Reductive immobilization of perrhenate in soil and groundwater using starch-stabilized ZVI nanoparticles

Perrhenate (ReO ₄ ^? ) was used as nonradioactive surrogate for the radionuclide pertechnetate (⁹⁹TcO ₄ ^? ) to investigate the potential of using starch-stabilized zero valent iron (ZVI) nanoparticles for reductive immobilization of pertechnetate in soil and groundwater. Batch kinetic tests indicated that the starch-stabilized ZVI nanoparticles were able to reductively remove ～96% of perrhenate (10 mg/L) from water within 8 h. XRD analyses confirmed that ReO₂ was the reduction product. A pseudo-first-order kinetic model was able to interpret the kinetic data, which gave a pseudo first order rate constant (k _obs) value of 0.43 h^?1 at pH 6.9 and room temperature (25°C). Increasing solution pH up to 8 progressively increased the reaction rate. However, highly alkaline pH (10) resulted in much inhibited reaction rate. Consequently, the optimal pH range was identified to be from 7 to 8. Increasing solution temperature from 15 to 45°C increased k _obs from 0.38 to 0.53 h^?1. The classical Arrhenius equation was able to interpret the temperature effect, which gave a low activation energy value of 7.61 kJ/mol. When the ReO ₄ ^? -loaded loess was treated with the stabilized nanoparticles suspension (Fe]=560 mg/L), the water leachable ReO ₄ ^? was reduced by 57% and nearly all eluted Re was in the form of ReO₂. This finding indicates that starch-stabilized ZVI nanoparticles are promising for facilitating in situ immobilization of ReO ₄ ^? in soil and groundwater.