J. Means, C. Alexander
1981
Citations
1
Influential Citations
69
Citations
Quality indicators
Journal
Nuclear and Chemical Waste Management
Abstract
Abstract Chelating agents are used in nuclear decontamination operations because they form very selective and strong complexes with numerous radionuclides. However, if environmentally-persistent chelated wastes are disposed of without pretreatment to eliminate the chelating agents, increased radionuclide migration rates from the disposal sites may occur. The environmental chemistry of the three most common aminopolycarboxylic acid chelating agents, NTA (nitrilotriacetic acid), EDTA (ethylenediaminetetraacetic acid), and DTPA (diethylenetriaminepentaacetic acid) is reviewed. This review includes information on their persistence in the environment, as well as their tendency to form complexes with actinides. Data on the sorption of chelated actinides by geologic substrates and on the uptake of chelated actinides by plants are also presented. Increased solubility and/or migration of radionuclides by chelating agents used in decontamination operations have been observed at two different radioactive waste burial grounds. EDTA was found to be promoting the migration of 6O Co and possibly other radionuclides from liquid waste disposal sites at Oak Ridge National Laboratory (1). Recently EDTA has again been identified in radioactive wastes-this time in trench waters containing from 600–16,100 pCi 238 Pu per liter from solid waste burial grounds in Maxey Flats, Kentucky (2). These observations at Oak Ridge and Maxey Flats suggest that the practice of disposing chelated radioactive wastes should be reevaluated. Three different technical options for disposing chelated low-level radioactive wastes are proposed: 1. [1] Bind the solidified chelated waste in some kind of solid matrix that has a slow leach rate and bury the waste in a “dry” disposal site. 2. [2] Substitute biodegradable chelating agents in the decontamination reagent for the chelating agents that are persistent in the environment. 3. [3] Chemically or thermally degrade the chelating agents in the waste prior to disposal. The relative advantages and disadvantages of each of these options are discussed. We feel that surprisingly little attention has been given to an obvious procedure for the disposal of chelated radioactive wastes: chemically or thermally degrading the chelating agent prior to disposal. Any of the above three options might in fact be a satisfactory approach to the disposal of chelated wastes. However, we suggest that the burial of chelating agents such as EDTA be avoided and that option [3] be given more consideration.