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Effect of Temperature on the Sorption of Chelated Radionuclides

Published online by Cambridge University Press:  26 February 2011

Ann S. Maest ,
David A. Crerar ,
Edward C. Dillon ,
Stephen M. Trehu  and
Tamara N. Rountree
Ann S. Maest
Affiliation:
U.S. Geological Survey, 345 Middlefield Rd., MS 427, Menlo Park, CA 94025
David A. Crerar
Affiliation:
Princeton University, Dept. of Geological and Geophysical Sciences, Princeton, NJ 08544
Edward C. Dillon
Affiliation:
Princeton University, Dept. of Geological and Geophysical Sciences, Princeton, NJ 08544
Stephen M. Trehu
Affiliation:
Princeton University, Dept. of Geological and Geophysical Sciences, Princeton, NJ 08544
Tamara N. Rountree
Affiliation:
U.S. Geological Survey, 345 Middlefield Rd., MS 427, Menlo Park, CA 94025
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Abstract

Temperature effects in the near-field radioactive waste disposal environment can result in changes in the adsorptive capacity and character of the substrate and the chemistry of the reacting fluids. This work examines the effect of temperature on 1) the kinetics of radionuclide sorption onto clays from 25°-75°C and 2) the degradation and metal-binding ability of two organic complexing agents found in chelated radioactive wastes and natural groundwaters. Clay-solution mixtures containing U, Co, Sr and Cs with kaolinite or montmorillonite were sampled over a 100-hour period for kinetic results at 25°, 50° and 75°C with and without EDTA. Three thermal degradation experiments with EDTA and oxalic acid were maintained at 250° for one week. Initial equilibrium concentrations were attained in the kinetics runs within 30 minutes in most cases. Possible sorption/retention mechanisms include ion exchange, physical adsorption and/or precipitation. EDTA decreased U and Co sorption, but slightly enhanced Sr and Cs sorption. Complexing of Al by EDTA may drive Sr and Cs to the clay surface to satisfy the resulting charge imbalance. Adsorption increased with increasing temperature for U, Co without EDTA and Sr, while Cs sorption decreased from 25°-75°C. Primary EDTA degration (at ∼200°C) products were mostly ethyl- and methyl-substituted amines with no metal-binding ability; therefore, to inhibit transport of low-level chelated radioactive wastes thermal or biological degradation is recommended. Interaction of high-level radioactive wastes with naturally-occurring organics in repository groundwaters may enhance migration of the actinides and 60Co.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 44: Symposium N – Scientific Basis for Nuclear Waste Management VIII , 1984 , 377
Copyright
Copyright © Materials Research Society 1985

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References

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