Am(lll) Hydrolysis Constants and Solubility of Am(lll) Hydroxide

Abstract

Americium(III) hydroxide solubility was measured in dilute salt solutions under an argon atmosphere. The equilibrium, attained in < 23 days, was approached from both over and undersaturation. Thermodynamic equilibrium constants (K/sub S10//sup 0/) for the solubility of Am(OH)/sub 3/ (amorphous) (Am(OH)/sub 3/ (amorphous) + 3 H/sup +/ in equilibrium Am/sup 3 +/ + 3 H/sub 2/O in equilibrium Am(OH)/sub n//sup 3-n/ + nH/sup +/) were calculated from the solubility data. The measured value of log K/sub S10//sup 0/ was 17.5 +/- 0.3. The values of log ..beta../sub 1//sup 0/, log ..beta../sub 2//sup 0/, and log ..beta../sub 3//sup 0/ were less than or equal to -8.2, -17.1 +/- 0.5, and less than or equal to -27.0, respectively. Contrary to predictions in the literature, Am(III) does not show amphoteric behavior in the pH range studied (i.e., no evidence for the existance of Am(OH)/sub 4//sup -/ species). 18 references, 2 figures, 5 tables.