Contribution of Iron and Aluminum Oxides to Electrokinetic Characteristics of Variable Charge Soils in Relation to Surface Charge

The contribution of iron and aluminum oxides to electrokinetic characteristics of variable charge soils was studied through determination of electrophoretic mobilities of the red soils treated with either removal of iron oxides or coating of aluminum oxides, and of those deferrated under natural conditions. After removal of the iron oxides, zeta potentials of the latosol and the red earth decreased obviously with a shift of IEP to a lower pH, from 6.4 to 5.3 and 4.1 to 2.4 for the former and the latter, respectively, and the electrokinetic change for the latosol was greater than for the red earth. Zeta potentials of the kaolinite sample increased markedly after coated with iron oxides. The striking effect of iron oxides on electrokinetic properties of the soils was also demonstrated by the electrokinetic differences between the samples from the red and white zones of a plinthitic horizon formed naturally, and between the samples from the gley and bottom horizons of a paddy soil derived from a red earth.