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POC-scale testing of a dry triboelectrostatic separator for fine coal cleaning. Second quarterly technical progress report, January 1, 1996--March 31, 1996

Description: The Pittsburgh Energy Technology Center (PETC) developed a triboelectrostatic separation (TES) process which is capable of removing mineral matter from coal without using water. A distinct advantage of this dry coal cleaning process is that it does not entail costly steps of dewatering which is a common problem associated with conventional fine coal cleaning processes. It is the objective of this project to conduct a series of proof-of-concept (POC) scale tests at a throughput of 200--250 kg/hr and obtain scale- up information. Prior to the POC testing, bench-scale test work will be conducted with the objective of increasing the separation efficiency and throughput, for which changes in the basic designs for the charger and the separator may be necessary. The bench- and POC- scale test work will be carried out to evaluate various operating parameters and establish a reliable scale-up procedure. The scale-up data will be used to analyze the economic merits of the TES process. All required documents associated with project planning were completed and submitted to DOE for approval during the second quarter of this project. Approval of the project work plan is still pending at this time subject to additional review by DOE of requested modifications to the statement of work. Accomplishments during this reporting period include the set-up of an apparatus for assessing tribocharger performance, continued construction of the bench-scale (1 kg/hr) triboelectrostatic separator and initial development of a fundamental model for predicting the motion of charged particles in a non-uniform electrostatic field.
Date: August 1, 1996
Creator: Yoon, R.-H.; Luttrell, G.H. & Adel, G.T.
Partner: UNT Libraries Government Documents Department

POC-scale testing of a dry triboelectrostatic separator for fine coal cleaning. Third quarterly technical progress report, April 1996--June 30, 1996

Description: The Pittsburgh Energy Technology Center (PETC) developed a triboelectrostatic separation (TES) process which is capable of removing mineral matter from coal without using water. A distinct advantage of this dry coal cleaning process is that it does not entail costly steps of dewatering which is a common problem associated with conventional fine coal cleaning processes. It is the objective of this project to conduct a series of proof-of-concept (POC) scale tests at a throughput of 200--250 kg/hr and obtain scale- up information. Prior to the POC testing, bench-scale test work will be conducted with the objective of increasing the separation efficiency and throughput, for which changes in the basic designs for the charger and the separator may be necessary. The bench- and POC- scale test work will be carried out to evaluate various operating parameters and establish a reliable scale-up procedure. The scale-up data will be used to analyze the economic merits of the TES process. At present, the project is at the stage of engineering design (Task 3). Work accomplished during this reporting period include the construction of a Faraday Cage for measurement of particle charges (Subtask 3.1), construction of a bench-scale triboelectrostatic separator (Subtask 3.2) and development of a theoretical model for predicting motion of charged particles in a non-uniform electrostatic field (Subtask 3.2). This model will be useful for designing the POC module.
Date: October 1, 1996
Creator: Yoon, R.-H.; Mesenyashin, A.; Yan, E.S.; Luttrell, G.H. & Adel, G.T.
Partner: UNT Libraries Government Documents Department

Development of enhanced sulfur rejection processes. Final technical progress report, third quarter (8. quarterly report), July 1--September 30, 1994

Description: Pyrite becomes hydrophobic upon superficial oxidation and floats without a collector. The flotation begins to occur at potentials above the stable potentials identified by the chronoamperometry experiments conducted with freshly fractured pyrite. This finding suggests that iron polysulfide, formed during the initial stages of oxidation, is responsible for the flotation. The collectorless flotation is suppressed above the potential where the mineral is aggressively oxidized, forming iron hydroxide and soluble sulfoxy species. The collectorless flotation is less significant at pH 9.2 than at pH 4.6, possibly due to the formation of iron hydroxide. At pH 9.2, the collectorless flotation increases in the presence of EDTA and hydrocarbon oil. The collectorless flotation of pyrite can be suppressed by galvanically coupling the mineral with reactive metals such as aluminum, manganese, and zinc. This effectively prevents the mineral from oxidation. The microflotation tests conducted with mono-sized pyrite samples show that the collectorless flotation can be suppressed effectively in the presence of metal powders. Bench-scale flotation experiments conducted using Denver laboratory flotation cell and a 2-inch diameter Microcel flotation column, also demonstrates that the collectorless flotation can be suppressed in the presence of the reactive metals. It has been established that the most important parameters determining the effectiveness of suppressing pyrite flotation by the galvanic coupling technique are the surface area of the galvanic contractors and the solids concentration of the slurry during conditioning.
Date: March 20, 1996
Creator: Yoon, R.H.; Luttrell, G.H.; Tao, D.P.; Lu, M.X. & Richardson, P.E.
Partner: UNT Libraries Government Documents Department

Hydrophobic Dewatering of Fine Coal. Topical report, March 1, 1995-March 31, 1997

Description: Many advanced fine coal cleaning technologies have been developed in recent years under the auspices of the U.S. Department of Energy. However, they are not as widely deployed in industry as originally anticipated. An important reason for this problem is that the cleaned coal product is difficult to dewater because of the large surface area associated with fine particles. Typically, mechanical dewatering, such as vacuum filtration and centrifugation, can reduce the moisture to 20-35% level, while thermal drying is costly. To address this important industrial problem, Virginia Tech has developed a novel dewatering process, in which water is displaced from the surface of fine particulate materials by liquid butane. Since the process is driven by the hydrophobic interaction between coal and liquid butane, it was referred to as hydrophobic dewatering (HD). A fine coal sample with 21.4 pm median size was subjected to a series of bench-scale HD tests. It was a mid-vol bituminous coal obtained from the Microcel flotation columns operating at the Middle Fork coal preparation plant, Virginia. All of the test results showed that the HD process can reduce the moisture to substantially less than 10%. The process is sensitive to the amount of liquid butane used in the process relative to the solids concentration in the feed stream. Neither the intensity nor the time of agitation is critical for the process. Also, the process does not require long time for phase separation. Under optimal operating conditions, the moisture of the fine coal can be reduced to 1% by weight of coal.
Date: December 31, 1997
Creator: Yoon, R.; Sohn, S.; Luttrell, J. & Phillips, D.
Partner: UNT Libraries Government Documents Department

POC-scale testing of a dry triboelectrostatic separator for fine coal cleaning. First quarterly technical progress report, September 27, 1995--December 31, 1995

Description: The Pittsburgh Energy Technology Center (PETC) developed a triboelectrostatic separation (TES) process which is capable of removing mineral matter from coal without using water. A distinct advantage of this dry coal cleaning process is that it does not entail costly steps of dewatering which is a common problem associated with conventional fine coal cleaning processes. It is the objective of this project to conduct a series of proof-of-concept (POC) scale tests at a throughput of 200--250 kg/hr and obtain scale- up information. Prior to the POC testing, bench-scale test work will be conducted with the objective of increasing the separation efficiency and throughput, for which changes in the basic designs for the charger and the separator may be necessary. The bench- and POC- scale test work will be carried out to evaluate various operating parameters and establish a reliable scale-up procedure. The scale-up data will be used to analyze the economic merits of the TES process. During the past quarter, a number of project tasks have been initiated. All documents required for project startup (i.e., work plans, management plans, etc.) have been submitted to DOE for approval. A bench-scale TES unit and an apparatus for studying tribocharging mechanisms have been designed and are currently being fabricated. One of the three coal samples to be used for bench-scale testing has been acquired.
Date: December 31, 1995
Creator: Yoon, R.H.; Luttrell, G.H. & Adel, G.T.
Partner: UNT Libraries Government Documents Department

Bench-scale testing of the multi-gravity separator in combination with Microcel. Volume of Appendices, Final report

Description: This volume contains the following appendices: Circuit design; test data and performance calculations; Box-Behnken statistical analysis; Response surface plots and computations; Test data and performance calculations; Long-duration test data and performance calculations; MGS partition curve data; Near-term test data and performance calculations; Economic evaluation; and CPPRF circuit drawings.
Date: March 1, 1995
Creator: Luttrell, G.H.; Venkatraman, P.; Phillips, D.I. & Yoon, Roe-Hoan
Partner: UNT Libraries Government Documents Department

Development of the chemical and electrochemical coal cleaning (CECC) process

Description: The Chemical and Electrochemical Coal Cleaning (CECC) process developed at Virginia Polytechnic Institute and State University was studied further in this project. This process offers a new method of physically cleaning both low- and high-rank coals without requiring fine grinding. The CECC process is based on liberating mineral matter from coal by osmotic pressure. The majority of the work was conducted on Middle Wyodak, Pittsburgh No. 8 and Elkhorn No. 3 coals. The coal samples were characterized for a variety of physical and chemical properties. Parametric studies were then conducted to identify the important operating parameters and to establish the optimum conditions. In addition, fundamental mechanisms of the process were studied, including mineral matter liberation, kinetics of mineral matter and pyrite dissolution, ferric ion regeneration schemes and alternative methods of separating the cleaned coal from the liberated mineral matter. The information gathered from the parametric and fundamental studies was used in the design, construction and testing of a bench-scale continuous CECC unit. Using this unit, the ash content of a Middle Wyodak coal was reduced from 6.96 to 1.61% at a 2 lbs/hr throughput. With an Elkhorn No. 3 sample, the ash content was reduced from 9.43 to 1.8%, while the sulfur content was reduced from 1.57 to 0.9%. The mass balance and liberation studies showed that liberation played a more dominant role than the chemical dissolution in removing mineral matter and inorganic sulfur from the different bituminous coals tested. However, the opposite was found to be the case for the Wyodak coal since this coal contained a significant amount of acid-soluble minerals.
Date: May 1, 1992
Creator: Yoon, Roe-Hoan & Basilio, C.I.
Partner: UNT Libraries Government Documents Department

Development of the Selective Hydrophobic Coagulation process

Description: A novel technique for selectively coagulating and separating coal from dispersed mineral matter has been developed at Virginia Tech. The process, Selective Hydrophobic Coagulation (SHC), has been studied since 1986 under the sponsorship of the US Department of Energy (Contracts AC22-86PC91221 and AC22-90PC90174). The SHC process differs from oil agglomeration, shear or polymer flocculation, and electrolytic coagulation processes in that it does not require reagents or additives to induce the formation of coagula. In most cases, simple pH control is all that is required to (1) induce the coagulation of coal particles and (2) effectively disperse particles of mineral matter. If the coal is oxidized, a small dosage of reagents can be used to enhance the process. During the quarter, the Anutech Mark IV surface force apparatus was used to generate surface force-distance data for the mica/dodecylamine hydrochloride system (Task 2.1.1). Work to characterize the hydrophobicity of this system and the mica/DDOA[sup [minus]] system was also initiated (Task 2.1.2). In Task 3, the mixing/coagulation characteristics of a small Kenics static mixer/agitation system have been investigated (Task 3.2.1), a lamella thickener for the recovery of coagula has been built (Task 3.3.1), and the test program for the recovery of coagula by column flotation has been initiated (Task 3.3.4).
Date: January 1, 1992
Creator: Yoon, R.H. & Luttrell, G.H.
Partner: UNT Libraries Government Documents Department

Development of enhanced sulfur rejection processes

Description: Research at Virginia Tech led to two complementary concepts for improving the removal of inorganic sulfur from much of the Eastern US coals. One controls the surface properties of coal pyrite (FeS[sub 2]) by electrochemical-.potential control, referred to as the Electrochemically Enhanced Sulfur Rejection (EESR) Process: The second controls the flotation of middlings, i.e., particles composed of pyrite with coal inclusions by using polymeric reagents to react with pyrite and convert the middlings to hydrophilic particles, and is termed the Polymer Enhanced Sulfur Rejection (PESR) Process. These new concepts are based on recent research establishing the two main reasons why flotation fails to remove more than about 50% of the pyritic sulfur from coal: superficial oxidization of liberated pyrite to form polysulfide oxidation products so that a part of the liberated pyrite floats with the coal; and hydrophobic coal inclusions in the middlings dominating their flotation so that the middlings also float with the coal. These new pyritic-sulfur rejection processes do not require significant modifications of existing coal preparation facilities, enhancing their adoptability by the coal industry. It is believed that they can be used simultaneously to achieve both free pyrite and locked pyrite rejection.
Date: March 23, 1993
Creator: Yoon, R.H.; Luttrell, G.; Adel, G. & Richardson, P.E.
Partner: UNT Libraries Government Documents Department

Development of the selective coagulation process

Description: The selective hydrophobic coagulation (SHC) process is based on the recent finding that hydrophobic particles can be selectively coagulated without using traditional agglomerating agents or flocculants. The driving force for the coagulation is the attractive energy between hydrophobic surfaces, an interaction that has been overlooked in classical colloid chemistry. In most cases, selective separations can be achieved using simple pH control to disperse the mineral matter, followed by recovery of the coal coagula using techniques that take advantage of the size enlargement. In the present work, studies have been carried out to further investigate the fundamental mechanisms of the SHC process and the parameters that affect the process of separating coal from the ash-forming minerals and pyritic sulfur. Studies have included direct force measurements of the attractive interaction between model hydrophobic surfaces, in-situ measurements of the size distributions of coagula formed under a variety of operating conditions, and development of a population balance model to describe the coagulation process. An extended DLVO colloid stability model which includes a hydrophobic interaction energy term has also been developed to explain the findings obtained from the experimental studies. In addition to the fundamental studies, bench-scale process development test work has been performed to establish the best possible method of separating the coagula from dispersed mineral matter. Two types of separators, i.e., a sedimentation tank and a rotating drum screen, were examined in this study. The sedimentation tank proved to be the more efficient unit, achieving ash reductions as high as 60% in a single pass while recovering more than 90% of the combustible material. This device, which minimizes turbulence and coagula breakage, was used in subsequent test work to optimize design and operating parameters.
Date: July 1, 1992
Creator: Yoon, R.H. & Luttrell, G.H.
Partner: UNT Libraries Government Documents Department

In-plant testing of microbubble column flotation

Description: Microbubble column flotation (MCF) was developed at the Virginia Center for Coal and Minerals Processing (VCCMP) for the selective recovery of fine particles. Bench-scale test work conducted at VCCMP, largely under the sponsorship of the U.S. Department of Energy (DOE), showed that the technology worked well for both coal and mineral applications. For the technology to be commercially successful, however, a full-scale demonstration of the MCF technology was deemed necessary. This report summarizes the results of work performed under the DOE project entitled In-plant Testing of Microbubble Column Flotation.'' The objectives of this research and development effort were to duplicate the bench-scale performance of the MCF process in a full-scale unit, to verify the scale-up procedure developed in an earlier project, and to demonstrate the applicability of the MCF technology to the coal industry.
Date: July 31, 1991
Creator: Yoon, R.H.; Luttrell, G.H.; Adel, G.T. & Mankosa, M.J.
Partner: UNT Libraries Government Documents Department

Development of the selective coagulation process

Description: The aim of this project is to develop an economical method for producing low-sulfur and low-ash coals using the selective hydrophobic coagulation (SHC) process. This work has been divided into three tasks: (1) project planning and sample acquisition; (2) studies of the fundamental mechanism(s) of the selective coagulation process and the parameters that affect the process of separating coal from both the ash-forming minerals and pyritic sulfur; and (3) bench-scale process development test work to establish the best possible method(s) of separating the hydrophobic and coagula from the dispersed mineral matter.
Date: January 1, 1991
Creator: Yoon, R.H. & Luttrell, G.H.
Partner: UNT Libraries Government Documents Department

Development of the selective hydrophobic coagulation process. Fourth quarterly technical progress report, July 1, 1992--September 30, 1992

Description: A novel technique for selectively coagulating and separating coal from dispersed mineral matter has been developed at Virginia Tech. The process, Selective Hydrophobic Coagulation (SHC), has been studied since 1986 under the sponsorship of the US Department of Energy. The SHC process differs from oil agglomeration, shear or polymer flocculation, and electrolytic coagulation processes in that it does not require reagents or additives to induce the formation of coagula. In most cases, simple pH control is all that is required to (i) induce the coagulation of coal particles and (ii) effectively disperse particles of mineral matter. If the coal is oxidized, a small dosage of reagents can be used to enhance the process. The technical work program was initiated on July 1, 1992. Force-distance curves were generated for DDOA Br-coated mica surfaces in water and used to calculate hydrophobicity constants and decay lengths for this system; and a new device for the measurement of water contact angles, similar to the Wilhelmy plate balance, has been built 225 kg samples of Pittsburgh No. 8 and Elkhom No. 3 seam coals were obtained; a static mixer test facility for the study of coagula growth was set up and was undergoing shakedown tests at the end of the quarter; a bench-scale lamella thickener was being constructed; and preliminary coagula/ mineral separation tests were being conducted in a bench-scale continuous drum filter.
Date: December 31, 1992
Creator: Yoon, R. H. & Luttrell, G. H.
Partner: UNT Libraries Government Documents Department

Development of the Selective Hydrophobic Coagulation process. Fifth quarterly technical progress report, October 1, 1992--December 30, 1992

Description: A novel technique for selectively coagulating and separating coal from dispersed mineral matter has been developed at Virginia Tech. The process, Selective Hydrophobic Coagulation (SHC), has been studied since 1986 under the sponsorship of the US Department of Energy (Contracts AC22-86PC91221 and AC22-90PC90174). The SHC process differs from oil agglomeration, shear or polymer flocculation, and electrolytic coagulation processes in that it does not require reagents or additives to induce the formation of coagula. In most cases, simple pH control is all that is required to (1) induce the coagulation of coal particles and (2) effectively disperse particles of mineral matter. If the coal is oxidized, a small dosage of reagents can be used to enhance the process. During the quarter, the Anutech Mark IV surface force apparatus was used to generate surface force-distance data for the mica/dodecylamine hydrochloride system (Task 2.1.1). Work to characterize the hydrophobicity of this system and the mica/DDOA{sup {minus}} system was also initiated (Task 2.1.2). In Task 3, the mixing/coagulation characteristics of a small Kenics static mixer/agitation system have been investigated (Task 3.2.1), a lamella thickener for the recovery of coagula has been built (Task 3.3.1), and the test program for the recovery of coagula by column flotation has been initiated (Task 3.3.4).
Date: December 31, 1992
Creator: Yoon, R. H. & Luttrell, G. H.
Partner: UNT Libraries Government Documents Department

Development of the selective coagulation process. Fourth quarter technical progress report, July 1, 1991--September 30, 1991

Description: The aim of this project is to develop an economical method for producing low-sulfur and low-ash coals using the selective hydrophobic coagulation (SHC) process. This work has been divided into three tasks: (1) project planning and sample acquisition; (2) studies of the fundamental mechanism(s) of the selective coagulation process and the parameters that affect the process of separating coal from both the ash-forming minerals and pyritic sulfur; and (3) bench-scale process development test work to establish the best possible method(s) of separating the hydrophobic and coagula from the dispersed mineral matter.
Date: December 31, 1991
Creator: Yoon, R. H. & Luttrell, G. H.
Partner: UNT Libraries Government Documents Department

Development of enhanced sulfur rejection processes. Third quarterly technical progress report, April 1, 1993--June 31, 1993

Description: Conclusions: Release analyses of Pittsburgh No. 8 and Illinois No. 6 coals show that the {minus}28 mesh size fraction is fine enough to liberate ash and pyrite. Galvanic coupling with sacrificial anodes such as zinc, manganese and aluminum can effectively lower the potential of pyrite. This effect is more significant at pH 4.6 than at pH 9.2. The most negative pyrite potential is achieved when the surface area ratio of anode to pyrite is approximately 4:1. When coupled with pyrite at pH 9.2, the zinc anode exhibited unique potential vs time behavior which is different from that observed with manganese and aluminum. This is believed to be related to the build- up and break-down of zinc hydroxides on the surface. Voltammograms of pyrite at pH 9.2 and 4.6 demonstrated that pyrite surfaces can be significantly changed by galvanic coupling with sacrificial anodes. In flotation tests, metal powders were used as galvanic contactors to reduce the potential and depress pyrite. The potenial may be low enough to remove sulfur species from the surface. Stirred solutions are preferred for the removal of oxidized sulfur species by galvanic coupling; oxygen in solution must to be depleted prior to the addition of sacrificial anodes to effectively lower the pyrite potential. Microflotation studies show that zinc, manganese and iron all depress pyrite. Zinc appears to be the most effective, followed by manganese and then iron. Voltammetry studies indicated that coupling pyrite with zinc, manganese and aluminum reduces and desorbs hydrophobic sulfur products on the surface of pyrite.
Date: October 12, 1993
Creator: Yoon, R. H.; Luttrell, G. H.; Adel, G. T. & Richardson, P. E.
Partner: UNT Libraries Government Documents Department

Development of enhanced sulfur rejection processes. First Quarterly technical progress report, October 1, 1992--December 31, 1992

Description: Research at Virginia Tech led to two complementary concepts for improving the removal of inorganic sulfur from much of the Eastern US coals. One controls the surface properties of coal pyrite (FeS{sub 2}) by electrochemical-.potential control, referred to as the Electrochemically Enhanced Sulfur Rejection (EESR) Process: The second controls the flotation of middlings, i.e., particles composed of pyrite with coal inclusions by using polymeric reagents to react with pyrite and convert the middlings to hydrophilic particles, and is termed the Polymer Enhanced Sulfur Rejection (PESR) Process. These new concepts are based on recent research establishing the two main reasons why flotation fails to remove more than about 50% of the pyritic sulfur from coal: superficial oxidization of liberated pyrite to form polysulfide oxidation products so that a part of the liberated pyrite floats with the coal; and hydrophobic coal inclusions in the middlings dominating their flotation so that the middlings also float with the coal. These new pyritic-sulfur rejection processes do not require significant modifications of existing coal preparation facilities, enhancing their adoptability by the coal industry. It is believed that they can be used simultaneously to achieve both free pyrite and locked pyrite rejection.
Date: March 23, 1993
Creator: Yoon, R. H.; Luttrell, G.; Adel, G. & Richardson, P. E.
Partner: UNT Libraries Government Documents Department

Development of the selective hydrophobic coagulation process

Description: A novel technique for selectively coagulating and separating coal from dispersed mineral matter has been developed at Virginia Tech. The process, Selective Hydrophobic Coagulation (SHC), has been studied since 1986 under the sponsorship of the US Department of Energy. The SHC process differs from oil agglomeration, shear or polymer flocculation, and electrolytic coagulation processes in that it does not require reagents or additives to induce the formation of coagula. In most cases, simple pH control is all that is required to (i) induce the coagulation of coal particles and (ii) effectively disperse particles of mineral matter. If the coal is oxidized, a small dosage of reagents can be used to enhance the process. The technical work program was initiated on July 1, 1992. Force-distance curves were generated for DDOA Br-coated mica surfaces in water and used to calculate hydrophobicity constants and decay lengths for this system; and a new device for the measurement of water contact angles, similar to the Wilhelmy plate balance, has been built 225 kg samples of Pittsburgh No. 8 and Elkhom No. 3 seam coals were obtained; a static mixer test facility for the study of coagula growth was set up and was undergoing shakedown tests at the end of the quarter; a bench-scale lamella thickener was being constructed; and preliminary coagula/ mineral separation tests were being conducted in a bench-scale continuous drum filter.
Date: January 1, 1992
Creator: Yoon, R.H. & Luttrell, G.H.
Partner: UNT Libraries Government Documents Department

Control of pyrite surface chemistry in physical coal cleaning

Description: The separation of pyrite from coal by flotation is based on exploiting the wettability difference between coal and pyrite. There is evidence that the wettability of coal pyrite changes upon superficial oxidation. Therefore, the oxidation of coal pyrite has been studied under carefully controlled electrochemical conditions. In order to identify the species responsible for the changes in wettability, the surface products formed during oxidation have been identified by means of various surface analysis techniques, including X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). It has been found that pyrite oxidation creates a sulfur-rich surface along with iron oxides/hydroxides. The ratio between these hydrophobic and hydrophilic species correlates well with the results of the wettability measurements.
Date: March 18, 1992
Creator: Yoon, R.H.; Luttrell, G.H.; Zachwieja, J.B. & Mielczarski, J.A.
Partner: UNT Libraries Government Documents Department

Control of pyrite surface chemistry in physical coal cleaning

Description: Over the past 10 years, much research has provided convincing evidence that one major difficulty in using froth flotation to separate pyrite from coal is the self-induced'' flotation of pyrite. Numerous studies have attempted to identify reactions that occur under moderate oxidizing conditions, which lead to self-induced flotation, and to identify the oxidization products. During the past two report periods, it was established that: (1) freshly fractured pyrite surfaces immediately assume, at fracture, an electrode potential several hundred millivolts more negative than the usual steady state mixed potentials. Within minutes after fracture, the electrodes oxidize and reach higher steady state potentials. It was also shown, by photocurrent measurements, that a negative surface charge (upward band bending) already exists on freshly fractured pyrite, and (2) particle bed electrodes can be used to control the oxidation of pyrite and to precisely determine the electrochemical conditions where flotation occurs, or is depressed. By circulating the solution phase to an ultraviolet spectrometer, soluble products produced on pyrite by oxidation and reduction can be determined, e.g., HS[sup [minus]] was identified as a soluble cathodic reduction product. These and other studies have provided considerable information concerning the anodic oxidation of pyrite. Much less is known about the mechanism and kinetics of oxygen reduction, the other half of the mixed potential reaction. To better understand pyrite oxidation kinetics and determine if oxygen reduction is rate determining, studies have been conducted during this report period on the oxygen reduction reaction with pyrite. In addition, to provide further support that the potential of particle bed electrodes can be controlled, the electro-adsorption and desorption of an organic surfactant was studied.
Date: January 1, 1992
Creator: Yoon, R.H. & Richardson, P.R.
Partner: UNT Libraries Government Documents Department

Control of pyrite surface chemistry in physical coal cleaning. Technical progress report for the ninth quarter, September 1--November 30, 1991

Description: The separation of pyrite from coal by flotation is based on exploiting the wettability difference between coal and pyrite. There is evidence that the wettability of coal pyrite changes upon superficial oxidation. Therefore, the oxidation of coal pyrite has been studied under carefully controlled electrochemical conditions. In order to identify the species responsible for the changes in wettability, the surface products formed during oxidation have been identified by means of various surface analysis techniques, including X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). It has been found that pyrite oxidation creates a sulfur-rich surface along with iron oxides/hydroxides. The ratio between these hydrophobic and hydrophilic species correlates well with the results of the wettability measurements.
Date: March 18, 1992
Creator: Yoon, R. H.; Luttrell, G. H.; Zachwieja, J. B. & Mielczarski, J. A.
Partner: UNT Libraries Government Documents Department

Control of pyrite surface chemistry in physical coal cleaning. Twelfth quarterly technical progress report, June 1, 1992--August 31, 1992

Description: Over the past 10 years, much research has provided convincing evidence that one major difficulty in using froth flotation to separate pyrite from coal is the ``self-induced`` flotation of pyrite. Numerous studies have attempted to identify reactions that occur under moderate oxidizing conditions, which lead to self-induced flotation, and to identify the oxidization products. During the past two report periods, it was established that: (1) freshly fractured pyrite surfaces immediately assume, at fracture, an electrode potential several hundred millivolts more negative than the usual steady state mixed potentials. Within minutes after fracture, the electrodes oxidize and reach higher steady state potentials. It was also shown, by photocurrent measurements, that a negative surface charge (upward band bending) already exists on freshly fractured pyrite, and (2) particle bed electrodes can be used to control the oxidation of pyrite and to precisely determine the electrochemical conditions where flotation occurs, or is depressed. By circulating the solution phase to an ultraviolet spectrometer, soluble products produced on pyrite by oxidation and reduction can be determined, e.g., HS{sup {minus}} was identified as a soluble cathodic reduction product. These and other studies have provided considerable information concerning the anodic oxidation of pyrite. Much less is known about the mechanism and kinetics of oxygen reduction, the other half of the mixed potential reaction. To better understand pyrite oxidation kinetics and determine if oxygen reduction is rate determining, studies have been conducted during this report period on the oxygen reduction reaction with pyrite. In addition, to provide further support that the potential of particle bed electrodes can be controlled, the electro-adsorption and desorption of an organic surfactant was studied.
Date: December 31, 1992
Creator: Yoon, R. H. & Richardson, P. R.
Partner: UNT Libraries Government Documents Department

Control of pyrite surface chemistry in physical coal cleaning. Final report

Description: In Part I, Surface Chemistry of Coal Pyrite the mechanisms responsible for the inefficient rejection of coal pyrite were investigated using a number of experimental techniques. The test results demonstrate that the hydrophobicity of coal pyrite is related to the surface products formed during oxidation in aqueous solutions. During oxidation, a sulfur-rich surface layer is produced in near neutral pH solutions. This surface layer is composed mainly of sulfur species in the form of an iron-polysulfide along with a smaller amount of iron oxide/hydroxides. The floatability coal pyrite increases dramatically in the presence of frothers and hydrocarbon collectors. These reagents are believed to absorb on the weakly hydrophobic pyrite surfaces as a result of hydrophobic interaction forces. In Part III, Developing the Best Possible Rejection Schemes, a number of pyrite depressants were evaluated in column and conventional flotation tests. These included manganese (Mn) metal, chelating agents quinone and diethylenetriamine (DETA), and several commercially-available organic depressants. Of these, the additives which serve as reducing agents were found to be most effective. Reducing agents were used to prevent pyrite oxidation and/or remove oxidation products present on previously oxidized surfaces. These data show that Mn is a significantly stronger depressant for pyrite than quinone or DETA. Important factors in determining the pyrite depression effect of Mn include the slurry solid content during conditioning, the addition of acid (HCl), and the amount of Mn. The acid helps remove the oxide layer from the surface of Mn and promotes the depression of pyrite by Mn.
Date: May 19, 1993
Creator: Luttrell, G. H.; Yoon, R. H. & Richardson, P. E.
Partner: UNT Libraries Government Documents Department

Development of enhanced sulfur rejection processes. Second quarterly technical progress report, January 1, 1993--March 31, 1993

Description: Research at Virginia Tech led to the development of two complementary concepts for improving the removal of inorganic sulfur from many eastern US coals. These concepts are referred to as Electrochemically Enhanced Sulfur Rejection (EESR) and Polymer Enhanced Sulfur Rejection (PESR). The EESR process uses electrochemical techniques to suppress the formation of hydrophobic oxidation products believed to be responsible for the floatability of coal pyrite. The PESR process uses polymeric reagents that react with pyrite and convert floatable middlings, i.e., composite particles composed of pyrite with coal inclusions, into hydrophilic particles. These new pyritic-sulfur rejection processes do not require significant modifications to existing coal preparation facilities, thereby enhancing their adoptability by the coal industry. It is believed that these processes can be used simultaneously to maximize the rejection of both well-liberated pyrite and composite coal-pyrite particles. The technical research was initiated on October 1, 1992, and a detailed work plan and work schedule were developed. During this reporting period, research was conducted to evaluate the liberation characteristics of various pyrite samples, to determine the electrochemical reactions that influence the hydrophobicity of pyrite, and to examine the potential use of electrochemical methods for controlling the flotation and depression of pyrite.
Date: June 14, 1993
Creator: Yoon, R. H.; Luttrell, G.; Adel, G. & Richardson, P. E.
Partner: UNT Libraries Government Documents Department