Chemical Equilibria of Selenium in Soils

Hydrological and geochemical investigations of selenium behavior at Kesterson Reservoir

“…This change in redox conditions should result in the progressive oxidation and solubilization of the selenium inventory (Geering et al, 1968;Elrashidi et al, 1987). These trends have been observed in several soil profiles at Kesterson (Tokunaga et al, 1991).…”

“…Its solubility and mobility in the environment are strongly dependent on its valence and specific chemical state. Common inorganic species include soluble selenate (Se(VI)), selenite (Se(IV)), insoluble elemental selenium (Se(O)), and various metal and organic selenides (Elrashidi et al, 1987;Masscheleyn et al, 1990). Selenite, which is stable under moderately reducing conditions, is soluble, but can strongly adsorb onto surfaces of common soil minerals and organic matter (Geering et al, 1968;Hingston et al, 1971;Hamdy et al, 1977;Balistrieri and Chao, 1987;Bar-Yosef and Meek, 1987;Neal et al, 1987;Christensen et al, 1989).…”

Selenium Poisoning of Wildlife and Western Agriculture: Cause and Effect

“…3 demonstrates that selenate is the dominant form in oxidizing waters. Indeed, most selenates are too soluble to persist in soils (Elrashidi et al 1987). The Eh/pH diagram also shows that selenite and hydrogen selenite dominate in reducing systems.…”

Extraction Characteristics of Selenium as Affected by Coal Fly Ash Type, Water Extractant, and Extraction Time

“…Once released into the environment, Se usually exists as the highly mobile selenate ( ) 2 4 SeO − or as the more toxic, but far less mobile selenite ( ) [28]. Changes in oxidation states affect Se's solubility, (re)adsorption, and mobility rates in soils [29]- [31]. Selenite behaves similar to phosphate (i.e., forms an inner-sphere surface complex), has a greater adsorption rate than selenate, and is controlled by its ability to bind to ferric hydroxides and aluminum oxides in acidic and neutral soils [32]- [35].…”

“…Selenite behaves similar to phosphate (i.e., forms an inner-sphere surface complex), has a greater adsorption rate than selenate, and is controlled by its ability to bind to ferric hydroxides and aluminum oxides in acidic and neutral soils [32]- [35]. In contrast, selenate is known to behave like the sulfate anion (i.e., forms an outer-sphere surface complex) with low adsorption rates, high solubility, and pronounced leachability causing selenate to be highly mobile in soils [29] [36] [37]. Recognizing and understanding the differences between species are critical for assessing the amount of Se that has been, and could be, released into the environment from an ash landfill and to better predict Se's natural mitigation, such as biotic or abiotic reduction of selenate to selenite and its subsequent precipitation and/or adsorption of selenite to Fe/Al oxides in soils.…”