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The Impact of Small Organic Acids on Iron and Manganese Mineral Transformations and the Fate of Trace Metals.

Record Type:	Electronic resources : Monograph/item
Title/Author:	The Impact of Small Organic Acids on Iron and Manganese Mineral Transformations and the Fate of Trace Metals./
Author:	Flynn, Elaine Denise.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
Description:	161 p.
Notes:	Source: Dissertations Abstracts International, Volume: 79-12, Section: B.
Contained By:	Dissertations Abstracts International79-12B.
Subject:	Geochemistry. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10792833
ISBN:	9780355858778

The Impact of Small Organic Acids on Iron and Manganese Mineral Transformations and the Fate of Trace Metals.
Flynn, Elaine Denise.

The Impact of Small Organic Acids on Iron and Manganese Mineral Transformations and the Fate of Trace Metals. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 161 p.

Source: Dissertations Abstracts International, Volume: 79-12, Section: B.

Thesis (Ph.D.)--Washington University in St. Louis, 2018.

This item is not available from ProQuest Dissertations & Theses.

Iron and manganese oxides are ubiquitous in soils and sediments and play a critical role in the geochemical distribution of trace elements and heavy metals through adsorption and coprecipitation. At redox interfaces, biogeochemical processes generate conditions with coexisting dissolved Fe(II) and solid-phase Fe(III). In such systems, Fe(II) induces the recrystallization of iron oxides through coupled mineral growth and dissolution due to electron transfer as oxidative adsorption of Fe(II) and reductive dissolution of Fe(III) occur. Aqueous Mn(II) adsorption onto Mn(III/IV) oxides also likely involves oxidation although likely through different mechanisms than that of the Fe system because of the potential for Mn(II)-Mn(IV) comproportionation reactions. During reactions between reduced and oxidized forms of Fe and Mn, trace metals may be redistributed among the mineral bulk, mineral surface, and aqueous solution. Many metals, including Ni and Zn, are important micronutrients but are also toxic at higher concentrations. It is important to identify the processes controlling the fate and availability of trace metals in the environment and this requires understanding the behavior and stability of Fe and Mn oxides. Small organic acids, produced as root exudates or by decomposition of organic matter in aerated soils, may potentially alter reactions involving Fe and Mn oxide minerals and trace metals through a series of cooperative or competitive processes: solution complexation, ternary surface complexation, surface site competition, ligand-promoted dissolution, and reductive dissolution. The effects of organic acids on trace metal fate in such systems is unclear because these processes may involve both trace metals and Fe or Mn oxides, and multiple processes may co-occur. The main objective of this dissertation is to determine how organic acids interacting with Fe and Mn oxides affect structural transformations of these minerals, including dissolution and recrystallization, and the resulting impact on trace metals micronutrient and contaminant fate. Three main research projects were conducted to meet this objective. First, the cooperative and competitive interactions between oxalate and Ni during adsorption to Fe oxide minerals were identified. Next, the effects of oxalate on Ni incorporation into and release from Fe oxides at pH 4 and 7 was investigated during Fe(II)-promoted recrystallization of these minerals. Finally, reductive transformations of layered Mn oxides by oxalate, citrate, and 4-hydroxybenzoate at pH 4, 5.5, and 7 were characterized as well as the associated changes in Ni and Zn adsorption extent and mechanisms. The addition of oxalate in macroscopic adsorption studies suppresses Ni uptake by goethite and hematite at pH 7. Aqueous speciation modelling indicates that this is dominantly the result of oxalate complexing and solubilizing Ni. Comparison of the Ni surface coverage to the concentration of free (uncomplexed) Ni2+ in solution suggests that oxalate also alters Ni adsorption affinity. Extended X-ray absorption fine structure and attenuated total reflectance Fourier transform infrared spectroscopies indicate that these changes in binding affinity are due to the formation of Ni-oxalate ternary surface complexes. When Ni is initially structurally-incorporated into hematite and goethite, oxalate and dissolved Fe(II) each promote the release of Ni to aqueous solution at pH 4 and 7. With the co-addition of both species, the effects on Ni release are synergistic at pH 7 but inhibitory at pH 4. This suggests that cooperative and competitive interactions vary with pH. In contrast, oxalate suppresses Ni incorporation into goethite and hematite during Fe(II)-induced recrystallization. Mn oxides may undergo redox and structural changes which can weaken trace metal binding and promote metal mobility. The conditions studied to date involve Mn(II) and are most similar to those found at redox interfaces which are limited in spatial extent in nature. Aging δ-MnO2 and hexagonal birnessite in the presence of small organic acids was investigated using powder X-ray diffraction and X-ray absorption fine structure spectroscopic measurements. Organic acids caused partial Mn reduction but did not substantially alter the phyllomanganates sheet structure nor result in transformations to Mn(III) oxyhydroxides or mixed-valent minerals. All organic acids were fully consumed, producing solid-phase Mn(II) and Mn(III) as well as dissolved Mn(II), the latter favored under acidic pH conditions. Citrate caused the greatest reduction, with its oxidation products continuing to react and near-complete mineralization observed at pH 4. These redox reactions improved stacking of the phyllomanganate sheets for δ-MnO2 at pH 7 and enhanced capping of vacancy sites by cations occurred for both minerals under all conditions studied. As a result of this mineral alteration, Ni and Zn adsorption behaviors were also modified. Net metal uptake did not change substantially at pH 7 where nearly all of the Ni and Zn in the system were adsorbed to the mineral surface. (Abstract shortened by ProQuest.).

ISBN: 9780355858778Subjects--Topical Terms:

539092
Geochemistry.
Subjects--Index Terms:

Adsorption

The Impact of Small Organic Acids on Iron and Manganese Mineral Transformations and the Fate of Trace Metals.
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245 1 4 $a The Impact of Small Organic Acids on Iron and Manganese Mineral Transformations and the Fate of Trace Metals.
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300 $a 161 p.
500 $a Source: Dissertations Abstracts International, Volume: 79-12, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Catalano, Jeffrey G.
502 $a Thesis (Ph.D.)--Washington University in St. Louis, 2018.
506 $a This item is not available from ProQuest Dissertations & Theses.
506 $a This item must not be sold to any third party vendors.
520 $a Iron and manganese oxides are ubiquitous in soils and sediments and play a critical role in the geochemical distribution of trace elements and heavy metals through adsorption and coprecipitation. At redox interfaces, biogeochemical processes generate conditions with coexisting dissolved Fe(II) and solid-phase Fe(III). In such systems, Fe(II) induces the recrystallization of iron oxides through coupled mineral growth and dissolution due to electron transfer as oxidative adsorption of Fe(II) and reductive dissolution of Fe(III) occur. Aqueous Mn(II) adsorption onto Mn(III/IV) oxides also likely involves oxidation although likely through different mechanisms than that of the Fe system because of the potential for Mn(II)-Mn(IV) comproportionation reactions. During reactions between reduced and oxidized forms of Fe and Mn, trace metals may be redistributed among the mineral bulk, mineral surface, and aqueous solution. Many metals, including Ni and Zn, are important micronutrients but are also toxic at higher concentrations. It is important to identify the processes controlling the fate and availability of trace metals in the environment and this requires understanding the behavior and stability of Fe and Mn oxides. Small organic acids, produced as root exudates or by decomposition of organic matter in aerated soils, may potentially alter reactions involving Fe and Mn oxide minerals and trace metals through a series of cooperative or competitive processes: solution complexation, ternary surface complexation, surface site competition, ligand-promoted dissolution, and reductive dissolution. The effects of organic acids on trace metal fate in such systems is unclear because these processes may involve both trace metals and Fe or Mn oxides, and multiple processes may co-occur. The main objective of this dissertation is to determine how organic acids interacting with Fe and Mn oxides affect structural transformations of these minerals, including dissolution and recrystallization, and the resulting impact on trace metals micronutrient and contaminant fate. Three main research projects were conducted to meet this objective. First, the cooperative and competitive interactions between oxalate and Ni during adsorption to Fe oxide minerals were identified. Next, the effects of oxalate on Ni incorporation into and release from Fe oxides at pH 4 and 7 was investigated during Fe(II)-promoted recrystallization of these minerals. Finally, reductive transformations of layered Mn oxides by oxalate, citrate, and 4-hydroxybenzoate at pH 4, 5.5, and 7 were characterized as well as the associated changes in Ni and Zn adsorption extent and mechanisms. The addition of oxalate in macroscopic adsorption studies suppresses Ni uptake by goethite and hematite at pH 7. Aqueous speciation modelling indicates that this is dominantly the result of oxalate complexing and solubilizing Ni. Comparison of the Ni surface coverage to the concentration of free (uncomplexed) Ni2+ in solution suggests that oxalate also alters Ni adsorption affinity. Extended X-ray absorption fine structure and attenuated total reflectance Fourier transform infrared spectroscopies indicate that these changes in binding affinity are due to the formation of Ni-oxalate ternary surface complexes. When Ni is initially structurally-incorporated into hematite and goethite, oxalate and dissolved Fe(II) each promote the release of Ni to aqueous solution at pH 4 and 7. With the co-addition of both species, the effects on Ni release are synergistic at pH 7 but inhibitory at pH 4. This suggests that cooperative and competitive interactions vary with pH. In contrast, oxalate suppresses Ni incorporation into goethite and hematite during Fe(II)-induced recrystallization. Mn oxides may undergo redox and structural changes which can weaken trace metal binding and promote metal mobility. The conditions studied to date involve Mn(II) and are most similar to those found at redox interfaces which are limited in spatial extent in nature. Aging δ-MnO2 and hexagonal birnessite in the presence of small organic acids was investigated using powder X-ray diffraction and X-ray absorption fine structure spectroscopic measurements. Organic acids caused partial Mn reduction but did not substantially alter the phyllomanganates sheet structure nor result in transformations to Mn(III) oxyhydroxides or mixed-valent minerals. All organic acids were fully consumed, producing solid-phase Mn(II) and Mn(III) as well as dissolved Mn(II), the latter favored under acidic pH conditions. Citrate caused the greatest reduction, with its oxidation products continuing to react and near-complete mineralization observed at pH 4. These redox reactions improved stacking of the phyllomanganate sheets for δ-MnO2 at pH 7 and enhanced capping of vacancy sites by cations occurred for both minerals under all conditions studied. As a result of this mineral alteration, Ni and Zn adsorption behaviors were also modified. Net metal uptake did not change substantially at pH 7 where nearly all of the Ni and Zn in the system were adsorbed to the mineral surface. (Abstract shortened by ProQuest.).
590 $a School code: 0252.
650 4 $a Geochemistry. $3 539092
653 $a Adsorption
653 $a Iron oxide
653 $a Manganese oxide
653 $a Mineral transformations
653 $a Organic acids
653 $a Trace metals
690 $a 0996
710 2 $a Washington University in St. Louis. $b Earth & Planetary Sciences. $3 3437717
773 0 $t Dissertations Abstracts International $g 79-12B.
790 $a 0252
791 $a Ph.D.
792 $a 2018
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10792833

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