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Kinetics of chromium transformations in the environment
F Y Saleh1, T F Parkerton, R V Lewis
1Institute of Applied Sciences, University of North Texas, Denton 76203.
The Science of the Total Environment
|October 1, 1989
Summary
Chromium transformations in the environment are governed by reaction rates, not just equilibrium. Understanding chromium kinetics in water, soil, and sediment is key for predicting its environmental fate.
Area of Science:
- Environmental Chemistry
- Geochemistry
- Environmental Science
Background:
- Chromium (Cr) speciation significantly impacts its environmental mobility and toxicity.
- Understanding the kinetics of chromium transformations is crucial for accurate environmental risk assessment.
Purpose of the Study:
- To systematically investigate the kinetics of chromium transformations under various environmental conditions.
- To evaluate oxidation and reduction rates of chromium in different aqueous and solid-phase systems.
- To determine the influence of environmental factors on chromium speciation and mobility.
Main Methods:
- Batch, microcosm, and column experiments were conducted.
- Reactions were studied in single-phase (water) and two-phase (water-solid) systems.
- Natural and reference waters, sediments, and soils were utilized.
Main Results:
- Instantaneous Cr(VI) reduction by S2- and Fe2+ under anaerobic conditions confirmed stoichiometric and equilibrium predictions.
- Slower Cr(VI) reduction by organics and Cr(III) oxidation by MnO2 demonstrated kinetic controls.
- Cr(III) oxidation to Cr(VI) was slow, with half-lives of 2-9 years, and did not exceed 15% extent.
- Dissolved oxygen alone did not significantly oxidize Cr(III) within 128 days.
Conclusions:
- Chromium transport and transformation can be predicted using kinetic data, Eh-pH, and system characteristics.
- Laboratory and microcosm results align well with predicted chromium concentrations.
- Kinetic data provides a robust framework for assessing chromium's environmental behavior.