56

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.