Reaction of Np(IV) with Orthosilicic Acid, Si(OH)4, in Acid Solutions

Abstract

Reaction of Np(IV) with Si(OH)4 within the range of pH 0-2.2 was studied spectrophotometrically. Under these conditions, a complex NpOSi(OH)33+ is formed. This composition was derived from the dependences of the complex concentration on [H+] and [Si(OH)4]. From the experimental electronic absorption spectra, the spectrum of NpOSi(OH)33+ was reconstructed. In this spectrum, the narrow band of the aqua ion at 723.2 nm shifts to 729.2 nm and becomes weaker by approximately half. The equilibrium constant K1 of the complex formation reaction and the stability constant of the complex β1 at the ionic strengths I = 0.1 and 1.0 were determined: logK1 = 0.71±0.05 and 0.41±0.02, β1 = 10.52±0.05 and 10.22±0.02, respectively. The Np(IV) speciation in the acid solution in the presence of Si(OH)4 was calculated.