[Adsorption-desorption and competitive adsorption of arsenic and phosphorus in purple soil].

A batch incubation test was conducted to study the characteristics of arsenic (As) and phosphorous (P) adsorption-desorption as well as the effects of the competitive adsorption of the two elements on their translocation and activation in three kinds of purple soil, the typical soil in Three Gorges Area. In the test acid, neutral, and calcareous purple soils, As and P adsorption-desorption had the similar characteristics, with their isothermal adsorption conformed to Langmuir and Freundlich equations. The maximum adsorption of As in the acid, neutral, and calcareous purple soils was 1428.6, 1250.0, and 1111.1 mg x kg(-1), and that of P was 322.6, 357.1, and 434.8 mg x kg(-1), respectively. The adsorption of As and P was fast at the beginning and slowed down then. The kinetics corresponding to the fast process was of first order, and that to the slow process was of Elovich type. The mechanism for the fast process might be exchange adsorption, and that for the slow process might be specific adsorption. When the As and P coexisted, the adsorption rate and quantity of P increased while those of As decreased, implying that the existence of As could promote the adsorption of P in purple soil, while the existence of P would restrain the adsorption of As.