Degradation of cationic and anionic dyes in coagulation-flocculation process using bi-functionalized silica hybrid with aluminum-ferric as auxiliary agent

Article abstract of DOI:10.1039/c5ra01346a

Cationic dye (methylene blue) and anionic dye (methyl orange) degradation in the coagulation process was demonstrated. The key material was a natural coagulant-laterite soil dominated by a silica component, while aluminum-ferric ions acted as an auxiliary agent in the degradation process. Charge neutralization, electrical double layer compression and sweeping flocculation were the mechanisms in the decolorization reaction. These results provided a new insight into effective dye degradation using a new class of natural coagulant-natural resources (laterite soil). The complex molecular structure of methylene blue and methyl orange was degraded into smaller hydrocarbon forms, accompanied by the formation of silsesquioxane. The silsesquioxane was the final product of degradation with promising flocculation and low volume sludge. Lastly, a comparison of the aluminum-based coagulant and a laterite soil natural coagulant shows a clear vision of the performance for both types of coagulant.

Full text of DOI:10.1039/c5ra01346a

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Degradation of cationic and anionic dyes in
coagulation–flocculation process using
Cite this: RSC Adv., 2015, 5, 34206
bi-functionalized silica hybrid with aluminum-ferric
as auxiliary agent
a
Yen-Yie Lau,a Yee-Shian Wong,ab Tjoon-Tow Teng, Norhashimah Morad,a
*
Mohd Rafatullaha and Soon-An Ongb
Cationic dye (methylene blue) and anionic dye (methyl orange) degradation in the coagulation process was
demonstrated. The key material was a natural coagulant–laterite soil dominated by a silica component,
while aluminum-ferric ions acted as an auxiliary agent in the degradation process. Charge neutralization,
electrical double layer compression and sweeping flocculation were the mechanisms in the
decolorization reaction. These results provided a new insight into effective dye degradation using a new
class of natural coagulant–natural resources (laterite soil). The complex molecular structure of
methylene blue and methyl orange was degraded into smaller hydrocarbon forms, accompanied by the
formation of silsesquioxane. The silsesquioxane was the final product of degradation with promising
flocculation and low volume sludge. Lastly, a comparison of the aluminum-based coagulant and a
laterite soil natural coagulant shows a clear vision of the performance for both types of coagulant.
Received 23rd January 2015
Accepted 7th April 2015
DOI: 10.1039/c5ra01346a
www.rsc.org/advances
coagulation,4–9 have been employed to study the dye degrada-
tion processes. Among them, coagulation is considered as one
1. Introduction
of the most practicable processes used in industrial wastewater
treatment.10 Coagulation stage is an instantaneous process
occurred when a coagulant is added into the colloidal disper-
sion wastewater. Subsequently, it leads to rapid breakage or
rearrangement and aggregation of particles. Coagulation
mechanisms can be accomplished by (1) electrical double layer
compression, (2) adsorption and charge neutralization, (3)
enmeshment in a precipitation, and (4) adsorption and inter-
particle bridging.11
The commonly used coagulants in industry are chemical-
based coagulants, such as aluminum sulphate (alum), ferric
chloride (FeCl3) and polyaluminum chloride (PACl). Application
of these chemical substances creates several impacts, such as
increase of metal concentration in water, voluminous toxic
sludge produced and detrimental effects on human health.
There is strong evidence linking aluminum-based coagulants to
the development of Alzheimer's disease in human being.12 Due
to the disadvantages of chemical coagulants, application of eco-
friendly and natural coagulant phenomena was approached in
order to substitute the chemical coagulants. Various coagulants
had been identied from animal and plant origins such as
chitosan,13 M. oleifera, tannin and cactus14 and okra extracted
from okra seeds pod tips, plant stalk and root.15 Scientic
results showed that requirement of alum could be reduced 50–
90 % upon replacement of okra as primary coagulant and
coagulant aid. Laterite soil which is naturally available on the
The potential adverse effect of dyes and pigments on the envi-
ronment is global nowadays. A wide range of industries such as
the paper, leather, plastics, cosmetics, food, printing and
pharmaceutical industries, apply dyes for their coloration
processes, but by far the dominant industry utilized dye is the
textile manufacturing industry. The dyeing process is the
concept to link dye molecules covalently to ber molecules,
however incomplete exhaustion of dyes onto textile bers has
become a major problem.1 Subsequently, various pollutants
such as remaining dyes, organic compounds and surfactants
could be found in textile effluents.2 Proper treatment is required
to ensure efficient removal of the pollutants before being dis-
charged into the environment. This is because incompletely
degraded products would create toxicological and ecotoxico-
logical issues due to their toxic, non-biodegradable and muta-
genic nature. For example, benzene can imperil human being
nervous and vascular systems; phenol can affect aquatic system
by hindering marine plants and organisms growth.3
Therefore, various methodologies, such as electro-peroxone,
photocatalytic, advanced oxidation process, aerobic and
anaerobic degradation using various microorganisms,
aSchool of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Pulau
Pinang, Malaysia. E-mail: ttteng@usm.my; Fax: +604-657-3678; Tel: +604-6532215
bSchool of Environmental Engineering, Universiti Malaysia Perlis, Kompleks Pusat
Pengajian Jejawi 3, 02600 Arau, Perlis, Malaysia
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earth is selected as natural coagulant since it contains elements coagulant to treat synthetic dye wastewater. The laterite soil was
of coagulation–occulation functions. Laterite soil is not mixed with ultrapure water and subsequently the mixtures were
underlying in animal and plants origin, therefore a new class of ltered with nylon cloth to remove the impurities. The laterite
natural coagulant is established which can be named as natural soil containing ltrate was collected and le to settle until
resources.
double layers were observed. The aqueous phase was drained
In this present work, a study of dye degradation using off and the laterite soil paste was dried under the sunlight. The
natural coagulant (laterite soil) was undertaken. Cationic dye procedure was repeated until the laterite soil was decolorized.
(methylene blue) and anionic dye (methyl orange) were selected The dried laterite soil was crushed into powder and sieved
to analyze coagulation mechanisms of laterite soil with the aid through 75 mm siever. The sieved laterite soil powder was mixed
of zeta potential measurements. Meanwhile, UV-Vis, GC-MS in ultrapure water and blended, followed by ltration to remove
and FT-IR analysis were used to identify the degradation inter- excessive uid. Laterite soil paste collected on the lter paper
mediates and products. Properties of degradation intermedi- was readily used as coagulant.
ates and products were essential to ensure zero potential
hazardous substances were released. The results provided
effectiveness comparison on laterite soil as natural coagulant
with chemical-based coagulants.
2.4 Coagulation experiments
The coagulation experiments on synthetic dye solutions were
performed using Jar-Test apparatus (JLT6 VELP Scientica). The
optimum pH was obtained by xing a coagulant dosage and
varying the initial pH from 1 to 9, using dilute hydrochloric acid
(HCl) or sodium hydroxide (NaOH) solution (0.01–0.1 M). The
pH of each solution was measured by 827 pH lab (Methrohm).
The mixtures of dye wastewater and laterite soil were stirred
rapidly at 200 rpm for 2 minutes, then slowly at 100 rpm for 15
minutes. Subsequently, the mixtures were allowed to settle for
30 minutes. 20 mL of liquid was collected at 2 cm beneath the
liquid in the settling beaker. The collected samples were ltered
through 20–25 mm pore size Whatman lter papers and the
ltrates were ready for analysis (Section 2.5). The identied
optimum pH was used and the experiments were continued by
varying the dosage of laterite soil coagulant. The procedures
were continued as mentioned above.
2. Methodology
2.1 Dyes
Methylene blue (C16H18N3SCl; molecular weight 373.90 g-molꢀ1
;
absorption wavelength 664.00 nm) and methyl orange (C14H14-
N3NaO3S; molecular weight 327.33 g-molꢀ1; absorption wave-
length 464.50 nm) were purchased from Sigma Aldrich. Their
molecular structures are shown in Fig. 1. Stock solution of dyes
was prepared by dissolving 1 g of dye with deionized water using
a 1 L volumetric ask. 50 mg Lꢀ1 of dye solutions were prepared
by diluting the stock solutions.
2.2 Characteristics of laterite soil
The morphology of laterite soil was analyzed using JEOL (Model
JSM-6460LA) Analytical scanning electron microscope. Energy
dispersive X-ray analysis (Model Oxford-50) was conducted for
identifying the element contents in the laterite soil. Fig. 2 shows
the morphology and topography of laterite soil. The character-
istic of laterite soil was further analyzed by using X-ray uo-
rescence (XRF) to distinguish the exact element content
percentage and the corresponding identied compounds are
shown in Fig. 3. The major constituents of laterite soil are SiO2
(36.30%), Al2O3 (27.10%) and Fe2O3 (26.86%) as illustrated in
the Fig. 2 and 3. The components in the laterite soil could act as
coagulant and occulant in the wastewater treatment.
2.5 Analysis
The color point (measure of dye concentration) of a dye solution
was determined by using Hitachi u-2800 UV-Visible Spectro-
photometer. The turbidity was determined by using Eutech TN
100 turbidity meter in Nephelometric Turbidity Unit (NTU).
Zeta potential of a solution was measured by using Dispersion
Technology – Acousto Phor Zeta Titration 310 method. Aer the
optimum pH and laterite soil dosage have been determined to
treat methylene blue and methyl orange, the sludge obtained at
these optimum conditions were sent for sludge volume index
(SVI) determination, Fourier transforms infrared spectropho-
tometry (FT-IR) and Thermogravimetric analysis (TGA) analyses.
SVI analysis was carried out in accordance with the standard
methods for the examination of water and wastewater.16 It is the
volume in milliliters occupied by 1 g of a suspension aer 30
min. settling. Equation used to calculate SVI is given below:
2.3 Preparation of laterite soil
The laterite soil was collected from Bukit Merah, Perlis,
Malaysia. The raw reddish laterite soil went through the
following pretreatment: it was decolorized before being used as
Settled sludge volume after 30 minutesðmL Lꢀ1Þ ꢁ 100
SVI ¼
Total suspended solidsðmg Lꢀ1
Þ
(1)
(2)
ðW2 ꢀ W1Þ ꢁ 1000
¼
Sample volume; mL
Total suspended solids; mg Lꢀ1
where W2 is weight of lter disc with dried residue and W1 is
weight of lter disc before use in milligram (mg).
Fig. 1 Chemical structures of dyes: (a) methylene blue; (b) methyl
orange.
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Fig. 2 (a) Morphology of laterite soil at low magnification 5000ꢁ (b) morphology of laterite soil at high magnification 40000ꢁ (c) topography
element contents of laterite soil by using energy dispersive X-ray analysis.
For the mechanism elutriation, the intermediate compounds
for methylene blue and methyl orange dyes removal were
identied and analyzed with Gas Chromatography-Mass Spec-
trometry (GC-MS) (GC-2010 Plus, Shimadzu corporation, Japan)
with BPX5 column.
3. Results and discussion
3.1 Effect of pH
Fig. 4 demonstrates the results of coagulation performance for
methylene blue and methyl orange at different pH values. The
results reveal that the dyes gave the highest performance at pH
Fig. 3 Components contained of laterite soil.
2. Generally, when the solution shied from acidic to alkaline
condition, it led to decrease in color removal and increase in
residual turbidity. When laterite soil is in contact with water,
FT-IR measurement on the sludge was carried out at room
compounds in laterite soil: SiO2 (36.30%), Al2O3 (27.10%) and
temperature on a Nicolet iS10 Smart OMNI-transmission FT-IR
Fe2O3 (26.86%) would form Si(OH)4, Al(OH)3 and Fe(OH)3. SiO2
Spectrometer. The sludge produced aer coagulation with
is able to act as a degradation catalyst as stated in the research
ꢂ
laterite soil was collected and dried in the oven at 105 C for 2
by Li et al.17 Lau et al.18 reported that pH 2 is the point of zero
hours. Solidied sludge was dried and ground into powder
charge (PZC) for laterite soil. At PZC, silica was present in
[SiOH2+] and [SiO32ꢀ] forms, which were able to accept both
subsequently, dispersed in a matrix to mix with potassium
bromide (KBr). The mixture was transferred to a die that has a
cationic methylene blue and anionic methyl orange dyes.
barrel diameter of 13 mm, subsequently the die was pressed to
Simultaneously atmospheric oxides in laterite soil: Al2O3, Fe2O3,
dissolved in strong acid to release Al3+ and Fe3+ ions which were
form a disc. The disc was removed carefully from the die and
placed in the FT-IR sample holder. The content in the disc was
then attracted to more stable anionic methyl orange dye mole-
cules. Therefore, the optimal pH value for the maximal
ready for the 4000–450 cmꢀ1 transmission spectrum analysis.
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Fig. 4 Effect of pH on the color removal and residual turbidity of methylene blue and methyl orange.
degradation of both dyes were pH 2 at which the dye colloids
and coagulant had agglomerated and settled down.
In alkaline condition, the performance of laterite soil to treat
the dyes decreased. This happened because addition of NaOH
to adjust the pH of the system caused the silica to form a stable
compound, Na2SiO3 19 as shown in the equation below:
Si(OH)4 + 2NaOH 4 Na2SiO3 + 3H2O
(3)
The removal of methylene blue could remain above 80% in
alkaline condition because aluminum and ferric ions which
react with OHꢀ ions tends to form hydroxylaluminate and
hydroxyl-ferric anions.20
Fig. 5 Zeta potential measurements for laterite soil as a function of pH.
ꢀ
Al(OH)3 + OHꢀ 4 Al(OH)4
(4)
(5)
Fe(OH)3 + OHꢀ 4 Fe(OH)4
ꢀ
Laterite soil would undergo acid-base amphoteric dissociation
since it contains hydroxyls (OHꢀ) on the surface (silanol group).
A schematic diagram of the dissociation is shown in Fig. 6. The
tendency for the hydroxyls to dissociate is strongly affected by
pH. Addition of acid into dye solutions increased the concen-
tration of protons in the solutions. Therefore SiO32ꢀ was formed
in the diffuse layer. As the solution became more acidic,
particularly at pH lower than 2, zeta potential readings became
higher. This indicates that the degree of repulsion between
similar charges dispersed in the diffuse layer, hence the colloids
resisted to aggregate.22 As a result, zeta potential at acidic pH
indicated positive values. On the other hand, at alkaline pH,
However, the residual turbidity of methylene blue increased
at a fast rate. This was attributed to the absence of silica which
functioned as occulant in the system. For the anionic methyl
orange, as the pH increased to alkaline condition, the color
removal decreased gradually and the residual turbidity
increased rapidly. This was happening because aluminum and
ferric in laterite soil were present as hydroxylaluminate and
hydroxyl-ferric anions. Thus strong repulsive forces occurred
between these anions and anionic methyl orange. Conse-
quently, no interparticle bridging and aggregation of particles
took place. Cationic and anionic dyes at different pH range did
affect the performance of laterite soil in coagulation process,
thus optimum pH should be taken into consideration to ensure
effective charge neutralization in the system. Effective charge
neutralization by adsorption of oppositely charged ions would
enhance colloidal occulation.21
OHꢀ ions were adsorbed onto silica surfaces to form SiOH+
,
2
resulting in negative zeta potential values. Hence, large diffuse
electrical double layer took place.23 The PZC for the laterite soil
with cationic and anionic dyes, both were detected at the pH
value of 2.5 where silica colloids remained stationary in an
electrical eld. At this point, silica colloids aggregated and
rearranged in order to balance the counter ions with
dye particles. Meanwhile, zeta potential supported the effect of
3.2 Zeta potential
Fig. 5 shows the changes of zeta potential for laterite soil as a pH on the color removal and residual turbidity of methylene
function of pH for the cationic and anionic dyes. Zeta potential blue and methyl orange which have been discussed in
measurements indicate the surface charges present on the Section 3.1.
laterite soil particles when it exists in aqueous suspension.
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Fig. 6 Schematic diagram for acid-base dissociation of silanol group in laterite soil.
Fig. 7 Scheme with intermediates and products proposed for the degradation of (a) methylene blue; (b) methyl orange.
charge neutralization by binding with the sulfate ion of meth-
ylene blue. When SiO3 was ion tied up with the sulfate ion,
methylene blue structure became unstable and led to breakage
at the weaker strength bond. As decolorization took place in a
rapid manner, thiazine was prone to cleave in the initial stage of
3.3 Degradation mechanism of cationic methylene blue dye
2ꢀ
Fig. 7a depicts degradation pathway of methylene blue at pH 2.
Methylene blue is a cationic dye favorable to bind with nega-
tively charged surface.24 Therefore, the surface charge of silica
2ꢀ
which carries SiO3
destabilized methylene blue through
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Fig. 8 UV-Vis absorption spectra of (a) methylene blue; (b) methyl orange as the function of coagulant dosage.
degradation which caused the disappearance of the absorbance
peak at 664 nm under UV-Vis spectra (Fig. 8a). As verication,
the FT-IR peaks shown in Fig. 9a from the range 1603 to 1394
cmꢀ1, which represents aromatic ring structures in methylene
blue, had almost vanished aer coagulation. This indicates
destruction of polyaromatic structure in methylene blue.
Hence, N,N-dimethylaniline (C6H5N(CH3)2) (intermediate I)
degradation intermediate released from the methylene blue
structure was identied in GC-MS analysis (Fig. 10).
Fig. 10 GC-MS analysis for N,N-dimethylaniline (C6H5N(CH3)2).
ꢀ
Simultaneously, unstable anion molecule of RSiO3 (interme-
diate II) was formed. Subsequently, when two molecules of
ꢀ
RSiO3 existed in the system, it tended to form siloxane mole-
2ꢀ
cule (R2SiO3). In general, one molecule of SiO3 was able to
neutralize two molecules of cationic methylene blue by forming
two molecules of N,N-dimethylaniline and one molecule of
siloxane molecule (R2SiO3) (intermediate III). Instantly, the ]
NH of the siloxane molecule tended to destabilize and detach,
subsequently forming diazene. Diazene (HN]NH), also known
as diimide, is a strong reducing agent for carbon–carbon double
bond, (–C]C–).25 Diazene scissored the –C]C– of benzene
rings. When the benzene rings were opened, linear products of
hydrocarbon, (CnHn) were created. Aromatic amine of interme-
diate I had undergone diazene reduction to form simple
hydrocarbon product. This has been conrmed from the FT-IR
spectra whereby peaks within 875 to 791 cmꢀ1 entirely dis-
appeared aer coagulation. Lastly, the siloxane molecule with
alkoxide group would undergo hydrolytic condensation reac-
tion to form silsesquioxane as the nal product of coagulation.26
A broad peak in FT-IR graph from range 1169 to 1000 cmꢀ1
veries the formation of silsesquioxane. The silsesquioxane
characteristics of dimensionality, high symmetry, and nano-
meter size enhanced the formation of organosilicon
compounds. The nal product has built a strong sweeping
occulation in the system.
3.4 Degradation mechanism of anionic methyl orange dye
When laterite soil was present in anionic methyl orange dye
system at pH 2, the surface charge of silica carries cationic
Fig. 9 FT-IR analysis before & after reaction for (a) methylene blue; (b)
methyl orange.
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charge has changed the molecular structure of methyl orange.
The decrease of the absorption spectra intensities of methyl
orange is shown in Fig. 8b. Degradation rate of methyl orange is
signicantly lower than methylene blue due to the molecular
structures of both dyes.27 As can be seen in this gure, the
gradually disappearance of the characteristic band of methyl
orange at 505.5 nm indicates that the rst stage of degradation
was the azo bond cleavage. The FT-IR band located at 1366 cmꢀ1
which is assigned to azo bond of methyl orange has entirely
vanished aer reaction with laterite soil as shown in Fig. 9b. The
breakage of azo bond led to formation of N,N-dimethyl-p-
phenylenediamine ((CH3)2NC6H4NH2) (intermediate I) and
p-amino-benzenesulfonic acid (C6H6NO3S) (intermediate II) as
illustrated in Fig. 7b. The –NH2 from intermediates I and II
proned to combine into diazene. Subsequently, the interme-
diate I structure reduced to N,N-dimethylaniline (C6H5N(CH3)2)
(intermediate III). Meanwhile, intermediate II had been
attacked by silica instantly accompanied by aluminum and
ferric ions. This happened since methyl orange is a strongly
bonded dye which was hard to degrade. Higher attraction force
is required to enhance the dye destabilization. Subsequently,
intermediates IV and V were formed. When sufficient diazene
was present to scissor the benzene rings of the intermediates IV
and V, linear hydrocarbon products, CnHnOn–Si^Al (interme-
diate VI) and (CnHnOn)2–Si]Fe (intermediate VII) were formed.
The FT-IR band within 1606 to 1519 cmꢀ1 range represents
aromatic rings in methyl orange which had been scissored aer
addition of laterite soil. The positions at 3500 to 3200 cmꢀ1 and
1650 to 1630 cmꢀ1 of FT-IR bands are evidence for the forma-
tion of intermediates VI and VII.28 From the proposed degra-
dation pathway (Fig. 7b), Si^Al was able to bind with only one
molecule of methyl orange, whereas Si]Fe was able to bind
with two molecules of methyl orange. Silica ion is more favor-
able to tie with oxide ions. Hence aer aluminum and ferric had
destabilized the methyl orange structure, these metal ions
would be detached from silica and formed metal hydroxides,
Fe–OH and Al–OH as detected in FT-IR 706 to 600 cmꢀ1 range.
The free radical side of silica would attract oxide ions to form
silsesquioxane. A broad peak in FT-IR graph from range 1160 to
1000 cmꢀ1 is the verication of silsesquioxane formation.
Similar to methylene blue, organosilicon structure was formed
at the nal degradation stage of methyl orange.
Fig. 11 Settling characteristics (a) methylene blue (b) methyl orange.
obtained for methylene blue and methyl orange are 98 and 74%,
respectively. Furthermore, the sludge settling velocity of
methylene blue (0.27 mL sꢀ1) was faster compared to methyl
orange (0.20 mL sꢀ1). This conrm that methylene blue and
methyl orange degradation led to the formation of high density
organosilicon structure with good settling properties. Sludge
volume index (SVI) for methylene blue and methyl orange are
18.69 and 26.77 mL gꢀ1, respectively, which are in the best
range according to the standard SVI test. Methylene blue has
lower SVI compared to methyl orange. This is because methyl
orange requires higher dosage of laterite soil for complete color
removal and degradation. Lower extent of sludge yielded is
preferable since industries can manage the sludge easily, thus
preserving the environment.
3.6 Sludge thermal degradability
3.5 Sludge characteristics
Thermogravimetric analysis (TGA) proles of sludge illustrated
Fig. 11 presents the sludge settling characteristics for methy- in Fig. 12 shows a weight loss of 1.43% in the temperature range
lene blue and methyl orange at the associated optimum dosages of 100–200 ꢂC. This phenomenon happened due to dehydration
of laterite soil. The settling intervals were constructed until 200 of sample and removal of volatile organic matter. An endo-
min to observe the settling condition of sludge. During the thermic weight loss of 3.65% within the temperature range
initial 10 min of settling, the claried water rose up whereas the around 210–370 ꢂC was observed. This endothermic weight loss
sludge formed moved downwards by gravity force in a fast rate. was due to oxidation of organic substances containing C and H.
For the proceeding settling, the settling rate began to decelerate As the energy of absorption was high, a partial oxidative
as the sludge entered compression region. The volume of sludge decomposition of high concentration dye may be involved.
continued to decrease until a time that it remained unchanged, When it reached the temperature of 398 ꢂC, a sharp weight loss
specically aer 40 min of settling for both dyes. The treated of 7.14% occurred. This weight loss contributed to further
dye solution zone and the settled sludge zone can be clearly decomposition of the remaining dye molecules or dye inter-
differentiated. The maximum percentage of water recovery connected with metal ions present in the sludge. The
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Fig. 12 TGA and DTA of sludge.
decomposition of metal coordinated ions continued until the presence of color removal agent, alum could not effectively
formation of metal oxide.29 This behavior indicates that the remove the colorant in the water; therefore color removal agent
sludge produced by laterite soil was thermally decomposable.
was essential to ensure high performance of alum in treating
dye wastewater.32 With the presence of coagulant aids such as
polyacrylamide based polymer (Cytec) and cethyltrimethyle-
ammoniumbromide (CTAB), dosages of alum used had been
successfully decreased. However the sludge yielded aer coag-
ulation was voluminous. Subsequently, higher expenses were
required to deal with the voluminous toxic sludge yielded.35 On
the other hand, photocatalytic process has been proven to be
effective for dye degradation.36 Photocatalysis process is able to
remove 80% of methylene blue at pH 9 using titanium dioxide
(TiO2) nanolm37 in 10 minutes. Besides, the photocatalysis
process of methyl orange is reported at 81.3% at pH 6 using
polyaniline modied zinc oxide (PANI/ZnO) in 2 hours.38
3.7 Comparison of the effectiveness of laterite soil as natural
coagulant with chemical coagulant
A review on the effectiveness of aluminum-based coagulant, a
chemical typed coagulant and a natural coagulant, laterite soil
used are compared (Table 1). Patel and Vashi30 and Qiu et al.31
revealed that without the presence of coagulant aid, high
dosage of aluminum-based coagulant was required to ensure
high performance of removal (70 000 mg Lꢀ1 to treat 74.50% of
textile wastewater; 36 000 mg Lꢀ1 to treat 97.00% of printing
wastewater). Only 23.00% removal was detected when 400 mg
Lꢀ1 of alum was used to treat dyeing wastewater. Without the
Table 1 Comparison of effectiveness of laterite soil as natural coagulant with chemical coagulant
Aluminum-based coagulant
Laterite Soil
50 mg Lꢀ1
Type of
Textile
Printing
Dyeing
Disperse and reactive Remazol red RB
Methylene Methyl
Acid
wastewater
wastewater wastewater wastewater dyes wastewater
textile dye (25 ppm)
blue
orange
orange 7
Flocculant
pH
Without
Without
7.01
36 000
97.00
Without
8.00
400
23.00
Large
Cytec
5.30
200
94.00
83.50
CTAB
10.05
100
Without
2.00
2500
Without
2.00
15 000
92.11
Without
2.00
10 000
98.47
5.70–6.50
Dosage, mg Lꢀ1 70 000
Removal (%)
SVI range
74.50
—
100.00
99.61
55.81
140.00 (voluminous) 18.69
(Best range)
26.77
21.70
quantities
Effect
Aluminum-based coagulants tend to develop Alzheimer's disease in human being
30 31 33 34 19
No possible hazards may present
due to its naturalism.
This study This study 18
References
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Contrast to chemical coagulant, laterite soil is able to treat
cationic and anionic dye wastewater with a high performance at
99.61% and 92.11% without the presence of any coagulant aids
and catalyst (photocatalysis). Moreover the sludge volume
produced is very low and laid on the best range in the index of
sludge volume. The massive impact of chemical coagulant to
environment and human is the most signicant. Aer coagu-
lation process, the sludge formed by chemical coagulant are
hard to degrade, thus tends to induce further environmental
issues. Additionally, chemical coagulant especially aluminum-
based coagulant had been proven for the development of Alz-
heimer's disease in human being. In the application of laterite
soil as natural coagulant in coagulation, the sludge yielded is
thermally decomposable and possessed zero hazards to envi-
ronment and public.
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4. Conclusion
A new concept for dye degradation by using laterite soil was
demonstrated. Laterite soil was a newly found natural coagulant
from natural resources which contained silica hybrid with
aluminum-ferric as auxiliary agents. Successful cationic dye
(methylene blue) and anionic dye (methyl orange) degradation was
accomplished through charge neutralization, electrical double
layer compression and sweeping occulation mechanisms.
Laterite soil was capable to degrade dye molecular structure into
simple hydrocarbon structure with the formation of silsesquioxane
as nal product. The silsesquioxane products had promising
occulation effect and low sludge production through formation
of high density and compact oc.
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Abbreviations and symbols
Al2O3
Aluminum oxide
Al(OH)3ꢀ
Al(OH)4
Fe2O3
Fe(OH)3ꢀ
Fe(OH)4
HCl
NaOH
PZC
SiO2
Aluminum hydroxide
Hydroxylaluminate anion
Ferric oxide
Ferric hydroxide
Hydroxylferric anion
Hydrochloric acid
Sodium hydroxide
Point of zero charge
Silicon dioxide
SVI
Sludge volume index
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Diimide, John Wiley & Sons, Inc., New York, 2004.
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2012, 2, 445–475.
27 S. A. Ong, L. N. Ho and Y. S. Wong, Desalin. Water Treat.,
2014, 54(2), 557–561.
Acknowledgements
The authors would like to express their thanks for the support
by Universiti Sains Malaysia (USM) and Universiti Malaysia
Perlis (UniMAP).
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W. J. Li, Desalination, 2011, 268, 270–275.
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