The pH value plays an important role with respect to the
adsorption of different ions on oxide surfaces. According to
Morterra [40], the pH of solution influences the distribution
of active sites on the surface of TiO2. At high pH, the OH−
on the surface provides the ability of binding cations. The
decrease of pH leads to the neutralization of surface charge,and OH− is displaced from the surface, so the adsorption of
cations onto TiO2 decreases quickly.
In order to evaluate the effect of pH, the pH values of
sample solutions were adjusted to a range of 1–9. The results
of the effect of pH on the recoveries of studied ions are shown
in Fig. 3. A quantitative recovery (>90%) was found for Cr
at the pH range of 6–9 and Cu at the pH range of 7–9. For
Cd and Mn, the highest recovery was obtained in the pH
range of 8–9. In order to preconcentration all studied ions
simultaneously, a pH of 8.0 was selected as the compromise
condition.