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Oxidation and sorption kinetics of a...

Lafferty, Brandon J.

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Oxidation and sorption kinetics of arsenic on a poorly crystalline manganese oxide.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Oxidation and sorption kinetics of arsenic on a poorly crystalline manganese oxide./
Author:	Lafferty, Brandon J.
Description:	126 p.
Notes:	Source: Dissertation Abstracts International, Volume: 71-11, Section: B, page: 6507.
Contained By:	Dissertation Abstracts International71-11B.
Subject:	Agriculture, Soil Science. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3423341
ISBN:	9781124240930

Oxidation and sorption kinetics of arsenic on a poorly crystalline manganese oxide.
Lafferty, Brandon J.

Oxidation and sorption kinetics of arsenic on a poorly crystalline manganese oxide. - 126 p.

Source: Dissertation Abstracts International, Volume: 71-11, Section: B, page: 6507.

Thesis (Ph.D.)--University of Delaware, 2010.

Manganese oxides (Mn-oxides) are some of the most reactive minerals in the environment, and are known to readily oxidize toxic arsenite (AsIII) to less toxic arsenate (AsV). However, AsIII oxidation by Mn-oxides can be quite complex, involving many simultaneous reactions. Also, when AsIII is oxidized by Mn-oxides, a reduction in the oxidation rate is often observed, which has been attributed to Mn-oxide surface passivation. Although AsIII oxidation by Mn-oxides has been studied, fundamental understanding of the mechanisms of AsIII oxidation, and subsequent Mn-oxide passivation by poorly crystalline, layered Mn-oxides (i.e. phyllomanganates), is lacking. In stirred-flow experiments, AsIII oxidation by delta-MnO 2 (a poorly crystalline phyllomanganate) is initially rapid but slows appreciably as the mineral surface became passivated. MnII is the only reduced product of AsIII oxidation by delta-MnO 2 during the initial period of the reaction, indicating that As III oxidation does not proceed through a MnIII intermediate. Also, X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) show that MnII sorption is the primary cause of delta-MnO 2 passivation during the early periods of AsIII oxidation. There is also evidence that formation of MnIII observed in previous studies is a result of conproportionation of MnII sorbed onto MnIV reaction sites of delta-MnO2. It is possible that MnIII formed through MnII/IV conproportionation also plays a role in delta-MnO2 passivation. Only AsV is observed bound to delta-MnO2 during AsIII oxidation, and it is present in several adsorption complexes that change as the MnIII content in delta-MnO2 increases. Although AsV is directly bound to the delta-MnO 2 surface, a significant fraction is quite mobile. These findings show that AsIII oxidation by poorly crystalline delta-MnO 2 involves several simultaneous reactions and emphasizes the importance of Mn oxidation state in the reactivity of Mn-oxides. Also demonstrated is the value of studying reaction mechanisms over a range of time scales.

ISBN: 9781124240930Subjects--Topical Terms:

1017824
Agriculture, Soil Science.

Oxidation and sorption kinetics of arsenic on a poorly crystalline manganese oxide.
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100 1 $a Lafferty, Brandon J. $3 1678662
245 1 0 $a Oxidation and sorption kinetics of arsenic on a poorly crystalline manganese oxide.
300 $a 126 p.
500 $a Source: Dissertation Abstracts International, Volume: 71-11, Section: B, page: 6507.
500 $a Adviser: Donald L. Sparks.
502 $a Thesis (Ph.D.)--University of Delaware, 2010.
520 $a Manganese oxides (Mn-oxides) are some of the most reactive minerals in the environment, and are known to readily oxidize toxic arsenite (AsIII) to less toxic arsenate (AsV). However, AsIII oxidation by Mn-oxides can be quite complex, involving many simultaneous reactions. Also, when AsIII is oxidized by Mn-oxides, a reduction in the oxidation rate is often observed, which has been attributed to Mn-oxide surface passivation. Although AsIII oxidation by Mn-oxides has been studied, fundamental understanding of the mechanisms of AsIII oxidation, and subsequent Mn-oxide passivation by poorly crystalline, layered Mn-oxides (i.e. phyllomanganates), is lacking. In stirred-flow experiments, AsIII oxidation by delta-MnO 2 (a poorly crystalline phyllomanganate) is initially rapid but slows appreciably as the mineral surface became passivated. MnII is the only reduced product of AsIII oxidation by delta-MnO 2 during the initial period of the reaction, indicating that As III oxidation does not proceed through a MnIII intermediate. Also, X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) show that MnII sorption is the primary cause of delta-MnO 2 passivation during the early periods of AsIII oxidation. There is also evidence that formation of MnIII observed in previous studies is a result of conproportionation of MnII sorbed onto MnIV reaction sites of delta-MnO2. It is possible that MnIII formed through MnII/IV conproportionation also plays a role in delta-MnO2 passivation. Only AsV is observed bound to delta-MnO2 during AsIII oxidation, and it is present in several adsorption complexes that change as the MnIII content in delta-MnO2 increases. Although AsV is directly bound to the delta-MnO 2 surface, a significant fraction is quite mobile. These findings show that AsIII oxidation by poorly crystalline delta-MnO 2 involves several simultaneous reactions and emphasizes the importance of Mn oxidation state in the reactivity of Mn-oxides. Also demonstrated is the value of studying reaction mechanisms over a range of time scales.
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710 2 $a University of Delaware. $b Department of Plant and Soil Science. $3 1021010
773 0 $t Dissertation Abstracts International $g 71-11B.
790 1 0 $a Sparks, Donald L., $e advisor
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