Adsorption–Desorption Behavior of Cadmium(II) and Copper(II) on the Surface of Nanoparticle Agglomerates of Hydrous Titanium(IV) Oxide

The adsorption/desorption behavior of Cd2+ and Cu2+ on/from nanostructured hydrous titanium(IV) oxide (NHTO) surfaces was studied at 30 °C and pH 5.0 (± 0.1). The pseudosecond-order kinetics model described the metal ion adsorption reactions with NHTO very well (R2 = 1.00). The isotherm equilibria were of a Langmuir type (R2Cd = 1.00, R2Cu = 0.95). The monolayer capacities evaluated were (0.15 and 0.46) mmol·g–1 for Cd2+ and Cu2+, respectively. Investigations on the desorption of adsorbed metal ions from NHTO surfaces with a variation of complexions, ionic strength (I), and solution pH showed that ethylenediaminetetraacetic acid (EDTA; 0.01 M) and the HCl (0.1 M) solutions were the most efficient. Kinetic data of the desorption reactions between M2+-NHTO (M2+ = Cd2+ or Cu2+) and EDTA (0.01 M) or HCl (0.1 M) were described by the first-order equation well (R2 = 0.96–1.00), except the kinetic data for the Cu2+ desorption by 0.01 M EDTA, which were described by the Elovich equation well (R2 = 0.96). The kinetics of the desorption reactions indicated that the 0.1 M HCl could desorb metal ions from NHTO surface with more efficiency than 0.01 M EDTA. The desorption of metal ions with 0.1 M HCl could be described by an ion-exchange reaction type.