Removal of Bi (III) with adsorption technique using...

CHAPTER 4

Removal of Bi (III) with adsorption technique using coconut shell activated

carbon as a low cost adsorbent

*This work has been communicated to “Chinese Journal of

Chemical Engineering” (Revised)

Cocos nucifera (Coconut)

Coconut

Coconut Shells

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REMOVAL OF DYES AND HEAVY TOXIC METALS WITH ADSORPTION TECHNIQUE USING LOW COST

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4.1 INTRODUCTION

The level of natural resources of bismuth is about 2 X 10-5 %. The world

production is about 5000 tones per year. Much of the bismuth produced in the U.S.

is obtained as by-product in refining lead, copper, tin, silver and gold ores.

Bismuth and its compounds are used in semiconductor, cosmetics preparation,

alloys and metallurgical additives also in the preparation and recycling of uranium

nuclear fuels [1, 2]. The inorganic bismuth salts are used for medical treatment.

The patients suffering from gastric disorder leaves 0.5 to 1 g pure bismuth per day.

Bismuth contamination is becoming an environmental problem [3]. Bismuth

containing compounds have been used for different medicinal purposes, especially

for the treatment of syphilis, gastritis, and ulcer. As the use of bismuth in

medicines is increasing, it has spread in the environment, and the exposure of

organisms to bismuth has increased. However, a number of toxic effects in

humans have been attributed to bismuth compounds such as nephropathy,

osteoarthropathy, hepatitis, and neuropathology [4]. Therefore the removal of

bismuth is essential for the elimination of bismuth contamination.

The methods available for the removal of heavy metals from aqueous

solution are electrochemical precipitation, ion exchange, ultrafiltration, reverse

osmosis, adsorption. Amongst all, adsorption technique is feasible option, both

technically and economically [5]. Especially, if the adsorbent is inexpensive and

readily available then adsorption process provides an attractive alternative.

Activated carbons are effective adsorbents for many pollutant compounds

(organic, inorganic, and biological) of concern in water and waste water treatment.

The major use of activated carbon is in solution purification and for the removal of

taste, color, odors and other objectionable impurities from liquids, water supplies

and vegetables and animal oils [6]. Activated charcoal derived from coconut shell

was found to be a good non-conventional adsorbent used for the removal of heavy

metals like, Cd(II) [7], Pb(II) [8] as well as cationic dye [9] etc. from aqueous

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solution. The green coconut shell was used without treatment for separation of

Cr(III), Cr(VI), As(V) and Cd(II) [10]. Coconut shell as well as coconut husk was

reported for removal of Cr(VI), Zn(II) and Ni(II) [11].

4.2 LITERATURE SURVEY OF METHODS FOR REMOVAL OF Bi(III)

Now a days it is well known, that the abundance increment in the world

population as well as the use of amenities with various technology which gave rise

to need of more production of required things is responsible to expanded pollution

by various pollutants. Amongst the various pollutants, pollution due to bismuth is

getting increased due to enhanced applications of bismuth. The several techniques

reported for removing Bi(III) from water include liquid-liquid extraction [12],

solid phase extraction [13], flotation [14] and adsorption [15]. The experimental

studies on Bi(III) adsorption by using resins [16] and the electrodes surface of

metals, such as Pt [17, 18], Au [19] and Si [20] had been reported. There are very

few reports on bismuth removal using adsorption [15].

The liquid-liquid extraction and recovery of Bi(III) from succinate solution

using 2-octylaminopyridine (2-OAP) as an extractant was reported. The

quantitative extraction of Bi(III) occurs from 0.004 to 0.007M sodium succinate

solution at pH 2.5-10 using 0.036 M 2-OAP in chloroform [1]. The N-n-

hexylaniline in xylene was used for the extraction separation of Bi(III) from

thiocyanate and sulphuric acid media. Bi(III) was extracted quantitatively with 10

mL 1.5% N-n-hexylaniline in xylene. It was stripped from the organic phase with

sodium acetate buffer [12]. In liquid-liquid extraction, required reagent is not

economical as well as the systems are not ecofriendly with respect to use of the

solvent.

The solid phase extraction was performed with 6 mL syringe cartridges

containing 500 mg octadecyl bonded silica (40 µm particles) modified with

cyanex 301 from Varian. The modified cartridge was preconditioned by passing a

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10 mL portion of 0.1M HCl solution, then 25 mL of the sample solution

containing 1 g of Bi(III) ions and 0.1M HCl, was passed through the cartridge by

applying a slight vacuum. The cartridge was dried completely by passing an air

through it. The extracted Bi(III) was stripped from the cartridge using appropriate

amounts of suitable mineral acids [21]. In the other report, the syringe was filled

with 0.5 g of silica gel modified with 3-aminopropyltriethoxysilane and in order to

retain the analyte elements, 5 mL of sample solution (pH 5) was drawn into the

syringe to 15s and discharged again in 15s. Then, 2.0 M HCl, as the eluent, was

drawn into the syringe and ejected back to desorb the analyte elements [22]. In

another case sample solution treated with and without ammonium pyrolidine

dithiocarbamate was drawn into the syringe filled with chromosorb-107. Analyte

elements adsorbed on the resin were quantitatively eluted with 3.0 M of HNO3

[13].

Ion flotation involves the removal of surface-inactive ions (colligend) from

aqueous solutions by adding surfactants which act as collectors. Precipitate

flotation is a foam separation process used to remove surface inactive substances

from aqueous dispersions. The component to be removed is precipitated before the

addition of a surfactant (collector). Flotation is a simple and quantitative technique

for the separation of Cd(II), Hg(II), Bi(III) and Sb(III). It depends on the formation

of metal iodide anion [MI4] (n-4)-, the combination with Fe(II)tris(1,10-

phenanthroline) reagent (I), and flotation of the resulting chemical associate with

oleic acid surfactant. The parameters influencing the flotation process were pH of

solution, iodide, Fe(II)tris(1,10-phenanthroline) and surfactant concentrations,

temperature and foreign ions [14]. In another case Bi(III) could be removed from a

water insoluble ternary association complex BiI4-·TBAB+ with tetrabutyl

ammonium bromide (TBAB) and KI in water solution. When the concentrations of

tetrabutyl ammonium bromide and KI in solution were 5.0×10-4 mol/dm3 and

3.0×10-3 mol/dm3 at pH 3.0, Bi(III) could be quantitatively separated from

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Mo(VI), Ga(III), Co(II), Mn(II), Zn(II), Rh(II), Al(III), Cr(III), V(V), Ni(II),

Sn(IV), W(VI) and Fe(II) [23].

Separations with the anion exchange resin Deacidite FF have proved

exceedingly useful for the separation of macro amounts of bismuth from small

amounts of thorium and uranium, without any significant losses of these latter

constituents. The use of ion-exchange resins, however, introduces problems in the

subsequent determination of the separated elements and the frequent need for the

removal of organic matter taken into solution from the resin, since the introduction

of a wet oxidation step considerably extends the time needed for the analysis [24].

Traces and larger amounts of bismuth (up to 50 mg) can be separated from gram

amounts of thallium, mercury, gold and platinum (up to 5 g) by sorption from a

mixture of 0.1 M hydrochloric acid and 0.4 M nitric acid on a column containing

3 g (8.1 mL) of AGMP-50, a macroporous cation-exchange resin. This resin

retains bismuth (III) much more strongly than does the usual microporous resin

(styrene-DVB with 8% cross-linkage) [25]. A method for the determination of

trace bismuth in lead using a high-performance chelating ion chromatography

system is described where chelating column was prepared from a neutral

hypercrosslinked polystyrene resin, MN200 (Purolite) [26].

Anodic stripping differential pulse polarographic method has been

developed for the determination of trace amount of bismuth in various samples

after adsorption of its 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex

on amberlite XAD-2 resin in the pH range of 2.0–3.0. The retained analyte on the

resin recovered with 10.0 mL of 2 M hydrochloric acid and bismuth is determined

by anodic stripping differential pulse polarography [27]. The determination of

trace bismuth is based on the adsorption of bismuth–bromopyrogallol red at a

carbon paste electrode. The overall analysis involved a three-step procedure:

accumulation, reduction, and anodic stripping [28].

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Impregnated resins prepared by the immobilization of an ionic liquid (IL,

Cyphos IL-101, tetradecyl(trihexyl)phosphonium chloride) into a composite

biopolymer matrix (made of gelatin and alginate) have been tested for recovery of

Bi(III) from acidic solutions. Maximum sorption capacity reached to 110–130

mg/g in 1 M HCl solutions [29]. An epoxy-group containing vinyl monomer was

appended uniformly across the porous sheet. Subsequently, a 1-octadecyl group

(C18H37) was introduced into the polymer chain grafted on the porous sheet. Tri-n-

octylphosphine oxide (TOPO), which contains octyl groups, was deposited on the

1-octadecyl group. The resultant TOPO-modified porous sheet had a higher

binding rate and a higher equilibrium binding capacity for bismuth than

conventional TOPO-modified beads [30].

The extraction chromatographic separation of Bi(III) was reported with

Versatic 10 coated on silanized silica gel. The result showed that the pH of

solution, influent volume, flow-rate and solution temperature would affect the

sorption of Bi(III). The extraction system has got good values of exchange

capacity (1.42 meq. of H+/g of dry exchanger at 298 K), breakthrough capacity

(19.75 mg/g at pH 5.5) and column efficiencies (300) with respect to Bi(III) [31].

Bismuth is extracted from 0.0l M citric acid at pH 3.0 with aliquat 3363 coated on

a silica gel column, by extraction chromatography. It was then stripped with 0.l M

sulphuric acid and determined spectrophotometrically [32].

A cloud point extraction method was used for separation and

electrothermal atomic absorption spectrometric method was used for determining

bismuth. The aqueous analyte was acidified with sulfuric acid (pH 3.0–3.5). Triton

X-114 was added as a surfactant and dithizone was used as a complexing agent.

[33]. A cloud point extraction method was used for the preconcentration of ultra-

trace bismuth in human serum prior to its determination by inductively coupled

plasma optical emission spectrometry. The method was based on the complex of

Bi(III) with 8-hydroxyquinoline and Triton X-114 used as non-ionic surfactant.

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The main factors affecting cloud point extraction efficiency were pH of solution,

concentration of complexing agent, concentration of non-ionic surfactant,

equilibration temperature and time [34].

The reversed-phase chromatography combines the selectivity of liquid-

liquid extraction and the advantages of chromatographic operation. In general, the

efficiency of reversed phase chromatographic separation depends on many

interrelated parameters including the particle size of the support, surface area, flow

characteristics and stationary phase. Polyurethane foam was used in a column

technique, where separation of Pd(II), Bi(III) and Ni(II) in the tributyl

phosphatethiourea-perchloric acid was achieved [35]. Trans-l,2-cyclohexane

diaminetetra-acetic acid (DCTA) chelates of bismuth(III), iron(III) and copper(II)

have been separated by two techniques using reversed-phase paired-ion

chromatography. The chelates in aqueous solution were separated within 20 min

on a 6.0 x 300 mm ERC-ODS column with 10-2 M tetrabutylammonium ion

(TBA+) in methanol-water mixture (45:55 v/v) as eluent. In the other, the metal

ions in aqueous solution were separated within 10 min by direct injection into an

ERGODS column with 10-2 M TBA+/10-3 M DCTA in methanol-water mixture

(40:60 v/v) as eluent [36].

A supported liquid membrane (SLM) using neutral extractants such as tri-n

octylphosphine oxide (Cyanex 921) is able to recover Bi(III) contained in highly

acidic solutions (from H2SO4/HCl media) [37]. The seperaration and recovery of

bismuth from a bismuth glance through leaching, purification and electro winning

from chloride solution is reported. A maximum current efficiency of >97% was

attained with an composition of 70 g/dm3 Bi, 25 g/dm3 NaCl, 4.5mol/dm3 HCl and

an analyte composition of 20 g/dm3 NaOH at 328 K and a cathode current density

of 200 A/m2 [38].

The metal surface electrodes were reported in last decade for adsorption of

bismuth. The growth of bismuth single crystals was studied when bismuth was

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deposited with a rate of about 6 monolayers per minute on the tungsten substrate

and kept at 470 K [39]. Co-adsorption of bismuth and hydrogen on the Si surface

was investigated. The formation of the morphology and electronic structure of the

Bi/H/Si interface at co-adsorption of bismuth and hydrogen on the Si surface was

investigated by scanning tunneling microscopy (STM), ultraviolet photoelectron

spectroscopy (UPS), low energy electron diffraction (LEED) and Auger electron

spectroscopy (AES) [40].

Some reports give information regarding the use of single crystal surface of

bismuth to adsorb the various organic compounds as well as halides like 2-methyl-

2-butanol [41], dodecyl sulfate anions on bismuth (011¯) [42], uracil [43], C1¯

and Br¯ ions on the (111) plane of a bismuth single crystal from solutions in 2-

propanol [44]. The adsorption of D-ribose [45] and the adsorption of I¯ ions on the

(111), (001) and (011) planes of a bismuth single crystal electrode from solutions

in ethanol has been investigated by means of differential capacity and electrode

charge measurements [46].

In present work, the adsorption study of bismuth on activated carbon

developed from coconut shell was carried out. The influence of adsorption time,

adsorbent dosage, shaking speed etc. has been studied. From experimental data the

isotherm models, kinetic model as well as the thermodynamic parameters has been

investigated for adsorption of Bi(III) on low cost, easily and abundantly available

adsorbent. The coconut shell activated carbon (CSAC) has good adsorption

capacity within a short period so it would be a good adsorbent.

4.3 EXPERIMENTAL

4.3.1 Preparation of materials

All chemicals were purchased from S. D. Fine Chem. Ltd. India. The

standard solution of 1 mg/mL Bi(III) was prepared from bismuth nitrate. The

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required solutions were prepared with dilutions from stock solution as per

necessity.

The adsorbent was prepared from dry coconut shell. The coconut was

collected from local market. To develop the activated carbon, the preparation

method was followed as given in the chapter 2 (2.3.1) using H2SO4 as

impregnating agent and sieved through BSS-25.

4.3.2 Characterization of adsorbent

The developed adsorbent was characterized with Fourier Transform Infra

Red Spectroscopy (FTIR) (Perkin Elmer Spectrum 100), Scanning Electron

Microscopy (SEM) (JEOL – JSM 6360 unit, Japan) and C, H, N, S analyzer (Euro

EA, Elemental Analyzer). The FTIR spectrum shows the peaks for functional

groups such as, O-H stretch, C-H, C=O stretch, C=C, SO2 and C-O stretch

respectively 3310.05, 2899.46, 1703.10, 1608.48, 1167.01, 1034.86 cm-1 values

(Fig. 4.1). For the better adsorption porous nature was required and it was

confirmed with SEM (Fig. 4.2). The elemental analysis reveals the presence of

carbon as the major quantitative element. The percentage amount of elements and

physical properties have also been investigated which are given in Table 4.1.

4.3.3 Batch adsorption experiment

The batch adsorption experiments were carried out by using orbital shaker

with Erlenmeyer flasks. The agitations were conducted at constant temperature of

299 ± 2 K for predetermined period. Adsorption study had been done with varying

the variables like initial concentration of metal ion, agitation period and speed etc.

The metal ion solution was maintained acidic through out the study with pH 2,

considering the fact that Bi(III) precipitates at pH values higher than 2.5 in

aqueous solution [8], the initial pH of each solution was adjusted to 2.0 with dilute

HNO3 or NaOH. The concentrations of Bi(III) in residual solutions were analyzed

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spectrophotometrically with xylenol orange as chromogenic reagent ( λmax =545

nm) (Elico SL 171) [47] and confirmed by Atomic Absorption Spectroscopy

(Perkin Elmer, AAnalyzer 300). The initial concentration of Bi(III) was varied

from 250 to 1000 mg/dm3 at constant adsorbent dose of 700 mg and adsorbent

mass was varied from 100 to 700 mg at constant 250 mg/dm3 of Bi(III). The

shaking period was varied from 15 to 300 min and the kinetic study was carried

out. For the thermodynamic study temperature was varied from 303 to 323 K. The

equilibrium adsorption capacity was evaluated using the formula given in chapter

2 (2.3.3).

4.4 RESULT AND DISCUSSION

4.4.1 Effect of time

From the study of effect of agitation time on the adsorption of Bi(III), it is

evident that time has a significant influence. The amount of adsorption of Bi(III)

was measured at different time intervals (Table 4.2). At the equilibrium time of

240 min, the Bi(III) adsorption was investigated to be 98.72% with initial

concentration of Bi(III) 250 mg/dm3 and other conditions like temperature,

agitation speed etc. were kept constant. Initially the rate of adsorption was very

fast, in 15 min the adsorption was 38.88% and in 90 min adsorption increases up

to 72.26%. Then after 240 min the adsorption of Bi(III) was found to be 98.72%

which remains constant thereafter. This may be due to availability of the all active

sites of adsorbent at the initial stage so rapid adsorption was observed and as the

time increased the repulsive forces increased due to adsorbed adsorbate. The

significant amount of 17.62 mg/g was adsorbed at 240 min which remained steady

for further increase in time (Fig. 4.3), so for further study 240 min time was kept

as fixed time.

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4.4.2 Effect of initial concentration of Bi(III)

Removal of Bi(III) was investigated with 250 mg/dm3 of Bi(III) for 240 min

agitation. As the initial concentration of Bi(III) was increased from 250 to 1000

mg/dm3 and the amount adsorbed was increased from 17.62 to 53.47 mg/g (Fig.

4.4, Table 4.3). The pH, temperatures as well as other conditions were kept

constant through out the study.

The removal of Bi(III) was found to be dependent on the initial

concentration, the amount adsorbed increased with increase in initial

concentration. Further, the adsorption was rapid in the early stages and then attains

an asymptotic value for larger adsorption time. The percentage removal of Bi(III)

decreases from 98.72 to 72.77% with an increase in initial Bi(III) concentration. It

may be due to an increase in the number of Bi(III) ions for the fixed amount of

CSAC. The amount of Bi(III) adsorbed per unit mass of activated carbon increases

with increase in Bi(III) concentration, this is due to the complete utilization of

adsorbent surface and active sites available which was not possible in low

concentration.

4.4.3 Effect of adsorbent dosage

The effect of adsorbent dosage was presented in Fig. 4.5 (Table 4.4) which

clearly indicates that the adsorption was quantitative with 700 mg CSAC dosage.

The study was carried out with 100 to 700 mg amount of adsorbent dosage with

250 mg/dm3 Bi(III) concentration and agitated for 240 min while other conditions

were kept constant. At the equilibrium 17.62 mg/g amount of Bi(III) was adsorbed

with 98.72 % maximum adsorption. As illustrated in Fig. 4.5, as the adsorbent

dose was increased from 100 to 700 mg the amount adsorbed and percentage

removal of Bi(III) was increased; this is due to increase in contact surface of

adsorbent particles and adsorption sites.

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4.4.4 Effect of agitation speed

The study was carried out by using orbital shaker under the controlled

temperature at 299 ± 2 K. The agitation speed for the Bi(III) was optimized by

varying rpm from 50 rpm to 200 rpm (Fig. 4.6, Table 4.5) when the concentration

of Bi(III) was 250 mg/dm3 and other conditions were constant. The removal of

Bi(III) became more quantitative with increase in rpm from 50 to 160 rpm with

98.72 % removal and it remained steady further, so 160 rpm was used throughout

study. At 50 rpm, the adsorption capacity was 12.81 mg/g and at 160 rpm it was

17.62 mg/g which was significant and remained constant further. The results show

that the speed of interaction played vital role and the contact between adsorbent

and adsorbate was significant at higher speed.

4.4.5 Adsorption isotherm

An adsorption isotherm, which describes the relation between the activity

of the adsorbent and the quantity of adsorbate on the surface at constant

temperature, is usually employed to describe adsorption. The L-shaped isotherm is

characterized by decreasing slope, as concentration of adsorbate increases since

vacant adsorption sites were decreased as the adsorbent gets covered. Such

adsorption behavior could be explained by the high affinity of the adsorbent for

the adsorbate at low concentrations, which then decreases as concentration

increases [48].

A variety of isotherm equations have been in use, some of which have a

theoretical foundation and some being of mere empirical nature. The adsorption

isotherm of Bi(III) adsorption on CSAC adsorbent is given in Fig. 4.7 (Table 4.6).

The Langmuir and Freundlich isotherm models were used for further study.

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4.4.6 Langmuir isotherm

The Langmuir model is probably the best known and most widely applied

adsorption isotherm. This model supposes a monolayer adsorption with a

homogeneous distribution of adsorption sites and adsorption energies, without

interactions between the adsorbed molecules. It has produced good agreement

with a wide variety of experimental data as discussed in chapter 2.

Further, the essential characteristics of the Langmuir isotherm can be

described by a separation factor or also called as dimensionless equilibrium

parameter, RL. In the present study, the computed values of RL are found to be

fraction as in the range of 0 to 1, indicating that the adsorption process is favorable

for the removal of Bi(III) ion by using CSAC adsorbent.

The adsorption of Bi(III) on CSAC follows the Langmuir isotherm model

for metal adsorption. For the experiment, the adsorbent dose was maintained 700

mg while the other conditions were kept constant. The plot of Langmuir isotherm

is shown in Fig. 4.8 (Table 4.7). The values of qm and KL have been evaluated

from the plot and results are given in Table 4.8. There was more correlation

between qm calculated value 53.47 mg/g and qm experimental value 54.35 mg/g.

The dimensionless parameter RL between 0.0305 to 0.7118 is consistent with the

favorable adsorption. The high value of correlation coefficient R2 indicates a good

agreement between the parameters and confirms the monolayer adsorption of

Bi(III) on the CSAC surface.

4.4.7 Freundlich isotherm

The Freundlich empirical model can be applied to non-ideal sorption on

heterogeneous surfaces as well as multilayer sorption which is discussed in

chapter 2 (2.4.8).

The values of Kf and n can be calculated from the intercept and slope (Fig.

4.9, Table 4.9) and presented in Table 4.10. The results showed that the adsorption

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fits better in the Langmuir equation. The equilibrium adsorption capacity

investigated from this isotherm which was found to be 17.62 mg/g while

experimental value was 13.41 mg/g, which was not good agreed.

4.4.8 Adsorption kinetics

Kinetics of sorption describes the solute uptake rate, which in turn governs

the residence time of sorption reaction. It is one of the important characteristics in

defining the efficiency of adsorption. The pseudo-first order equation (Lagergren

Equation) as given in chapter 2 (2.4.9) is applied here also. The rate constant k1 is

for the pseudo-first order adsorption process. The plot of log (qe - qt) vs. t (Fig.

4.10, Table 4.11) gives a linear relationship, from which k1 and qe can be

determined by using the slope and intercept of the plot, respectively.

Lagergren plot was studied with the adsorption of Bi(III) by CSAC dosage

of 700 mg with 250 mg/dm3 concentration of Bi(III) ion. At constant temperature

the Bi(III) was agitated with fixed 50 mL quantity and 160 rpm. The study was

made from 0 min to 240 min and removal was observed. The k1 and qe value for

the initial concentration of 250 mg/dm3 are found to be 0.66x10−3 min−1 and 16.17

mg/g. The true value of qe obtained from experiments was 17.78 mg/g. The

correlation coefficients for the pseudo first order kinetic model obtained at all the

studied concentrations were low.

The pseudo-second order adsorption kinetic rate equation was applied as

discussed in chapter 2 (2.4.9). The rate constant k2 (g mg-1min-1) of pseudo

second-order adsorption was determined from the plot of t/qt vs. t (Fig. 4.11, Table

4.12). The values obtained from graph for pseudo-first and pseudo-second order

models are given in Table 4.13. The results found that pseudo-second order was

more followed than the pseudo first order.

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4.4.9 Intraparticle diffusion study

The most commonly used technique for identifying the mechanism

involved in the sorption process is by fitting the experimental data in an

intraparticle diffusion plot. In intraparticle diffusion model, a good fit to the

experimental data reveals that the sorption rate is governed by intraparticle

diffusion and the intraparticle diffusion process is the rate-limiting step.

The kid (mg/g min1/2) value can be obtained from the slope of the plot of qt

(mg/g) versus t1/2 for bismuth ion from Fig. 4.12 (Table 4.14). The slope of the

linear portion of the plot has been defined as the intraparticle diffusion parameter

kid (mg/g min1/2). On the other hand, the intercept of the plot reflects the boundary

layer effect. The larger the intercept, greater is the contribution of the surface

adsorption in the rate limiting step. Higher values of the intraparticle parameters

illustrate an enhancement in the rate of adsorption [49]. However, these plots

indicated that the intraparticle diffusion was not the only rate controlling step

because it did not pass through the origin. The rate constant of intraparticle

diffusion is shown in Table 4.15. The intraparticle diffusion process is controlled

by the diffusion of ions within the adsorbent.

4.4.10 Effect of temperature

The adsorption of Bi(III) on CSAC at different temperatures from 303 to

323 K is shown in Fig. 4.13 (Table 4.16), the adsorption capacity increased when

the temperature was increased. The adsorption capacity increased from 54.90 to

59.09 mg/g for the initial concentration of 1000 mg/dm3 at pH 2.0. The increase in

adsorption capacity was due to the creation of active sites at higher temperature.

The thermodynamic parameters such as free energy (ΔG°) (kJ/mol),

enthalpy (ΔH°) (kJ/mol) and entropy (ΔS°) (J/k /mol) for adsorption of Bi(III) on

CSAC were determined. The ∆H○ and ∆S○ were obtained from the slope and

intercept of the Van’t Hoff’s plot of ln Kc vs. 1/T as shown in Fig. 4.14, Table

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4.17. Positive value of ΔH○ indicates that the adsorption process is endothermic.

The negative values of ΔG○ (Table 4.18) reflect the feasibility of the process and

the values become more negative with increase in temperature as well as it shows

that, the adsorption is highly favorable and spontaneous. The positive values of

standard ΔS° entropy (Table 4.18) show the increased disorder and randomness at

the solid solution interface of bismuth ion with CSAC. The enhancement of

adsorption capacity of the activated carbon at higher temperatures was attributed

to the enlargement of pore size and activation of the adsorbent surface. The

enrichment in the adsorption capacity may be due to the chemical interaction

between adsorbates and adsorbent, creation of some new adsorption sites or the

increased rate of intraparticle diffusion of Bi(III) ions into the pores of the

adsorbent at higher temperatures [50].

4.5 CONCLUSION

1) The adsorbent could be easily prepared from dry coconut shell which is

abundantly available as waste all over. It has developed as porous, effective

and economically affordable activated carbon which showed the maximum

percentage removal of Bi(III) i.e. 98.72 %.

2) The formation was confirmed with various characterizations like C, H, N, S

analyzer, SEM, FTIR and other properties.

3) This developed activated carbon is having the high capacity to adsorb Bi(III)

ions from aqueous solution with amount adsorbed from 17.62 mg/g to 53.47

mg/g with increase in the initial concentration up to 1000 mg/dm3 and the

required period was only 240 min.

4) The adsorption isotherm was followed with L shaped curve which indicate

the competition between adsorbent and adsorbate was less, so that the

adsorption was good.

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5) The isotherm models such as Langmuir and Freundlich were also studied,

amongst them Langmuir equation shows more applicability to the

experimental data than Freundlich isotherm; as Langmuir isotherm gives

maximum adsorption capacity 54.35 mg/g.

6) The rate of adsorption was also investigated with kinetic study and it was

found that the experimental data fits better in pseudo second order than

pseudo first order with 0.978 as regression factor.

7) The adsorption was feasible, spontaneous and endothermic, which was

confirmed by the evaluation of thermodynamic parameters viz. ∆H○, ΔG○ and

∆S○.

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Table 4.1

Elemental analysis and properties of CSAC

Property Result

Ash content 12.62%

Bulk density 0.7685 gm/ cm3

Moisture content 6.75%

Carbon 59.23%

Hydrogen 3.41%

Sulphur 3.84%

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Table 4.2

Effect of time on removal, % and amount adsorbed mg/g of adsorption of Bi(III),

on CSAC.

Bi(III) =250 mg/g, T= 299 ± 2 K, CSAC=700 mg, agitation speed= 160 rpm,

pH=2

Time, min Amount adsorbed, qt mg/g Removal of Bi(III), %

15 6.94 38.88

30 10.41 58.21

60 11.48 64.32

90 12.90 72.26

120 13.81 77.32

150 15.18 85.01

180 16.60 92.96

210 17.45 97.76

240 17.62 98.72

270 17.62 98.72

300 17.62 98.72

Chapter 4


ADSORBENTS

197

Table 4.3

Effect of initial concentration of Bi(III) on amount adsorbed mg/g and removal, %

on CSAC

Time= 240 min, T= 299 ± 2 K, CSAC=700 mg, agitation speed= 160 rpm, pH=2

Initial conc. Bi(III)

mg/dm3

Amount adsorbed,

q mg/g

Removal of Bi(III), %

250 17.62 98.72

300 20.95 97.73

400 27.77 97.21

500 33.72 94.42

600 39.33 91.79

700 45.72 91.44

800 49.68 86.95

900 52.90 82.29

1000 53.47 74.86

Chapter 4


ADSORBENTS

198

Table 4.4

Effect of adsorbent dosage on removal, % and amount adsorbed, mg/g of Bi(III)

Bi(III) = 250 mg/dm3, Time= 240 min, T= 299 ± 2 K, agitation speed= 160 rpm,

pH=2

CSAC mg Amount adsorbed,

q mg/g

Removal of Bi(III), %

100 13.86 11.09

200 14.32 22.91

300 14.57 34.97

400 15.72 50.29

500 16.69 66.52

600 17.31 83.09

650 17.56 92.34

700 17.62 98.72

Chapter 4


ADSORBENTS

199

Table 4.5

Effect of agitation speed on removal, % and amount adsorbed, mg/g of Bi(III)

Bi(III)= 250 mg/g, Time= 240 min, T= 299 ± 2 K, CSAC =700 mg, pH=2

Agitation speed, rpm Amount adsorbed, q mg/g Removal of Bi(III), %

50 12.81 71.72

70 13.45 75.32

100 14.41 80.68

120 16.68 94.40

140 17.50 98.00

160 17.62 98.72

180 17.62 98.72

200 17.62 98.72

Chapter 4


ADSORBENTS

200

Table 4.6

Adsorption isotherm of Bi(III) adsorption on CSAC


Ce q

3.20 17.62

6.80 20.95

11.15 27.77

27.92 33.72

49.27 39.33

59.89 45.72

104.42 49.68

159.44 52.90

251.42 53.47

Chapter 4


ADSORBENTS

201

Table 4.7

Langmuir isotherm for adsorption of Bi(III) on CSAC


Ce Ce/q

3.20 0.1816

6.80 0.3246

11.15 0.4015

27.92 0.8280

49.27 1.2527

59.89 1.3099

104.42 2.1019

159.44 3.0140

251.42 4.7021

Table 4.8

Langmuir isotherm constant for adsorption of Bi(III) on CSAC

qm (mg/g)

KL(1/mg)

R2

54.350

0.1265

0.995

Chapter 4


ADSORBENTS

202

Table 4.9

Freundlich adsorption isotherm for adsorption of Bi(III) on CSAC


log Ce log qe

0.5052 1.2461

0.8325 1.3212

1.0473 1.4436

1.4460 1.5279

1.6926 1.5947

1.7774 1.6601

2.0188 1.6962

2.2026 1.7235

2.4004 1.7282

Table 4.10

Freundlich constant for adsorption of Bi(III) on CSAC

Kf

n

R2

13.41

3.669

0.969

Chapter 4


ADSORBENTS

203

Table 4.11

Pseudo first order model for adsorption of Bi(III) on CSAC

Bi(III) =250 mg/dm3, T= 299 ± 2 K, CSAC=700 mg, agitation speed= 160 rpm,

pH=2

t min log (qe-qt)

0 1.2500

15 1.0350

30 0.08675

60 0.7994

90 0.6889

120 0.6628

150 0.4150

180 0.0719

210 -0.4815

Chapter 4


ADSORBENTS

204

Table 4.12

Pseudo second order model for adsorption of Bi(III) on CSAC


pH=2

t t/qt

0 0

15 2.16

30 2.88

60 5.23

90 6.98

120 8.69

150 9.69

180 10.85

210 12.04

240 13.62

Table 4.13

Kinetic parameters for the adsorption of Bi(III) on CSAC

Pseudo first order Pseudo second order

qe exp.

(mg/g)

k1x10–3

(min–1)

qe calc.

(mg/g)

R2 k2 x10–3 qe calc.

(mg/g)

R2

17.62

0.66

16.17

0.869

2.159

18.62

0.978

Chapter 4


ADSORBENTS

205

Table 4.14

Intraparticle diffusion for the adsorption of Bi(III) on CSAC


pH=2

t1/2 qt

3.873 6.94

5.477 10.41

7.746 11.48

9.487 12.90

10.955 13.81

12.248 15.18

13.417 16.60

14.491 17.45

15.492 17.62

Table 4.15

Study of intraparticle diffusion for adsorption of Bi(III) on CSAC

kid

(mg g−1min−1)

R2

0.880

0.976

Chapter 4


ADSORBENTS

206

Table 4.16

Effect of temperature on amount of Bi(III) adsorbed on CSAC

Bi(III) = 1000 mg/dm3, Time= 240 min, CSAC=700 mg, agitation speed = 160 rpm, pH=2

T K Amount adsorbed, q mg/g

303 54.90

308 56.74

313 57.83

318 58.62

323 59.09

Chapter 4


ADSORBENTS

207

Table 4.17

Van't Hoff plot for removal of Bi(III) on WASAC

Bi(III) = 1000 mg/dm3, Time= 240 min, CSAC=700 mg, agitation speed= 160 rpm, pH=2

1/T lnKc

0.00330 1.1232

0.00324 1.1560

0.00319 1.1751

0.00314 1.1886

0.00309 1.1967

Table 4.18

Thermodynamic parameters for adsorption of Bi(III) on CSAC

T K ΔG○ kJ/mol ∆H○ kJ/mol ∆S○ J/mol k

303 -2.830

0.348

2.279

308 -2.960

313 -3.058

318 -3.143

323 -3.214

Chapter 4


ADSORBENTS

208

Fig. 4.1

FTIR spectrum of CSAC

4000 3500 3000 2500 2000 1500 1000 50080

90

100

110

120

130

140

150

1034.86

1167.01

1608.48

1703.10

2899.463310.05

Tra

nsm

issi

on (

%)

Wavenumber (cm-1)

Chapter 4


ADSORBENTS

209

Fig. 4.2(a)

SEM image of CSAC

Fig. 4.2 (b)

SEM image of CSAC

Chapter 4


ADSORBENTS

210

0

20

40

60

80

100

0 100 200 300

Time, min

Re

mo

va

l of

Bi(

III),

%

0

4

8

12

16

20

Am

ou

nt

ad

so

rbe

d o

f B

i(III

), m

g/g

Fig. 4.3

Effect of time on removal, % and amount adsorbed, mg/g of Bi(III), on CSAC


pH=2

Chapter 4


ADSORBENTS

211

0

20

40

60

80

100

200 400 600 800 1000

Initial Conc. of Bi(III), mg/dm3

Rem

oval o

f B

i (III

),%

0

10

20

30

40

50

60

Am

ou

nt ad

so

rbed

of B

i(III

), m

g/g

Fig. 4.4

Effect of initial concentration of Bi(III) on amount adsorbed, mg/g and removal, %

of Bi(III)


Chapter 4


ADSORBENTS

212

0

20

40

60

80

100

0 200 400 600 800

Adsorbent dose, mg

Re

mo

va

l of

Bi(I

II), %

0

4

8

12

16

20

Am

ou

nt

ad

so

rbe

nt

of

Bi(

III),

mg

/g

Fig. 4.5

Effect of adsorbent dosage on removal, % and amount adsorbed, mg/g of Bi(III)

on CSAC

Bi(III) = 250 mg/dm3, Time= 240 min, T= 299 ± 2 K, agitation speed= 160 rpm,

pH=2

Chapter 4


ADSORBENTS

213

0

20

40

60

80

100

0 50 100 150 200 250

rpm

Re

mo

va

l of

Bi(

III),

%0

4

8

12

16

20

Am

ou

nt a

ds

orb

ed

of B

i(III)

, mg

/g

Fig. 4.6

Effect of agitation speed on removal, % and amount adsorbed, mg/g of Bi(III) on

CSAC

Bi(III) = 250 mg/g, Time= 240 min, T= 299 ± 2 K, CSAC=700 mg, pH=2

Chapter 4


ADSORBENTS

214

0

10

20

30

40

50

60

0 50 100 150 200 250 300

Ce mg/dm3

qe m

g/g

Fig. 4.7 Adsorption isotherm for Bi(III) adsorption on CSAC


Chapter 4


ADSORBENTS

215

0

1

2

3

4

5

0 50 100 150 200 250 300

Ce

Ce/q

Fig. 4.8 Langmuir isotherm for adsorption of Bi(III) on CSAC


Chapter 4


ADSORBENTS

216

1

1.2

1.4

1.6

1.8

2

0 0.5 1 1.5 2 2.5 3

log Ce

log

qe

Fig. 4.9 Freundlich isotherm for adsorption of Bi(III) on CSAC


Chapter 4


ADSORBENTS

217

-0.6

-0.3

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200 250

t min

log

(q

e-q

t)

Fig. 4.10 Pseudo-first order plot for adsorption of Bi(III) on CSAC


pH=2

Chapter 4


ADSORBENTS

218

0

4

8

12

16

0 50 100 150 200 250 300

t min

t/q

t

Fig. 4.11 Pseudo-second order plot for adsorption of Bi(III) on CSAC


pH=2

Chapter 4


ADSORBENTS

219

0

5

10

15

20

0 5 10 15 20

t1/2

qt

Fig. 4.12 Intraparticle diffusion for adsorption of Bi(III) on CSAC


pH=2

Chapter 4


ADSORBENTS

220

50

52

54

56

58

60

300 305 310 315 320 325

T K

qe

Fig. 4.13 Effect of temperature on amount of Bi (IIII) adsorbed, mg/g on CSAC Bi(III) = 1000 mg/dm3, time= 240 min, CSAC=700 mg, agitation speed= 160 rpm, pH=2

Chapter 4


ADSORBENTS

221

1.1

1.12

1.14

1.16

1.18

1.2

1.22

0.00305 0.0031 0.00315 0.0032 0.00325 0.0033 0.00335

1/T K

lnK

c

Fig. 4.14

Vant Hoff’s plot for adsorption of Bi(III) on CSAC

Bi(III) = 1000 mg/dm3, time= 240 min, CSAC=700 mg, agitation speed= 160 rpm, H=2

Chapter 4


ADSORBENTS

222

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