| Abstract |
| The thermal feature of the precipitating treatment of phosphate-containing wastewater by aluminium has been investigated based on thermodynamic estimation. The distribution diagram of orthophosphates in aqueous environment was constructed using MINTEQ program and the amounts of H3PO4 and PO43- were shown to be increased with temperature, however, the amounts of H2PO4- and HPO42- were examined to be relatively decreased as temperature rises. The increasing extent of the amount of PO43- with temperature was investigated to be greater than that of H3PO4 and the extent of the decrease in the amount of HPO42- with temperature was shown to be bigger than that of H2PO4-. The Pourbaix diagram for Al-water system was constructed by equilibrium calculation using thermodynamic data and it was observed that Al3+ ion changes into Al2O3·3H2O at around pH 4, which was examined to be lowered with temperature. Based on the Pourbaix diagram for orthophosphate-water system, the stable region of PO43- ion was investigated to be enlarged as temperature rises and the defined reactivity of Al3+ ion and PO43- ion was examined to decrease and increase with temperature, respectively. Finally, the precipitate-formation reaction of AlPO4 was negatively affected by the rise of temperature and it was suggested that the thermal condition for the precipitating treatment process of phosphate-containing wastewater employing aluminium should be established by considering both equilibrium and kinetic aspects of the process. |
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| Key Words |
| Orthophosphate, Aluminium ion, Precipitating treatment, Temperature effect, Eh-pH diagram |
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