EQUILIBRIUM STUDY OF SELENIUM ADSORPTION ONTO SOME SOUTHERN IRAQI SOILS

The thermal equilibrium of selenium adsorption at concentrations of (25, 50, 150, 300, 450, and 600) g Se mL -1 was studied in eight soils with different properties from southern Iraq.Adsorption data were tested into a some of physicochemical models: Langmuir, Freundlich, Dubinin-Redushckevich (D-R) and Temkin.These equations were tested to describe selenium adsorption by calculating correlation coefficient (R 2 ) and Marguardt's Percent Standard Deviation (MPSD) values.The Freundlich models' superiority to describe most of the soils, recording R 2 values ranging between (0.949 -0.9935) and MPSD values ranging from (7.537-21.919).The constants of this equation, Kf, were recorded to range from (4.216-16.462)ml g 1-and 1/n to (0.880-1.131) g g 1-.The D-R equation also provided a good description of some soils.The mean free energy of selenium adsorption on soil colloid surfaces (E) was calculated, and values ranged from (5.814-7.042)kJ mol 1-.The Langmuir model I and II, gave provided a successful description for only two soils (soil2-soil8) Comparing with Freundlich and D-R models, while the selenium adsorption data were not successfully described using the Temkin model.