Thermodynamics of peat-, plant-, and soil-derived humic acid sorption on kaolinite.
Humic acids (HAs) form coatings on clays and minerals that can play an important role in nutrient and contaminant migration in soil and water. Humic acid-clay mineral interactions are known to be affected by pH and ionic strength, but little attention has been paid to the effects of temperature. In this paper we report the stoichiometry and thermodynamics of interactions of aqueous HAs (isolated from two peats, two soils and a marine alga with a method that removes lipids) with kaolinite clay, Al2Si2O5(OH)4, at seven temperatures from 5.0 to 35.0 degrees C in 0.05 M NaCl at pH 3.5. All the sorption isotherms exhibit consecutive steps ascribed to HA monolayer and bilayer formation, respectively. Site capacity comparisons suggest different HA molecular conformations on kaolinite. Linearly correlated enthalpy and entropy changes for HA sorption point to the importance of hydration and dehydration in the sorption mechanism.
Ghabbour
Elham A
EA
Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115-5000, USA. eghabbour@neu.edu
Davies
Geoffrey
G
Goodwillie
Melissa E
ME
O'Donaughy
Kelly
K
Smith
Tammy L
TL
D000327:Adsorption; D000538:Aluminum Silicates; D000077215:Clay; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D012987:Soil; D013816:Thermodynamics
D000538:Aluminum Silicates; D006812:Humic Substances; D012987:Soil; D007616:Kaolin; D000077215:Clay