Enhanced sequestration of Cr(VI) by copper doped sulfidated zerovalent iron (SZVI-Cu): Characterization, performance, and mechanisms

The reactivity of zero valent iron (ZVI) for sequestering Cr(VI) is self-inhibiting in aquatic environments, which limits the application of ZVI. A series of improvement strategies have been proposed. In this study, a coppersulfidated ZVI (SZVI-Cu) material was prepared by depositing copper onto sulfidation modified ZVI to enhance the sequestration efficiency and capacity of Cr(VI). Comparative experiments were used to demonstrate the superiority of SZVI-Cu for sequestration of Cr(VI) with ZVI, sulfidated ZVI (SZVI) and iron-copper (ZVI-Cu). In addition, SZVI-Cu exhibited a prominent ability for sequestration of Cr(VI) over a wide pH range of 4-8. The sequestration efficiency of Cr(VI) by SZVI-Cu reached 97.9% within 20 min even at pH 8.0, and the sequestration rate of Cr(VI) increased 2.4-59.7 folds compared with other three materials. Batch experiments were also used to evaluate the removal efficiency under various factors such as SZVI-Cu dosage and mixing rate. The positive correlation between the sequestration efficiency of Cr(VI), the produced rate of Fe(II) and the inhibited removal of Cr(VI) in the presence of 1,10-phenanthroline indicated that Fe(II) played an important role to the sequestration of Cr(VI). The mechanism analysis showed that sulfidation can facilitate the electron transfer from iron metal to contaminant and strengthen Fe(II) releasing from ZVI, and loading Cu-0 can also be conducive to the production of Fe(II) due to the potential difference between the two metals. Cu combined with ZVI function as galvanic cells not only accelerates the reaction rate but also increases the sequestration capacity of Cr(VI). SZVICu is promising for rapid and effective sequestration of Cr(VI) over a wide pH range.