melting point of cast iron to prevent the inner surface of the mold from melting, which would result in the welding of the ingot to the mold. The skin of an ingot, which solidities immediately upon contact with the relatively cold walls of the mold, must soon become thick enough to contract on the fluid mass and pull away slightly from the sides of the mold. The separation of the ingot from the mold depends entirely on the heat taken up by the mold from the steel.

Jan 1, 1944

INCREASING realization that pouring and ingot-mold practices involve many factors of fundamental importance to ingot quality and general steel-mill operations has caused these phases of steelmaking to become major concerns of operators and metallurgists engaged in control of quality and costs. Methods of pouring steel from the ladle into the ingot molds have some direct effects on ingot quality. The mold itself governs solidification and dimensions of the ingot and in so doing exerts some very tangible influences not only on ingot quality but also on product yields and general steel-mill processing. In addition, practices are employed in the handling of molds during daily open-hearth operations that are important to quality and production costs. Therefore, pouring and mold practices must be considered highly specialized and important steps in steel-mill operations. MOLD DESIGN Mold design is difficult to discuss in a precise manner because it varies greatly throughout the industry, both in theoretical concepts and practical application, and few well developed data are available. Most ingot molds are designed to meet conditions peculiar to a given plant wherein quality standards are dictated by end-use requirements, which may differ considerably even for the same grade of steel. The mold designer must also consider the equipment available to process ingots and the product obtained from them. Such equipment, used for stripping, heating, blooming and finishing operations, is seldom, if ever, exactly the same in any two steel plants. Thus, pronounced contrasts in mold designs can be expected to continue, even among plants making strictly comparable types of product, particularly because some producers are just beginning to realize the benefits possible from specialized designs. Certain fundamentals are used in mold design but even these

Jan 1, 1964

By A Kondratiev, A E. Moiseev

Viscosity of oxide melts is one of the fundamental physicochemical properties that plays a crucial role in important technological and natural processes like slag flow, slag/metal separation, volcano eruptions etc. However, many oxides melt at extremely high temperatures and are highly corrosive in the liquid state, which makes experimental measurement of melt viscosity by traditional experimental techniques a difficult and expensive, if not unachievable, task. In this case it might be useful to employ other methods of viscosity determination such as modelling or simulation. In the present paper the shear viscosity coefficients of selected pure refractory oxides (CaO, MgO, Al2O3 and others) have been simulated at temperatures above their melting points via the classical molecular dynamics and compared to the available viscosity data (eg experimental viscosities, other model predictions) collected by the authors. The simulation has been carried out using the noncommercial molecular dynamics simulation package LAMMPS and the Born-Mayer-Huggins potential, which parameters for the selected oxides were taken from the literature. Several viscosity calculation techniques (the Stokes-Einstein and Green-Kubo equations, the so called Einstein relations, and the non-equilibrium molecular dynamics methods) have been applied to ensure a more reliable viscosity calculation. It has been demonstrated that the simulated viscosity of the selected melts agrees with the available experimental data. It has also been shown that the simulated viscosity of a number of the oxide melts investigated is close to that calculated by phenomenological viscosity models, which supports viscosity extrapolation from the corresponding binaries and ternaries, if no experimental data is present for unary systems. In general, it has been demonstrated that the molecular dynamics simulation could provide a reasonable estimation of viscosity if no other viscosity data is available.

Jun 19, 2024

By Wei-Tong Du, Xiao-Ping Liang, Yu Wang

The structural properties for ternary molten CaO–SiO2–B2O3 system with varying B2O3/SiO2 ratios at a fixed CaO content were calculated by molecular dynamics (MD) simulation. The simulation results revealed that with the increasing of B2O3/SiO2 mol ratio, the bond length of B-O was approximately constant at 1.35 Å, and the coordination number for B (CNB-O) was observed to vary from 3.40 to 3.51, and the average angle of O-B-O increases from 105° to nearly 120°, implying that the geometric stability of structure is reducing sharply. AlsoQ3 andQ4 tetrahedral species (tetrahedron with three and four bridging oxygens respectively) decrease with the increasing of B2O3/SiO2 mol ratio, and the proportion of (Q3 + Q4) decrease linearly from 0.6 to nearly 0, suggesting that B2O3 may behave as a network-breaking basic oxide in the CaO–SiO2–B2O3 system.

Mar 1, 2017

Considerable attention has been, and is being, given to the physics of water-films associated with bubble interactions at surfaces. In contrast, little information on the chemistry of such films has been reported. This communication reports a method using sum frequency vibrational spectroscopy (SFVS) to describe hydrogen bonding of interfacial water molecules in water films created with bubbles at hydrophilic and hydrophobic surfaces. The SFVS spectra of water films at hydrophilic silica surfaces differ significantly from the spectra of water at a hydrophobic silica surface. The SFVS spectra indicate that a very ordered water structure exists in water films at the hydrophilic silica surface during contact with a bubble and that the extent of hydrogen bonding increases with an increase in contact pressure. Such structural considerations as well as repulsive electrostatic and Van der Waals forces account for film stability for a bubble at the hydrophilic silica surface. In contrast, the SFVS spectra of water at a hydrophobic silica surface show a lack of hydrogen bonding and are characterized by a distinct absorption at about 3700 cm-1 similar to the spectrum of the air/water interface. These results suggest the presence of a water void, or water exclusion zone, at the hydrophobic surface, as supported by X-ray reflectivity measurements reported in the literature, by atomic force microscopy, and by the results from molecular dynamics simulations. Of course the water film at the hydrophobic surface is unstable with film thinning and rupture upon bubble contact. Under these circumstances it is shown that an attractive Van der Waals force between the bubble and the hydrophobic surface can be expected when the water exclusion zone is taken into consideration. As the thickness of the water exclusion zone increases to a thickness corresponding to the size of nano bubbles, the calculated attractive Van der Waals force increases. This analysis may help to explain the so-called ?short range? and ?long range? hydrophobic forces. Keywords: SFVS spectra, hydrophilic silica surface, hydrophobic silica surface

Sep 1, 2012

By Micheal Mitariten

The recovery of natural gas (primarily methane) from coalbed deposits is an established and growing source for the U.S and accounts for over 7% of its total production. The gas from on-purpose degassing is often pipeline quality and requires only compression and dehydration before being admitted to the pipeline grid. However, the raw gas is sometimes contaminated with nitrogen (N2) and/or carbon dioxide (CO2) that can make the gas inadmissible to the transportation pipeline. In general, the N2 must be 4% or less and the CO2 should be 2% or less. In treating gas produced from virgin coal bed or from degassing operations where CO2 is present, amine systems are traditionally used for its removal. Engelhard’s Molecular Gate® adsorption system offers an attractive alternative due to its skid-mounted equipment, low pressure and unattended operation, cost and high on-stream reliability. Natural gas can also be sourced from the residual coal, after the coal has been mined. This source can be the GOB or gas remaining in abandoned coal mines. This source is almost universally contaminated, often with a combination of CO2 and N2. If the source is from air intrusion, the source can also be contaminated with O2. In treating CO2 / N2 contaminated feeds, the Molecular Gate adsorption system removes both of the impurities along with a level of O2 within a single processing step. To date, ten Molecular Gate units are underway with three systems having been installed for upgrading gas from abandoned coal mines. The technology consists of specialty adsorbents and advanced PSA processes that are jointly offered as fabricated packaged equipment by Engelhard Corporation and Guild Associates, Inc. Upgrading requirements, project challenges and project arrangements are discussed in this paper.

Jan 1, 2005

By D. Pienaar, C. O’Connor, B. McFadzean

Dithiophosphate (DTP) is classically used as a co-collector in sulphide mineral flotation, where xanthate-DTP mixtures have been shown to synergistically improve mineral flotation performance. Notwithstanding the improved recoveries observed, ethyl DTP does not appear to behave as a conventional collector, since it has been shown that it does not adsorb onto certain sulphide mineral surfaces. Recent investigations have nevertheless indicated that when ethyl DTP does not adsorb onto the sulphide mineral surface, the presence of a non-ionic frother can activate a synergistic increase in pulp phase mineral recovery, and bubble-particle attachment probability. A regular solution approach was used to determine the interactions between thiol collectors and non-ionic frothers at the air-water interface. Attractive interactions were observed between longer alkyl chain DTPs and frothers, whereas the activity of xanthates at the air-water interface were too weak to determine if an interaction was occurring. This is the first time that such interactions have been shown for the DTP-frother system and represents an important contribution to our understanding of the role of DTP reagents in the flotation process. Keywords: Collector-frother interaction, dithiophosphate, surfactant synergism

Jan 1, 2020

By M Badawi, Y Foucaud, C Veloso, J Laine, A C. Araujo

Iron is one of the most exchanged commodities worldwide. Its use for steelmaking explains the growing demand in the metal which remains mainly produced by the mining and the beneficiation of iron ores. Flotation is the most used mineral separation technique worldwide, processing several billion tonnes (Bt) of ore annually, including, in some cases, hematite and magnetite ores. Based on the physicalchemical properties of mineral surfaces, flotation aims to selectively adsorb molecules that render mineral surfaces either hydrophobic or hydrophilic, known as collectors and depressants, respectively. Hydrophobic particles are then recovered in the froth by the injection of gas bubbles travelling up in the cell and attaching the hydrophobic particles. However, despite the popularity and the good performances of flotation, mining industry faces new challenges of decreasing grades and increased mineralogical complexness in ores. Many flotation variables, especially when related to reagent adsorption, remain poorly understood and it becomes necessary to gain knowledge to enhance the existing processes. Molecular modelling techniques like the density functional theory or molecular dynamics simulations (ie Classical molecular dynamics or Ab initio Molecular Dynamics) currently represent powerful tools for different applications in material sciences, like catalysis or depollution purposes. They have recently been successfully applied in the flotation area, with an increasing number of publications dealing with this topic every year. These tools provide crucial information on bulk and surface properties as well as on the adsorption mechanisms of reagents on mineral surfaces, key step in the flotation process, and synergetic effect of collector mixtures. A better understanding of the adsorption mechanisms of flotation reagents, provided by molecular simulations, will help to finely choose flotation reagents, and even lead to the development of new reagents formulations. Overall, these tools enable the discovery of practical and industrial solutions to improve the flotation process, which will undoubtedly help the mining industry to face its future challenges.

Nov 8, 2021