Polymerization study of o-Si(OH)4 and complexation with Am(III), Eu(III) and Cm(III)

The stability constants of Am+3, Cm3+ and Eu3+ with ortho silicate, View the MathML sourceo-Si(OH)3- were measured at pH 3.50 and in ionic strengths of 0.20–1.00 M (NaClO4) by the solvent extraction method. The Am+3, Cm3+ and Eu3+ forms 1:1 complex with ortho silicate ion at pH 3.60 with the stability constant (log β1) value of 8.02 ± 0.10, 7.78 ± 0.08 and 7.81 ± 0.11, respectively. The stability of these metal ions decrease with increased ionic strength from 0.20 to 1.00 M (NaClO4) for silicic acid concentrations of 0.002–0.020 M. Increasing silicic acid concentration above 0.02 M increased the amount of M3+ extracted into the organic phase, contrary to the trend usually observed for increased ligand concentration in solvent extraction. This reversed trend is likely due to the extraction of cationic species of silicic acid by HDEHP. Aging time (60–300 min) had no effect on the stability constant of these metal ions for 0.002–0.020 M silicic acid at pH 3.50 and I = 0.20 M (NaClO4). The fraction of polymeric silicic acid present in solutions of 0.20–4.50 M NaClO4 solutions at pH 3.0–10.0, T = 0–60 °C and aging time = 5–300 min was measured for determination of the silicomolybdate reaction to ascertain the proper conditions to study metal–silicate complexation.