Individual effects of different co-existing ions and polystyrene (PS) microplastics on the reactivity of sulfidated nanoscale zero-valent iron (S-nZVI) toward EDTA-chelated CdII removal

Recently, EDTA-chelated CdII (CdII-EDTA) was effectively removed by sulfidated nanoscale zero-valent iron (S-nZVI). However, few studies have been performed to investigate the influence of co-existing ions and emerging contaminants (such as microplastics) on the performance of S-nZVI toward CdII-EDTA, which is vital for the application of S-nZVI in practical wastewater treatment. In this study, the individual effects of different co-existing ions (NO3−, SO42−, PO43−, Mg2+, Cu2+, and Zn2+) and polystyrene (PS) microplastics with different concentrations on the removal of CdII-EDTA by S-nZVI were systematically investigated. The removal capacity of S-nZVI toward CdII-EDTA fell in the range of 579.3–644.7, 612.3–670.2, 607.4–691.3, 533.3–623.6, 79.9–545.3, 544.3–631.7, and 568.6–663.8 mg/g for the presence of NO3−, SO42−, PO43−, Mg2+, Cu2+, Zn2+, and PS microplastics over the concentration range of 10.0–150.0 mg/L, respectively, which were all smaller than that of the system of CdII-EDTA alone (746.6 mg/g), indicating that all of the investigated co-existing substances showed inhibitory effects on CdII-EDTA removal. As for NO3−, SO42−, or Mg2+-containing system, the inhibitory effect was ascribed to the influence of S-nZVI corrosion rate; As for PO43−, Mg2+, Cu2+, Zn2+, or PS microplastics-containing system, the negative effect was caused by changing the corrosion of S-nZVI and occupying the reactive sites at the surface of S-nZVI. The final corrosion products of S-nZVI under different reaction conditions were strongly dependent on the species and concentration of co-existing substance with the combinations of γ-FeOOH, α-Fe2O3, FeO, or β-FeOOH as the dominant corrosion products.