Sulfidated microscale zero-valent iron (S-mZVI^bm) for uranium immobilization: accelerated electron transfer and...

As a cheap and accessible electronic repository, microscale zerovalent iron (mZVI) has up-and-coming applications in uranium wastewater disposal. Yet, its reactivity is still constrained by the inert oxide shell. To overcome this shortcoming, a ball milling technique was used to prepare sulfidated microscale zerovalent (S-mZVI^bm) for treating uranium wastewater. Under ambient conditions, the oxide layer formed on the surface of mZVI^bm due to the passivation of dissolved oxygen was replaced by the sulfide layer of S-mZVI^bm. Theoretical calculations and characterization results showed that the sulfide layer not only enhanced surface coordination and enrichment of uranium, but also promoted the electron transfer from the iron core to the surface. The work function of S-mZVI^bm was lower than that of mZVI^bm, emphasizing the excellent electron-donating potential exhibited by S-mZVI^bm. The calculated apparent rate constant k₂ (4.47 × 10^-3 g·mg·min^-1) and removal efficiency (90.0%) of S-mZVI^bm within 5 h were 20.1 and 7.5 times larger than those of mZVI^bm within 10 h, respectively. Moreover, the content of uranium could be decreased to levels below the standard limit value for drinking water quality (30 μg L^-1) with S-mZVI^bm in real uranium wastewater. These findings offer novel insights into treating uranium wastewater through ZVI-based technology.