Zero valent iron (ZVI) is currently under consideration for treatment of volatile contaminants recovered in off-gas condensate from vitrification of radioactive waste at the Hanford site. It is a commonly used reactive agent for reductive removal of contaminants, including reducible metal ions. However, there has not been a systematic study of the reductive capacity of ZVI with variable synthesis methods and particle sizes. Moreover, although Tc is the major risk driver, significantly greater concentrations of Cr(VI) in the waste stream may lead to competition for reductive capacity. The objective of this research is to quantify the kinetics of reductive removal of both Cr(VI) and 99Tc using ZVI.<br/>Batch experiments and solid phase characterization studies have been conducted to quantify the reductive removal of Tc and Cr in the presence of a suite of different ZVI materials (100 nm to 1-2 mm in diameter). In addition, dissolution of Fe(II/III) was monitored and solid phases were analyzed to measure oxidation of the materials over time. Both variable pH and isotherm experiments were conducted in order to estimate the kinetics of reductive removal and potential loading capacity for Tc and Cr.<br/>Contrary to theory, ZVI with relatively large particle size ranges (2 to 0.075 mm diameter) synthesized by an electrolytic process exhibited distinctively better reductive behavior than ZVI of smaller particle sizes ranges including nano ZVI (0.1 to 3 µm). Dissolution of Fe(II) was also higher for the iron materials of larger size ranges and is correlated with reductive removal of Tc(VII). These data suggest that removal is dependent on synthesis process as well as available surface area of ZVI. Moreover, although the theoretical redox potential for reduction of Cr(VI) is above Tc(VII), reduction and removal kinetics are significantly faster for Tc than Cr.<br/>

Reductive removal of Tc and Cr from a waste stream using zero valent iron

256th National Meeting (2018)

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