Performance of Nano-Magnetite for Removal of Selenium from Aqueous Solutions

Abstract

Selenium (Se) is emerging as a contaminant that must be dealt with in many areas of the world, especially those areas impacted by past or current mining activities. In this study, we evaluate the effectiveness of synthesized nano-magnetite when used as an adsorbent to remove anionic selenium species from aqueous solutions. In conjunction with studies on the effects of pH, temperature, concentration, contact time, and presence of competing anions on selenium removal efficiency, a series of batch adsorption experiments were conducted to study adsorption isotherms and adsorptive thermodynamics. Compared with either natural magnetite ( < 5 lm) or nano-iron (*10 nm), nano-magnetite (10-20 nm) was found to be a better adsorbent for selenite, while nano-iron showed better adsorption performance for selenate. From an initial selenium concentration of 100 lg-Se/L, which is comparable to those commonly found in mine water or mining impacted streams, a final concentration of < 5 lg-Se/L could be achieved, using nano-magnetite. Low pH favored selenite adsorption, and elevated temperature enhanced selenium removal. Selenite adsorption followed the Freundlich isotherm model, and the presence of common anions did not significantly affect the adsorption capacity of nano-magnetite for selenite. Selective adsorption demonstrated that nano-magnetite could be a very promising nano-sorbent to treat selenium contaminated water.

The role of counter ions in nano-hematite synthesis: Implications for surface area and selenium adsorption capacity

“…Se(VI) has a lower affinity for nα-Fe2O3 than Se(IV), which is in agreement with other reports [12]. The values reported for qm (Figure 3a and b) are greater than that previously reported for other single-phase iron or aluminum oxide nano-sorbents [6,11,16,29,42]. Since the adsorption capacity of Se by nα-Fe2O3 is higher than or similar to the nγ-Al2O3, no other comparison was conducted.…”

“…Of the four main oxidation states of inorganic Se, selenite (Se(IV)) and selenate (Se(VI)) are of greatest significance because they are soluble, mobile and bioavailable [6]. At relevant aquatic pH and pE conditions, Se(IV) and Se(VI) exist primarily as the oxyanions HSeO3and SeO4 2-, respectively [1,2].…”

“…With the development of nanotechnology, the applicability of nano materials in engineered systems has also grown [8,12]. In general, nano metal oxides possess increased surface area per mass, suggesting a larger sorption capacity per mass than their micro-and macro-scale counterpart [6,8].…”

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

“…Doped ferrites (x = 0.1-0.5) are superior to un-doped ferrites (x = 0) regarding the active sites, functional groups and fluoride adsorption [312]. Compared with either natural magnetite (< 5 µm) or nanaosized zerovalent iron (NZVI) (~10 nm), MNP (10-20 nm) is a better adsorbent for selenite, while NZVI shows better adsorption performance for selenate [313]. Competition of anions for adsorption on MNPs and their hybrids needs to be more fully evaluated for practical applications.…”

Simultaneous removal of selenite and selenate from drinking water using mesoporous activated alumina

“…This trend also agrees with the results obtained from zeta potential measurements. As per the reported literature, for most of the adsorbents, the adsorption capacity drastically reduces in alkaline pH (Das et al 2013;Jordan et al 2013;Wei et al 2012;Su et al 2008). The lowering of adsorption efficiency at the alkaline pH range may be due to competition of OH − at the active sites of the adsorbent.…”