Search

The latest results in the Eu-B(OH)3-Organic System are presented: 1) New approach to determine the formation constant of a Eu borates 2) Formation of the solid Eu borate in NaCl medium 3) Quantitative synthesis of Eu borate and structure characterization

Boric acid (B(OH)3) and (poly)borates are of great interest regarding the mobilization of trivalent actinides in nuclear waste repositories, particularly in salt deposits. This work describes approaches to determine the stability constant in the Eu(III)-borate system. The stability constant between Eu(III) and borates is in the order of magnitude of 1...2, and with it the borate complexation is very weak. Furthermore, in presence of polyborates at pH 6 the formation of a solid Eu borate species is observed. The formation rate of the solid Eu borate species depends on the polyborate concentration and salt concentration/type (NaClO4/NaCl). Some structural information of the solid Eu borate were provided from IR spectroscopy, solid-state NMR (11B) and solid-state TRLFS.

Boric acid (B(OH)3) and (poly)borates are of great interest regarding the mobilization of trivalent actinides in nuclear waste repositories, particularly in salt deposits. This work describes the influence of boric acid on the Eu salicylate complexation due to the formation of a borate ester of salicylate, which could be the key to determine the stability constants of Eu-borate complexes. Furthermore, at pH 6 the formation of a solid Eu borate species in presence of polyborates is observed. The formation progress of the solid Eu borate species depends on the polyborate concentration and salt concentration. The solid formation could be an interesting possibility for the immobilization of trivalent actinides in a nuclear waste repository.

Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers. The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution. At pH 6 the formation of a Eu borate solid species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.