Journal of Water Resource and Protection, 2012, 4, 464-473 Published Online July 2012 (
Improvement of Fe(II)-Adsorption Capacity of
FeOOH-Coated Brick in Solutions, and Kinetics Aspects
Saint Charles Dehou1, Joseph Mabingui1, Ludovic Lesven2, Michel Wartel2, Abdel Boughriet2,3*
1Chaire Unesco sur la Gestion de l’Eau, Laboratoire Hydrosciences Lavoisier,
Faculté des Sciences, Université de Bangui, Bangui City, République Centrafricaine
2Université de Lille1 Laboratoire Géosystèmes Equipe Chimie Analytique et Marine,
CNRS UMR 8217, Villeneuve d’Ascq, France
3Département de Chimie, Université Lille Nord de France, I.U.T de Béthune,
Rue de l’Université, Béthune, France
Email: *
Received April 12, 2012, revised May 11, 2012; accepted May 30, 2012
The adsorbent, iron oxy-hydroxide coated brick, was used in the present work for removal of iron(II) from aqueous so-
lutions. 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 1 M 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 pseudo-sec-
ond-order reaction kinetics, suggesting a chemisorption process, and the rate constant increased with a temperature in-
crease, 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.
Keywords: Brick; Ferrous Ion; Iron Oxyhydroxide; Acid Activation; Adsorption; Kinetics; Activation Energy; Water
1. Introduction
To remove soluble iron efficiently from ground waters,
various modern processes could be implemented for their
treatments. For instance, an important water-treatment
technology that is often used by drinking water supply
companies in developed countries to remove soluble iron
from ground waters consists to inject O2-rich water into
an aquifer [1]. However, industrial methods are ex-
tremely expensive for poor people in developing coun-
tries. This has led many researchers to develop low-cost
effective and economic techniques that can be easily
used in rural and remote regions. On this view, many
works demonstrated the beneficiary effects of surface
coatings of iron oxide(s)/hydroxide(s) on the sorption
behavior towards metal ions onto, for instance: 1) silica
and Al(OH)3/SiO 2 [2-8]; 2) aluminosilicate minerals such
as zeolite [9,10]; and 3) hydrated magnesium silicate
mineral, sepiolite [11]. One possible solution to this
problem is to use the brick material which is composed
predominantly of sand and clays. Recently published
works had allowed us to show that brick pellets reco-
vered with FeOOH represented an appropriate material
for removing soluble iron from ground waters [12].
The first objective of the present work had been to im-
prove the Fe(II)-adsorption capacity performances of the
brick made by craftsmen in Central African Republic.
The adsorption capacity of a new absorbent (FeOOH
deposited onto 6 M HCl-treated brick pellets) was inves-
tigated by carrying out column experiments, and data
were compared to those obtained with untreated brick
grains and ones that were previously gently treated in a 1
M HCl solution at RT before their FeOOH coating.
The second objective of this work had been to investi-
gate the adsorption kinetics and isotherm models of
iron(II) removal from aqueous solutions by this new
composite, and to elucidate the resulting Fe(II)—adsorp-
*Corresponding author.
opyright © 2012 SciRes. JWARP
S. C. DEHOU ET AL. 465
tion mechanism .
2. Materials and Experiments
2.1. Materials
Bricks were made by craftsmen and used for construction
activity by local people in Bangui region (Central Afri-
can Republic). Bricks makers extracted starting material
directly near their homes at 0.2 m below ground.
Briefly, extracted soils were mixed with water and the
obtained mud was shaped manually; Resulting air-dried
(48 h) bricks were placed in efficient stackings in order
to ensure a continuous air flow through a setting up as-
similated to a basic oven (that was built simply on
ground), heat treated with dry wood for a period of about
three days at temperatures ranging from 500˚C to 800˚C
and finally cooled progressively up to ambient tempera-
ture during two/three days. In order to increase the sur-
face area of the brick material, this latter was broken in
grains manually by using a hammer. The brick particles
were afterwards sieved with a mechanical sieves and the
fraction containing particles sizes which varied from 0.7
to 1.0 mm, was kept for our experiments. This fraction
was washed with Milli-Q water and then decanted; After
settling, the water was eliminated and brick grains were
dried at 105˚C. The dried solid particles thus obtained
were ready for two leaching procedures: the first one
consisted of washing brick pellets with a 1 M HCl solu-
tion for one day and with Milli-Q water several times,
and finally dried them at 105˚C; the second one consisted
of leaching the material in a 6 M HCl solution at a con-
stant temperature of 90˚C for six hours. Afterwards, a
deposition of FeOOH onto modified brick grains was
performed by the precipitation of a 0.25 M ferric nitrate
solution in the presence of a 6 NaOH solution followed
by a 1 M NaOH solution in order to adjust pH at 6 - 7;
and finally, the resulting pellets were washed several
times with Milli-Q water in order to eliminate the excess
of FeOOH not attached to grains.
Specific surface areas pore volumes of brick pellets
before and after chemical treatments were determined by
nitrogen adsorption isotherm analyses (BET) using Sor-
ptomatic 1990 Carlo Erba at –196˚C.
2.2. Column Experiments
All the experiments were conducted in a glass column
with an inner diameter of 1.4 cm, a height of 25 cm, and
a medium—porosity sintered—pyrex disc at its bottom in
order to prevent any loss of material. This column was
packed with an absorbent composite (14.1 g) which con-
tained either sand or brick as the support material. The
adsorption capacity of these different absorbents was in-
vestigated for a bed height of about 10 cm. The iron(II)-
containing influent ([Fe2+] = 9.6 mg/L) passed at room
temperature through the column downward using a peri-
staltic pump at a flow rate of 10 mL per minute. Before
being used in every experiment, about 5 bed volumes of
Milli-Q water were passed through the column: 1) first in
order to remove any unbound and thin particles/iron ox-
ide(s)/hydroxide(s); 2) second to check the absence of
soluble iron in the effluent by ICP-AES (Inductively
Coupled Plasma Atomic Emission Spectroscopy); and 3)
third to confirm the stability of the FeOOH coating on
brick grains. Effluent samples were collected at various
time intervals, and the concentration of soluble iron in
the effluent was analyzed with time using an ICP-AES
spectrometer model: Varian Pro axial view.
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
(Ct* 100/ Co)(% )
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
0Fe% d
t tfinal
3. Results
3.1. Improvement of Adsorption Performances
of Brick
There was evidence in the literature [13-16], that clay
minerals could be chemically modified to enhance their
adsorption capacity, particularly, when amorphous meta-
kaolinite (which is a mineral present in the study brick
[12]) was thermally treated with concentrated inorganic
acids. In our case, this suggestion was clearly confirmed,
indeed, the surface area (S.A.) and pore volume (Vpore) of
crushed brick increased notably after acid leaching from:
S.A. = 31.2 cm2/g and Vpore = 0.15 cm3/g in 1 M HCl-
washed brick pellets at room temperature for 24 hours, to:
S.A = 76 cm2/g and Vpore = 0.23 cm3/g in 6 M HCl-
treated ones at 90˚C for 6 h. Recently, more exhaustive
studies (not reported here) revealed that HCl concentra-
tion and reaction temperature/time induced dramatic mor-
phological, compositional, textural, and surficial modifi-
cations of Bangui-brick grains, resulting in more micro-
porous structures in which clay minerals played a pre-
dominant role [17].
On the other hand, the effects of contact time on the
adsorption of Fe2+ ions onto FeOOH-coated brick pellets
were examined in the present work. Overall, it can been
seen in Figure 1 that Fe(II) adsorption was found to be a
more rapid process when pellets were previously pre-
treated with a 6 M HCl solution at 90˚C for 6 hours than
when they were simply washed with a 1 M HCl solution
for 1 day. This observation confirmed the importance of
medium acidity and temperature on the chemical treat-
ment of the brick in order to improve its properties as a
support material. Thus, owing to the acid pre-activation
of Bangui brick more than 80% of the reaction occurred
within the first 8 min, and the solid-liquid equilibrium
was attained in less than 25 min.
Finally, Fe(II)-adsorption capacities of different adsor-
bents in aqueous media were investigated in a fixed-bed
column. The influent with a Fe(II) concentration of 9.5
mg/L was continuously passed through a glass column at
Figure 1. Variation of Fe2+-ions concentration versus con-
tact time at room temperature during Fe(II) adsorption
onto the composite FeOOH-coated brick: (a) With brick
previously washed in a 1 M HCl solution for 24 h; (b) With
brick previously pre-activated in a 6 M HCl solution at
90˚C for 6 h. Co represented the initial concentration of
iron(II) in the medium, and Ct was the Fe(II) content at the
adsorption time, t.
a flow rate of 10 mL/mn and at a pH range 5.5 - 5.9. As
a whole, for either raw sand or iron oxides-coated sand,
barely 40% of Fe2+ ions in this influent were adsorbed by
these adsorbents at the beginning of the experiments
(Figure 2), and these quantities decreased rapidly up to
reach Fe(II) levels close to those initially measured in the
influent. As for raw brick, its iron(II) removal process
was found to be better than that observed for raw sand
and modified sand, and increased drastically when brick
pellets were previously recovered with FeOOH (Figure
It was further shown that, before FeOOH coating, the
pre-treatment of the brick in a 6 M HCl solution at 90˚C
for 6 hours contributed to enhance strongly its Fe(II)-
adsorption capacity (see Figure 2). The maximum co-
lumn capacity, qmax (in mg), for a given feed concentra-
tion and flow rate was calculated from the equation: qtotal
= FCoA/105, where F was the volumetric flow rate (in
ml/min), and A represented the area under the plot of the
adsorbed Fe(II) percentage versus time that was evalu-
[where Fe% =
ated from:
(Co – C)·100/Co, with Co = influent Fe(II) concentration
(in mg/L) and C = effluent Fe(II) concentration(in
mg/L)]. We found: qtotal = 9.9 mg for FeOOH-coated
brick, and qtotal = 22.6 mg for FeOOH-coated (pre-acti-
vated) brick (qtotal values were determined for a brick
mass of 14.1 g inside the glass column). The equilibrium
uptake (Qe) representing the amount of iron(II) adsorbed
onto brick surfaces per unit mass of dry material in the
column was calculated from the equation: Qe =
qtotal/mbrick, where mbrick (14.1 g) corresponded to the total
mass of dry adsorbent inside the column. We found: Qe =
0.7 mg/g for FeOOH-coated brick, and Qe = 1.6 mg/g for
FeOOH-coated (pre-activated) brick. These values indi-
Copyright © 2012 SciRes. JWARP
Copyright © 2012 SciRes. JWARP
pre -tre a teO A TED (6M - HCl
0 0.5 1 1.5 2 2.5 3 3.5
Figure 2. Evolution of Fe(II) concentration in the effluent (in mg/L) as a function of influent volume (containing 9.6 mg of
iron per liter)) passed through a glass column (which was packed with different adsorbents at a bed height of 10 cm) at a flow
rate of 10 mL/mn: raw sand (); iron oxides-coated sand (); raw brick (); FeOOH-brick composites prepared with brick
pellets treated in a 1 M-HCl solution at room temperature for 24 hours (), and in a 6 M-HCl solution at 90˚C for 6 hours ().
cated clearly that the acidic and thermal treatment of the
brick contributed to generate a better support material
(with greater surface areas, as evidenced above) for
FeOOH deposition and, as a consequence, to improve the
Fe(II)-adsorption characteristics of FeOOH-brick com-
3.2. Adsorption Kinetics Characteristics
The kinetics of Fe(II) adsorption onto Bangui brick was
studied by carrying out a batch of experiments at several
constant temperatures ranging from 17˚C to 45˚C, and by
monitoring the content of adsorbed Fe2+ ions with time.
The kinetic mechanism involved in the study system was
examined in terms of different kinetic models: 1) pseudo-
first order kinetics; 2) pseudo-second order kinetics; 3)
Elovich equation; and 4) intra-particle diffusion (for
more details, consult e.g. [18] and references therein).
The rates of Fe(II) adsorption onto FeOOH-coated brick
in aqueous media were then examined by plotting the
following curves: 1) Ln(Qe – Qt) versus time for a
pseudo-first order kinetics; 2) t/Qt versus time for a
pseudo-second order kinetics; 3) Qt versus Ln(t) accord-
ing to Elovich equation; and 4) Qt versus (t1/2) in case
Fe2+ ions were assumed to be transported from the liquid
phase towards the brick surface according to an intrapar-
ticle diffusion phenomenon [where Qe and Qt represented
the contents of Fe(II) adsorbed (mg/g) at equilibrium and
at time t (min), respectively]. In order to find the best
kinetic model, the fitting of experimental data to kinetic
equations was tested, and kinetic constants and correla-
tion coefficients were determined (Table 1). In this table,
e which represented the quantity of iron deposited
onto brick pellets was determined experimentally from
the equation [(Ci – Ce)·V]/(1000·mbrick), where Ci was the
initial concentration of Fe2+ ions in contact with brick
pellets, Ce was that obtained when the system reached the
equilibrium state, and mbrick was the mass of brick pellets
in interaction with a V(mL) volume of Fe(II) solution;
and e was calculated from the mathematiccal treat-
ment of the first-order and second-order kinetics plots
As a whole, our findings showed that: 1) the pre-ac-
tivation of brick pellets with HCl contributed to enhance
significantly the rate constants for Fe2+-ions adsorption
with values increasing at room temperature from 0.078 to
0.102 (1/mn) for the first-order kinetics and from 0.060
to 0.830 g/(mg·min) for the second-order kinetics; and 2)
a rise in temperature from 20˚C to 39.5˚C led to an in-
crease of the pseudo-first order kinetic constant k1 (from
0.102 to 0.159 1/min) and the pseudo-second order ki-
netic constant k2 (from 0.830 to 1.315 g/(mg·min)). It
could also be noticed that: 1) second-order plots (t/Qt vs
time) had better linearity with correlation coefficients
0.997 R2 0.998 than those obtained for a first-order
kinetics [Ln(Qe – Qt) vs time] : 0.907 R2 0.994; 2) the
calculated Qe values (where Qe represented the amount of
Table 1. Kinetics constants obtained for Fe(II) adsorption onto FeOOH-coated (pre-activated) brick pellets at different tem-
Pseudo-first-order Pseudo-second-order
Temperature (˚C) exp
Q (mg/g) calc
(mg/g) K1 (1/min) R2 (mg/g) K2 (g/(mg·min)) R2
17 0.292 0.301 0.097 0.994 - - -
20 0.393 0.185 0.102 0.947 0.423 0.830 0.998
25 0.349 0.276 0.122 0.991 - - -
30 0.380 0.236 0.1 0.985 0.408 1.085 0.997
35 0.352 0.226 0.157 0.985 0.376 1.12 0.998
39.5 0.358 0.248 0.165 0.907 - - -
39.5 0.355 0.237 0.159 0.992 0.385 1.315 0.998
45 0.315 0.230 0.167 0.980 - - -
Fe2+ ions adsorbed onto brick per mass unit at equilib-
rium) which were obtained from second-order kinetics
plots, were closer to the experimental ones than the cal-
culated Qe ones found from first-order kinetics plots (see
Table 1); and 3) consequently the pseudo-second order
model exhibited lower
² values (0.0012
² 0.0020)
than those determined for the pseudo-first-order model
² 0.0087), where
represented a general-
ized error function, defined as:
² = (1/N)i=1..N
Qe)2, with e corresponding to the experi-
mental values of adsorbate per gram of adsorbent and
e being the calculated ones. These observations sug-
gested that Fe(II) adsorption onto brick might be ap-
proximated to the pseudo-second order kinetics model.
This finding indicated that a chemisorption process or an
activated reaction occurred more predominantly in the
rate controlling step. Such a model then assumed that one
iron ion was sorbed onto two sorption sites (noted 2A) on
the brick surface according to:
exp calc
  
rick solutionbrick
2AFeA Fe
Also, in the assumption that solid surfaces in this mo-
dified brick were energetically heterogeneous, we could
apply to our pseudo-second-order kinetic system Elovich
equation defined as: Qt = [Ln(αβ)]/β + [Ln(t)]/β, where Qt
was the sorption capacity at time t; α (in mg/(g·min)) was
the initial sorption rate of Elovich equation; and the pa-
rameter β (in g/mg) was dependent upon the extent of
surface coverage and activation energy of the considered
chemisorption reaction. From our experimental data, Elo-
vich plots were drawn, and the lines were found to be
linear at different temperatures ranging from 25˚C to
45˚C (0.968 R2 0.991). Table 2 lists the kinetic con-
stants obtained from Elovich equation under the follow-
ing experimental conditions: the initial concentration, Ci,
was 30 mg of iron per liter, and the brick mass, mbrick,
was 4 g in 100 mL of Milli-Q water.
Overall, it can be seen that the initial adsorption rate, α,
and the β coefficient do not change significantly with
Table 2. Kinetic parameters determined from Elovich equ-
Temperature (˚C) α (mg/(g·min)) β (g/mg) R2
25 0.480 15.36 0.991
35 0.445 13.40 0.978
39.5 0.434 12.58 0.973
45 0.517 16.13 0.968
temperature: α varying from 0.434 to 0.517 mg/(g·min)
and β from 12.58 to16.13 g/mg.
On the other hand, in order to check whether or not the
overall kinetics of Fe(II) adsorption reaction was con-
trolled by surface/intra-particle diffusion, the intra-parti-
cle model developed by Weber and Morris [19] was also
tested to our system by plotting Qt against t1/2 (not shown
here). The obtained curves at the beginning of the kinetic
process were roughly linear; however, their straight lines
did not pass through the origin, what meant and con-
firmed that the intra-particle diffusion was not the rate-
controlling step. Instead, we believed that the formation
of solid solutions as: Fe(II)xFe(III)y(OH)z at the external
surface of brick pellets might be responsible for this ad-
sorption, thus preventing the sorbate molecules to move
into the interior of sorbent particles (FeOOH coatings),
and thereby limiting any binding of Fe2+ ions on / with
interior sites of the sorbent by diffusion.
3.3. Adsorption Isotherms Characteristics
In order to gain more information about Fe(II) adsorption
mechanism and surface characteristics and affinities of
Bangui brick, three adsorption isotherm models were
applied to our system (for more details, see e.g. [20] and
references therein): 1) Ce/Qe versus Ce (Langmuir adsor-
ption isotherm); 2) Log(Qe) versus Log(Ce) (Freundlich
adsorption isotherm); and 3) Qe versus Ln(Ce) (Temkin
adsorption isotherm). In this latter case, the plots ob-
tained (not shown here) were badly linear with correla-
Copyright © 2012 SciRes. JWARP
S. C. DEHOU ET AL. 469
tion coefficients R2 0.85, and this model was therefore
Feundli ch m odel
y = 0.460 9x - 1.3047
= 0.9502
0. 00
0.00 0.200.40 0.60 0.801.00 1.20
As for Freundlich and Langmuir models, all the plots
were found to be linear with correlation coefficients R2
0.95 (see Figure 3 and Table 3).
The slope and intercept of these curves were used to
calculate relevant parameters: 1) first Freundlich ones,
KF and n, which are two constants indicative of the rela-
tive adsorption capacity and adsorption intensity, respec-
tively; and 2) second Langmuir ones, KL being the equi-
librium adsorption constant and Qmax representing the
maximum amount of Fe2+ ions per unit mass of brick.
Considering Freundlich adsorption model data, the n
values were found to be higher than 1, and further the
Freundlich constant KF increased with temperature. All
these findings suggested that: 1) Fe(II) ions interacted
favorably with brick according to a chemisorption me-
chanism and 2) this process was endothermic. The iso-
therm plots of Log(Qe) vs Log(Ce) at room temperature
showed clearly that, when attaining the equilibrium state,
FeOOH-coated (pre-activated) brick possessed better
adsorption characteristics of Fe(II) ions than those ob-
served in original (untreated) brick: indeed the extent of
adsorption in percentage and the Fe(II) content adsorbed
per unit mass of modified brick pellets (Qmax) were found
to increase appreciably (see Table 3).
Thus, from the linear Freundlich plots obtained for
no-activated brick (with correlation coefficients 0.95
R2 0.98), the Freundlich isotherm capacity, KF, varied
from 0.036 to 0.050 mg/g and the adsorption intensity, n,
ranged from 1.581 to 2.170 (see Table 3); whereas from
the linear Freundlich plots obtained for activated brick
(with R2 0.88), KF and n were found to be: 0.348 and
4.531, respectively (see Table 3).
Langmuir isotherm plots found for our system had also
good linearity with regression coefficient, R2, ranging
from 0.990 to 0.993, indicating strong monolayer chemi-
sorption. It is also worth noting that the Langmuir equili-
brium coefficient, KL, was indicative of the way in which
the presumed equilibrium reaction was displaced:
brick + Fe(II)(in aqueous phase) <=> brick – Fe(II)
As a whole, when brick pellets were pre-treated by
HCl at 90˚C, larger KL values were found and confirmed
better association between brick and Fe(II) ions. Also,
acid activation was found to have further positive effect
on the maximum adsorption capacity, Qmax increasing
from 0.179 - 0.264 mg/g to 0.669 mg/g by enhancing the
Langmuir capacity of brick by about 300%. This phe-
nomenon can be explained by the generation of a great
number of additional adsorption sites through the HCl
treatment of brick pellets preceding their FeOOH coat-
The essential features of Langmuir isotherm can be
expressed by the dimensionless constant separation fac-
Langmuir m odel
y = 17.704 x + 5.5932
= 0.99
0.00 0.501.00 1.50
1/ Ce(L/mg)
1/ Qe(g/m g)
Figure 3. Typical Langmuir and Freundlich isotherms ob-
tained for Fe(II) adsorption on to FeOOH-coated (pre-ac-
tivated) brick pellets at room temperature. The initial con-
centration of Fe(II) solution was 30 mg of iron per liter; and
the amount of brick grains, mbrick, in the medium was 4 g in
100 mL.
Table 3. Adsorption parameters determined from Lang-
muir and Freundlich isotherms.
Langmuir constants Freundlich constants
Qmax KL K
Adsorbents (mg/g)(L/mg) R2 (mg/g) n R2
FeOOH-coated brick
pellets 0.1790.3159 0.990 0.050 2.1700.950
(brick grains were
previously washed with
HCl 1 M at RT for
24 hours
0.2640.2297 0.993 0.036 1.5810.981
FeOOH-coated brick
(brick grains were
pre-activated with HCl
6 M at 90˚C for 6 hours)
0.6690.659 0.919 0.348 4.5310.881
tor or equilibrium parameter: RL = 1/(1 + KLCo), where
KL is the Langmuir isotherm constant, and Co represents
the initial Fe2+-ions concentration in the study aqueous
medium [21]. The values of RL calculated for Fe(II) ad-
sorption on to FeOOH coated-brick pellets were found to
be, in all cases, within 0 and 1, suggesting a highly fa-
vorable adsorption process, in addition, with a more ele-
vated adsorption efficiency when Fe(II) content in-
Copyright © 2012 SciRes. JWARP
creased in solution [raw brick pellets: 0.14 RL 0.68;
and pre-treated (activated) brick : 0.04 RL 0.08].
3.4. Effect of Temperature and Activation
Parameters for Fe(II) Adsorption onto
Modified Brick
The above kinetic investigations by considering either a
pseudo-first-order or a pseudo-second-order allowed us
to show that: 1) the adsorption was controlled by chemi-
cal sorption; and 2) an increase in temperature favored
Fe(II)-adsorption onto brick pellets, and consequently,
that this process was endothermic.
The linear form of Arrhenius equation as: Lnk =
–Ea/RT + Cst was used successfully in the temperature
range 17˚C - 45˚C in order to assess the activation energy
for Fe2+ ions adsorption onto brick grains: Lnk1 and Lnk2
were plotted against 1/T, and the corresponding curves
yielded straight lines with regression coefficient values
of = 0.95 and 2 = 0.97, respectively (see Figure
4). It should be noted that the curve Lnk1 vs 1/T con-
tained more experimental aligned dots and in addition its
regression coefficient was found to be better than that
determined from the curve Lnk2 vs 1/T, suggesting that
the pseudo-first-order model correlated better with Ar-
rhenius equation. The activation energies, Ea1 and Ea2,
were evaluated from the slope –Ea/RT: we found Ea1 =
16.20 ± 0.40 kJ/mole and Ea2 = 16.93 ± 0.85 kJ/mole.
These positive values of activation energy were found to
be closer each other and further revealed that the rise in
the solution temperature enhanced Fe(II) adsorption onto
treated brick according to an endothermic process. In
other words, a rise in temperature then led to help more
Fe2+ ions to overcome this energy barrier, Ea, and thereby
to get attached to brick surfaces/sites. On the other hand,
the activation energies for Fe(II) adsorption onto modi-
fied brick exceeded largely 4.2 kJ/mole. This Ea value is
usually considered as the maximum one measured for
physical adsorption since the forces involved in such a
process are low [22].
Accordingly, the involvement of a physical adsorption
process in our system should be excluded. Instead, Ea1
and Ea2 were found to be in the range of activation ener-
gies obtained for activated chemical adsorptions, i.e.: 8.4
–83.7 kJ/mole [22-24].
To provide a better understanding of the adsorption
thermodynamics of Fe2+ ions onto FeOOH-coated brick
pellets, the thermodynamic activation parameters of this
process were assessed using Eyring equation: Ln(k/T) =
Ln(kB/h) + ΔS/R – ΔH/RT, where kB is the Boltzmann
constant (1.3807 × 10–23 J·K–1); h is the planck constant
(6.6261 × 10–34 J·s); and ΔS and ΔH are the changes in
entropy and enthalpy of activation, respectively. Ln(k1/T)
and Ln(k2/T) were plotted against 1/T, see Figure 5, and
the slopes allowed us to determine –ΔH1/R and –ΔH2/R,
Figure 4. Activation energies measured for adsorption ki-
netics of soluble ions on to FeOOH-coated (activated) brick
pellets by plotting Ln(k) versus 1/T, where k represents the
pseudo-first order (k1) and pseudo-second order (k2) kine-
tics constant, and T is the reaction temperature.
Figure 5. Thermodynamic parameters obtained for adsorp-
tion kinetics of iron(II) on to FeOOH-coated (activated)
brick pellets by plotting Ln(k/T) against 1/T, where k
represents the pseudo-first order (k1) and pseudo-second
order (k2) kinetics constant, and T is the reaction tempera-
Copyright © 2012 SciRes. JWARP
S. C. DEHOU ET AL. 471
and the intercepts [Ln(kB/h) + ΔS1/R] and [Ln(kB/h) +
ΔS2/R]; And from these results, the changes in entropy of
activation (ΔS1 and ΔS2) and in enthalpy of activation
(ΔH1 and ΔH2) were evaluated and reported in Table 4.
Also, the free energies of activation, ΔG1 and ΔG2
this process were calculated at different temperatures
ranging from 17˚C to 45˚C from the equation: ΔG = ΔH
– TΔS (see Table 4).
It should be noted that ΔS1 and ΔS2 were negative,
suggesting that Fe2+ ions at the solid-solution interface
were more organized than those located far in the bulk
solution phase, and consequently, their degree of free-
dom decreased [25-28]. The magnitude and sign of ΔS1
and ΔS2 were good indicators to know whether the study
reaction is an associative or dissociative mechanism
[29-31]. Our ΔS values did confirm that Fe(II) adsorption
onto this treated brick was an associative mechanism. As
for the changes in enthalpy of activation, ΔH, they were
found to be largely lower than –TΔS in all cases, which
meant that the reorientation step was mainly entropy
controlled at the activation state. The values of free en-
ergy indicated that the adsorption reaction was not a
spontaneous one and instead the system consumed en-
ergy from an entropic source that resulted from the stru-
ctural organization of Fe2+ ions at the brick surface; and
this free energy further increased with an increase in
temperature (see Table 4).
4. Conclusion
The research described here was devoted to examine the
Fe(II)-removal efficiency of FeOOH-brick composites in
aqueous solutions following a thermal acid pre-treatment
of the brick used as a support material. BET data re-
vealed larger surface areas on the modified brick, favor-
ing FeOOH coating. Column experiments indicated that
Fe(II)-adsorption characteristics of the new composite
were strongly improved when compared results to those
obtained for raw brick, FeOOH-coated (no-treated) brick
and iron oxides-coated sand. Fe(II) adsorption kinetics
was found to be better described by the pseudo-second-
order equation, showing that the chemical adsorption/
Table 4. Thermodynamic parameters for adsorption kine-
tics of iron(II) onto FeOOH-coated (pre-activated) brick.
Thermodynamic parameters First order Second order
H (kJ/mole) 15.07 16.55
S (J/mole/K) 173.69 152.25
G (kJ/mole) at 20˚C 65.96 61.16
G (kJ/mole) at 25˚C 66.83 61.92
G (kJ/mole) at 30˚C 67.70 62.68
G (kJ/mole) at 35˚C 68.57 63.44
G (kJ/mole) at 39.5˚C 69.35 64.13
chemisorption was the rate-limiting step in the study
system. Also, the equilibrium data were better described
by the Langmuir equation, thus showing the involvement
of a monolayer coverage of iron(II) onto brick-grains
surfaces. The activation energy of this process was eva-
luated: Ea2 = 16.93 ± 0.85 kJ/mole. The magnitude of the
Ea value indicated clearly that the adsorption was con-
trolled by an activated chemical adsorption. Results from
this study did suggested that FeOOH—coated brick
could be used as an effective adsorbent for iron(II) re-
moval from contaminated waters in developing countries,
particularly when an acid pre-treatment of the support
material “brick” was initially performed.
5. Acknowledgements
This work is partly funded by the “Agence de l’Eau Artois-
Picardie”, the “Region Nord Pas-de-Calais”, the “Conseil
Général du Nord”, and the Town Hall of Villeneuve
d’Ascq. This study is part of the first-author (St C. De-
hou) Ph.D. thesis, and results from the cooperation be-
tween the University of Lille1 (France) and the Univer-
sity of Bangui (Central African Republic). This collabo-
ration and the Grant-in Aid to Mr. St C. Dehou for his
scientific research are financially supported by the Em-
bassy of France to Bangui.
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