The adsorbent, iron oxy-hydroxide coated brick, was used in the present work for removal of iron(II) from aqueous solutions. The adsorption performances of this composite were significantly improved when brick pellets...The adsorbent, iron oxy-hydroxide coated brick, was used in the present work for removal of iron(II) from aqueous solutions. The adsorption performances of this composite were significantly improved when brick pellets (as a support material) were pre-treated in a 6 M HCl solution at 90°C for 6 hours, when compared to untreated ones and those pre-washed in a 1M HCl solution at RT for 1 day. This phenomenon was attributed to larger surface areas measured for modified brick by BET, thus enabling a better FeOOH deposition. The ability of this new composite to better adsorb Fe2+ ions from synthetic solutions was evidenced from fixed-bed column experiments: data were compared to those obtained from raw brick and iron oxides - coated sand columns. The adsorption mechanism followed better pseudosecond-order reaction kinetics, suggesting a chemisorption process, and the rate constant increased with a temperature increase, revealing the endothermic nature of Fe(II) adsorption. Furthermore, the equilibrium data fitted the Langmuir isotherm model with a maximum monolayer sorption capacity Qmax = 0.669 mg/g and a Langmuir constant KL = 0.659 L/mg at room temperature. The activation energy (Ea) of Fe(II) adsorption and the changes in entropy (ΔS), enthalpy (ΔH) and free energy (ΔG) of activation were determined, with values suggesting the involvement of an activated chemical adsorption and an associative mechanism.展开更多
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 (SE...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.展开更多
文摘The adsorbent, iron oxy-hydroxide coated brick, was used in the present work for removal of iron(II) from aqueous solutions. The adsorption performances of this composite were significantly improved when brick pellets (as a support material) were pre-treated in a 6 M HCl solution at 90°C for 6 hours, when compared to untreated ones and those pre-washed in a 1M HCl solution at RT for 1 day. This phenomenon was attributed to larger surface areas measured for modified brick by BET, thus enabling a better FeOOH deposition. The ability of this new composite to better adsorb Fe2+ ions from synthetic solutions was evidenced from fixed-bed column experiments: data were compared to those obtained from raw brick and iron oxides - coated sand columns. The adsorption mechanism followed better pseudosecond-order reaction kinetics, suggesting a chemisorption process, and the rate constant increased with a temperature increase, revealing the endothermic nature of Fe(II) adsorption. Furthermore, the equilibrium data fitted the Langmuir isotherm model with a maximum monolayer sorption capacity Qmax = 0.669 mg/g and a Langmuir constant KL = 0.659 L/mg at room temperature. The activation energy (Ea) of Fe(II) adsorption and the changes in entropy (ΔS), enthalpy (ΔH) and free energy (ΔG) of activation were determined, with values suggesting the involvement of an activated chemical adsorption and an associative mechanism.
文摘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.
