Removal of EDTA-chelated CdII by sulfidated nanoscale zero-valent iron: Removal mechanisms and influencing factors

Abstract

The removal mechanism of sulfidated nanoscale zero-valent iron (S-nZVI) toward Cd II -EDTA. • Fe and S had coupled effect on Cd II -EDTA removal. • The removal capacity of S-nZVI toward Cd II -EDTA was 746.6 mg/g within 90 min. • The removal of Cd II -EDTA by S-nZVI consisted of two-step replacement reactions. • pH 0 had great influence on the removal of Cd II -EDTA by S-nZVI. In this study, the removal mechanisms of sulfidated nanoscale zero-valent iron (S-nZVI) toward EDTA-chelated Cd II (Cd II -EDTA) and the detailed effects of some critical factors on Cd II -EDTA removal by S-nZVI were systematically investigated. The results showed that the removal capacity of S-nZVI toward Cd II -EDTA within 90 min of reaction was 746.6 mg/g (when the initial concentration of Cd II -EDTA, the dosage of S-nZVI, and the initial solution pH were 300.0 mg Cd II /L, 0.3 g/L, and 2.6, respectively), which was 6.2 and 2.5 times higher than that of nZVI and Na 2 S, respectively, indicating that Fe and S had coupled effect on Cd II -EDTA removal. The removal mechanisms of Cd II -EDTA by S-nZVI consisted of two-step replacement reactions. In brief, Fe III generated from the corrosion of S-nZVI firstly replaced the Cd II in Cd II -EDTA, and then the decomplexed Cd II ions were immobilized by occurring the second-step replacement reaction with FeS in S-nZVI and forming CdS phase. Batch experiment results indicated that the removal of Cd II -EDTA by S-nZVI decreased as the initial Cd II -EDTA concentration increased and S-nZVI dosage decreased. Under the same S-nZVI dosage (0.3 g/L) and initial Cd II -EDTA concentration (300.0 mg Cd II /L), the acidic initial pH (pH 0 = 2.6) was favorable for the removal of Cd II -EDTA. This study demonstrated that S-nZVI could be a viable choice for the Cd II -EDTA-contaminated wastewater treatment.