Effect of Humic Acid on the Selenite Adsorption onto Hematite

In the present study, we investigated the adsorption of selenite [Se(IV)] onto hematite, which usually exists in soils and rocks, focusing on the effect of humic acid. The selenite adsorption onto hematite varied with the contact time, finally reaching an equilibrium state in 5 hours. The result was in good agreement with the Parabolic diffusion equation (R 2 = 0.97). The adsorption with different initial selenium concentrations was reproduced fairly with a Langmuir isotherm (R 2 = 0.92). The adsorption efficiency of selenite increased with decreasing pH. It increased with increasing ionic strength. Freundlich isotherm successfully described the partition behavior between humic acid and hematite (R 2 = 0.95). In the presence of humic acid (selenite-hematite-humic acid ternary system), the adsorption of selenite onto hematite increased at high pH, but decreased at low pH. The amount of selenite adsorbed on hematite decreased with the concentration of humic acid, and then saturated above 50 mg/L. Key-Words: Selenium, Selenite, Adsorption, Hematite, Humic Acid, pH, Ionic Strength