Caption: Figure 4: Electrochemical results obtained with three-electrode cells for the monolith ACF25-M: (a) cyclic voltammetry recorded at 0.1 mV [s.sup.-1] in the total voltage range and in the voltage ranges for [H.sub.3][O.sup.+] and HS[O.sub.4.sup.-]: (b-d) galvanostatic plots obtained at 1mA [cm.sup.-2]: (b) for both ions in the total voltage range; (c) for the
hydronium ion; and (d) for the bisulfate ion.
Hydronium ions pass through the proton exchange membrane, which is a solid electrolyte in electrochemical cell.
It can be concluded that
hydronium ion concentration on the membrane surface decreases with increasing pH causing decrease in removal of chromium (VI).
In the second, a water molecule picks up a proton, creating a
hydronium ion (H3O+).
Na+ or Li+) and hydrogen H+ or
hydronium ions H3O+ of the attacking leaching solution.
The reaction in acidic conditions was accompanied by a marked increase in pH, due to consumption of
hydronium ions. Two mechanisms maybe envisaged for this process.
At the same time, oxygen gas and
hydronium ions are formed in the anodic chamber.
The low Cd biosorption at pH less than 4 has been suggested to the competition among metal ions from
hydronium ions for the available biosorption sites.
At pH values that are too low it is expected that
hydronium ions, [H.sub.3][O.sup.+], would associate with the adsorbent surface sites thus restricting access to the surface sites by the metal ions through repulsive forces.