Retention of 99mTc at Ultra-trace Levels in Flowing Column Experiments – Insights into Bioreduction and Biomineralization for Remediation at Nuclear Facilities

ABSTRACTThe behavior of technetium at ultra-trace (<10−10 mol l−1) concentrations in bioreducing sediment column experiments was investigated using 99mTc γ-camera imaging. Four flowing sediment columns were biostimulated for varying periods of time, using acetate as an electron donor, such that on the day of imaging they represented oxic, early metal-reducing, Fe(III)-reducing and sulfate-reducing conditions. Prior to imaging, columns were spiked with 9.6 MBq of 99mTc(VII)O4−, which is relevant to the 99Tc mass concentrations observed at nuclear facilities, run under site relevant flow conditions, and imaged using γ-camera imaging at 20 min intervals over 12h. In the oxic column 99mTc behaved as a conservative tracer and did not interact significantly with the sediment. In all of the biostimulated columns 99mTc associated with the sediment although the spike was least mobile in the order sulfate < Fe(III)-reducing < early metal-reducing columns, confirming higher reactivity for 99mTc under increasingly re...