Kinetics for the aquatic environment

Pankow, James F.; Morgan, James J.

doi:10.1021/es00092a004

Cited by 72 publications

(16 citation statements)

References 14 publications

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“…On the other hand, the data obtained in the present study showed that the citrate that formed a stable complex with Fe(II) (log K = 4.40, Sposito and Mattigod, 1979) retarded the oxidation of Fe(II) considerably (Figures 1 and 2; Table 1). This is in agreement with the theoretical conclusions of Pankow and Morgan (1981). Increasing levels of citrate stabilized Fe(II) (i.e., retardation of oxidation) by attenuating [Fe 2 § ], because increasing levels of citrate increased the proportion of Fe 2 § bound as Fe(II)-citrate complex, which therefore decreased the proportion of Fe(II) present as Fe 2+.…”

Section: Discussionsupporting

confidence: 91%

Influence of Citrate on the Kinetics of Fe(II) Oxidation and the Formation of Iron Oxyhydroxides

Krishnamurti

Huang

1991

Clays and clay miner.

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Abstract--The rate of Fe(II) oxidation at a constant rate of oxygen supply in the presence of citrate was measured at pH 6.0 at various citrate/Fe(II) molar ratios at 23.5~ in 0.01 M ferrous perch/orate system. The kinetics followed a first-order reaction with respect to Fe(II) concentration at constant pH (6.0) and aeration (5 ml/min). The rate constant decreased exponentially from 41.3 x 10 -4 to 7.6 x 10-"/min with an increase in the citrate/Fe(II) molar ratio from 0 to 0.1.The nature of the hydrolytic products formed after 120 min of oxidation was arrived at by X-ray powder diffraction (XRD), infrared spectrometry (IR), and transmission electron microscopic (TEM) analyses. In the absence of citrate, goethite (a-FeOOH) and poorly crystalline lepidocrocite (7-FeOOH) were the oxidation products formed at pH 6.0. The formation of lepidocrocite was promoted at the expense of goethite at citrate/Fe(II) molar ratios of 0.0005 to 0.005. The formation of lepidocrocite was especially pronounced at a citrate/Fe(II) molar ratio of 0.001, as observed from the width at half height (WHH) and the area of the 020 XRD peak of lepidocrocite. At a citrate/Fe(II) molar ratio of 0.01, however, the crystallization was perturbed resulting in the formation of noncrystalline Fe oxides, and no precipitate was observed at a citrate/Fe molar ratio of 0.1. The strong complexation of Fe(II) with citrate retarded the kinetics of Fe(II) oxidation and the formation and hydrolysis of Fe(III). The complexation, electrostatic, and steric effects of the coexisting citrate anions in solution apparently influenced the oxygen coordination and the way by which the double rows of edge-sharing Fe(O,OH)6 octahedra linked during crystallization, resulting in the formation of lepidocrocite.

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Section: Discussionsupporting

confidence: 91%

Influence of Citrate on the Kinetics of Fe(II) Oxidation and the Formation of Iron Oxyhydroxides

Krishnamurti

Huang

1991

Clays and clay miner.

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“…Pankow and Morgan (1981) proposed that specific adsorption was responsible for the high affinity of Mn oxides for Mn 2 § similar to adsorption of other transition metal ions on oxide surfaces of A1 and Fe. It was suggested that the sorbed Mn 2+ on the surface of Mn oxides was oxidized to Mn *+ and the oxidation reaction was catalyzed by Copyright 9 1994, The Clay Minerals Society the oxide surface at which the Mn 2+ and OH-accumulated.…”

Section: Introductionmentioning

confidence: 98%

Transformations of Synthetic Birnessite as Affected by pH and Manganese Concentration

1994

Clays and clay miner.

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AImtract--The amount of Mn 2+ adsorbed or removed from solution by birnessite is several times greater than its reported cation exchange capacity. Extractability of the sorbed Mn 2+ decreases with aging. It is uncertain whether the sorbed Mn 2+ is oxidized on the surface or incorporated into the structure of birnessite. Using X-ray powder diffractometry and transmission electron microscopy, a study was conducted to examine the mineralogical alteration of birnessite after treatment with various concentrations of MnSO4 and solution pH.The sorbed Mn 2+ was not directly oxidized and remained on the birnessite surface. The sorption of Mn 2+ was followed by alteration ofbirnessite with the formation of new Mn minerals. The specific Mn minerals formed were governed by the pH of the reaction, and the rate of the transformation was determined by Mn 2+ concentration and pH. Nsutite and ramsdellite were identified at pH 2.4, cryptomelane at pH 4, groutite at pH 6, and mangarfite at pH 8. Other Mn minerals formed at these and other pH levels could not be identified. As the concentration of Mn in the solution decreased, the time required to form new minerals from the birnessite increased. The newly formed phases were the result of structural conversion since dissolution of birnessite and reprecipitation of new phases were not observed.

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“…Kinetic factors play a great role in formation of various species of elements in a system (Pankov and Morgan, 1981a). Natural aquatic system is dynamic rather than being in equilibrium, although a recent model such as BLM assumes chemical equilibrium among the metals, its complexes and sensitive sites on biological surfaces (Slaveykova and Wilkinson, 2005).…”

Section: Resultsmentioning

confidence: 99%

“…Natural aquatic system is dynamic rather than being in equilibrium, although a recent model such as BLM assumes chemical equilibrium among the metals, its complexes and sensitive sites on biological surfaces (Slaveykova and Wilkinson, 2005). Certain dynamic situations, especially in the case of very slow and fast reactions occurring in riverine systems (Pankov and Morgan, 1981b), can be treated by chemical equilibrium theories. Certain complexation or precipitation reactions, which are very slow, can lead the system to metastable conditions under which equilibrium computations, with total concentration of various metals and ligands as inputs, fail to converge.…”

Section: Resultsmentioning

confidence: 99%

Modeling chemical speciation of copper in River Yamuna at Delhi, India

Jagadeesh¹,

Azeez²,

Banerjee

2006

Chemical Speciation & Bioavailability

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Chemical modeling of copper in the river Yamuna was attempted by an equilibrium constant method, using a computer program COCSOC developed for the purpose. Concentrations of metals (Cu, Ca and Mg), ligands (organics, carbonates and bicarbonates) and stability constants of the probable complexes were the inputs for the modified Newton -Raphson iteration. The model adequately predicted concentrations of various copper species, even without taking into consideration solid phases, other competing metals and ligands. The free cupric ion concentrations estimated were in the range of 10 À 17 to 10 À 16 M, undetectable by ion selective electrodes in the water from the river. The non-convergence of equilibrium computations for certain data sets at some sampling sites indicates the prevailing nonequilibrium conditions in the river due to large-scale release of ligands and metal ions through several drains.

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Kinetics for the aquatic environment

Cited by 72 publications

References 14 publications

Influence of Citrate on the Kinetics of Fe(II) Oxidation and the Formation of Iron Oxyhydroxides

Influence of Citrate on the Kinetics of Fe(II) Oxidation and the Formation of Iron Oxyhydroxides

Transformations of Synthetic Birnessite as Affected by pH and Manganese Concentration

Modeling chemical speciation of copper in River Yamuna at Delhi, India

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