TITLE:
Implication of Electrostatic Forces on the Adsorption Capacity of a Modified Brick for the Removal of Divalent Cations from Water
AUTHORS:
Oscar Allahdin, Michel Wartel, Joseph Mabingui, Abdel Boughriet
KEYWORDS:
Brick, Divalent Cation, Adsorption, Electrostatic Forces, Free Energy, Coulombic, Solvation
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.6 No.1,
January
9,
2015
ABSTRACT: Adsorption
properties of brick for the removal of divalent cations increased significantly
after this material were pre-activated by HCl and subsequently impregnated with
ferrihydrite. Scanning electron microscopy (SEM) and energy dispersive X-ray
spectroscopy (EDS) analysis demonstrated that ferrihydrite was preferentially
attached to clays (mainly to metakaolinite) and possessed Na atoms at levels
higher than those observed in iron-poor aggregates. Sodium is bound to hydroxyl
groups which have a function as reactive sites and give rise to surface charge.
Zeta potential measurements were conducted to determine the isoelectric point
(IEP) and salt-addition method was used to assess the point of zero charge
(PZC) of this brick. Modified brick has a positive charge in water up to pH ≈ 3.2
and negative charge above this pH. Moreover, pH was found to be the most
important factor affecting the adsorption process, suggesting the possible
implication of electrostatic forces at the brick-water interface. The
complexation model proposed by James and Healy was applied to our system:
theoretical data on free-energy changes due to effects associated both with
electrostatic attraction and solvation, were found to be in agreement with
those determined from kinetic experiments. Column experiments permitted further
to show that adsorption reactions were strongly inhibited by addition of an
inert electrolyte (like NaNO3). Under this condition, ionic strength
increased and most surface sites of the brick would be occupied by Na+ ions, leading to a charge neutralization and thereby a depletion of
electrostatic forces.