The Hanford Site is currently planning to dispose of all high and low level, aqueous radioactive waste by encapsulation in glass. However, some contaminants of concern will be volatilized during vitrification process at the high temperatures. These contaminants, like hexavalent chromium, Cr(VI), and technetium (99Tc), will be recovered in off-gas condensate liquids, which could be treated in a secondary process to avoid continuous recycling. Zerovalent iron (ZVI) is a promising material for reductive removal of Cr(VI) and 99Tc from the aqueous phase. However, Cr(VI) may serve as a competitor to Tc reduction since its concentration in the off-gas condensate is expected to be more than 99Tc. The objective of this research is to determine the suitability of ZVI for reductive separation of Cr(VI) from synthetic off-gas condensate solutions. The kinetics of Cr(VI) reduction was examined in batch experiments with 0.5 g/L of ZVI. Experiments were conducted for a range of concentrations of Cr(VI) (from 0.5 mg/L –to 150 mg/L) prepared at variable pH from 4-10 in the presence of 0.8 M NaCl. A 200-mesh (&lt; 75 µm) ZVI prepared by an electrolytic process was chosen for these experiments due to its high reductive efficiency compared to other pre-tested ZVI materials. All ZVI –free controls and samples amended with Cr(VI) were prepared in triplicate. ICP-OES was used to measure total Cr concentration in each of the samples with limits of detection of approximately 10 ppb. Significant reduction of Cr(VI) was observed in samples amended with less than 50 mg/L. However, the kinetics of reduction was slow. For example, samples at 10 mg/L of Cr(VI) had to react for approximately 9.6 days to reach 50% removal. These data will also be presented with best fits with kinetic and isotherm models.

Potential for treatment of a chromium waste stream with zerovalent iron

256th National Meeting (2018)

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