ADSORPTION OF TRIVALENT CATIONS ON SILICA

Gadolinium and yttrium show very similar adsorption behaviors on silic a. For the both trivalent cations, the adsorption isotherms are insens itive to the ionic strength. The slope of the log-log adsorption isoth erms at a constant pH is considerably lower than 1, except for the ran ge of very low equilibrium concentrations. This behavior can be explai ned without invoking surface heterogeneity considering the presence of a small concentration of anions, An(2-), as an impurity. A hypothetic al ternary complex SiOGdAn is very strong and this leads to enhanced u ptake at low initial concentrations. When [Gd3+] much greater than [An (2-)], only a small fraction of Gd can be adsorbed as SiOGdAn and the percentage of uptake is low. (C) 1997 Academic Press.