Mechanism of uranium removal from the aqueous solution by elemental iron

Abstract

The effectiveness of elemental iron (Fe 0 ) to remove uranium (U) from the aqueous phase has been demonstrated. While the mitigation effect is sure, discrepancies in the removal mechanism have been reported. The objective of this study was to investigate the mechanism of U(VI) removal from aqueous phases by Fe 0 . For this purpose a systematic sequence of bulk experiments was conducted to characterize the effects of the availability and the abundance of corrosion products on U(VI) removal. Results indicated that U(VI) removal reactions did not primary occur at the surface of the metallic iron. It is determined that U(VI) co-precipitation with aging corrosion products is a plausible explanation for the irreversible fixation under experimental conditions. Results of XRD analyses did no show any U phases, whereas SEM-EDX analyses showed that U tended to associate with rusted areas on the surface of Fe 0 .Recovering U with different leaching solutions varied upon the dissolution capacity of the individual solutions for corrosion products, showing that the irreversibility of the removal 2 depends on the stability of the corrosion products. U(VI) co-precipitation as removal mechanism enables a better discussion of reported discrepancies.

A CRITICAL REVIEW ON THE PROCESS OF CONTAMINANT REMOVAL IN FE0–H2O SYSTEMS

“…Elusive arguments have been proposed to rationalize this experimental evidence. However, from the above discussion and recent experimental works from Noubactep and co-workers [55,56,107], it is evident that the lag time is the time for sufficient corrosion products to be generated [41]. For example, in a non-disturbed 'Fe 0 -H 2 O-FeS 2 -U(VI)' system at pH 4.0-4.5, this lag time could lengthen to 40 days [107].…”

“…Instead, the vast majority of experiments have been conducted under mixing (bubbling, shaking, stirring) conditions [41]. Under mixing conditions, however, iron corrosion is accelerated and the formation of the oxide film at the Fe 0 surface is disturbed [55][56][57]. In fact, mixing Fe 0 -H 2 O systems is mostly considered as an important tool to facilitate the transport of contaminants from the solution to the surface of Fe 0 materials.…”

“…These transport processes can only be observed if the Fe 0 -H 2 O system remains undisturbed [33,41,99]. In this regard, because of the disturbance of oxide film formation, mixing can be considered as the major disturbing factor for hitherto mechanistic investigations with Fe 0 materials [56,99].…”

Retention and chemical speciation of uranium in an oxidized wetland sediment from the Savannah River Site

“…long term U immobilization in wetlands include the chemical and/or microbial reduction of soluble U(VI) ions to fairly insoluble U(IV) species (Kalin et al, 2005;Lovley et al, 1991;Noubactep et al, 2006;Turick et al, 2008), mineral precipitation, sorption onto NOM (Wan et al, 2011), ion exchange or sorption to sediment minerals (Akber et al, 1992;Dong et al, 2012;Grybos et al, 2007), and accumulation in plants (Hinton et al, 2005;Knox et al, 2008).…”

Comments on “Comparison of reductive dechlorination of p-chlorophenol using Fe0 and nanosized Fe0” by R. Cheng, et al. [J. Hazard. Mater. 144 (2007) 334]

“…For this purpose, the use of vigorous mi xing operations Generally, the Fe 0 mass loading (ρ m in g/L) is given and considered for example in the expression of k obs to account for the available surface area [8]. But ρ m alone is meaningless, even though Fe 0 is in large excess in the large majority of works [9,10].…”