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Soil Sci. Soc. Am. J
Vol. 69, No: xx, 2005; Pages: 531–538


Clay Mineralogical Transformations over Time in Hanford Sediments Reacted with Simulated Tank Waste

Kholoud Mashal, James B. Harsh, and Markus Flury*

Dep. of Crop and Soil Sciences, Center for Multiphase EnvironmentalResearch, Washington State Univ., Pullman, WA 99164-6420.

Abstract

Buried waste storage tanks at the USDOE Hanford Reservationin Washington State have released solutions containing high concentrations of Na, OH, NO3, and Al into the vadose zone. When suchsolutions contact vadose zone sediments, mineral transformations willchange the sediment matrix. We hypothesized that Si, dissolved fromprimary and secondary minerals, will combine with Al from the tankwaste to form crystalline or poorly crystalline network silicates suchas zeolites and feldspathoids. In this study, we characterized the colloidal (<2 m equivalent diam.) minerals formed when simulated tank solutions reacted with vadose zone Hanford sediments. Variablesstudied included simulated tank waste (STW) composition, reactiontime, and temperature. Hanford sediments were reacted with a seriesof simulated tank solutions in batch experiments at 25 and 50oC for 1, 10, 25, 40, and 50 d. The mineralogical, structural, and chemicalproperties of the resulting colloidal fractions and bulk solutions weredetermined by x-ray diffraction (XRD), Fourier transform infrared(FTIR), 27Al- and 29Si-magic angle spinning-nuclear magnetic resonance (MAS-NMR), scanning electron microscopy (SEM), energydispersive x-ray analysis (EDAX), colorimetry, atomic absorptionspectroscopy, and inductively coupled plasma–atomic emission spectroscopy (ICP–AES). Upon contact with STW, Si was released fromthe sediments and a portion was incorporated into poorly crystallinesolids. The amount of poorly crystalline solids increased initially andreached maximum quantities between 0 and 25 d. Lability of mineralsin the presence of NaOH followed the order quartz-> kaolinite-> illite. New secondary minerals, NO3-cancrinite, NO3-sodalite, andzeolite A, were formed at the expense of the original clay minerals.Zeolite A was labile and disappeared after about 25 d of reaction time.Cancrinite and sodalite, however, appeared to be stable and increasedin abundance with time.

Keywords:Na, OH, NO3;vadose zone;simulated tank waste;x-ray diffraction;energydispersive x-ray analysis;colorimetry;atomic absorptionspectroscopy;mineralogical;scanning electron microscopy;radionuclide.


Corresponding author:

E-mail: flury@mail.wsu.edu

 

 
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