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Title: Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study

Abstract

Naturally occurring pyrite commonly contains minor substituted metals and metalloids (As, Se, Hg, Cu, Ni, etc.) that can be released to the environment as a result of its weathering. Arsenic, often the most abundant minor constituent in pyrite, is a sensitive monitor of progressive pyrite oxidation in coal. To test the effect of pyrite composition and environmental parameters on the rate and extent of pyrite oxidation in coal, splits of five bituminous coal samples having differing amounts of pyrite and extents of As substitution in the pyrite, were exposed to a range of simulated weathering conditions over a period of 17 months. Samples investigated include a Springfield coal from Indiana (whole coal pyritic S = 2.13 wt.%; As in pyrite = detection limit (d.l.) to 0.06 wt.%), two Pittsburgh coal samples from West Virginia (pyritic S = 1.32-1.58 wt.%; As in pyrite = d.l. to 0.34 wt.%), and two samples from the Warrior Basin, Alabama (pyritic S = 0.26-0.27 wt.%; As in pyrite = d.l. to 2.72 wt.%). Samples were collected from active mine faces, and expected differences in the concentration of As in pyrite were confirmed by electron microprobe analysis. Experimental weathering conditions in test chambers were maintained asmore » follows: (1) dry Ar atmosphere; (2) dry O{sub 2} atmosphere; (3) room atmosphere (relative humidity {approx}20-60%); and (4) room atmosphere with samples wetted periodically with double-distilled water. Sample splits were removed after one month, nine months, and 17 months to monitor the extent of As and Fe oxidation using As X-ray absorption near-edge structure (XANES) spectroscopy and {sup 57}Fe Mossbauer spectroscopy, respectively. Arsenic XANES spectroscopy shows progressive oxidation of pyritic As to arsenate, with wetted samples showing the most rapid oxidation. {sup 57}Fe Mossbauer spectroscopy also shows a much greater proportion of Fe{sup 3+} forms (jarosite, Fe{sup 3+} sulfate, FeOOH) for samples stored under wet conditions, but much less difference among samples stored under dry conditions in different atmospheres. The air-wet experiments show evidence of pyrite re-precipitation from soluble ferric sulfates, with As retention in the jarosite phase. Extents of As and Fe oxidation were similar for samples having differing As substitution in pyrite, suggesting that environmental conditions outweigh the composition and amount of pyrite as factors influencing the oxidation rate of Fe sulfides in coal.« less

Authors:
;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930388
Report Number(s):
BNL-81110-2008-JA
Journal ID: ISSN 0883-2927; APPGEY; TRN: US200904%%670
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Geochemistry; Journal Volume: 22; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; ABSORPTION; ALABAMA; ARSENIC; BITUMINOUS COAL; COAL; ELECTRON MICROPROBE ANALYSIS; HUMIDITY; INDIANA; MOESSBAUER EFFECT; OXIDATION; PITTSBURGH; PYRITE; SEMIMETALS; SENSITIVITY; SPECTROSCOPY; SULFATES; SULFIDES; WATER; WEATHERING; WEST VIRGINIA; national synchrotron light source

Citation Formats

Kolker,A., and Huggins, F. Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study. United States: N. p., 2007. Web. doi:10.1016/j.apgeochem.2006.10.006.
Kolker,A., & Huggins, F. Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study. United States. doi:10.1016/j.apgeochem.2006.10.006.
Kolker,A., and Huggins, F. Mon . "Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study". United States. doi:10.1016/j.apgeochem.2006.10.006.
@article{osti_930388,
title = {Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study},
author = {Kolker,A. and Huggins, F.},
abstractNote = {Naturally occurring pyrite commonly contains minor substituted metals and metalloids (As, Se, Hg, Cu, Ni, etc.) that can be released to the environment as a result of its weathering. Arsenic, often the most abundant minor constituent in pyrite, is a sensitive monitor of progressive pyrite oxidation in coal. To test the effect of pyrite composition and environmental parameters on the rate and extent of pyrite oxidation in coal, splits of five bituminous coal samples having differing amounts of pyrite and extents of As substitution in the pyrite, were exposed to a range of simulated weathering conditions over a period of 17 months. Samples investigated include a Springfield coal from Indiana (whole coal pyritic S = 2.13 wt.%; As in pyrite = detection limit (d.l.) to 0.06 wt.%), two Pittsburgh coal samples from West Virginia (pyritic S = 1.32-1.58 wt.%; As in pyrite = d.l. to 0.34 wt.%), and two samples from the Warrior Basin, Alabama (pyritic S = 0.26-0.27 wt.%; As in pyrite = d.l. to 2.72 wt.%). Samples were collected from active mine faces, and expected differences in the concentration of As in pyrite were confirmed by electron microprobe analysis. Experimental weathering conditions in test chambers were maintained as follows: (1) dry Ar atmosphere; (2) dry O{sub 2} atmosphere; (3) room atmosphere (relative humidity {approx}20-60%); and (4) room atmosphere with samples wetted periodically with double-distilled water. Sample splits were removed after one month, nine months, and 17 months to monitor the extent of As and Fe oxidation using As X-ray absorption near-edge structure (XANES) spectroscopy and {sup 57}Fe Mossbauer spectroscopy, respectively. Arsenic XANES spectroscopy shows progressive oxidation of pyritic As to arsenate, with wetted samples showing the most rapid oxidation. {sup 57}Fe Mossbauer spectroscopy also shows a much greater proportion of Fe{sup 3+} forms (jarosite, Fe{sup 3+} sulfate, FeOOH) for samples stored under wet conditions, but much less difference among samples stored under dry conditions in different atmospheres. The air-wet experiments show evidence of pyrite re-precipitation from soluble ferric sulfates, with As retention in the jarosite phase. Extents of As and Fe oxidation were similar for samples having differing As substitution in pyrite, suggesting that environmental conditions outweigh the composition and amount of pyrite as factors influencing the oxidation rate of Fe sulfides in coal.},
doi = {10.1016/j.apgeochem.2006.10.006},
journal = {Applied Geochemistry},
number = 4,
volume = 22,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Pyrite was oxidized under {sup 18}O{sub 2} gas in H{sub 2}{sup 16}O solutions, with and without added ferric ion, and the sulfate produced was analysed by vibrational spectroscopy to determine the relative amounts of sulfate isotopomers (S{sup 16}O{sub n}{sup 18}O{sub 4{minus}n}{sup 2{minus}}) formed. At 70C and pH 1, with no added Fe{sup 3+}, the majority of the sulfate formed was that which derived all four oxygen atoms from water (i.e., S{sup 16}O{sub 4}{sup 2{minus}}), but significant amounts of two other isotopomers, S{sup 16}O{sub 3}{sup 18}O{sup 2{minus}} and S{sup 16}O{sub 2}{sup 18}O{sub 2}{sup 2{minus}}, which derive one or two oxygen atomsmore » from molecular oxygen were observed. When Fe{sup 3+} was added at the start under identical conditions, no S{sup 16}O{sub 2}{sup 18}O{sub 2}{sup 2{minus}} was observed. The major isotopomer formed was still S{sup 16}O{sub 4}{sup 2{minus}}, with S{sup 16}O{sub 3}{sup 18}O{sup 2{minus}} present as a minor product. Experiments which were performed at initial pH 7 yielded similar results, as did others performed at 20C, although the amounts of the minor isotopomers fromed vary with temperature. All of the results were confirmed by performing identical experiments with the source of the oxygen isotopes reversed, that is, by oxidixing pyrite under air in H{sub 2}{sup 18}O solutions and obtaining the same products in isotopic reverse.« less
  • In the first known kinetic application of the technique, synchrotron 57Fe-Mossbauer spectroscopy was used to follow the rate of heterogeneous electron transfer between aqueous reagents and a solid phase containing Fe. The solid, a synthetic 57Fe-enriched Fe(III)-bearing pyroaurite-like phase having terephthalate (TA) in the interlayer[Mg3Fe(OH)8(TA)0.5 2H2O], was reduced by Na2S2O4 and then re-oxidized by K2Cr2O7 using a novel flow-through cell. Synchrotron Mossbauer spectra were collected in the time domain at 30-s intervals. Integration of the intensity obtained during a selected time interval in the spectra allowed sensitive determination of Fe(II) content as a function of reaction time. Analysis of reactionmore » end member specimens by both the synchrotron technique and conventional Mossbauer spectroscopy yielded comparable values for Mossbauer parameters such as center shift and Fe(II)/Fe(III) area ratios. Slight differences in quadrupole splitting values were observed, however. A reactive diffusion model was developed that fit the experimental Fe(II) kinetic data well and allowed the extraction of second-order rate constants for each reaction. Thus, in addition to rapidly collecting high quality Mossbauer data, the synchrotron technique seems well-suited for aqueous rate experiments due to the penetrating power of 14.4 keV X-rays and high sensitivity to Fe valence state.« less
  • No abstract prepared.
  • One of the cost-effective mercury control technologies in coal-fired power plants is the enhanced oxidation of elemental mercury in selective catalytic reduction (SCR) followed by the capture of the oxidized mercury in the wet scrubber. This paper is the first in a series of two in which the validation of the SCR slipstream test and Hg speciation variation in runs with or without SCR catalysts inside the SCR slipstream reactor under special gas additions (HCl, Cl{sub 2}, SO{sub 2}, and SO{sub 3}) are presented. Tests indicate that the use of a catalyst in a SCR slipstream reactor can achieve greatermore » than 90% NO reduction efficiency with a NH{sub 3}/NO ratio of about 1. There is no evidence to show that the reactor material affects mercury speciation. Both SCR catalysts used in this study exhibited a catalytic effect on the elemental mercury oxidation but had no apparent adsorption effect. SCR catalyst 2 seemed more sensitive to the operational temperature. The spike gas tests indicated that HCl can promote Hg{sup 0} oxidation but not Cl{sub 2}. The effect of Cl{sub 2} on mercury oxidation may be inhibited by higher concentrations of SO{sub 2}, NO, or H{sub 2}O in real flue-gas atmospheres within the typical SCR temperature range (300-350{sup o}C). SO{sub 2} seemed to inhibit mercury oxidation; however, SO{sub 3} may have some effect on the promotion of mercury oxidation in runs with or without SCR catalysts. 25 refs., 9 figs., 2 tabs.« less