恒电荷土壤和可变电荷土壤动电性质的研究　Ⅰ.阳离子吸附和pH的影响

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

本工作研究了阳离子吸附和pH对恒电荷土壤（黄棕壤、棕壤、暗棕壤和黑土）和可变电荷土壤（砖红壤）动电性质的影响。研究结果表明，砖红壤在不同溶液中的ζ电位随pH升高由正值变为负值，均有一个等电点（IEP）；pH＞5时，在不同溶液之间砖红壤ζ电位的变化顺序为：MnCl2＞ZnCl2≥CaCl2＞NaCl。作为恒电荷土壤的黄棕壤、棕壤、暗棕壤和黑土在不同溶液中的ζ电位均为负值，没有等电点；ζ电位-pH曲线的形状随土壤、电解质和pH而异。阳离子吸附后使土壤粘粒的ζ电位正移。阳离子专性吸附对ζ电位的贡献△ζ在不同土壤、不同离子之间的顺序如下：砖红壤K+＜Zn2+＜Ca2+＜Cu2+＜Mn2+，黄棕壤和黑土Ca2+＜K+＜Mn2+＜Cu2+＜Zn2+。

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.