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The interaction of the two chemical homologues [Cm(III) and Eu(III)] with calcium silicate hydrates (CSH phases) at pH 13.3 has been investigated in batch-type sorption studies using Eu(III) and complemented with time-resolved laser fluorescence spectroscopy (TRLFS) using Cm(III). The sorption data for Eu(III) reveal fast sorption kinetics and a strong uptake by CSH phases with distribution ratios of (6 +/- 3) x 10(5) L kg(-1). Three different Cm(III) species have been identified: A nonfluorescing species, which was identified as a curium hydroxide (surface) precipitate, and two fluorescing Cm(III)/CSH-sorbed species. The fluorescing sorbed species have characteristic emission spectra with main peak maxima at 618.9 and 620.9 nm and fluorescence emission lifetimes of 289 +/- 11 and 1482 +/- 200 micros, respectively. From the fluorescence lifetimes, it was calculated that the two fluorescing Cm(III) species have one or two and no water molecules left in their first coordination sphere, suggesting that these species are incorporated into the CSH structure. A structural model for Cm(III) and Eu(III) incorporation into CSH phases is proposed based on the substitution for Ca at two different types of sites in the CSH structure.

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A review of literature data concerning complex properties of humic substances with actinides (Th, U, Np, Pu, Am) and with cations largely present in natural waters is presented. From data which have been selected according to criteria discussed in the present paper, speciation diagrams of actinides have been calculated in the most representative conditions for natural systems (pH range 4-9; [humic substances] 0.1 to lOppm). Humic substances dominate actinide (Th, U, Am) speciation up to pH 7 (or even 8). Above these pH, inorganic complexes regulate actinide speciation. The presence of competing cations (Ca or Al) modifies actinide speciation in the pH range 4-6.