Indian Journal of Chemical Technology Vol. 9. November 2002. pp. 499-503 Articles Activated carbon from parthenium as adsorbent: Adsorption of Hg(II) from aqueous solution K Kadirvelu" C Sivasankari b , M Jambuligam b & S Pattabhi a * "Department of Environmental Science, bDepartment of Chemistry, PSG College of Arts and Science. Coimbatore 641 014. India Rece ived 27 JUl1 e 200 I; revised received 10 April 2002; accepTed 5 AugllsT 2002 Activated carbon (AC) prepared from parthenium was used to remove Hg(II) from aqueous solution by adsorption technique under varying conditions of agitation time, metal ion concentration, adsorbent dose and pH. Adsorption equilib- rium reached within 165 min for all concentrations studied (10 to 50 mg/L). Adsorption is dependents on solution pH. Hg ( II ) concentration, carbon concentration and contact time. Adsorption followed both Langmuir and Freundlich isotherm mode ls . The adsorption capacity was found to be 10 mg/g of AC at initial pH of 5.0 at 30+2°C for the particle size of 125- 250flm. The percent removal increased with pH from 2 to 6 and remained constant up to pH 10.0. Environmental contamination due to heavy metal is caused by several industries, metal plating, mining, and radiator manufacturing, and by agricultural proc- ess such as fertilizers and fungicidal sprays I. The presence of mercury in the environment is a major concern because of its toxicity and threat for human life and for the environment, especially when toler- ance level is exceeded 2 . Mercury is generally consid- ered to be one of the most toxic metals found in envi- ronment' . Once mercury enters the food chain, larger accumulation of mercury compounds takes place in human and animals. According to the Bureau of In- dian Standards (BIS) the tolerance limit for Hg(II) for discharge into land surface waters is IOf-lg /L 4 and for drinking water, If-lg/L5. Mercury causes damage to the central nervous system and chromosomes , impairment of pulmonary function and kidney, chest pain and dysphoeao. Hence , it is essential to remove Hg (II) from wastewaters. The general treatme nt methods employed for removing mercury from industrial wastewaters include sulphide precipitation, ion exchange, alum and iron coagulation, activated carbon adsorption, electro-deposition, ultrafilteration and various biological process 7. The above methods for removal of Hg(II) from wastewater are not economical in the Indian context. "' For correspo nd ence (E-mail ps!!cas@ lll d2.vs n1.n c t.i.!!; Fax 0422-575(22) Some works of low-cost, non-conventional adsorbents have been carried out for heavy metal removal. Ad- sorbents used include waste such as coir pith carbonx. coconut tree sawdust carbon lJ, peanut hull carbon 10, waste rubber II , agricultural wastes 1 2. ", car- b . d d l4 b ' d . IS b' olllze woo , car onlze waste newspnnt ., ttu- minous coal and fly ash 17. The objective of the present study was to explore the feasibility of using parthenium plant as raw mate- rial for preparation of acti vated carbon for the re- moval of Hg(II). Experimental Procedure Adsorbent The parthenium plant was collected in and around Coimbatore city, Tamil Nadu State, India and made into small pieces and dried in sunlight. The dried patthenium was used for carbon preparation by mix- ing I part of parthenium and 1.5 part of concentrated H 2 S0 4 and keeping it at l20±5 °C for 24 h. Th e car- bonized material was then washed with distilled water to remove the free acid and soaked in I % sodium bi- carbonate solution for overnight to remove any resid- ual acid. This material wa s then washed with distill ed water and dried at I05°e. The particle size of 125-250 f-lm was used for Hg (II) removal studies. Character- istics of parthenium activated carbon are presented in Table I. All the chemicals used were of analytical reagent grade and were obtained from BDH , E-Merk. SDs and/or Ranbaxy. All the solutions were prepared in distilled water.
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Indian Journal of Chemical Technology Vol. 9. November 2002. pp.
499-503
Articles
Activated carbon from parthenium as adsorbent: Adsorption of Hg(II)
from aqueous solution
K Kadirvelu" C Sivasankarib , M Jambuligamb & S Pattabhia
*
"Department of Environmental Science, bDepartment of Chemistry ,
PSG College of Arts and Science. Coimbatore 641 014. India
Received 27 JUl1 e 200 I; revised received 10 April 2002; accepTed
5 AugllsT 2002
Activated carbon (AC) prepared from parthenium was used to remove
Hg(II ) from aqueous solution by adsorption technique under varying
conditions of agitation time, metal ion concentration, adsorbent
dose and pH. Adsorption equilib rium reached within 165 min for
all concentrations studied (10 to 50 mg/L). Adsorption is
dependents on solution pH. Hg (II ) concentration, carbon
concentration and contact time. Adsorption followed both Langmuir
and Freu ndlich isotherm models. The adsorption capacity was found
to be 10 mg/g of AC at initial pH of 5.0 at 30+2°C for the particle
size of 125- 250flm. The percent removal increased with pH from 2
to 6 and remained constant up to pH 10.0.
Environmental contamination due to heavy metal is
caused by several industries, metal plating, mining,
and radiator manufacturing, and by agricultural proc
ess such as fertilizers and fungicidal sprays I . The
presence of mercury in the environment is a major
concern because of its toxicity and threat for human
life and for the environment, especially when toler
ance level is exceeded2 . Mercury is generally consid
ered to be one of the most toxic metals found in envi
ronment' . Once mercury enters the food chain, larger
accumulation of mercury compounds takes place in human and animals.
According to the Bureau of In
dian Standards (BIS) the tolerance limit for Hg(II) for
discharge into land surface waters is IOf-lg /L 4 and for
drinking water, If-lg/L5. Mercury causes damage to the
central nervous system and chromosomes, impairment
of pulmonary function and kidney , chest pain and
dysphoeao. Hence, it is essential to remove Hg (II)
from wastewaters. The general treatment methods
employed for removing mercury from
industrial wastewaters include sulphide precipitation,
ion exchange, alum and iron coagulation, activated
carbon adsorption, electro-deposition, ultrafilteration and various
biological process 7.
The above methods for removal of Hg(II) from wastewater are not
economical in the Indian context.
"' For correspondence (E- mail ps!!cas@ llld2.vs n1.nct.i.!!; Fax
0422-575(22)
Some works of low-cost, non-conventional adsorbents have been
carried out for heavy metal removal. Ad sorbents used include
waste such as coir pith carbonx. coconut tree sawdust carbon lJ,
peanut hull carbon 10, waste rubber II , agricultural wastes 12. ",
car-
b . d d l4 b ' d . IS b' olllze woo , car onlze waste newspnnt .,
ttu- minous coal and fly ash 17.
The objective of the present study was to explore the feasibility
of using parthenium plant as raw mate rial for preparation of acti
vated carbon for the re moval of Hg(II).
Experimental Procedure Adsorbent
The parthenium plant was collected in and around Coimbatore city,
Tamil Nadu State, India and made
into small pieces and dried in sunlight. The dried
patthenium was used for carbon preparation by mix ing I part of
parthenium and 1.5 part of concentrated
H2S04 and keeping it at l20±5°C for 24 h. The car
bonized material was then washed with distilled water
to remove the free acid and soaked in I % sodium bi
carbonate solution for overnight to remove any resid ual acid. Thi
s material was then washed with distilled water and dried at I05°e.
The particle size of 125-250 f-lm was used for Hg (II) removal
studies. Character istics of parthenium activated carbon are
presented in Table I. All the chemicals used were of analytical
reagent grade and were obtained from BDH, E-Merk.
SDs and/or Ranbaxy. All the solutions were prepared in distilled
water.
Articles
Table l--Characteristics of activated parthenium carbon Parameter
Value
pH( I % solution ) Moisture content (%) Ash content (%) Apparent
density (g/ml) Water soluble matter (%) Acid soluble matter (%)
Methylene blue adsorption (mg/g) Surface area (m2/cm)
Batch mode adsorption studies
6.9 3.8 3.9 0.5
265.0
An adsorbate stock solution of 1000 mg/L Hg (II) was prepared by
dissolving 1.3S40 g of mercuric chloride in double distilled water
acidified with S mL of concentrated HN03 to prevent hydrolysis and
made up to 1000 mL. This stock solution was diluted to re quired
concentration for obtaining standard solution containing 10 to 40
mg/L of Hg (II) . Batch mode ad sorption studies were carried out
with 100 mg of ad sorbent and SO mL of Hg (II) solution of desired
con centration at initial pH of 6.0 in 100 mL conical flasks and
were agi tated at ISO rpm for predetermined time intervals at room
temperature (30±2°C) in a mechani cal shaker. At the end of
agitation time, the adsorbate and adsorbent were separated using
centrifugation at SOO rpm and estimated spectromatically using rho
damine 6G 1s
. Effect of carbon concentration on per cent removal was studied
with carbon concentration from 2S-300 mg/SOmL while maintammg Hg
(II) concentration at 10, 20 and 30 mg/L. Lang muir isotherm study
was carried out with different initial concentrations of Hg (II)
from 10 to 40 mg/L while maintaining the adsorbent dose at 100
mg/SOmL. Freundlich isotherm was obtained from the effect of carbon
concentrations on Hg (II) removal. Effect of pH on Hg (II) removal
was studied using 100 mg of carbon dose and Hg (II) concentration
of 10 mg/L. To correct any adsorption of Hg (II) on containers,
control experiments were carried out in duplicate. There was no
adsorption by container walls. Experiments were carried out in
duplicate. The maximum deviation was within 3%.
Results and Discussion
Effect of agitation time and initial Hg (II) concen tration 'on Hg
(II) adsorption
Fig. 1 shows the effect of agitation time on the re moval of Hg
(II) by parthenium carbon. The removal
SOO
100.---------=-a:::;~~~F~ii
Time (min)
Fig . l--Effect of agitation time and initial Hg(lJ) concentration
on Hg(IJ) adsorption
1· 0
-0·6
o
Agitation ti~ (min)
Fig. 2--Plot of log(q,-q) versus time (I)
increases with time and attains equilibrium within 16S min for the
all the concentrations studied (10 to 40 mg/L). The curves were
single, smooth and continu ous till the saturation of Hg (II) on
activated carbon surface.
Adsorption kinetics The adsorption kinetics of Hg (II) adsorption
on
parthenium carbon follows first order rate expression given by
Lagergren 19.
... (I)
Kadirve lu el (I/.: Activated carbon from parthenium as adsorbent:
Adsorption of Hg(II ) from aqueous solution Articles
where, Kat! (llmin) is the rate constant of adsorbent, q and q" are
the amount of Hg (II) adsorbed (mg/g) at time t (min) and
equilibrium time. Linear plots of log- 10 (qe-q) versus t (Fig. 2)
show the applicability of above equation for parthenium carbon. The
Kat! values at different initial metal ion concentrations were cal
culated from the slope of the linear plots and are pre sented in
Table 2. The Kat! values were comparable with recently reported
values for Hg (II) removal by acti vated carbonss,lO.
Effect of carboll dosage 011 Hg (II) removal Fig. 3 shows the
effect of carbon dosage on Hg (II)
adsorption. The Fig. 3 shows that the removal of Hg (II) increases
with increase in carbon concentration. It can be seen from removal
of Hg (II) from 1000 mL of 10,20 and 30 mg/L Hg (II) required 3.0,
3.5 and 4.0 g of carbon, respectively.
Adsorption isotherms The Langmuir isotherm was applied for
adsorption
equilibrium of Hg (II) onto patrhenium carbon20.
C,o I C" -=--+- ql' Qoh Qo
... (2)
where, Ce is the equilibrium concentration (mg/L), qe is the amount
of Hg (II) adsorbed (mg/g) , Q" and bare Langmuir constants related
to adsorption capacity and energy of adsorption, respectively. The
linear plot of C/q" versus Ce shows that the adsorption follows
Langmuir isotherm model for Hg (II) adsorption (Fig. 4). The value
of Q" and b were calculated from the slope and intercept of the
plot, respectively. The values obtained were Q" = 10 mg/ g, b = 0.1
l/min. The adsorption capacity of parthenium carbon is equal to
that of GAC (12.38 mg/g) and rice hull carbon (8.76 mg/g)S.2
1.
The essential characteristics of Langmuir isotherm can be expressed
in terms of dimensionless separation factor of equilibrium
parameter RL
I9 , which is defined
RL =( 1/1 +bCo) ... (3)
where, Co is the initial Hg (II) concentration mg/L and b is the
Langmuir constant(Llmg). The parameter in dicates the shape of
isotherm as follows
RL values between 0 and 1 (0.099-0.022) at different
Table 2-Kinetics constants for Hg (II ) adsorption
Hg (II) concen- qe (mg/g) tration
Adsorption rate constant
Concentration of Hg
Adsorbent dosage (mg/50mL)
2·0
1· 6
Ce (mg/L)
Type of isotherm
en S!
1 .2r---__________________________ ~
0·6
0·4
0·2
OL---~ ____ ~ __ ~ ____ ~ __ ~ ____ ~ 0·2 0·4 0· 6 0·8 1·0
x Fig. 5--Plot of log - versus log Cc
m
' ·2
concentration (10 to 40 mg/L) indicates favourable adsorption for
Hg (II) onto parthenium carbon.
The Freundlich equation is widely used in the envi ronmental
engineering practice to model adsorption of pollutants from an
aqueous medium empirically22. The expression of Freundlich equation
is given as
KfC l in qe= e (4)
The linear form of Freundlich equation is given by the following
expression
log J()(X//II ) = log JOKf + lin log JOCe ... (5)
where, X is the amount of Hg (II) adsorbed at equilib rium (mg ),
/J1 is the weight of adsorbent used (mg), Ce is the equil ibrium
concentration of Hg (II) in solu tion (mg/L) and Kr & 11 are
the constants incorporating all facto rs affecting the adsorption
process (adsorption capacity and intensity of adsorption). Linear
plots of the log X/11l versus log Ce show that the adsorption
follows Freundlich isotherm (Fig. 5). The Freundlich constants Kr
and II found have been reported. The constants fou nd were Kf 4.8
and n 2.7, for 20 mg/L Hg (11) concentration. According to
Traybal23
, it has been shown using mathematical cal culations that n values
between 1 and 10 represent the
502
100
80
beneficial adsorption. Effect of pH on Hg (II) removal
Fig. 6 presents the effect of initial pH on the re moval of Hg
(II) by parthenium carbon. It can be shown by stability constant
calculation that in the presence of chlorine the predominant
species at pH>4.0 is HgCl 2 II. The formation of HgCl2 has been
found to decrease the Hg (II) sorption onto a commer cial
activated carbon Fs- 400 GAC8
. Accordingly , the Hg (II) adsorption decreased when the pH was
low ered from 6.0 to 2.0 with dilute HCI for parthenium carbon and
on increasing the pH fro m 2.0 to 6.0 it became quantitative over
the pH range of 6.0 to I 1.0. This implies that Hg (OHh, species
may be retained in the micro-pores of carbon by chemisorption in
volving surface complexes l9
. The influence of pH on Hg (II) removal may be acidic pH
conditions; both adsorbent and adsorbate are positively charge (M2+
and H+) and therefore the interaction is that of electro static
repulsion8
, lo. Beside, the higher concentration of H+ ions for the surface
adsorbing sites results in de crease in the removal of Hg (II).
The concentration of Hg (II) remains constant resulting in increase
in the removal of Hg (II ).
Conclusion
The objective of this work was to study the de pendence of
adsorption on parthenium carbon in the case of Hg (II). Based on
the results of this study, it is concluded that parthenium carbon
is an effective low cost adsorbent for the removal of Hg (II)
aqueous so lutions. In batch mode adsorption studies, the adsorp
tion is dependent on the solution pH, initial Hg (II)
Kadirvelu el al.: Activated carbon from parthenium as adsorbent:
Adsorption of Hg(lJ) from aqueous so lution Articles
concentration and carbon concentration. Adsorption followed both
Langmuir and Freundlich isotherm models. The adsorption capacity
was found to be IOmg/g of parthenium carbon at initial pH 5.0 to
30±2°C for the particle size of 125-250 !-un. The pres ent removal
increases with pH from 2 to 6 and re mained constant up to pH
10.0.
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