武汉市红壤黄棕壤的粘粒矿物组成与土壤表面电荷特征

THE CLAY MINERAL COMOSITION AND SURFACE CHARGE CHARACTERISTICS OF RED EARTH AND YELLOW BROWN EARTH IN WUHAN

Clay mineral composition and surface charge characteristics of red earth and yellow brown earth were studied. Kaolinite and illite are the main clay minerals in red earth together with a certain amount of 14A intergrade mineral and a little vermiculite and quartz. Illite, kaolinite and vermiculite are major clay minerals and there is a little 14A intergrade mineral in yellow brown earth. The external specific surface of red earth clay is larger than that of yellow brown earth, but the internal specific surface and total specific surface of red earth is smaller than that of yellow brown earth. The zero point of charge (pH0 ) for red earth is equal to 3.57 while for yellow brown earth, pH0 is equal to 3.06. Adsorbed calcium ions shift the pH0 to lower values and specifically adsorbed sulfate anions shift the pH0 to higher values. For red earth, the zero point of net charge ( ZPNC ) is equal to 1.55, for yellow brown earth ZPNC is equal to 1.59. The pH0 of the two types of soils are larger than their ZPNC. It was found that a negative permanent charge exists for these two types of soils by using the surface charge model developed by Uehara and Gillman ( 1980) . The negative permanent charge of yellow brown earth equals 8.22meq/100g soil, and of red earth equals 10.10meq/100g soil.