Author(s)

Oscar Allahdin¹, Michel Wartel², Joseph Mabingui¹, Abdel Boughriet^2,3*

¹Chaire Unesco “On the Management of Water”, Lavoisier Laboratory of Hydrosciences, Faculty of Sciences, University of Bangui, Bangui, Central African Republic.
²Laboratory of Geosystems, and Analytical and Marine Chemistry, University of Lille, UMR CNRS 8217, BatC8, 59655 Villeneuve d’Ascq cedex, France.
³Department of Chemistry, I.U.T of Béthune, University of Lille, Northern France, Rue de l’Université, B.P.819, 62408 Béthune Cedex, France.

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.

Brick, Divalent Cation, Adsorption, Electrostatic Forces, Free Energy, Coulombic, Solvation

Allahdin, O. , Wartel, M. , Mabingui, J. and Boughriet, A. (2015) Implication of Electrostatic Forces on the Adsorption Capacity of a Modified Brick for the Removal of Divalent Cations from Water. American Journal of Analytical Chemistry, 6, 11-25. doi: 10.4236/ajac.2015.61002.