Fig. 1. Humic substance (HS) adsorption isotherms on minerals: (a) different HS on kaolinite, (b) different HS on hematite, (c) purified Aldrich humic acid (PAHA) ultrafiltration (UF) fractions on kaolinite, and (d) PAHA UF fractions on hematite. Adsorption experiments were performed at pH 7 and 0.1 M NaCl in duplicate or triplicate. Error bars for some data points are smaller than the symbols. The solid lines represent the respective Langmuir model fits to the data.