Adsorption-dissolution reactions affecting the distribution and stability of Co[sup II]EDTA in ion oxide-coated sand
- Pacific Northwest Lab., Richland, WA (United States)
The time-variant chemical behavior of Co[sup II]EDTA (and other metal-EDTA complexes) was investigated in suspensions of iron oxide-coated sand to identify equilibrium and kinetic reactions that control the mobility of Me[sup II]-EDTA complexes in subsurface environments. Batch experiments were conducted to evaluate the adsorption as a function of pH, concentration, and time and to quantify the rate-controlling step(s) of dissolution of the iron oxide by EDTA complexes. Ionic Co[sup 2+] exhibited typical cation-like adsorption, whereas Me[sup II]EDTA adsorption was ligand-like, increasing with decreasing pH. Adsorption isotherms for all reactive species exhibited Langmuir behavior, with site saturation occurring at molar values of <0.5% of Fe[sub tot]. The adsorption of Me[sup II]EDTA enhanced the apparent solubility of the iron oxide phase, which destabilized the Co[sup II]EDTA complex, liberating Co[sup 2+] and Fe[sup III]EDTA. The dissolution rate was an order of magnitude slower at pH 6.5 than at pH 4.5 and was influenced by the re-adsorption of solubilized Fe[sup III]EDTA. Two multireaction kinetic models were developed that each included Langmuir adsorption for Co[sup 2+] and metal-EDTA species but differed in their depiction of the dissolution mechanism (i.e., ligand-versus proton-promoted dissolution). 45 refs., 8 figs., 6 tabs.
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 7124611
- Journal Information:
- Environmental Science and Technology; (United States), Journal Name: Environmental Science and Technology; (United States) Vol. 28:9; ISSN ESTHAG; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400102 -- Chemical & Spectral Procedures
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54 ENVIRONMENTAL SCIENCES
540230* -- Environment
Terrestrial-- Radioactive Materials Monitoring & Transport-- (1990-)
540330 -- Environment
Aquatic-- Radioactive Materials Monitoring & Transport-- (1990-)
ADSORPTION
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHELATING AGENTS
COBALT 60
COBALT COMPLEXES
COBALT ISOTOPES
COHERENT SCATTERING
COMPILED DATA
COMPLEXES
DATA
DIFFRACTION
DISSOLUTION
EDTA
EQUILIBRIUM
INFORMATION
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IRON COMPOUNDS
IRON OXIDES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LAND POLLUTION
LIGANDS
MATERIALS
MINUTES LIVING RADIOISOTOPES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
POLLUTION
RADIOACTIVE MATERIALS
RADIOACTIVE WASTES
RADIOISOTOPES
SAND
SCATTERING
SORPTION
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
WASTES
WATER POLLUTION
X-RAY DIFFRACTION
YEARS LIVING RADIOISOT