Influence of some chelates of aluminium on the sorption of phosphate by hydrous Al‐oxides

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Abstract
Sorption of phosphate by hydrous oxides of aluminium was studied as a function of pH, presence of chelates of aluminium and of the specific surface areas of the oxides.Aluminon was most effective in reducing P sorption followed by oxalic acid and EDTA. Acetylacetone, 8‐hydroxyquinoline, salicylic acid and fluoride affected little P sorption. The sorption was found to be higher the higher the value of the specific surface area of the oxide, but the shape of the sorption curve was the same for all the oxides studied, exhibiting a maximum at about pH 5. This maximum was found to coincide with the point of zero charge as determined in the presence of acetate ions. The sorption data are explained in terms of a ligand exchange mechanism in which phosphate chemisorbs on surface aluminium atoms displacing uncharged surface hydroxyls.

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