[en] Sodium selenate and Na²₇₅SeO⁴ were used with a synthetic groundwater and hydrazine to determine selenate-selenium sorption characteristics of crushed Umtanum basalt between 40 to 60₀C. Selenium sorption kinetics from both oxidizing and reducing solutions followed an equation of the type (C_I-C) = Kt^b, where C_I was the initial selenium concentration in molarity, C was the selenium concentration in molarity at time t in hours, and K and b are constants. Relatively constant b values of a wide C_I range allowed K determination over the whole initial concentration range investigated (C_I = approx. 10^-₅ to 10^-₁₂ M). Selenium desorption kinetics in 60₀C oxidizing systems were described by C = At^d, where A and d are constants and other quantities defined above. Equilibrium results conformed to a Freundlich sorption isotherm. The enthalpy change was independent of temperature within the range studied and yielded δH values of from +27.23 kcal/mole at 1.266 x 10^-₁₄ moles Se/g basalt to +28.47 kcal/mole at 2.061 x 10^-₉ moles Se/g basalt. Chemisorption was indicated by the magnitude of the enthalpy change. Desorption kinetics at 60₀C were only modestly less rapid than sorption kinetics suggesting a relatively small sorption activation energy. Reduced (Eh = -150 to -200 mV) selenium did not desorb