3.1. Effect of pH on metal biosorption
It is well known that pH could affect the protonation of the func-tional groups on the biomass as well as the metal chemistry. The study of biosorption of Pb2+,Cd2+and Ni2+on OPAA as a functionof pH was accomplished; the results are presented inFig. 1.
As the pH of the heavy metal ions solution increased from 2.0 to 7.0, the
biosorption yield of Pb2+,Cd2+and Ni2+ions was changed.
The per-cent biosorption is minimum at pH 2.0 and increases as the pH increases from 2 to 5.5.
The minimum biosorption at low pH 2.0 may be due to the fact that high concentration and high mobility of H+ ions, the hydrogen ions are preferentially adsorbed rather
than the metal ions.
At higher pH values, the lower number of H+ and greater number of ligands with negatives charges results in greater metal ions biosorption.