title: Trace contaminant concentration affects mineral transformation and pollutant fate in hydroxide-weathered Hanford sediments.
abstract: Prior work has shown that when silicaceous sediments are infused with caustic radioactive waste, contaminant fate is tightly coupled to ensuing mineral weathering reactions. However, the effects of local aqueous geochemical conditions on these reactions are poorly studied. Thus, we varied contaminant concentration and pCO(2) during the weathering of previously uncontaminated Hanford sediments over 6 months and 1 year in a solution of caustic waste (pH 13, high ionic strength). Co-contaminants Sr, Cs and I were added at "low" (Cs/Sr: 10(-5)m; I: 10(-7)m) and "high" (Cs/Sr: 10(-3)m; I: 10(-5)m) concentrations, and headspace was held at atmospheric or undetectable (<10ppmv) CO(2) partial pressure. Solid phase characterization revealed the formation of the zeolite chabazite in "high" samples, whereas feldspathoids, sodalite and cancrinite, were formed preferentially in "low" samples. Sr, Cs and I were sequestered in all reacted sediments. Native calcite dissolution in the CO(2)-free treatment drove the formation of strätlingite (Ca(2)Al(2)SiO(7)·8H(2)O) and diminished availability of Si and Al for feldspathoid formation. Results indicate that pCO(2) and contaminant concentrations strongly affect contaminant speciation in waste-weathered sediments, and are therefore likely to impact reaction product stability under any remediation scenario.
authors: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721, USA. perdrial@email.arizona.edu
authors: Nicolas
authors: N
authors: Perdrial
authors: Nelson
authors: N
authors: Rivera
authors: Aaron
authors: A
authors: Thompson
authors: Peggy A
authors: PA
authors: O'Day
authors: Jon
authors: J
authors: Chorover
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry*; D006878:Hydroxides / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D017550:Spectroscopy, Fourier Transform Infrared; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D006878:Hydroxides; D014874:Water Pollutants, Chemical