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CHAPTER 2
MATERIALS AND METHODS
2.1 MATERIALS
2.1.1 APPARATUS
1. Spectrophotometer of Systronics model with 1cm Quartz cell
2. An atomic absorption spectrometer model Elico SL 163 with
air-acetylene burner.
3. FT-IR Spectrophotometer of model Shimadzu 84005 FT-IRS
4. Scanning Electron Microscope of model JOEL JSM 6360
5. Digital pH meter of model ELICO LI-120 with combined
electrode
6. Glass Column of 30 cm height and 2.5cm diameter with
Teflon stopper.
7. Thermostatically controlled mechanical shaker for equilibrium
studies
8. Hot air oven
9. ASTM test sieves
2.1.2 Reagents
All reagents used were of analytical grade and distilled water was
used for dilution purposes.
57
2.1.2.1 Reagents for batch and column studies
Stock solutions of the following ions were prepared as follows: The
stock solutions were prepared fresh on the day of use.
i) Mercury (II) solution (1000mg L-1): Prepared by dissolving
1.354g of mercury (II) chloride in distilled water and diluted
to 1000 mL.
ii) Nickel solution (1000mg L-1): Prepared by dissolving 4.479g
of nickel sulphate (NiSO4.6H2O) in distilled water and diluted
to 1000mL.
iii) Cadmium Solution (1000 mg L-1): Prepared by dissolving
2.282g of cadmium sulphate in diluted distilled water and
diluted to 1000mL.
Appropriate volumes of stock solutions were suitably diluted with
water to obtain a concentration of 10mg L-1 for batch experiments. For
column studies 5 liter each of 200mg L-1 of mercury, nickel and cadmium
were prepared by diluting suitable volumes of respective stock solutions.
2.1.2.2 Reagents for regeneration of carbons
Regeneration of mercury (II), nickel (II) and cadmium (II) ions:
Hydrochloric acid of approximately 1N was prepared by diluting 86 ml of
concentrated HCl to 1000mL. 1N HCl was diluted to varying concentration
ranging from 0.05 to 0.5N solutions.
58
2.1.2.3 Reagents for determination of carbon characteristics (ISI, 1977)
i) Hydrochloric acid (0.25N): Appropriate volume of
concentrated hydrochloric acid (specific gravity 1.19) was
mixed with water and the strength was corrected using
standard solution of sodium carbonate.
ii) Methylene blue solution (0.15 %): 0.15 g of methylene blue
was dissolved in 100 ml of water.
iii) Hydroxylamine hydrochloride (10%): 10 g of
hydroxylamine hydrochloride was dissolved in 100ml of
water.
iv) Ammonium acetate buffer (approximately pH 4.0): 250 g of
ammonium acetate was dissolved in 150 ml of water. To
this 700 ml of glacial acetic acid was added.
v) Sodium acetate (31.25%): 250 g of sodium acetate trihydrate
(CH3 COONa. 3H2O) was dissolved in 800 ml of water.
vi) 1, 10 Phenanthroline (0.1 %): 0.1g of 1, 10 – phenanthroline
hydrochloride was dissolved in 100ml of water.
vii) Stock iron solution (200 mg L-1): In a mixture of 20 ml of
concentrated sulphuric acid and 50 ml of water, 1.404g of
ferrous ammonium sulphate was dissolved, 0.1 N potassium
permanganate solution was added drop wise until a faint
pink colour persisted. The solution was diluted to one liter.
viii) Standard iron solution: Appropriate volumes of stock
solution were diluted to get a concentration of 1 mg L-1.
59
ix) Standard potassium dichromate solution (0.025 N): 1.226g
of potassium dichromate was dissolved in water and made
upto one liter.
x) Sodium thiosulphate solution (approximately 0.25 N):
6.205g of sodium thiosulphate was dissolved in water and
diluted to one liter.
xi) Starch solution: 1.25 g soluble starch was boiled with
200mL of water .The solution was prepared fresh on the day
of use.
xii) Potassium iodide (10%) solution: 10g of potassium iodide
was dissolved in 100ml of water.
xiii) Brominating mixture: 2.784g of anhydrous potassium
bromate and 10g of potassium bromide were dissolved in
water and diluted to one liter.
xiv) Sodium hydroxide solution (0.1 N): About 4g of sodium
hydroxide was dissolved in water and diluted to one liter.
The strength was corrected using standard solution of
hydrochloric acid.
xv) Acetic acid (0.15 N): 8.8 ml of glacial acetic acid was
dissolved in 1000ml of water. Exact normality was
established by standardizing against standard NaOH
solution.
xvi) Phenol solution (approximately 0.1 %): 0.1g of phenol
crystals were dissolved in water and diluted to 100ml.
xvii) Sodium sulphate solution (0.25M): 35.5 g of anhydrous
sodium sulphate was dissolved in water and diluted to one
liter.
60
2.2 METHODS
2.2.1 Preparation of Bicarbonate impregnated Coconut Oilcake
Residue Carbon (BCORC)
Coconut Oilcake Residue procured from the market was washed
with distilled water, dried at 100ºC ± 5ºC, cut into small pieces and pulverized
to 300 to 800µm (20-50 ASTM) particle size. Then it was treated with
concentrated sulphuric acid under a weight ratio of 1:1 and heated in the hot
air oven at a temperature of 160±5ºC for 24h. The carbonized material was
washed with distilled water to remove the excess acid and dried at 100 ± 5ºC.
Then the carbon was soaked in 2% sodium bicarbonate solution for 24h to
remove any free acid. It was then washed with distilled water to remove
excess sodium bicarbonate, dried at 100±5 ºC and again sieved to 300 to
800 µm particle sizes. Preliminary studies were carried out with raw coconut
oilcake residue, sulphuricacid treated coconut oilcake residue carbon and
bicarbonate treated coconut oilcake residue carbon (BCORC) for the removal
of mercury (II), nickel (II) and cadmium (II). Based upon their efficiency,
BCORC was chosen for further studies. The commercial activated carbon
(CAC) procured from SD fine chemicals, was sieved to 300 to 800 µm
(20-50 ASTM) particle size and subsequent experiments were carried out with
BCORC and CAC.
2.2.2 Batch Experiments
Batch experiments were conducted in polythene bottles of 300ml
capacity provided with screw caps. The polythene bottles were washed well
with chromic acid before and after use. 100ml of the solution containing
metal ion equivalent to 10 mg L-1 concentrations under investigation were
taken in the bottles. After the addition of carbon, the bottles were equilibrated
for predetermined periods of time in a rotary mechanical shaker. At the end
61
of the equilibration period, the solutions were centrifuged and the liquid was
separated. The concentration of metal ions remaining in the supernatant was
analyzed using atomic absorption spectrometer.
Triplicate runs of each test were conducted and the obtained data
vary less than 1% suggesting accuracy of the results. Metal ion removal
percent (%) was calculated using Equation (2.1)
Removal (%) i f
i
C C100
C (2.1)
Where Ci and Cf are the initial and final metal ions concentrations
(mg L-1) respectively.
To find out the effect of equilibrium time required for the removal
of mercury(II), nickel(II), and cadmium(II) experiments were carried out
using 100mL of mercury(II), nickel(II), and cadmium(II)solutions of
concentration 10 mg L-1 containing 0.1 g carbon at pH 5.0 ± 0.2 for ranging
periods from 1 to 10 h. At the end of the agitation time, the solutions were
centrifuged, analyzed and the percentage of mercury (II), nickel (II) and
cadmium (II) removed in each case was calculated for both BCORC and CAC
carbons.
To find out the optimum pH for maximum removal of
mercury (II), nickel (II) and cadmium (II), experiments were carried out by
varying the pH of the aqueous mercury (II), nickel (II) and cadmium (II)
solutions over the range 1.0 to 10.0±0.2.After the optimum equilibration time
of agitation, the solutions were analysed and the percentage of mercury (II),
nickel (II) and cadmium (II) removal was established for both BCORC and
CAC carbons.
62
To find out the minimum amount of carbon required for maximum
removal of mercury (II), nickel (II) and cadmium (II) for both BCORC and
CAC carbons, carbons ranging from 0.025 g – 0.55 g per 100 mL were
agitated with 10 mg L-1 of mercury (II), nickel (II) and cadmium (II) solution
at an optimum pH. The mercury (II), nickel (II) and cadmium (II) removed in
each instance was established after equilibration under optimum time.
2.2.3 Column Experiments
Column experiments were performed with 30 cm long glass column
of 2.5 cm diameter. The carbon under study was transferred after making it
into slurry with distilled water. The slurry was transferred slowly to a glass
column packed with glass wool at the bottom. After complete transfer of the
carbon, the bed was washed several times with water and solutions of ions
under study were stored in polythene containers of 5 liters capacity.
Polythene tubing was connected to the bottle with a tap at the bottom. The
other end of these tubing was connected to a glass socket containing
flow – regulating valve, outlet of the valve was fixed to the top of the column,
which was kept at a lower level. The columns were provided with pinch
cocks at the bottom to control the flow rates. For all column experiments, a
pressure head of 10-15 cm (4 – 6 ) was maintained over the carbon beds.
The inflow and outflow rates were maintained at a constant rate for a
particular experiment. Frequent checks were made at regular intervals to
correct any alteration in the flow rates. The schematic representation of the
column is shown in Figure 2.1.
63
Figure 2.1 Schematic representation of the Column
Lot volumes of 100 mL were separately collected. Each lot volume
was analyzed for the concentrations of the metal ions under study, using
atomic absorption spectroscopy after appropriate dilutions if necessary.
Percolation of the metal ion solution was stopped as soon as the concentration
in the effluent exceeded 0.1 mg/100 mL or 1 mg L-1 (Break point).
To find out the optimum flow rate for maximum uptake of metal
ions, experiments were carried out using 200 mg L-1 of metal ion solution
with 10 g of BCORC and CAC adjusted to optimized pH. The solutions were
made flow through the column containing carbon beds at flow rates ranging
from 5 to 25 mL min-1. Each lot of 200 mL fractions of the effluent was
separately collected and analyzed using AAS method. Percolation of the
solution was stopped as soon as the concentration of metal ion exceeded the
64
break point. The adsorption capacity of the carbon for metal ion removal was
calculated by summing up the amount removed in each lot to 100 mL up to
break point.
To find out the influence of bed height on the removal of
metal ions, experiments were conducted with both carbons using different
weights of carbon ranging from 5 to 25 g. Percolation of metal ion solution
was done at the optimized flow rate. Each lot of 100 mL fractions were
collected and analyzed for metal ion content. Percolation of metal ion solution
was stopped as the concentration in the effluent exceeded break point. The
adsorption capacities of the carbons were calculated.
To find out the effect of common anions and cations present in
water on the capacity of both carbons, the metal ion solution was added with
sodium chloride, sodium sulphate, sodium bicarbonate, calcium chloride and
magnesium sulphate individually to a level of 1000 mg L-1 of interfering ions.
Percolation of the solution was done at optimized flow rate through optimized
bed heights of BCORC and CAC. Each lot of 100 mL fractions of the
effluents were separately collected and analyzed for metal ion content. As
soon as the concentration in the effluent exceeded break point, percolation of
the solutions was stopped and the capacity of the carbon in each instance was
calculated.
To find out the efficiency of the carbons after regeneration
experiments were performed using columns containing optimized be height of
the carbons. Metal ion solution containing 200 mg L-1 was allowed to
percolate through the column at optimized flow rate till the break point. The
breakthrough capacity of each carbon was established. Regeneration of the
columns were done by carefully collecting the carbons after adsorption and
soaked in 250 mL of 0.5 N HCl for 24 h. BCORC was then thoroughly
washed to remove excess acid and further soaked in 250 mL of 2%
65
NaHCO3 for 24 h. It was then washed with distilled water to remove excess
acid, and packed in the column. The breakthrough capacities of the
regenerated carbons were established by percolating metal ion solution of
200 mg L-1.
The process of regeneration was repeated as above at the end of
second cycle and carbons were put to use for the next cycle of operation. In
this manner the carbon beds were put to reuse over 5 cycles of operation.
In order to get an idea of the extent of particle size degradation after
repeated cycles of operation, both BCORC and CAC were carefully removed
from the column at the end of the fifth cycle, dried and sieved with
20-50 mesh screens. Particle size degradation (%) was calculated from the
ratio of loss in weight of carbon to the initial weight.
2.2.4 Analytical Procedure
2.2.4.1 Principle of Atomic Absorption Spectrometer
In atomic absorption spectroscopy, the absorbance A is given by the
logarithmic ratio of the intensity of the incident light signal Io to that of the
transmitted light It.
A = log Io / It = K L No. (2.2)
Where, No = is the concentration of atoms in the flame (number of
atoms per mL),
L = is the path length through the flame (cm) and
K = is a constant related to the absorption co-efficient
Hence, Absorbance path length and concentration of atomic vapour.
concentration of analyte.
66
2.2.4.2 Principle of operation
AAS involves the determination of the element at its line center by
using a narrow line source emitting the given resonance line, whose emission
line profile is less than the absorption line profile of its analyte in the flame.
The flame gases are treated as a medium containing free, unexecuted atom
capable of absorbing radiation from an external source when the radiation
corresponds exactly to the energy required radiation corresponds exactly to
the energy required for transition of the test element for the ground electronic
state to an upper excited electronic state. Unabsorbed radiation passes
through a monochromatic that isolates the exciting spectral line and into a
photo detector. Absorption is measured by the difference in transmitted signal
in the presence and absence of the test element.
The liquid samples to be analyzed are passed through a capillary
tube and atomized in a standard (or) modified flame photometer burner. The
procedure is based on flame absorption rather than flame emission and
depends upon the fact that metal atoms absorb strongly at discrete
characteristic wavelengths (Table 2.1), which coincide with the emission
spectral lines of the particular metal.
Table 2.1 Discrete Wavelength of Elements
S.No. Element Wavelength (nm)
1 Mercury – Hollow cathode lamp 253.7
2. Nickel – hollow cathode lamp 232.0
3. Cadmium – hollow cathode lamp 228.8
The absorbance of the flame for light of reasonable wavelength is a
direct measure of the concentration of the absorbing atoms in the flame and
67
hence of the concentration of atoms in the dissolved material. The great
advantage of atomic absorption over other procedures is its high degree of
freedom from interference (by the presence of other elements). Traces of one
element can be accurately determined in the presence of a high concentration
of other elements (Vogel 1961).
The following conditions were maintained to operate the
instrument / depending upon the analytical procedure.
Acetylene and air were used as fuel and oxidant respectively in AAS
for the determination of mercury, nickel and cadmium quantitatively. The
temperature of the flame was approximately 2300ºC. Air – acetylene flame
was used along with the flow rate of about 1 to 3L min-1 as per the
recommended procedure. Peak energy was maintained over the range 1 to 3V
as per the recommended procedure.
In practice, the quantitative measurements are generally based on
calibration curve.
2.2.5 Standard Calibration Curves.
Calibration curves are prepared from a series of solutions of sample
element in known concentration, by measuring the absorbance of each
solution and then plotting the absorbance against the concentration.
2.2.5.1 Determination of Mercury
Mercury (II) was estimated using atomic absorption spectrometer.
Standard solutions of concentrations 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and
3.5 g mL-1 were prepared by diluting appropriate volumes of stock solution.
The absorbance of each solution was measured at 253.7 nm using mercury
68
hollow cathode lamp and plotted against concentration to obtain the
calibrative curve. Average value of ten replicates was taken for each
determination.
A suitable aliquot of the sample solution was diluted if the
concentration exceeded 10 g mL-1. The solution was nebulised into the
atomic absorption spectrometer and the absorbance was measured. By
measuring the absorbance, the concentration of the metal ion was established
by referring to the calibration curve shown in Figure 2.2
R2 = 0.9974
0
0.05
0.1
0.15
0.2
0.25
0.3
0 1 2 3 4
CONCENTRATION OF MERC URY (II) (ppm)
AB
SO
RB
AN
CE
Figure 2.2 Standard graph of mercury
2.2.5.2 Determination of Nickel
Nickel (II) was estimated using atomic absorption spectrometer.
Standard solutions of concentrations 1, 2, 3, 4 and 5 g mL-1 were prepared
by diluting appropriate volumes of stock solution. The absorbance of each
solution was measured at 232 nm using nickel hollow cathode lamp and
69
plotted against concentration to obtain the calibration curve. Average value
of ten replicates was taken for each determination.
A suitable aliquot of the sample solution was diluted if the
concentration exceeded 10 g mL-1. The solution was nebulised into the
atomic absorption spectrometer and the absorbance was measured. By
measuring the absorbance, the concentration of the metal ion was established
by referring to the calibration curve shown in Figure 2.3.
R2 = 0.9978
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0 1 2 3 4 5 6
CONC ENTRATION O F NICKEL (II) (ppm)
AB
SO
RB
AN
CE
Figure 2.3 Standard graph of nickel
2.2.5.3 Determination of Cadmium
Cadmium (II) was estimated using atomic absorption spectrometer.
Standard solutions of cadmium (II) concentration 0.5, 1.0, 1.5, 2.0, 2.5 and
3.0 g mL-1 was prepared by diluting appropriate volumes of stock solution.
The absorbance of each solution was measured at 228nm using cadmium
hollow cathode lamp and plotted against concentration to obtain the
calibration curve. Average value of ten replicates was taken for each
determination.
70
A suitable aliquot of the sample solution was diluted if the
concentration exceeded 10 g mL-1. The solution was nebulized into the
atomic absorption spectrometer and the absorbance was measured. By
measuring the absorbance the concentration of the metal ion was established
by referring to the calibration curve shown in Figure 2.4.
R2 = 0.9975
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 0.5 1 1.5 2 2.5 3 3.5
CONCENTRATION OF CADMIUM (II) (ppm)
AB
SO
RB
AN
CE
Figure 2.4 Standard graph of Cadmium
2.2.6 Methods for the Determination of Carbon Characteristics
2.2.6.1 Moisture
About 10g of the material was weighed in a petridish. The dish was
placed in an electric oven maintained at 110 ± 5ºC for about 4h. The dish was
covered, cooled in a desiccator and weighed. Heating, cooling and weighing
was repeated at 30 minutes intervals until the difference between the two
consecutive weighings was less than 5 mg (ISI 1977).
71
Moisture Content 100x(M X)M
(2.3)
Where, M = Mass in gram of the material taken for the test.
X = Mass in gram of the material after drying.
2.2.6.2 Ash content
2g of the carbon under examination was weighed accurately into a
tarred porcelain crucible. The crucible and its contents were placed in an
electric oven at 110 ±5ºC for about 4h. The crucible was removed from the
oven and the contents were ignited in an electric muffle at a temperature of
1000ºC for about 3h. The process of heating and cooling was repeated until
the difference between two consecutive weighings was less than 1 mg
(The ash was preserved for the determination of iron) (ISI 1977).
Ash Content 1M x100
Mx(100 X) / 100
110,000 x M
Mx(100 X) (2.4)
Where, M1 – Mass of the ash in grams.
M – Mass of the material taken for the test in grams.
X – Percentage of moisture content present in the material
taken for test.
2.2.6.3 Apparent density test
A 100 mL graduated cylinder was weighed accurately. For the
determination of apparent density, a trip balance was used to fill the carbon in
the cylinder. A sufficient amount of the carbon was poured with constant
72
tapping and filled up to the 50mL mark. The shaker attached to the balance
was adjusted so that the carbon filled the graduated cylinder at approximately
1 mL Sec-1. After filling the graduated cylinder with the carbon, it was
weighed accurately. The apparent density was calculated by dividing the
weight of carbon by 50 (ISI 1997).
2.2.6.4 Porosity
Porosity was determined from the specific gravity (S) and bulk
density (D) value of BCORC and CAC (Wilde et al 1972).
Porosity (%) S Dx 100
S (2.5)
2.2.6.5 Matter soluble in water
10g of the carbon material of known moisture content was weighed
accurately and transferred into a one liter beaker. About 300 ml of distilled
water was added and heated to boiling with constant stirring. Stirring was
continued for 5 minutes after the flame was removed. The material was then
allowed to settle and the supernatant liquid was filtered through a gooch
crucible fitted with an asbestos mat. The procedure was repeated thrice with
the residue in the beaker using 300ml of water each time. This combined
filtrate was concentrated to less than 100 ml over a water bath, cooled and
made upto 100 ml mark in a volumetric flask. Exactly 50 ml of the
concentrate was transferred to a china dish and evaporated to almost dryness
on a boiling water bath and finally fried in an electric oven, maintained at
110 ±5ºC, coded in a desiccators and weighing was repeated at 30 min
intervals, until the difference between two consecutive weighing was less than
5 mg (ISI 1977).
73
Matter soluble in water (%)1
Mx 100 x 2
M x (100 X) (2.6)
Where, M – Mass of the residue in grams
M1 – Mass of the material taken for the test in grams.
X – Percentage of moisture present in the material.
2.2.6.6 Matter soluble in acid
10g of the carbon under study was weighed accurately and
transferred into a one liter beaker. 300 mL of 0.25 N HCl was added and
heated to boiling with continuous stirring. Stirring was continued for about 5
minutes after the flame was removed. The material was then allowed to settle
and the supernatant liquid was filtered through a gooch crucible fitted with an
asbestos mat into a 2 liter beaker. The procedure was repeated thrice with the
residue in the beaker using 300 mL of acid each time. After the fourth
treatment, the combined filtrate was concentrated to less than 100ml and
made upto the mark in a 100mL of volumetric flask. Exactly 50ml of the
concentrate was transferred to a china dish and evaporated to dryness on a
water both. The residue was finally dried in an electric oven maintained at
110 ±5ºC. The dish was then covered cooled in desiccator and weighed. The
above procedure of drying, cooling and weighing was repeated at 30 minutes
intervals until the difference between two consecutive weighings was less
than 5 mg. Acid soluble matter was calculated using the same expression as
in the case of matter soluble in water (ISI 1977).
Acid soluble matter1
20000x A
M x (100 X) (2.7)
Where, A – Mass of the dried residue in grams.
74
M1- Mass of the material taken for test in grams.
X - Percentage of moisture content present in the material taken for
test.
2.2.6.7 pH
10g of the dried carbon material was weighed and transferred into a
one liter beaker. 300 ml of freshly boiled and cooled water (adjusted to
pH 7.0) was added and heated to boiling. After digesting for 10 minutes, the
solution was filtered while hot, rejecting the first 20 ml of the filtrate. The
remaining filtrate was cooled to room temperature and the pH was determined
using a pH meter (ISI 1977).
2.2.6.8 Decolourizing Power
About 0.1g of the carbon was transferred to a 50 mL glass stoppered
flask. 1 mL of methylene blue solution (0.15%) was added from a burette and
shaken for 5 minutes. Addition of methylene blue solution and shaking was
continued till the blue colour persisted for atleast 5 minutes. The decoloursing
power of carbon is expressed in terms of milligrams of methylene blue
adsorbed by 1 g of activated carbon (ISI 1977).
Decolourising power (mg g-1) = 1.5 x V/M (2.8)
Where, V – Volume in ml of methylene blue solution.
M – Mass of the material taken for the test in grams.
2.2.6.9 Phenol Number
Phenol number (or) the phenol value of any carbon is defined as the
amount of carbon in milligrams per liter required to decrease 100 g of phenol
75
by 90% (Fair et al 1971). The phenol strength was first established by
pipetting out 20 ml of the phenol solution into a conical flask. 50 mL of the
distilled water followed by 5.7 mL of concentrated hydrochloric acid were
added. A known volume of brominating mixture was then added from burette
with shaking till a pale permanent yellow color persisted in the solution. The
flask was kept aside for 10-20 minutes for the completion of bromination.
Then 20mL of 10% solution of potassium iodide was added and the liberated
iodine was titrated against standard sodium thiosulphate solution using starch
as an indicator. The strength of the brominating solution was also established.
Phenol solution taken = 20 mL
Let 20mL of brominating solution = V1 mL sodium thiosulphate
40 mL of brominating solution = 2V1 mL sodium thiosulphate.
Let the volume of sodium thiosulphate consumed after bromination
reaction = V2 mL
Phenol present per liter of the solution = 11 2(2V V )x N x 15.66g L
20 (2.9)
Where, N – Normality of sodium thiosulphate solution
15.66 – Equivalent weight of phenol.
Different weights of carbon ranging from 0.5 to 10g were added to
300 mL stoppered glass bottles containing 100 mL of 100 mg L-1 of phenol
solution. The solutions were mixed well and allowed to stand for 24h. After
the adsorption process, the phenol content was determined by the above
procedure. The percentage of phenol removed was plotted against carbon
dosage added as shown in Figure 2.5 and the carbon requirement for 90%
removal of phenol was established.
76
0
20
40
60
80
100
120
0 5 10 15
DOSAGE OF CARBON (g /100 mL)
PERCEN
T P
HENO
L R
EM
OV
AL
BCORC
CAC
Figure 2.5 Determination of phenol number of BCORC and CAC
2.2.6.10 Iron Content
The iron content of the carbon was determined by the
1, 10 – phenanthroline method (ISI 1977). The ash obtained under ash
content test was transferred to a 150 mL conical flask using 50 mL of dilute
hydrochloric acid and heated to boiling. The contents were then cooled to
room temperature and filtered through a whatman No.42 filter paper. The
contents of the fitter paper were washed with distilled water, and the filtrate
and entire washings were made up to 250mL. 50 mL of the made up sample
was pipetted out into 125 Erlenmeyer flask. 2mL of hydrochloric acid and
1mL of hydroxylamine hydrochloride solution (10%) were added and heated
to boiling. Boiling was continued till the volume was reduced to about
10-15 mL. The solution was then transferred to 100mL standard flask and
10ml ammonium acetate buffer, followed by the addition of 2mL of
1, 10 – Phenanthroline solution and made up to the mark. The absorbance at
77
525 nm was measured using spectrophotometer against the blank using 1cm
cell. A calibration curve was prepared using 10-200 g mL-1 of iron by
following the above procedure using standard iron (II) solution. Iron content
was determined by referring to the calibration graph in Figure 2.6.
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0 50 100 150 200
C ONC ENTRAIO N O F IRO N (III) (ppm)
AB
SO
RB
AN
CE
Figure 2.6 Standard graph of Iron
2.2.6.11 Ion Exchange capacity
About 1g of carbon was taken in a beaker and sufficient amount of
distilled water was added to cover the carbon. The slurry was carefully
transferred to the burette. The column was never allowed to drain completely
and the level of the liquid was maintained at about 1 cm above the carbon
bed.
250 mL of a solution of 0.25 M sodium sulphate was allowed to drip
into the column at a rate of 2 mL min-1 and the effluent was collected in a
500 mL conical flask. When all the solution has passed through the column,
78
the effluent was titrated with standard 0.1 N sodium hydroxide solution using
phenolphthalein as indicator. The ion exchange capacity of the bed in
milli equivalents per gram is given by (Jeffery et al 1991).
Ion exchange capacity = avw
, milli equivalents/ gm (2.10)
Where, a is the normality of the sodium hydroxide solution,
v is the volume in mL
W is the weigh of the carbon.
2.2.6.12 Determination of surface area (p - nitro phenol adsorption
method)
A stock solution containing 1000mg L-1 of p - nitro phenol (PNP)
was suitably diluted to a solution of concentration 100 mg L-1. Aliquots
ranging from 0-5 mL of this 100 mg L-1 solution were transferred into 100 mL
standard flasks. To each, 2 mL of 0.1N sodium hydroxide was added and
diluted to 100 mL. Absorbance of these solutions was measured at 400nm
using 1 cm cell against the reagent blank. A calibration graph was prepared
using 1-5 mg L-1 of p – nitro phenol.
About 0.5g of carbon samples were accurately weighed to the
nearest milligram and added to a 250 mL stoppered plastic bottles. p – nitro
phenol solutions in the range 50-1000 mg L-1 were prepared separately and
100 mL of these solutions were added to each of these bottles. The bottles
were tightly stoppered and then shaken in rotary mechanical shaker for 24h.
At the end of the equilibration period, a suitable volume of supernatant
solution was transferred to a 100 mL standard flask and 2 mL of sodium
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hydroxide was added and diluted to 100 mL. The absorbance of this solution
measured at 100 nm using 1 cm cells against a reagent blank.
The concentration (C) of PNP in each instance was established by
reference to the calibration graph. From the difference in initial and final
concentrations of PNP, the number of millimole of PNP adsorbed by 1g of the
carbon was calculated and designated as “N”.
The ratio of the concentration of PNP remaining in each instance (c)
to millimole of PNP adsorbed per g (N) of the carbon (C/N) was plotted
against the concentration of PNP remaining in the solution (C) as shown in
Figure 2.7. The reciprocal of the slope of the linear plot gave the number of
millimoles of PNP required per g of carbon to firm a monolayer, which was
designated as Nm. By assuming that the molecular cross sectional area ( ) of
PNP as 52.5 Å2, the area available in m2 g-1 of the carbon was calculated using
the following expression (Giles and D.Silva 1969).
A = Nm x No x x 10-20 (2.11)
Where, No = Avogadro number
Nm = Number of moles per gm required to form monolayer
(obtained from Slope value)
= Molecular cross sectional area given in square Angstroms.
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R2 = 0.9784
R2 = 0.9966
0
20
40
60
80
100
120
0 0.05 0.1 0.15
C (mg L-1)
C/N
BCORC
CAC
Figure 2.7 Determination of surface area of BCORC and CAC
The carbon characteristics of BCORC and CAC were examined by
above procedure and the values are recorded in Table 2.2.
Examination of the carbon characteristics in (Table 2.2) show both
the carbons BCORC and CAC possess bulk density of 0.66g mL-1 and
0.56g mL-1 respectively in which the bulk density of BCORC is higher than
CAC which is generally favorable for use in column applications.
Moisture content is the amount of water physically bound on the
activated carbon under normal condition. It reduces the adsorption capacity
of carbon and if the moisture content of the adsorbent is more, it will dilute
the action of the activated carbon and it necessitates utilizing some extra load
of carbon. This would not influence the adsorptive power of activated carbon.
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Table 2.2 Characteristics of Bicarbonate treated Coconut Oilcake
Residue Carbon (BCORC) and Commercial Activated
Carbon (CAC)
No. Parameter BCORC CAC
1. Bulk density ( g/mL) 0.66 0.56
2. Moisture (%) 6.78 6.62
3. Ash (%) 5.50 2.40
4. Solubility in water (%) 1.93 1.15
5. Solubility in acid (%) 6.44 5.94
6. pH 7.60 8.20
7. Decolourizing power (%) 6.75 4.50
8. Phenol number 20.78 12.25
9. Ion exchange capacity (m equiv / g) 0.75 nil
10. Surface area (m2 / g) (p - nitrophenol
method)
214 211
11. Iron (%) 0.73 1.29
12. Porosity (%) 1.74 1.49
Ash content is the inorganic, inert, amorphous and unusable part
present in the activated carbon. This ash comes initially from the basic
material. Lower the ash content, the better the activated carbon. The practical
limit for the level of ash content allowed in the activated carbon various
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within 2 to 5%. The higher ash content in BCORC is due to the agricultural
origin. The solubility value in water and acid for BCORC was found to be
higher than CAC due to more soluble inorganic materials introduced by the
carbonization process.
The pH value of activated carbon indicates whether the carbon is
acidic or basic. The pH of BCORC and CAC were found out to be 7.6 and
8.2 respectively. The pH value of BCORC suggested that the carbon is neutral
in nature whereas CAC is completely basic.
The values of decolourizing capacity were found out to be
6.75 mg g-1 and 4.5 mg g-1 respectively for BCORC and CAC. The phenol
number was 20.78 and 12.25 for BCORC and CAC respectively. The lower
values of phenol number and decolorizing power of both the carbons
indicated that they could also be applied for organic adsorption.
The ion exchange capacity of BCORC was calculated as 0.75meq g-1,
showed that the activation of coconut oilcake residue with sulphuricacid
might have introduced ion exchangeable groups due to which BCORC could
be very effective in the removal of heavy metals. But CAC showed no ion
exchange capacity.
The surface area of activated carbon is directly related to the
porosity of carbon. The porosity and surface area are important factors for an
adsorbent as they greatly influence the adsorption process. It could be noted
that BCORC possessed higher porosity than that of CAC. The treatment of
sulphuricacid has produced more porous structure in BCORC. The iron
content of BCORC was found to be less than CAC indicating the suitability of
BCORC in water treatment.
Recommended