Removal or Immobilization of Radionuclides and Trace-metals in Water, Soil and Poultry Litter Using Stabilized Nanoparticles

Abstract

Two kinds of stabilized nanoparticles were synthesized and tested for the in situ immobilization of metals and radionuclides in soil and groundwater, namely Fe-Mn binary oxide nanoparticles for adsorptive immobilization and zero valent iron (ZVI) nanoparticles for reductive immobilization. A water-soluble starch or food-grade carboxymethyl cellulose (CMC) was used as a stabilizer to facilitate the in situ delivery of the particles into the contaminated soil. The Fe-Mn nanoparticles showed rapid sorption kinetics and high sorption capacities toward trace metals such as selenium, arsenic and phosphate. The Langmuir maximum capacity was determined to be 110 and 95 mg-Se/g-Fe, and 310 and 300 mg-P/g-Fe for starch- and CMC-stabilized nanoparticles, respectively, and this high uptake was observed over the typical groundwater pH range of 5-8. Column breakthrough tests indicated that both stabilized Fe-Mn and ZVI nanoparticles were deliverable in a model sandy soil while non-stabilized particles were not. When Se(IV)-spiked soil was treated in situ with the Fe-Mn nanoparticles, >92% water leachable Se(IV) was transferred to the nanoparticle phase and immobilized as the particles were retained in the downstream soil matrix. When applied to poultry litter (PL), the stabilized Fe-Mn nanoparticles reduced the water soluble P from 66% (for untreated PL) to 4.4% and peak soluble P concentration from 300 to <20 mg/L under simulated land application conditions, while at the same time reducing the water soluble As from 79% to 5%. By transferring the peak soluble P to nanoparticle-bound P, the Fe-Mn nanoparticles therefore not only greatly reduce the potential runoff loss of P from PL, but also provide a long-term slow-releasing nutrient source. The ZVI nanoparticles converted soluble U(VI) to its immobile form U(IV) very effectively, thereby greatly reducing the mobility and bioavailability of the uranium. Batch experiments indicated that the U(VI) leachability of the contaminated soil was reduced by nearly 99% when a U(VI) spiked sandy soil (395 mg-U/kg-soil) was amended with the CMC-nZVI (0.1 g/L) at a soil-to-liquid ratio of 1 g/50 mL at pH 6.0. When subjected to remobilization tests, <1% of the immobilized U(IV) was released into the aqueous phase under anoxic conditions. There were no inhibition effects of the natural microbial activity on the U immobilization and CMC-nZVI also effectively reduced the bio-toxicity of U(VI). When the soil column was treated with 50 pore volumes of the nanoparticle suspension at pH 6.0, water soluble U was reduced by 93%. In all cases, the nanoparticle amendment reduced the leachability of the contaminant in soil. This technology holds the potential to fill a major technology gap in the remediation of metal-contaminated soil and groundwater.