Americium binding to humic acid.

Peters, Adam J. and Hamilton-Taylor, John and Tipping, Edward (2001) Americium binding to humic acid. Environmental Science and Technology, 35 (17). pp. 3495-3500. ISSN 0013-936X

Abstract

The binding of americium (Am) by peat humic acid (PHA) has been investigated at Am concentrations between 10-11 and 10-7 M at pH 2.6 in the presence and absence of Cu as a competing ion. Cu−PHA binding was also investigated in order to derive independent binding constants for use in modeling the competitive binding studies. Humic ion-binding model VI was used to compare the acquired data with previously published binding data and to investigate the importance of high-affinity binding sites in metal−PHA binding. Am was not observed to bind to high-affinity, low-concentration binding sites. The model VI parameter ΔLK2 takes into account the small number of strong sites in PHA and was found to be important for Cu−PHA binding but not for Am−PHA binding, regardless of whether Cu was present. Analysis of the PHA sample revealed that it contained a considerable quantity of Fe not removed by the extraction procedure, much of which is believed to be present as Fe(III). Model VI was then used to investigate the possible importance of the presence of Fe(III) in the Am−PHA binding experiments. When Fe(III) was assumed to be present, improved descriptions of the data by model VI were obtained by assuming that all of the metals [Am, Cu, and Fe(III)] undergo strong binding. This highlights the importance of Fe(III) competition in metal−PHA binding studies and possible shortcomings in the extraction procedure used to extract PHA.