Redox speciation method for neptunium in a wide range of concentrations

Abstract

Summary The adsorption method for determination of the distribution of neptunium among its oxidation states by the use of solvent impregnated resins and bismuth phosphate precipitates as adsorbents is described. For neptunium in concentration ranging from ∼10-10 to ∼10-2.5M, Np(IV) and Np(VI) were quantitatively adsorbed on the impregnated resin in a solution of the acidity 1.0-0.1M HClO4, while Np(V) remained in the liquid phase. In the same condition, the precipitate of bismuth phosphate absorbed Np(IV) selectively, leaving Np(V) and Np(VI) in the liquid phase. By carrying out these adsorption methods in Ultrafree-MC Microporous Centrifugal Filter Units (Millipore Corporation), the oxidation state distribution of neptunium in acid solution can be determined in a simple manner with a small sample volume (500μl) regardless of its concentration.