2.3. Adsorption Experiments
Kinetics studies on Fe(II) adsorption onto Bangui brick were carried out with brick grains with 0.7 - 1.0 mm sizes that were first pre-treated with a 6 M HCl solution at 90°C for six hours, and second coated with FeOOH. Experimental data were afterwards compared to those found for FeOOH-brick composites that were prepared directly from raw brick grains and from ones pre-washed in a 1 M HCl solution for 24 hours. 50 mL of a Fe2+ ions solution [prepared from the salt: Fe(NH4)2(SO4)2, 6H2O] at a concentration of 30 mg of iron per liter were trans-ferred into a cell containing 4 g of brick pellets (with average diameters varying from 0.7 to 1.0 mm). The mixture thus prepared was shaken gently at a constant speed of 120 rpm using a mechanical shaker (Model: IKA Labortechnik KS 250 basic). 1 mL of the super-natant (which was filtered through a 0.45 μm pore di-ameter cellulose nitrate filter) was collected at various time intervals from 0 to 30 minutes and analyzed for the determination of iron level by using an ICP-AES spec-trometer (Inductively Coupled Plasma Atomic Emission Spectroscopy; Model: Varian Pro axial view). The re-producibility of concentration measurements was ensured by repeating three times the same experiments under identical experiment conditions. This procedure permit-ted us to determine average values of iron content in the reaction solution, and standard deviations of these analy-ses were evaluated to be within ±3%. The Fe(II) adsorp-tion capacity of brick was calculated by using the fol-lowing equation: Qe = (Co – Ce)V/m, where Qe repre-sented the adsorption capacity of iron(II) on FeOOH- coated brick (in mg/g); Co was the initial content of iron(II) in the cell (in mg/L); Ce represented the equilib-rium solute concentration (in mg/L); and m and V corre-sponded to the mass of brick used (g) and the volume of Fe(II) solution used (L), respectively.
Adsorption-isotherms studies were performed in ten 100 mL-flasks each one containing 2 g of brick pellets in which were added 50 mL of an iron(II) solution having a concentration ranging from 2 to 20 mg/L. These flasks Copyright © 2012 SciRes. JWARP
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were placed on a mechanical shaker (as mentioned above) and gently shaked at a speed of 120 rpm. Preliminary sorption experiments showed that a reaction time of 4 hours at a temperature of 17°C ± 1°C was sufficient for the system to attain thermodynamic equilibrium. After-wards, suspensions were filtered and the recovered solu-tion was analyzed to determine Fe2+ ions concentrations using ICP-AES. The quantity of iron adsorbed onto brick pellets, noted Qe (in mg/g), was assessed from the dif-ference between the initial and the equilibrium contents of iron(II) in the liquid phase. It should be noted that all these experiments were at least triplicated and data were averaged.