A series of experiments were performed at different pH values to obtain the optimum conditions for Cu(II) and Pb(II) metal ion removal.
The results are presented in Fig. 4.
Metal ions have low biosorption capacities in low pH ranges. In acidic media,
the active sites of the biosorbent were protonated and metal ion biosorption decreased.
When the pH values increased,
the biosorption capacities of the biosorbents increased for both metal ions.
Therefore, the optimum pH was selected as 5.5 precipitation can occur.
As the pH increased,
the biosorbent surface became less positive and the electrostatic attraction between the metal ions and the biosorbent surface increased as expected
and no clear changes observed