Modeling Sulfate Adsorption-Desorption Process by Soils in South China with Isotherms

The properties of sulfate adsorption-desorption by soils in South China was studied by means of equilibrium test. Eight soils collected from four provinces were tested. Na 2SO 4 was added in a series of nine concentrations as adsorption solution, while deionized water, NaNO 3 and NaH 2PO 4 were used as desorption solution. The data were modeled with three sorts of isotherms, namely Freundlich, Langmuir and Temkin isotherms. It was found that Freundlich and Langmuir adsorption isotherms were fit to the data of sulfate adsorption by soils with high coefficient, while Temkin isotherm was not fit well yet. But none of the three isotherms was fit to the data of sulfate desorption by soils. The results indicate that the capacity of sulfate adsorption and the firmness of sulfate adsorption by soils is decided by soil properties, especially the soil components, and that the desorption is not the simply reverse process of adsorption. As to the pure minerals, the three isotherms were all fit well to the data of sulfate adsorption and desorption.