Sorption and precipitation of Co(II) in Hanford sediments and alkaline aluminate solutions |
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| Institution: | 1. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA;2. Canadian Light Source, University of Saskatchewan, Saskatoon, Canada SK S7N 0X4;3. Stanford Synchrotron Radiation Laboratory, SLAC, MC 69, Menlo Park, CA 94025, USA;1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, People''s Republic of China;2. Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, School of Metallurgy and Environment, Central South University, Changsha 410083, China;1. State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, PR China;2. Shanxi Key Laboratory of Safety and Durability of Concrete Structures, Xijing University, Xian 710123, PR China;3. Powerchina Guiyang Engineering Corporation Limited, Guiyang 550081, PR China;1. Hubei Key Laboratory for Processing and Application of Catalytic Materials, Huanggang Normal University, Huanggang 438000, China;2. Key Lab of Mesoscopic Chemistry MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China |
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| Abstract: | Sorption and precipitation of Co(II) in simplified model systems related to the Hanford site high-level nuclear waste tank leakage were investigated through solution studies, geochemical modeling, and X-ray absorption fine structure (XAFS) spectroscopy. Studies of Co(II) sorption to pristine Hanford sediments (ERDF and Sub), which consist predominantly of quartz, plagioclase, and alkali feldspar, show an adsorption edge centered at pH ≈ 8.0 for both sediments studied, with sorption >99% above pH ≈ 9.0. Aqueous SiO2 resulting from dissolution of the sediments increased in concentration with increasing pH, though the systems remained undersaturated with respect to quartz. XAFS studies of Co(II) sorption to both sediment samples reveal the oxidation of Co(II) to Co(III), likely by dissolved O2, although this oxidation was incomplete in the Sub sediment samples. The authors propose that Fe(II) species, either in aqueous solution or at mineral surfaces, partially inhibited Co(II) oxidation in the Sub sediment samples, as these sediments contain significantly higher quantities of Fe(II)-bearing minerals which likely partially dissolved under the high-pH solution conditions. In alkaline solutions, Al precipitated as bayerite, gibbsite, or a mixture of the two at pH > 7; an amorphous gel formed at pH values less than 7. Aqueous Co concentrations were well below the solubility of known Co-bearing phases at low pH, suggesting that Co was removed from solution through an adsorption mechanism. At higher pH values, Co concentrations closely matched the solubility of a Co-bearing hydrotalcite-like solid. XAFS spectra of Co(II) sorbed to Al-hydroxide precipitates are similar to previously reported spectra for such hydrotalcite-like phases. The precipitation processes observed in this study can significantly reduce the environmental hazard posed by 60Co in the environment. |
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