Formation of americium(III) complexes with aqueous silicic acid

Abstract

The interaction of americium(III) with aqueous silicic acid was studied by competitive solvent extraction with 0.1 M thenoyltrifluoroacetone (HTTA) as extractant. The aqueous phase contained only 0.2 M NaClO4or additionally 0.03 M silicic acid at p[H] 3.0-3.8 adjusted with perchloric acid.241Am was used in tracer amounts and its distribution ratio was measured γ -spectrometrically. Silicic acid solutions were prepared by hydrolysis of tetramethylorthosilicate (TMOS). Kinetic investigations with the molybdate reaction showed polymeric silica fractions between 10-17% within the p[H] range investigated. Extraction times of about 1.5 hours were taken to assure distribution equilibrium for the241Am extraction. The occurrence of a 1:1 complex of americium with silicic acid according to the reaction Am3++ Si(OH)4↔ AmOSi(OH)32++ H+could be demonstrated and a formation constant of K1= (6.9±0.7)×10-3[log K1= -2.16±0.04] at I = 0.2 M was calculated.