Polyhydroxy carboxylates, such as gluconate (Gluc–
) play an essential role in a variety of
industrial processing. Gluc–
is used in large quantities because of its complexing ability: for
example NaGluc is a common additive in the construction industry and employed to improve
certain properties of cement. In low- and intermediate-level (LL/IL) radioactive waste
repositories, containers are filled with cement to prevent leakage, but upon water intrusion, the
alkaline pore water might promote the complexation of metal ions by Gluc–
, therefore these
complexing processes have been excessively studied in the past decades.
Gluc–
has been proven to be an efficient complexing agent for alkaline-earth (Ca(II),
Mg(II)) and transition (Cu(II), Co(II), Ni(II), Mn(II), Zn(II)) metal ions, therefore it cannot be
disregarded that it might be capable of enhancing the solubility of tri- and tetravalent actinides
and lanthanides in alkaline media. Anoxic conditions characteristic of radioactive waste
repositories ensure that actinides are present in reduced oxidation states (Cm(III), Am(III),
Pu(III), Pu(IV)). Possible complexing agents are also present in these repositories such as
organic ligands generated by the decomposition of contaminant cellulosic materials
(isosaccharinate, Isa–
) or present as cement additives (Gluc–
).
It is of high priority to study the capability of these ligands to enhance the solubility of
actinide ions in case of water intrusion, since the calculation of the degree of mobilization these
metal ions can reach is integral for estimating the associated risk of disposal. Due to the
pronounced chemical analogies, stable (III) oxidation state lanthanide ions share with trivalent
actinides, tri- and tetravalent actinides can be modeled by less elaborate lanthanide ions.
To obtain a simplified and relevant model of possible complexation processes in radioactive
waste repositories, neodymium (Nd(III)) and Gluc–
have been employed previously as model
ions in measurements carried out in aqueous solutions, but data acquired in alkaline equilibria
are scarce.