Coupled Effect of Sulfidation and Ferrous Dosing on Selenate Removal by Zerovalent Iron Under Aerobic Conditions

Abstract

Both the reactivity and the removal capacity of zerovalent iron (ZVI) for the target contaminant are important for applying ZVI in wastewater treatment. In this study, the feasibility of combining sulfidation treatment and Fe2+ dosing (S-ZVI/Fe2+) to enhance the performance of ZVI for Se­(VI) removal was comprehensively investigated under aerobic conditions. Se­(VI) was first adsorbed on the surface of ZVI particles and then reduced to Se­(IV) and Se(0) with Se(0) being the final product in S-ZVI/Fe2+ system. This system bore the advantages of both sulfidation treatment (S-ZVI) and Fe2+ dosing (ZVI/Fe2+) for Se­(VI) removal. The amounts and rate constants of Se­(VI) removal in S-ZVI/Fe2+ system were increased by 1.8–32.8 times and 11.7–194.0 times, respectively, compared to those in pristine ZVI system. Sulfidation significantly accelerated the corrosion of Fe0 thus improved the removal rate of Se­(VI). The promoting effect of Fe2+ on Se­(VI) sequestration by S-ZVI should be mainly associated with the following facts: Fe2+ could maintain a relatively low pH level during Se­(VI) removal by S-ZVI; Compared to S-ZVI alone, the consumption of Fe0 in S-ZVI/Fe2+ by O2/H+ was slower, and thus the electron efficiency of S-ZVI was elevated; Fe2+ dosing facilitated electron transfer by forming semiconductive Fe3O4.

Reactivity and selectivity of zerovalent iron toward selenium oxyanions under aerobic conditions

“…This suggested that the coexisting ions may influence the EE by affecting Se(VI) adsorption and the subsequent electron transfer from the Fe 0 core to Se(VI) at the water-particle interface. Given these facts, Fan et al (2019b) further confirmed that sulfidation coupled with Fe (II) dosing could synergistically improve the reactivity and selectivity of ZVI toward Se(VI) under aerobic conditions (Figure 5…”

“…Therefore, future research should focus on illustrating the performance of the ZVI/Fe 2+ system toward Se(VI) on a pilot-scale (Fan et al, 2019a). Moreover, the feasibility of employing Fe 2+ to enhance the performance of ZVI should be examined with ZVI of different origins, different target contaminants, and in the presence of different background matrices (Fan et al, 2019a), as well as coupled with WMF or sulfidation (Fan et al, 2019b).…”

Simply closing the reactor improves the electron efficiency of zerovalent iron toward various metal(loid)s removal

“…EE describes the fraction of electrons transmitted to the target contaminant over the amounts of electrons provided by ZVI and had been used to assess the selectivity of ZVI for reductive removal of the target contaminant (Fan, Sun, et al, 2019; Xu, Avellan, et al, 2020). Specific removal capacity (SRC) is defined as the ratio of the amount of removed metal(loid)s to the consumed Fe 0 , and it can be used to indicate the capacity of consumed Fe 0 to remove contaminants, regardless of the removal mechanism (Fan, Li, et al, 2019).…”

“…This phenomenon could be highly related to the surface properties of ZVI altered by the metal(loid)s in solution. For example, the surface of ZVI could be passivated by Se(VI) at elevated concentration (Fan, Li, et al, 2019; Fan, Sun, et al, 2019; Liang et al, 2015), which decelerated both the consumption of DO and the removal of contaminants by ZVI. It was found that both the consumption rate of DO and the removal rate of the certain metal(loid) under open condition were larger than those under closed condition.…”

“…Plenty of studies have proved that ZVI corrosion is a necessity for metal(loid)s sequestration by ZVI (Fan, Li, et al, 2019; Guan et al, 2015; Sun et al, 2016), and the removal of metal(loid)s by ZVI is hard to be achieved when ZVI corrosion is strongly inhibited (i.e., passivation) (Fan, Li, et al, 2019; Qin et al, 2017). However, the rapid corrosion of ZVI leads to its useless consumption, resulting in the relatively low selectivity and capacity of ZVI toward metal(loid)s removal (Fan et al, 2019). Many previous studies focused on enhancing the reactivity of ZVI while few of them have considered the electron efficiency (EE) of ZVI, the ratio of electrons from ZVI used to reduce the targeted contaminants (Xu, Liu, et al, 2020).…”