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This article in SSSAJ

  1. Vol. 63 No. 4, p. 850-857
    Received: Apr 13, 1999

    * Corresponding author(s): jdc7@psu.edu
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Quinoline Sorption on Kaolinite–Humic Acid Complexes

  1. Jon Chorover *a,
  2. Mary Kay Amistadia,
  3. William D. Burgosb and
  4. Patrick G. Hatcherc
  1. a Soil Science Program, Dep. of Agronomy, Pennsylvania State Univ., University Park, PA 16802 USA
    b Dep. of Civil and Environmental Engineering, Pennsylvania State Univ., University Park, PA 16802 USA
    c Dep. of Chemistry, Ohio State Univ., Columbus, OH 43210 USA


Adsorption of quinoline ( pK a = 4.92) and background electrolyte (LiCl) onto specimen kaolinite was measured as a function of surface-bound humic acid (HA) concentration (f OC = 0–0.5% ), pH (3–10), and ionic strength (1–10 mM). Complexation of HA on the kaolinite surface (4.5 mg C kg−1) reduced the point of zero net charge (pznc) for kaolinite by more than one pH unit and resulted in a significant increase in negative surface charge. Maximum sorption of quinoline occurred near its pKa for all sorbents. Below the pKa, quinoline sorption increases with increasing pH and decreasing proton competition. Above the pKa, sorption is reduced in parallel with (but offset to a higher pH from) the ionized fraction. Competition with Li+ for surface sites is apparent from diminished quinoline adsorption with increasing ionic strength, but sorption of the ionized form of quinoline is always favored and kaolinite exhibits selectivity for cationic quinoline over Li + (K exc = 65 at pH 5) However, increasing f OC diminishes quinoline sorption and selectivity (K exc = 32 at pH 5) and increases sorption reversibility relative to uncoated kaolinite. Humic acid alone exhibits lower selectivity for quinoline (K exc = 4 at pH 5) The results indicate that mineral-sorbed humic substances can diminish retention of cationic quinoline despite an increase in overall cation-exchange capacity.

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