PNNL

Abstract

Speciation calculations were done to determine whether organic complexants facilitate transport of radionuclides leached from waste buried in soils. EDTA readily mobilizes divalent transition metals and moderately impacts trivalent actinides. Picolinate readily mobilizes only Ni2+ and Co2+. These speciation predictions ignore the influence of soil adsorption and biodegradation that break apart the complexes. In adsorption studies, picolinate concentrations have to be >10-4 M to lower the adsorption of Ni and Co. For Sm(III), Th(IV), Np(V), U(VI), and Pu, the picolinate concentration must be >10-3 M before adsorption decreases. EDTA forms strong complexes with divalent transition metals and can stop adsorption of Ni and Co when EDTA solution concentrations are 10-5 M. EDTA complexes with Np(V), U(VI), and Pu are much weaker; EDTA concentrations would have to be >10-3 M to adversely effects non-transition metal/radionuclide adsorption. Most picolinate and ETDA-metal complexes appear to readily dissociate during interactions with soils. The enhanced migration of radionuclide-organic complexes may be limited to a few unique conditions. We recommend that mixtures of metal/radionuclides and EDTA should not be solidified or co-disposed with high pH materials such as cement. For weaker binding organic complexants, such as picolinate, citrate and oxalate, co-disposal of decontamination wastes and concrete should be acceptable.