In Situ Immobilization of Arsenic in Water and Soil Using Polysaccharide Stabilized Iron Manganese Binary Oxide Nanoparticles

Stabilized Fe-Mn binary oxide nanoparticles were synthesized and tested for removal and in-situ immobilization of arsenic, As(III) and As(V), in simulated groundwater and soil. A water soluble starch or carboxymethyl cellulose (CMC) was used as a stabilizer to prevent the particles from aggregation and facilitate in situ delivery of the particles into contaminated soil. Both bare and stabilized Fe-Mn nanoparticles showed rapid sorption kinetics and high capacity. The maximum Langmuir capacity was determined to be 338 mg-As/g-Fe for As(III) and 272 for As(V) at pH 5.5. The highest sorption capacity was observed over the pH range of 5-8 for As(III), while acidic pH favored the uptake of As(V). Column breakthrough tests demonstrated that CMC-stabilized nanoparticles were deliverable in a model sandy soil. Column breakthrough tests coupled with filtration modeling indicated that the delivered nanoparticles will remain virtually immobile in soil under typical groundwater conditions, serving as a fixed sink for the contaminants. When the pre-contaminated soil was treated with CMC-stabilized Fe-Mn at an Fe-to-As molar ratio of 6.5-39, the water-leachable As(III) was reduced by 91-96%, and the TCLP-based leachability was reduced by 94-98%. Column elution tests showed that when an As(III)-laden soil was amended with 22 pore volumes of the nanoparticles suspension, nearly all water-soluble As(III) was transferred to the nanoparticle phase, and eventually immobilized as the particles were immobilized in soil. The technology holds the potential to fill a major technology gap and substantially cut down the cost in remediation of arsenic-contaminated soil and groundwater.