Kinetics of Reductive Immobilization of Rhenium in Soil and Groundwater Using Zero Valent Iron Nanoparticles

Abstract

Abstract This study reports experimental results and modeling analysis of reductive removal of perrhenate (a surrogate for radioactive pertechnetate) from water using a class of starch-stabilized zero valent iron (ZVI) nanoparticles. Thermodynamic analysis of the reduction pathway indicated that reduction of Re(VII), and possibly Tc(VII), is highly favorable with a ΔG of=−316.66 kJ/mol for Re(VII) and −448.66 kJ/mol for Tc(VII). The final reduced product was ReO2, which is much less mobile and less bioavailable than ReO4−. Starch-stabilized ZVI nanoparticles were able to rapidly and completely reduce and remove perrhenate at ambient temperatures. The reaction rate constant increased from 0.351 h−1 at 15°C to 0.428 h−1 at 45°C and a fairly low activation energy level of 5.13 kJ/mol was determined. A surface blocking effect on the ZVI nanoparticles was evident due to surface precipitation of the resulting ReO2. As a result, the pseudo first order rate constant decreased from 0.356 to 0.230 h−1 when the init...