Estudo da adsorção de íons ortofosfato em hidróxido de alumínio
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2009-05-26
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Universidade Federal de Goiás
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Aluminum hydroxides are efficient phosphate adsorbents. In this work it was investigated the adsorptions of phosphate in three different forms of aluminum hydroxide (amorphous, bayerite and pseudo-boehmite). The adsorption isotherms present the amount of phosphate adsorbed as a functions of the equilibrium concentration of orthophosphate ions aqueous solutions, in pH = 5. The products of adsorption were characterized by infrared spectroscopy, 27Al e 31P NMR spectroscopy, XRD analysis, and by zeta potential measurements of the aqueous dispersions. The adsorption isotherms of phosphate on aluminum hydroxide showed that when the hydroxides are treated with diluted phosphate solutions (< 2,0 mmolL-1) the three hydroxides adsorb similar amount of phosphate. When the hydroxides are treated with concentrated phosphate solutions (> 2,0 mmolL-1) bayerite and amorphous aluminum hydroxide incorporate much more phosphate than pseudo-boehmite. The IR and the NMR 27Al and 31P analysis of the adsorption products showed that when the adsorption is carried out in low concentrate phosphate solutions, the adsorbed species are surface aluminum phosphate complexes, while in samples treated with concentrated phosphate solution the products of adsorption are solid phases of aluminum phosphate. These results suggest that the incorporation of phosphate by the three aluminum hydroxides studied occur in two steps. In the first step the phosphate are adsorbed yielding surface complexes; in the second step the incorporation of phosphate occur via the process of aluminum dissolution and precipitation of an aluminum phosphate phase. The XRD analysis showed that the precipitate formed during the dissolution-precipitation process is amorphous and become crystalline after heated at 750 °C for 30 min. The slope of the zeta potential measurements of the aqueous suspensions of the adsorption products suggests that the concentration of the phosphate solution at which the transition of phosphate incorporation by adsorption changes to phosphate incorporation by dissolution-precipitation is similar for the three hydroxides (2 mmolL-1). The results showed that the incorporation of phosphate by precipitation-dissolution occur on the three hydroxides but with lower extension on pseudo-bohemite. This behavior might by related to the lower dissolution of pseudo-bohemite because it is more condensed than amorphous aluminum hydroxide and bayerite
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DAMASCENO, Fernando Cruvinel. Study of adsorption of orthophosphate ions on aluminum hydroxide. 2009. 87 f. Dissertação (Mestrado em Educação em Química) - Universidade Federal de Goiás, Goiânia, 2009.