| The basic properties, clay mineral association for brown soil, red soil and laterite were analyzed. Charge character, Cu2+ adsorption-desorption of soils with variable charge and permanent charge and the relation between them were studied by using back-titration method and adsorption equilibrium method respectively. The main results were shown as follows.1. For the clay mineral association of permanent charge soil, the main clay minerals in brown soil are hydromica (35%) and vermiculite (30%). Whereas for the clay mineral association of variable charge soils, the prodominent clay mineral in laterite is kaolinite (95%) and the main clay minerals in red soil are kaolinite (45%) and hydromica (40%). Differences are also shown as to the content of ferrallitic oxides for soil colloid with permanent or variable charge. The amount of free iron oxide in different soil colloid is in the following order : laterite > red soil > brown soil.2. The amount of variable negative charge of permanent charge soil is higher than that of variable charge soils, and enhanced with the increase of pH value in the system. However, the zero point of charge (PZC) for them is opposite. These differences between permanent charge and variable charge soils are related to the composition and the amount of soil clay mineral and Fe, Al oxides.3. The amount of Cu2+adsorbed by permanent charge soil and variable charge soil is raised with the increase of Cu2+ concentration in the equilibrium solution at a certain range of Cu2+concentration, and the amount of Cu2+adsorbed by the former is more than that adsorbed by the latter. These are in accordance with colloid composition and the charge character of soils tested.4. The amount of Cu2+desorbed by KC1 from permanent charge soil is larger than that desorbed from variable charge soil, and enhanced with the increase of the amount of Cu2+adsorption. So does the desorption ratio of Cu2+. These are tightly related with the amount of variable negative charge of soils tested. Results show that the ratio for the amount of electrostatic adsorption Cu2+to the total amount of adsorption Cu2+ on permanent charge soil is higher than, that in the variable charge soils tested.5. Opposite to the amount of Cu2+ desorbed by KC1, the amount of Cu2+ desorbed by deionised water from variable charge soils is larger than that from permanent charge soil, which is consistent with the content of Fe^ Al oxides hi these testing soils tested. But the types of Cu2+ adsorption desorbed by deionised water is still unknown.6. The amount of Cu2+ desorbed by KC1 from permanent charge soil is much larger than that desorbed by deionised water, and The amount of Cu2+ desorbed by KC1 from red soil is a little larger than that desorbed by deionised water, whereas from laterite is the same as or a little bit lower than that desorbed by deionised water. All of these are closely related to the charge character and condition of Cu2+adsorption-desorption of soils.7. With the Cu2+ adsorption of these soils tested, PZC of permanent charge soil and variable charge soil will be enhanced, whereas amount of variable negative charge of them will be reduced. But the increase or decrease magnitude of variable charge soil is more than that of permanent charge soil. It is worthy of note that when same amount of Cu2+ ion adsorbed by the soil, the effect of them on charge character for variable charge soils tested was stronger than that of permanent charge soil.8. The amount of Cu2+ adsorbed and the pH value of Cu2+ adsorption equilibrium solution will affect the charge character of soils tested. The PZC value of red soil will be enhanced with the amount increase of Cu2+ adsorbed and the pH value of adsorption equilibrium solution. The amount of surface variable negative charge of them will decrease with the increment of pH value of Cu2+ adsorptionequilibrium solution in the range of pH3.8~pH5.1. Whereas with the amount increase of Cu2+ adsorbed, the amount of surface variable negative charge of red soil will firstly decrease...
|
PDF Full Text Request