Complexation of Eu3+ with a polycarboxylate based concrete superplasticizer in chloride media

In this work, we present a complexation study of Eu{3+} with a commercial polycarboxylate based concrete
superplasticizer Glenium® 51 in NaCl media at low to medium ionic strengths. The complexation is investigated
using time-resolved laser fluorescence spectroscopy (TRLFS) at pHm = 5.1 ± 0.1. With the charge neutralization
model, conditional stability constants log K’m were determined for ionic strengths up to Im (NaCl) = 2.47 mol
kg 1 H$_2$O$^{-1}$. Eu$^{3+}$ only forms one complex with this complexant under these conditions. The conditional stability
constants decrease significantly at elevated ionic strengths by almost three orders of magnitude. Thus, the Eu$^{3+}$-
Glenium® 51 complex formation is reduced at high ionic strengths. The determination of the conditional stability
constants allows to extrapolate to the stability constant at zero ionic strength by using the specific ion interaction
theory (SIT). A log K0 m = 8.54 ± 0.9 has been determined, which highlights the strong complexation properties of
the superplasticizer. Moreover, this novel study presents first insights into the interaction of Glenium® 51 with
Eu$^{3+}$ at various ionic strengths. ... mehrSince Eu$^{3+}$ is used as a surrogate for trivalent actinides, these results are very
important for understanding actinide behavior in cementitious systems present at the geotechnical barrier of a
repository in clay rock formations of Northern Germany containing pore and formation waters with elevated
ionic strength.