Enhanced dyes removal by sulfidated zerovalent iron: Kinetics and influencing factors

Sulfidation has been considered to be a promising method to improve the performance of zerovalent iron (ZVI). In this study, taking different kinds of dyes (including azo, anthraquinone and triphenylmethane dyes) as model contaminants, the feasibility of applying sulfidation (herein sulfidated ZVI was synthesized by ball-milling with ZVI and elemental sulfur (S-ZVI ^bm)) to enhance the reactivity of ZVI was systematically investigated. The results showed that, S-ZVI^bm could enhance dyes removal efficiency from 52.8–79.4% to 69.5%–100% within 150 min and the ratio of rate constants for dyes decolorization by S-ZVI^bm to that of unsulfidated ZVI generally fell in the range of 1.3–4. Although the decolorization process of Acid Red 27 (AR27) by S-ZVI^bm could be inhibited when solution pH values increased from 4.0 to 10.0, S-ZVI^bm still achieved higher removal rate and efficiency than unsulfidated ZVI. For Pri-ZVI and ZVI^bm, the decolorization rate of AR27 increased linearly with iron dosage. However, it was interesting to observe that the kinetic constants of AR27 removal by S-ZVI^bm increased more sharply than unsulfidated ZVI, implying more available reactive sites could be provided after sulfidation treatment. In sum, from a wide-spectrum perspective, this study provided some insights into the effects of sulfidation on ZVI performance toward various dyes removal.