Mobility of organic complexes of some non-TRU fission and activation products: a selective review

Abstract

Zr, Nb, Ni, and possibly Tc are mobile in the presence of aqueous organic complexing agents to a certain extent. Low pH appears to be required for efficient complex formations with organic ligands in aqueous media. Zr complexes with a number of synthetic chelating agents such as EDTA, and DTPA to form stable, water-soluble complexes in acidic and neutral aqueous systems. Zr also complexes with HIMDA or HXG to form a stable, water soluble complex in any aqueous system and with ..cap alpha..-hydroxy carboxylic acids in alkaline aqueous systems. Uncomplexed Zr would be readily absorbed by or precipitated on soil. It is predicted that the organic complexes of Zr would be absorbed less by soil than uncomplexed zirconium. Nb generally forms the most stable complexes with nitrogen containing chelating ligands such as EDTA, and less stable complexes with ..cap alpha..-hydroxy carboxylic acids and monodentate ligands. Uncomplexed Nb would be efficiently absorbed by or precipitated on soil from aqueous systems. Despite the high stability constants of complexed Nb, one would predict that organic complexes of niobium would be absorbed by soil because of hydrolysis of complexed Nb to insoluble hydrous niobium oxide. Ni complexes strongly with a number of oxygen and nitrogen containing organic ligands. Uncomplexed Ni is absorbed by soil in acidic and neutral aqueous systems and precipitated on soil in alkaline aqueous systems. Two complexes of Ni are known to be absorbed to a much lesser extent by soil (Ni-DTPA, Ni-EDTA). Fulvic acid and synthetic chelating agents are known to greatly enhance the movement of Ni in soil and to reduce Ni absorption by soil. Tc complexes with organic ligands in a reducing environment but the behavior of these complexes in a nonreducing environment is unknown. 8 tables, 3 figs. 62 refs.