American Journal of Analytical Chemistry, 2013, 4, 689-695
Published Online December 2013 (
Open Access AJAC
Bioremediation of Lead(II) from Polluted Wastewaters
Employing Sulphuric Acid Tr eated Maize Tassel Biomass
Mambo Moyo, Linda Chikazaza
Department of Chemical Technology, Midlands State University, Gweru, Zimbabwe
Received September 30, 2013; revised October 29, 2013; accepted November 15, 2013
Copyright © 2013 Mambo Moyo, Linda Chikazaza. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
The ability to modify a waste by-product precursor, maize tassel biomass using sulfuric acid as the activating agent with
specific focus on Lead(II) ion from water has been proposed. The treating of maize tassel using sulphuric acid is be-
lieved to enhance sorption capacity of Lead(II) ions. For this, batch adsorption mode was adopted for which the effects
of initial pH, adsorbent dosage, contact time and initial concentration were investigated. Consequently, it was found that
the adsorbent capacity depends on pH; since it increases up to 4.5 and then decreases. The highest percentage of Lead(II)
ion removal was achieved in the adsorbent dosage of 1.2 g and at an initial concentration of 10 mg/L metal ion. In an
attempt to determine the capacity and rate of Lead(II) removal, isotherm and kinetic data were modeled using appropri-
ate equations. To this end, the adsorption data fitted best into the Langmuir model with an R2 (0.9997) while kinetically
the Lead(II) adsorption followed the pseudo-second-order model. Furthermore, as a way to address issues related to
sustainability, maize tassel is recommended since the process is considered to be a dual solution for environmental
cleaning. From one side, it represents a better way to dispose the maize tassel which has no use after fertilization and on
the other hand it is an economic source of carbonaceous materials.
Keywords: Maize Tassel; Adsorption; Removal; Wastewater Treatment, Lead(II) Ion
1. Introduction
The presence of heavy metals in the environment poses a
serious and complex environmental and public problem
due to their non-degradability [1]. Among the heavy
metals, Lead (Pb) is very toxic because it is carcinogenic
in nature [2]. Lead is the most significant toxin of the
trace metal ions, and human exposure is through inges-
tion of food and water, and inhalation. Lead affects mainly
the peripheral nervous system and hematopoietic, renal,
gastrointestinal, cardiovascular and reproductive systems.
According to World Health Organization [3], the permis-
sible level for Pb in drinking water is 0.05 mg/L. Conse-
quently, the occurrence of very low concentration levels
of lead in drinking water is considered as highly toxic
and requires more efficient removal, extraction, and treat-
ment methodologies.
The removal of metals from water has been previously
achieved by various methods such as ion exchange, pre-
cipitation, oxidation, reduction and membrane filtration
[4,5]. Currently, adsorption technology using cheap, eas-
ily available agricultural plants, algal biomass and cyano-
bacteria has increased in recent years. However, the use
of raw sorbents in adsorption may cause problems since
most plants contain a green pigment known as chloro-
phyll (sparingly soluble in water) and some organic mat-
ter may be leached out, consequently affecting the taste
and colour of the treated waters [6,7]. In spite of the ver-
satility of commercial activated carbon as an adsorbent in
wastewater treatment with its high surface area, micro-
porous characteristics, and high adsorption capacity; its
high cost and loss during the regeneration restrict its ap-
plications in developing countries [8,9]. Given these dis-
advantages, efforts have now been geared towards intro-
ducing low cost precursors that can serve as alternative
sources for water cleaning after modification using dif-
ferent activation agents. In the recent years, modified
sorbents derived from locally available materials such as
Ceiba pentandra hulls [8], Euphorbia rigida [10], ha-
zelnut husks [11], wheat bran [12], coirpith [13], and
coconut shell [14] have received increasing attention for
the removal and recovery of heavy metals from water
and wastewater systems.
Maize tassel is an inexhaustible, non-edible, mesopor-
ous and renewable polymeric material resource, which is
discarded as waste by most farmers after fertilization
[15]. Hence, the present study aims to assess the applica-
bility of acid treated maize tassel for the adsorptive re-
moval of Lead(II) from aqueous solution and to investi-
gate the effect of operating parameters on the adsorption
process. The parameters studied include contact time,
initial Lead(II) concentration, adsorbent dosage and ini-
tial solution pH.
2. Materials and Methods
2.1. Modification of Maize Tassel
The maize tassel was collected from Morris farm in
Northlea, Gweru, Zimbabwe. Maize tassel was plucked
off the woody parts of the maize plant, thoroughly washed
with water and sun dried for 5 days. The dry biomass
was milled and then fractionated using 100 - 300 µm
analytical sieves. Then, the modification was prepared
according to reported procedure [16-18]. Briefly, the frac-
tionated maize tassel powder (200 g) was weighed in a
clean dry beaker of capacity 1 L containing (200 mL,
97% H2SO4 for 24 h) followed by refluxing in a fume
hood for 4 h. After cooling, the reaction mixture was
filtered, and the filtrate was washed repeatedly with ul-
tra-pure water and soaked in 1% NaHCO3 solution to
remove any remaining acid. The sample was then washed
with distilled water until the pH of the acid treated maize
tassel was between 6 - 7, dried in an oven at 120˚C over-
night and kept in a glass bottle until use.
2.2. Characterization of Prepared Acid Treated
Maize Tassel
The bulk density, loss of mass on ignition, simple spe-
cific surface area, pH and moisture content of the acid
treated maize tassel were determined following reported
procedures [19,20]. Briefly, for bulk density, acid treated
maize tassel was transferred to a 10 mL measuring cyl-
inder of about 1.0 cm diameter. Sufficient quantity of
powder was added to occupy a volume of 10 mL under
the condition, and it was subsequently weighed. The bulk
density was expressed as grams per litre (the weight of
the acid treated maize tassel filling a graduated cylinder
on gentle tapping, divided by the volume of the cylinder
10 mL). The loss of mass on ignition was done by
weighing 15 g of the acid treated maize tassel and put
inside furnace at constant temperature of 600˚C for 2 h.
After roasting, the sample became charred and was re-
moved from the furnace then put in a desiccator for
cooling. The residual product was then weighed, and the
difference in mass represented the mass of organic mate-
rial present in the sample. For moisture content, 10 g of
acid treated maize tassel was weighed into a crucible and
heated in the oven for 5 h at constant temperature of
105˚C. The sample was then removed and put in a desic-
cator in so that moisture from atmosphere could not be
absorbed. The sample was reweighed. This procedure was
repeated several times until a constant weight was ob-
tained. The difference in the mass constitutes the amount
of moisture content of the adsorbent
23 21
%moisture 100ww ww  (1)
where w
w1 is weight of crucible,
w2 is initial weight of crucible with sample,
w3 is final weight of crucible with sample.
2.3. Preparation of Synthetic Solution
A stock solution of Lead(II) ion (1000 mg/L) was pre-
pared by dissolving Pb(NO3)2 (Merck, South Africa) in
ultra-pure water (resistivity ˃ 18 M·cm1). The pro-
gressive dilution procedure of the stock solution was
employed in the preparation of working solutions. The
pH of the working solutions was adjusted to the required
value with 0.1 M·NaOH or 0.1 M·HCl. All the chemicals
used were of analytical reagent grade.
2.4. Batch Adsorption Studies
A weighed amount of acid treated maize tassel was in-
troduced into stoppered reagent bottles containing vari-
ous concentrations with 100 mL aqueous solutions of
Lead(II) ions. The suspensions were shaken at room tem-
perature (25˚C ± 1˚C) using a mechanical shaker for a
prescribed time at 160 rpm. The solutions were filtered
through Whatman 42 filter paper and the residual con-
centration of metal ion was determined by AAS method.
The effects of concentration (10 - 50 mg/L), contact time
(5 - 300 min), solution pH (2 - 12) and adsorption dose
(0.1 - 2.5 g) were studied. The percentage of removed
Lead(II) ions (R%) in solution was calculated by using
Equation (2):
The amount of metal adsorbed by acid treated maize
tassel was calculated from the difference between metal
quantity added to the biomass and metal content of the
supernatant using Equation (3):
where qe is the metal uptake (mg metal adsorbed per g
adsorbent), Ci and Ce are the initial and equilibrium metal
concentration in solution (mg/L), V is the volume of the
solution (mL) and M is the weight of acid treated maize
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tassel (g).
2.5. Desorption Studies
For the desorption studies, contact was made between 1.2
g of acid treated maize tassel and a 100 mL Lead(II) so-
lution. After Lead(II) ion sorption, the acid treated maize
tassel was filtered, washed three times with ultra-pure
water to remove residual Lead(II) ions on the surface,
and kept in contact with different concentrations (0.05 -
0.3 mol/L) of 100 mL·HCl solution. The mixtures were
shaken in a rotary shaker for 60 min. The filtrates were
analyzed to determine the concentration of Lead(II) ions
after desorption using AAS.
2.6. Adsorption Isotherms
In the present study, the equilibrium data for the ad-
sorbed Lead(II) ions onto acid treated maize tassel was
expressed using Langmuir and Freundlich isotherm. The
Freundlich isotherm [21] is given by Equation (4):
qKC (4)
The parameters can be linearized by taking logarithms
to find the parameters KF and n:
ln lnln
qK C
A plot of ln qe versus ln Ce gives a straight line and KF
and n can be calculated from the intercept and slope, re-
spectively. The linear form of the Langmuir isotherm
model [22] can be represented by Equation (6):
max max
11 11
qqbq C
A plot of 1/qe versus 1/Ce was found to be a straight
line with 1/qmax as intercept and 1/qmax b as slope and
hence qmax and b can be calculated. In addition, a dimen-
sionless constant called separation factor, RL can be used
to express an essential feature of Langmuir isotherm
where, Cm is the initial concentration of Lead(II). The
value of RL indicates the type of the isotherm to be either
unfavorable when RL ˃ 1, linear if RL = 1, favorable if 0
˂ RL ˂ 1 or RL = 0.
2.7. Adsorption Kinetics
The pseudo-second order model has been widely used for
adsorption for the following reasons: it does not have the
problem of assigning an effective adsorption capacity,
the adsorption constant capacity, rate constant and initial
adsorption rate can all be determined from the equation
without knowing any parameter beforehand [24]. Hence
in the present study, adsorption of Lead(II) ions on acid
treated maize tassel has been described by pseudo-sec-
ond-order model [18]. The general form of the pseudo-
second-order kinetic model:
kq (8)
where qe and qt (mg/g) are the amounts of the Lead(II)
ions sorbed at equilibrium and at time t (min), respec-
tively and k2 (mg/g·min) is the second order rate constant.
The slope of the plot (t/qt) versus t gives the value of qe
and from the intercept k2 can be calculated
3. Results and Discussion
3.1. Physicochemical Characteristics of Acid
Treated Maize Tassel
The physico-chemical characteristics like pH, moisture
content, bulk density, surface area, and loss of mass on
ignition were determined and given in Table 1.
3.2. Effects of Dosage
The effect of biomass dosage on the biosorption of Pb (II)
ions was studied using biomass dosage in the range 0.1 -
2.5 g (Figure 1). As shown in Figure 1, the percentage
removal increases sharply from 58.5% to 92.2%, but be-
yond this, the percentage removal did not increase sig-
nificantly and reached a maximum at 92.3%. This phe-
nomenon can be due to the greater availability of activity
sites or surface area making easier penetration of the
Lead(II) ions to the adsorption sites and increasing this
number had no effect after equilibrium is reached. These
results are in agreement to other results reported in lit-
erature [2,25].
3.3. Effect of pH
The effect of initial pH of a solution is a major factor
used to determine the adsorption property of an adsorb-
ent from wastewater. The possible reasons are its effects
on the chemistry of the ions and the activity of functional
groups (carboxylate, phosphate and amino groups) on the
cell walls [12]. As shown in Figure 2, there is an in-
Table 1. Characteristics of the acid treated maize tassel
developed from maize tassel.
Parameter Value
pH 6.9
Moisture (%) 0.3
Bulk density (g·mL1) 0.52
Surface area (m2/g) 250
Particle size range 100 - 300 µm
% Loss of mass on ignition 0.7
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Figure 1. Dosage versus percentage removal of Lead(II) ion
(contact time: 60 min; pH 5.4; initial concentration 10 mg/L;
Error bar = ±S.D. and n = 3).
Figure 2. pH against percentage removal of Lead(II) ion
(contact time: 60 min; dosage 1.2 g; initial concentration 10
mg/L; Error bar = ±S.D. and n = 3).
crease in the quantity of adsorbed Lead(II) ions onto acid
treated maize tassel by increasing pH of the medium up
to a maximum value of pH 5.4. At low pH values, the
adsorbent is positively charged since the pH is lower than
the isoelectric point or point of zero charge (PZC) [26].
Hence the removal yield of Lead(II) ions is very low due
to the electrostatic repulsion forces between positively
charged H3O+ and Pb2+ ions. Thereafter the adsorption
percentage decreased in alkaline medium perhaps due to
the formation of Pb(OH)2 and soluble hydroxyl com-
plexes such as PbOH+, aqueous Pb(OH)2 and Pb(OH)3
and adsorbent was deteriorated with the accumulation of
metal ions making true adsorption studies impossible
[25,27]. The results obtained in this study showed that
the acid treated maize tassel is more effective in remov-
ing Lead(II) ions from an aqueous system with more than
94% removal as compared to raw maize tassel 75% [28];
physically prepared AC 78% [29]. Therefore, pH 5.4 was
selected to be the optimum pH for all further studies.
3.4. Effect of Agitation Time and Initial
The effect of agitation time is one of the important fac-
tors when designing batch sorption systems for eco-
nomical wastewater treatment plant application [13]. As
shown in Figure 3, the relationship between agitation
time and Lead(II) ion sorption onto acid treated maize
tassel at different initial Lead(II) concentrations is deter-
mined by plotting the percentage biosorption of Lead(II)
ion against agitation time for the interaction time inter-
vals of between 2 to 300 min.
It was observed that 52%, 60%, 65% and 70% of
Lead(II) ions was removed in the first 2 min for the dif-
ferent concentrations 10, 20, 30 and 50 mg/L respec-
tively and the process was rapid up to 60 min reaching
91.8%. Beyond 60 min, the percentage of biosorption is
almost constant indicating the attainment of equilibrium
conditions. The presence of adequate external surface area
on the acid treated maize tassel may have boosted the
rate of adsorption to be fast in the initial stages which
was followed by a slower internal diffusion process, which
maybe the rate determining step. From the observed ad-
sorption trend of Lead(II), the binding may be through
van der Waals forces of attraction present on the surface
of the acid treated maize tassel. Therefore, all other ex-
periments were conducted at an agitation time of 60 min.
The effect of initial concentration on the percentage
removal is also shown in Figure 3. The concentration
range from 10 to 50 mg/L for the metal ion has been
studied. The removal of Lead(II) ions by acid treated
maize tassel was found to decrease with increase in ini-
tial Lead(II) concentration. The observed behavior can be
attributed to the increase in the amount of Lead(II) ions
to the unchanging number of available active sites on the
acid treated maize tassel. Hence, more metal ions were
left in solution. Thus it can be said that removal of
Lead(II) ion is highly concentration dependent.
3.5. Interference Studies
The selectivity of the acid treated maize tassel on the
adsorption efficiency of Lead(II) were studied in the
Figure 3. Agitation time against percentage removal Lead
(II) ion (concentrations: a to d: 10 to 50 mg/L, adsorbent
dosage: 1.2 g; pH: 5.4, Error bar = ± S.D. and n = 3).
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presence of anions such as F, Cl, 3, NO 2
and cations such as Fe2+, Mg2+, Ca2+, Na+ and K+.
There was no significant reduction in the adsorption of
Lead(II) when the concentration of the above ions in-
creased up to 50 mg/L in aqueous solution. It can be
concluded that with proper treatment of the industrial
wastewater, adsorption of Lead(II) ions on the surface of
the adsorbent up to 94% in the presence of the studied
anions and cations up to 50 mg/L is possible.
3.6. Isotherm and Kinetics Study
Figures 4(a) and (b) show the Langmuir isotherm and
the Freundlich adsorption isotherm respectively. The
Freundlich constants n and KF, Langmuir constants b and
qmax and the correlation coefficient R2 are given in Table
2. The calculated value of Freundlich constant n is within
the range (0.1 < n < 1), reported in literature [30] show-
ing that adsorption is favorable. However, the linearized
equation did not give a good correlation for the removal
of Lead(II) onto acid treated maize tassel, indicating that
Lead(II) adsorption by acid treated maize tassel fits bet-
ter to the Langmuir model than to the Freundlich model.
The calculated RL was 0.62 indicating that the adsorption
of the Lead(II) was a favorable process. The plot of t/qt
versus t is shown in Figure 4(c). The values of k2 and qe
were 0.135 g/mg min and 2.02 mg/g respectively. The R2
value was 0.998, indicating a chemisorptions process.
3.7. Treatment of Industrial Wastewater
The suitability of the sulphuric acid treated maize tassel
for the removal of Lead(II) was tested with the leachates
from an electroplating plant. The leachate sample pH was
maintained between 5.4 - 5.9 and the determined compo-
sition of leachate from an electroplating plant is tabulated
in Table 3.
The treatment of Lead(II) in leachates was signifi-
cantly good (p < 0.05). Almost 93.9% removal from
wastewater was possible with 1.2 g of the adsorbent.
Thus, the results corroborate well with what is obtained
from the batch adsorption mode conducted for Lead(II)
removal in synthetic wastewater samples. Furthermore,
preliminary treatment of the leachates is essential before
application of acid treated maize tassel as the adsorbent.
3.8. Desorption Studies
For wastewater treatment, the successful application of
desorption reduces the dependence on thermal activation,
incineration, and land disposal, which directly or indi-
rectly increases environmental pollution. In this study,
effect of HCl concentration on the desorption of Lead(II)
ion is shown in Figure 5. It can be observed that desorp-
tion rate increases with the increase in HCl concentration
but attained a constant at 0.2 M·HCl.
Figure 4 (a) Langmuir isotherm; (b) Freundlich isotherm
for Lead(II) ion removal; (c). Pseudo-second-order kinetic
fit for Lead(II) adsorption.
Table 2. Langmuir and Freundlich constants for Lead(II)
adsorption using acid treated maize tassel.
Adsorption isotherm Parameter Value
Langmuir qmax (mg/g) 37.31
b (L/mg) 0.062
R2 0.9997
Freundlich KF 0.077
n 0.482
R2 0.9515
4. Conclusion
The present study showed that acid treated maize tassel
can be used for the effective removal of Lead(II) ions
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Table 3. Composition of leachates sample from an electro-
plating plant.
Parameter Value
pH 3.9
Total dissolved salts (mg/L) 5056.44
Turbidity (NTU) 1.22
Electrochemical conductivity (μmhos/cm) 3044.28
COD (mg/L) 30.56
Chloride (mg/L) 320.58
Sulphate (mg/L) 1005.56
Calcium (mg/L) 95.35
Lead (mg/L) 98.28
Zinc (mg/L) 18.25
Figure 5. Effect of different HCl concentrations on desorp-
tion of Lead(II) ion (concentrations: a to d: 10 to 50 mg/L
Error bar = ±S.D. and n = 3).
from wastewater. Lead(II) adsorption was found to be pH
dependent and maximum removal was observed at pH
5.4. An increase in the acid treated maize tassel dosage
leads to an increase in Lead(II) ions removal due to a
corresponding increase in the number of active sites. The
Langmuir adsorption isotherm was demonstrated to pro-
vide the best correlation (R2 = 0.9997) for the adsorption
of Lead(II) ions onto acid treated maize tassel confirming
monolayer coverage. Adsorption obeyed a pseudo-sec-
ond-order model. It can be concluded that the acid treated
maize tassel from maize tassel adds to the global discus-
sion of its cost-effective utilization in wastewater treat-
5. Acknowledgements
The authors are grateful for the Department of Chemical
Technology, Midlands State University, Gweru, Zimbab we
for providing facilities.
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