The Research of Potenia-pH Diagram of Se-H2O System at Different Temperatures.

This paper presents the calculation and analysis of the important mononuclear complexes in the Se-H₂O system. Based on the thermodynamic data of S0 + ΔfG0 + ΔfH0 and CP of each reaction substance at standard state, the dominant region distribution of the dissolved species ni Se(-II):H₂O, Se(IV):H₂O and Se(IV)-H₂O systems were calculated at different pH values under the temperature range of 298-573 K. Combined with the equilibrium thermodynamic data of the oxidaton and reduction reactions of Se containing substances at different temperatures, the potential-pH diagrams of the Se-H₂O system at 298, 373,473 and 573 K were constructed. It was found that both H₂Se and H₂SeO₃ could exist stably in high acid content solution, while H₂SeO₄ could only exist in high-temperature and high add content solution. At 298 - 573 K,Se could exist stably in aqueous solution. In the range of 298 - 473 K, H₂SeO₃^-, HSeO₃ and SeO₃^2- could be directly reduced to elemental Se. Therefore, by controlling a certain pH value and potential, Se could be removed from the solution by precipitation in the form of elemental Se. With the increase of temperature, the stable region of H₂O decreased, and the region of Se, which exssted in the sold phase, also gradually decreased. In the liquid phase, the stable regions of H₂SeO₃^-, HSeO₃^- and SeO₃^2- with Se(+IV) continued to increase. With the increase of temperature, the oxidation potential of elemental selenium oxidized to Se (IV) and further to Se(VI) decreased slightly, and the oxidation reaction could be easier to carry out. [ABSTRACT FROM AUTHOR]