Effects of borate on Europium sorption onto calcium silicate hydrate formed as a secondary mineral under water-saturated conditions

Calcium silicate hydrate (C–S–H) plays a key role in the retention of radionuclides. This study examined the effects of boric acid on C–S–H formation and the sorption of Eu(III), an analogue of Am(III), under water-saturated conditions. C–S–H was synthesized in the presence of boric acid and Eu, and characterized using ICP-OES, Raman spectroscopy, and fluorescence spectroscopy. The results revealed that B retention depended on the Na/B ratio and solution alkalinity, and that boric acid may alter silicate polymerization and Ca coordination. Fluorescence spectra and fluorescence decay behavior indicated that Eu interacts with C–S–H even in the presence of 600 mM boric acid at Na/B = 0.2, while the concentration of boric acid and the pH potentially influence Eu sorption. These results provide valuable insights into C–S–H formation in boron-bearing systems and the sorption behavior of trivalent radionuclides.