Modeling the Rate of Cadmium and Selenite Adsorption on Micro- and Mesoporous Transition Aluminas

Assessing the speciation and the biogeochemical processes affecting the mobility of selenium from a geological repository of radioactive wastesto the biosphere

“…Kinetics of the Se(IV) adsorption reactions are not yet well understood but the sorbed Se(IV) amounts as a function of time curves show a two steps behaviour: the first part of the curve indicate a fast and linear retention wh i ch becomes slower with time [44,50,53,58]. On clays, the initial reaction was assigned to adsorption while the second p rocess would correspond to an occlusion [44].…”

“…On clays, the initial reaction was assigned to adsorption while the second p rocess would correspond to an occlusion [44]. In other works, it was assumed that adsorption rate is controlled by an intraparticular mass transfer in the solid [54,58].…”

Modeling Pb sorption to microporous amorphous oxides as discrete particles and coatings

“…They have large surface areas, porous structures, and an abundance of binding sites; therefore, they have a significant impact on contaminant mobility [11,12]. In the sorption of heavy metals to hydrous oxides, numerous studies have demonstrated that this process is a two-step one [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]: rapid adsorption of metal ions to the external surface is followed by slow intraparticle diffusion along the micropore walls of the oxide. Benjamin and Leckie [13] observed that adsorption of Cd, Zn, Cu, and Pb on amorphous iron oxyhydroxide was initially fast followed by a much slower second step.…”

Heavy metal adsorption by humic umbrisols: selectivity sequences and competitive sorption kinetics

“…The fast reaction is most likely adsorption via electrostatic attraction and/or innersphere complexation with functional groups present on the soil components. There are several possible reasons for the slow sorption steps, such as slow interparticle diffusion in porous minerals and organic matter, formation of precipitates on surfaces, which can sometimes be slower than typical sorption, and adsorption onto sites that have relatively large activation energies [6][7][8][9]. It is possible that multiple slow reaction mechanisms are responsible for the slow sorption reactions in soils.…”