Kinetics of trace metal complexation: role of alkaline-earth metals
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 half-life for inorganic copper reacting with EDTA in seawater is /similar to/2 h at 10/sup /minus/7/M 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 completion of copper by humic acid is not observably affected by high calcium concentrations.
- Research Organization:
- Massachusetts Institute of Technology, Cambridge (USA)
- OSTI ID:
- 6258734
- Journal Information:
- Environ. Sci. Technol.; (United States), Journal Name: Environ. Sci. Technol.; (United States) Vol. 22:12; ISSN ESTHA
- Country of Publication:
- United States
- Language:
- English
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Aquatic-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
ALKALINE EARTH METAL COMPLEXES
AMINO ACIDS
CALCIUM COMPLEXES
CARBOXYLIC ACIDS
CHELATING AGENTS
CHEMISTRY
COMPLEXES
COPPER
EDTA
ELEMENTS
HALF-LIFE
HYDROGEN COMPOUNDS
KINETICS
LIGANDS
METALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
REACTION KINETICS
SEAWATER
TRACE AMOUNTS
TRANSITION ELEMENTS
WATER
WATER CHEMISTRY