Selenium(IV) Uptake by Maghemite (γ-Fe₂O₃)

Abstract

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11). Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing ((2)C) and bidentate mononuclear edge-sharing ((1)E) inner-sphere surface complexes was observed, with a trend toward solely (1)E complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the Se(IV)O3 unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters.

Inorganic engineered nanoparticles in drinking water treatment: a critical review

“…Arsenic removal is the most studied case of magnetic iron oxides application in water treatment. 158,159,160,161,162,163,164,165,166 A number of publications for the removal of As, Cr(VI), Cu 2+ , Se and Co 2+ suggest ferrite nanoparticles as a magnetically activated system for water treatment. 102 In these studies, the adsorption capacity was getting higher following the decrease in the dimensions of nanoparticles.…”

Adsorption of Selenite and Selenate by Metal Oxides Studied with Fluorescent DNA Probes for Analytical Application

“…The maximal contamination level of selenium in water is 50 lg/L (*0.6 lM) as defined by the US Environmental Protection Agency (EPA). In addition, 79 Se is a radionuclide found in nuclear fuel wastes, and it is a major environmental concern [3]. Inorganic selenium exists mainly in SeO 3 2-(selenite or Se(IV)) and SeO 4 2-(selenite or Se(VI)).…”

“…In addition, 79 Se is a radionuclide found in nuclear fuel wastes, and it is a major environmental concern [3]. Inorganic selenium exists mainly in SeO 3 2-(selenite or Se(IV)) and SeO 4 2-(selenite or Se(VI)). H 2 SeO 3 is a weak acid with two pK a values (2.6 and 8.3), while H 2 SeO 4 is a quite strong acid with its two pK a 's around 1.8 [2].…”

“…A few materials were tested for this purpose, including iron oxide [4][5][6], alumina [7,8], and titania [9]. In particular, iron containing oxide, hydroxide, and minerals has been the most extensively studied for this purpose [3,[10][11][12].…”

Sorptive uptake of selenium with magnetite and its supported materials onto activated carbon

“…The impregnation of magnetite nanomaterials onto carbonaceous supports offers several unique advantages. Studies related to the uptake of selenium species have been reported; iron oxides [13][14][15][16][17][18][19], composite materials [20][21][22], and a recent review [23] on the subject. The formation of metal oxides such as magnetite (Fe 3 O 4 ) nanoparticles on the surface of activated carbon (AC) or within its pores may contribute to the formation of a stable composite material.…”