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Waterlogged acid soils Aerated alkaline soils <br />Se (1q I I Se 101 <br />slow <br />f- <br />Selenide <br />HZSe IogK, _ - 3.81 <br />IogK2= -14.96 <br />Case IogKsp= 10.87 <br />Ag2Se IogKsp= -63.70 <br />CdSe IogKsp= -35.20 <br />PbSe IogKsp= -42.10 <br />Elemental Se <br />Red crystalline Se <br />Red amorphous Se <br />Black, vitreous Se <br />Very insoluble <br />in water <br />Se (IV) <br />Se (VI) <br /> slow <br /> <br />Selenite ~-- <br />Selenate <br /> HZSe03 IogK, _ -2.57 HZSe04 IogK, = 1.97 <br /> IogK <br />=-7 <br />03 -~ Io <br />K <br />= <br />1 <br />9 <br /> 2 <br />. g <br />2 <br />- <br />. <br />1 <br />slow CaSe03 • H2O IogKsp = - 5.44 slow CaSeO, • H2O IogKsp = - 3.09 <br /> Ag2Se03 IogKsp= -15.55 Ag2Se0a IogKsp= -6.91 <br /> CdSe03 IogKsp= - 8.84 CdSe04 IogKsp= -2.27 <br /> PbSe03 IogKsp=-12.11 PbSeOa IogKsp=-6.84 <br /> Strong adsorption ~ Weak adsorption <br />excretion ~ s\o~ <br />ORGANIC Se COMPOUNDS <br />GRAZING ~ PLANTS <br />ANIMALS <br />KpHpL HL- + H+ <br />Ky:HL- H' + Lz <br />Ksp:MeL(c) Me + L <br />Where L is a See-, SeO~,- or Se04- <br />and Me is a metal or alkaline earth. <br />Fig. 1-2. A schematic diagram illustrating the chemistry of Se [after Sarquis & Mickey (1980) and Mayland (1985)]. The acidity constants and solubility <br />products are for 25 °C and 0.101 MPa and were taken from Elrashidi et al. (1987). <br />A <br />.~ <br />z <br />r~ <br />r <br />CO <br />r <br />.. <br />-~ <br />"A <br />.. <br />r <br />