Immobilization of As(III) in Soil and Groundwater Using a New Class of Polysaccharide Stabilized Fe-Mn Oxide Nanoparticles

A new class of stabilized Fe-Mn binary oxide nanoparticles was prepared with a water-soluble starch or carboxymethyl cellulose (CMC) as a stabilizer. The nanoparticles were characterized and tested with respect to sorption of As(III) and As(V) from water and for immobilization of As(III) in soil. While arsenic sorption capacities were comparable for bare, or stabilized Fe-Mn nanoparticles, particle stabilization enabled the nanoparticles to be delivered into soil for in situ immobilization of arsenite. High As(III) sorption capacity was observed over a broad pH range of 5-9. Column breakthrough tests demonstrated soil mobility of CMC-stabilized nanoparticles. Once delivered, the nanoparticles remain virtually immobile in soil under typical groundwater conditions, serving as a fixed sink for arsenic. When an As(III)-laden soil was treated with CMC-stabilized Fe-Mn at an Fe-to-As molar ratio of 6.5-39, the water leachable arsenic was reduced by 91-96%, and the TCLP leachability was reduced by 94-98%. Column elution tests of an As(III)-laden soil indicated that application of CMC-stabilized Fe-Mn transferred nearly all water-soluble As(III) to the nanoparticle phase. Consequently, As(III) is immobilized as the nanoparticles are immobilized in the soil. The nanoparticle amendment was able to reduce the TCLP leachability of As(III) remaining in the soil bed by 78%.