That requires a presence of negatively charged
centers or coordination site in the chemical structure of sorbents
used. While, in alkaline medium, the removing of the metal ions is
attained by the adsorption of metal ions in negatively charged
forms, and also the precipitation of the metal oxides or hydroxides
takes place. Precipitation of metal hydroxides takes place between
the networks of adsorbents, which increases considerably the
efficiency of metal removal.