Indian Journal of Chemical Technology
Vol. I. November 1994, pp. 351-355
Removal of Fe(II) by waste Fe(m) / Cr(III) hydroxide from aqueous solution
and electroplating industry wastewater
C Namasivayarn" & K Ranganathan
Environmental Chemistry Division, Department of Environmental
Coimbatore 641046, India
Sciences, Bharathiar University,
Received 25 January 1994; accepted II July 1994
The effects of Fe(lI) concentration, contact time, adsorbent dosage, particle size, temperature and
on adsorption of Fe(lI) by waste Fe(lII)/Cr(lII) hydroxide have been studied. The per cent Fe(lI) adsorbed increased with decrease in initial concentration of Fe(ll), increase in adsorbent dosage and temperature. The equilibrium data fit well with the Langmuir and Freundlich isotherms. The adsorption
rate constants and thermodynamical parameters are presented. Removal of Fe(ll) by the adsorbent is
also testified using electroplating industry wastewater.
pH
Iron is discharged into aquatic environment from
minings, steel processing, zinc processing plants
and electroplating industries 1. T he undesirable
colour, taste, odour and growth of iron bacteria in
water due to the presence of Fe(lI) are objecting
to its applicability in the food processing, textile
and paper industries. Several attempts have been
made to remove Fe(Il) from wastewaters containing more than the tolerance limit 2 • The general
methods for the removal of iron are oxidation followed by solid/liquid separation, ion exchange,
coordination, chlorination followed by filtration'
and adsorption on activated carbon", As these
methods are expensive, low-cost adsorbents and
biological oxidation methods are also being investigated.
Fe(III) / Cr(III) hydroxide is a waste by-product
produced in the treatment of wastewaters containing Cr(VI). Chromium(VI) in the wastewaters is
reduced to Cr(III) using Fe(II), which is generated
electrolytically". Fe(III) and Cr(III} ions, which are
formed, are precipitated as metal hydroxides using
lime. The resultant
Fe(lII}/Cr(III} hydroxide
sludge is discarded as waste. The 'Fe(III}/ Cr(III)
hydroxide sludge' has already been used for the
treatment of wastewaters from fertilizer", dyeing",
dairy", distillery? and tannery industries"!". It was
also used for the adsorption of heavy metals and
pesticide":" from wastewaters. The present work
deals with the ability of waste Fe(m}/Cr(m} hydroxide for the removal of Fe(ll} from aqueous solution and electroplating industry wastewater. Par•Author to whom correspondence
should be addressed
ameters such as initial Fe(I1) concentration, agitation time, adsorbent dosage, adsorbent particle
size, temperature and pH have also been studied.
Experimental Procedure
Materials-Dry waste Fe(III)/Cr(III) hydroxide,
obtained from Southern Indian Petrochemical Industries Corporation Limited (SPIC), Tuticorin,
was ground, screened to different particle sizes,
washed with distilled water to remove fine dust
and dried at 60°C for 10 h. The characteristics of
the adsorbent are: Fe/Cr, 5.5% (w/w); Ca, 5%; acid insoluble matter, 9.6%; loss on ignition, 30%;
apparent density, 0.89.5 glmL; pHzpc 8.3 and porosity 63%. The Fe(IIl}/Cr(III) hydroxide did not
release Fe(III) or Cr(IlI) in the pH range 3-11
studied. All the chemicals used were of AR grade.
Synthetic wastewater containing ferrous ion was
prepared using FeS04 and the pH was adjusted to
3.0. For pH adjustment, O.IN HCI04 and O.IN
NaOH solutions were used. Wastewater from electroplating industry was collected from Ganapathy
area, Coimbatore.
Adsorption studies-Batch adsorption studies
were carried out by agitating 50 mL of Fe(II) solution with 0.1 g Fe(IIl)/Cr(IIl) hydroxide for different agitation times at 120 rpm using a temperature
controlled water bath cum shaker. Control experiments were carried out and the containers were
tightly closed to avoid any oxidation by atmospheric oxygen. The adsorbent and adsorbate were
separated by centrifugation at 10,000 rpm for 20
min and the remaining Fe(ll) in the supernatant
was determined using 1,10-phenonthroline13
by a
352
INDIAN 1. CHEM. TECHNOL., NOVEMBER 1994
Hitachi Spectrophotometer
(model U-321O). Effects of initial Fe(II) concentration, particle size
and temperature at different agitation times were
also carried out.
For pH studies 50 mL of the 50 mglL Fe(II)
solution with ionic strength 0.01 M KN03 was adjusted to different initial pH values and agitated
with 50 mg of the Fe(III)/Cr(III) hydroxide at
30°C for the equilibrium time and remaining Fe(II)
in the solution was estimated as before.
In the case of electroplating industry wastewater, pH was adjusted to 3.0 and 50 mL of the effluent was agitated at 120 rpm with different dosages of Fe(III)/Cr(III) hydroxide of particle size
100-200 .urn for 120 min at room temperature
30°e. Then the supernatant was centrifuged and
analysed for Fe(II) as before.
All the experiments were done in triplicate and
maximum deviation was 5%.
Results and Discussion
Effect of agitation time and initial Fd}l) concentration- The per cent adsorption of Fe(II) on
Fe(III)/Cr(III) hydroxide of particle size 100-200
.u m increased with the increase in agitation time
and decrease in initial Fe(II) concentration. Equilibrium was attained in 120 min and per cent removal was found to be 89, 69, 58 and 53% at the
initial concentrations
of 50, 75, 100 and
125 mglL of Fe(II), respectively, at 30°C (Fig. 1).
Equilibrium time was independent of Fe(U) concentration.
Effect of agitation time and particle size-Ferrous
solution of 100 mg/L concentration was agitated
with 100 mg of Fe(III)/Cr(III) hydroxide of different particle size ranges, < 53, 100-200, 200-250
and 250-500 .urn for different agitation times at
30°e. Maximum removal was found at the agitaAdsor~nt
do~
PNticl~ size
h~r
••ture
tion time of 75, 120, 120 and 150 min and the
per cent removal was 100, 58, 40 and 37%, respectively (Fig. 2). This shows that decreasing particle size increases the adsorption of Fe(II) on
Fe(III)/Cr(III) hydroxide. Aqcording to Weber14
the breaking of larger particle tends to open tiny
cracks and channels on the particle surface, providing added surface area which can be employed
in the adsorption process. For the larger particles,
intra particle diffusion will be the predominant mechanism for a greater portion of the adsorption
process than with the smaller particles, since the
Fe(II) ions will have a further intraparticle distance
to diffuse".
Effect
of
adsorbent
dosage-Dosage
of
Fe(III)/Cr(III) hydroxide was varied from 0.5 to
6.0 g/L for 50 mL of 100 mg/L of Fe(II) solution
(Fig. 3). The result shows that the 4.0 glL of the
adsorbent is sufficient for complete removal of
100 mg/L of Fe(II) at the equilibrium time of
120 min.
Effect of temperature-The
effect of agitation
time and temperature on Fe(II) removal by Fe(III)/
Cr(III) hydroxide are shown in Fig. 4. Increase of
temperature from 20 to 40°C increased the ad~i •• 1 F~(l1)conen.
Amor~t
do~
TrmpPriltu.-.
~
60
80
: 100mgIL
: 2g/L
: JO!.
rc
m ~ ~ ~ m m
~
T_. min
Fig. 2-Effect of agitation time and particle size on Fe(II) removal by Fe(III)/Cr(III) hydroxide [(0) < 53 ,urn, (e) 100-250
,urn, (A) 200-250 ,urn, (0) 250-500 ,urn]
. 2 9IL
: 100- 200 pm
. 30 ~ i'c
1E
..
cr
Initi~1 F.(IJ) concn.: 100 mg/l
P~rticl. siz.
: 100 - 2oo}JlTl
Equilibrium tim.
: 120 min
40
60
80
100
120
140
160
180
200
220
T.m~r~tur.
: 30 ~ I'C
Tune , min
Fig. I-Effect of agitation time and initial concentration on
Fe(II) removal by Fe(III)/Cr(III) hydroxide [Fe(II) concentration: (0) 50 rng/L, (A) 75 mg/L, (e) 100 rng/L, (0)
125 mg/L]
1·0
2 -0
Doug.ot
Fig. 3-Effect
3·0
4·0
5·0
6·0
F.{\D}/Cr(IlI)hydroxid.,
,·0
8·0
g/l
of adsorbent dosage on Fe(II) removal
NAMASIVAYAM & RANGANAlHAN:
REMOVAL OF Fe(TI) By Fe(m)/Cr(m)
sorption of Fe(II} from 47 to 68%. Equilibrium
time was found to be 120 min for the temperatures studied. At higher temperatures the enlarging
of pore sizes or activation of adsorbent surface
may enhance the adsorption capacity of the adsorbent. Similar observations have been reported for
the adsorption of Ni(II} by fly-ash", As(V} by china-clay'? and Cr(VI} by the waste Fe(III}1 Cr(III}
hydroxide".
Thermodynamical
parameters were obtained
from the following equations and are given in
Table 1.18.
K = CAe
c
C,
... (1)
Il.Go=
... (2)
<R'Tsn K,
Il. SO
Il. If
.,.
10gKc= 2.303 R - 2.303 RT
100
Inillal F•• (II) concn.
Adsorb••nl dos..
: 100mg IL
: 2 g/L
Particle-
.
siZe>
(3)
100 - 200 .,um
where C, is the equilibrium concentration in solution in mg/L and C Ac is the equilibrium concentration on the adsorbent in mg/L. Fig. 5 shows a
van't Hoff plot of log
vs 1/ T. Il. IfO and Il. So
were obtained from the slope and intercept of the
plot, which are 35 kJ/mol and 117 J IK mol, respectively. The positive value of Il. HO suggests the
endothermic nature of adsorption. At 20°C, Il. GO
is positive and at 30 and 40°C, Il. GO is negative
(Table 1). This indicates non-spontaneous nature
of adsorption at 20°C and spontaneous nature of
adsorption at 30° and 409C. The positive value of
Il. So suggests the increased randomness at the solid-solution interface during the adsorption of
Fe(II) ions on Fe(III)/Cr(III) hydroxide. During the
adsorption of Fe(II), the adsorbed solvent molecules, which are displaced by the adsorbate species, gain more translational entropy than is lost
by the adsorbate ions, thus allowing the prevalence of randomness in the system 16.
Adsorption isotherms-Langmuir
adsorption isotherm model was applied for adsorption equilibrium at 20, 30 and 40°CIY
x,
Co
q:
1
=
Co
QO b + QO
Table I-Langmuir
Temperature.
60
80
100
120
1100 160
180
200
220
·c
Tim~, min
Fig. 4-Effect of agitation time and temperature on Fe(II)
removal by Fe(m)/cr(m) hydroxide at (~) 20·(:, (0) 30"<:,
(0) 40·C.
Q.
Inilial F••(II) conen.. l00mg/L
Adsor~nl dos..
: 2 g/L
Partiel•• siz..
: l00-2OO}In
~Iibrium
linw
: 120",.,
353
HYDROXIDE
20
30
40
...
(4)
constants and thermodynamical parameters
Langmuir constants
Q()
Thermodynamical
parameter
b
mg/g
Limg
Kc
~G"
kJ/mol
27.78
34.48
38.46
0.092
0.190
0.333
0.88
U81
2.125
+0.312
-0.814
- 1.962
4.(K----------------,
Initial F••(II) eonen. : 50 - 125mgl L
Adsorb<'nl oose
. 2 g/L
Partiel •• size
: 100- 200 }Jm
Equilibrium lim<'
. 120min
0·3
3·
02
u
'"
~
2·
01
uV
1·
o.
-o~o
3.1
3·5
36
3-7
20
30
40
50
60
70
80
90
C. , mg/L
Fig. 5-Arrhenius
plot for the adsorption of fe(lI)
Fe(m)/cr(m) hydroxide; logKc vs liT
on
Fig. 6-Langmuir plots for the adsorption of Fe(lI) on waste
Fe(III)/Cr(III) hydroxide at ("") 20·C, (0) 30"C, (0) 40·C.
354
INDIAN J~CHEM. TECHNOL.,
where C, is the equilibrium concentration (mg!L),
q e is the amount adsorbed at equilibrium (mg! g)
and QO and b are Langmuir constants related to
adsorption capacity and energy of adsorption, respectively. The linear plots of C e/ q e VS Ce show
that the adsorption obeys Langmuir model (Fig.
6). Values of QO and b are determined from the
plots and are presented in Table 1.
The equilibrium parameter, RL is defined as
follows.
R
=--L
1
...
1 + b C,
(5)
where Co is the initial concentration (mg/L) and b
is the Langmuir constant (L/mg). RL values between 0 and 1 indicate favourable adsorption for
all the initial concentrations
and temperatures
studied (Table 2).
Adsorption of Fe(II) on Fe(III)/Cr(lIl) hydroxide was also found to conform to the Freundlich
adsorption isotherm at different temperatures/".
log q c = log k f + ( 1/ n) log C e
... (6)
where C, is the equilibrium concentration (mg/L)
and qe is the amount adsorbed (mg/g). Plots of
log q e vs log C e show a group of linear lines each
representing a temperature (Fig. 7). k f and n were
determined from the Freundlich plots and found
to be 9.6 and 4.6, 14.5 and 6.5, and 21.4 and 7.4
at 20, 30 and 40°C, respectively. It is generally
stated that the values of n in the range 2-10 repreTable 2-Equilibrium
InitiaJ concentration
of Fe(I1), mg/L
NOVEMBER
1994
sent good adsorption 19. Langmuir and Freundlich
constants indicate that the adsorption capacity of
the Fe(III)/Cr(III) hydroxide increased with increase in temperature.
Adsorption dynamics-The kinetics of Fe(II) adsorption on Fe(lII)/ Cr(IIIl hydroxide follows first
order rate expression given by Lagergren".
kad t
2.303
log(qe-q)=logqe-
...
( )
7
where q is the amount of Fe(II) adsorbed (mg/g)
at time t (min) and qe is the amount adsorbed
(mg/g) at equilibrium time. Linear plots of
log(qe - q) vs t indicate the applicability of the
above equation (Fig. 8). The kad values, calculated
from the slopes of the plots at 20, 30 and 40°C
are 2.8 x 10-2,
3.13 X 10-2
and 3.32 x 10-2
1.75r-----------------,
Iniliill F~(II) conen. : 100 mg/l
Adsor~nl dose
: 2 9 Il
Particle size
: 100- 200,um
I.
a,
1.0
r#
~
0·75
0·50
0·25
9
Time,
min
Fig. 8-Lagergren
plots for the adsorption
Fe(U) on
Fe(III)/Cr(III) hydroxide [(L'.) 20·C, (0) 30°C, (0) 40°c.j
parameter
R[
100
20°C
30·C
40°C
50
75
0.179
0.127
0.095
0.057
0.038
100
125
0.098
O.ORO
0.066
0.050
0.040
90
80
0.030
0.023
70
60
••
>
Inil,.1 F~ (11)conen
Adsorb.mt
P.rtrcle-
oose
SIZ~
EqUilibrium
timt!'
2·0
..
50
~
40
0
50 - 125 mg/L
2 g/L
E
0::
100-2(0)Jm
120 min
Initial F~(II) concn. : 50 mg/L
Adsor~nt dose
: I g/l
Par ticte sin
: 100-200,um
Eq\.'ilibrium tim~
. 120min
30
~IE
20
10
o
05
10
log C.
15
20
Fig. 7-Freundlich
plots for the adsorption of Fe(U) on waste
Fe(III)/ Cr(lIl) hydroxide [( L'.) 20°C, (0) 30°C, (0) 40°Cj
0
3
"
5
6
Initial pH
8
9
10
Fig. 9-Effect of initiaJ pH on removaJ of Fe(U). [(0) Adsorp·
tion by Fc(I1I)/Cr(III) hydroxide, (0) Hydroxide precipitation.
~~
.,
NAMASIVAYAM & RANGANATHAN:
Table 3-Characteristics
Parameter
pH
Conductivity, mS/cm
Total solids, mg/L
Turbidity, NTU
COD,mg/L
Chloride, mg/L
Sulphate, mg/L
Fe(II), mg/L
Total iron, mg/L
355
REMOVAL OF Fe(.lI) By Fe(III)/Cr(III) HYDROXIDE
':-1
of electroplating industry wastewater
I
1.53
14.83
8,650.0
1.0
Nil
414.0
4,400.0
56.5
157.0
Ni,mg/L
Na,mg/L
250.0
Ca,mg/L
50.0
80
Q
;;;
>
o
•.
o
E
Partiel e
'•" • 4
SIZ"
:
tOO-200
)Jm
Equilibrturn
time'
120 min
Te rnperature
: 30 ~ I'C
I nllial
10
20
30
4~
Dosag e of
50
Fe (III)
60
pH
70
3·0
6·0
I Cr (01) hydroxi.,...
90
100
110
gft
1250.0
1/ min, respectively. The results indicate that increase of temperature increased the adsorption
rate constant.
Effect of pH-The
influence of initial pH on the
adsorption of Fe(II) by Fe(III)/Cr(III) hydroxide is
shown in Fig. 9. For comparison ferrous hydroxide precipitation by NaOH is also given. Increasing pH increased the per cent removal of Fe(II)
both by adsorption and hydroxide precipitation.
However, at any pH Fe(II) removal by adsorption
is very much greater than by hydroxide precipitation. Complete removal was achieved when the initial pH was :<! 4.5 for adsorption on Fe(III)/
Cr(III) hydroxide and 6.5 for hydroxide precipitation.
Test with electroplating industry wastewater-The
characteristics of electroplating industry wastewater are presented in Table 3. Effect of adsorbent
dosage on Fe(II) removal is shown in Fig. 10. Increasing adsorbent dosage increased the per cent
removal of Fe(lI). Complete removal of Fe(II) was
attained with 9.0 giL of the adsorbent. These results show that the waste Fe(III)/Cr(III) hydroxide
can be used for the effective removal of Fe(II)
from electroplating industrial wastewaters.
Conclusions
The present study shows that waste Fe(III)/
Cr(III) hydroxide can be reused as an adsorbent
for the effective removal of Fe(II) from aqueous
solution. Increasing adsorbent dosage and temperature and lowering adsorbent particle size increased the adsorption. The data may be useful in
designing and fabrication of an economic treatment plant for the removal of Fe(II) from industrial wastewaters.
Acknowledgements
Authors are grateful to Dr R M Krishnan, Manager, R&D, SPIC Ltd., Tuticorin, for providing
Fig. IO-Effect
of adsorbent dosage on Fe(II) removal from
electroplating industry wastewater
waste Fe(III)/Cr(III) hydroxide sample and Dr K
M Marimuthu, Vice-Chancellor of Bharathiar University for the Central Instrumentation Lab facility. One of us (KR) is indebted to Council of
Scientific & Industrial Research, New Delhi, for
the award of Senior Research Fellowship.
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