Kinetics of Trace Metal Complexation: Role of Alkaline-Earth Metals

Janet G. Herlngf; Francois M. M. Morel

doi:10.1021/es00177a014

Kinetics of Trace Metal Complexation: Role of Alkaline-Earth Metals

Janet G. Herlngf, Francois M. M. Morel

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140 Scopus citations

Abstract

The rate of reaction of inorganic copper with the model ligand ethylenediaminetetraacetic acid (EDTA) is significantly retarded in the presence of calcium at seawater concentrations. The (pseudo-first-order) half-life for inorganic copper reacting with EDTA in seawater is ̰2 h at 10^-7M EDTA. This kinetic hindrance to the formation of the thermodynamically favored CuEDTA species results from several factors: (1) the preponderance of the calcium complex in the speciation of EDTA, (2) the competition of calcium and copper for reaction with any free EDTA formed by the dissociation of CaEDTA, and (3) the slow kinetics of direct attack of copper on CaEDTA compared to reaction with free or protonated EDTA species. If metal-complexing agents in natural waters behave as discrete ligands, then the reaction of a metal at strong binding sites may also be kinetically hindered at high alkaline-earth concentrations. In contrast with the reaction of EDTA, however, the rate of complexation of copper by humic acid is not observably affected by high calcium concentrations.

Original language	English (US)
Pages (from-to)	1469-1478
Number of pages	10
Journal	Environmental Science and Technology
Volume	22
Issue number	12
DOIs	https://doi.org/10.1021/es00177a014
State	Published - Dec 1 1988

All Science Journal Classification (ASJC) codes

Chemistry(all)
Environmental Chemistry

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Herlngf, J. G., & Morel, F. M. M. (1988). Kinetics of Trace Metal Complexation: Role of Alkaline-Earth Metals. Environmental Science and Technology, 22(12), 1469-1478. https://doi.org/10.1021/es00177a014

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title = "Kinetics of Trace Metal Complexation: Role of Alkaline-Earth Metals",

abstract = "The rate of reaction of inorganic copper with the model ligand ethylenediaminetetraacetic acid (EDTA) is significantly retarded in the presence of calcium at seawater concentrations. The (pseudo-first-order) half-life for inorganic copper reacting with EDTA in seawater is ̰2 h at 10-7M EDTA. This kinetic hindrance to the formation of the thermodynamically favored CuEDTA species results from several factors: (1) the preponderance of the calcium complex in the speciation of EDTA, (2) the competition of calcium and copper for reaction with any free EDTA formed by the dissociation of CaEDTA, and (3) the slow kinetics of direct attack of copper on CaEDTA compared to reaction with free or protonated EDTA species. If metal-complexing agents in natural waters behave as discrete ligands, then the reaction of a metal at strong binding sites may also be kinetically hindered at high alkaline-earth concentrations. In contrast with the reaction of EDTA, however, the rate of complexation of copper by humic acid is not observably affected by high calcium concentrations.",

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N2 - The rate of reaction of inorganic copper with the model ligand ethylenediaminetetraacetic acid (EDTA) is significantly retarded in the presence of calcium at seawater concentrations. The (pseudo-first-order) half-life for inorganic copper reacting with EDTA in seawater is ̰2 h at 10-7M EDTA. This kinetic hindrance to the formation of the thermodynamically favored CuEDTA species results from several factors: (1) the preponderance of the calcium complex in the speciation of EDTA, (2) the competition of calcium and copper for reaction with any free EDTA formed by the dissociation of CaEDTA, and (3) the slow kinetics of direct attack of copper on CaEDTA compared to reaction with free or protonated EDTA species. If metal-complexing agents in natural waters behave as discrete ligands, then the reaction of a metal at strong binding sites may also be kinetically hindered at high alkaline-earth concentrations. In contrast with the reaction of EDTA, however, the rate of complexation of copper by humic acid is not observably affected by high calcium concentrations.

AB - The rate of reaction of inorganic copper with the model ligand ethylenediaminetetraacetic acid (EDTA) is significantly retarded in the presence of calcium at seawater concentrations. The (pseudo-first-order) half-life for inorganic copper reacting with EDTA in seawater is ̰2 h at 10-7M EDTA. This kinetic hindrance to the formation of the thermodynamically favored CuEDTA species results from several factors: (1) the preponderance of the calcium complex in the speciation of EDTA, (2) the competition of calcium and copper for reaction with any free EDTA formed by the dissociation of CaEDTA, and (3) the slow kinetics of direct attack of copper on CaEDTA compared to reaction with free or protonated EDTA species. If metal-complexing agents in natural waters behave as discrete ligands, then the reaction of a metal at strong binding sites may also be kinetically hindered at high alkaline-earth concentrations. In contrast with the reaction of EDTA, however, the rate of complexation of copper by humic acid is not observably affected by high calcium concentrations.

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