Alkaline Selenide, Polyselenide Electrolytes: Concentrations, Absorption-Spectra and Formal Potentials

Abstract

Spectrophotometric, titrimetric, electron spin resonance and 77Se nuclear magnetic resonance studies made on the alkaline selenide, selenium electrolyte showed that soluble selenium species existed in four oxidation states, none of the species was a radical, and the mean state of oxidation of the Se-saturated solution was equivalent to Se3.82. It was concluded that the species were Sen2- with n = 1, 2, 3 and 4, or their protonated forms. On the basis of the Nernst equation, we analysed independently (A) the titration Eredox against the mean state of oxidation of the solution and (B) the absorption spectra of solutions with different mean states of oxidation. Thus formal redox potentials E′ were determined as E′12 = -0.935, E′13 = -0.931 and E′14 = -0.914 V against s.c.e. for the couples Se2-, Se22-; Se2-, Se32-; and Se2-, Se42- respectively in 1 mol dm-3 KOH supporting electrolyte at 304 K. It followed that E′23 = -0.919 for Se32-,Se32- and E′34 = -0.778 for Se32-,Se42-. The concentration of each species at each redox potential and the absorption spectrum of each distinct oxidation state were found. Excellent fits and agreement between the two analyses were observed. Ultraviolet absorption spectra showed that the reduced ion was approximately 50% protonated in 1 mol dm-3 KOH supporting electrolyte.

Solubility of Selenium at High Ionic Strength under Anoxic Conditions

“…This peak was assigned to HSe À . 4,5,10) At pH between 9 and 13, the sample solutions were reddish and showed absorption bands at 220, 282, and 377 nm. These results are indicative of the formation of Se 4 2À .…”

“…These results are indicative of the formation of Se 4 2À . 4,5) The UV-Vis spectra of the 1.0 mol dm À3 NaCl sample solutions at pH 7 and pH 10 are shown in Fig. 4 as representative examples.…”

“…1). Since the chemical conditions under deep underground environments are likely to be anoxic and reducing, a Se(-II) species of HSe À is considered to be dominant in neutral groundwater, 3) and polyselenide species of Se n 2À (n ¼ 1{4) is considered to be dominant in alkaline groundwater [3][4][5] induced by cementitious materials in radioactive waste repositories (Fig. 1).…”

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

“…Figure 2 shows the UV-Vis spectra of the Se(-II) starting solution of 0.1 mol dm À3 NaCl and the experimental solution in the high-concentration reservoir of 2-9 cells (0.1 mol dm À3 NaCl, bentonite/sand = 5/5) after diffusion experiment as representative examples. The UV-Vis spectra show an absorption band at 245 nm, which was assigned to HSe À , 31,32) and the ones assigned to Se 4 2À at 282 and 377 nm. 31,32) The same patterns were observed in samples under other conditions.…”

“…The UV-Vis spectra show an absorption band at 245 nm, which was assigned to HSe À , 31,32) and the ones assigned to Se 4 2À at 282 and 377 nm. 31,32) The same patterns were observed in samples under other conditions. The concentration of Se, C Se , present as HSe À in the starting solution was determined to be 1:9 Â 10 À5 mol dm À3 from the absorbance (a ¼ 0:142 at 245 nm), molar extinction coefficient, (" ¼ 7500 cm À1 mol À1 dm 3 at 245 nm for HSe À ), 31) and path length, l (1 cm) according to the Beer-Lambert law 32)…”