CALCITE AS A HOST FOR CHROMATE AND IODATE OXYANIONS
A series of batch experiments were conducted using different methods [i.e., variations of mixing CaCl2 and either (NH4)2CO3 or NaCO3] to form calcite in the presence of chromate or iodate. Variables included the concentration of the calcite forming solutions (0.1M or 1M), chromate and iodate concentrations (0 ppb to 500 ppb), timing of contaminant addition (during or after calcite formation) and pH. Results of these batch experiments have shown incorporation of these contaminants in calcite may be occurring at the Hanford site. In the chromate tests, post-experiment XRD analysis determined that the presence of chromate delayed the transformation of vaterite to calcite; the vaterite structure may be a better fit for incorporation of chromate oxyanions. In the iodate experiments, the iodate removed from solution was correlated with the initial iodate concentration and the molarity of the starting solutions. Both experiments show incorporation of these contaminants in calcite, despite the unsuited match between the structure of the oxyanions and the calcite structure. These results will help to better characterize, conceptualize, and ultimately remediate the contaminated subsurface at the Hanford site.