Effect of pH and Uranium Concentration on Interaction of Uranium(VI) and Uranium(IV) with Organic Ligands in Aqueous Solutions

Abstract

The effect of pH and uranium concentration on the interactions of uranium(VI) and uranium(IV) with organic ligands was studied by employing dialysis and ultrafiltration techniques. The interactions of U(VI) and U(IV) with organic ligands in nitrate or chloride aqueous solution have been found to be pH-dependent. The stability constants of uranium-organic complexes decrease in the order: fulvic acid > humic acid > tannic acid for U(VI) and humic acid > tannic acid > fuivic acid for U(IV). Scatchard plots for the uranium-organic acid systems indicate two types of binding sites with a difference In stability constants of about 102. Ultrafiltration of uranium-humic acid complexes indicates that U(VI) and U(IV) ions are concentrated in larger molecular size fractions (>5.1 nm) at pH⩽3 and in smaller molecular size fractions (in the range 5.1-3.1 nm and 2.4-1.9 nm) at pH⩾5. © 1980, American Chemical Society. All rights reserved.