Research Article
Open Access
Adsorption Dynamics of Ecofriendly Litter Wastes
For Zn(II)/Cr(VI) From Electroplating Effluents -
Continuous Column Method
N Muthulakshmi Andal1, S Charulatha2, J Anuradha2 and Gayathri NS2
1Assistant Professor, Department of Chemistry, PSGR Krishnammal College for Women, Coimbatore.
2 Research Scholar, Department of Chemistry, PSGR Krishnammal College for Women, Coimbatore.
2 Research Scholar, Department of Chemistry, PSGR Krishnammal College for Women, Coimbatore.
*Corresponding author: N Muthulakshmi Andal, Assistant Professor, Department of Chemistry, PSGR Krishnammal College for Women, Coimbatore-4, E-mail: @
Received: September 18, 2016; October 05, 2016; Published: October 20, 2016
Citation: Andal NM, Charulatha S, Anuradha J, Gayathri NS(2016) Adsorption Dynamics of Ecofriendly Litter Wastes For Zn(II)/
Cr(VI) From Electroplating Effluents - Continuous Column Method. SOJ Mater Sci Eng 4(3): 1-5.DOI: http://dx.doi.org/10.15226/sojmse.2016.00138
AbstractTop
Electroplating industries, play a momentous role in the
development and growth of numerous metal manufacturing, but
also equally pollute the environment through various means. Most
of the electroplating industries operated in Coimbatore are reported
under Red category list, their main source of pollution being heavy
metal leaching into aquatic streams. The present work deals with the
sorption of Zn(II) and Cr(VI) being highly prevalent electroplating
effluents. The process of biosorption has many attractive features
compared to the conventional effluent treatment methods adopted
so for. Batch studies are conducted at varying operating factors to
assess the best sorption efficiency amongst the chosen cost effective
and eco-friendly materials viz., Mussel Shell Powder (MSP), Prosopis
juliflora Bark (PJB), Terminallia cattapa Seed Shell (TCSS) and Aegle
marmelos correa (AMC). Based on the experimental data the Treated
Mussel Shell Powder (TMSP) and Treated Prosopis juliflora Bark
(TPJB) are found to be the best sorbent for Zn(II) and Cr(VI) removal
respectively. The scaling up process through column experiments
are performed to quantify the efficiency of the fixed sorbents under
optimized conditions. The long term analysis at the laboratory levels,
reveal 100% and 92% metal removal for Zn(II)-TMSP and Cr(VI)-
TPJB systems respectively.
Keywords: Electroplating; Effluent; Biosorbents; Column; Coimbatore
Keywords: Electroplating; Effluent; Biosorbents; Column; Coimbatore
Introduction
Industrial sectors expansion involves increased usage of
non-biodegradable heavy metals and leading of excess toxic
pollutants through liquid effluents. This is an issue of growing
concern for humanity and its ecosystem. The wastewaters
emanating from such industries viz., plating, tanning, metallurgy
require treatment before discharging, but least cared, wherein
heavy metal ions like Cr(VI) and Zn(II) are present.
The tolerance limit for Cr(VI) and Zn(II) ions from the effluent discharges into surface waters are 0.1 mg/L and 5.0 mg/L respectively. In potable water, it is 0.05 mg/L and 10.0 mg/L correspondingly [1]. The health risks of Cr(VI) and Zn(II) ions while exceeding the permissible limits results in skin allergy, liver, stomach problems and also found to be carcinogenic [2]. It is essential to sequestrate these ions from polluted areas, suggesting suitable methodology.
Various methodologies such as electrochemical, ion exchange, membrane filtration, evaporation, solvent extraction, emulsion per traction technology, reverse osmosis and chemical coagulation, are available for trapping of heavy metal ions. But these methods possess their own disadvantages, often involving high capital/operational costs and generation of secondary wastes [3, 4].
Biosorption process is one of the efficient methods in trapping toxic metal ions, due to its simplicity, sludge-free operation, easiness in handling, availability of various adsorbents and also efficient removal of heavy metals at lower-concentration levels itself [5]. Biosorbents are prepared from natural waste biomasses that are available in large quantities or certain waste collected from agricultural operations. These low/ no cost materials are reported to have excellent sorption potential that are affordable and eco-friendly.
The current study evaluates the biosorption capacity of litter wastes in trapping Cr(VI) and Zn(II) ions via batch / column method. MSP, PJB, TCSS and AMC were identified, prepared, treated before experimental verification. Removal of heavy metal ions employing the above said eco-friendly materials have not been reported elsewhere in literature.
The tolerance limit for Cr(VI) and Zn(II) ions from the effluent discharges into surface waters are 0.1 mg/L and 5.0 mg/L respectively. In potable water, it is 0.05 mg/L and 10.0 mg/L correspondingly [1]. The health risks of Cr(VI) and Zn(II) ions while exceeding the permissible limits results in skin allergy, liver, stomach problems and also found to be carcinogenic [2]. It is essential to sequestrate these ions from polluted areas, suggesting suitable methodology.
Various methodologies such as electrochemical, ion exchange, membrane filtration, evaporation, solvent extraction, emulsion per traction technology, reverse osmosis and chemical coagulation, are available for trapping of heavy metal ions. But these methods possess their own disadvantages, often involving high capital/operational costs and generation of secondary wastes [3, 4].
Biosorption process is one of the efficient methods in trapping toxic metal ions, due to its simplicity, sludge-free operation, easiness in handling, availability of various adsorbents and also efficient removal of heavy metals at lower-concentration levels itself [5]. Biosorbents are prepared from natural waste biomasses that are available in large quantities or certain waste collected from agricultural operations. These low/ no cost materials are reported to have excellent sorption potential that are affordable and eco-friendly.
The current study evaluates the biosorption capacity of litter wastes in trapping Cr(VI) and Zn(II) ions via batch / column method. MSP, PJB, TCSS and AMC were identified, prepared, treated before experimental verification. Removal of heavy metal ions employing the above said eco-friendly materials have not been reported elsewhere in literature.
Materials and Methods
Collection/Treatment of adsorbent materials
The identified litter waste materials Mussell Shell (MSP),
Prosopis juliflora Bark (PJB), Terminallia cattapa Seed Shell
(TCSS) and Aeglemarmeloscorrea (AMC) (Figure 1) were
collected from localities of Coimbatore, Kangeyam, Salem and
coastal areas of Tamil Nadu. Collected PJB, MSP and AMC were
washed, sun dried, crushed down into small pieces and then
sieved. The sieved particles of different mesh sizes for the four
materials were treated with 0.1N HCl for 3 hours, washed several
Figure 1: Raw and treated adsorbent materials.
times to neutralize and then air dried. The several washings
during neutralization procedure ensure the increase in surface
area while soaking the materials. The acid treated Mussell Shell
powder (TMSP), Prosopisjuliflora Bark (TPJB), Terminallia
cattapa Seed Shell (TTCSS) and Aegle marmeloscorrea (TAMC)
were stored in air tight containers.
Chemicals
All the chemicals employed were of Analytical Reagent
grade. Doubly Distilled (DD) water was used for preparation and
dilutions of solutions. A stock of 1000 ppm metal solutions was
prepared by dissolving required amount of K2Cr2O7 and Zn(NO3)2
in 1000 ml of standard flask. The pH of the solutions were
adjusted using 0.1N HCl and 0.1N NaOH.
Batch equilibration studies
The equilibration of Cr(VI) and Zn(II) aqueous solutions
(50ml volume) with the materials were experimentally verified
in a mechanical shaker (KEMI) to define the role of variable
parameters viz., particle sizes (0.18mm, 0.24mm, 0.30mm,
0.42mm and 0.52mm) and dosages (200 mg, 400mg, 500mg,
1g, 2g) of the treated adsorbents, initial concentrations of the
aqueous Cr(VI) and Zn(II) solutions (100-1000mg/L : 100 mg/L
interval), preset time intervals between the sorbent and sorbate
species (10-120 minutes : 30 minutes interval), pH of the medium
(2,4,7,9 and 11) and temperature (293K-333K : 10 K interval)
in order to assess the sorption efficiencies under laboratory
conditions. The agitated samples were filtered and the residual
metal ion (Cr(VI) and Zn(II)) concentrations were analyzed using
Atomic Absorption Spectrophotometer: Shimadzu (AA 6200)
(Figure 2) as per standard methods.
All experiments were carried out in duplicate and mean values are presented with the maximum deviation of 2.0%. The percentage removal and amount adsorbed were determined as follows:
Removal percentage (%) = (C1 - C2) / C1 X 100
Amount adsorbed (mg/g) = (C1 - C2) X V/M
where,
C1= initial metal concentration (mg/L), C2= final metal concentration (mg/L), V= volume (ml) and M= mass of adsorbent (mg).
All experiments were carried out in duplicate and mean values are presented with the maximum deviation of 2.0%. The percentage removal and amount adsorbed were determined as follows:
Removal percentage (%) = (C1 - C2) / C1 X 100
Amount adsorbed (mg/g) = (C1 - C2) X V/M
where,
C1= initial metal concentration (mg/L), C2= final metal concentration (mg/L), V= volume (ml) and M= mass of adsorbent (mg).
Results and Discussion
Effect of Particle Size
Tables 1(a)-1(b) show the influence of variable particle
sizes of the sorbent materials on the varying systems indicating
0.18mm size to be the favorable size for maximum removal. This
is owed to the surface phenomenon, smaller adsorbent size offers
larger surface area for metal binding.
Effect of Contact Time/Initial Concentration
The effect of contact time at varying time intervals and that
of initial concentrations for the systems are listed in tables 2(a)
and 2(b), wherein the registered data indicate the enhancement
in amount adsorbed only up to certain metal ion concentrations.
This may be of the saturation in the sorption sites on the sorbent
as the concentration of the metal ions increased. The varying time
intervals for the systems indicate the attainment of equilibrium
up to specific contact time, further increase in time interval
registered a decline.
Effect of Dosage
The amounts of metal ion adsorbed at different dosages are
listed in tables 3(a) & 3(b). The maximum sorptive ability of the
materials under varying conditions depict their potentiality as
able adsorbents in sequestering heavy metal ions.
Effect of pH
Maximum uptake was observed at pH 2.5 for Cr(VI). At
increasing pH environments, a sharp decline in uptake was observed, which is in good agreement with previous reports. The
speciation studies of Cr(VI) in aqueous solution shows that H2CrO4
predominates at pH less than 1.0, HCrO4− for pH between 1.0
and 6.0 and CrO4
2− at pH above 6. This is due to the electrostatic
attraction between the positively charged surfaces of the
adsorbent with HCrO4
− ions. But in highly acidic medium (pH=1.0),
H2CrO4 (neutral form) is the predominant species of Cr(VI).
Hence, percentage removal decreased due to the involvement of
less number of HCrO4
− anions to the positive surface. At higher
pH value, the reduction in adsorption may be due to the dual
competition of both OH− and CrO4
2− ions to get adsorbed on the
surface of the adsorbent among which OH− predominates. These
results are in agreement with several previous investigations on
metal removal by a variety of materials.
The pH dependence for Zn(II) systems registered maximum removal between 5-7; the other ranges exhibit irregular curves. The reason being that at low acidic medium, the H+ ions compete with the metal ions to get sorbed on the materials and under higher basic conditions metal ions combine with OH- ions to form respective precipitates.
The optimized conditions resulted from the batch studies for the chosen materials are, Cr(VI) system: 0.18 mm, 200 mg, 1000ppm, 60 min, pH 2.5 , 300C ; Zn(II) system: 0.18 mm, 1.5g,
The pH dependence for Zn(II) systems registered maximum removal between 5-7; the other ranges exhibit irregular curves. The reason being that at low acidic medium, the H+ ions compete with the metal ions to get sorbed on the materials and under higher basic conditions metal ions combine with OH- ions to form respective precipitates.
The optimized conditions resulted from the batch studies for the chosen materials are, Cr(VI) system: 0.18 mm, 200 mg, 1000ppm, 60 min, pH 2.5 , 300C ; Zn(II) system: 0.18 mm, 1.5g,
Figure 2: Atomic Absorption Spectrophotometer Shimadzu (AA 6200).
Table 1a: Cr (VI)-Particle Size.
Adsorbents |
Amount Adsorbed (mg/g) |
||||
0.18 mm |
0.24 mm |
0.30 mm |
0.42 mm |
0.71 mm |
|
TTCSS |
16.8854 |
4.335 |
4.3340 |
4.542 |
4.452 |
TPJB |
22.6303 |
6.876 |
5.93834 |
5.826 |
5.8337 |
TMSP |
13.1202 |
7.85 |
6.9756 |
6.7262 |
4.3826 |
TAMC |
11.3931 |
9.384 |
6.837 |
6.383 |
5.3836 |
Table 1b: Zn(II)-Particle Size.
Adsorbents |
Amount Adsorbed (mg/g) |
|||
0.18 mm |
0.24 mm |
0.30 mm |
0.42 mm |
|
TTCSS |
38.23 |
28.21 |
19.74 |
22.23 |
TPJB |
55.43 |
44.43 |
33.17 |
27.72 |
TMSP |
83.76 |
25.52 |
22.29 |
19.32 |
TAMC |
41.87 |
34.32 |
27.28 |
28.38 |
Table 2a: Cr (VI)-Contact Time/Initial Concentration.
Adsorbents |
Time (min) |
Amount Adsorbed (mg/g) |
||||
100 ppm |
250ppm |
500ppm |
750ppm |
1000 ppm |
||
TTCSS |
30 |
2.7165 |
3.827 |
5.726 |
6.837 |
5.342 |
60 |
3.9482 |
5.9147 |
9.2536 |
10.5213 |
16.8854 |
|
120 |
2.9726 |
3.98216 |
6.726 |
8.8726 |
10.765 |
|
TPJB |
30 |
3.726 |
4.7236 |
7.837 |
10.872 |
6.865 |
60 |
4.1617 |
9.9872 |
15.009 |
17.921 |
22.6303 |
|
120 |
3.5262 |
5.837 |
14.763 |
12.2726 |
7.976 |
|
TMSP |
30 |
0.564 |
1.987 |
4.676 |
4.765 |
6.876 |
60 |
1.2867 |
3.4775 |
8.5776 |
9.6274 |
13.1202 |
|
120 |
0.9875 |
2.234 |
6.765 |
6.9765 |
10.976 |
|
TAMC |
30 |
0.9876 |
1.234 |
3.654 |
4.876 |
7.9876 |
60 |
2.4485 |
2.9872 |
7.1107 |
7.5983 |
11.3931 |
|
120 |
1.2343 |
1.7654 |
4.7656 |
5.764 |
8.654 |
|
Table 3a: Cr (VI)-Dosage.
Adsorbents |
Amount Adsorbed (mg/g) |
||||
200 mg |
300 mg |
400 mg |
500 mg |
1000 mg |
|
TTCSS |
16.8854 |
11.625 |
10.298 |
9.937 |
8.282 |
TPJB |
22.6303 |
17.2726 |
15.765 |
11.7598 |
10.282 |
TMSP |
7.282 |
8.2822 |
9.765 |
11.272 |
13.1202 |
TAMC |
11.3931 |
9.2826 |
8.875 |
5.3837 |
5.3837 |
Table 3b: Zn (II)-Dosage.
Adsorbent |
Amount adsorbed (mg/g) |
||||
100mg |
200mg |
300mg |
500mg |
1000mg |
|
TTCS |
24.85 |
26.87 |
29.76 |
31.87 |
38.23 |
TPJB |
11.23 |
29.87 |
31.98 |
37.45 |
55.43 |
TMSP |
38.65 |
46.87 |
52.87 |
61.87 |
83.76 |
TAMC |
26.85 |
33.76 |
34.98 |
39.87 |
41.87 |
750ppm, 60 min, pH 5.6, 300C. Further increase in agitation time,
beyond the attainment of equilibrium, registered least changes
in the residual concentrations of the metal ions. The most
suitable adsorbent for maximum removal of Cr(VI) is observed
to be TPJB, since it is a natural bio accumulator of Cr(VI) by the
transaction of metal to the aerial part of the plant [5]. It is an
active transport mechanism and the preferential order being
TPJB>TTCSS>TMSP>TAMC. TMSP is found to be best for Zn(II)
system, for the reason that the TMSP is more porous in nature
when compared to other adsorbents and the preferential order
being TMSP>TPJB> TTCSS> TAMC.
Column Studies
The Batch mode studies are the basic pilot studies performed
to screen the biosorbents before adopting the adsorption method
to the field levels. The results of the Batch equilibration method
insist the feasibility and compatibility of the chosen systems
for their promising application. Based on batch studies results,
column studies were carried out to quantify the adsorbents’
efficiencies in the continuous columns’ running with the aqueous Cr(VI) and Zn(II) solutions with TPJB and TMSP respectively
[6]. Later, the column schemes are extended to the effluent
discharges.
Column packing
The column is made up of cylindrical glass tube, the inner
diameter is 2.5 cm and the height is 30 cm. It was packed with
sorbent materials between two supporting layers of glass wool,
spread with the glass beads at the top of the already packed glass
wool layer placed at the bottom. The step by step packing is as:
Glass wool layer (3cm thickness), glass beads (2cm thickness),
TPJB /TMSP (50/300 g: 6cm height), glass wool (1cm thickness).
These materials were loaded from the top of the column and
allowed to settle by gravity force. The bottom of the column was
fitted with rubber with flow adjustable knob and thus the outflow
rate was controlled by adjusting the knob (Figure 5).
1000 mg/L aqueous solutions of Cr(VI) and Zn(II) were prepared and poured from the top of columns slowly and the flow rate through the columns were fixed as 100 ml/5 mins for Cr(VI)-TPJB system and 100ml/20 seconds for Zn(II)-TMSP system after several trials. Maximum removal of 98% and 100% were registered for Cr(VI)-TPJB & Zn(II)-TMSP respectively, after analysis in AAS. The percentage removal was observed to decline upto 90% after passing 20 litres of inlet solutions. Further decline was envisaged upto 30 litres and then the column went exhausted.
1000 mg/L aqueous solutions of Cr(VI) and Zn(II) were prepared and poured from the top of columns slowly and the flow rate through the columns were fixed as 100 ml/5 mins for Cr(VI)-TPJB system and 100ml/20 seconds for Zn(II)-TMSP system after several trials. Maximum removal of 98% and 100% were registered for Cr(VI)-TPJB & Zn(II)-TMSP respectively, after analysis in AAS. The percentage removal was observed to decline upto 90% after passing 20 litres of inlet solutions. Further decline was envisaged upto 30 litres and then the column went exhausted.
Collection of Effluent Samples
Wastewaters containing Cr(VI) and Zn(II) ions above the
tolerance levels were found at various electroplating industries
located in Kurumbapalayam region of Coimbatore. 10 litres of
these effluent samples were collected in pre cleaned PET bottles
of 1 litre capacity and analyzed for Cr(VI) and Zn(II) ions of
initial concentrations (AAS) after a series of dilutions, Cr(VI):
720 mg/L, Zn(II): 40 mg/L. The pH and conductivity values of
the samples were also recorded using LABTRONICS pH meter
and conductivity meter respectively (Table 4). Zinc plating bath,
the processing, uncoated/ Zn plated materials and the effluents
generated are represented in figure 4.
Table 4: Effluent Samples – Initial Concentrations
S. No |
Name of Industries |
Cr(VI) |
Zn(II) |
Conductivity (mv) |
pH |
1 |
Unit I |
71.52 |
25.87 |
21.76 |
2.3 |
2 |
Unit II |
695.75 |
3.398 |
32.98 |
1.98 |
3 |
Unit III |
211 |
2.817 |
29.82 |
2.98 |
4 |
Unit IV |
6.4647 |
23.298 |
87.87 |
5.35 |
5 |
Unit V |
5.875 |
5.876 |
90.79 |
0.57 |
6 |
Unit VI |
449.6 |
4.383 |
24.4 |
1.82 |
7 |
Unit VII |
720.05 |
40.08 |
-0.693 |
3.45 |
Analysis of Industrial Effluents- Batch/Column
Methods
Effluent concentrations of 50 mg/L were fixed for the batch
studies and experimentally verified (TPJB and TMSP) under the
optimized conditions. The results revealed an appreciable 70%
removal of Cr(VI) and Zn(II) ions under batch mode.
sorptive nature of the sorbent materials was quantitatively estimated by the performance of the column studies, on the basis of the long term analysis at the laboratory conditions. The values recorded are 100% and 92% for Zn(II) and Cr(VI) ions respectively.
sorptive nature of the sorbent materials was quantitatively estimated by the performance of the column studies, on the basis of the long term analysis at the laboratory conditions. The values recorded are 100% and 92% for Zn(II) and Cr(VI) ions respectively.
Conclusion
Batch equilibration method was adopted to analysis the
effect of the variables viz., particle sizes and dosages of the
adsorbents (TTCSS, TPJB, TMSP, TAMC), initial concentrations
Figure 3a: Effect of pH - Cr(VI.)
Figure 3b: Effect of pH - Zn(II).
Figure 4a: Zinc Plating bath.
Figure 4b: Work at the bath plating.
Figure 4c: Material before platting.
Figure 4d: Material after platting.
Figure 4e: Effluent generated from the bath.
Figure 5: Column packing.
of the adsorbate solutions (Zn(II), Cr(VI)), predetermined time
intervals between the sorbent - sorbates materials, pH of the
solution media and temperatures. TPJB and TMSP were derived
to be the best sorbents amongst all the identified materials based
on the optimized conditions through batch equilibrium studies.
Quantification of these results was justified by column method
for the aqueous metal solutions with the fixed sorbent materials.
Various electroplating industries located in and around
Coimbatore were identified and surveyed for the extent of metal
pollution. The effluent samples containing 40mg/L of Zn(II) and
720mg/L of Cr(VI) were collected from Electroplating Industries
at Kurumbapalayam area and the performance of the column for
these effluent discharges revealed 100% and 92% removal for
Zn(II) and Cr(VI) ions respectively. The concluding remarks holds
good for TPJB and TMSP to be promising litter waste materials in
the sequestrating Cr(VI) and Zn(II) ions at field levels.
Financial Support
The authors submit their due acknowledgment to Defence
Research & Development Organization (DRDO), New Delhi for
the timely Financial Support in execution of the research work
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