This work involved
evaluation of palm kernel shell activated carbon (PKSAC) as adsorbent for
removal of iron from water through column studies. PKS was collected, washed,
sundried and carbonized at 5000C for 3 hours after which it was
crushed, then activated with 3.0M of KOH and heated using a burner for 30 mins.,
then packed and stored for the experiment after cooling. The activated carbon
prepared from the PKS was characterized. Column studies were carried out on
the adsorption of Fe from wastewater from Itakpe
Iron Ore Company using PKS adsorbent under conditions such as bed height and
flow rate. Experimental data were fitted to kinetic models in order to
estimate the carbon adsorption capacity and establish the breakthrough
profile. Results showed that optimum adsorption capacity was found at lower
flow rate of 20 ml/min, and 12 cm bed height. The appropriate service times
to breakthrough were 195 – 210 mins. The sorption
capacity by the column was 32.49 mg/g. Yoon–Nelson, Thomas and Bohart-Adams models were used in predicting the behaviour
of the breakthrough curve. For the Yoon-Nelson model, the kYN
values and τ value, more so, the R2 values (0.88 – 0.96)
specify that the model can be used to describe the metals - PKSAC sorption
system. The Thomas and Bohart-Adams model were also
suitable for the description of the sorption column with high R2
values. This study showed that activated carbon prepared from palm kernel
shell is suitable for the adsorption of Fe ions and as such could be used as
a cost-effective adsorbent in the treatment of polluted water.
The
advancement of technology has given us much comfort, but has also contributed
greatly to environmental pollution, e.g water
pollution, soil pollution and air pollution. These problems are often
associated with factors such as inappropriate substance use, high toxicity of
certain products, lack of health and safety information, run-off from
agricultural lands, and inordinate disposal of wastewater into water bodies.
There may be different kinds of contaminants such as nitrates, oxides,
bacteria, viruses, fluorides, organic molecules, pesticides, solvents, oil
spills, dyes and heavy metal ions pollution in water such as Cr6+,
Cu2+, Pb2+, Cd2+, Fe2+, Zn2+,
Ni2+, As3+, Hg2+, etc. The ecological effects of
heavy metals are varied and are often interrelated. Heavy metal ions are
non-biodegradable in nature and can accumulate in the human body continuously
and could have severe adverse effects such as brain damage, skin diseases,
liver damage, kidney failure, anemia, hepatitis, ulcers and are also
carcinogenic [1][2][3]. The water pollution is making the lives of millions of
people at great risks of diseases, illness and even deaths. In addition, water
pollution is continuously shortening the availability of drinking water and
water for irrigation purposes [4].
Several methods such as reverse osmosis,
coagulation, precipitation, hydrolysis, phytoremediation and adsorption in the
removal of contaminants from water and wastewater have been used [5][6][36], however, most of these methods have shown some
limitations and shortcomings. Most of these methods have high operational and
maintenance costs, generates toxic sludge and has complicated procedures in the
treatment. Compared to all these techniques, adsorption process using activated
carbon is considered to be the best for water treatment because of convenience,
ease of operation, and simplicity of design [7].Obtaining a low cost and highly efficient
precursor for activated carbon production for the treatment of water and
wastewater remains a challenge.
Raw materials for the
production of activated carbon can be gotten from agricultural wastes generated
as a result of agricultural activities and they are disposed off due to their low economic value; e.gpalm kernel shell, mango seeds, rice husk, raw bagasse, coconut
shells, e.t.c. Raw materials for activated carbon can
also be gotten from industrial wastes generated and often disposed off at the end of the manufacturing processes; examples are
furnace flue dust and aluminum oxide. Commercial activated carbon is produced
from commercial products; they may be plastic graphite, lignite materials. This
category also has a high cost of regeneration, hence are not so economically
viable to be used as raw materials for the production of activated carbon.
Modes of adsorption
operation include both batch system and column flow system. In the column
operation, the carbon is continuously in contact with a fresh solution;
consequently, the concentration in the solution in contact with a given layer
of carbon in a column is relatively constant. For continuous operation, the
solid adsorbent may be added at the top of the column and spent adsorbent
withdrawn from the bottom. Three types of continuous flow systems are usually encountered,
namely the fixed bed adsorption system, the fluidized bed adsorption system,
and the moving beds (or the expanded bed adsorption system).
This study aims to
investigate the removal of Fe from Iron Ore Mining effluent using adsorbent
derived from palm kernel shell in a packed adsorption column method and to fit
the experimental data to kinetic models in order to estimate the carbon
adsorption capacities and establish the breakthrough profile.
2.MATERIALS AND METHODS
Study Area
Itakpe Iron ore
mining region is located within Okehi Local
Government Area of Kogi State. It lies within latitudes 7036′N
to 7039′N and longitudes 6017′E to 6022′E.
Itakpe has common boundaries with Lokoja to the
North, Kabba/Ijumu to the
west, Adavi (Ogaminana) and
Okene to the south and Ajaokuta
to the east. The map of Kogi State showing the
study area (Itakpe, Kogi State, Nigeria) is shown in Figure 1.
Itakpe
is surrounded by ridges of hills with average height of about 360 metres above mean sea level. Itakpe area is underlain by
Precambrian rocks which form more than 70% of the rocks in the area [8]. The
climate is characterized by alternate wet (April-October) and dry
(November-March) seasons. The area has an average annual rain fall of 1300mm
with high relative humidity in July. Itakpe is characterized by an average
surface temperature of about 300C, with evaporation rate of 700mm
between April and October. This climatic condition has a remarkable effect on
the alternate intensive heat in dry season and torrential rainfall usually
accompanied by cold conditions in the wet seasons [8]. A number of rivers took
their sources from Eika hills and discharge their
contents into river Niger. These rivers include; Eika-Adagu,
Osara river, River Ero and
their tributaries. All these rivers are seasonal except Eika-Adagu
River [9]. Generally the topography is characterized by ridges of hills and
undulating plains with relative low slope angle. The soil is that of ferrallitic soils. These are climtogenic
soils of areas in the ecotone between rainforest and
guinea savanna.
Figure 1: Map of Kogi State Showing the Study Area(Itakpe, Kogi State, Nigeria)
Collection of Palm
Kernel Shells (PKS) and Processing
Palm
kernel shell (PKS) was used as precursor for the production of the activated
carbon. The Palm kernel shells were collected from palm oil mill, in Ikanekpo, Ankpa Local Government
Area, Kogi State, Nigeria. The sample was washed with
distilled water to remove impurities and then sun-dried for three days, after
which the PKS was crushed using a milling machine. The crushed particles were
then sieved to obtain the particle sizes of 1 – 3 mm. The pictorial view of the
PKS is shown in Plate 1.
Carbonization
Carbonization
was done using a digital furnace in Metallurgy Engineering Laboratory, Kogi
State, Polytechnic, Itakpe campus. The pictorial view of the furnace in-use for
the carbonization of the PKS is shown in Plate 2. The PKS was taken to the
furnace where it was heated at constant temperature of 500oC for 3
hours for carbonization.
After the carbonization, the sample
was allowed to cool at room temperature. The carbonized sample was crushed
using mortar and pestle and then sieved to obtain particle sizes of 1 – 3mm.
The pictorial view of the carbonized PKS is shown in Plate 3.
Plate 1: The Pictorial
View of Palm Kernel Shell (PKS)
Plate 2: The Furnace
in use for the Carbonization of the PKS
Plate 3: The
Pictorial View of the Carbonized PKS
3.2.2Activation
The
modification was done by chemical treatment of the sieved carbonized PKS with 3.0
M potassium hydroxide (KOH) heated with a burner for 30 mins
for activation. The modified sample was washed with de-ionized water and then
sun-dried. The sample was again crushed and then sieved, now, to obtain the
particle sizes of 0.5 mm – 3mm for the studies. The product (adsorbent) was
stored in a clean and dry polythene bag and labeled accordingly as shown in
Plate 4 below. The adsorbent is referred to as palm kernel shell activated
carbon (PKSAC) in this report.
Plate 4:
Prepared and Labeled Palm Kernel Shell
Activated
Carbon (PKSAC)
Description of the column experiment
Continuous flow adsorption
experiments were conducted; the reactor setup used in this study was
constructed of pyrex plastic
tube of 30 cm height, and 3 cm internal diameter. The column was made in a
methacrylate cylinder, thus allowing for visual examination of the progress of
the wetting front and detection of preferential flow channels along the column
walls. At the bottom of the column, a glass wool was placed. Known quantities
of adsorbent were placed into the column on different occasions to obtain the
bed height of 6 cm (24 g), 9 cm (36 g) and 12 cm (48 g) at constant optimum
flow rate of 20ml/min for each. Wastewaters of known concentration were
introduced downward through the column bed by gravity. Samples were collected
at the column outlet at 15 minutes intervals and was analysed
for Fe concentration using ICE 3000
Series Atomic Absorption Spectrometer. The flow rate was varied from 20
to 40ml/min (20, 30 and 40 ml/min) at optimum constant bed height of 6cm.
Figure 2 shows the schematic diagram of the laboratory scale column set-up.
Figure 2: Schematic Diagram of the Laboratory Scale
Column Study
Kinetic models
a.Thomas Model
The Thomas model is known
as the bed-depth-service-time (BDST) model. The BDST approach is based on the
irreversible isotherm model by Bohart and Adas [10]. This simplified design model ignores both the intraparticle (solid) mass transfer resistance and the
external (fluid-film) resistance directly. This means that the rate of
adsorption is controlled by the surface reaction between the adsorbate and the unused capacity of the adsorbent. This
expression by Thomas for an adsorption column is given by equation (1) and the
linearized form of the Thomas model is given by equation (2).
(1)
where, KT is
the Thomas rate constant (l/(min mg)) and Q is the volumetric flow rate (l/min).
The linearized form of the Thomas model is as shown in equation 23:
ln) = (2)
Where Ce and Co = the effluent and inlet solute
concentrations (mg/l) respectively, q0 = the maximum adsorption
capacity (mg/g), M= the total mass of the adsorbent (g), Q = volumetric flow
rate (ml/min), T = breakthrough time and KT = the Thomas rate
constant (ml/min/mg).
b.Yoon
and Nelson model
The
Yoon and Nelson equation regarding to a single component system has been given
as equation (3). The linearized form of the Yoon and Nelson model equation is
as given in equation (4).
(3)
where k is the rate
constant (min-1), τ the time required for 50% adsorbate breakthrough (min) and t is the breakthrough
(sampling) time (min), Co = Initial concentration and Ce = Final concentration.
ln) = (4)
3RESULTS AND DISCUSSION
Characterization
Physicochemical
properties describe the usability of an adsorbent for a sorption process. The physico-chemical parameters of the activated carbon
prepared from KOH modified Palm Kernel Shell are as in Table 1. The parameters
show that PKSAC is a very good adsorbent, with high
surface area of 772.29m2/g and 85% organic carbon. The pH of 7.5
(near neutral) is also a good indicator of high quality of the adsorbent, as
near neutral pH are helpful for the treatment of all cases of wastewater and
the carbons can also be used for drinking water purification [11][12].
Figure
3 shows the morphology (Scanning Electron Microscopy) of the PKSAC before the
adsorption of Fe ion. The PKS morphology is rough with some layers stacking on
top of one another. The FTIR analysis was used to examine the surface
functional groups of the adsorbents and to identify those groups responsible
for adsorption. The FTIR spectrum of the PKSAC is shown in Figure 4. Also the
energy dispersive X-ray (EDX) showing high carbon content is shown in Figure 5.
Table 1: Physico-chemical
characteristics of Palm Kernel Shell Activated Carbon
S/No.
Parameters
Composition
1
Moisture
content
0.095
%
2
pH
7.5
3
Bulk
density
0.7130
g/cm3
4
Particle
size
0.1
– 0.3 mm
5
Organic
carbon
85
%
6
Organic
matter
1.47
%
7
Specific
surface area
722.29
m2/g
Figure 3: The
Morphology of the PKSAC
Figure 4: FTIR
spectrum of the PKSAC
Figure 5: Energy
Dispersive X-ray (EDX) of the PKSAC
Effect of flow rate
The
column was operated at three flow rates of 20ml/min (1.2L/hr),
30ml/min (1.8L/hr) and 40 ml/min (2.4L/hr) with constant optimum bed height of 6cm (that is, PKSAC
of 24g). The breakthrough curves achieved is presented in Figure 6.
Figure
6 showed that the breakthrough time as well as the exhaustion time increased
with a decrease in flow rate for Fe adsorption respectively. The slope of the
plots from breakthrough time to exhaustion time increased as the flow rate was
increased from 1.20 l/hr. to 2.40 l/hr. It means that the breakthrough curve
produced steep slopes with the increased flow rate for Fe adsorption. A higher
flow rate resulted in a lower residence time in the column and vice versa. An
increase in the flow rate reduced the contact time between metal ions and
PKSAC; and also reduced the volume of effluent efficiently treated before the
bed became saturated. Therefore, it decreased the service time of the bed
(Figures 6); this implies that the column was saturated early. On the other
hand, lower flow rates resulted in longer contact time, as well as a shallow
adsorption zone. Higher flow rates are seen by the steeper curve with
relatively early breakthrough and exhaustion time; they resulted in less
adsorption uptake [13].
Kananpanahet al. [14] reported that decrease in the volumetric flow rate favour more ion exchange conditions. As flow rate
increased, the breakthrough curves become steeper and reached the breakthrough
quickly. They further buttress that this is because of the residence time of
the adsorbate in the column, which is long enough for
adsorption equilibrium to be reached at high flow rate. This means that the
contact time between the adsorbate and the adsorbent
is minimized, leading to early breakthrough [15] as seen in this our findings.
It might occur due to bypass of flow in a clod formation at higher flow rate.
Increasing the flow rate gave rise to a shorter time for saturation while
decreasing the flow rate gave rise to longer time for saturation.
Figure
6: Breakthrough Curves for Fe Sorption onto PKSAC at Different Flow Rates (Bed
Height = 6cm, Particle Size >0.5mm, Adsorbent weight = 24g, influent pH = 7.0
and temperature = room temperature).
Effect of bed height
The
bed height is an important parameter for designing a fixed bed column for
continuous water treatment system. In this context, three bed heights of 6cm
(24g of PKSAC), 9cm (36g of PKSAC) and 12cm (48g of PKSAC) were used for
removal of Fe from the solution at constant optimum flow rate of 20ml/min.. The
experimental result is shown in Figure 7.
The
bed height is an important parameter for designing a fixed bed column for
continuous water treatment system. There
was significant effect of bed height on the effluent concentration of Fe. As
the bed height increases, the metals concentrations decreased at various flow
time (service time) and vice-versa. Similar results were earlier reported by
[16][17] and [18]. The lower concentration obtained at
higher bed height could be due to the large amount of the binding sites that
are available than that obtained with lower bed heights. Furthermore the
smaller bed height is saturated in less time than higher bed heights, hence
they corresponds to less amount of adsorbent and subsequently, a smaller
capacity for the smaller bed to adsorb adsorbate from
solution.
It
is visible from the plot (Figure 7) that a characteristic ‘S’ shaped profile is
generated in ideal sorption systems. It can be said that the breakthrough
volume varies with bed height. Axial dispersion phenomena predominate in the
mass transfer and reduce the diffusion of metallic ions when the bed height is
reduced. The solute (Fe ion) does not have enough time to diffuse into the
whole of the adsorbent mass [19].
As
observed from Figures 7, the total metal (Fe) removed were increased as the bed
height was increased from 6cm to 12 cm even at the same flow rate of 1.2 l/hr (20 ml/min). The treated volume of water increased, but
was not commensurate to the drastic increase observed in the total metal
removed (Table 2).Treated volume of water increased with increase in bed height due
to the availability of more number of sorption sites, this agrees with the
findings of Sivakumar and Palanisamy
[15]. At higher bed height the PKSAC sorbent were not dispersed properly
in the used flow rate so as the treated volume is reduced [20][21].
At smaller bed height, the effluent adsorbate
concentration ratio increased more rapidly than for a higher bed height.
Furthermore, the bed is saturated in less time for smaller bed heights. Small
bed height corresponds to fewer amounts of adsorbent and binding sites while
higher bed height corresponds to more adsorbents and binding sites.
Figure 7: Breakthrough Curves for Fe
Sorption onto PKSAC at Different Bed Height (Flow rate = 1.2 L/hr., Particle
Size >0.5mm, Adsorbent weight = 24g, influent pH = 7.0 and temperature =
room temperature)
Metals ions uptake at
different column operation parameters
Maximum
column capacity, qtotal (mg) for a given
set of conditions in the column was calculated from the area under the plot of
adsorbed Fe concentration, Cad (mg/l), versus time as given by the
equation (5) as presented by Ahmad and Hameed [22]:
= (5)
where Cad = C0-Ce
(mg/l), ttotal is the total flow time
(min) at breakthrough, Q is the flow rate (ml/ min) and A is the area under the
breakthrough curve (cm2).
The
equilibrium uptake (qe(exp)),
i.e. the amount of Fe adsorbed (mg) per unit dry weight of adsorbent (mg/g) in
the column, was calculated by following equation 6.
(6)
wherem
is the total dry weight of PKSAC in the column (g). The total volume treated, Veff (ml), was calculated from the following
equation [23]:
(7)
The
column data obtained during the experimental run are presented in Table 2. Data
from laboratory tests is useful for the design of a full-scale adsorption
column. It is found that as the flow rate increases, the volume of effluent
treated increased while the uptake decreased (Table 2).
The
optimum adsorption capacity was found at 20 ml/min flow rate, and 12 cm bed
height (Table 2). This study showed that the sorption capacity by the column
was 32.49 mg/g (Table 2), which was 28.04 times better than that reported in a
batch system studied by Acheammponget al. [24]. The enhanced capacity by
the column method can be said to be due to the continuously increasing
concentration gradient in the interface of the sorption zone as it passes
through the column, whereas the gradient concentration decreases with time in
batch system [20].
Influence of functional parameters on breakthrough curves
The appropriate
service times to breakthrough were 195 – 210 mins.
The removal capacity are in the order of 30 > 20 > 40 ml/min. A high flow
rate means inadequate time for Fe ion to diffuse into the pores of the
adsorbent, leading to low uptake capacity and removal efficiency [25]. This may
be due to the ions leaving the column before being adsorbed and the equilibrium
could be attained [26].
As
the bed height increased, the metals ions had more time to contact with more
PKSAC particles, resulting in a higher uptake of Fe in the column (Table 2).
Hence, when the bed height increases, the maximum sorption capacity of the
column also increases [27]. At higher bed height the sorbent particles stay in
compact condition and do not expose to uptake the ions. The slight increase in
the slope of the breakthrough curves with increasing bed height resulted in a
broadened mass transfer zone.
Table 2: Uptake of Fe
at Different Operating Conditions
Metals name
Bed Height
Z(cm)
Flow
Rate
Q(ml/min)
Initial Conc.
C0
(mg/L)
Total Flow Time, ttotal (min)
Total Treated
Volume
Veff (ml)
Total Metals
Removed,
qtotal(mg)
Equilibrium
Adsorption Capacity,
qe(exp.) (mg/g)
Fe
6
20
1.7462
225
4500
502.32
20.93
6
30
1.7462
210
6300
779.76
32.49
6
40
1.7462
210
8400
454.08
18.92
9
20
1.7462
240
4800
815.11
22.64
12
20
1.7462
240
4800
1426.07
29.71
Evaluation of column
data by dynamic models
The
successful design of a column adsorption process depends on the proper
prediction of the concentration-time profile or breakthrough curve for effluent
parameters. A number of mathematical models have been developed for use in the
design of continuous fixed bed biosorption columns.
In this work, the Yoon and Nelson model, Thomas model, and Bohart-Adams
model were used in predicting the behavior of the breakthrough curve because of
their effectiveness.
Evaluation of column data by models
The successful design
of a column adsorption process depends on the proper prediction the
concentration-time profile or breakthrough curve for effluent parameters. A
number of mathematical models have been developed for use in the design of
continuous fixed bed biosorption columns. In this
work, Yoon–Nelson, Thomas and Bohart-Adams models
were used in predicting the behaviour of the
breakthrough curve because of their effectiveness.
(a)Yoon-Nelson model
Yoon
and Nelson devised a model to examine the breakthrough behaviour
of adsorbate gases on activated carbon which is known
as Yoon-Nelson model [28]. This model was based on the assumption that the rate
of decrease in the probability of biosorption of each
adsorbate molecule is proportional to the probability
of the adsorbate adsorption and the adsorbate breakthrough on the adsorbent [29].
The magnitudes of the Yoon-Nelson parameters
(kYNand τ) were
calculated from the plot of ln[(Ce/(C0-Ce)]
versus t at various operating conditions (Table 3). Figures 8 and 9 shows Yoon
and Nelson kinetic plot for the adsorption of Fe onto PKSAC at different flow
rates and different bed heights respectively.
The
values of kYN (rate constant), and (time required for 50% Fe breakthrough) were
estimated from the slope and intercept of Yoon-Nelson
plot at different bed height and flow rates as shown in Table 3. The kYN values decreased with increasing flow rate
from 20 to 30ml/mins and then increased when flow
rate was increased from 30ml/min to 40ml/min, but increases with increase bed
height, while the values increased as the flow rate increased.
Increase in as flow rate increases shows that as flow rate
increases, the rate at which the adsorbent bed is exhausted is slower which is
desirable for the adsorption process. From the table,
the value of (min.) represents the time at which 50% of the
adsorbent in the column would reach breakthrough point. The higher the value of , the better the
performance of the column as similarly reported by Malkoc and Nuhoglu,
[27].The R2 values in the
range of 0.8819 – 0.9690 for Fe (Table 3) specify a good fit in all cases,
viewing that the Yoon-Nelson model can be used to describe the Fe - PKSAC
sorption system.
Figure
8: Yoon and Nelson kinetic Plot for the Adsorption of Fe onto PKSAC at
Different Flow Rate (Bed Height = 6cm)
Figure
9: Yoon and Nelson kinetic Plot for the Adsorption of Fe onto PKSAC at
Different Bed Height (Flow Rate = 20ml/min.)
(b)Thomas model
Figures 10 and 11
shows Thomas kinetic plot for the adsorption of Fe onto PKSAC at different flow
rates and different bed heights respectively. The result show that KTH
decreased with the increase of flow rate from 20 – 30ml/min., but increased
with the increasing flow rate from 30 to 40ml/min. which is in agreement with
the report [30]. However, as the bed height increases, the values of both KTH
and q0 decreased as opposed to that obtained by Vijayaraghavan
and Prabu [30].As the flow rate increased, the value of q0 decreased, which
is because of unavailability of reaction sites. The high q0 and R2
confirms the well-fitting of the experimental data with the Thomas model, which
indicates that the external and internal diffusion is not the limiting step.
The R2 value of the Thomas model means that the Langmuir type
adsorption (that is, monolayer adsorption) of Fe onto the surface of PKSAC
occurred.
The Thomas model is one of the most
extensively applied models in demonstrating the column performance and
prediction of breakthrough curves [31]. This model follows the Langmuir model
of adsorption-desorption [30]. It presumes that a negligible axial dispersion
happen in the column adsorption since the rate driving force obeys the
second-order reversible kinetics [23]. The Thomas model equation is as shown in
equation 1. This model was applied to the experimental data and model
parameters were determined from the linear plot. A plot of ln[(C0/Ce) –1] against ‘t’ gives a straight line from
which the values of kTH and q0
were determined from the intercept and the slope, respectively. The calculated
parameters are presented in Table 3.
Figure
10: Thomas kinetic Plot for the Adsorption of Fe onto PKSAC at Different Flow
Rate (Bed Height = 6cm)
Figure
11: Thomas kinetic Plot for the Adsorption of Fe onto PKSAC at Different Bed
Height (Flow Rate = 20ml/min.)
(c)Bohart-Adams model
Figures
12 and 13 shows Bohart-Adams kinetic plot for the
adsorption of Fe onto PKSAC at different flow rates and different bed heights
respectively. This approach was focused on breakthrough, relative values of KAB
(coefficient of mass transfer) and N0 (maximum adsorption
capacity) were calculated using linear regression analysis and they are
presented Table 3. The values of kAB were
found to increase with increase in flow rate indicating that the overall system
kinetics was dominated by external mass transfer while its value decreased with
increase in bed height. No value increased with increased flow rate
but follows the reverse with increase in bed height. Of all the models, the Bohart-Adams model has lower R2 values in the
range (0.6–0.9) for Fe, but still indicates that the model has application in
adsorption process [31] In general, the values of KAB increased as
the flow rate increased from 20 to 40ml/min and the KAB decreased as
the bed height increases from 6 – 12 cm, signifying that the adsorption process
is based on surface reaction theory [32]. The adsorption rate is in linear
relation with the fraction of adsorption capacity that remains on the surface
of the adsorbent.
The Bohart-Adams
model was chosen to calculate the performance of the adsorption column. The Bohart-Adams model is extensively applied for designing a
fixed-bed column; it is based on surface reaction theory [32]. The adsorption
rate is in linear relation with the fraction of adsorption capacity that
remains on the surface of the adsorbent. The mathematical relationship is as
given in equation8.
The linear form of Bohart-Adams model can be expressed as follows:
(8)
Table
3 shows Yoon-Nelson, Thomas, and Bohart-Adams models
parameters for Fe sorption onto PKSAC at different bed heights and flow rate
respectively.
Figure
12: Bohart-Adams kinetic Plot for the Adsorption of
Fe onto PKSAC at Different Flow Rate (Bed Height = 6cm)
Figure
13: Bohart-Adams kinetic Plot for the Adsorption of
Fe onto PKSAC at Different Bed Height (Flow Rate = 20ml/min.)
Fixed bed column
design
The time required for
sorbates breakthrough (t) obtained from the
Yoon-Nelson model agreed well with the experimental data at all conditions
examined. Consequently, the Yoon-Nelson model showed a good illustration of the
metals-PKSAC system. The Yoon-Nelson model has been used successfully to
predict the time required for breakthrough of the biosorption
of Fe ion onto different biosorbents [30][33][34]. These results established that the model set of
equations can be used as an appropriate numerical illustration of the sorption
process carried out in continuous flow fixed bed columns for PKSAC.
The
sorption capacity predicted by the Thomas model (q0: Table 10)
showed fair agreement with those obtained from the experimental results (qe(exp): Table 9). Although, this
demonstrated that the Thomas model might not adequately portray the biosorption system in this study, however, the high R2
values (0.88 – 0.96) shows a fair suitability of the model for the design of
the biosorption column and as such can be described
as been fit to describe the sorption system.
A
layer of liquid film on the adsorbent surface has a direct effect on the mass
transfer resistance [23]. The higher flow rates enhance the mass transfer of
the Fe ion from the liquid film to the PKSAC surface, resulting in earlier
saturation of the adsorbent bed [24]. The increase in q0 as the flow
rate was increased (Table 3) was due to proper dispersion to provide for the Fe
ion to diffuse into the PKSAC bed [24][35]. To design
a sorption column with the Thomas model, low flow rates should be utilized for
optimal Fe uptake.
Table 3: Yoon-Nelson,
Thomas and Bohart-Adams Models Parameters for Fe
Sorption onto PKSAC at Different Bed Heights and Flow Rate
Experimental Conditions
Yoon-Nelson Model Parameters
Thomas Model Parameters
Bohart-Adams Model
Parameters
Z
(cm)
Q
(ml/min)
C0
(mg/L)
KYN
(mg/g)
R2
q0
(mg/g)
KTH
(ml/mg.min)
R2
KAB
(ml/mg.min)
No
Mg/L
R2
Fe
6
20
1.7462
0.0333
105.74
0.9215
153.89
0.0190
0.9197
0.0036
140.56
0.7555
6
30
1.7462
0.0200
110.31
0.9543
109.36
0.0115
0.9543
0.0093
209.49
0.8128
6
40
1.7462
0.0268
121.76
0.9344
354.03
0.0226
0.9344
0.0107
291.72
0.8010
9
20
1.7462
0.0394
121.81
0.9690
117.94
0.0153
0.9690
0.0101
104.42
0.9195
12
20
1.7462
0.0217
133.09
0.8819
97.05
0.0124
0.8819
0.0060
91.54
0.9875
4.CONCLUSION
The
physico-chemical properties, SEM, FTIR and EDX of the
activated carbon produced from the palm kernel shell in this experiment and
ability to remove Fe reveals that it had improved adsorption behaviour comparable to those of high performance
adsorbents. It was observed that the higher the carbon bed height, the higher
the adsorption rate. Results also showed that optimum adsorption capacity was
found at lower flow rate. The Yoon-Nelson model specify that the model can be
used to describe the metals - PKSAC sorption system. The Thomas and Bohart-Adams model were also suitable for the description
of the sorption column with high R2 value. Based on this study,
activated carbon prepared from palm kernel shell is suitable for the adsorption
of Fe ion and as such could be used as a cost-effective adsorbent in the treatment
of polluted water.
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Cite
this Article:Ogbaje, H; Onoja, SB; Nwakonobi, TU; Udochukwu, MO (2024). Packed bed Column Adsorption of
Iron in effluent from Itakpe Iron Ore Mining Company using Palm Kernel Shell
as Adsorbent. Greener Journal of
Science, Engineering and Technological Research, 13(1): 46-60.
