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Controlling Of Incipient Oxidation Of Pyrite For Improved Rejection Sixth Quarterly Technical Progress Report January 1 1994 March 31 1994
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Book Synopsis Controlling of Incipient Oxidation of Pyrite for Improved Rejection. Sixth Quarterly Technical Progress Report, January 1, 1994--March 31, 1994 by :
Download or read book Controlling of Incipient Oxidation of Pyrite for Improved Rejection. Sixth Quarterly Technical Progress Report, January 1, 1994--March 31, 1994 written by and published by . This book was released on 1994 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The major objectives of this work are (1) to determine the Eh-pH conditions under which pyrite is stable, (2) to determine the mechanism of the initial stages of pyrite oxidation, and (3) to determine if the semiconducting properties of pyrite affect its oxidation behavior. It is known that moderate oxidation of pyrite produces a hydrophobic surface product. This hydrophobic product makes it extremely difficult to depress pyrite in coal flotation circuits. The eventual objective of this work is to prevent pyrite oxidation in order to better depress pyrite in coal flotation circuits. In this work clean, unoxidized pyrite surfaces are being produced by fracturing pyrite electrodes in an electrochemical cell. It has been shown that by holding the potential at different values during fracture and measuring the current passed at fracture, pyrite oxidation or reduction can be precisely controlled, or prevented. It has also been found that fresh pyrite surfaces, created by fracture in an electrochemical cell, begin to oxidize at potentials that are about 200 mV more negative than the potentials reported in the literature for pyrite oxidation. This is attributed to the fact that most work on pyrite has employed polished electrodes that have preexisting oxidation products on the surface. Electrochemical reduction and oxidation of these preexisting products essentially mask the oxidation of pyrite itselL In addition, photocurrent measurements show that freshly-fractured pyrite surfaces are charged negatively. This negative charge is believed to result from an intrinsic, acceptor-like surface state. This report period, voltammetric and photocurrent studies have been carried out as a function of pH and the photoresponse of pyrites from different sources have been determined.
Book Synopsis Controlling Incipient Oxidation of Pyrite for Improved Rejection. Eighth Quarterly Technical Progress Report, July 1, 1994-September 30, 1994 by :
Download or read book Controlling Incipient Oxidation of Pyrite for Improved Rejection. Eighth Quarterly Technical Progress Report, July 1, 1994-September 30, 1994 written by and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Controlling Incipient Oxidation of Pyrite for Improved Rejection. Technical Progress Report for the Ninth Quarter, October 1-December 31, 1994 by :
Download or read book Controlling Incipient Oxidation of Pyrite for Improved Rejection. Technical Progress Report for the Ninth Quarter, October 1-December 31, 1994 written by and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Research Abstracts written by and published by . This book was released on 1995 with total page 782 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Studies of Incipient Oxidation of Pyrite for Improved Rejection. Fifth Quarterly Technical Progress Report, October 1, 1993--December 31, 1993 by :
Download or read book Studies of Incipient Oxidation of Pyrite for Improved Rejection. Fifth Quarterly Technical Progress Report, October 1, 1993--December 31, 1993 written by and published by . This book was released on 1993 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxidation of fresh surfaces of coal- and mineral-pyrite has been studied using electrochemical and photoelectrochemical techniques. This work was undertaken to better understand the oxidation processes that cause self-induced flotation of pyrite. Fresh surfaces were created by fracturing pyrite in situ, i.e., in solution. Chronoamperometry was used to determine the potential at which a newly created surface does not show oxidation or reduction currents. The ''stable'' potentials for pyrite are -0.28 V (SHE) at pH 9.2 and 0 V at pH 4.6. Subsequent cyclic voltammograms show the incipient oxidation mechanism that involves the formation of sulfur products, which are believed to be hydrophobic. It is shown that the lower flotation edge of pyrite coincides with its incipient oxidation potential. The photocurrent generated at fractured pyrite surfaces by chopped illumination was used to determine the semiconducting characteristics of the electrodes. The results indicate that a spontaneous depletion layer is formed on the fresh surfaces of n-type pyrite. The depletion layer is attributed to an intrinsic, acceptor-like surface state. Charge storage in this surface state pins the band edges over a wide potential range, accounting for the metallic-like electrochemical behavior that has been reported for pyrite. The existence of an intrinsic surface state is consistent with XPS studies on pyrite surfaces prepared in vacuum, which reveal an FeS-like species in the surface region. During this report period, all of the data previously obtained has been analyzed in an attempt to better understand the mechanism of pyrite flotation with respect to its oxidation. The results of this analysis are included in this quarterly report. In addition, samples of pyrite from seven different sources were obtained. In situ fracture, photoelectrochemical and cyclic voltammetry studies have been conducted on electrodes made from these pyrites.
Book Synopsis The Rich Photographic Legacy of Edward Curtis by :
Download or read book The Rich Photographic Legacy of Edward Curtis written by and published by . This book was released on 1972 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Studies of Incipient Oxidation of Pyrite for Improved Rejection: Technical Progress Report, July 1, 1993 to September 30, 1993 by :
Download or read book Studies of Incipient Oxidation of Pyrite for Improved Rejection: Technical Progress Report, July 1, 1993 to September 30, 1993 written by and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Studies of Incipient Oxidation of Coal-pyrite for Improved Pyrite Rejection. First Quarterly Technical Progress Report, October 1, 1992--December 31, 1992 by :
Download or read book Studies of Incipient Oxidation of Coal-pyrite for Improved Pyrite Rejection. First Quarterly Technical Progress Report, October 1, 1992--December 31, 1992 written by and published by . This book was released on 1992 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to foster the development of advanced coal cleaning technologies fundamental studies.of the initial stages of pyrite oxidation have been.initiated. This work is being done on pyrite surfaces that are freshly fractured in an electrolyte solution. This procedure produces surfaces that are initially unoxidized, allowing the subsequent oxidation processes to be studied in detail. It is shown that freshly fractured pyrite electrodes instantaneously (at fracture) assume a rest potential several hundred millivolts more negative than the usual open-circuit potential. A finite, anodic photocurrent, is also observed on the fractured electrodes. Following cleavage, the rest potential increases, indicating an oxidation reaction occurring on the electrodes. The photocurrent is relatively insensitive to this oxidation process, and to moderate anodic and cathodic polarization. However, strong cathodic polarization to about -0.76 V (SHE) at pH 9.2 causes the photocurrent to decrease to zero. No reversal in the sign of the photocurrent is observed and it is believed that the flat band potential occurs near -0.76 V, i.e., where the photocurrent goes to zero. Voltammetry indicates that pyrite also undergoes cathodic decomposition at -0.76 V. This establishes that pyrite must be cathodically decomposed to reach the flat band potential.
Book Synopsis Controlling of Incipient Oxidation of Pyrite for Improved Rejection by :
Download or read book Controlling of Incipient Oxidation of Pyrite for Improved Rejection written by and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Government Reports Announcements & Index by :
Download or read book Government Reports Announcements & Index written by and published by . This book was released on 1995 with total page 622 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Development of Enhanced Sulfur Rejection Processes. Second Quarterly Technical Progress Report, January 1, 1993--March 31, 1993 by :
Download or read book Development of Enhanced Sulfur Rejection Processes. Second Quarterly Technical Progress Report, January 1, 1993--March 31, 1993 written by and published by . This book was released on 1993 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Pyrite Oxidation and Its Control by : V. P. Evangelou
Download or read book Pyrite Oxidation and Its Control written by V. P. Evangelou and published by CRC Press. This book was released on 2018-04-27 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pyrite Oxidation and its Control is the single available text on the market that presents the latest findings on pyrite oxidation and acid mine drainage (AMD). This new information is an indispensable reference for generating new concepts and technologies for controlling pyrite oxidation. This book focuses on pyrite oxidation theory, experimental findings on oxidation mechanisms, as well as applications and limitations of amelioration technologies. The text also includes discussions on the theory and potential application of novel pyrite microencapsulation technologies for controlling pyrite oxidation currently under investigation in the author's laboratory.
Book Synopsis Controlling Incipent Oxidation of Pyrite for Improved Rejection. Final Report by :
Download or read book Controlling Incipent Oxidation of Pyrite for Improved Rejection. Final Report written by and published by . This book was released on 1996 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Development of Enhanced Sulfur Rejection Processes. Final Technical Progress Report, Third Quarter (8. Quarterly Report), July 1--September 30, 1994 by :
Download or read book Development of Enhanced Sulfur Rejection Processes. Final Technical Progress Report, Third Quarter (8. Quarterly Report), July 1--September 30, 1994 written by and published by . This book was released on 1996 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Government Reports Annual Index by :
Download or read book Government Reports Annual Index written by and published by . This book was released on 1994 with total page 1220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Oxidation of Coal and Coal Pyrite Mechanisms and Influence on Surface Characteristics. Quarterly Technical Progress Report, December 1, 1993--May 31, 1994 by :
Download or read book Oxidation of Coal and Coal Pyrite Mechanisms and Influence on Surface Characteristics. Quarterly Technical Progress Report, December 1, 1993--May 31, 1994 written by and published by . This book was released on 1996 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical cleaning processes. The results will provide fundamental insight into oxidation, in term of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the fourteenth and fifteenth quarters, flotation tests were done on Upper Freeport coal from the Troutville No. 2 Mine, Clearfield County, Pennsylvania and on coal samples from the Pennsylvania State Coal Bank. The influence of electrode potential on the surface properties of coal pyrite was tested using contact angle measurements on polarized Pittsburgh coal pyrite electrode.
Book Synopsis Pyrite Surface Characterization and Control for Advanced Fine Coal Desulfurization Technologies. Tenth Quarterly Technical Progress Report, January 1, 1993--March 31, 1993 by :
Download or read book Pyrite Surface Characterization and Control for Advanced Fine Coal Desulfurization Technologies. Tenth Quarterly Technical Progress Report, January 1, 1993--March 31, 1993 written by and published by . This book was released on 1993 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the project is to conduct extensive fundamental studies on the surface chemistry of pyrite oxidation and flotation and to understand how the alteration of the coal-pyrite surface affects the efficiency of pyrite rejection in coal flotation. This report summarizes the studies in the following three aspects: (1) the effects of borate, used as pH buffer or electrolyte, on the pyrite surface oxidation and flotation; (2) the quantification of pyrite surface oxidation kinetics under different oxidation potentials; and (3) finding new coal-pyrite depressants. It has been demonstrated, for the first time, that borate, a pH buffer and electrolyte used by many previous investigators in studying pyrite oxidation, actively participates in the surface oxidation of pyrite. In high borate concentration solutions, the surface oxidation of pyrite is strongly enhanced. The anodic oxidation potential of pyrite is lowered by more than 0.4 volts. At low borate concentration, borate is chemisorbed on pyrite surfaces. In the intermediate concentration range, borate dissolves surface iron compounds. Consequently, the flotation of pyrite in borate solutions (using fuel oil as collector) displays depression-flotation-depression phenomena as the borate concentration is increased. The oxidation kinetics of pyrite surfaces has been determined by AC impedance spectroscopy. At low oxidation potentials, only capacitive behavior is observed. However, at high oxidation potentials, an inductive loop appears. The charge transfer resistance decreases with increasing potential, indicating that the oxidation rate increases with increasing potential. A chemical reagent has been found to be very effective in depressing the flotation of coal-pyrites from different sources, while it has little effects on the flotation of coal. The surface chemistry involved in the selective pyrite depression by this new reagent has been investigated by electrochemical studies and contact angle measurements.
