Acid-base properties of aquatic fulvic acid

The acid-base properties of aquatic fulvic acid, concentrated from the Göta River, were studied by means of potentiometri titrations. The forward and reverse titrations exhibited hysteresis, which decreased as the fulvic acid underwent repeated titration. A simple model based on six titratable groups, within the pH range 2.5–10.4, could explain the acid-base properties. Electrostatic polymeric effects and heterogeneity of the fulvic acid (i.e., a distribution of constants rather than a set of distinct constants) were not included in the model. It was found that the three most acidic groups were carboxylic.