Selenium (Se) retention by soil colloids is an important process to maintain the environmental quality. Little information is available on Se adsorption in highly weathered tropical soils, and there are few numerical parameters that can be used as references to aid on adoption management strategies in contaminated areas. Increasing amounts of Se (5, 10, 25, 50, 100 and 250 mg L-1), added as Na2SeO3, were equilibrated with samples of ten Brazilian Oxisols [three Typic Hapludoxes (TH-1, TH-2 and TH-3), two Rhodic Eutrudoxes (RE-1 and RE-2), two Xanthic Hapludoxes (XH-1 and XH-2), one Rhodic Hapludox (RH), one Rhodic Acrudox (RA) and one Anionic Acrudox (AA)]. Adsorption isotherms were obtained and the experimental results fitted to Langmuir and Freundlich models. The Langmuir equation fitted better to the experimental data than the Freundlich model. All isotherms had an L-type (exponential) shape, except for TH-1 and TH-2, which had a C-type (linear) shape. Selenium Ads max varied between 135 mg kg-1 (TH-3) and 2.245 mg kg-1 (XH-1) and the affinity constant (K L) varied from 0.002 (TH-2) to 0.326 L kg-1 (TH-3). Affinity constant (Kf) values between 13.7 (TH-2) and 180.1 L kg-1 (AA) were obtained from the Freundlich model. A high Se retention potential was observed on RH and on acric Oxisols (AA and RA), while qualitative parameters indicated RE-2, RH, TH-3 and RA as Oxisols with high Se affinity. No correlations were observed between soil attributes and Langmuir parameters. The Freundlich coefficient (Kf) correlated with clay content (r = 0.42*) and with anion exchange capacity (AEC) (r = 0.64*).
isotherms; Langmuir; Freundlich; tropical soils
