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.
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
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.