Determination of sorbent point zero charge: usefulness in sorption studies

Potentiometric mass titration (PMT) technique has been adapted to determine the pH (pzc) of four vegetable wastes: grape stalks, cork, yohimbe bark and olive stones wastes used for Cu(II) removal. The pH at the point zero charge (pH (pzc)), determined by PMT, are compared with that obtained by two classical techniques: mass titration (MT) and immersion technique (IT). PMT has been found to be an easy and appropriate technique to determine pH (pzc) of the studied materials. From the results, the knowledge of sorbents pH (pzc) provides information about the possible attraction and repulsion between sorbent and sorbate but in any case enables to ensure that electrostatic force is one of the mechanisms that takes place in metal sorption.