Investigations into the Influence of Organic Complexing Agents on the Leaching Behaviour and Mobility of Radionuclides Solidified in ILW Forms

Abstract

Within the frame of a research programme of the Commission of the European Communities investigations into the influence of the synthetic organic complexing agents dibutylphosphate (DBP), tributylphosphate (TBP), ethylenediaminetetraacetic acid (EDTA), citrate and oxalate on the solubilities and sorption behaviour of Agl, CsN0 3 , Na 2 U 2 0 7 , NpOjOH, Pu(OH) 4 and Am(OH) 3 or Eu(OH) 3 were carried out in systems representing the near field of a repository of radioactive waste located in a salt dome. The results obtained show the strong influence of the ligands EDTA, citrate and oxalate on the chemical behaviour of the actinide elements under these simulated practical conditions. They must definitely be taken into consideration for modelling safety aspects of waste repositories.

Rational Design of Sequestering Agents for Plutonium and Other Actinides

“…These include the rate of dissolution from solid hydrolysis and polymeric products formed by the metal, the stability of the metal−ligand complex, and the ability of the complex to compete with other substrates to retain the metal. The effects of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), citrate, humic acid, fulvic acid, nitrilotriacetic acid (NTA), and siderophores (naturally occurring iron-coordinating species) on the migration of Pu(IV) and Th(IV) have been studied. − Both EDTA and DTPA have been shown to increase the uptake of plutonium and americium into certain plants, with major implications for the introduction of actinides into the food chain. − The circumstances in which introduction of actinides into the food chain could occur require additional study of the formation constants of the actinide complexes of the substrates of concern as well as the potential for the substrates themselves to be present in high environmental concentrations …”

Specific Sequestering Agents for the Actinides. 29. Stability of the Thorium(IV) Complexes of Desferrioxamine B (DFO) and Three Octadentate Catecholate or Hydroxypyridinonate DFO Derivatives: DFOMTA, DFOCAMC, and DFO-1,2-HOPO. Comparative Stability of the Plutonium(IV) DFOMTA Complex1

“…The ability of a complexing agent to transport actinide(IV) ions depends on many factors, including the rate of dissolution from solid hydrolysis products and other natural substrates, the adsorption of the metal−ligand complex onto substrates, and the stability of the metal−ligand complex as compared to other complexes that could form (i.e., protonated forms of the metal−ligand complex or other ligand complexes). The effects of EDTA, DTPA, citrate, humic acid, fulvic acid, NTA, and siderophores (including DFO) on the migration of Pu 4+ and Th 4+ have been studied. − Both EDTA and DTPA have been shown to increase the uptake of plutonium and americium into certain plants, − with major implications for the introduction of actinides into the food chain. To model accurately the migration of actinide(IV) ions in soil and ground water, accurate formation constants with the metal ions of interest must be determined.…”

“…The effects of EDTA, 17 DTPA, citrate, humic acid, fulvic acid, NTA, and siderophores (including DFO) on the migration of Pu 4+ and Th 4+ have been studied. [18][19][20][21][22][23][24] Both EDTA and DTPA have been shown to increase the uptake of plutonium and americium into certain plants, [25][26][27][28][29] with major implications for the introduction of actinides into the food chain. To model accurately the migration of actinide(IV) ions in soil and ground water, accurate formation constants with the metal ions of interest must be determined.…”

Chelating Agents in the Environment

“…Elevated concentrations of chelating agents enhance the transport of metals (e.g. Zn, Cd, Ni, Cr, Cu, Pb, and Fe) in soils (101)(102)(103)(104)(105)(106)(107) and enhance the undesired transport of radioactive metals away from disposal sites (10,81,(108)(109)(110). Low concentrations of chelating agents may either stimulate planktic algae growth or decrease it while high concentrations inhibit activity (111)(112)(113).…”