Bioresource Technology 97 (2006) 15–20
Removal of chromium from industrial waste by using eucalyptus bark
Vikrant Sarin, K.K. Pant
*
Department of Chemical Engineering, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India
Received 16 November 2004; received in revised form 31 January 2005; accepted 18 February 2005
Available online 7 April 2005
Abstract
Several low cost biomaterials such as baggase, charred rice husk, activated charcoal and eucalyptus bark (EB) were tested for
removal of chromium. All the experiments were carried out in batch process with laboratory prepared samples and wastewater
obtained from metal finishing section of auto ancillary unit. The adsorbent, which had highest chromium(VI) removal was EB.
Influences of chromium concentration, pH, contact time on removal of chromium from effluent was investigated. The adsorption
data were fitted well by Freundlich isotherm. The kinetic data were analyzed by using a first order Lagergren kinetic. The Gibbs free
energy was obtained for each system and was found to be 1.879 kJ mol1 for Cr(VI) and 3.885 kJ mol1 for Cr(III) for removal
from industrial effluent. The negative value of DG0 indicates the feasibility and spontaneous nature of adsorption. The maximum
removal of Cr(VI) was observed at pH 2. Adsorption capacity was found to be 45 mg/g of adsorbent, at Cr(VI) concentration in
the effluent being 250 mg/l. A waste water sample containing Cr(VI), Cr(III), Mg, and Ca obtained from industrial unit showed
satisfactory removal of chromium. The results indicate that eucalyptus bark can be used for the removal of chromium.
2005 Elsevier Ltd. All rights reserved.
Keywords: Adsorption; Eucalyptus bark (EB); Hexavalent chromium; Lagregren kinetic; Freundlich isotherm
1. Introduction
Water pollution by chromium is of considerable concern, as this metal has found widespread use in electroplating, leather tanning, metal finishing, nuclear power
plant, textile industries, and chromate preparation.
Chromium exists in two oxidation states as Cr(III) and
Cr(VI). The hexavalent form is 500 times more toxic
than the trivalent (Kowalski, 1994). It is toxic to microorganism plants, animals and humans. Human toxicity
includes lung cancer, as well as kidney, liver, and gastric
damage (US Department of Health and Human Services, 1991; Cieslak-Golonka, 1995). The tanning process is one of the largest polluters of chromium all
*
Corresponding author. Tel.: +91 11 26596172; fax: +91 11 2652
1120.
E-mail address: [email protected] (K.K. Pant).
0960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2005.02.010
over the world. Most of the tanneries in India adopt
the chromium tanning process because of its processing
speed, low costs, and light color of leather and greater
stability of the resulting leather. In the chromium tanning process, the leather takes up only 60–80% of applied
chromium, and the rest is usually discharged into the
sewage system causing serious environmental impact.
Chromium ion in liquid tanning wastes occurs mainly
in trivalent form, which gets further oxidized to hexavalent Cr(VI) form, due to the presence of organics.
The maximum levels permitted in wastewater are
5 mg/L for trivalent chromium and 0.05 mg/L for hexavalent chromium (Acar and Malkoc, 2004). With this
limit, it is essential for industries to treat their effluents
to reduce the Cr to acceptable levels. Due to more stringent environmental regulations, most of the mineral
processing plants, metal-finishing industries are facing
nowadays the difficult problem of disposal of wastewater produced in huge quantities, laden with Cr.
16
V. Sarin, K.K. Pant / Bioresource Technology 97 (2006) 15–20
Chromium metal ions are usually removed by precipitation (Patterson, 1977), although ion exchange (Tiravanti et al., 1997) and adsorption (Dahbi et al., 1999;
Orhan and Buyukgangor, 1993) are also used for its removal. The hydroxides of heavy metals are usually
insoluble, so lime is commonly used for precipitating
them. The most important factor in precipitation of
heavy metal is the valence state of metal in water. Cr
whose hexavalent form, chromate ðCrO2
4 Þ, is considerably more soluble than trivalent form, Cr(III). In this
case, the chromate, in which Cr is present as Cr(VI)
must be reduced usually with SO2 available from sodium
metabisulphite at low pH for removal of chromium as
Cr(III) by precipitation process. Another aspect of
precipitation process is the zeta potential of the initial
heavy metal colloidal precipitate. In many plants where
heavy metals are being removed, one of the principal
problems in reaching the desired effluent limits is the colloidal state of precipitated materials—they have not
been properly neutralized, coagulated and flocculated.
A final aspect of heavy metals is the possible formation
of complex ions, which is common when dealing with
wastewaters containing ammonia, fluoride, or cyanide
ions along with heavy metals. Because of these important aspects in the precipitation of heavy metals, there
is no way to predict the best solution of a specific problem without undergoing a series of bench tests to evaluate the alternative available (Kemmer, 1988).
The present study is aimed at selection of a low cost
biosorbent, which can adsorb chromium from the wastewater. Detailed batch studies with the selected adsorbent, eucalyptus bark has been carried out in the
present investigation. The effect of pH, contact time,
adsorbent concentration, thermodynamics study, and
metal ion/adsorbent ratio were also investigated.
grounded to small particles of size 120 < dp < 500 lm.
It was washed with deionized water and then dried. To
avoid, the release of color by bark in to the aqueous
solution during adsorption, it was treated with formaldehyde (Randall et al., 1976). For this 5 mL of aqueous
formaldehyde was added to 100 mL of 0.1 M H2SO4
and then 10 g of grounded and washed bark was added
to this solution. The final mixture was stirred and heated
at 50 C for 24–48 h till the mixture became thick slurry.
The slurry (treated bark) was washed with deionized
water until the pH of the filtrate was more than 4.5.
Finally the bark was air-dried and sieved. Particles in
the range of 120–500 lm size were collected as the final
adsorbent. Surface area of the sorbent was determined,
using BET apparatus, using liquid nitrogen as
adsorbent.
Further, ultimate and proximate analysis of the EB
adsorbent was also carried out. The detailed characteristics of EB obtained are shown in Table 1.
2.3. Determination of chromium content
The chromium concentration in raw and treated effluent was determined by UV (Varian, Australia) spectrophotometer. The wavelength of operation was kept at
540 nm. For this purpose, K2Cr2O7 solutions of different
concentrations were prepared and their absorbance recorded by using a UV-spectrophotometer. A calibration
plots for Cr(VI) were drawn between Ô%Õ absorbance
and standard Cr(VI) solutions of various strengths
(APHA, 1992). Runs were made in triplicate. Cr(III)
concentration was determined by measuring the difference between total chromium concentration and Cr(VI)
concentration. Total Cr concentration was determined
by oxidizing Cr(III) to Cr(VI) using KMnO4 and then
determining final Cr(VI) content in the sample (APHA,
1992).
2. Methods
2.4. Experimental
2.1. Materials
All the chemicals used were of analytical grade.
K2Cr2O7, HCHO, NaOH, diphenyl carbizide, KMnO4,
HNO3 and H2SO4 were procured from Merck. The
adsorbents selected for the preliminary study were baggase, charred rice husk, activated charcoal, and eucalyptus bark (EB). These were grounded and washed with
deionized water. The adsorbents were dried at room
temperature, (32 ± 1 C) till a constant weight of the
adsorbent was achieved. A uniform particle size of the
adsorbent was maintained between 120 and 500 lm.
2.2. Preparation of eucalyptus bark adsorbent
Eucalyptus bark of Eucalyptus globulus tree species
was collected from the local area. The bark was
Stock solution of 1000 ppm of Cr(VI) was prepared
by dissolving K2Cr2O7 (AR grade), in deionised,
double-distilled water. All the batch adsorption studies
Table 1
Characteristics of eucalyptus bark (EB) adsorbent
Characteristics
Values
2
Surface area (m /g)
Bulk density (g/cm3)
Moisture content (%)
Ash content (%)
Volatile matter (%)
Fixed carbon (%)
Carbon (%)
Hydrogen (%)
Nitrogen (%)
Oxygen (%)
0.59 ± 0.05
0.25 ± 0.02
10.1 ± 0.3
19.0 ± 0.5
65.7 ± 2.0
15.3 ± 0.5
43.68 ± 1.3
8.14 ± 0.25
0.43 ± 0.01
47.75 ± 1.4
V. Sarin, K.K. Pant / Bioresource Technology 97 (2006) 15–20
were carried out using 100 mL of solution of appropriate concentration as desired by dilution of the stock
solution. Requisite quantity of adsorbent was added to
250 mL plastic reagent bottles containing 100 mL of
synthetic effluent of Cr(VI). The bottles were placed in
a shaker at 32 ± 1 C, for 24 h. The speed of shaker
was kept at 100 rpm. After 24 h the bottles were
removed and the content of the bottles was filtered
through a filter paper. The filtrate was analyzed for
pH and final chromium concentration using UV Spectrophotometer. The removal of Cr(VI) was studied by
using various adsorbents such as baggase, charred rice
husk, activated charcoal, and eucalyptus bark. For all
these runs the adsorbent dose was kept at 5 g L1 of synthetic effluent of Cr(VI) and Cr(VI) concentration was
kept at 50 ppm at pH of 5.2. Further studies on chromium removal were carried out using adsorbent as
EB. This involved, varying initial Cr(VI) concentration
ranging from 50 to 250 ppm. The pH was varied from
1.5 to 9 of with different initial concentrations. The
contact time in batch was varied from 0.25 h to 24 h.
The studies were also carried with industrial effluent
obtained from metal finishing industry (Automobile
ancillary unit, manufacturing brake shoes, Sahibabad,
U.P). The characteristics of industrial effluent is as
follows: Cr(VI) concentration 200 mg/L, Cr(III) concentration 44.5 mg/L, total dissolved solids 780 mg/L, Ca
concentration 135 mg/L and Mg concentration 92 mg/
L. The samples were characterized by standard APHA
method (APHA, 1992).
3. Results and discussion
3.1. Performance of various adsorbents for Cr removal
The performances of these sorbents were evaluated
for the percent removal of chromium. The maximum
(87.4%) removal of chromium was achieved with EB.
The percent chromium removal with other three sorbents
were significantly low as compared to EB (charred rice
husk 36%, activated carbon 9% and bagasse 35%) therefore not considered for further investigations. The variation in the sorption capacity between the various
adsorbents could be related to the nature and concentration of surface groups responsible for interaction with
the metal ions. The selected adsorbents were cellulose
based plant fibers having many hydroxyl groups that
may bind the Cr(VI) ion. Formaldehyde pretreatment
of eucalyptus bark led to crosslinking of compounds in
the bark to form a phenol–formaldehyde copolymer that
preserved high capacity of the support towards the
adsorption of cations. This can be explained by the interactions in the solutions between the cations and the water
extracted moieties, leading to complexities that precipitate on the support surface (Saliba et al., 2002).
17
The adsorptive properties of activated carbon are due
to its porous nature. Over 99% of the active sites for
adsorption in GAC are located in the interior of the
particle. Activated carbon particles have macropores
having diameters 30 to 100,000 Å and the micropores
having diameters in the range of 10 to 30 Å (Weber,
1967). Results of our investigation revealed that eucalyptus bark has highest percent removal and sorption
capacity. Further investigations were made with this
sorbent. A comparison of the sorbent capacity with various sorbents studied in literature is given in Table 2
and compared with EB.
3.2. Effect of pH
Effect of solution pH on removal of Cr was studied
using EB as sorbent. As the pH of the solution was increased from 1.5 to 9 the adsorption of Cr(VI) decreased. Increasing pH from 1.5 to 5, percent removal
of Cr(VI) decreased 99 to 93, whereas as the pH was
increased from 5 to 9 the % removal decreased significantly from 93 to 63. It was observed that the maximum
percentage of removal of Cr(VI) was at pH 2. Almost
100% of Cr(VI) removal was observed at this pH at
50 ppm Cr(VI) concentration. Dominant form of Cr(VI)
at initial pH of 2 is HCrO
4 (Namasivayam and Yamuna, 1995). Increase in pH shifts concentration of
2
HCrO
4 to other forms, CrO4 and Cr2 O7 . It can be
concluded that the active form of Cr(VI) that can be adsorbed by EB was HCrO
4 . Further it was observed that
there was an increase in pH during adsorption. The
increase in pH with contact time explained by hydrolysis
of the adsorbent in water, which will create positively
charged sites. Upon adsorption of HCrO
4 , a net
production of hydroxide ions will occur as shown below
(Saliba et al., 2002).
þ
OHþ
2 þ HCrO4 $ OH2 ðHCrO4 Þ
ð1Þ
Every mole of HCrO
4 adsorbed results in the release of
two moles of hydroxyl ions in the solution, which raises
the solution pH (Namasivayam and Yamuna, 1995).
This change in pH at lower initial pH is very small since
the solutions at lower pH are well buffered by the acids
used in this pH range.
3.3. Effect of contact time
Fig. 1 shows the effect of contact time. Increasing
contact time from 0.25 h to 3 h increases % Cr removal.
Maximum Cr removal was observed with in first 2 h.
The kinetic data was fitted to the Lagergren equation
(Singh and Pant, 2004).
logðxe xÞ ¼ log xe K ads t=2:303
ð2Þ
x = the amount of solute, Cr(VI), (mg/g of adsorbent)
removed at time t, xe = amount removed at equilibrium
18
V. Sarin, K.K. Pant / Bioresource Technology 97 (2006) 15–20
Table 2
Adsorption capacity of various adsorbents as reported in literature
Adsorbent
Maximum
adsorption
capacity (mg/L)
Optimum pH
Maximum
concentration
C0 (mg/L)
References
Saw dust
Coconut husk fibers
Sugar cane bagasse
Sugar beet pulp
Palm pressed fibers
Activated carbon (Filtrasorb-400)
Biogas residual slurry
Wool
Pine needles
Eucalyptus bark
39.7
29.0
13.4
17.2
15.0
57.7
5.87
8.66
5.36
45.00
2.0
2.05
2.0
2.0
2.0
–
2.0
2.0
2.0
2.0
1000
–
500
500
–
–
40
100
100
250
Sharma and Foster (1994)
Huang and Wu (1977)
Sharma and Foster (1994)
Sharma and Foster (1994)
Tan et al. (1993)
Huang and Wu (1977)
Namasivayam and Yamuna (1995)
Dakiky et al. (2002)
Dakiky et al. (2002)
Present study
2.5
120
2
80
log(Xe - X)
Chromium(VI) removal (%)
100
60
1.5
1
40
I.E., Cr(VI), at pH - 3.41
I.E., Cr(III), at pH - 3.41
pH - 2
pH - 3
pH - 4.7
20
0
0
15
30
45
60
75
90 105 120 150 180 210
Time (min)
Fig. 1. Effect of contact time on removal of Cr(VI) by eucalyptus bark
from synthetic effluent (S.E.) having Cr(VI) 200 ppm, pH 4.7 and
industrial effluent (I.E.) having Cr(VI) 200 ppm, Cr(III) 44.5 ppm and
pH 3.41. Adsorbent dosage was 5 g/L.
and Kads = the rate constant of adsorption (1/min). The
effect of contact time was studied for removal of Cr from
effluent containing 200 ppm of Cr(VI) at 32 ± 1 C,
pH 2, pH 3, pH 4.7. Experiments were also carried out
industrial effluent containing Cr(VI) 200 ppm and
Cr(III) 44 ppm. For EB the contact time of 3 h was
needed to establish equilibrium. The kinetic on different
solution of Cr(VI) at different pH with EB as adsorbent
was found to follow the first order rate. Fig. 2 depicts
the Lagergren plots with a regression coefficient more
than 0.9. Adsorption rate constant is given in Table 3.
3.4. Adsorption isotherm
Adsorption isotherms, which are the presentation of
the amount of solute adsorbed per unit of adsorbent,
as a function of equilibrium concentration in bulk solution at constant temperature, were studied. The equilibrium data obtained were fitted to Langmuir and
Freundlich isotherms.
Linear form of Langmuir equation,
1=X ¼ 1=X m þ ð1=C e Þð10 =b X m Þ
ð3Þ
pH - 2
pH - 3
pH - 4.7
I.E., Cr(VI), at pH - 3.41
I.E., Cr(III), at pH - 3.41
0.5
0
0
20
40
60
Time (min)
80
100
120
Fig. 2. Lagergren plot for the adsorption of Cr(VI) by eucalyptus bark
adsorbent from synthetic effluent having Cr(VI) 200 ppm, pH 4.7 and
industrial effluent having Cr(VI) 200 ppm, Cr(III) 44.5 ppm and pH
3.41. Adsorbent dosage was 5 g/L.
Table 3
Adsorption rates constant for EB for various systems
Cr(VI) concentration
(mg/L)
pH
Particle
size (lm)
Rate constant
kads (min1)
R2
200 ppm
200 ppm
200 ppm
200 ppm
2.0
3.0
4.7
3.41
120–500
120–500
120–500
120–500
1.9806 · 102
1.2206 · 102
1.0133 · 102
5.758 · 103
0.9723
0.9718
0.9640
0.9662
3.41
120–500
1.4040 · 103
0.9723
200 ppm
Cr(VI)
Cr(VI)
Cr(VI)
(Ind effluent)
Cr(VI)
(Ind effluent)
Cr(III)
X = x/m, where ÔxÕ is in mg the amount of solute adsorbed, ÔmÕ is unit gram of adsorbent, Ce is the equilibrium concentration of solute (mg L1); Xm is the
amount of solute adsorbed per unit weight of adsorbent
required for monolayer coverage of the surface also
called monolayer capacity and b is a constant related
to the heat of adsorption.
Freundlich equation indicates the adsorptive capacity
or loading factor on the adsorbent, x/m is a function of
the equilibrium concentration of the solute. It can be
V. Sarin, K.K. Pant / Bioresource Technology 97 (2006) 15–20
used for calculating the amount of adsorbent required to
reduce any initial concentration to predetermined final
concentration.
The Freundlich equation is expressed linearly as:
log x=m ¼ log K f þ 1=n log C e
ð4Þ
ðK 0c Þ
The thermodynamic equilibrium constant
for various systems using EB as adsorbent was obtained at
32 ± 1 C.
K 0c ¼
Ca
;
Ce
ð5Þ
where Ca is concentration of Cr(VI) on the adsorbent at
equilibrium in mg L1 and Ce is the equilibrium concentration of Cr(VI) in solution in mg L1.
The initial Cr(VI) concentrations tested were 200 ppm
of synthetic effluent and true industrial effluent having
Cr(VI) as 200 ppm and Cr(III) as 44.5 ppm at an adsorbent dosage of 5 g L1. The adsorption followed Freundlich isotherm. Freundlich plot is shown in Fig. 3.
Linearity of these plots shows that first order mechanism is followed in this process. The Kf and n values
as calculated from the Fig. 3 for synthetic effluent having 200 ppm of Cr(VI) and pH 4.7 was found out to
be as 6.74 mg/g and 4.66, respectively. Industrial effluent
having 200 ppm of Cr(VI) and 44.5 ppm of Cr(VI) at
3.41 pH had Kf and n values as 21.69 mg/g and 9.8 for
Cr(VI), and 18.26 mg/g and 7.88 for Cr(III), respectively. A higher than 1 value of n indicates that the
adsorption on EB is favorable and capacity is only
slightly reduced at the lower equilibrium concentrations.
These values are comparable with several published
literature reported for various sorbents (Sharma and
Foster, 1994; Namasivayam and Yamuna, 1995; Dakiky
et al., 2002). Significantly higher values of adsorption
capacity obtained with eucalyptus bark indicate that it
can be used for the treatment of chromium waste.
1.6
1.4
1.2
log x/m
1
0.8
0.6
0.4
Cr(VI) of I.E.
0.2
Cr(III) of I.E.
S.E. of Cr(VI)
19
Table 4
Thermodynamic parameters for the adsorption of Cr(VI) by EB
Effluent
Effluent
concentration
of Cr
pH
Equilibrium
constant Kc
Gibbs free
energy
DG0 kJ mol1
Pure solution
Pure solution
Pure solution
Industrial
effluent
Industrial
effluent
250
200
200
200
2
3
4.7
3.41
9.0
4.95
1.36
2.10
5.572
4.057
0.795
1.884
3.41
4.60
3.872
Cr(VI)
Cr(VI)
Cr(VI)
Cr(VI)
44.5 Cr(III)
The Gibbs free energy (DG0) for the adsorption process for each effluent was obtained using the formula:
DG0 ¼ RT ln K 0c
0
ð6Þ
ÔK 0c Õ
Values of DG and thermodynamic constant
for various systems are shown in Table 4.
The Gibbs free energy indicates the spontaneity of the
adsorption process, where higher negative values reflect
a more energetically favorable adsorption process. The
negative DG0 values obtained for various systems in this
study confirm the feasibility of the adsorbent and spontaneity of adsorption. The studies further confirm that
as the pH of the system is reduced the adsorption of
Cr increases. With all the industrial samples there was
more than 90% of Cr removal without any significant
interference of other metal ions. This indicates that EB
has higher affinity towards Cr adsorption.
4. Conclusion
Removal of poisonous hexavalent form of chromium
from solutions was possible using selected adsorbents.
Eucalyptus bark (EB) was the most effective for which
the removal reached more than 99% for Cr(VI) at concentration of 200 ppm and at pH 2. Increase in the dose
of adsorbent, initial concentration of Cr(VI) and increase in contact time upto 2 h are favorable for all
increase the adsorption of Cr(VI). The kinetic of the
Cr(VI) adsorption on EB was found to follow first order
mechanism. The Gibbs free energy was obtained for
each system. It was found to be 1.884 kJ mol1 for
Cr(VI) and 3.872 kJ mol1 for Cr(III) for removal
from industrial effluent. The adsorption data can be satisfactorily explained by Freundlich isotherm. Higher
sorption capacity of this sorbent indicates that eucalyptus bark can be used for the treatment of chromium
effluent.
0
-3
-2
-1
0
1
2
3
log Ce
Fig. 3. Freundlich plot for the adsorption of Cr(VI) from synthetic
effluent having Cr(VI) 200 ppm and pH 4.7 and industrial effluent
(I.E.) having Cr(VI) 200 ppm, Cr(III) 44.5 ppm and pH 3.41 at 32 C.
Adsorbent dosage was 5 g/L.
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