Previous studies show that some radionuclides present in reactor decontamination wastes form strong complexes with the organic complexing agents used to decontaminate reactor cores and piping. Further, the metal-ligand complexes exhibit reduced adsorption to soils. Flow through column tests were used to study the adsorption of metal-organic ligand complexes to two soils. The breakthrough curves for metals and organic ligands for four tests are shown. In all the column tests, the adsorption of the organic ligand-metal complex, or the free organic ligand and free metal (disassociated species) was reversible. That is, close to the total mass injected was recovered in the flushing stage with untraced background solution.
Two tests that used the iron oxide coated sand show complicated behavior that was interpreted as being caused by ligand (both EDTA and picolinate) interacting with the ferric oxides. The Ni-organic ligand complex in both cases appears to exchange Ni for Fe to some extent such that free Ni+2 is produced and Fe (III)-organic complexes are formed that adsorb with different strengths. Further, we suspect that the organic ligand is dissolving some of the ferric oxide coatings and destroying sorption sites. The combination of all these reactions leads to rather complicated breakthrough curves. In tests with picolinate there is partial disassociation of the metal and ligand such that the breakthrough curves for the metal and ligand are different
A recommendation is made to not bury EDTA-laden decontamination wastes with cement. Another observation is that predictions that use simple constant Kd and constant source release constructs may not be exclusively conservative in predicting concentrations of contaminants in water down-gradient from disposal sites.