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The adsorption of Chromate ions on vanadium pentoxide from aqueous solutions has been studied by a radiotracer technique. The effects of (i) pH and ionic concentration on adsorption in the absence of as well as in the presence of certain added cations and anions, (ii) certain interfering/complexing ions, (iii) the concentration of Na 2 51 Cr0 4 on adsorption kinetics, and (iv) temperature on adsorption as well as desorption kinetics have been investigated. The observed change in adsorption with change in pH is due to surface hydroxyl ions and their subsequent dissociation at pH below and above the isoelectric point producing cationic and anionic species at the surface, respectively. The applicability of the Freundlich isotherm and a first order rate law have established the exothermic behaviour of the adsorption process. The activation energy of the desorption (75.63 kj) is greater than that of the adsorption process (18.19 kj) showing that the adsorption process is more feasible and physical in nature.

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The interfacial properties of zirconium oxide, titanium oxide and bismuth oxide have been studied under various experimental conditions. The oxides were characterized by means of their pH titration curves, intrinsic dissociation constants [pKai*(intr.), i = 1, 2) and point of zero charge (pHpzc) in varying concentrations of KNO3 and Na2CrO4 solutions. The pHpzc values of all the oxide samples tended to shift to higher pH values in the presence of Na2CrO4 solution and remain the same in the presence of KNO3 solution. A mechanism for the sorption process is proposed proceeding through an exchange with surface OH– or H2O groups and is interpreted as a case of specific adsorption.