INTRODUCTION:
Most of the industries in Ethiopia, i.e.,
textile, paper, plastics,
leathers, food and cosmetics industry, etc use dyes or pigments to color their
final products. Such extensive use of dyes and pigments often poses problems in
the form of colored wastewater that requires pretreatment for the color prior
to disposal into the receiving water bodies or publicly owned treatment work.
Unless they are properly treated, these dyes significantly affect
photosynthetic activity in aquatic life due to reduce light penetration and may
also be toxic to some aquatic life due to the presence of metals1.
Conventional primary and secondary systems
of wastewater treatment plants are not suited to treating these effluents as
the dyes are typically non-biodegradable2-5. Physical and
chemical processes of color removal have been investigated6-11,
including coagulation, flocculation, biosorption, photo-decomposition and
ultrafiltration12, reverse osmosis13, and
activated carbon adsorption14. These technologies do not show
significant effectiveness or economic advantage. Activated carbon is the most
popular and widely used adsorbent but there are certain problems with its use.
It is expensive and the higher the quality the greater the cost. Furthermore,
regeneration using solutions produces a small additional effluent, while
regeneration by refractory technique results in a 10–15% loss of adsorbent and
its uptake capacity. Therefore, there is a growing interest in using low-cost,
easily available materials for the adsorption of dye colors. Such materials can
be used once, and then disposed of by burning them as fuel.
Many investigators have studied the
feasibility of using low cost materials, such as waste orange peel15;
banana pith16; chrome sludge17; bagasse
pith, maize cob, natural clay10; fly ash18;
charred plant material19; palm fruit bunch20, and
aquatic plants21-22 as adsorbents for the removal of various
dyes from wastewaters. Among these materials, several low- cost adsorbents
showed extraordinary properties as sorbents. This makes the adsorption a
practical and an economically feasible treatment process among its competitors.
The objectives of the present
investigate was to study the adsorption of methyl violet and Congo red by
low-cost adsorbent under various experimental conditions.
Adsorbent:
In this study, a locally available soil-type
geo-material was used as adsorbent. This natural, material is being used among
the rural community in one of a water deficit part of western Hararghe to
clarify/purify flood water collected for drinking and other domestic uses. It
was purchased from the local market and washed with distilled water, to remove
any attached dirt and soluble impurities, dried in the open air and then
pulverized using mortar. The powder was sieved using laboratory sieve and the
adsorbent remaining between 25-32 mesh (500
m)
fractions was separated. The powder was dried in the oven (Model: D5C, Made in
England 105ºC and kept in the desiccators until later uses.
Characterization of adsorbent:
A chemical analysis of adsorbent was
performed using a complete silicate analysis method by Geo-Chemical Laboratory
(Addis Ababa, Ethiopia) and the result is shown in Table 1. The major
constituent, calcium oxide, was measured at 29.68%, by weight. The loss on
ignition (LOI) was found to be 11.28% by weight (see Table1).
Photo: Partial Western Hararghe Soil
Modification
of surface properties:
For possible chemical
activation/deactivation of the natural adsorbent, surface modification of the
material was made by using a quaternary amine; hexadecyltrimethylammonum
bromide (HTAB, C19H42BrN), which is a cationic
surfactants, obtained from the Central Analytical Laboratory of the Haramaya
University. The Molecular weight of HTAB is 364.46g. The procedure of surface
modification is given by23. It should be noted that 0.02M of
the HTAB is approximately 7.3g and that amount was used to modify 50g of the
natural adsorbent. After agitation on the natural adsorbent in HTAB solution,
the solids were washed with distilled water twice until no HTAB is present.
Therefore, it is safe to assume that no HTAB was released to dye solution
during sorption experiments. Finally the adsorbent was dried in the open air
and heated at 1050C for 2hrs and kept in the desiccators until
further uses.
Analytical methods and instrument:
UV-Vis spectrophotometer (SANYO SP65) is selected as an analytical tool to determine the
concentration of dye solutions. This selection is made based on the fact that
most dyes absorb electromagnetic radiation in the Uv-vis region. Uv-vis
spectrophotometer that operates in the Uv-vis range was used to determine the
wave length of maximum absorbance (λmax) and to measure all the
samples. Concentration of dye solution was calculated from the absorbance
measurements using Lambert Beer’s law.
The dye removal capacity of the adsorbent is
expressed as follows:
Batch adsorption studies:
Experimental solutions were prepared by
pipetting a known amount of dye into a 1 liter (L)
Erlenmeyer flask and diluting it with a known amount of distilled water. Batch experiments for decolorization were conducted in 500mL conical flask
containing 250mL of dye solution at room temperature
(23 ± 2 C0), to evaluate dye removal efficiency and capacity of the media. The media (waste residue) was placed in the
flask and then stirred continuously at a constant slow
mixing rate with magnetic stirrer during the experiment.
To ensure that dye does not adsorb on the inner walls of the adsorption vessels, blank runs were performed simultaneous.
In this procedure a 100 mg/L dye solution was added to a
glass vessel and the concentration measured at different time intervals. The
effect of dose of the media, contact time, system pH and initial concentration
of the dye were investigated by varying any one of the process parameters and
keeping the other parameters constant.
Effect of dose and contact time:
To investigate the effect of dose and
contact time experiments were conducted by varying adsorbent doses (0.6 to
11g/L) for Congo red and Methyl violet at constant initial dye concentration of
100 mg/L. The residual dye concentrations were measured by taking samples at
different contact time. The effects of adsorbent dose at the optimum contact
time were also studied on the same initial dye concentration with adsorbent
doses varied 0.6 and 11 g/L and stirring slowly in aqueous solution at the
ambient pH values. The remaining concentration was determined spectrophotometrically
at its corresponding λmax when the equilibrium contact time is
reached.
Effect of system pH:
The effect of system pH on the adsorption of
the dyes onto the media was studied by varying the adsorbate-adsorbent system
pH for two dyes. The pH was adjusted to the desired level either with 0.1 M
NaOH or 0.1 M HCl solution by
using a pH- meter (JENWAY, 3310) with a combined pH electrode. The pH meter was
calibrated with buffer solutions (pH= 4, pH= 7, and pH= 10) before every
measurement. The dye concentration was determined using SP65 UV-Vis
spectrophotometers. Parameters such as particle size of the adsorbent, dye
concentration, adsorbent dosage and temperature were kept constant while
carrying out the experiments.
The residual dyes concentration was determined after 3h contact time.
Effect of initial dye concentration:
To investigate the effect of initial dye
concentration, experiments were conducted by varying dye concentrations. Two different concentration ranges were used
in these studies, one below 100mg/L and the other between 100 and 220 mg/L. For
this experiment, 2g/L of adsorbent for MV and 3g/L of adsorbent for CR were
added separately to different concentrations of the experimental solution in 1L
Erlenmeyer flask (Keeping other factors constant).The final dye concentration was analyzed
from the absorbance of the supernatant.
Kinetics of adsorption:
The kinetic analysis of the adsorption data
is based on reaction kinetics of pseudo-first order and pseudo-second-order
mechanisms. Adsorption kinetics was determined using constant adsorbent dose
and corresponding to the initial dye concentration of 100mg/L. Residual dye
concentrations were measured at different time intervals by taking samples
periodically.
Isotherm studies:
All adsorption measurements carried out
through batch technique at room temperature and desired pH. In each
measurement, 250mL of the dye solution of desired concentration and appropriate
amount of the media were taken in a 500mL graduated airtight conical flask and
mechanically agitated for about 3h to achieve equilibrium. The adsorbent were
now removed from the solution after carefully filtering by Whatman filter paper
No. 42 and the concentration of the dye was determined spectrophotometrically
by recording the absorbance at λmax.
Statistical Analysis:
All the Experimental data were statistically
analyzed with origin16 Software.
All the experiments were performed in triplicate and the mean values were
reported.
Fig. 1 shows the extent of adsorption, calculated as
percentage of dyes adsorbed by the adsorbent, increased as the dosage of the
adsorbent was increased. The increase in dye adsorption was due to the increase
in availability of dye binding sites resulting from an increase in adsorbent
dosage24 and no effect after equilibrium was reached. The
point at which the percentage uptake of the dye starts leveling off reflects
the optimum dose of the adsorbent under that particular condition. Similar
results were obtained for the biosorption of basics by water hyachinth roots22
and adsorption of Congo red onto burnt clay25.
Fig. 1 The relationship between natural and
HTAB treated adsorbent dose verses percentage of removal dye (Co= 100mg/L,
contact time 24hrs, solution pH 7.4 and 7.8 for MV and CR, respectively[Where N: natural adsorbent and T: HTAB treated adsorbent]
A reverse trend was observed in the loading capacity (qt)
as the adsorbent dosage was increased from 0.6 to 11g. That is., loading
capacity the natural adsorbent decreased from 16.78 mg/g to 2.2 mg/g for CR and
12.25 mg/g to 2.13 mg/g for MV (Fig.2). Similar results were obtained for the
biosorption of basic dye by giant duckweed26 and rice husk27.
The decrease in the amount of dye adsorbed qt (mg/g) with increasing
adsorbent mass may be due to concentration gradient between solute
concentration in the solution and the solute concentration in the surface of
the adsorbent27. Thus, with increase in adsorbent mass, the
amount dye adsorbed per unit weight of adsorbent mass gets reduced, hence
causing a decrease in qt value and increasing adsorbent weight dose.
It may also be due to particle- particle interactions. In systems with higher
solid mass contents, these interactions perhaps physically blocked some
adsorption sites from the adsorbing solutes, thus causing decrease in
adsorption. Or the decrease in adsorption with increasing dose of adsorbent is
basically due to adsorption sites remaining unsaturated during the adsorption28.
For HTAB treated adsorbent, the amount of dye adsorbed decreases from5.25 to
2.0 mg/g and 7.5 to 1.75 mg/g for CR and MV, respectively. In general, the
result from Fig.1 is in agreement with the expected relationship between the
percentages of dye removal and adsorbent dose. As the concentration used is
kept constant, it is expected to reach a point where an increase in adsorbent
dosage removes no more of sorbate. This point where the dye uptake levels off
may be considered as the optimal dose at that particular reaction condition.
This dose was 2 and 3 g/L for MV and CR, respectively.
Fig.2 The relationshipbetween natura and HTAB adsorbent verses removal
capacity (Co= 100mg/L, contcat time 24hrs, solution pH 7.4 and 7.8 for MV and
CR)
Fig.3 Residual concentration and % of removal of MV and CR at different
contact time for two different initial concentrations of 50 and 100 mg/L
(dose=2g/L and 3g/L; pH= 7.4 and 7.8 for MV and CR, respectively)
Effect
of contact time:
Contact time is one of the most important parameters
for the assessment of practical application of adsorption process29.
As can be seen in Fig.3, most of the adsorption of the dye takes place in the
first 3h and due to this reason 3h was selected as contact time for all
experiments.
Effect
of contact time and concentration:
Fig. 4 show that, percent removal of MV the dye
increased from 90% to 95% as the dye concentration increase from 50 mg/L to 100
mg/L and the percentage of dye removal was nearly equal to 
86%
as the concentration increases from 150 mg/L to 200 mg/L. Fig.5 also show that
with increasing dye concentration from 50 to 200 mg/L, the amount of dye
adsorbed by the natural adsorbent increases from 5.5 to 21.75 mg/g. For HTAB
treated adsorbent, the amount of dye adsorbed increased from 4.6 to 7.23 mg/g
as the dye concentration increased from 50 to 100 mg/L and decreased from 6.45
to 3.88 when the concentration of the dyes increases from 150 to 200 mg/L. For
HTBA treated adsorbent, the percent removal of MV decreased from 90% to 36% as
the dye concentration increased from 50 mg/L to 200 mg/L. In addition to this,
the percentage uptake of the dye molecules increases with settling time to some
extent. Further increase in settling time does not increase the uptake due to
deposition of dyes on the available adsorption site on adsorbent material. At
this point, the amount of dye adsorbed onto the adsorbent was a state of
dynamic equilibrium with the amount of dye desorbed from the adsorbent. The
time required to attain this state of equilibrium was termed the equilibrium
time and the mount of dye adsorbed at the equilibrium time reflects the maximum
dye adsorption capacity of the adsorbent under these condition. The result of
the experiment showed that large portion of a dye’s adsorption was performed in
the first 3h of the process (Fig.6).
The maximum amounts of CR adsorbed by natural adsorbent
were increased from 3.0 to 14.0mg/g as the concentration increased from 50 to
200 mg/L (Fig.7), and for HTAB treated adsorbent; the amount of CR dye adsorbed
increased from 3.75, 5.5 and 6.75 mg/g as the concentration of dye increased
from 50 to 150 mg/L and decreases to 6.0 mg/g when the concentration of dye is
200 mg/L. This indicates that there exists a reduction in the immediate solute
adsorption, owing to lack of available active sites required for high initial
concentration of the dyes.
Fig.7 Plot of the amount of CR adsorbed onto natural adsorbent and HTAB
treated adsorbent versus contact time, Solution pH 7.8 and masas of
adsorbent 3g/L.
For natural adsorbent, with increase in the initial
concentration of MV from 20 to 80 mg/L, the removal efficiency increased from
83.5% to 90.0% (Fig.8). That is at lower concentrations, all the dye present in
the adsorption medium could interact with the binding sites on the surface of
adsorbent so that higher adsorption yields were obtained. In other worlds, at
lower dye concentrations the solute concentration to adsorbent sites ratio is
becoming higher. This in turn causes an increase in color removal. While for
dye concentration more than 80 mg/L, the efficiency slightly decreased and
reached about 81% for the dye concentration of 220 mg/L. That is at higher
concentrations, lower adsorption yields were observed because of the saturation
of the adsorbent sites. Similar results were obtained for the adsorption of
Methyl blue by dehydration of wheat bran carbon30. In the
case of CR, the reverse process was observed. i.e., with increased in the
initial dye concentration from 20 to 220 mg/L, the percent removal efficiency
increased from 25 to 82%. The increase in proportion of removed dye may be due
to equilibrium shift during the adsorption process. For HTAB treated adsorbent,
with increase in the initial concentration of MV and CR from 20 to 40mg/L, the
removal efficiency increased from 67 to 82% and 73 to 82% respectively. At
lower concentrations the adsorption capacity of HTAB treated adsorbent is
higher than natural adsorbent for CR. For higher concentration, the removal
efficiency decreased and reached about 15.3% and 27% for MV and CR,
respectively. This indicates that there exists a reduction in immediate solute
adsorption, owing to the lack of available active sites.
Fig.8 Effect of initial dye concentration on percentage of dye removal
of MV (contact time 3h, 2g/L, and solution pH 7.4) and CR: contact time 3h,
3g/L and solution pH 7.8).
As shown in Table 1, about 15% of the composition of
the adsorbent is quartz (SiO2). Silicon and oxygen are structural
elements; the Si-O bond has about 50% covalent character. The siloxane groups,
SiOSi interact with water forming –SiOH31. In the presence of
water, surface of mineral oxides, such as those of Al, Fe and Si are usually
covered with hydroxyl groups. As a result of hydration and dissociation of
these groups, pH dependent surface charge is formed. The magnitude of surface
charge depends on the charge of ionization and pH of the system32.
The results obtained show that the molecular form of CR in solution medium
changes markedly in the pH range 3-5 and at the alkali pH of 9, e.g. the color
of CR changes from dark blue at pH 3-5 to red at pH 9. However, the red color
is different from the original red in the pH range 6-9. But in the case of MV,
there is no color change in the pH range 3-9. At lower pH, surface of the
adsorbent are protonated and the surface becomes positively charged.
Table 1 Chemical Composition of adsorbent in percent
|
Chemical composition
|
Percent (wt. %)
|
|
CaO
SO3
SiO2
H2O
LOI
Al2O3
Fe2O3
MgO
K2O
P2O5
MnO
TiO2
Na2O
pH(22C0)
|
29.68
23.34
15.14
12.36
11.28
5.02
2.83
0.64
0.5
0.06
0.03
0.02
<0.01
7.8
|
MOH + H+ MOH2+
Where M stands for metal present on the surface of the
adsorbent
The interaction of CR (anionic dye) and the positively
charged adsorbent surface at lower pH are shown below.
Dye-SO3Na (s) Dye-SO3-
(aq) +Na+ (aq)
MOH+ + Dye-SO3-
(aq) MOH+ -O3S-Dye(s)
[strong interaction due to opposite charges]
When initial dye solution pH is 3, for which the final
pH is 7.23, the percent removal of the dye is the highest and about 83% for
natural adsorbent and 73% for HTAB treated adsorbent. This result indicates
that a significantly high electrostatic attraction exists between the surface of
the adsorbent and the dye. Similar trend were observed in the adsorption of
Congo red on Wollastonite33, Waste Fe (III/Cr (III) hydroxide34
and open burnt clay25. At higher pH, the surface of the
adsorbent becomes negatively charged and electrostatic repulsion decreases with
rising pH due to the reduction of the positive charge density on the adsorption
sites thus resulting in an increasing cationic dye (MV+) adsorption.
This mechanism can be shown as follow:
MOH + OH- MO- +
H2O
MO- + MV+ MO-
+MV
When the initial dye solution pH is 6, for which the
final pH is 7.53, the percent removal of MV is the highest and about 87% (for
natural adsorbent) and 68% (for HTAB treated adsorbent) (Fig. 9). This is
because at higher pH, the number of ionizable sites on the adsorbent increases.
Similar results were obtained for the Adsorption of basic dyes on granular
carbon and natural zeolite35.
Fig.9 Effect of initial pH on percentage of
dye removal (initial dye concentration, 100mg/L, 2g/L solution pH 7.4 and
contact time 3hfor MV and 3g/L, solution pH 7.8 and contact time 3h for CR).
Adsorption Isotherm:
Adsorption equilibrium isotherm models usually describe
adsorption process and the results obtained were analyzed using Langmuir
isotherm36 and Freundlich isotherm37.
Langmuir Equation is given by:
(3)
Where, Ce is the concentration of dye (mg/L) at
equilibrium. The constant Qo signifies the adsorption capacity and b is related
to the energy of adsorption. Linear plot of Ce/qe Vs Ce shows that the
adsorption follows Langmuir isotherm. The value of Qo and b were calculated
from the slope (1/Qo) and intercept (1/Qob) of the linear plot and are
presented in Table 2.
Table 2 Comparison
of adsorption isotherm (Langmuir constant) characteristics between natural and
HTAB treated adsorbent and other studies on adsorbents for textile
|
Adsorbent
|
Dyes
|
Qo(mg/g)
|
b (L/mg)
|
Refs.
|
|
Pseudomonas luteola
|
Reactive dye
|
96.4
|
NA
|
[42]
|
|
Natural adsorbent (soil)
|
CR
|
19.65
|
0.0924
|
Present work
|
|
HTAB treated adsorbent
|
CR
|
6.45
|
0.130
|
Present work
|
|
Fe(III)/Cr(III) hydroxide
|
CR
|
1.01
|
0.870
|
[40]
|
|
Natural adsorbent
|
MV
|
16.08
|
0.0518
|
Present work
|
|
Basaltic Tephra (Natural adsorbent)
|
Reactive
|
-3.0
|
NA
|
[41]
|
|
Basaltic Tephra (HTAB treated)
|
reactive
|
4.7
|
NA
|
[41]
|
NA: Not available
Table 3.Kinetic parameters for the adsorption of MV and CR by natural
adsorbent at different dyes concentrations (mg/L)
|
Pseudo first order
|
Pseudo second order
|
|
Concentration (mg/L)
|
Dyes
|
qe exp.
|
qe cal.
|
K1x10-3
|
R2
|
qe cal.
|
K2 x10-3
|
h=K2qe2
|
R2
|
|
50
|
MV
|
3.195
|
0.505
|
9.05
|
0.958
|
3.55
|
3.94
|
0.049
|
0.998
|
|
100
|
MV
|
9.5
|
0.6397
|
16.47
|
0.992
|
9.72
|
7.60
|
0.718
|
0.999
|
|
50
|
CR
|
1.575
|
0.778
|
69.1
|
0.980
|
1.66
|
107.6
|
0.296
|
0.998
|
|
100
|
CR
|
5.98
|
0.831
|
191.4
|
0.974
|
6.29
|
16.9
|
0.668
|
0.999
|
N.B: K1=min‑1, qe=mg/g, K2=g
mg-1min-1, h= mg/g.min
The value of RL indicates the shape of the isothermal
to be either unfavorable (RL>1), linear (RL =1), favorable (RL
=0<RL<1) or irreversible (RL =0). The result showing that RL values were
in the range of 0-1 indicates that the adsorption of the dyes on the natural
adsorbent is favorable. Dealing with the comparative study (Table 2),
revealed that the natural adsorbent could be considered as a promising
adsorbent to remove textile dye as compared to Fe (III)/Cr (III) hydroxide40
and basaltic Tephra41.
However, other adsorbent have shown higher dye removal capacities among them
Pseudomonas luteola42
QO values in the Langmuir analysis indicate
the monolayer capacity of adsorbent for the two dyes. According to Langmuir
equation both dyes show a strong affinity for natural adsorbent than for HTAB
treated adsorbent. MV and CR being adsorbed onto the natural adsorbent, have a
monolayer capacity of 16.08 mg/g and 19.65 mg/g, respectively. For both natural
and HTAB treated adsorbent Congo red shows higher monolayer capacity than
Methyl violet. This can be accounted by the fraction of active colored material
in the commercial salt or Molecular structure of the dye Molecules (symmetric
or asymmetric). The higher adsorption capacity of for both dyes for natural
adsorbent in comparison to HTAB treated adsorbent, might be due to high pore
fraction capable to adsorb the dye molecules.
The experimental kinetics data of adsorption studies
were applied to first order and second order kinetics model. In order to study
the rate constants of MV and CR, the first-order rate equation was tested, and
straight line was not obtained (Graph is not displayed). Even though, the
correlation coefficients for the model were reasonably high in some cases,
however, all the intercepts of the straight line plots did not yield predicted
qe values equal or reasonably close to the experimental qe value
(Table 3). The pseudo second order kinetics model considers the rate-limiting
step as the formation of chemo-sorption bond involving sharing or exchange of
electrons between the sorbate and the adsorbent. The experimental data is fitted
to the pseudo second order equation and the parameters obtained from this model
are shown in Table 3. According to the correlation coefficient, second order
model gives satisfactory fits, and at the same time, the qe, cal.
corresponding to pseudo second-order model agrees more well with the
experimental data than the pseudo first order model. Thus, pseudo second order
is more suitable to describe the adsorption kinetic data. The value of rate
constant (k2) decreases with increasing initial dye concentration
(for CR), while the initial adsorption rate increases with increasing initial
dye concentration. Furthermore, the adsorption capacity of the adsorbent
increases as initial dye concentration increases and similar kinetics results
have been reported for the adsorption of acidic and basic dye on Coir peat
carbon46 and Brewery Waste47.
Fig. 10 Amount of
dye adsorbed on natural adsorbent versus t1/2 for intra-particle
transport of MV and CR on natural adsorbent at different initial dye
concentration.
Internal (or intra-particle) diffusion analysis:
The results obtained from the analysis using intra
particles diffusion model is shown in Fig.10 below. According to this figure,
the first sharper portion of the plot t1/2 vs. amount of dye
adsorbed is attributed to the diffusion of sorbate through or the boundary
layer diffusion of solute molecules. The second portion describes the gradual
adsorption stage, where intra-particle diffusion is rate limiting. The third
portion is attributed to the final equilibrium stage where intra-particle
diffusion starts slow down due to the extremely low sorbate concentrations in
the solution48, and it was found that the initial sharp
point with subsequent linearity indicated that more than one mode of adsorption
mechanism was in operation. The first sharp point may be due to external
surface adsorption stage are instantaneous adsorption. The second gradual
linear portion may be due to gradual intra-particle diffusion stage. The third
linear may be due to final equilibrium stage (chemical reaction). The
multi-linearity curve indicates that intra-particle diffusion is not operative
mechanism in the adsorption of MV and CR by the natural adsorbent. The linear
portion of the plot attributed to the intra-particle diffusion was linearized
at different initial concentrations. It is possible that some of the dyestuffs
diffuse in to the pores before chemo-sorption took effect. The intra-particle
diffusion rate constants Kid have value from 0.070 to 0.136 mg/g
(min) ½ and 0.0056 to 0.0145 mg/g (min) ½ for MV and CR,
respectively (Table 4). The rate constant increased with an increased in dyes
concentration. This observation agreed with the studies by21-22. As
shown in Table 5 none of the plots have zero intercepts, as proposed by45
this could be a pointer to the possibility that intra particle diffusion may
not be a prominent rate controlling steps.
Table 4 Parameters of intra-particle diffusion model
|
Initial dye con
(mg/L)
|
Dyes
|
Intercepts
|
Kid(mgg-1min1/2)
|
R2
|
|
50
|
MV
|
3.46
|
0.070
|
0.922
|
|
100
|
MV
|
9.00
|
0.136
|
0.881
|
|
50
|
CR
|
2.02
|
0.0056
|
0.830
|
|
100
|
CR
|
7.25
|
0.0145
|
0.980
|
CONCLUSION:
The ability of locally available low-cost
material to remove textile dyes from aqueous solutions was investigated. The
results reveal that the locally available low-cost material has important
practical implications for removal of dyes from textile wastewater. Therefore, there are quite promising perspectives for its utilization on
an industrial scale, keeping in mind that it is a very abundant adsorbent,
whose price may be considered negligible when compared with that of activated
carbon. The obtained results stimulate the prosecution of this research,
because there are still several very important aspects to clarify.
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