With growing uranium mining and disposal of nuclear wastes, U(VI) has been widely detected in soil and groundwater. Due to its high solubility and mobility, U(VI) is considered the major species that threatens the environmental and human health. Yet, there has been no cost-effective technology available to in-situ remediate U-contaminated soil and groundwater, especially when the contaminant plume is located in deep aquifers. To fill this technology gap, we prepared and tested a class of polysaccharide stabilized zero-valent iron (ZVI) nanoparticles for in-situ reductive immobilization of U(VI) in soil. A water soluble starch or carboxymethyl cellulose (CMC) was used as a stabilizer to prevent particle aggregation and facilitate soil deliverability. The nanoparticles were able to effectively convert soluble U(VI) to its immobile form U(IV), thereby greatly reducing the mobility and bioavailability of uranium. Batch experiments indicated that the U(VI) leachability of the contaminated soil was reduced by nearly 89% when a U(VI) spiked sandy soil (395 mg-U/kg-soil) was amended with the CMC-stabilized ZVI (0.1 g/L as Fe) at a soil-to-liquid ratio of 1 g/25 mL at pH 6.0. Slightly acidic pH favors the reduction, e.g. the leachability of U(VI) at pH 8.0 was 2 times higher than that at pH 6.0. Column tests indicated that the stabilized ZVI nanoparticles are deliverable in the soil. When the soil column was treated with 45 pore volumes of the nanoparticle suspension (0.1 g/L as Fe) at pH 6.5, water soluble U(VI) was reduced by 94%. In addition, the ZVI treatment reduced the TCLP leachability of U(VI) in the soil by 93%. When subjected to desorption tests, <1% of immobilized U(IV) was released into aqueous phase under anaerobic conditions, while 27% under aerobic conditions and 40% in the presence of bicarbonate (1 mM) under aerobic conditions.

In-situ reductive immobilization of uranium in soil using stabilized iron nanoparticles

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.