Immobilization of selenite in soil and groundwater using stabilized Fe–Mn binary oxide nanoparticles

•First study on stabilized Fe–Mn nanoparticles for in situ immobilization of Se(IV).•The stabilized nanoparticles offer much higher sorption capacity than other sorbents.•The stabilized nanoparticles are deliverable in a sandy soil under moderate pressure.•The stabilized nanoparticles reduce water soluble Se(IV) from the soil by 92%.•Delivered nanoparticles act as an immobile sink for Se(IV) under natural conditions.

Stabilized Fe–Mn binary oxide nanoparticles were synthesized and tested for removal and in-situ immobilization of Se(IV) in groundwater and soil. A water-soluble starch or food-grade carboxymethyl cellulose (CMC) was used as a stabilizer to facilitate in-situ delivery of the particles into contaminated soil. While bare and stabilized nanoparticles showed rapid sorption kinetics, starch-stabilized Fe–Mn offered the greatest capacity for Se(IV). The Langmuir maximum capacity was determined to be 109 and 95 mg-Se/g-Fe for starch- and CMC-stabilized nanoparticles, respectively, and the high Se(IV) uptake was observed over the typical groundwater pH range of 5–8. Column breakthrough tests indicated that the stabilized nanoparticles were deliverable in a model sandy soil while non-stabilized particles were not. When a Se(IV)-spiked soil was treated in situ with the nanoparticles, >90% water leachable Se(IV) was transferred to the nanoparticle phase, and thereby immobilized as the particles were retained in the downstream soil matrix. The nanoparticle amendment reduced the TCLP (toxicity characteristic leaching procedure) leachability and the California WET (waste extraction test) leachability of Se(IV) by 76% and 71%, respectively. The technology holds the potential to fill a major technology gap in remediation of metals-contaminated soil and groundwater.

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