A Kinetic Study of Am(III)/Humic Colloid Interactions

Abstract

The interaction kinetics of the Am(III) ion with aquatic humic colloids is investigated under near-natural conditions by column experiments with a sandy aquifer sample rich in humic substancesforthe appraisal of the migration behavior of Am. The association and dissociation kinetics of the Am ion onto and from humic colloids control the migration of colloid-borne Am. As the contact time between Am and humic colloids prior to introduction into a column is increased, the mobility of colloid-borne Am is enhanced and hence the recovery of Am in the effluent increases. On the other hand, an increase of the migration time and residence time in column, respectively, reduces the Am recovery. Considering these experimental results a refined version of the kinetic model KICAM (Kinetically Controlled Availability Model), which suggests different Am binding modes with humic colloids, was developed. Applying KICAM it is possible to predict static and dynamic experiments affected by the kinetically controlled Am/humic colloid interactions over the range of 1 h up to several months. However, to apply these experimental results to long-term conditions, the Am binding scheme as proposed in KICAM needs to be verified. This paper provides, therefore, a basis for a better understanding of the colloid-borne Am migration in porous aquifer systems.

Using atmospheric fallout to date organic horizon layers and quantify metal dynamics during decomposition

“…3). The Camels Hump soil profile preserved sharp concentration maximums of 4 temporally distinct tracers that are all well-documented to strongly bind to organic matter (Appleby et al, 1991;Kim et al, 1997;Sauve et al, 2000;Artinger et al, 2002), suggesting that Coniferous O horizons can record a stratigraphy of litter inputs and atmospheric fallout elements that bind strongly to organic matter in the upper layers. It is interesting to note again, that at Amli, which had the "youngest" O horizon layers ( Table 2) had most of the NAE Pb and the 241 Am inventory in the upper mineral soil (A + Bs), which, shows how rapid O horizon turnover can result in the transfer of elements to the mineral soil.…”

“…The weaponsfallout concentration maxima traces organic matter that was exposed during early 1960s (Cambray et al, 1989). Similar to Pb, these atoms hydrolyze even in acidic soils and thus strongly adsorb to mineral or organic phases (Kim et al, 1997;Artinger et al, 2002). Because the input functions for gasoline-derived Pb and the weapons fallout can be treated essentially as single short-duration events, and the atoms are sequestered by forest vegetation (Russell et al, 1981), the distributions are similar in the soil profiles: a contaminated layer at depth is overlain by fresh "clean" litter, and underlain by even older material that pre-dates the era of peak atmospheric contamination.…”

“…Atmospherically-deposited 210 Pb, weapons-derived 241 Am and 207 Bi, and cosmogenic 7 Be have a strong affinity for organic matter functional groups (Kim et al, 1997;Sauve et al, 2000;Artinger et al, 2002). These tracers along with other pollutants offer a potentially powerful tool for studying poorly understood biogeochemical processes on the short but extremely pertinent timescale of 1-100 years (Kaste et al, 2007;Klaminder and Yoo, 2008;Dixon et al, 2009).…”

In situ uranium stabilization by microbial metabolites

“…Humics can form innersphere complexes with metals (Xia et al, 1997) and polyelectrolytes are also capable of electrostatic interactions (Choppin and Labonne-Wall, 1997). The mobility of metal/humic-colloid complexes decreases as a result of humic interactions with the soil particles (Artinger et al, 2002).…”

Laser-induced breakdown detection combined with asymmetrical flow field-flow fractionation: application to iron oxi/hydroxide colloid characterization

“…The role of aquatic colloids is well known for the aquatic chemistry and migration of radionuclides and trace elements in aquifers [1][2][3][4][5][6]. Especially smaller sized particles with diameters <50 nm at trace concentrations, typical in natural water, are difficult to detect by conventional light scattering methods.…”