Fig. 2. Correlations between Langmuir adsorption parameters (pH 7, 0.1 M NaCl) and log weight-average molecular weight (MW_w) for purified Aldrich humic acid (PAHA) ultrafiltration (UF) fractions and different humic substances (HS) on kaolinite: (a) maximum adsorption density and (b) Langmuir adsorption constant. Error bars for some data points are smaller than the symbols.