ADSORPTION AND DESORPTION OF SELENITE AND SELENATE SELENIUM ON DIFFERENT SOILS

Abstract

The adsorption of selenite and selenate Se and desorption by sulfate and phosphate in normal, calcareous, high organic C saline, and alkali soils were studied. Initial Se solutions contained 5-150 .mu.mol Se/g soil and desorbing solutions contained 500 .mu.mol P or S/g soil. All soils sorbed variable amounts of selenite and selenate in the order: high organic C soil > calcareous soil > normal soil > saline soil > alkali soil. Adsorption of both selenite and selenate forms of Se was influenced positively by organic C, clay content, CaCO3 and CEC [cation exchange capacity] and negatively influenced by high salt content, alkalinity and pH. Conventional and rearranged Langmuir equations were tested. Langmuir curve analysis of Eadie-Hofstee was valid in normal and calcareous soils for selenite and in calcareous and saline soils for selenate. The analysis of Syers et al did not fit well in any case. The adsorption of selenite and selenate showed differential behavior and indicated that a part of both selenite and selenate is adsorbed on differential qualitative sites. Selenate was always sorbed in higher amounts than selenite. The desorption of selenite Se showed no preference for sulfate or phosphate, but selenate was more effectively desorbed by phosphate than sulfate in all soils.