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Colloid Chemistry of Kaolinitic Tropical Soils
- Chorover, Jon, Sposito, Garrison
- Soil Science Society of America journal 1995 v.59 no.6 pp. 1558-1564
- tropical soils, acid soils, soil pH, ionic strength, electrolytes, charge characteristics, colloids, soil organic matter
- Highly weathered soils of the humid tropics may exhibit loss of aggregate stability and dispersion of hydroxyl-bearing soil constituents as a result of management-induced changes in soil solution chemistry. The effects of pH and 1:1 “indifferent” electrolyte concentration on the surface charge and flocculation of colloids extracted from four representative kaolinitic tropical soils were examined by microelectrophoresis and light scattering methods. Electrophoretic mobilities () of clay-sized particles (0.1-1.0-µm diameter) were predominantly negative between pH 2 and 6 for all soils, but decreased in magnitude with increasing solution proton concentration. Measured values were between −3.0 × 10 and +0.5 × 10 msV, with isoelectric points (i.e.p.) ≤ 2.5. Photon correlation spectroscopy revealed an abrupt change from small to large particle size with increasing proton concentration in the pH range 2.5 to 3.5. Light scattering by whole-soil suspensions indicated a proton-induced transition from kinetically stable to kinetically unstable suspensions in the same pH range. Rapid flocculation occurred in the electrophoretic mobility range −1.2 to −1.8 × 10 m s V. The pH and ionic strength dependence of colloidal stability observed for the soils is consistent with an electrostatic stabilization mechanism among their clay-sized particles.