Americium binding to humic acid

The binding of americium (Am) by peat humic acid (PHA) has been investigate d at Am concentrations between 10(-11) and 10(-7) M at pH similar to2.6 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 mo deling 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 bin ding. Am was not observed to bind to high-affinity, low-concentration bindi ng sites. The model VI parameter Delta LK2 takes into account the small num ber 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 p resent as Fe(III). Model Vl was then used to investigate the possible impor tance 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) Competiti on in metal-PHA binding studies and possible shortcomings in the extraction procedure used to extract PHA.