Research Group at Stanford University, we have investigated adsorption processes that could lead to the sequestration of Cr, Co, Sr, and U on minerals representative of the Hanford Vadose Zone sediments and precipitation processes resulting in alkali aluminate solids that form from the highly alkaline and aluminum-rich leachates reacting with these sediments. These elements are among the most important pollutants of concern to the Department of Energy at the Hanford Site in Washington State. The aqueous solutions used in these experiments were simplified surrogates of Tank leachates (i.e., they contained high Na and Al and had pH values of 10-12 in many cases). We have examined the following processes that could lead to sequestration of these pollutant elements: (1) the sorption/coprecipitation of these elements in solids formed from reaction of alkaline aluminate solutions with simple systems of minerals representative of those found in the soils and sediments underlying the Hanford Tank Farm (e.g., quartz, feldspars, clay minerals, iron oxides); (2) the sorption/coprecipitation of these elements in solids formed from reaction of alkaline aluminate solutions with soil and sediment samples obtained from the Hanford site; and (3) the effect of aging on the stability of sorption complexes on Al-oxide and Al-oxyhydroxide surfaces formed from neutralization and homogeneous nucleation of alkaline aluminate solutions. Our investigations have utilized X-ray Absorption Fine Structure (XAFS) spectroscopy, electron and X-ray microprobe analyses, X-ray diffraction and small angle X-ray scattering, and inductively coupled plasma emission spectrometry analysis, as described below.
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