東華大學圖書館 |

Effects of Solution Chemistry on Mn(II)-induced Structural Transformation of Birnessite.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Effects of Solution Chemistry on Mn(II)-induced Structural Transformation of Birnessite./
作者:	Yang, Peng.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
面頁冊數:	261 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-02, Section: B.
Contained By:	Dissertations Abstracts International81-02B.
標題:	Soil sciences. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13881122
ISBN:	9781085599511

Effects of Solution Chemistry on Mn(II)-induced Structural Transformation of Birnessite.
Yang, Peng.

Effects of Solution Chemistry on Mn(II)-induced Structural Transformation of Birnessite. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 261 p.

Source: Dissertations Abstracts International, Volume: 81-02, Section: B.

Thesis (Ph.D.)--University of Wyoming, 2019.

This item must not be sold to any third party vendors.

Hexagonal birnessite, the most common manganese (Mn) oxide in the natural environment, has extraordinary adsorption and oxidation capacities towards nutrients and metals because it has an open structure, structural defects, negative charges, and a small particle size. It is the primary and initial product of the biotic oxidation of divalent Mn (Mn(II)) and can transform to other Mn oxides such as other types of layered Mn oxides, tunneled Mn oxides, and low-valence Mn oxides. Owing to the different adsorption and oxidation capacities of diverse Mn oxide phases, the transformation of hexagonal birnessite to other Mn oxides highly affects the environmental behavior of Mn oxides towards the cycling of nutrients and metals. Recent studies showed that reactions with Mn(II) can drive hexagonal birnessite to transform to other Mn oxide phases, which has been deemed as an important driving force in the natural environment. However, the effects of solution chemistry, such as pH, O2 content, coexisting metal cations and anions, and the ratios of Mn(II) to birnessite, on the Mn(II)-induced transformation of hexagonal birnessite remain largely unknown. This dissertation studies the impacts of solution chemistry on the Mn(II)-induced structural transformation of hexagonal birnessite. Results show that solution chemistry greatly affects the transformation kinetics and products of hexagonal birnessite.Specifically, Mn(II) induces δ-MnO2 (an analogue to vernadite, a naturally occurring nanoparticulate hexagonal birnessite) to rapidly transform into a 4 x 4 tunneled Mn oxide in a 100-mM NaCl solution at room temperature and circumneutral pH (6 - 8). The transformation is promoted by a large number of Mn(III) produced on Mn vacancies through the comproportionation between vacancy-adsorbed Mn(II) and adjacent Mn(IV) in δ-MnO2. Triclinic birnessite is an intermediate product during the transformation, depending on pH conditions. Under anoxic conditions, pH 6 and 8 slow down the transformation due to the less Mn(III) produced (pH 6) and the formation of high crystalline triclinic birnessite (pH 8), respectively. The presence of O2 retards the transformation at pH 8 but accelerates the transformation at pH 6. pH 7 is the optimal pH for the transformation in both the presence and absence of O2. This finding challenges our previous understanding of the extremely slow transformation of layered Mn oxides to tunneled Mn oxides at room temperature and circumneutral pH and highlights the essential role of vacancy-adsorbed Mn(III) in the transformation.The transformation to 4 x 4 tunneled Mn oxide as occurring in NaCl solution also happens in solutions containing Li+ or K+ with triclinic birnessite as an intermediate product, except with different transformation rates and crystallinity of the products. In contrast, the presence of divalent metal cations, i.e., Mg2+ and Ca2+, favors the formation of triclinic birnessite but inhibits the transformation to tunneled Mn oxides. More strikingly, transition metal cation, Cu2+, greatly inhibits the formation of either triclinic birnessite or tunneled Mn oxides, thus preserving hexagonal birnessite. The different effects of metal cations on the transformation can be explained by their different binding strength (Cu2+ > Mg2+ and Ca2+ > Li+, Na+ and K+) to δ-MnO2. Their adsorption decreases the surface energy of δ-MnO2 and the decreased amount follows the same order. The reduced surface energy stabilizes layered Mn oxides, with Cu2+ having the strongest effect. Similarly, the presence of oxyanions, such as phosphate and silicate, retards the transformation of δ-MnO2 to both triclinic birnessite and tunneled Mn oxides, through their adsorption on δ-MnO2 surfaces. The transformation in seawater is similar to that in the Ca2+ system, forming poorly-crystalline triclinic birnessite at low Mn(II) to birnessite ratios. These observations explain why layered Mn oxides are dominant over tunneled Mn oxides in the natural environment although thermodynamically they are less stable than tunneled Mn oxides.At high Mn(II) to birnessite ratios, the transformation products are low-valence Mn oxides including hausmannite (Mn3O4), groutite (α-MnOOH), feitknechtite (β-MnOOH), manganite (γ-MnOOH), and δ-MnOOH. The transformation products are diverse at an Mn(II) to birnessite ratio of 0.5, mainly hausmannite and manganite at a ratio of 1.0, and mainly hausmannite at a ratio > 1.74. Higher ionic strength (controlled by NaCl and KCl) accelerates the transformation and enhances the crystallinity of the products. The transformation in seawater is slowed down and the morphology of hausmannite is changed from cubic/spherical to elliptical and the needles of MnOOH become shorter, especially at low Mn(II) to birnessite ratios. These observations are due to the strong interaction of Mg2+ and Ca2+ in seawater with the structure of primary particles of products, which interfere with the mineral transformation.These findings provide important implications for understanding the genesis of tunneled Mn oxides, the relationships of layered Mn oxides to others and their impacts on the cycling of trace metals in Mn-rich environments.

ISBN: 9781085599511Subjects--Topical Terms:

2122699
Soil sciences.

Effects of Solution Chemistry on Mn(II)-induced Structural Transformation of Birnessite.
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520 $a Hexagonal birnessite, the most common manganese (Mn) oxide in the natural environment, has extraordinary adsorption and oxidation capacities towards nutrients and metals because it has an open structure, structural defects, negative charges, and a small particle size. It is the primary and initial product of the biotic oxidation of divalent Mn (Mn(II)) and can transform to other Mn oxides such as other types of layered Mn oxides, tunneled Mn oxides, and low-valence Mn oxides. Owing to the different adsorption and oxidation capacities of diverse Mn oxide phases, the transformation of hexagonal birnessite to other Mn oxides highly affects the environmental behavior of Mn oxides towards the cycling of nutrients and metals. Recent studies showed that reactions with Mn(II) can drive hexagonal birnessite to transform to other Mn oxide phases, which has been deemed as an important driving force in the natural environment. However, the effects of solution chemistry, such as pH, O2 content, coexisting metal cations and anions, and the ratios of Mn(II) to birnessite, on the Mn(II)-induced transformation of hexagonal birnessite remain largely unknown. This dissertation studies the impacts of solution chemistry on the Mn(II)-induced structural transformation of hexagonal birnessite. Results show that solution chemistry greatly affects the transformation kinetics and products of hexagonal birnessite.Specifically, Mn(II) induces δ-MnO2 (an analogue to vernadite, a naturally occurring nanoparticulate hexagonal birnessite) to rapidly transform into a 4 x 4 tunneled Mn oxide in a 100-mM NaCl solution at room temperature and circumneutral pH (6 - 8). The transformation is promoted by a large number of Mn(III) produced on Mn vacancies through the comproportionation between vacancy-adsorbed Mn(II) and adjacent Mn(IV) in δ-MnO2. Triclinic birnessite is an intermediate product during the transformation, depending on pH conditions. Under anoxic conditions, pH 6 and 8 slow down the transformation due to the less Mn(III) produced (pH 6) and the formation of high crystalline triclinic birnessite (pH 8), respectively. The presence of O2 retards the transformation at pH 8 but accelerates the transformation at pH 6. pH 7 is the optimal pH for the transformation in both the presence and absence of O2. This finding challenges our previous understanding of the extremely slow transformation of layered Mn oxides to tunneled Mn oxides at room temperature and circumneutral pH and highlights the essential role of vacancy-adsorbed Mn(III) in the transformation.The transformation to 4 x 4 tunneled Mn oxide as occurring in NaCl solution also happens in solutions containing Li+ or K+ with triclinic birnessite as an intermediate product, except with different transformation rates and crystallinity of the products. In contrast, the presence of divalent metal cations, i.e., Mg2+ and Ca2+, favors the formation of triclinic birnessite but inhibits the transformation to tunneled Mn oxides. More strikingly, transition metal cation, Cu2+, greatly inhibits the formation of either triclinic birnessite or tunneled Mn oxides, thus preserving hexagonal birnessite. The different effects of metal cations on the transformation can be explained by their different binding strength (Cu2+ > Mg2+ and Ca2+ > Li+, Na+ and K+) to δ-MnO2. Their adsorption decreases the surface energy of δ-MnO2 and the decreased amount follows the same order. The reduced surface energy stabilizes layered Mn oxides, with Cu2+ having the strongest effect. Similarly, the presence of oxyanions, such as phosphate and silicate, retards the transformation of δ-MnO2 to both triclinic birnessite and tunneled Mn oxides, through their adsorption on δ-MnO2 surfaces. The transformation in seawater is similar to that in the Ca2+ system, forming poorly-crystalline triclinic birnessite at low Mn(II) to birnessite ratios. These observations explain why layered Mn oxides are dominant over tunneled Mn oxides in the natural environment although thermodynamically they are less stable than tunneled Mn oxides.At high Mn(II) to birnessite ratios, the transformation products are low-valence Mn oxides including hausmannite (Mn3O4), groutite (α-MnOOH), feitknechtite (β-MnOOH), manganite (γ-MnOOH), and δ-MnOOH. The transformation products are diverse at an Mn(II) to birnessite ratio of 0.5, mainly hausmannite and manganite at a ratio of 1.0, and mainly hausmannite at a ratio > 1.74. Higher ionic strength (controlled by NaCl and KCl) accelerates the transformation and enhances the crystallinity of the products. The transformation in seawater is slowed down and the morphology of hausmannite is changed from cubic/spherical to elliptical and the needles of MnOOH become shorter, especially at low Mn(II) to birnessite ratios. These observations are due to the strong interaction of Mg2+ and Ca2+ in seawater with the structure of primary particles of products, which interfere with the mineral transformation.These findings provide important implications for understanding the genesis of tunneled Mn oxides, the relationships of layered Mn oxides to others and their impacts on the cycling of trace metals in Mn-rich environments.
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