Enhanced hydrodeiodination of iodinated contrast medium by sulfide-modified nano-sized zero-valent iron: Kinetics, mechanisms and application prospects

Abstract

The performance and possible mechanisms of iodinated contrast medium diatrizoate (DTA) removal by sulfide-modified nano-sized zero-valent iron (S-nZVI) without the presence of oxygen were investigated in this study. It was shown that the degradation efficiency of 30 μM DTA was observably enhanced by 2 g L−1 S-nZVI (S/Fe = 0.25) compared to nZVI. Kinetic analysis indicated that the three-step deiodination process of DTA removal by S-nZVI could be appropriately fitted by pseudo-first-order kinetic model. The first-step kinetic rate constant of DTA removal reached to 2.22 h−1 with the utilization of S-nZVI, which was 5.2 times higher than that of nZVI. The enhancement mechanism for DTA removal by S-nZVI was confirmed as accumulating more atomic hydrogen (H*) via the inhibition of hydrogen recombination. Moreover, it was found that the degradation rate of DTA was optimal when the S/Fe ratio attained at 0.25. The DTA removal performance exhibited a promoting trend with the increasing of S-nZVI dosage, while the existence of humic acid or artificial groundwater environment showed an inhibition effect on the degradation rate of DTA by S-nZVI. Additionally, the comparison of reduction capacity between S-nZVI and nZVI was evaluated in continuous flow systems, indicating that S-nZVI would likely present more practical application prospects on DTA removal than nZVI.