STUDIES ON ELECTROKINETIC PROPERTIES OF CONSTANT CHARGE SOILS AND VARIABLE CHARGE SOILS Ⅰ. EFFECT OF CATION ADSORPTION AND pH

Li Cheng-bao;Ji Guo-liang(Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008)

Cation adsorption, pH,Electrokinetic properties, Constant charge soil,Variable change soil

In this work, the effect of cation adsorption and pH on the electrokinetic properties of constant charge soils and variable charge soils were studied. A laterite was used as a representative variable charge soil and yellow brown earth, brown earth,dark brown earth and black soil were used as representative constant charge soils.The results showed that the zeta potential of laterite in different electrolyte solutions changed to negative in sign from positive in sign with the increase in pH and an isoelectric point (IEP) occurred on all the zeta potential -- pH curves. When the pH value was higher than 5, the zeta potential of lateial in different electrolytes was of the order MnCl2 > ZnCl2 > CaCl2 > NaCl. On the other hand, all the zeta potential of constant charge soils, i. e., yellow brown earth, brown earth, dark brown earth and black soil, in different electrolyte solutions were always negative in sign and no IEP occurred on zeta potential--pH curves. The shape of zeta potential--pH curves varied with soil type, electrolyte kind and PH. Cation adsorption caused the zeta potential of clay particles to change towards positive potential direction. The contribution, △, of cation specific adsorption to zeta potential of different soils were of the orders: K+ < Zn2+ < Ca2+ < Cu2+ < Mn2+ for laterite, and Ca2+ < K+ < Mn2+< Cu2+ < Zn2+ for yellow brown earth and black soil.