Understanding the positive effects of low pH and limited aeration on selenate removal from water by elemental iron

Efficient selenate removal by zero-valent iron in the presence of weak magnetic field

“…Under N 2 purging conditions, less than 10% of Se(VI) was removed by ZVI in 8 h even in the presence of WMF, as demonstrated in Fig. 2(a), consistent with the results reported by Klas and Kird [30] and Yoon et al [20]. In their studies, magnetic stirrer was employed to offer mixing and thus WMF was introduced by the magnetic stirrer in their studies although the authors did not notice the WMF effect on Se(VI) removal by ZVI.…”

“…Although there was still 157 mg L À1 Fe 2+ after 5 h of reaction when ZVI was applied at 1.5 g L À1 , negligible Se(VI) was removed after 5 h even there was still 9.3% Se(VI) residual in the solution, indicating that Fe 2+ was not an effective electron donor for reductive removal of Se(VI) [29]. Klas and Kird [30] reported that the electron donor for Se(VI) reduction was not Fe 0 but a reactive Fe 2+ -bearing solid formed during oxidation of Fe 0 by O 2 , thus more rapid Se(VI) removal by ZVI was observed under oxic conditions, which did not agree with our observations. Because more Fe 2+ was generated, more oxygen was consumed and less Se(VI) was residual at higher ZVI dosage, ORP dropped to a greater extent and rebound more slowly at higher ZVI dosage, as shown in Fig.…”

Reductive removal of selenate by zero-valent iron: The roles of aqueous Fe2+ and corrosion products, and selenate removal mechanisms

“…Previous studies showed that the addition of a certain amount of Fe 2þ could significantly accelerate nitrate reduction by Fe 0 (Xu et al, 2012) and TCE dechlorination by aged Fe 0 (Liu et al, 2013). Similarly, selenate reduction by ZVI was favored under acidic or aerobic condition (Yoon et al, 2011;Klas and Kirk, 2013), which probably attributed to Fe 2þ deriving from iron dissolution at low pH or aerobic condition. Therefore, the objectives of this study were 1) to investigate the role of externally supplied Fe 2þ and iron corrosion products in selenate reduction by ZVI; and 2) to elucidate the mechanisms of selenate removal in a ZVI-Fe 2þ system by chemical and instrumental analysis.…”

“…It has also been proved that ZVI (Yoon et al, 2011;Gibson et al, 2012) or nano-ZVI (Olegario et al, 2010) was effective for Se VI removal from wastewater by reducing to more adsorptive Se IV and/or to insoluble Se species (i.e., Se 0 , Se ÀI and Se ÀII ). However, most of previous studies primarily focused on the effects of co-existent ions, contaminants, and the operational parameters such as pH, dissolved oxygen and reagent concentration (Klas and Kirk, 2013;Puranen et al, 2009). But none of them has clearly illustrated the role and evolution of Fe 2þ during selenate reduction by ZVI.…”

Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism

“…Mishra and Farrell's study (2005) showed that the reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism for nitrate removal with ZVI. Klas and Kirk (2013) reported that limited aeration dramatically increased the Se(VI) removal rate under both acidic and basic conditions due to the formation of reactive Fe(II)-bearing solid intermediates on the ZVI particles. Based on these results, Fe(II)-containing oxides on the surface of ZVI was the major factor for the increase of kinetic for the removal of Se(VI).…”