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Adsorption of reactive dyes onto thermally treated waste from aluminum
lamination
Article in Water Practice & Technology · September 2018
DOI: 10.2166/wpt.2018.076
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Water Practice & Technology Vol 13 No 3
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Adsorption of reactive dyes onto thermally treated waste from aluminum
lamination
Tiago José Marques Fraga*, Daysianne Mikaella dos Santos Marques Fraga,
Tereza Cristina da Silva, Marilda Nascimento Carvalho and Maurício Alves da Motta
Sobrinho
Chemical Engineering Department of Universidade Federal de Pernambuco (UFPE), 1235 Prof. Moraes Rego Avenue, Cidade
Universitária, 50670-901, Recife/PE, Brazil
*Corresponding author. E-mail: tiago_mfraga@hotmail.com
Abstract
The lamination process of aluminum sheets generates a flammable oil-soaked waste, which had been thermally
treated (TTW) and used as adsorbent of reactive Remazol Black B (RB) and Remazol Red RB133 (RR), two of the
most used dyes in the printing processes on textile industries, with reported carcinogenic and toxic properties.
The adsorbent was characterized by Brunauer–Emmett–Teller (BET)-specific surface area, scanning electron
microscopy and X-ray diffraction analysis. Kinetic and equilibrium studies were performed to evaluate the TTW
adsorption parameters and the isotherm model which best represented the process. It was observed that the
system reached the equilibrium state after 5 min for both dyes and obtained their maximum adsorption capacity
(qm) at pH 4: 0.69 mg·g1 and 2.89 mg·g1, for RB and RR respectively; moreover, the pseudo-second-order model
better fitted the adsorption kinetics. The equilibrium data were better fitted to Langmuir isotherm compared to
Freundlich’s for the RB and RR adsorption. The maximum removal efficiency obtained in the experiments was
80.2% for RB and 80% for RR; moreover, after the acid activation of TTW, the RB removal efficiency increased
from 84.9% to 93.7%.
Key words: adsorption, aluminum lamination waste, reactive dyes, remazol, textile, wastewater
INTRODUCTION
The textile industry has long been known to have a significant environmental impact, due to its discharges of huge volumes of industrial wastewater with a high content of organic compounds and
strongly colored effluents (Santos & Boaventura 2016). Besides the water consumption of the textile
industry, the use of dyes has been a major concern as they degrade into toxic and carcinogenic products (Tahir et al. 2016). Moreover, dye consumption has continually increased over the years, not just
in the textile industry, but also in rubber, plastic, leather, paper, cosmetic, pharmaceutical and food
industries (Rani et al. 2017). Total dye consumption in the textile industry worldwide is more than
10,000 tons per year and about 10–15% of this amount is discharged as wastewater during the
dyeing processes (Gupta et al. 2013; Sen & Dawood 2014). Dyes can be classified as a function of
the charge in reactive, anionic, cationic and non-ionic compounds; among them, the reactive azo
dyes are those most commonly used by the textile industry, which is a major concern due to their
anaerobic degradation process, which releases toxic aromatic amines (Aguiar et al. 2017).
Adsorption techniques are widely used to remove several classes of pollutants from waters,
especially those which are not easily biodegradable, remaining in the water bodies even after conventional treatments. Therefore, a combination of biological treatment and adsorption on activated
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carbon became more common for the removal of dyes from wastewater. Activated carbon, a porous
material, has been widely applied as an adsorbent in the treatment of textile wastewater; however, the
high cost of activated carbon has made it difficult for companies with limited resources to utilise in
their treatment processes (Moreira et al. 2017). Waste products from different industrial and agricultural processes have also been studied for their toxic dye adsorbent properties by many authors, such
as eucalyptus bark (Tahir et al. 2016), cupuassu shell (Cardoso et al. 2011), coconut activated carbon
(Cazetta et al. 2016), coconut shell fibers (Rani et al. 2017), modified flax shives (Wang et al. 2017),
electroplating industry waste (Santos & Boaventura 2015), Victorian brown coal (Yuliani et al. 2017),
tire waste activated carbon (Brahim et al. 2014), and many others.
Recycling a waste to treat another waste is a philosophy inside the concept of an industrial Circular
Economy (CE), which has been pursued by many researchers, and can bring many benefits to those
who adopt it, such as financial savings from conventional waste treatments and reduction of the cost
of traditional methods to remove toxic substances from liquid effluents. The recycling, reuse and the
reduction of materials consumed emphasizes nowadays the need to add value to materials through
their application in high value operations (Hu et al. 2011; Clark et al. 2016; Korhonen et al. 2018).
The objective of this work is to propose a new application for aluminum industry waste as an adsorbent of two reactive dyes widely used in the textile industry: Remazol Black B and Remazol Red
RB133, denominated in this work as RB and RR, respectively.
MATERIALS AND METHODS
Reactive dyes
In order to evaluate the efficiency of thermally treated waste (TTW) as a dye adsorbent, two dyes were
used: the reactive RB and RR, due to their widespread use in the dyeing processes of the textile industry. All the dyes were supplied by Dystar do Brasil S/A. Figure 1 presents the molecular structures for
RB (a) and RR (b), with a molecular weight 991.79 g·mol1 and 984.18 g·mol1, respectively. Prior to
the sorption experiments, a complete scan of a 100 mg·L1 solution of each dye was undertaken to
detect their wavelength of maximum absorbance (λmax) in order to calibrate the UV-vis spectrophotometer. The λmax obtained for RB and RR were 597 nm and 514 nm, respectively. These data were
Figure 1 | Molecular structures of the dyes: (a) RB; (b) RR.
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used to build the calibration curve for each dye concentration, using the range of 0.11 mg·L1 to
11.0 mg·L1.
Waste thermic treatment
Fresh aluminum lamination waste was provided by Arconic Alumínio S/A, Itapissuma, Brazil. It is
composed of a mixture of two types of earth: Celite 503, a diatomite clay usually found in Mexico,
and Tonsil Optimum, an acidified bleaching earth derived from raw bentonite clay. After its use in
the oil filtration and recycling process in the aluminum industry, the mix of filtering earth becomes
steeped in oil, soaps and aluminum filings. The waste samples were submitted to direct combustion
to eliminate the oil content. The waste was then calcined in a muffle model Quimis Q318M
(Brazil) at 500°C for 4 h until the organic matter impregnating the filtering earth was completely
removed.
TTW cost analysis
Arconic’s aluminium plant generates 45 tons of filtration earth waste per month and pays on average
USD 212.21/ton for transport and treatment of the waste. The power cost in Pernambuco State is BRL
0.45 per kWh (USD 0.14 per kWh). The muffle potency is 1.72 kW and the average load of waste is
80–100 g per cycle. The cost of the thermic treatment is USD 2.54 per kilogram of waste, mostly due
to the energy consumption of calcination; however, it is considerably cheaper than activated carbon
in the local market (USD 29.93 per kilogram). However, the thermic treatment cost can be eliminated
if calcination could be performed through the energy generated by the direct burning, in which the
residue itself should provide the fuel for the calcination oven. A short comparative overview of
some reported adsorbents of azo-reactive dyes is provided at the end of this work. Furthermore, a
preliminary economic evaluation of production and operational costs for each sorbent is given
based on the costs of raw materials, reactants, additives, transport and energy consumption according
to their reported methodology (Supplementary Material 1).
Acid activation of the adsorbent
The acid activation was performed using the method proposed by Hai et al. (2015) to enhance the
RB removal by TTW and its adsorption capacity. 50 g of TTW was separated and put in contact
with 900 mL of HCl 6.0 mol·L1 in a flask, under agitation of 500 rpm for 4 h. After the activation
process, the sample was washed with distilled water to eliminate excess HCl and then dried in an
oven at 100°C for 24 h (Tsai et al. 2004). The acidified TTW was used to remove RB from an
aqueous solution kept at its natural pH (6.0), with a stirring speed of 300 rpm. The adsorbent
dosages used were 2.0, 4.0 and 6.0 g and the RB removal efficiencies were compared for each
condition.
Adsorbent characterization methods
The characterization of the adsorbent after the direct burning and the calcination process was made
through the analysis of specific superficial area through the Brunauer, Emmet and Teller (BET)
Method, undertaken at the Catalytic Processes Lab of the Chemical Engineering Department of
UFPE. Scanning electron microscopy (SEM) with dispersive energy spectroscopy (DES) and X-ray
diffraction (XRD) were undertaken in the Pernambuco Institute of Technology – ITEP. SEM analysis
of the virgin earths and the TTW before and after the thermic process was performed to evaluate the
textural properties, such the surface morphology, and possible changes that may have occurred during
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the thermic treatment; the analyses were performed using a scanning electron microscope with DES
SS-550 (Shimadzu, Kyoto, Japan). The mineralogical compositions of the raw materials and TTW
samples were determined using an X-ray diffractometer from Rigaku Ultima (Tokyo, Japan). The
specific surface area (SBET) and total pore volume (VP) of TTW samples were performed through a
specific superficial area analyzer (BET) (Nova 100e, Quantachrome Instruments, Boynton Beach,
FL, USA) and the data was obtained using the BET technique through N2 physisorption by assuming
the section area of nitrogen molecule to be 0.098 nm2.
Batch sorption experiments
The initial concentration for each dye was 10 mg·L1, which represents the average dye concentration
after conventional treatment of textile wastewaters, such as bioremediation, according to the data
reported in the literature (Chakraborty et al. 2003; Wang et al. 2011; Fazal et al. 2018). Volumes of
1,000 mL of 10 mg·L1 dye solution were prepared for RB and RR dyes and 50 mL of each dye solution was transferred to flasks of 125 mL. The varying amounts of adsorbent were added to the
dye solution for 10 min. After the contact time, the samples were then centrifuged to separate the
adsorbent from the solution. The solution concentrations were measured in a UV-Vis spectrophotometer (GenesysTM 10-S, Thermo Fisher Scientific, Waltham, MA, USA).
Afterwards, the dye removal efficiency (η in %), or adsorption degree (Rani et al. 2017), and the
adsorption capacity (q in mg·g1) were calculated using data analysis software, using the following
equations:
Removal efficiency: h(%) ¼
Adsorption capacity: q ¼
C0 C
100
C0
(C0 C)V
m
(1)
(2)
where C0 is the initial concentration (mg·L1), C is the equilibrium state or final concentration
(mg·L1), V is the volume of the solution (L) and m is the mass of the adsorbent (g).
Influence of pH and the zero point of charge
The point of zero charge (pHPZC) for the TTW was obtained in order to estimate the ranges where the
surface charge is positive – below PZC – and negative – above PZC (Santos & Boaventura 2016). The
pHPZC of the adsorbent was determined by adding 2.5 g of the adsorbent to several Erlenmeyer flasks.
The total volume of solution with the adsorbent in each flask was 50 mL. A range of initial pH values
(pHinitial) of the solutions were adjusted from 2.0 to 12.0 by adding solutions of 0.1 mol·L1 of HCl
and 0.1 mol·L1 of NaOH. The influence of the pH changes on the adsorption rate was evaluated
in further equilibrium studies, where equilibrium curves q vs C were obtained for each initial
solution’s pH value as well as the maximum adsorption capacity (qm) and its variation according
to the changes in solution pH.
Adsorption kinetics
The adsorption kinetics were analysed to discover the moment which the system reached equilibrium.
To discover this point, solutions of 50 mL of adsorbate were separated into flasks of 125 mL. TTW
samples of an equal weight were then added to the flasks containing the adsorbate. The time of
contact between adsorbent and adsorbate varied from 1 to 30 min. All the experiments were
conducted at environmental temperature (25°C), in duplicate, and using the dye solutions at their
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natural pH value of 6.0. The influence of varying adsorbent amount was observed by performing
different experiments with the adsorbent weight changing between 1.0 g and 0.5 g.
Equilibrium studies and adsorption isotherms
The equilibrium studies were undertaken using a range of concentration values: 2, 5, 10, 15, 20, 30, 40
and 50 mg·L1, through which it was possible to determine the adsorption isotherm models which
better described the adsorption mechanisms. The classical adsorption isotherms that are most often
applied are the Langmuir’s and the Freundlich’s. After the experiments, all data were treated and
the curves were plotted, then the experimental data were linearized to obtain the isotherm which
best represented the adsorption process; the process parameters, such as the equilibrium constant
(KL) and the maximum adsorption capacity (qm) were obtained. The saturation values were affected
by the initial dye concentration, and at identical values of C0 the dye uptake was lower for the coarsest
particles, according to reported results obtained with silica. For finer particles, on the other hand, the
values did not differ much.
Two models were tested to describe the adsorption process studied in this paper: the Langmuir’s and the combined Langmuir-Freundlich’s. The Langmuir adsorption isotherm has been
applied to many other real sorption processes and it has used to explain the sorption of dyes
by various adsorbents. The experimental results have been fitted to the Langmuir and Langmuir-Freundlich models (Ruthven 1984). The Langmuir adsorption isotherm follows the
expression in Equation (3):
q
KL C
¼
qm 1 þ KL C
(3)
where qm is the maximum adsorption capacity or the adsorption capacity when the system
achieves equilibrium (mg·g1); KL is the equilibrium constant (L·mg1); C the adsorbate concentration at equilibrium state (mg·L1); e q the adsorption capacity for each concentration.
Freundlich’s model is derivate assuming a non-uniform distribution of the adsorption energy
over the adsorbent’s heterogeneous surface. The Freundlich’s mathematical model is given by
Equation (4):
q ¼ KF C 1=n
(4)
where C is the solution concentration; q the adsorption capacity; KF is the Freundlich constant
(mg11/n·L1/n·g1), 1/n is the factor of heterogeneity; and KF and 1/n are indicative of adsorption
capacity and adsorption intensity, respectively (Ncibi et al. 2008).
The combined Langmuir-Freundlich isotherm (L-F) considers adsorption to occur across multiple
layers, therefore being useful to describe adsorption on heterogeneous surfaces, and can be applied
to species of the same molecular size and nature and focuses on the steps of adsorption on the sorbent
surface (Carvalho et al. 2012; Soares et al. 2016). The L-F model is given by Equation (5). This model
was used to fit the experimental data by a linear model and consequently to achieve the adsorption
parameters (qm, KL and n).
KLn C n
q
¼
qm 1 þ KLn C n
(5)
where qm is the maximum adsorption capacity (mg·g1), C is the concentration of the adsorbate in
the equilibrium state (mg·L1), KL is the affinity constant for adsorption and n is the heterogeneity
factor.
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RESULTS AND DISCUSSION
BET analysis
The calcined waste presented a high specific surface area in comparison to the burned waste, due to
the elimination of the excess organic material impregnated on its surface. The morphological parameters of the TTW were: specific surface area (SBET) ¼ 55.39 m2·g1 and total pore volume (VP) ¼
2.34·102 cm3·g1. The surface area is considerably lower compared to classical adsorbents, such as
activated carbon, which presents an elevated surface area of SBET ¼ 1,250 m2·g1–2,400 m2·g1.
The total volume of pores is also considerably lower in comparison to the activated carbon: VP ¼ 0.57
cm3·g1. The BET specific surface area results obtained for the Spanish virgin diatomaceous clay and
the acid treated Taiwan’s spent diatomaceous earth, respectively, showed SBET ¼ 3.07 m2·g1 and
2.85 m2·g1, very close to the Celite result, which forms one of the raw materials of the waste (Tsai
et al. 2004; Tlili et al. 2012).
Scanning electron microscopy with DES
Figures 2(d) and 2(e) show the microphotographs of the waste after direct burning and after calcination at 500°C, respectively. The right images show the material at a higher magnification. Through
these photographs, is possible observe the presence of a small amount of diatomaceous grains
mixed with the bleaching earth and oxides aggregated with the material.
The dispersive energy spectrometry (electron microscopy with DES) technique was applied to analyse the material’s overall chemical composition, combined with the images obtained through the
electronic microphotography (EM). The elements which make up the diatomaceous clay Celite 503
presented in the waste are: O (70.07%); Si (29.53%), basically due to the presence of silicon dioxide
(SiO2), which is the main component in the diatomaceous earth (Tsai et al. 2004; Al-Ghouti et al.
2009); Na (0.36%) and K (0.05%). The chemical composition of the Tonsil was mostly O (68.66%),
Si (21.32%), and in smaller amounts, Al (4.46%), C (3.23%) and Fe (1.17%).
DES analysis also showed that the fresh bleaching earth is mostly made up of SiO2 (71.27%), followed by Al2O3 (12.56%) and Fe2O3 (5.40%), all data given in atomic wt. %. These results point to
an increase in the oxygen content in the diatomaceous clay from 36.12% to 70.07%, due to the
oxides formed in the direct burning process and during calcination at 500°C. The metallic elements
(Si, Al, Ca, K) in the raw materials remain practically unchanged after the direct burning and calcination. There was a reduction, but only slightly, of the Ca presented in the Celite clay due to the burning
process – it was eliminated in the form of oxides. Similar behavior was seen for Fe – there was a minimal decrease from 1.36% to 1.17%. It is also possible to verify the removal of magnesium after the
calcination of the acidified bleaching earth Tonsil.
X-ray diffraction
The XRD analysis of TTW revealed an intense peak on 2θ ¼ 2.17°, which characterizes the Tonsil
earth diffraction plane 002 (Figure 2(b)). It can be observed in Figure 2(c) that the TTW has characteristic peaks of Celite 503 and the Tonsil Optimum, confirming the mixing of both virgin earths
which form the adsorbent. It’s also feasible to verify that the calcination process has not caused
great changes to the clay material’s composition, only the increase of pick’s intensity in 2θ from
23°, which is due to the oxides formed during calcination. This aggregated on the material’s surface,
giving the material a smooth aspect, as observed on the electronic microscope images. Through the
diatomaceous clay analysis was performed before and after thermic treatment, it mostly showed an
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Figure 2 | X-ray diffraction patterns for: (a) Celite 503; (b) Tonsil Optimum; (c) aluminum lamination waste (TTW) after calcination at 500°C. TTW Electronic microphotography 1,000x: (d) after direct burning; (e) TTW after calcination.
amorphous silica phase, revealed by a large peak between 16° and 26° (2θ), but also presented characteristic peaks of quartz and some carbonates, such calcite and ankerite (Benkancem et al. 2016).
Effect of pH
The equilibrium curves for the three different pH rates are presented in Figure 3(a) and 3(b) for RB and RR,
respectively. The maximum adsorption capacities (qm) in each pH range were obtained after adjusting the
Langmuir model to the adsorption data. Better values of adsorption capacity (q) were obtained at pH 4.0
for both dyes. Furthermore, at pH 8.0, qm values were not satisfactory, indicating that the adsorption is
favorable when pH , pHPZC (Figure 3(c)). According to the literature data, it is rather difficult to determine an absolute PZC for the clays (Errais et al. 2012); however, low pH leads to an increase in Hþ
ions on the surface of TTW, which results in a strong electrostatic attraction between the negatively
charged dye molecules and the positively charged active sites of the adsorbent (Al-Degs et al. 2008).
Hydroxyl groups presented on the surface of the diatomite can gain or lose a proton; at low pH, surface
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Figure 3 | Equilibrium curves, with experiments performed at pH 6.0 ( ), pH 8.0 ( ) and pH 4.0 ( ): (a) RB and (b) RR; (c) TTW
point zero of charge (pHPZC). Adsorption experiments conducted at 25°C, 300 rpm, 50 mL of dye solution and 1.0 g of adsorbent.
sites are protonated and the surface becomes positively charged and increases the electrostatic interactions with the sulfonate groups present in RB (Al-Ghouti et al. 2009). Figure 3(c) shows the PZC
analysis, in which at pHPZC 6.3, the residual charge of the TTW is zero.
Adsorption kinetics
The kinetics experiments were conducted under the following experimental conditions: initial
concentration of 10.0 mg·L1, volume of solution of 50 mL. Figures 4(a) and 4(b) present the
curves of adsorption capacity versus time obtained after the adsorptive process involving both dyes.
From Figure 4(a) is possible verify that the RB reached the equilibrium state after 5 min with q ¼
0.10 mg·g1. RR also reached the equilibrium after 5 min with q ¼ 0.20 mg·g1 (Figure 4(b)). The
results indicate that the adsorption rate of the two dyes onto the TTW is very fast at the early
stages (0–5 min) and then slows down gradually. Sorbent dosage evaluation showed that higher
values for the adsorption capacity were achieved with a lower amount of adsorbent – 0.5 g. The
removal efficiencies obtained at the equilibrium state per adsorbent weight for RB were: 50.21%
(0.5 g) and 85.48% (1.0 g); for RR: 58.86% (0.5 g) and 81.00% (1.0 g). The short time necessary to
achieve the equilibrium state (below 5 min) is characteristic of the monolayer physisorption process,
in which the adsorbate binds to the adsorbent surface through weak intermolecular interactions such
as van der Waals forces, hydrophobicity, hydrogen bonding, polarity, static interactions, dipole-dipole
interactions and π-π interactions (Ruthven 1984; Sen & Dawood 2014; Scheufele et al. 2016). The
pseudo-second-order model best fit the experimental data, with a good coefficient of determination
(R2) for both dyes.
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Figure 4 | Adsorption kinetics for (a) RB and (b) RR; experiments proceeded: (●) with 1.0 g of adsorbent; ( ) with 0.5 g of
adsorbent; pseudo-first-order (▪) and pseudo-second-order ( ) models applied on the experimental data (1.0 g of adsorbent):
(c) RB; (d) RR. Experiments conducted at 25°C, 300 rpm, solution volume 50 mL and pH 6.0.
Equilibrium studies
The equilibrium isotherm q versus C (Figure 5(a) and 5(c)) for both dyes showed a type I isotherm,
characteristic of microporous adsorbents, in which the sorbent pore size is not larger than the sorbate
molecular diameter (Ruthven 1984). Langmuir isotherm better fitted the adsorption for both dyes
with a good coefficient of determination (R2 . 0.99) in comparison to the Langmuir-Freundlich
model. Maximum adsorption capacity (qm) was 0.69 mg·g1 and 2.89 mg·g1 for RB and RR, respectively. The better adjustment of the Langmuir model to the experimental data is due to the
homogeneous distribution of the active sites on the surface of the adsorbent, since the Langmuir
equation assumes the homogeneity of the surface and the equal distribution of energy on each
active site (Ncibi et al. 2008). Once the system is working in a sorbate low concentration range, it
is assumed that there are no interactions between the molecules adsorbed on the sorbent sites and
those still in solution (Ruthven 1984).
The adsorption capacity (q) obtained by the experiments with RR was higher than that obtained by
the RB, due to a major electrostatic interaction with the sulfonate groups (present in greater amount
in the RR structure, and which gives an anionic behavior to both dyes) with the active sites on the
surface of the TTW, characterized by the oxides and hydroxyl groups; these groups are distributed
across the surface of diatomaceous clay (Al-Ghouti et al. 2009).
Removal of RB by acidified TTW
The evaluation of the influence of TTW acid activation on the adsorption efficiency showed that RB
removal increased after chemical treatment with HCl; however, this was not observed when a smaller
weight of adsorbent of 2.0 g was used (Figure 6). RB removal increased from 84.9% to 93.7% after
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Figure 5 | (a) Equilibrium isotherm (q vs C) for RB; (b) linearized models of Langmuir and Langmuir-Freundlich (n ¼ 2) for RB; (c)
equilibrium isotherm (q vs C) for RR; (d) linearized models of Langmuir and Langmuir-Freundlich (n ¼ 2) for RR. Experiments
proceeded at 25°C, 300 rpm, with 0.50 g of adsorbent, a solution volume of 50 mL and a pH of 4.0.
Figure 6 | RB removal by acidified and non-acidified TTW at different mass of adsorbent. Experiments conducted at environmental conditions of 25°C, 300 rpm, solution volume of 50 mL and pH 6.0.
chemical activation, when 4.0 g of acidified TTW was used. Similar behavior was observed, though at
a lower intensity, when 6.0 g of acidified TTW was used – RB removal increased from 80.2% to 82.3%.
This suggests that the treatment of diatomite earth with strong acid can reduce mineral impurities,
such as Fe2O3 and alkali metal oxides (CaO, MgO), and eliminate carbonates; however the original
geometry of the pores is preserved, thus enhancing the adsorption of RB (Benkancem et al. 2016).
Further studies using different acids or even hydroxides to enhance the adsorbent would be helpful
to better understand the charging exchange mechanisms on the TTW surface and their impact on
the reactive dyes sorption process.
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Table 1 | Adsorption parameters and preliminary economic comparison for the different adsorbents evaluated for azo reactive
dye removal in other studies. TTW adsorption parameters were obtained at 25°C, 300 rpm, solution volume 50 mL
and pH 4.0.
Average
SBET
2
1
qm
Removal
1
T
(%)
(min)
(USD·kg
208.84
70.00
–
358.00
820.00
109.40
40.00
–
Bentonite clay with
silica pillars
608.00
127.07
87.00
Moroccan crude
clay
42.43
54.00
Ceria hollow
spheres
36.27
Diatomite/chitosan
composite
Adsorbent
(m ·g
)
Activated carbon
820.00
Activated carbon
(mg·g
)
Op. cost
cost
(USD·[kg of
1
)
1
dye]
)
Dye evaluated
Reference
1,710.00
C.I. Reactive
Blue 2
Al-Degs et al.
(2008)
358.00
3,270.00
C.I. Reactive
Red 4
Al-Degs et al.
(2008)
40
584.10
4,600.00
Remazol Violet
5R
Aguiar et al. (2017)
75.00
20
14.78
270.00
Basic Red 46
Karim et al. (2009)
173.60
50.90
120
7,282.00
41,950.00
Acid Black 210
Hu et al. (2017)
–
35.12
88.37
40
105.60
2,999.50
Methyl Orange
Zhao et al. (2017)
Coconut shells
carbonized waste
372.00
22.30
12.00
88
27.52
1,230.00
Sunset Yellow
Cazetta et al.
(2016)
Fouchana clay
80.00
6.89
98.00
20
800.00
116,000.00
Reactive Red
120
Errais et al. (2012)
Aluminum
lamination waste
55.39
2.89
80.20
5
2.54
880.00
Remazol Red
RB133
This work
Aluminum
lamination waste
55.39
0.69
80.00
5
2.54
3,680.00
Remazol Black
B
This work
Low-cost adsorbents – a comparative overview
Table 1 summarizes the sorption results obtained from studies using TTW and classical adsorbent, as
well as recently developed low cost adsorbents, reported in the literature. It is easily inferable that, for
some adsorbents, the higher the adsorbent specific surface area, the higher its maximum adsorption
capacity, as observed in the activated carbon data. The results of TTW maximum adsorption capacity
showed relatively low values in comparison with the data presented by other adsorbents; moreover it
showed a lower BET specific surface area. However, TTW’s cost of treatment is considerably lower
than other reported sorbents, in terms of capital and operational cost. Moreover, TTW’s further use
in the masonry industry maintains the material cycle, hence contributing to the industrial CE (detailed
information can be found in Supplementary Material 1). Furthermore, RB and RR’s high removal efficiency (%) by TTW suggests that it can be applicable as a post conventional treatment adsorbent,
where the effluent concentration is lower than it is at the end of pipe. However, it can be proposed
that activating the waste using an acid treatment method increases the TTW’s adsorption capacity
to remove this class of dyes, as showed in the previous section.
CONCLUSIONS
The removal of reactive dyes from wastewaters is a challenge to small industries due to the cost of
conventional treatment and the environmental impact caused by illegal discharges. In this study, a
new adsorbent material was suggested which can be used to remove dye from textile wastewater: a
flammable residue, which has been submitted to a thermic treatment. This study presents the potential
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of TTW as a replacement for traditional, but expensive, adsorbents, such as activated carbon. Preliminary studies determined conditions of adsorbent mass, stirring speed and pH for the two dyes
evaluated in this paper. It was observed that good dye removal results were obtained at a low pH. Kinetic and equilibrium studies showed that the adsorption process reached equilibrium quickly (before
5 min), suggesting the monolayer and physical adsorption characteristics; moreover, the Langmuir
isotherm better fitted the adsorption process, with an elevated coefficient of determination. Despite
the results showing good RB and RR removal efficiency, the adsorbent presented a low maximum
adsorption capacity in comparison to activated carbon and other classical adsorbents presented in
the literature. However, its adsorption capacity and removal efficiency can be enhanced through
an acid activation procedure, already applied for clay sorbents. Moreover, using TTW forms a key
step in the process of value aggregation of the clay residue, in accordance with the concepts of the
industrial circular economy.
ACKNOWLEDGMENTS
The authors are grateful for the financial and technical support provided by the Brazilian scientific
agencies CAPES and CNPq; the company Arconic Alumínio S/A for providing the aluminum cold
lamination waste; and the other labs that provided the complementary analysis necessary to achieve
the work’s conclusions.
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