removal of trace (beryllium, cadmium, nickel...
TRANSCRIPT
REMOVAL OF TRACE METALS (BERYLLIUM, CADMIUM, COPPER, NICKEL AND ZINC) FROM
AQUEOUS SOLUTIONS
Water pollution by heavy metals is a serious global problem because of
extensive industrial applications of heavy metals in electroplating, metal
polishing, paint manufacture, battery manufacture, nuclear weapons, leather
tanning etc. Metals in the waste water occur in various forms, ranging from
particles of pure metal in suspension to metal ions and complexes in solution.
Because of high toxicity of heavy metals and possible entry into food chain
through waste discharges into natural bodies of water, it is essential t o
remove these metals from industrial effluents before discharging into
environment. The methods commonly employed for the removal of heavy
metals from water and waste water are precipitation, coagulation, membrane
filtration, ion-exchange and adsorption.
Eskenazyl reported the adsorption and desorption of ionic beryllium
by peat and coal samples. In this method the author reported that high pH
favours the adsorption of beryllium. The desorption of adsorbed beryllium
was carried out by 1N HC1 and H,O. Dean et al.2 reviewed the chemical
(lime) precipitation, cementation, electrodeposition, solvent extraction,
ultrafiltration, ion-exchange and activated carbon adsorption methods for the
removal and recovery of Cr, Mn, Fe, Ni, Co, Cu, Zn, Hg and Pb from waste
waters of different industries. Wentink and Etze13 studied the removal of
metal ions viz., Cr, Cu and Zn from aqueous solutions by Xenia slit loam,
Chalmers silty clay loam and Elston loam. The exchange capacity of three
soils tested were increased as the clay mineral content increased and particle
size decreased. Netzer et a1.4 employed a precipitation technique for the
removal of Cd, Cr, Al, Co, Cu, Fe, Pb, Mn, Ni, Ag and Zn from waste water
by lime. Discarded automobile tyres and lime were used as adsorbents for the
removal of Al, Cd, Cr, Co, Cu, Fe, Pb, Mn, Hg, Ni, Ag and Zn from aqueous
solutions was reported by Netzer et al.'. The authors used continuous bench
scale studies, the results showed that the removals were >99.5% for most of
the metals. Gaikwad and Bharadwaj"emonstrated the adsorptive capacities
of fly ash for zinc(T1) removal from aqueous solutions. Laperle7 reported the
removal of metals from photographic effluents by sodium sulphide
precipitation. Sundaresan et al.' employed serpentine mineral as an
adsorbent for the removal of Fe, As, Nn, Cu, Pb and Cd in water. The
adsorption of Cu(I1) was studied by Elliott and Huangg in the presence of
chelating agents like nitrilotriacetic acid (NTA), glycine and aspartic acid by
MO,, SiO, and TiO,. The results showed that the chelating agents improved
the extent of Cu(1I) adsorption. The use of rubber from old tyres for the
adsorption of Cd(I1) from aqueous solutions was reported by McPherson and
~ o w l e ~ " . In this method a glass column containing rubber particles were
used for the adsorption of Cd(I1) from aqueous solutions. The adsorption of
Cu(II) by alumino silicates with varying SiIAl ratios was investigated by
Elliott and Huang". In this method six alumino silicates are employed for
the removal of Cu(I1) from aqueous solutions and the Si/AI ratio of alumino
silicates influenced the cation exchange capacity.
Prabhu et a1.12 assessed that fly ash was a good adsorbent for zinc(I1)
removal from aqueous solutions. Millward and Moore13 described the
adsorption of Cu, Mn and Zn by iron(II1) hydroxide in model estuarine
solutions. The authors reported that the adsorption isotherms for Cu(I1)
were independent of salinity, but those of Mn(I1) and Zn(1I) showed an
increase in the pH of the adsorption edge with increasing salinity.
Christensen and Delwichel~employed the hydroxide precipitation,
flocculation and ultrafiltration techniques for the removal of Cr, Ni, Cu and
Zn from electroplating rinse waters. Bye et al.15 reported the adsorption of
Cu(I1) from aqueous solutions by five silica samples. The adsorption
isotherms of copper(I1) was fitted into Langrnuir isotherm model. Burba and
Willmer16 used cellulose as adsorbent for the removal of Al, Be, Cd, Cr, Fe, Pb
and 2; from aqueous solutions. Bhattacharya and venkobachar17 studied the
removal of cadmium(I1) from aqueous solutions by giridish bituminous coal
and crushed coconut shell. Mechanism of Cd(II), Hg(I1) and Pb(II)
adsorption from aqueous solutions by waste tyre rubber was examined by
Rowley et d l 8 . In this method Hg(I1) and Cd(I1) uptake are accompanied by
displacement of zinc and therefore probably involve an ion-exchange type
mechanism. Application of fly ash as adsorbent for the removal of copper (11)
from aqueous solutions was reported by Panday et al.19 . The results
indicated that the removal of copper (11) by adsorption on fly ash was
dependent on concentration, pH and temperature. Panday et a120 studied the
removal of copper from aqueous solutions by homogeneous 1:l mixture of fly
ash and wollastonite (FW), China clay and wollastonite (CW) or fly ash and
China clay (FC). Adsorption of Cu(II), Ni(I1) and Co(I1) by oxide adsorbents
from aqueous ammonical solutions was reported by Fuerstenau and Osseo-
AsareZ1.
Schindler et as.'' studied the removal of Cu(II), Cd(1I) and Pb(I1) from
aqueous solutions at 298.2 K as a function of both pH and ionic strength of
the aqueous phase. In this method the extent of adsorption increased with
increasing pH and with decreasing ionic strength. Adsorption of niekel(I1)
and cobaSt(I1) from aqueous solutions on levextrel resin containing acidic
organophosphinic extractant, cynex 272 and chelating resins containing
phosphorus based acidic functional groups was studied by Inoue et a1.23.
Huang et a1.24 reported that the fresh and freeze-dried fungal biomass were
good adsorbents for the removal of cadmium(I1) from dilute aqueous
solutions. The adsorption capacity of fungal biomass was compared with
other adsorbents such as activated carbon, oxide, soil and hydroxyapatite.
Choi and 1hmZ5 developed foam separation techniques of precipitation and
adsorbing colloid flotation with Fe(II1) for the removal of copper(I1) from
aqueous solutions. Amorphous iron hydroxide used as adsorbent for the
removal of Cu, Co and Ni from aqueous electrolyte solutions was reported by
Mustafa and Haq2? The equilibrium data was explained using Langmuir
equation. Lokesh and Tare" studied the removal of cadrnium(I1) from
aqueous solutions by water soluble xanthate (SSX). The results of
equilibrium batch tests identified SSX as good adsorbent for Cd(I1) removal.
Adsorption of Cu(I1) from aqueous solutions by natural kaolinite was studied
by Pilipenko et a1.28. The desorption of adsorbed Cu(I1) ions was studied with
KC1 or HCI solutions. Zhuang and wightman2' employed the adsorption and
desorption of copper(I1) from aqueous solutions. Wollastonite used as
adsorbent for zinc (11) removal from aqueous solutions was reported by
Sharma et ala30. Huang et al. 31 studied the removal of copper(I1) from dilute
aqueous solutions by saccharomyces cerevisiae. In this method a total of 30
mmol Cu (II)/g uptake by live yeast and the adsorption was strongly
dependent on pH. Srivastava and ~ r i v a s t a v a ~ ~ demonstrated the batch
studies of adsorption and desorption of zinc(I1) from aqueous solutions. The
adsorption of Zn(I1) from aqueous solutions on Fe(OH), was carried out at
the pH of zero point of charge of hydroxide (ZPC 6.85) and also on both acidic
(5.5) and alkaline (8.2) pH of ZPC. The desorption experiments also revealed
that desorption of adsorbed Zn(I1) decreased with an increase in pH.
Adsorption of Cu(II), Zn(II), Cd(II1, Hg(I1) and Pb(I1) from aqueous solutions
on a 2- mercaptobenzimidazole - modified silica gel was studied by Moreira
et al.". The results indicated that under the batch conditions retentions of
100% were achieved for all metals except for Pb(I1) where 93% was attained
and optimum column conditions recoveries of 100% were obtained for all
metals. Kuznicki and Thrush3' employed the removal of Pb, Cd, Zn, Cr, AS
and Hg from aqueous solutions by wide-pore molecular sieves such as ETS -
10 or ETAS - 10. Weyls and Linderrnann3"eveloped oxalate precipitation
method for the removal of Fe, Cu, Mn, Pb, Cd, Sn, Co, Zn, Ni and Ag from
waste solutions in electroplating, cleaning or photographic development.
Hasamy et studied the removal of micro amounts of zinc on titanium
oxide from aqueous solutions. The adsorption data was fitted into both
Freundlich and Langrnuir isotherm models. The results showed that zinc
adsorption was dependent on the pH of aqueous solution, amount of oxide
and zinc concentration.
Kamaraj et al.37 developed sulphide precipitation technique for the
removal of Pb, Cd and Ag from aqueous solutions. The results indicated that
the sulphide precipitation technique was effective in simultaneous removal
of Pb, Cd and Ag. The adsorption of copper (11) onto goethite was studied by
Kooner3'. He studied the function of pH, total dissolved copper
concentration, surface area of goethite and ionic strength on the adsorption.
Papachristou et al." reported ion-exchange method for the adsorption of
nickel (11) from aqueous solutions by natural clinoptilolite. The authors
reported that ion-exchange process is a past process for both NH,' and Na
converted clinoptilolite. Singh and Rawat" studied the removal of Zn(1I)
from waste water on fly ash by adsorption. The Langmuir adsorption
isotherm was used to represent the data and the process followed 1st order
kinetics. Singh and Rawat" evaluated the adsorptive capacities of bituminous
coal for the removal of copper (11) from aqueous solutions. Luo and Huang42
developed Fe (111) hydroxide - sodium dodecyl sulphate foam flotation method
for the removal of copper (11) from aqueous solutions. A two - step batch
method has the advantages of higher efficiency and lower copper residue
when dealing with samples of high copper concentration. Reed et al." studied
the removal of lead and cadmium from aqueous waste streams by granular
activated carbon column method. Application of Fe (111) hydroxide and
sodium dodecyl sulphate (SDS) for removal of copper (11) from aqueous
solutions was reported by Lin and ~ u a n g ' ~ . Nukatsuka et al.45 developed a
novel enrichment method for the adsorption of trace amounts of beryllium
(11) from aqueous solutions on the surface of silica fibers. Application of
peanut hulls, an agricultural waste by-product for the removal of nickel (11)
from aqueous solutions and nickel plating industry waste water was studied
by Periaswamy and ~arnns iva~am'~ . The authors reported that the process
of uptake obeys both Freundlich and Langmuir adsorption isotherms.
Mishra and studied the removal of cadmium (11) from aqueous
solutions by hydrous ceric oxide as a function of solution concentration,
temperature and pH. Lopez et al.*' evaluated the adsorptive capacities of
blast furnace sludge for the removal of copper ions from aqueous solutions.
The studies revealed that the adsorption corresponds to a typical endothermic
physical adsorption process and the kinetics followed the Langmuir isotherm.
Sepiolite used as adsorbent fbr the removal of Zn (11) and Pb (11) from
industrial waste water was reported by Brigatti et a ~ . ~ ' In this method
weighed amounts of sepiolite were placed in two conventional
chromatographic columns and percolated at constant temperature, flow rate
and pH.
Gardea-Torresdey et al.50 employed the removal of nickel ions from
aqueous solutions by biomass and silica-immobilized biomass of medicago
sativa (alfalfa). Batch lab experiments showed that approximately 80% of the
nickel ions bound to the aLfnLfa in less than 5 minutes. Application of
granular activated carbon for the removal of single copper and nickel system
and in binary Cu-Ni, Cu-Cd and Cu-Zn systems was reported by Seco et aL51.
Leyva-Ramos et al." studied the removal of cadmium (11) from aqueous
solutions by activated carbon. The batch studies showed that the amount of
Cd(I1) adsorbed was reduced about 3 times by increasing the temperature
from 10 to 40°C. Lee and an^^^ reported the copper removal in aqueous
solutions by apple wastes as a function of pH, ionic strength, ligands and
particle size. The column experiments showed that the dynamic capacity of
chemically modified apple residues was 4-5 times higher than that of raw
residues which contained acidic groups. The results indicated that the
optimal pH was 5.5-7.0, and the maximum copper removal was 91.2%. The
sorption of nickel (11) ions by some raw clays, metal oxides and synthetic
exchangers was investigated by Al-SuhybaniM. The removal behaviour of Zn
(11) ions at micro and tracer concentration levels from aqueous solutions by
adsorption with sodium titanate as adsorbent was discussed by Mishra et
a1.55. The authors investigated various physicochemical parameters such as
concentration, temperature, pH and acids on the adsorption process.
KeaneZ6 evaluated the adsorptive capacity of zeolite-Y ion exchangers for the
removal of copper (IT) and nickel (11) from aqueous solutions. In this method
batch adsorption studies were carried by solid Li-, Na-, K-, Rb- and Cs- based
U zeolites. The authors reported that Cu(I1) removal was much greater than
that of Ni (11) for all the zeolite exchangers under identical experimental
conditions. G ~ p t a ~ ~ developed activated slag from blast furnace waste
material for the adsorption of Cu (11) and Ni (11) from aqueous solutions. The
sorption data were correlated with Langmuir and Freundlich adsorption
models. The results revealed that maximum removal was obtained at pH 5.0
for Cu (11) and 4.0 for Ni (11). Ahmed et alS8 studied the removal of cadmium
(11) and lead (11) from aqueous solutions by ion-exchange with Na-Y zeolite
under competitive and non-competitive conditions. The authors reported that
lead removal was much greater than that of cadmium under experimental
conditions and Na-Y exchange capacity was increased in the order of Ni (11)
< Gu (11) < Cd (11) < Pb (11).
Rice husk carbon used as adsorbent for the removal of cadmium (11)
from aqueous solutions was reported by Khalid et al.59. In this method the
radiotracer technique was used to determine the distribution of cadmium.
13ajpaiG0 reported the effect of temperature on removal of Ni (11) from aqueous
solutions by adsorption on to fire clay. The amount of Ni (11) removal was
highly dependent on temperature. Narnasivayam and Senthil KumarG1
studied the adsorption of copper (11) by waste Fe (III)/Cr (111) hydroxide from
aqueous solutions and radiator manufacturing industry waste water.
Adsorption of nickel (11) from aqueous solutions on activated carbon was
studied by Goyal et al.". The authors reported that the adsorption of Ni (11)
ions increases on oxidation and decreased on degassing of the carbon surface.
Activated red mud used as adsorbent for the removal of nickel (11) from
aqueous solutions was reported by Pradhan et The experimental data
agreed well with Langrnuir and Freundlich adsorption isotherms.
Barbier et al." demonstrated the removal of Pb (11) and Cd (11) from
aqueous solutions by montrnorillonite as a function of pH. Application of
cellulosic graft co-polymers on the removal of zinc ions from aqueous
solutions was studied by Erornosele and Bayero6'. The cellulosic graft co-
polymers were prepared by the reaction of bast fibers of the Hibiscus
cannabinus with acrylonitrile and methacrylonitrile monomers in aqueous
media initiated by the ceric ion-toluene redox pair. The authors reported that
for each metal ion, the cellulose - polyacrylonitrile graft co-polymer was more
effective sorbent than the cellulose - polymethacrylonitrile derivative.
sarma6' stuided the removal of Ni (11) and Cu (11) from aqueous solutions
using lignite-based carbons. The results showed that lignite-based carbon
was a good adsorbent for the removal of Ni (11) and Cu (11). Banat et al.67
reported batch zinc removal from aqueous solutions using dried animal
bones. In this method batch kinetics and isotherm studies were carried out
to investigate the effect of contact time, initial concentration of adsorbate,
particle size, temperature and pH. The authors reported that the adsorbed
zinc ions was desorbed with different acid eluents and it was found that
II,SO, is the most effective desorption agent. Seafood processing waste
sludge used as adsorbent for the removal of copper (11) and cadmium (11) from
aqueous solutions was studied by Lee and Davis68. Trainor et examined
the adsorption and precipitation of zinc (11) from aqueous solutions by
alumina powders. Hequet et a1.I' studied the removal of Cu (11) and Zn (11)
from aqueous solutions by sorption on to mixed fly ash. In this method
various parameters such as temperature, fly ash to ion ratio and ash quality
were studied.
The review of literature shows various methods viz., precipitation,
coagulation, membrane filtration, ion-exchange and adsorption are used for
the removal of beryllium, cadmium, copper, nickel and zinc. Among all the
above methods adsorption is one of the promising process for the removal of
heavy metals from water and waste water, because it has the advantage of
regeneration of adsorbent by suitable desorption process and it is highly
effective and economical. The literature studies also revealed that several
adsorbents such as activated carbon, activated red mud, wollastonite, rise
husk carbon, fly ash, coconut shells, cellulose graft polymers, zeolite Y, raw
clays, waste Fe (111) / Cr (111) hydroxide, peanut hulls are used as adsorbents
for the removal of Be, Cd, Cu, Ni and Zn. But zeolites and clay minerals have
not used for the removal of aforesaid metals from aqueous effluents. Zeolites
and clay minerals have good adsorption potential because these adsorbents
have small particle size and high surface area. The clay minerals are ill-
difined g o u p of secondary minerals formed at near the earth's surface by
weathering or hydrothermal alternation of feldspars and other aluminous
silicates. Most clay minerals are phyllosilicates with sheet structures based
on combinations of brucite type layers of octahydrally co-ordinated cations
and Si,O,,layers of tetrahedrally co-ordinated cations (si4' or A13'). The clays
carry net negative charge due to the broken bonds around the edges of the
silica alumina units that would give rise to unsatisfied charges which would
be balanced by adsorbed cations7'. Montrnorillonite, kaolinite and illite are
the major clay minerals which are widely used as adsorbents for the removal
of heavy metal ions from water and waste waters.
Zeolites are complex inorganic polymers based on the infinitely
extending three-dimensional, four cornered network of [Al (O,),] and
[Si(O,),] tetrahedra. The tetrahedra are linked to each other by sharing of
oxygen atoms to give rise to building blocks of cubic, hexagonal, octagonal
and polyhedra72. The negative charge on alumino silicate structure arising
out of the stoichiometric substitution of Si by A1 is distributed all over the
anionic frame work. Consequently, the positively charged metal counter ions
(Na') are loosely held on zeolite frame work. These counter ions on zeolite
frame work are exchanged with heavy metal ions. Zeolites of the type A, X
and U are widely employed for large variety of separation and purification
appli~ations73,74.
In the present work removal of beryllium, cadmium, copper, nickel and
zinc from aqueous solutions by zeolite 4A, zeolite 13X and bentonite has been
studied . Parameters such as effect of contact time, effect of pH, adsorbent
dose, on adsorption were investigated. The data were fit into Freundlich
isotherm model. The desorption studies for the regeneration of adsorbent
was also carried out using sodium chloride solution. The concentration of
metal ions in solution was determined by atomic absorption spectrometry
PROCEDURE FOR BATCH ADSORPTION STUDIES
Batch adsorption studies were conducted to study the influence of
parilmcters such as time of equilibrium, effect of adsorbent dose and
effect of pII on adsorption. A number of stoppered reagent bottles containing
volumes ( 100 m 1 ) of metal (Be, Cu, Cd, Ni and Zn) solution of varying
concentrations wcre talicn, pH was adj~~sted to desired value by adding
ammonii~ solut.i(~n t 1 : 1 1 or IlCI ( 1 + 1). Accurately weighed amounts of
adsorbcrlt were int'roduced into each reagent bottles. The bottles were
shaken [it roorn t,tsinpel.;iturp (30 + 1" C) using an mechanical shaker. The
adsor\rttnt and i~dso~*l-~at,e wc1.c separated by centrifugation at 10,000 rpm and
analysed i.hc concc~~ i , r a t io~~ of'metals (Be, Cd, Cu, Ni and Zn) in supernatant
by atomic ;lhsoryt,ion spcctl.olnetric method. Beryllium was determined using
nitrous osirlc~-:l~clt~ylc~~~ci fl;ilnc and Cu, Cd, Ni and Pb were determined using
air-ac.ct.ylcncl fla~ncb. Single. c:lc>ment, hallow cathode lamps were used for all
dete~.nninilt.io~~s. 'I'llrl c)~)cb~.aI,i~lg conditions wcre presented in Table 2.2.
Blank solu t.ions sinli lilrly t~.c:itecl (without adsorbent) were taken as the
initial conc.c~nt,l*iit,io~~s.
5.2 l~II;ISOI.tI~r~'IO~ SrI'UI)IIi:S
'I'llr ti(~soq)!.ion st,udics worc carricd out with NaCl solution. The
adso~*httnt.~, zro1it.o 4A, zoolitc 1 :1X and bentonite, which contain metals (Be,
Cd, Ch, Ni ;ir1(1 % I , ) on i,ll(*ir sut-fiicc wcre taken into a stoppered reagent
bottles. '1'0 t,llis 100 1111 of' NilCl ul' different concentrtion solutions were
added. Thc bottlcs wcrc shaken a t room temperature (30 +. 1°C) using an
n-uxhanical shaker. Tho &sorbed metals were separated by centrifugation at
10,000 rpm. The concentration of metals (Be, Cd, Cu, Ni and Zn) desorbed
into aqueous solution was determined as described in general procedure
section 5.1.
5.3 DETERMINATION OF TRACE METALS IN PRESENCE OF COUNTER IONS
The effect of counter ions on the adsorption of trace metals (Be, Cd,
Cu, Ni and Zn) on zeolite 4A, zeolite 13X and bentonite were studied. 10 mg
of each Ca", Na', Mg", Fe'3 containing solution in 100 ml was added to 10
mg/100 ml initial concentration of beryllium, 50 mg of each of Ga+', Na+,
Mg'2, ~ e + ~ in 100 ml was added to 40 mg/l00 ml initial concentrations of
cadmium, copper and 50 mg/l00 ml initial concentrations of nickel, zinc and
adsorption studies of each element were carried out as described in general
procedure section 5.1.
5.4 ADSORPTION ISOTHERM MODEL
To quantify the adsorption capacity of zeolite 4A, zeolite 13X and
bentonite for the removal of beryllium from water, the Freundlich adsorption
equation75 was applied. x 1 log - = log K + - log Ce m n
Where x is the amount of adsorbate adsorbed, m is the amount of adsorbent
required to adsorb adsorbate (x), K and l/n are the empirical constants and
Ce is the equilibrium concentration. The values of K and l/n are equal to the
intercept and slope of the line obtained by plotting log x/m Vs log Ce.
5.5 RESULTS AND DISCUSSION
The equilibrium time is one of the characteristics defining efficiency
of sorption in the removal of trace metals. The dependence of adsorption of
Be, Cd, Cu, Ni and Zn on contact time by zeolite 4A, zeolite 13X and
bentonite was shown in Tables 5.1 to 5.5 and the data are graphically
presented in Figures 5.1 to 5.5. The results indicate that the rate of
adsorption of Be, Cd, Cu, Ni and Zn was rapid by all the three adsorbents.
For example, over 70% uptake is completed within 20 minutes and
equilibrium was reached around 90 minutes for Be, Cd and Zn and 120
minutes for Cu and Ni. This is due to the rapid diffusion of metal ions from
solution to the external surface where the metal ions sorb at the active
surface of the three adsorbents.
5.5.2 Effect of pH on adsorption
The effect of pH on the adsorption of beryllium, cadmium, copper,
nickel and zinc from water on zeolite 4A, zeolite 13X and bentonite measured
at 30" C were graphically shown in Figures 5.6 to 5.10 and Tables 5.6 to 5.10.
It can be observed that the adsorption of Be, Cd, Cu, Ni and Zn was highly
dependent on the pH of solution. Results showed that the per cent (%)
removal of Be, Cd, Cu, Ni and Zn increased with increase in pH by all the
three adsorbents. At low pH the uptake of Be, Cd, Cu, Ni and Zn was very
small. It is known that mineral acids affect the structure of zeolites and
clays. The extent of the damage to their structure by the acids depends on
pH. The structure of zeolites and clays particularly with low Si / A1 ratio may
Table 5.1 Effect of contact time on per cent removal of berylli
All values are per cent removal of beryllium
S.No.
I
2
3
4
5
6
7
8
9
Table 5.2 Effect of contact time on per cent removal of ea
Contact time rnin
20
40
60 PPP
70
80
90
100 -- - -
All values are per cent removal of cadmium
S.No.
1
2
3
4
5
6
7
8
9
Adsorbenta
Zeolite 4A
80.02
87.11
91.04
110
120
Contact time min
20
40
60
70
80
90
100
110
120
Zeolite 13X
77.0
83.96
89.02
96.0
96.0
Adsorbenta
Bentonite
75.02
81.98
87.0
92.50
94.02
96.0
96.0
94.0
94 0
Bentonite
70.24
76.87
87.37
91.62
93.64
94.75
94.75
94.75
94.75
Zeolite 4A
78.21
85.62
93.24
94.95
96.86
99.15
99.15
99.15
99.15
91.08
92.8
94.0
94.0
91.98
91.98
Zeolite 13X
75.38
82.76
91.14
93.23
94.97
97.2
97.2
97.2
97.2
89.04
90.65
91.98
91.98
100
Table 5.3 Effect of contact time on per cent removal of copper
" All values are per cent removal of copper
Table 5.4 Effect of contact time on per cent removal of nickel
All values are per cent removal of nickel
S.No.
1
2
3
4
5
6
7
8
9
10
Contact time min
20
40
60
80
90
100
110
120
130
140
Adsorbent"
Zeolite 4A
80.12
86.23
92.18
95.21
96.02
97.32
98.1
99.0
99.0
99.0
Zeolite 13X
75.32
83.16
89.63
92.45
94.22
95.14
96.20
97.62
97.62
97.62
Bentonite
72.18
80.37
87.09
90.52
92.46
94.1
95.16
96.21
96.21
96.21
Table 5.5 Effect of contact time on per cent removal of zinc
All values are per cent removal of zinc
S.No.
1
2
3
4
5
6
7
8
9
10
Contact time min
20
40
50
60
70
80
90
100
110
120
Adsorbenta
Zeolite 4A
75.0
82.5
87.1
91.02
93.45
95.86
97.0
97.0
97.0
97.0
Zeolite 13X
72.5
80.0
83.96
87.5
91.45
93.38
95 .O
95.0
95.0
95.0
Bentonite
70.1
77.5
82.1
85.02
88.5
91.2
92.4
92.4
92.4
92.4 A
collapse in the presence of acids when pH was lower than 5, but the severity
would be more below pH 3.0. In fact zeolites are not recommended as
adsorbents a t pH less than 5.07" Both zeolites and clays are very stable at
higher pH and not affect the adsorption. The maximum removal was
observed at pH 5.0 for Cd and Be, pH 6.0 for Ni and Zn and pH 8.0 for
copper. Hence pH 5.0 for Cd and Be, pH 6.0 for Ni and Zn and pH 8.0 for Cu
was chosen for the removal of aforesaid metal ions in aqueous solutions.
5.5.3 Effect of adsorbent dose
Data relating to the percentage (%I) removal of beryllium, cadmium,
copper, nickel and zinc in aqueous solution of 100 ml as a function of dosage
of adsorbent (zeolite 4A, zeolite 13X and bentonite) was graphically shown in
Figures 5.11 to 5.15. The results showed that the adsorption is increased
with increasing adsorbent dose up to a critical value and then there was no
further increase of adsorption. The maximum removal of beryllium 96%,
94%, and 92% at 3 mg 100 ml-', cadmium 99.15%, 97.2% and 94.85% at 25 mg
100 ml-', copper 99.1%, 97.3% and 94.7% at 20 mg 100 ml-' , nickel 99%,
97.2% and 96% a t 25 rng 100 ml-', zinc 97%, 94.96% and 92.4% at 25 mg 100
ml-' initial concentrations was obtained will1 5 g 100 rnl-I on adsorbent dose
of zeolite 4A, zeolite 13X and bentonite respectively.
Table 5.6 EfEect of pH on per cent removal of berylli
All values are per cent removal of beryllium
S.No.
1
2
3
4
5
6
7
8
Table 5.7 Effect of pH on per cent removal of cadmi
PH
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
" All values are per cent removal of cadmium
Adsorbenta
S.No.
1
2
3
4
5
6
7
Zeolite 4A
10.0
79.96
90.02
94.0
96.0
96.0
96.0
96.0
PH
1 .O
2.0
3.0
4.0
5.0
6.0
7.0
Adsorbenta
Zeolite 13X
8.0
75.98
87.04
91.98
94.0
94.0
94.0
94.0
Bentonite
22.16
60.0
80.01
79.99
94.85
87.0
75.0
Zeolite 4A
30.14
75.02
90.04
95.0
99.15
89.96
80.0
Bentonite
7.0
70.02
84.95
89.96
91.98
91.98
91.98
91.98
Zeolite 13X
28.25
68.12
84.98
93 .O
97.2
91.96
85.02
Table 5.8 Effect of pH on per cent removal of copper
" All values are per cent removal of copper
S.No.
1
2
3
4
5
6
Table 5.9 Effect of pH on per cent removal of nickel
PH
1 .O
2.0
3.0
4.0
5.0
6.0
All values are per cent removal of nickel
Adsorbenta
S.No.
1
2
3
4
5
6
7
8
Zeolite 4A
26.32
35.64
46.72
67.95
85.77
96.18
PH
1 .O
2 .O
3.0
4.0
5.0
6.0
7 .O
8.0
Adsorbenta
Zeolite 13X
22.18
30.26
43019
63.72
82.16
93.23
Bentonite
22.11
50 .O
80.12
88.08
93 .O
96.2
96.2
96.2
Zeolite 4A
30.1
60.06
90.0
95.02
97.0
99.0
99.0
99.0
Bentonite
20.37
26.76
37.64
57.94
75.29
90.22
Zeolite 13X
26.04
55 .O
84.7
90.04
95.0
97.6
97.6
97.6
Table 5.10 Effect of pH on per cent removal of zinc
i' All values Lire per cont removal of zinc
S.No.
1
2 -- .
3
4
IS
--
6
7
8
pH
1 .0
2.0 --
3.0
4 .O
5.0
6.0 -
7.0
8.0
Adsorbenta
Zeolite 4A
23.6
35.8
60.3
88.0
95.05
97.0
92.1
88.0
Zeolite 13X
20.71
-~ 29.6
-.
55.71
81.78
92.0
95.0
90.02
85.08
Bentonite
16.8
- 25.78
-
45.5
77.0
89.1
92.4
86.12
80.02
4 d S O O C @ Q W N P 4 m
5.5.4 Adsorption isotherms
Freundlich adsorption isotherms of beryllium, cadmium, copper, nickel
and zinc measured at 30' C were graphically shown in Figures 5.16 to 5.20.
The shape of the isotherms on the three adsorbents was identical indicating
similar type of adsorption process. This is expected as in all the three
adsorbents the process of adsorption is through ion-exchange. The negative
charge on the alumino silicate structure arising out of the stoichiometric
substitution of Si by A1 is distributed all over the anionic framework.
Consequently the positively charged metal counter ions (Na+) are loosely held
on to the zeolite framework. These counter ions on zeolite framework are
exchanged with Be2+, CuZt , Cd2+, Ni2+ and Zn2+ ions.
In bentonite Si4' is substituted by A13+ in tetrahedral sheet and Mg'
substituted by octahedral sheet consequently creating anion framework with
high cation exchange capacity. Sodium ions which are attached loosely to
anion framework (the charge compensate exchangeable cation) are replaced
by Be2+, Cu2+, Cd2+? Ni2+ and Zn2+ ions. The bentonite and zeolites which
have chemical composition as shown in Table 2.1, have good sorption
capacities for removal of heavy metal ions. The adsorption capacity for the
three adsorbents fall in the order zeolite 4A > zeolite 13X > bentonite.
Zeolite 4A with its lowest Si/Al ratio of 1 has got highest theoretical
ion-exchange capacity. Zeolite 13X with Si/Al ratio of 1.25 has got lower
theoretical exchange capacity than zeolite 4A.
Table 5.11 The observed metal removal capacity for zeolites and bentonite
The observed metal adsorption capacities for zeolite 4A, zeolite 13X
and bentonite are given in Table 5.11. These results demonstrate that the
removal of beryllium is substantially lower because beryllium with its smaller
ionic size (radius 0.31 A') has less adsorption capacity. For divalent ions the
ion-exchange capacity decreases with decrease in size7'. Hence beryllium
with its small ionic size the exchange on zeolite 4A, zeolite 13X and bentonite
is less when compared to the other heavy metals. The adsorption of Cd, Cu,
Ni and Zn is substantially high on both zeolites and bentonite. This is due
to their higher ionic radius (Cd - 0.97 P, Cu - 0.72 k, Ni - 0.72 K and Zn -
0.74 A"). Cadmium which has highest ionic radius has highest adsorption on
zeolites and bentonite. All these results indicate that the charge and size of
the cations play important role in the removal of heavy metals from aqueous
S.No.
1
2
3
solutions.
Adsorbent
Zeolite4A
Zeolite 13X
Bentonite
Removal capacities for different metal ions(mg/g)
Be
0.58
0.56
0.55
Cd
4.96
4.86
4.74
Cu
3.96
3.89
3.79
Ni
4.95
4.86 -~
4.80
Zn
4.85
4.75 - -
4.62 A
5.5.5 Effect of counter ions
The results pertaining to the effect of counter ions viz., Ca+2, Nat,
IMgt2, F'et3 that are normally present in water on the removal of beryllium,
cadmium, copper, nickel and zinc by zeolite 4A, zeolite 13X and bentonite are
presented in Table 5.12. The results reveal that in the range of 10 to 50 ppm
Na' ion has no effect on the removal of Be, Cd, Cu, Ni and Zn by all the
three adsorbents where as Ca2+ and Fe3+ has small effect. There is about 5 to
10 per cent decrease in the adsorption of heavy metals due to the presence of
these ions by the aforesaid adsorbents. The data also indicated that Mg'2
exhibited significant effect on the adsorption of Be, Cd, Cu, Ni and Zn by all
the three adsorbents viz., zeolite 4A, zeolite 13X and bentonite. The
decreasing order of counter ions effect was M~~~ > ~ e + ~ > cai2 Na+.
However all the counter ions exhibited lower effect on bentonite than on
zeolite 4A and zeolite 13X.
Table 5.12 Effect of counter ions on per cent removal of berylli , copper, nickel. and zinc
Metal
Be
Cd
Cu
Ni
Adsorbent
Zeolite 4A
Zeolite 13X
Bentonite
Zeolite 4A
Zeolite 13X
Bentonite
Zeolite 4A
Zeolite 13X
Bontonite
Zeolite 4A
Initial concen- tration
mgilooml
10
10
10
40
40
40
40
40
40
50
Zn
69.2
66.3
93.32
88.0
83.4
Per cent removal
Zeolite 13X
Bentonite
Zeolite 4A
Zeolite 13X
No counter
ion
88.0
83.01
79.02
94.9
92.1
87.1
98.29
95.25
91.18
71.2
64.2
59.1
85.16
80.0
78.64
50
50
50
50
Na
88.0
82.81
78.62
94.39
92.1
86.71
98.06
95.20
91.14
71.0 _ _ L _
58.1
55.98
80.0
74.02
76.12
69.5
66.5
93.54
88.0
Bentonite 50
63.3
58.1
83.02
77.1
77.81 83.6
Ca
79.0
78.02
74.0
88.02
83.0
82,O
83.0
82.3
79.1
66.12
Mg
72.0
72.1
70.0
82.1
80.2
78.02
77.0
74.96
74.98
60.15
Fe
78.02
74.0
72.0
85.06
82.04
80.0
81.12
77.2
78.0
64.22 -
5.5.6 Desorption studies
Results relating to desorption of beryllium, cadmium, copper, nickel
and zinc from the surface of adsorbents by sodium chloride solution are
summarised in Tables 5.13 to 5.17. The results demonstrated that with
increasing concentration of sodium chloride, the desorption also increased
upto 10% NaCl concentration but attained constant results at higher
concentration of NaCl solution. The desorption of Be, Cd, Cu, Ni and Zn
from adsorbents by NaCl fall in the order of zeolite 4A > zeolite 13X >
bentonite. This shows that bentonite which expands freely allow internal
diffusion of Be2+, CuZt , Cd", Ni2' and Zn2' ions and hence the desorption
process becomes difficult when compared to zeolites. Hence the regeneration
capacity of zeolite 4A is more than zeolite 13X and bentonite. The
regeneration capacity with zeolite 4A with 10% NaCl are 87% for beryllium,
76% for cadmium, 85% for copper, 80% for nickel and 80% for zinc. These
results shows that zeolite 4A has highest adsorption for all the metals studied
and also desorption is highest. This demonstrate that zeolite 4A could be
used for the removal or heavy metals from aqueous effluents in order $0
minimize water pollution by toxic metals and it can be easily regenerated for
the successive use in the treatment plants.
Table 5.13 Data corresponding to desorption studies for beryllium
A 11 values are per cent recovery of beryllium
Adsorbent
Zeolite 4A
Zeolite 13X
Bentonite
Initial concentration
Be(I1) (mg / 100 ml)
3
5
10
15
20
3
5
10
15
20
3
5
10
15
20
Desorptiona with 5%
NaCl
70
7 3
74
79
81
67
73
71
82
78
63
64
67
72
63
Desorptiona with 10%
NaCl
75
77
82
86
87
73
78
80
85
83
68
67
Desorptiona with 15%
NaC1
75
78
82
85
86
74
78
79
86
83
67
67
74
81
70
73
82
70
Table 5.14 Data corresponding to desorption studies for cadmi
All values are per cent recovery of cadmium
Adsorbent
Zeolite 4A
Zeolite 13X
Bentonite
Initial concentration
Cd(I1) (mg / 100 ml)
20
40
60
80
100
20
40
60
80
100
20 - 40
60
80
100
Desorptiona with 5%
NaCl
60
62
64
70
71
58
60
67
65
66
56
57
63
61
65
Desorptiona with 10%
NaCl
65
67
70
75
76
63
65
73
72
74
60
62
68
65
70
Desorptiona with 15%
NaCl
64
66
7 1
7 6
7 7
6 3
64
74
71
73
5 8
6 3
67
64
69
Table 5.15 Data corresponding to desorption studies for copper
" All valucs are per cent recovery of copper
Zeolite 13X
Bentonite
60
80
100
20
40
60
80
100
20
40
60
80
100
80
77
80
70
72
77
75
71
68
72
68
75
77
85
83
84
74
78
82
80
76
7 2
76
7 3
80
82
84
84
84
74
77
83
81
7 5
70
74
73
81
8 3
Table 5.16 Data corresponding to desorption studies for nickel
All values are per cent recovery of nickel
Adsorbent
Zeolite 4A
Zeolite 13X
Bentonite
1
Initial concentration
Ni (11) (mg 1 100 ml)
25
35 -
50
75
100
25
35
50
75
100
25
35
50
75
100
Desorptiona with 5%
NaCl
60
68
70
73
75
56
67
65
70
72
50
59
62
70
68
with 10% NaCl
67
77
78
80
82
65
75
73
76
78
60
69
70
76
72
DesorptionVesorptiona with 15%
NaCl
68
7 9
7 9
80
81
66
75
74
7 7
79
59
68
7 1
77
70
Table 5.17 Data corresponding to desorption studies for zinc
All values are per cent rccovcry of zinc
Bentonite
35
50
75
100
25
35
50
75
100
66
70
68
65
54
63
67
65
71
70
75
73
71
60
71
76
74
72
61
68
72
68
75
70
7 1
69
76