KINETICS OF SULFATE AND SELENATE ADSORPTION/DESORPTION ONTO γ -Al_2O_3 BY THE PRESSURE-JUMP TECHNIQUE

摘要

Sulfate and selenate adsorption/desorption on γ-Al_2O_3 in aqueous suspension were investigated thermodynamically and kinetrically. The triple-layer model fit the experimental data well when adsorbed sulfate and selenate were assumed to form outer-sphere complexes (SOH~+_2-SO~2-_4 and SOH~+_2-SeO~2-_4 ) .The intrinsic equilibrium constants (K_eq~int) of the complex were 10~10.6 M~-2 for SHO~+_2-SeO~2-_4. Pressure-jump relaxation was used to determine the kinetics of SO~2-_4 and SeO~2-_4 adsorption/desorption on γ -Al_2O_3. A single relaxation was observed due to the adsorption/desorption/desorption process. Based on the relaxation theory and combined results of TLM simulations, a single-step process is proposed. The intrinsic values of the adsorption and desorption rate constants were determined to be k~int_1=2.7 x 10~8 M~-2s~-1 and k_-1~int=1.1 x 10~-2 s~-1 in the SO~2-_4/γ-aL_2O_3 system and k_1~int=4.3 x 10~8 M~-2 s~-1 and k~_2~int=4.4 x 10~-2 s~-1 in the SO~2-_4/γ-Al_2O_3 system. The intrinsic equilibrium constants from kinetic measurements (K_kin~int) were 10~10.4 M~-2 for SO~2-_4 and 10~10 M~-2 for SeO~2-_4, which were similr to the intrinsic equilibrium constants (K_eq~int) 10~10.9 M~-2 for SO~2-_4 and 10~10.6 m~-2 for the equilibrium studies.