Reductive immobilization of pertechnetate in soil and groundwater using synthetic pyrite nanoparticles

- First study on reductive immobilization of Tc(VI) using synthetic pyrite particles.
- Synthetic FeS2 particles effectively reduce and immobilize TcO4− in water and soil.
- Fe(II) ions on FeS2 surface are the primary e-donor for reducing Tc(VII) to Tc(IV).
- pH, iron concentration and DOM significantly affect the Tc(VII) reduction rate.
- Synthetic FeS2 particles may serve as an effective PRB material for Tc-laden water.

Radioactive technetium (99Tc) is of intense concern because of its toxicity and high mobility in the environment. Reduction of Tc(VII) to Tc(IV) decreases the mobility and availability of technetium in soil and groundwater. In this study, pyrite nanoparticles (FeS2) were synthesized, characterized and tested for immobilizing/removing 99Tc(VII) in soil and groundwater through batch and column experiments. Influences of particle dosage, dissolved organic matter (DOM), and pH on the reductive immobilization kinetics were examined. At a dosage of 0.28 g/L as Fe, the pyrite nanoparticles were able to rapidly and completely remove 4.88 × 10−7 M of Tc(VII) by converting it to insoluble Tc(IV), with a retarded first-order rate constant of 0.30 h−1. The presence of high concentrations of DOM only moderately inhibited the reduction effectiveness, and acidic pH was more favorable for Tc(VII) reduction. Column experiments showed that embedding a 0.8 cm pyrite layer of the material in a soil bed, simulating a permeable reactive barrier, was able to retard technetium transport 710 times more than a model sandy soil. The results demonstrated that the pyrite particles may serve as a long-lasting reactive material to remediate Tc-contaminated soil, groundwater and solid wastes.