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Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems.

Gao T, Shen Y, Jia Z, Qiu G, Liu F, Zhang Y, Feng X, Cai C - Geochem. Trans. (2015)

Bottom Line: The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite.The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days.The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan, 430070 People's Republic of China.

ABSTRACT

Background: In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated.

Results: To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn(2+) and K(+) ions, a significant decrease in Fe(2+) concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30 days. Fe(2+) exhibited much higher catalytic activity than Mn(2+) during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn(2+) were compared to estimate the redox rates of birnessite and Fe(2+) under different conditions.

Conclusions: Redox rate was found to be controlled by chemical reaction, and increased with increasing Fe(2+) concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined effects of manganese oxide and air on the transformation of Fe(2+) to ferric oxides. Graphical abstract:Lepidocrocite and goethite were formed during the interaction of ferrous ion and birnessite at pH 4-7. Redox rate was controlled by the adsorption of Fe2+ on the surface of birnessite. The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

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The concentration of Fe2+, Mn2+and K+ in reaction system of 20 mM Fe2+oxidized by 1.0 g L−1 birnessite with pH 5.5 in nitrogen atmosphere(a) and in air (b) at differenttimes
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Fig5: The concentration of Fe2+, Mn2+and K+ in reaction system of 20 mM Fe2+oxidized by 1.0 g L−1 birnessite with pH 5.5 in nitrogen atmosphere(a) and in air (b) at differenttimes

Mentions: During the reaction process, the concentration of Fe2+,Mn2+ and K+ was quantified as shown inFig. 5a. It was observed thatFe2+ concentration decreased significantly from1120 mg L−1 in the initial stage to about150 mg L−1 at 720 min, and the released Mn2+and K+ concentration increased to 420 and68.5 mg L−1, respectively, at 720 min. Organic matter, silicate,phosphate, and metal ions also participate in the formation of ferric oxides and exhibit differenteffects on transformation rate [31, 32, 37]. The presenceof Fe2+ and Mn2+ might participate in thetransformation of ferric oxides including lepidocrocite and goethite.Fe2+ works as electron mediators and accelerate the formation ofgoethite, however, the other metal ions, such as Ti4+,Cu2+ and Cr3+, effectively interfere with thetransformation for the interruption of electron transfer [10, 31]. In order to study the influenceof Fe2+ and Mn2+ on the transformation offerric oxides, Fe2+ and Mn2+ were added toFe2(SO4)3 solution with pH 5.5and solid products were analyzed.Fig. 5


Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems.

Gao T, Shen Y, Jia Z, Qiu G, Liu F, Zhang Y, Feng X, Cai C - Geochem. Trans. (2015)

The concentration of Fe2+, Mn2+and K+ in reaction system of 20 mM Fe2+oxidized by 1.0 g L−1 birnessite with pH 5.5 in nitrogen atmosphere(a) and in air (b) at differenttimes
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4585411&req=5

Fig5: The concentration of Fe2+, Mn2+and K+ in reaction system of 20 mM Fe2+oxidized by 1.0 g L−1 birnessite with pH 5.5 in nitrogen atmosphere(a) and in air (b) at differenttimes
Mentions: During the reaction process, the concentration of Fe2+,Mn2+ and K+ was quantified as shown inFig. 5a. It was observed thatFe2+ concentration decreased significantly from1120 mg L−1 in the initial stage to about150 mg L−1 at 720 min, and the released Mn2+and K+ concentration increased to 420 and68.5 mg L−1, respectively, at 720 min. Organic matter, silicate,phosphate, and metal ions also participate in the formation of ferric oxides and exhibit differenteffects on transformation rate [31, 32, 37]. The presenceof Fe2+ and Mn2+ might participate in thetransformation of ferric oxides including lepidocrocite and goethite.Fe2+ works as electron mediators and accelerate the formation ofgoethite, however, the other metal ions, such as Ti4+,Cu2+ and Cr3+, effectively interfere with thetransformation for the interruption of electron transfer [10, 31]. In order to study the influenceof Fe2+ and Mn2+ on the transformation offerric oxides, Fe2+ and Mn2+ were added toFe2(SO4)3 solution with pH 5.5and solid products were analyzed.Fig. 5

Bottom Line: The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite.The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days.The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan, 430070 People's Republic of China.

ABSTRACT

Background: In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated.

Results: To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn(2+) and K(+) ions, a significant decrease in Fe(2+) concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30 days. Fe(2+) exhibited much higher catalytic activity than Mn(2+) during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn(2+) were compared to estimate the redox rates of birnessite and Fe(2+) under different conditions.

Conclusions: Redox rate was found to be controlled by chemical reaction, and increased with increasing Fe(2+) concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined effects of manganese oxide and air on the transformation of Fe(2+) to ferric oxides. Graphical abstract:Lepidocrocite and goethite were formed during the interaction of ferrous ion and birnessite at pH 4-7. Redox rate was controlled by the adsorption of Fe2+ on the surface of birnessite. The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

No MeSH data available.


Related in: MedlinePlus