Colloid-Facilitated Transport of Radionuclides Through the Vadose Zone

Given that there is a wide range of chemical compositions of Hanford Tank Waste, we have studied mineral formation and transformation by systematically varying anion composition and OH concentrations of simulated tank solutions in presence and absence of Cs. The feldspathoids and zeolite formed in the presence of Cs were analyzed with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and solid state NMR. The presence of Cs in the simulant solutions did not affect the types of minerals formed in 1 M NaOH solutions until the Cs concentration was greater than 0.1 M, a concentration that is not likely to occur in the sediment underlying the Hanford tanks. Elemental mapping indicated that incorporated Cs was homogeneously distributed in cancrinite and sodalite. High concentrations of Cs promoted the formation of highly crystalline cancrinite in hexagonal bar shape. The presence of Cs in solutions precluded the influence anions have shown in the non-cesium system. The presence of chloride anion was favorable for the formation of pure sodalite in a non-cesium solution, yet no sodalite has been found in the precipitates formed at high Cs concentration (0.5 M). Adsorption experiments indicated that Cs could access the internal parts of LTA, cancrinite and sodalite, but the diffusion appeared more difficult than that of Na and K. Cesium exchange in cancrinite and sodalite caused structural disordering of the minerals as reflected by the XRD patterns