Complex formation of Np(V) with humic acid and polyacrylic acid

Abstract

By using239Np and/or237Np, the complexation of Np(V) with Aldrich humic acid and polyacrylic acid has been studied at the concentration of Np(V) from ~10-13to ~10-4M by the solvent extraction method using TTA and 1,10-phenanthroline in isoamyl alcohol. By defining the apparent formation constant as βα=[ML]/([M]CRα), where CRis the total concentration of proton exchanging sites and α is the degree of dissociation, [M] and [ML] respectively denote the concentrations of free and bound NpO2+, log βαhave been obtained at pH 6-7 in 0.1 and 1.0 M NaClO4. For both humate and polyacrylate, log βαslightly increased with the degree of dissociation, and slightly decreased with ionic strength. While the variation of Np(V) concentration had no appreciable influence on the log βαof polyacrylate (ranging from 1.8 to 3.0 depending on pH and ionic strength), log βαof humate decreased from 4.7-5.3 (depending on pH and ionic strength) at [M] < 10-9M to 2.8-3.1 at [M] = 10-5M, indicating the coexistence of weak and strong binding sites in the humic acid.