Cadmium adsorption on hydrous aluminium (III) oxide: effect of adsorbed polyelectrolyte |
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| Institution: | 1. IFP Energies nouvelles, Fluid Mechanics Department, Rond-point de l’Echangeur de Solaize, BP 3, Solaize 69360 France;2. Department of Mathematics, University of British Columbia, 1984 Mathematics Road, Vancouver, BC, V6T 1Z2, Canada;3. Departement of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canada;4. Departement of Mechanical Engineering, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, BC, V6T 1Z4, Canada |
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| Abstract: | Freshly precipitated hydrous oxides of Al (flocs) are important sorbents of heavy metal ions and are used in water treatment processes. The addition of chelating agents or polyelectrolytes can increase the efficiency of heavy metal removal by flocs. The polymer polyethylenimine is commonly used as a flocculant aid in water treatment and has been modified with phthalic acid. Adsorption studies have shown that the addition of millimolar concentrations of polyelectrolyte increases the removal of Cd ions from a 29.7 μM aqueous solution by aluminium flocs from ca. 40% to up to 75%. Experiments in which the pH was varied demonstrated that the observed enhancement of Cd adsorption is caused by a shift of the pH edge to lower pH values in the presence of polyelectrolyte. Maximum polyelectrolyte adsorption occurs between pH 6 and pH 7, corresponding to the point of enhanced Cd adsorption in the presence of polyelectrolyte. The enhancement of Cd adsorption observed below pH 7 is therefore likely to be due to the formation of a ternary surface complex. At pH values above pH 8 the polyelectrolyte forms a stable complex with Cd and Al ions in solution causing floc dissolution and decreased Cd adsorption. |
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