HR: 1330h
AN: H32A-0506    [PDF]
TI: Sequestration of Metals by wet-dry Cycling of Soil and Soil Minerals at the Idaho Engineering and Environmental Laboratory (INEEL)
AU: * Wright, K E
EM: wrigke@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, PO Box 1625 MS 2025, Idaho Falls, ID 83415-2025 United States
AU: Cooper, D C
EM: coopdc@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, PO Box 1625 MS 2025, Idaho Falls, ID 83415-2025 United States
AU: Redden, G D
EM: reddgd@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, PO Box 1625 MS 2025, Idaho Falls, ID 83415-2025 United States
AU: Bauer, W F
EM: wlb@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, PO Box 1625 MS 2025, Idaho Falls, ID 83415-2025 United States
AB: The INEEL is the site of soil contamination by heavy metals and nuclides stemming from decades of nuclear waste processing, storage, and disposal. Much of the contamination is located within 1m of the surface, where contaminant movement can be influenced by the cyclic wetting and drying cycles that result from large amounts of infiltration in the spring followed by months of hot weather with little precipitation. We hypothesize that such wetting and drying cycles can retard contaminant migration by sequestering metals in less reactive phases. INEEL soil, quartz, goethite-coated quartz (Fe-quartz), andesine, Ca-montmorillonite, K-feldspar, calcite, smectite-illite, kaolinite and a no-matrix control were exposed to 200$\mu$M Cs, Sr, Cd, Cr, and U. After a two-week equilibration period, metals were analyzed using ICP-AES and ICP-MS. Samples were then evaporated to dryness and were subsequently re-wetted with air-equilibrated deionized water. This process was repeated four times; results were compared to continuously wet control samples. Preliminary results indicate that wet-dry cycling generally reduces metal availability, but the magnitude of the effect depends on the metal and the substrate with which it interacts. Control samples with no solid substrate showed no decrease in metal content throughout the experiment except for [U$^{6+}$-aq] and [Cd$^{2+}$-aq], which were oversaturated at the experiment's inception. The largest differences between wet-dry cycled samples versus their continuously wet counterparts occurred with U, Cd, and Cr. [U$^{6+}$-aq] was reduced by nearly 100% in cycled andesine samples compared to 25% in continuously wet control samples. [Cd$^{2+}$-aq] in cycled soil, Fe-quartz, quartz, and no matrix samples was up to 50% lower in concentration than that present in control samples. Results for [Cr$^{6+}$-aq] were similar, but with no difference in concentration for the no-matrix control. Differences in [Sr$^{2+}$-aq] and [Cs$^{+}$-aq] for cycled samples compared to control samples were largest for andesine and calcite. Concentrations of [Sr$^{2+}$-aq] and [Cs$^{+}$-aq] for cycled samples were 25-60% lower than that of control samples. Differences in wet-dry cycled clay samples compared to control samples for [Sr$^{2+}$-aq] and [Cs$^{+}$-aq] were present albeit smaller than that of andesine and calcite. Cycled samples were 1-5% lower in [Sr$^{2+}$-aq] and [Cs$^{+}$-aq] than was present in control samples. Microprobe analysis of soil and andesine suggests that Sr and Cs removal is controlled at least in part by ion-exchange with clays. X-ray diffraction evidence indicates that otavite and an unidentified U-bearing phase precipitate although the kinetics of precipitation are quite slow. Wet-dry cycling appears to enhance sorption processes; the impact of the process on transport and bioavailability will depend on reversibility and rates of reverse reactions.
DE: 1099 General or miscellaneous
DE: 1655 Water cycles (1836)
DE: 1806 Chemistry of fresh water
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2003 Fall Meeting