The effects of the tricarboxylic organic acid, citric acid, on the adsorption of lead (II) to hematite were examined over a range of pH conditions and citric acid concentration using macroscopic adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The macroscopic data display an increase in lead (II) adsorption in the presence of citric acid at pH below 5.0.  The opposite was observed at pH above 5.0. The ATR-FTIR results indicate citric acid binds hematite as an inner-sphere complex. In this case, the adsorbed citric acid could still coordinate lead using an unbound carboxylic group, even at low pH. As pH increases, citric acid adsorption decreases; however, the coordination of citric acid with lead (II) in solution increases.  This results in a concomitant decrease in lead (II) adsorption. Our results indicate citric acid modifies lead (II) adsorption and at low pH suggest the presence of citrate-bridged interactions.

Effect of citric acid on lead (II) adsorption to hematite: Evidence for acid-bridged interactions

243rd National Meeting (2012)

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