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Chapter 3

APPLICATIONS OF COAGULANTS

Chapter 3 Applications of Coagulants

Ph. D. Thesis 93 Kunal N. Trivedi

3.1. FLUORIDE REMOVAL FROM AQUEOUS SOLUTION BY

COAGULATION-FLOCCULATION

3.1.1. Introduction

The sources of water contamination may be by natural or human activities.

One such contaminant is fluoride (F). Fluoride is an important micronutrient in

humans or animals, which is widely distributed in the environment in several forms

and at varied concentrations. Fluoride ions pollute the water through two ways which

are natural source and anthropogenic facilities. Fluoride ions are found in waste

discharges from the process streams of number of the industries with glass

manufacturers, electroplating operations, steel and aluminum, pesticides and fertilizer,

groundwater and semiconductor industry [1-4] being the major contributors. Fluorides

are also released into the environment naturally through weathering and dissolution of

rock minerals, in emissions of volcanoes, and in marine aerosols. The two most

populated countries of the world, China and India, stand at the top in the list of worst

hit nations in groundwater contamination with fluoride. In both these countries, the

major source of fluoride pollution is the natural weathering process [5].

The presence of F ions in drinking water may be advantageous or

disadvantageous for human or animal depending upon its concentration limit [6, 7].

Fluoride is beneficial especially to young children below eight years of age when

present within permissible limits of 1.0-1.5 mg l-1

F ion for calcification of dental

enamel [8]. Indian standards for fluoride in drinking water recommend 1.0 ppm for

suitable concentration and 1.5 ppm is permissible limit for potable water [6]. Excess

fluoride intake causes different types of fluorosis, primarily dental and skeletal

fluorosis. White line striations followed by brown patches and, in severe cases,

brittling of the enamel are common symptoms of dental fluorosis. Skeletal fluorosis

first causes pain in the different joints, then limits joint movement and finally causes

skeletal deformities, which become particularly acute if fluoride uptake occurs during

growth. Since these ailments are incurable, fluorosis can only be mitigated by

preventing intake of excess fluoride [9].

It has been observed that very few proven sustainable options are available for

fluoride removal, especially in developing countries, where its impact of the issue is

highly intense. Though the considerable amount of research undertaken worldwide



has thrown up many technologies, each having its own advantages and limitations, a

lasting solution are still at large [10]. National Environmental Engineering Research

Institute (NEERI), Nagpur, India has developed Nalgonda Technique for the fluoride

removal from water, and used in many developing countries [7]. It involves addition

of aluminum salt which is responsible for fluoride removal [11]. Although, lime

treatment was used for the fluoride removal by adding excess lime or other calcium

salts, but it is inappropriate for field application due to some disadvantages [7, 12].

For the de-fluoridation many techniques are used like coagulation, adsorption, ion

exchange, electro coagulation, reverse osmosis, electro dialysis, etc [6, 13-21].

Coagulation with aluminum (Al) (III) salt has been employed for Fluoride

removal from long time. The coagulation technique involves precipitation or co-

precipitation of fluoride by using suitable reagents like lime, calcium and magnesium

salts, and alum and poly aluminum chloride [22, 23]. The precipitation or adsorption

may occur when the Al (III) is added to the fluoride containing water with the general

formula Aln Fm(OH)3n−m (Eq. 3.1.1) and/or by adsorption/ligand exchange (Eq. 3.1.2)

[12]. Efficiency of Al on fluoride removal depends on the pH and alkalinity. Due to

low solubility constant of the Al(OH)3 and Al-F complexation is difficult to dissolve

[4]. The pH range 5.5-6.5 is most appropriate for de-fluoridation by coagulation [24].

nAl3

(aq) + 3n − m OH−

(aq) + mF−

(aq) → AlnFm(OH)3n − m(s)___________ Eq. 3.1.1

Aln(OH)3n(s) + mF−

(aq) → AlnFm(OH)3n − m(s) + mOH−

(aq)____________ Eq. 3.1.2

The polyaluminum chloride (PACl) is an inorganic coagulant containing Al in

different species form. To identify the quality and quantity of Al species as

monomeric, polymeric and colloidal form, well-known Al-Ferron timed complexation

assay has been used [25, 26]. Different Al species of PACl was also characterized by

the 27

Al-Nuclear magnetic resonance (NMR) spectra and provided direct evidence for

the existence of this species [27, 28].

Chapter 3.1 describes how hydroxyl-aluminum species are acting during

fluoride removal. Removal of fluoride from aqueous solution using

coagulation/flocculation technique with inorganic coagulant namely PACl was

studied. Influence of Al species, OH/Al ratio and pH was investigated in detailed.

Study for determining optimum coagulant and sufficient dosage for F ion and



turbidity removal was done. Comparative studies of PACl at B = 2.4 showed better

efficiency on turbidity removal and PACl at B = 0.5 was observed to appropriate for F

ion removal.

3.1.2. Materials and Methods

3.1.2.1. Preparation of Standard Fluoride Solution

Fluoride stock solution was prepared using sodium fluoride (AR grade)

purchased from Qualigenes, India and used as received. The 1000 ppm solution of

NaF was prepared in Millipore water by dissolving 2.21 g of NaF, obtained from the

Milli-Q Gradient A-10 water purification system (Milli-Q, Germany). The fluoride

solution was standardized using EA 940 Orion 94-09, (USA) ion selective electrode

cum potentiometer.

3.1.2.2. Coagulants Preparation

The PACls selected for these studies were synthesized at 0.5 and 2.4 B values

using 0.5 molar alkali and 1.0 molar Al concentration with the base titration method.

The PACls at B = 0.5 and at B = 2.4 with 0.5 molar alkali and 1.0 molar Al

concentration have maximum content of monomeric and polymeric Al species

respectively. The synthesis procedure was, calculated volume of 1.0 M of

AlCl3•6H2O (Sigma Aldrich, U.S.A.) solution neutralized with 0.5 M of NaOH (AR

grade, S. D. Fine Chemicals, Mumbai, India) at the rate of 0.5 ml min‾1 (Masterflex

L/S Peristaltic Pump, Cole-Parmer) under rapid stirring using magnetic stirrer (Scoot,

Germany) at 400 rpm. Final pH of the PACls solution was measured using pH meter

(Toshniwal Instruments Ajmer, India).

3.1.2.3. Al-Ferron Complexation Timed Spectroscopy

Ferron reacted with different form of Al (III) species and formed the Al-

Ferron complexes. The Al-Ferron complexes measurement has been reported in the

literature [29, 30]. Absorbencies of the complexes were measured at 370 nm on 3101

PC UV-Visible spectroscopy (Shimadzu, Japan). To analyze the species distribution

0.1 ml of PACl was added to 50 ml of Ferron solution (0.2%). Reaction sample was

quickly added to 1 cm quartz cuvette after homogeneous shaking. Baseline correction

was performed using Ferron solution having known amount of Ferron dissolved in

Millipore water. Absorbencies were measured from 1 min to 24 h. Absorbance at 1



min indicates the percentage of the monomeric species, absorbance from 1-180 min

represent the percentage of the polymeric species. Absorbance from 180 min to 24 h

shows the colloidal Al species. Last absorbance after 24 h was assumed as total Al.

Percentage of different Al species was obtained as the total Al minus monomeric and

polymeric absorbencies.

3.1.2.4. 27

Al-NMR Spectroscopy

27

Al-NMR spectra of PACls were recorded on Bruker 500 MHz NMR

spectrometer at the scanning frequency 130.32 MHz with deuterated water (D2O)

used as NMR locks for maintaining the field stability.

3.1.2.5. Water Samples

For the jar test experiments tap water and model turbid water were used. The

tap water was obtained from institute with initial turbidity 1.7 Nephelometric

Turbidity Units (NTU) and pH 7.92. The model turbid water was prepared by

reported method [30] and has initial turbidity of 165 NTU and pH 6.83. Typical

analysis of the water samples was done using TN 100 Eutech Turbidity Meter,

Singapore and Toshniwal Instruments Ajmer, India for turbidity and pH respectively.

Analysis of the water samples described earlier was performed after addition of

fluoriding 5 ppm in each experiment. The concentration was confirmed using ion

selective electrode EA 940 Orion 94-09.

3.1.2.6. Jar Test Conditions

All coagulation experiments were conducted in 1000 ml glass graduated

beaker using a square jar test apparatus from Pooja Scientific Instruments, New Delhi,

India. For each experiment known amount of PACl was added to the beaker

containing 1000 ml of sample water. After the dosage was applied, water was first

stirred rapidly at 140 rpm for 2 min and then at a slow speed at 40 rpm for 8 min

followed by sedimentation for 30 min. After sedimentation, supernatant water was

withdrawn for final turbidity, pH and Fluoride measurement.

3.1.3. Results and Discussion

3.1.3.1. Different Al Speciation Interact with Ferron

Ferron assay can indentify monomeric, polymeric and colloidal Al species in

Al (III) species in the PACl solution [30, 31]. Species distribution of Al in PACl was



obtained using Al-Ferron complexation timed spectroscopy and content of the

different Al species were calculated from absorption values (Figure 3.1.1). Results are

tabulated in Table 3.1.1. It can be seen from the Table 3.1.1 that distribution of Al

species was affected by B value. Absorbencies of Al-Ferron complexes were formed

to change with time, and changes in absorbencies depend on the B value. With lower

B an initial absorbance started from a much higher value and had a short period of

gradual increase before reaching the plateau. An initial absorbance was very low and

rapid increase of absorbance lasted much longer time before reaching the plateau with

higher B [26, 29, 32].

Relative results of Al species distributions in PACls were observed in Al-

Ferron assay (Figure 3.1.1). It was observed that absorbance had highly gone up

within a 1 min due to high amount of the monomeric Al species, and reached the flat

trend in PACl at B = 0.5. Whereas for PACl at B = 2.4 the initial short absorbance

within 1 min was associated with the reaction of the Ferron with the monomeric Al

species, the absorbance was seen to go up to higher values between 1-180 min. This is

related to reaction of the Ferron with the polymeric Al species in largest amount.

Entire Al species completely react with Ferron and absorbance reaches to flat terrain

after 24 h (Figure 3.1.1).

0

0.4

0.8

1.2

1.6

0 300 600 900 1200 1500

Time (min)

Ab

sorb

an

ce

B = 0.5

B = 2.4

Figure 3.1.1. Absorbencies of different Al-Ferron complexes of different Al species

in PACl synthesized at 0.5 and 2.4 B value observed at 370 nm with different time



Table 3.1.1. Distribution of diverse Al species in PACls with different B and pH

values

B values pH Monomeric

Al species (%)

Polymeric

Al species (%)

Colloidal

Al species (%)

0.5 3.0 99 ─ 1

2.4 3.97 13 80 7

3.1.3.2. Influence of pH on Species Distribution

The pH plays important role in the formation of different Al species [31]. The

pH of the PACls depends upon the B value (Table 3.1.1). The content of the

polymeric Al species increased with an increase in pH. At pH 3.97 maximum

polymeric Al were obtained. No polymeric Al species were detected at less than pH

3.0 (Table 3.1.1).

3.1.3.3. 27

Al-NMR Interpretation of PACls

27Al-NMR of partially neutralized Al solutions at targeted B values of 0.5 and

2.4 were recorded on a Bruker 500 MHz. Usually, two peaks are observed in PACl at

0.0 and 62.5 ppm, and peak position depended on different forms of Al [26-28, 33-

35]. Two signals were observed at δ ~ 1.0 and ~ 64 ppm (Figure 3.1.2). Resonance

peaks at δ ~ 1.0 and ~ 64 ppm are assigned to the monomeric, and polymeric and

colloidal Al species respectively [36, 37].

Figure 3.1.2. 27

Al-NMR of the PACls (A) PACl synthesized at 0.5 B and (B) PACl

synthesized at 2.4 B

(A)

ppm (t1) -1000100200 ppm (t1) -1000100200

(B)



For PACl at B = 0.5 the 27

Al-NMR showed a sharp peak at δ ~ 1.0 ppm due to

monomeric Al species (Figure 3.1.2 (A)). Sharp peak at ~ 1.0 ppm and broad peak at

~ 64 ppm were observed for PACl at B = 2.4 showing the presence of monomeric and

polymeric species along with colloidal Al species (Figure 3.1.2 (B)).

3.1.3.4. Efficiency of PACls at Various B Value

Mechanism of the fluoride and turbidity removal is strongly related to pH,

dosage of PACl, OH/Al ratio and distribution of Al species. The initial concentration

of hydroxide ions and the amount of Al (III) affect the pH of the solution [4, 25].

PACl with higher B value has high percentage of the polymeric Al species and

showed better coagulation efficiency. With an increasing of B value from 0.5 to 2.4,

there was an increased in the turbidity removal efficiency of PACl due to the increase

in the degree of polymerization, and required low dosage (Figures 3.1.3 and 3.1.4).

The monomeric Al species, which are the most reactive species, have lower

coagulation efficiency. Monomeric Al species could not form flocks large enough to

settle down efficiently and remains mostly in the colloidal form. The monomeric Al

species formed insitu are not as stable as polymeric species preformed and undergoes

rearrangement quickly and transforms into colloidal form [25, 38, 39]. Furthermore,

the hydrolyzed monomeric species have a strong tendency to complex with anionic

compounds such as carbonate, sulfate, fluoride and phosphate etc. Due to the low

solubility of Al(OH)3 and Al-F, these complexes are difficult to dissolve and get

precipitate out [40, 41] and help in removal of F ions.

Tap water and model turbid water samples were used for optimized the PACls.

Relation between PACl and turbidity removal and between PACl and F ion removal

with pH at different OH/Al ratio are shown in Figures 3.1.3, 3.1.4 and 3.1.5.

Distribution of Al species was tabulated in Table 3.1.1. Changes in residual turbidity,

fluoride and pH of water samples after dosing were investigated in details. Dosages of

the PACls were varied in steps to see the efficiency of the PACls for turbidity and

fluoride removal with pH.

3.1.3.5. Evaluation of the Efficiency of PACls and Influence of pH on Turbidity

and Fluoride Removal

Firstly, tap water (1.7 NTU) with 5 ppm fluoride ion was used for fluoride

removal study and treated by PACl of 2.4 B value. Due to the low turbidity of used



water it was difficult to generate flocks after dosing and hence excess dosage of PACl

was required to remove turbidity [39]. The PACl dosage was varied from 1-4 ppm of

Al (Figure 3.1.3 (A)). As the PACl with B = 2.4 with low monomeric Al species

(Table 3.1.1), its fluoride removal efficiency was very low, may be due to the weak

complexation of fluoride with polymeric species. Therefore, F was observed to remai

in water after treatment (Figure 3.1.3. (C)). It was confirmed by final pH

measurement (Figure 3.1.3 (B)) which was higher than the reported optimal pH for F

ion removes, in the range of pH 5.5-6.5 [42-44].

Figure 3.1.3. Coagulation efficiency of PACl at B = 2.4 on tap water (A) Turbidity

removal; (B) Effect on pH and (C) Fluoride removal

Earlier model turbid water was treated with PACls for fluoride removal study,

the blank experiments were carried out to check the efficacy of the model turbid water

(containing clay) for fluoride removal study. The 5 ppm of fluoride was added to the

model turbid water placed in jar test apparatus and stirring at 140 rpm for 60 min

having local applied followed by sedimentation of the sample for 30 min. Due to high

0

10

20

30

40

50

0 1 2 3 4 5

Dosage Al (ppm)

Tu

rb

idit

y R

em

ov

al

(%)

(A)6

6.5

7

7.5

8

0 1 2 3 4 5

Dosage Al (ppm)

pH

(B)

0

0.002

0.004

0.006

0.008

0.01

0 1 2 3 4 5

Dosage Al (ppm)

Flu

orid

e R

em

oval (%

)

(C)



swelling capacity clay forms gel-like masses when added to Millipore water [45].

Sediment sample was centrifuged at 7000 rpm for 60 min under 25 °C (Kubota 6500,

Japan). The final turbidity, pH and F ions concentration of supernatant sample of

centrifuged water were 7.95 NTU, 6.55 and 4.8 ppm respectively. From the

experimental results it was confirmed that model turbid water was unable to remove F

ions, may be due to the poor uptake capacity of fluoride by clay [10].

Figure 3.1.4. Coagulation efficiency of PACl at B = 2.4 on model turbid water; (A)

Turbidity removal; (B) Effect on pH and (C) Fluoride removal

When, PACl (B = 2.4) dosage was applied to model turbid water containing 5

ppm of F, ~ 100% turbidity got removed was achieved at 1.7 ppm Al dosage, however

~ 90% of F ion remained in water at final pH 6.7 (Figure 3.1.4 (A), (B) and (C)). The

PACl with 2.4 B value has high percentage of the polymeric Al species, better

coagulation efficiency and required low dosage for turbidity removal. Maximum

turbidity was removed at the neutral or acidic water pH [38]. To remove the F ion, 2.4

0

25

50

75

100

0 1 2 3

Dosage Al (ppm)

Tu

rb

idit

y R

em

ov

al

(%)

(A)

0

5

10

15

20

0 1 2 3

Dosage Al (ppm)

Flu

orid

e R

em

oval (%

)

(C)

5

5.5

6

6.5

7

0 1 2 3

Dosage Al (ppm)

pH

(B)



ppm Al dosage was given and ~ 20% of F ion can be removed at pH 6.6 (Figure 3.1.4

(B) and (C)). The PACl with 2.4 B value has less percentage of monomeric Al

species, (Table 3.1.1) responsible to make complexes with F ion. The removal of F

also depended on pH and final pH of the solution un-appropriate to remove F (Figure

3.1.4 (B)) [42].

The experimental results (Figure 3.1.5) showed PACl at 0.5 B value has

maximum monomeric Al species, and require three time higher dosage than PACl (B

= 2.4) for turbidity removal. The monomeric Al species were unable to aggregates the

destabilize particles to form flocks large enough to set down efficiently and remain

mostly in the colloidal form. To remove remaining colloids particles excess dosage

was required [38].

Figure 3.1.5. Coagulation efficiency of PACl at B = 0.5 on model turbid water; (A)

Turbidity removal; (B) Effect on pH and (C) Fluoride removal

0

20

40

60

80

100

0 2 4 6

Dosage Al (ppm)

Tu

rb

idit

y R

em

ov

al

(%)

(A)

0

20

40

60

80

0 2 4 6

Dosage Al (ppm)

Flu

orid

e R

em

oval (%

)

(C)

5

5.5

6

6.5

7

0 2 4 6

Dosage Al (ppm)

pH

(B)



Figure 3.1.5 (A) and (C) show that with an increased dosage of PACl,

turbidity and [floride] were found to decrease simultaneously. The PACl (B = 0.5)

required 6 ppm Al dosage to remove ~ 100% of turbidity and ~ 80% of F ion. The

higher concentration of monomeric Al species present in PACl with 0.5 B (Table

3.1.1) that easily reacts with F to form Al-F complexes and resulted in the ~ 80% of F

was removed. The pH of the final solution was ~ 5.5 (Figure 3.1.5 (B)) may be due to

more acidic nature of PACl with 0.5 B than PACl with 2.4 B (Table 3.1.1), and was

optimum pH for F removal through coagulation [24].

From the experiments results it is evident that clay present in the model turbid

water was unable to remove F from aqueous solution and required PACl for removal

of fluoride. The PACl with B = 2.4 have higher polymeric Al species showed better

turbidity removal efficiency and poorer efficiency for F ion removal due to low

monomeric Al species. In contrast PACl with B = 0.5 showed poorer efficiency for

turbidity removal as it required three times higher dosages than PACl with B = 2.4.

However it gave better efficiency on F removal due to maximum monomeric Al

species.



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3.2. REMOVAL OF REMAZOL BRILLIANT BLUE R FROM

WATER USING PACl

3.2.1. Introduction

Large volumes of colored effluents are discharged from various chemical

industries such as textiles, leathers, printings, laundries, tanneries, rubbers, plastics

and paintings, etc., [1]. Wastewater from industries is a considerable source of

environmental contamination, and its treatment for de-colorization and removal of

dye substances represents a substantial part of the integral processes for industrial

wastewater purification [2]. The presence of very low concentrations of these

effluents are highly visible and undesirable and potentially inhibiting photosynthesis.

Owing to their chemical structure, dyes are resistant to fading when exposed to light,

water and chemicals [3]. The effluent from the dye industry is characterized by strong

color, high pH, high COD, high temperature and low or no biodegradability. There

are more than 10,000 dyes incorporated in the Color Index and available

commercially, most of which are difficult to decolorize due to their complex aromatic

molecular structure and synthetic origin [2]. Discharge of this highly colored waste is

not only aesthetically displeasing, but it also impedes light penetration, thus upsetting

biological processes within a stream. In addition, many dyes are toxic to some

organisms and may cause direct destruction of aquatic species. On the other hand, dye

polluted natural waters can result in serious disturbance to aquatic biosphere due to

the reduction of sunlight penetration and depletion of dissolved oxygen [4, 5].

During the last decade among different classes of dyes, the use of reactive dye

continually increased, mainly because of the increased utilization of cellulose fibers in

the textile industries [6]. These are colored compounds highly solubility in water, and

have reactive groups which are able to form covalent bonds between dye and fiber

[7]. Untreated disposal of this colored water into receiving water body causes damage

to aquatic life and also it severe damages to the human bodies [8-10]. Azo,

Phthalocyanine, Anthraquinone, Formazane, Oxazine as Chromophore is functional

groups of reactive dyes. During the dyeing process under the influence of heat in

alkaline conditions, reactive sites of dye's react with the functional groups of the fiber.

However, a large fraction of the applied reactive dye is wasted because in the process

of dyeing reactive dye is hydrolyzed to some extent and some of the reactive dyestuff



is inactivated by this competing hydrolysis reaction. Compared with other dyes,

reactive dyes represent severe pollutants [11]. Removal of dyes from wastewaters is a

major environmental problem and complete dye removal is necessary because dyes

will be visible even at very low concentrations [12, 13]. Remazol Brilliant Blue R

(RBBR) is one of the most important dye and frequently used in the textile industry

[14].

Various methods have been investigated for treating dye containing effluents,

based on physical and chemical processes, and in combinations such as

coagulation/flocculation, precipitation, ozonation, adsorption, bio-sorption, chemical

oxidation, foam flotation, electrolysis, biodegradation, membrane filtration and photo

catalysis [2, 15-33]. Each treatment method has its advantages and disadvantages. For

example, advanced oxidation processes are effective to remove dyes but a common

problem with such operations is their relatively high cost in large-scale utilization [34,

35]. In addition, chemical oxidation typically removes only the chromophore groups

of dyes instead of mineralizing organic dyes. Moreover, the possible occurrence of

some more toxic intermediate products could be of concern. Adsorption showed better

efficacy for treatment of dye-containing water if high performance and cheap

adsorbents are available [36]. Membrane filtration has some special features

unrivalled by other methods, and has high cost and blockage problems associated with

this method.

Coagulation/flocculation is one of the commonly employed unit operations in

water and wastewater treatment and extensive use for pre-, main and post-treatment.

However, from all these processes pre-treatment is needed for removal of dye and

organic materials, consisting of coagulation and sedimentation. This process can be

used in large-scale operation with relatively high operability and cost effectiveness

[37-39]. During the last decades, inorganic polymer coagulants are receiving more

and more attention as a new generation of coagulants. Polyaluminum chloride (PACl)

a polymerized form of aluminum (Al) is one of the most important polymers

coagulant and widely used. The removal of reactive dyes by regular coagulation has

been studied by some researchers [40-45]. The polymeric Al species in PACl are

relatively stable after dosing, and thus their effectiveness can be less influenced by the

specific water quality conditions [46-50]. Several species have been proposed to form

during hydrolysis of Al (III). Different Al species in PACl solution were characterized



by 27

Al-Neuclear Magnetic Resonance (NMR) and powder X-ray diffraction (powder

XRD) [51, 52].

In chapter 3.2 the efficacy of powder PACl was optimized on synthetic

wastewater having artificial turbidity. For these experiments, powder PACl was

synthesized using AlCl3•6H2O and NaHCO3. The synthesized PACl was characterized

by 27

Al-NMR and PXRD. RBBR containing synthetic wastewater with artificial

turbidity was used for efficacy tests. The synthetic wastewater was used as the

characteristics of wastewater released from the dyeing process vary from plant to

plant, sampling time and process conditions. Concentration of RBBR was measured

using UV-Visible spectroscopy. Sufficient dosage for turbidity removal and decrease

of dye concentration from wastewater were optimized using jar test condition.

3.2.2. Materials and Methods

3.2.2.1. Materials

Remazol Brilliant Blue R (RBBR or Reactive Blue-19) the reactive textile dye

(C. I. 61200) was obtained from M/s. Atul Industries, Atul, India. Purity of dye was

50%. Chemical structure of dye is shown in Figure 3.2.1.

Figure 3.2.1. Structure of Remazol Brilliant Blue R dye

Analytical grade AlCl3•6H2O, NaHCO3 and HCl were purchased from S. D.

Fine Chemicals Mumbai, India, and used as received. All the chemicals received were

used without further purification. The bentonite clay was collected from Akli Mines

Barmer, India. Only Millipore water was used in this study, obtained from Milli-Q

Gradient A-10 water purification system.



3.2.2.2. Synthesis of Polyaluminum chloride

Powder PACl was prepared using AlCl3•6H2O and NaHCO3. 0.5 N of

NaHCO3 was dissolved in calculated volume of Millipore water at room temperature.

10% of AlCl3•6H2O and intended volume of HCl (35%) was dissolved in calculated

amount of Millipore water at 40-60 °C. Al (III) solution was neutralized by NaHCO3

within 30 min with mention temperature under rapid stirring on magnetic stirrer

(Schott, Germany). Final clear solution was aged for 2 h at similar temperature. The

clear solution was placed in vacuum oven at 70 °C till the solution got converted into

dry powder and finally the powder PACl was obtained.

3.2.2.3. Powder XRD

Powder X-ray diffraction (PXRD) pattern of polymeric Al species in PACl

was recorded on a Phillips X-Pert MPD diffractometer X’ Pert MPD using

PW3123/00 curved Cu-filtered Ni-Kα radiation. The pattern of Al species was

observed in the range of 2θ at 2-80 scan with scan speed of 0.4°/s.

3.2.2.4. 27

Al-NMR Spectroscopy

27

Al-NMR spectrum of PACl solutions were recorded on Bruker 200 MHz

NMR spectrometer at the scanning frequency of 52.12 MHz. The deuterated water

(D2O) was used as NMR locks system for maintaining magnetic field stability.

3.2.2.5. Water Samples

For the jar test studies tap and artificial turbid water were used. Tap water was

obtained from CSMCRI, Bhavnagar with initial turbidity of 3.1 Nephelometric

Turbidity Units (NTU) measured using turbidity meter (TN 100 Eutech, Singapore)

having pH 8.07 measured on pH meter (Toshniwal Instruments Ajmer, India). For

artificial turbid water 0.250 g of clay was added to 1000 ml of Millipore water. Initial

turbidity of water was 132 NTU and pH 6.8.

3.2.2.6. Synthetic Dye Wastewater

Known amount of RBBR (0.100 g) was added in 1000 ml of artificial turbid

water under rapid stirring for homogenous solution. Turbidity and pH of initial

synthetic wastewater was 132 NTU and pH 5.75. Concentration of dye was measured

at 663 nm on UV-Visible spectrophotometer (3101 PC, Shimadzu, Japan). UV-

Visible measurements were carried out Ax at room temperature equipped with a



quartz cell having a path length of 1 cm from the range of 800-200 nm. A baseline

correction was performed using known concentration of dye dissolved in Millipore

water. Initial Concentration of dye was calculated by the equation Eq. 3.2.1.

__________ Eq. 3.2.1

Where; C = Concentration

3.2.2.7. Jar Test Experiments

All coagulation experiments were conducted using a conventional jar test

apparatus equipped with stirring paddles and provision for controlled mixing. The

flock size and its settling ability was observed with the illuminating device at the base

of the apparatus. Experiments were conducted in 1000 ml of dye containing water

sample. To determine the efficacy of powder PACl known amount of dosage was

added to the 1000 ml sample water, stirred rapidly at 140 rpm for 1 min and then at a

slow speed at 40 rpm for 4 min followed by sedimentation for 30 min. After

sedimentation, supernatant water was withdrawn and the final turbidity, pH and dye

concentration were measured.

3.2.3. Results and Discussion

3.2.3.1. Characterization of PACl

Figure 3.2.2. PXRD pattern of PACl



PXRD of prepared PACl (Figure 3.2.2) gave a sharp signal in the 2θ range

from 5 to 25° due to the presence of polymeric Al species namely Al13[51].

The sample showed diffraction pattern of sodium chloride in the range of 2θ

>25°. Sodium chloride was the by-product formed during the hydrolysis and

polymerization of Al3+

and was difficult to remove. XRD is sensitive to sodium

chloride and even a very low content of sodium chloride can give fairly strong signals

[51] the entire spectrum (Figure 3.2.2) well matches with reported value.

PACl was further characterized by 27

Al-NMR spectroscopy. 27

Al-NMR gave

typical signals at 0.0, 62.5 and 80 ppm due to the monomeric and dimeric, the Al13 as

polymeric and Al(OH)4¯ respectively [52, 53]. The synthesized PACl showed two

sharp peaks at ~ 0 ppm due to monomeric or dimeric Al species and at ~ 62.5 ppm

due to polymeric Al species observed in 27

Al-NMR (Figure 3.2.3). This result is in

good agreement with the PXRD results.

Figure 3.2.3. 27

Al-NMR of PACl

3.2.3.2. Efficiency of PACl

The model turbid water was prepared by taking 1.5 g of clay in 1000 ml of

Millipore water and it was stirred for 30 min under jar test apparatus (Pooja Jar Test

Apparatus, Pooja Scientific Instruments, New Delhi, India) and followed by

sedimentation for overnight. After sedimentation turbidity was ~ 1000 NTU. From the

Figure 3.2.4, it was observed that 250 mg of clay produced ~ 130 NTU turbidity in



1000 ml of water. Based on dilution study, the amount of clay was fixed for further

experiments.

Figure 3.2.4. Decreasing in turbidity (NTU) with dillution of clay concentretion

Coagulation efficiency of PACl was evaluated using synthetic wastewater

having 130 NTU artificial turbidity. Results showed the PACl required 30-40 mg

dosage to remove ~ 100% of turbidity from it (Figure 3.2.5).

0

25

50

75

100

0 25 50 75 100 125 150

Dosage PACl (mg/L)

Tu

rb

idit

y R

em

ov

al

(%)

Figure 3.2.5. Turbidity (NTU) removal (%) from sample water using PACl

The synthetic wastewater with model turbidity containing 100 ppm RBBR was

placed in jar test apparatus and stirring at 140 rpm for 60 min, then the sample was

sediment overnight and the water was analyzed for turbidity and RBBR concentration.

There was no change in the turbidity, pH and RBBR concentration of sediment



sample. Due to high swelling capacity clay forms gel-like masses when added to de-

ionized water [54].

In the second set of experiments the synthetic water having 130 NTU turbidity

was used for the removal of RBBR. The dosage of PACl was varied from 25-150 mg.

From experimental results, it was observed that with an increase in PACl the pH of

the solution decreased. As the dosage of the PACl increases from 25-150 mg, there

was decreased in the absorbance along with pH. Absorbance was measured at 663 nm

and the decrease in absorbance due to decrease in dye concentration was calculated by

equations Eqs. 3.2.2 and 3.2.3. Maximum dye was removed at pH 4.52 and 150 mg of

PACl required. UV-Visible spectra of treated and un-treated water sample by PACl

was recorded (Figure 3.2.6).

________________________________________ Eq. 3.2.2

_____________ Eq. 3.2.3

Where, Ɛ = Extinction coefficient

200 300 400 500 600 700 800

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

663 nm

Ab

sorb

an

ce

Wavelength (nm)

Dosage PACl

0.0 mg/L

0.025 mg/L

0.050 mg/L

0.075 mg/L

0.100 mg/L

0.125 mg/L

0.150 mg/L

Figure 3.2.6. UV-Visible spectra’s of synthetic wastewater with artificial turbidity

treated by PACl; (1) 0.0 mg/L; (2) 25 mg/L; (3) 50 mg/L; (4) 75 mg/L; (5) 100 mg/L;

(6) 125 mg/L and (7) 150 mg/L



Figure 3.2.7 showed that increase in the amount of PACl concentration of dye

was found to decrease (%). It was clearly observed that ~ 100% of the dye could be

removed from the sample water.

0

25

50

75

100

0 25 50 75 100 125 150

Dosage PACl (mg/L)

RB

BR

Rem

ov

al (%

)

Figure 3.2.7. RBBR (Dye) removal (%) from sample water by PACl

200 300 400 500 600 700 800

0

1

2

3

4

663 nm

Ab

sorb

an

ce

Wavelength (nm)

Dosage PACl (150 mg/L)

Before Treatment

After Treatment

Figure 3.2.8. UV-Visible spectra of untreated and treated tap water containing RBBR

(Dye) by PACl

Tap water was used for RBBR removal experiment. Turbidity and pH of the

tap water has been described earlier. Optimized dosage of PACl (150 mg) was applied

to tap water containing 100 ppm RBBR. The final turbidity and pH was 0.10 NTU

and 7.38 respectively. Results showed that, it was unable to remove the RBBR

completely (Figure 3.2.8) from low turbid water (tap water). It may be due to the



inadequate generation of flocks due to low turbidity of water. The probability of

chemical flocculation was lower as the reactive dye is highly soluble in water [55].

Based upon the experimental results the model turbid water (containing clay)

without treated with PACl; and the tap water having low turbidity even treated with

PACl (150 ppm) were unable to remove RBBR from aqueous solution, whereas the

model turbid water (132 NTU) containing 100 ppm of RBBR dye treated by PACl

(150 ppm) removed ~ 100% of RBBR from it.



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