1 1. INTRODUCTION Till recent years, the surge of industrial activities has intensified more environmental problems as seen for example in the deterioration of several ecosystems due to the accumulation of dangerous pollutants such as heavy metals. Heavy metals are still being used in various industries due to their technological importance. Yet, imperfect treatment of waste products from these industries will carry other issues to human health and environment. Aside from the environmental damage, human health is likely to be affected as the presence of heavy metals beyond a certain limit bring serious hazard to living organisms. For instance Cadmium(ΙΙ), Copper(ΙΙ), and Nickel(ΙΙ) ions have been proven to cause kidney damage, liver damage or Wilson disease and dermatitis or chronic asthma [8]. Several methods have been employed to remove heavy metals from wastewater, which include precipitation, floatation, ion exchange, membrane related process, electrochemical technique and biological process. Low efficiency performance particularly when used on very small concentration of heavy metal, the necessity of using expensive chemicals in some methods as well as accompanying disposal problems are among the drawbacks of these conventional methods. In regard of its simplicity and high efficiency characteristics even for a minute amount of heavy metals, adsorption is looked upon as a better technology. Activated carbon is a well known adsorbent and proven to be useful for removal of heavy metals. Nevertheless, the application of activated carbon for wastewater treatment is not feasible due to its high price and cost associated with the regeneration as a result of high degree of losses in real process. Removal of heavy metals using agricultural waste and its industrial by-products has been massively investigated due to the abundance of agricultural-related materials in nature and its low cost. The use of living and dead microbial cells in adsorption of heavy metals has been demonstrated as well. Adsorption is one the physico-chemical treatment process found to be effective in removing heavy metals from aqueous solutions. Adsorbent can be considered as low cost or cheap if it is abundant in nature and requires little processing and is a by-product of waste material from waste industry. Plant wastes are inexpensive as they have no or very low economic value. Some of the advantages of using plant wastes for wastewater treatment include simple technique, good adsorption capacity, selective adsorption of heavy metal ions, low cost, free availability and easy regeneration. However, the application of untreated
Transcript
1
1. INTRODUCTION
Till recent years, the surge of industrial activities has intensified more environmental
problems as seen for example in the deterioration of several ecosystems due to the
accumulation of dangerous pollutants such as heavy metals. Heavy metals are still being used
in various industries due to their technological importance. Yet, imperfect treatment of waste
products from these industries will carry other issues to human health and environment.
Aside from the environmental damage, human health is likely to be affected as the presence
of heavy metals beyond a certain limit bring serious hazard to living organisms. For instance
Cadmium(ΙΙ), Copper(ΙΙ), and Nickel(ΙΙ) ions have been proven to cause kidney damage,
liver damage or Wilson disease and dermatitis or chronic asthma [8].
Several methods have been employed to remove heavy metals from wastewater, which
include precipitation, floatation, ion exchange, membrane related process, electrochemical
technique and biological process. Low efficiency performance particularly when used on very
small concentration of heavy metal, the necessity of using expensive chemicals in some
methods as well as accompanying disposal problems are among the drawbacks of these
conventional methods. In regard of its simplicity and high efficiency characteristics even for
a minute amount of heavy metals, adsorption is looked upon as a better technology. Activated
carbon is a well known adsorbent and proven to be useful for removal of heavy metals.
Nevertheless, the application of activated carbon for wastewater treatment is not feasible due
to its high price and cost associated with the regeneration as a result of high degree of losses
in real process.
Removal of heavy metals using agricultural waste and its industrial by-products has
been massively investigated due to the abundance of agricultural-related materials in nature
and its low cost. The use of living and dead microbial cells in adsorption of heavy metals has
been demonstrated as well.
Adsorption is one the physico-chemical treatment process found to be effective in
removing heavy metals from aqueous solutions. Adsorbent can be considered as low cost or
cheap if it is abundant in nature and requires little processing and is a by-product of waste
material from waste industry. Plant wastes are inexpensive as they have no or very low
economic value. Some of the advantages of using plant wastes for wastewater treatment
include simple technique, good adsorption capacity, selective adsorption of heavy metal ions,
low cost, free availability and easy regeneration. However, the application of untreated
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wastes as adsorbents can also bring some problems such as low adsorption capacity, high
chemical oxygen demand (COD) and biological oxygen demand (BOD) as well as total
organic carbon (TOC) due to release of soluble organic compounds contained in the plant
materials. The increase of the COD, BOD, and TOC can cause depletion of oxygen in the
water and can threaten the aquatic life. Therefore, plant wastes need to be modified or treated
before being applied for the decontamination of heavy metals [1].
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2. LITERATURE SURVEY
Sawdust obtained from wood industry is an abundant by-product which is easily
available in the countryside at negligible price. An experiment on the efficiency of the
sawdust in removal of Cu and Zn ions was conducted by researchers. Two kinds of sawdust,
poplar and fir wood were treated with NaOH and Na2CO3 solutions and the adsorption
capacities were compared with untreated sawdust. For unmodified sawdust, both types of
woods showed higher uptakes of Cu2+ ions than Zn2+ ions, and adsorption followed Langmuir
isotherm model. Equivalent amounts of adsorption capacities were recorded by both types of
sawdust for Zn and Cu ions, although these two adsorbents have different anatomical
structure and chemical composition. After treating with NaOH, a marked increase in
adsorption capacity was observed for both heavy metal ions, especially for Zn2+ ions (2.5
times for Cu2+ and 15 times for Zn2+). The adsorption capacities shown by Langmuir model
were 6.92 mg/g (poplar sawdust) and 12.70 mg/g (fir sawdust) for Cu, and 15.83 mg/g
(poplar sawdust) and 13.41 mg/g (fir sawdust) for Zn respectively [1].
Fly ash is a by-product of coal burning in different industrial applications. It is
regarded as an irritant responsible for air pollution as well as posing disposal problems.
Firstly, fly ashes are now widely used in the manufacture of cement. Secondly, some research
articles reported that alkaline fly ash can serve as stabilizer or binding reagent for the fixation
of heavy metal and nutrients contained in hazardous wastes and organic wastes. Thirdly,
many researchers have reused or converted fly ashes as adsorbents for wastewater or air
pollution control [5].
The by-product eggshell weighs approximately 10% of the total mass of hen egg,
representing a significant waste from the egg derived products processor because it was
traditionally useless and commonly disposed of in landfills without any pretreatment.
However, the waste management was not a desirable practice in view of the environmental
odor from biodegradation. Because of its high nutrition contents such as calcium,
magnesium, phosphorus, the utilization of this food processing by-product was usually reused
as a fertilizer, soil conditioner or an additive for animal feed. Due to its intrinsic pore
structure in the calcified eggshell and the amount in abundance, it is thus feasible to grind the
eggshell agro waste in the preparation of fine [3].
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Table 1: TYPICAL EFFLUENTS PRODUCED BY COMMERCIAL, INDUSTRIAL,
AND AGRICULTURAL ACTIVITIES AND THEIR CONCERN [2]
Name Use Concern
Arsenic Alloying additives for metals, battery
grids, cable sheaths, boiler tubes.
Carcinogenic and mutagen
sometimes can cause fatigue
and loss of energy and
dermatitis.
Cadmium Bearing and low melting alloys, brazing
alloys, fire protection system, basis of
pigments used in ceramic glazes,
fungicide.
Flammable in powder form,
toxic by inhalation of dust or
fumes, soluble compounds are
highly toxic.
Chromium Alloying and plating element on metal
and plastic substrates for corrosion
resistance, nuclear research, protective
coating for automotive.
Hexavalent Cr compounds are
carcinogenic and corrosive on
tissues, kidney damage.
Lead Storage batteries, gasoline additives,
piping, tank linings, solder and fusible
alloys, ammunition.
Toxic by ingestion or inhalation
of dust or fumes, brain and
kidney damage, birth defects.
Mercury Amalgams, catalyst, electrical apparatus,
cathodes for production of chlorine and
caustic soda, mercury vapor lamps.
Highly toxic by skin absorption
and inhalation of fumes or
vapor, toxic to central nervous
system.
Silver Electronics, xerographic plates, TV
cameras, photocells, magnetic computer
cores, solar batteries, catalyst.
Toxic metal, permanent gray
discoloration of skin, eyes, and
mucous membrane.
Copper Electronics, alloying metal, cables and
wires
Toxic metal, skin diseases,
Williams disease.
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Table 2: TYPICAL DISCHARGE LIMITS FOR TOXIC CONSTITUENTS FOUND IN
SECONDARY EFFLUENTS. [2]
Constituents Daily (µg/L)
Cadmium 1.1
Chromium 11
Copper 4.9
Lead 5.6
Mercury 2.1
Nickel 7.1
Zinc 58
Arsenic 20
Silver 2.3
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3. FUNDAMENTALS OF ADSORPTION
Although adsorption has been used as a physical-chemical process for many years, it is
only over the last four decades that the process has developed to a stage where it is now a
major industrial separation technique. In adsorption, molecules distribute themselves between
two phases, one of which is a solid whilst the other may be a liquid or a gas. Unlike
absorption, in which solute molecules diffuse from the bulk of a gas phase to the bulk of a
liquid phase, in adsorption, molecules diffuse from the bulk of the fluid to the surface of the
solid adsorbent forming a distinct adsorbed phase. Adsorption may be equally effective in
removing trace components from a liquid phase and may be used either to recover the
component or simply to remove a noxious substance from an industrial effluent.
Adsorption occurs when molecules diffusing in the fluid phase are held for a period of
time by forces emanating from an adjacent surface. The surface represents a gross
discontinuity in the structure of the solid, and atoms at the surface have a residue of
molecular forces which are not satisfied by surrounding atoms such as those in the body of
the structure. These residual or van der Waals forces are common to all surfaces and the only
reason why certain solids are designated “adsorbents” is that they can be manufactured in a
highly porous form, giving rise to a large internal surface. In comparison the external surface
makes only a modest contribution to the total, even when the solid is finely divided.
The adsorption which results from the influence of van der Waals forces is essentially
physical in nature. Because the forces are not strong, the adsorption may be easily reversed.
In some systems, additional forces bind absorbed molecules to the solid surface. These are
chemical in nature involving the exchange or sharing of electrons, or possibly molecules
forming atoms or radicals. In such cases the term chemisorption is used to describe the
phenomenon. This is less easily reversed than physical adsorption, and regeneration may be a
problem. Chemisorptio n is restricted to just one layer of molecules on the surface, although
it may be followed by additional layers of physically adsorbed molecules.
When molecules move from a bulk fluid to an adsorbed phase, they lose degrees of
freedom and the free energy is reduced. Adsorption is always accompanied by the liberation
of heat. For physical adsorption, the amount of heat is similar in magnitude to the heat of
condensation. For chemisorption it is greater and of an order of magnitude normally
associated with a chemical reaction. If the heat of adsorption cannot be dispersed by cooling,
the capacity of the adsorbent will be reduced as its temperature increases.
It is often convenient to think of adsorption as occurring in three stages as the adsorbate
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concentration increases. Firstly, a single layer of molecules builds up over the surface of the
solid. This monolayer may be chemisorbed and associated with a change in free energy
which is characteristic of the forces which hold it. As the fluid concentration is further
increased, layers form by physical adsorption and the number of layers which form may be
limited by the size of the pores. Finally, for adsorption from the gas phase, capillary
condensation may occur in which capillaries become filled with condensed adsorbate, and its
partial pressure reaches a critical value relative to the size of the pore.
Although the three stages are described as taking place in sequence, in practice, all three
may be occurring simultaneously in different parts of the adsorbent since conditions are not
uniform throughout. Generally, concentrations are higher at the outer surface of an adsorbent
pellet than in the centre, at least until equilibrium conditions have been established. In
addition, the pore structure will consist of a distribution of pore sizes and the spread of the
distribution depends on the origin of the adsorbent and its conditions of manufacture [9].
3.1. The Nature of Adsorbents
Adsorbents are available as irregular granules, extruded pellets and formed spheres. The
size reflects the need to pack as much surface area as possible into a given volume of bed and
at the same time minimize pressure drop for flow through the bed. Sizes of up to about 6 mm
are common.
To be attractive commercially, an adsorbent should embody a number of features:
(a) It should have a large internal surface area.
(b) The area should be accessible through pores big enough to admit the molecules to be
adsorbed. It is a bonus if the pores are also small enough to exclude molecules which it is
desired not to adsorb.
(c) The adsorbent should be capable of being easily regenerated.
(d) The adsorbent should not age rapidly, that is losing its adsorptive capacity through
continual recycling.
(e) The absorbent should be mechanically strong enough to withstand the bulk handling and
vibration that are feature of any industrial unit [9].
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3.2. TYPES OF ADSORBENTS
Conventional Non conventional
Chemical precipitation Sawdust
Ion exchange Coconut husk
Electro flotation Fly ash
Membrane separation Eggshell
Electro dialysis Rice husk
Reverse osmosis Spent grain
Solvent extraction Weeds
3.3. COMPOSITION OF ADSORBENTS [1]
3.3.1. Sawdust
It is a by-product obtained from wood industry in abundant amount. It mainly consists of
various organic compounds such as lignin, cellulose, hemi cellulose with polyphenolic
groups that could bind heavy metal ions through different mechanisms.
3.3.2 Fly ash
It is a finely divided residue that results from the combustion of pulverized coal and is
transported from the combustion chamber by exhaust gases. Fly ash is basically a mixture of
metallic oxides with silica (44.28% by weight), alumina (28.24% by weight) as its major
constituents. Other constituents of fly ash are iron oxide, magnesia and titanium dioxide.
3.3.3. Eggshell
It is a by-product obtained from poultry. It consist of two regions: the mam-millary matrix
(i.e., eggshell membrane) consisting of interwoven protein fibers and spherical masses, and
the spongy matrix (i.e., calcified eggshell) made of interstitial calcite or calcium carbonate
crystals. The chemical composition (by weight) of by-product eggshell has been reported as
It contains cellulose (32.24%), hemi cellulose (21.34%), lignin (21.44%), mineral ash
(15.05%).
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3.4. Adsorption Isotherms [4]
The study of adsorption isotherm is fundamentally important in the determination of
maximum adsorption capacity of the adsorbent
3.4.1 Langmuir isotherm
The Langmuir isotherm has been used by many researchers to study the adsorption of heavy
metals. The model assumes uniform energies of adsorption onto the surface and no
transmigration of adsorbent in the plane of the surface.
The langmuir isotherm is represented by equation;
Ceb
CebaQe
+=
1
Where Ce = Equilibrium concentration of solution mg/L,
Qe = Amount of solute adsorbed by unit mass of adsorbent mg/g,
a, b = Constants.
3.4.2 Freundlich isotherm
The Freundlich model is an indicator of the extent of heterogenecity of the adsorbent surface.
For this model, the concentration of solute in solution at equilibrium (Ce) and the amount of
solute adsorbed being Qe are connected by the following equation,
bCeaQe =
Where Ce = Equilibrium concentration of solution mg/L,
Qe = Amount of solute adsorbed by unit mass of adsorbent mg/g,
a, b = Constants.
3.5. EQUIPMENT
3.5.1. Packed Column
In general, packed towers are used for bringing two phases in contact with one another and
there will be strong interaction between the fluids. Normally one of the fluids will
preferentially wet the packing and will flow as a film over its surface; the second fluid then
passes through the remaining volume of the column. With gas (or vapor)–liquid systems, the
liquid will normally be the wetting fluid and the gas or vapors will rise through the column
making close contact with the down-flowing liquid and having little direct contact with the
packing elements.
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Since packed columns consist of shaped particles contained within a column, their behavior
will in many ways be similar to that of packed beds. The shapes too are specially designed
to produce good mass transfer characteristics with relatively small pressure gradients.
3.5.2. UV Spectrophotometer
The UV-VIS double beam spectrophotometer provides an advanced optical system coupled
with latest in system design, integrated together with a windows based, user friendly,
validated software for unparalled power and performance. The spectrophotometer
incorporates a large number of utility tools, making it extremely convenient to operate. The
method, data and information banks, an integral part of the software, posses a wealth of
information useful for analyst. Typically, the information included in these banks relate to the
various normal spectra, deviation spectra, compounds, solvents, lambda max, method of
analysis etc. These banks can be upgraded and configured by the user to suit the analysis of
laboratory.
3.5.2.1. Working principle
Spectrophotometer working is based on Beer’s law.
According to Beer’s law,
CkeI
I −=0
Where Io – Incident light intensity on sample,
I – That amount of light intensity that passes through the sample and
strikes the detector,
e – Exponential,
k – Absorption coefficient for the specific sample at specific wavelength,
C – Concentration of sample.
Thus, CkI
I =0
log
The term on the left side of the above equation is equivalent to absorbance (ABS) of a
sample. Therefore,
CkABS =
As can be seen by the above equation, the absorbance of sample is directly proportional to the
sample’s concentration.
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4. EXPERIMENTAL
4.1. Apparatus and Instrumentation
UV-VIS spectrophotometer has been used for determination of copper concentration in
aqueous solution. A priori, absorbance of standard copper solution of concentration 500 mg/L
has been established in order to be able to read the concentration of residual solutions.
All filtrations during this work have been carried out by means of filter millipore- 0.2µm.
4.2. Preparation of Adsorbent
Sawdust obtained from locally used wood, with mean size of 0.331 mm has been used as an
adsorbent for removal copper ions from aqueous solution. The sawdust was washed with
water and sun dried before use.
4.3. Adsorbate Solution
Synthetic aqueous solutions containing copper have been prepared by dissolution of copper
sulphate in locally distilled water.
4.4. Continuous Experiment Procedure
The experiment was carried out in column packed with adsorbent. The column of length 160
cm and 2 cm diameter has used. The column was packed with known dose of adsorbent. The
sample of known concentration was allowed to flow though the column continuously and
sample of unknown concentration was collected at the bottom of column after contact time of
10 min. The supernant is then filtered to remove particulates and used for the analysis. The
metal content was determined by spectrophotometer.
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5. OBSERVATIONS
Wavelength of light intensity for copper = 797 nm.
Concentration of original copper solution = 500 mg/L
Absorbance of original copper solution = 0.054
6. Calculations
Plot of Concentration verses Absorbance
By using linear regression model we find the concentration of unknown sample.
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Table 3: For Coconut husk
Time (min) Absorbance Concentration (mg/l)
10 0.010 65.54
20 0.020 160.84
30 0.025 208.49
40 0.028 237.06
50 0.029 246.61
60 0.029 246.61
70 0.029 246.61
80 0.030 256.14
90 0.032 275.20
100 0.033 284.73
110 0.035 303.79
120 0.038 332.38
130 0.039 341.91
140 0.040 351.44
150 0.042 370.50
160 0.043 380.03
170 0.044 389.56
180 0.045 399.09
190 0.045 399.09
200 0.046 408.62
210 0.048 427.68
220 0.050 446.74
230 0.051 456.27
240 0.052 465.80
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Table 4: For Fly Ash
Time (min) Absorbance Concentration (mg/l)
30 0.018 141.78
60 0.019 151.31
90 0.021 170.37
120 0.023 189.43
150 0.023 189.43
180 0.025 208.49
210 0.028 237.08
240 0.033 284.73
270 0.035 303.79
300 0.037 322.85
330 0.038 332.38
360 0.039 341.91
390 0.041 360.97
420 0.045 399.07
450 0.047 418.17
480 0.049 437.21
510 0.051 456.27
540 0.053 475.33
15
Table 5: For Sawdust
Table 6: Absorbance of Different Samples
Concentration (mg/L) Absorbance
100 0.012
200 0.026
300 0.035
400 0.046
Time (min) Absorbance Concentration (mg/l)
10 0.005 17.89
20 0.006 27.42
30 0.015 113.19
40 0.023 189.43
50 0.026 218.02
60 0.028 237.06
70 0.030 256.14
80 0.030 256.14
90 0.029 246.61
100 0.032 275.2
110 0.035 303.79
120 0.035 303.79
130 0.039 341.91
140 0.043 380.03
150 0.046 408.62
160 0.048 427.68
170 0.051 456.27
180 0.052 465.80
190 0.052 465.80
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7. RESULTS
7.1. Amount of Metal Adsorbed
To find the amount copper adsorbed on the surface of adsorbent, we use Langmuir isotherm
Ceb
CebaQe
+=
1
Where, a = 8.4597 b = 0.0942
For Coconut husk,
Ce = 65.54 mg/L, Qe = 7.28 mg/g of adsorbent.
For Fly ash,
Ce = 141.78 mg/L, Qe = 7.87 mg/g of adsorbent.
For Sawdust,
Ce = 17.89 mg/L, Qe = 5.30 mg/g of adsorbent.
7.2. Percentage Removal
Percentage removal is calculated as,
Where C0 = Initial concentration of metal ions in solution mg/L,
C1 = Concentration of metal ions in filtrate mg/L.
100%0
10 ×−
=C
CCREMOVAL
17
Table 10: Amount of Metal Adsorbed and Percentage Removal for
Coconut Husk
Time (min) Amount adsorbed (mg/g) % removal
10 7.28 86
20 7.93 67
30 8.04 58
40 8.09 52
50 8.11 50
60 8.11 50
70 8.11 50
80 8.12 48
90 8.14 44
100 8.15 43
110 8.17 39
120 8.19 33
130 8.20 31
140 8.21 29
150 8.22 26
160 8.22 24
170 8.23 22
180 8.24 20
190 8.24 18
200 8.24 18
210 8.25 14
220 8.26 10
230 8.26 8
240 8.27 7
18
Table 11: Amount of Metal Adsorbed and Percentage Removal for Fly ash
Time (min) Amount adsorbed mg/g % removal
30 7.87 71
60 7.90 69
90 7.96 66
120 8.01 62
150 8.01 62
180 8.04 58
210 8.09 52
240 8.15 43
270 8.17 39
300 8.19 35
330 8.19 33
360 8.20 31
390 8.21 28
420 8.24 20
450 8.25 16
480 8.25 12
510 8.26 8
540 8.27 5
19
Table 12: Amount of Metal Adsorbed and Percentage Removal for
Sawdust
Time (min) Amount adsorbed mg/g % removal
10 5.30 96
20 6.09 94
30 7.73 77
40 8.01 62
50 8.06 56
60 8.09 52
70 8.12 48
80 8.12 48
90 8.11 50
100 8.14 45
110 8.17 39
120 8.17 39
130 8.20 31
140 8.22 24
150 8.24 18
160 8.25 14
170 8.26 8
180 8.27 7
190 8.27 7
20
7.6. Langmuir and Freundlich Plot for Coconut Husk
21
7.7. Langmuir and Freundlich Plot for Sawdust
22
7.8 Langmuir and Freundlich Plot for Fly Ash
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8. MASS BALANCE FOR SINGLE STAGE BATCH ADSORPTION
PROCESS
Freundlich Isotherm: Herbert Max Finley Freundlich, a German physical chemist,
presented an empirical adsorption isotherm for non ideal sorption on heterogeneous surfaces
as well as multilayer sorption and is expressed by the equation:
Qe = KfCe1/nf (1)
Equation (1) is used for the calculation of residual solute concentration at equilibrium (Ce) at
a given volume of wastewater containing solute particles/quantity of adsorbent (Vo/Xo).
Experimental values Ce and Qe values were compared to calculated ones. Adsorption in a
batch reactor can be considered as a single staged equilibrium operation and it depends on
two basic constraints, that of equilibrium and that of a mass balance. The mass balance for
the sorbate particles is:
VoCo + XoQo = VoCe + XoQe (2)
Co(Co – Ce) = Xo (Qe – Qo) (3)
- Vo/Xo (Ce – Co) = (Qe – Qo) (4)
equation (4) represents the straight line
Y = mX
(Qe – Qo) = -Vo/Xo (Ce – Co) (5)
The line which passes through (Co, Qo) and (Ce, Qe) with slope (-Vo/Xo) is termed the
operation line of this stage. So the single staged batch operation is (Ce versus Qe) and can be
obtained by drawing a operating line and the Freundlich equation respectively. Some of the
important advantages of equation (5) are as follows:
• (Vo/Xo) for a desired purification can be calculated
• (Ce/Qe) values at desired Vo/Xo values can be determined from this figure for a given
initial concentration or feed solute concentration.
24
By mass balance Co = Ce + Cx,e (6)
Where Cx,e is the concentration of solute in the solid phase at equilibrium. Using equation (6), Cx,e can be calculated. If calculation is required Freundlich equation can be directly substituted in equation (6):
-Vo/Xo (Ce – Co) = (KfCe1/nf – Qo) (7)
at time t = 0; Qo = 0; then equation (7) becomes:
-Vo/Xo (Ce – Co) = (KfCe1/nf – 0) (8)
Therefore,
e
nef
CC
CK
X
V f
−=
0
1
0
0 (9)
Vo/Xo can be calculated for desired purification (or) Ce/Cx,e at a given Vo/Xo for a given initial solute feed concentrations.
25
9. ADVANTAGES
1. The efficiencies of various non-conventional adsorbents towards adsorbate removal vary
generally between 50% and 90% depending on the characteristics and particle size of the
adsorbent, and the characteristics and the concentration of the adsorbate, etc. Hence, low-cost
adsorbents can be employed efficiently in removal of heavy metals.
2. Non-conventional adsorbents are much cheaper relative to conventional adsorbents, and
when readily available locally lead to much reduced transportation cost.
3. Non-conventional adsorbents require simple alkali/acid treatment for the removal of lignin
before application in order to increase their efficiency.
4. Non-conventional adsorbents require less maintenance and supervision.
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10. CONCLUSION
An application of low cost adsorbents like coconut husk, sawdust, fly ash, eggshell has been
investigated for removal of Cu (ΙΙ) from aqueous solutions. The following conclusions can be
drawn:
1. These adsorbents can be successfully used for Cu (ΙΙ) removal.
2. The removal is highly dependant on initial concentration of Cu (ΙΙ) in solution and
higher removal has been observed in lower concentration ranges.
3. Effect of different important parameters on the removal of Cu (ΙΙ) has been discussed.
The data obtained can serve as background data for designing treatment plants of Cu (ΙΙ)
wastewater economically. Though a detailed cost analysis is yet to be carried out, process of
removal seems to be economically viable for developing countries like India.
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11. REFERENCES
1. W S Wan Ngah & M A K M Hanafiah, “Removal of heavy metal ions from wastewater by
using chemically modified plant waste as an adsorbent- A review”, Bioresource technology,
