ALUMINUM BINDING TO HUMIC SUBSTANCES DETERMINED BY HIGH-PERFORMANCE CATION-EXCHANGE CHROMATOGRAPHY

Aluminum binding to humic substances is studied using high performance cation exchange chromatography (HP-CEC) in both laboratory and field samples. HP-CEC provides independent quantification of both free and c omplexed AI(III), eliminating many of the uncertainties associated wit h previous measurements of aluminum speciation. We formulate and calib rate a simple aluminum complexation model, using solutions with variab le total Al(III) (0.2-11 mu M) and pH (4.0-8.2) and constant organic c omposition (12.4 mg/l Suwannee River fulvic acid, FA). The model is ve rified with HP-CEC data from a group of acid lakes and from literature data. The results indicate that AI(III) complexation by natural organ ic matter in several environments is similar to complexation by FA, an d that Al dimers are potentially important species even at low environ mental concentrations of Al. Furthermore, organic complexation of Al i s not limited to acidic waters but appears to be important even at the alkaline pH values typical of marine systems. Copyright (C) 1997 Else vier Science Ltd