Different routes of bismuth mineral transformation during pertechnetate and perrhenate uptake for subsurface remediation†

We investigated basic bismuth subnitrate for removal of radioactive technetium-99 as pertechnetate (⁹⁹TcO₄⁻) from contaminated groundwater. This material removed 93% of the initial concentration of ⁹⁹TcO₄⁻ within a week via formation of pH-dependent mineral phases that were identified here, but not reported previously. Perrhenate (ReO₄⁻) removal was also studied because it is a widely used non-radiological analogue for ⁹⁹TcO₄⁻, considering their similar physicochemical properties. We found that removal of ReO₄⁻ was not identical to removal of ⁹⁹TcO₄⁻ and led to formation of an additional transitional phase. This demonstrates that perrhenate and pertechnetate have different kinetics of contaminant removal as a result of variations in mineral transformation.