Sorption behavior of hydroselenide (HSe⁻) onto iron-containing minerals

Abstract

The sorption behavior of selenium onto iron-containing minerals such as goethite, ferrous oxide, magnetite, and biotite under reducing conditions were investigated by batch sorption experiments. Selenium was spiked as HSe − and Se 4 2− in the experimental solutions and reducing conditions were maintained throughout the sorption periods. The sorption behaviors of HSe − were analyzed by the triple-layer surface complexation model with the Visual Minteq computer program. The sorption data and the model calculations suggested that the dominant sorption mechanisms of HSe − were inner-sphere surface complexation for goethite and ferrous oxide but outer-sphere surface complexation for magnetite and biotite. The intrinsic equilibrium constant of the inner-sphere surface complexation reaction of HSe − with goethite, logK int HSe = 6.0, was determined by the fitting to the experimental results. The value of the equilibrium constant for outer-sphere complexation for magnetite and biotite was estimated to be around 12.

Selenide [Se(−II)] Immobilization in Anoxic, Fe(II)-Rich Environments: Coprecipitation and Behavior during Phase Transformations

“…This implies that β-FeSe will form regardless of the degree of overpack corrosion, ensuring that Se(−II) could be quickly immobilized upon being released into an actively corroding overpack. Previous studies of the Se(−II) uptake by magnetite attributed the strong uptake by magnetite to surface adsorption; 24,25 this assumption thus needs to be reassessed. One of the commonly assumed solubility-limiting phases for Se at reducing conditions is FeSe 2 .…”

“…Previous investigations on Se immobilization with corrosion products have focused mostly on Se­(IV) and Se­(VI), but anoxic conditions in the subsurface, coupled with the reducing conditions imposed by H 2 generation during steel corrosion, are likely to keep Se in the −II oxidation state. It is commonly assumed, based on thermodynamics, that iron selenides control Se­(−II) concentrations at reducing and ferruginous conditions. − Most studies of Se­(−II) have thus focused on “secondary” immobilization reactions with iron oxides and sulfides, assuming Se concentrations close to equilibrium with iron selenides; − but fundamental information about the primary reactions forming iron selenides is scarce. Specifically, what role does Se­(−II) coprecipitation and its interactions with transient, metastable corrosion products like Fe­(OH) 2 play in initial immobilization?…”

Sorption behavior of thorium onto granite and its constituent minerals

“…In the calculations for biotite, the measured surface area (4.3 m 2 g −1 ), the surface acidity constants (log K a1 = 4.6 and log K a2 = −6.4) [43,44] and the surface site density (3.81 sites nm −2 ) for mica [15] were adopted. The formation constants of surface species for biotite are not available.…”

Recent activities in the field of nuclear waste management

“…Redox potential and molar entropy between tetravalent and hexavalent selenium were determined using cyclic voltammetry [12,13]. Interaction between selenium and iron is also important because corrosion of overpack made of carbon steel releases iron(II) in the Japanese high-level radioactive waste (HLW) disposal system [14]; therefore, sorption behavior of selenium(II) onto iron-containing minerals were studied, and the selenium sorption modeling was performed [15]. Bioreduction of selenium(IV) under iron-containing conditions were also studied, and selenium(II) precipitate was observed under Fe(III)-citrate-containing conditions [16].…”