Interactions of humic acids and aluminum salts in the flocculation process

Abstract The surface complexation of three humic acids on in situ formed aluminum hydroxide at pH = 7 was studied by a pH-titration method. The results can be described by a Langmuir-equation, including the ligand content of humic acids and an affinity constant for the hydroxide surface. About 50% of the acidic functions in humic substances are complexing groups, forming 1:1-compounds. The density of complexing groups increases with the molecular weight. The effects of dilution, neutral salts and preozonation on complexation equilibria were studied and discussed. Removal of the organic carbon and aluminum by membrane filtration indicated the formation of soluble or colloidal hydroxo-humate products. Experiments with synthetic organic acids support the assumption, that salicylic acid groups are involved in surface complexing.

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