The migration behavior of Np(V) in sandy soil and granite media in the presence of humic substances

Abstract

Migration behavior of Np(V) in sandy soil and granite media was studied in the presence of humic substances using a column method. Two kinds of naturally occurring fulvics were isolated from groundwater at the Chalk River Laboratories of AECL (hereafter, CRL-fulvics) and at the Underground Research Laboratory of AECL (hereafter, URL-fulvics). The commercial humics from Aldrich Co. (hereafter, Aldrich-humics) was also used to compare the influence of humics from different origin on the migration behavior of Np(V). The dominant molecular size of these humic substances was under 5,000 daltons for the fulvics, and in the range from 30,000 to 100,000 daltons for Aldrich-humics. An enhanced elution of Np(V) from the sandy soil column under coexistence of CRL-fulvics at 20 mg/L was observed in comparison with the studies in the absence of humic substances. On the other hand, Np(V) under coexistence of Aldrich-humics was retarded. The difference in the effects of the humic substances on the migration behavior of Np(V) may be caused by the difference in the molecular size distribution of the humic substances. That is, the CRL-fulvics, being smaller in size, has lower sorption ability on the sandy soil than the Aldrich-humics, and thereby Np-fulvics complexes may be able to easily migrate through the sandy soil column. In the case of granite column experiments, again an enhanced elution of Np(V) under the coexistence of URL-fulvics was found and this observation was similar to that found with the CRL-fulvics. From these observations, it is likely that the migration behavior of Np(V) is influenced by the presence of humic substances.

Sorption of Np(V) and Np(IV) onto kaolinite: Effects of pH, ionic strength, carbonate and humic acid

“…Furthermore, it has been shown that Np(V) is reduced to Np(IV) by humic substances (e.g., Zeh et al, 1999;Shcherbina et al, 2007;Schmeide and Bernhard, 2009). The resulting formation of Np(IV) humate complexes strongly increased Np migration through sandy sediment and granitic material columns in laboratory experiments (Artinger et al, 2000;Sakamoto et al, 2000). The impact of redox active humics on Np sorption onto goethite has been studied by Kalmykov et al (2008).…”

Preparation and use of humic coatings covalently bound to silica gel for Np(V) and Pu(V) sequestration

“…However, when metal loading approaches 5-10% of the total ionized carboxylate concentration, coagulation of HS-An(IV) complexes occurs. Below this percentage, actinide-HS complexes are mobile in flow-through porous medium [10][11][12]. HS have been shown to reduce metals with estimated reduction potentials of 0.5-0.7 V [13].…”

Literature Review and Assessment of Plant and Animal Transfer Factors Used in Performance Assessment Modeling

“…Moulin et al (1992) reviews the aqueous speciation of neptunium in the presence of humic substances in soils and natural waters. The complexation and reduction of Np(V) with humic substances has also been investigated by various laboratories with different experimental methods (Artinger et al 2000;Sakamoto et al 2000;Zeh et al 1999;Kim 1996, 1998;Rao and Choppin 1995;Choppin 1992;Kim and Sekine 1991). The results of these studies suggest that humate complexation of Np(V) may play an important role in systems with relatively high humic acid concentrations.…”