Sorption of Atrazine by Al- and Ca-Saturated Smectite

B. L. Sawhney1 and S. S. Singh2
1 The Connecticut Agricultural Experiment Station, New Haven, Connecticut 06504
2 Land Resource Research Center, Agriculture Canada, Ottawa, Ontario K1AOC6, Canada

Abstract: Because of the large surface area and common occurrence of smectites in the clay fractions, they are important in sorption/desorption reactions of organic pollutants entering soils and sediments. Results of sorption and desorption of atrazine by Al- and Ca-saturated smectite reported here showed that Al-saturated smectite sorbed much higher amounts of atrazine than Ca-saturated smectite. Al-saturated smectite sorbed 3820 mg kg−1 as compared to 1902 mg kg−1 by the Ca-saturated smectite during 5 consecutive sorptions from 10 ppm atrazine solution. Sorption isotherms over 2–10 ppm atrazine concentration range were nonlinear in all cases. Freundich coefficients, Kf, obtained from the sorption isotherms were much higher for Al- than Ca-saturated smectites; Kf varied from 405 to 3035 for Al-saturated and 100 to 306 for Ca-saturated. The pH values of Al- and Ca-saturated smectites were 3–4 units higher than the pKa (1.68) of atrazine, which suggests that atrazine was sorbed as neutral molecules. Stronger H-bonding between the more polarized H2O associated with the trivalent Al ion than the divalent Ca ion is likely responsible for the greater sorption by Al-smectite.

Key Words: Cation-Polarization • Nonionic Organics • Smectite • Surface-Hydrophobicity

Clays and Clay Minerals; June 1997 v. 45; no. 3; p. 333-338; DOI: 10.1346/CCMN.1997.0450304
© 1997, The Clay Minerals Society
Clay Minerals Society (www.clays.org)