Evaluation of performance of chemically treated date stones: Application for the removal of cationic dyes from aqueous solutions

Abstract

Chemically treated date stones (CTDS) used in this study as adsorbent for the removal of methylene blue (MB) and crystal violet (CV) from aqueous solutions in batch system. The effect of contact time, initial dye pH, temperature and initial dye concentration on the adsorptive removal process was studied. The results show that the removal of MB and CV is rapid and superior adsorption efficiency of MB and CV onto CTDS. In this study Langmuir and Freundlich isotherms were investigated for adsorption of MB and CV onto CTDS. The Langmuir isotherm has the highest correlations coefficients, with maximums monolayers capacities of MB and CV were 515.46 mg/g and 543.47 mg/g, at 50 °C, respectively. Pseudo-first-order and pseudo-second- order models were studied to analyze adsorption kinetics. The result shows the adsorption kinetic is the best with pseudo-second-order model. Desorption and regeneration experiments using HNO3 (0.1N) eluent were only possible with CTDS, which performed well in four repeated cycles with high MB and CV removal efficiencies.

Full text

Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers
journal homepage: www.elsevier.com/locate/jtice
Evaluation of performance of chemically treated date stones:
Application for the removal of cationic dyes from aqueous solutions
Noureddine El Messaoudi
a , ∗, Mohammed El Khomri
a
, Safae Bentahar
a
, Abdellah Dbik
a
,
Abdellah Lacherai
a
, Bahcine Bakiz
b
a
Laboratory of Applied Chemistry and Environment, Department of Chemistry, Faculty of Science, University Ibn Zohr, 80 0 0 0 Agadir, Morocco
b
Laboratory of Materials and Environment, Department of Chemistry, Faculty of Science, University Ibn Zohr, 80 0 0 0 Agadir, Morocco
a r t i c l e i n f o
Article history:
Received 19 March 2016
Revised 25 June 2016
Accepted 22 July 2016
Available online 30 July 2016
Keywo rds:
Date stones
Chemical treatment
Adsorption
Crystal violet
Methylene blue
a b s t r a c t
Chemically treated date stones (CTDS) used in this study as adsorbent for the removal of methylene blue
(MB) and crystal violet (CV) from aqueous solutions in batch system. The effect of contact time, initial
dye pH, temperature and initial dye concentration on the adsorptive removal process was studied. The re-
sults show that the removal of MB and CV is rapid and superior adsorption efficiency of MB and CV onto
CTDS. In this study Langmuir and Freundlich isotherms were investigated for adsorption of MB and CV
onto CTDS. The Langmuir isotherm has the highest correlations coefficients, with maximums monolayers
capacities of MB and CV were 515.46 mg/g and 543.47 mg/g, at 50 °C, respectively. Pseudo-first-order and
pseudo-second- order models were studied to analyze adsorption kinetics. The result shows the adsorp-
tion kinetic is the best with pseudo-second-order model. Desorption and regeneration experiments using
HNO
3 (0.1 N) eluent were only possible with CTDS, which performed well in four repeated cycles with
high MB and CV removal efficiencies.
©2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction
The textile industry generates large amounts of wastewater
containing dyes and synthetic chemical additives [1] . The presence
of dyes in textile effluents even at very low concentrations is visi-
ble and undesirable. Color wastewater affects the aesthetic nature
of the water and reduces the penetration of light and also the pho-
tosynthesis of aquatic organisms [2] . The releases may have major
drawbacks as well on the man on his environment because of their
stability and formulation [3] .
The treatment of liquid effluents of these industries after fin-
ishing step is usually based on the physico-chemical and biologi-
cal processes. Among the physico-chemical methods, there is the
adsorption which is a simple and effective method for the elimi-
nation of many organic pollutants [4,5] . The principle of treatment
by adsorption is entrapping dyes by a solid compound. In general,
in the various studies conducted by scientists, activated carbon is
a good for treatment of discoloration but it poses problems of high
cost it saturates quickly and it should be removed after use [6] .
∗Corresponding author. Fax: + 212 528220100.
E-mail addresses: noureddine.elmessaoudi@edu.uiz.ac.ma (N.E. Messaoudi),
a.lacherai@uiz.ac.ma (A. Lacherai).
The aim of our work is the development of new materi-
als for use as adsorption media and can make simple purifi-
cation processes and less expensive. Date stones, agricultural
waste, lignocelluloses biomass, abundant in Morocco, available
and no toxic, fall into this category. In fact this material has
physicochemical properties that can induce significant adsorbent
activity.
The treatment of lignocellulosic biomass with acids aims to ac-
tivate the functional adsorption sites and that the increase of the
binding capacity of the screw material of the screw to remove ad-
sorbates. This can be achieved in several ways: by reducing the
content of cellulose, lignin and hemicelluloses from the solid sub-
strate to be processed, increasing the porosity of the matrix, or by
increasing its surface area [7] .
This study attempts to improve the adsorption capacity of
methylene blue and crystal violet on date stones with chemical
treatment by sulfuric acid H
2
SO
4
(2 N) followed the sodium bi-
carbonate NaHCO
3
(1%).The methylene blue and crystal violet are
dyes used in the textile industry, cationic dyes, which have been
shown to have harmful effects on living organisms on short peri-
ods of exposure. Ingestion of dye through the mouth produces a
burning sensation and may cause nausea, vomiting, diarrhea and
gastritis. Accidental large dose creates abdominal and chest pain,
severe headache, profuse sweating, mental confusion, painful mic-
turation and methemoglobinemia [8] .
http://dx.doi.org/10.1016/j.jtice.2016.07.024
1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253 245
Fig. 1. Chemical structures of methylene blue and crystal violet.
Also in this study we proposed a mechanism of interactions be-
tween the functional groups available on the surface of chemically
treated date stones (CTDS) and methylene blue (MB) and crystal
violet (CV).
The raw and treated date stones were characterized by Fourier
transform infrared (FTIR) coupled by attenuated total reflectance
(ATR) technique, thermo gravimetric analysis (TGA) and Scanning
electron microscopy (SEM) analysis.
Adsorption of MB and CV on CTDS was performed by vary-
ing parameters such as contact time, initial dye pH, tempera-
ture and initial dye concentration. The behavior of the equilib-
rium sorption was investigated using the Langmuir, and Freundlich
isotherms models. Adsorption kinetics of MB and CV was tested by
the pseudo-first-order and pseudo-second-order kinetics models.
Desorption behavior MB and CV from CTDS was studied in batch
experiments. Four adsorption-desorption cycles also evaluated. The
developed CTDS demonstrates rapid and excellent removal efficacy
of MB dye than that of various adsorbents reported in the liter-
ature. Finally, we propose the mechanism of interaction between
the ions of MB and CV and surface CTDS.
2. Materials and methods
2.1. Preparation of MB and CV solutions
Methylene blue (molecular weight: 319.86 g/mol, chemical for-
mula: C
16
H
18
N
3
SCl, color index: 52,015) and crystal violet (molec-
ular weight: 407.99 g/mol, chemical formula: C
25
H
30
N
3
Cl, color in-
dex: 42,555), the basic dyes. A stock solution of 1 g/L was prepared
by dissolving 1 g of MB or CV powder in 1 L of distilled water.
The working solutions were prepared by diluting the stock with
distilled water to give the appreciate concentration of the work-
ing solutions. The Chemical structures of MB and CV are shown in
Fig. 1 .
Fig. 2. Photos of original waste (a) and CTDS (b).
2.2. Pretreatment and characterization of adsorbent
Date stones ( Fig. 2 a) were collected in Tinghir (South East of
Morocco). They are washed and placed in an oven at 105 °C for
24 h, then ground on a laboratory mill Retsch SM10 and sieved
to different sizes (50–100, 100–315, 315–50 0 and 50 0–10 0 0 μm)
on laboratory sieve. 1 g of the prepared date stones (50–100 μm)
is mixed with 100 ml of solution sulfuric acid H
2
SO
4
(2 N), well
subjected to heating under reflux for 8 h. After-cooled, the sup-
port was washed with distilled water to remove excess sulfuric
acid before undergoing filtration through filter paper, then washed
with solution of sodium bicarbonate NaHCO
3
(1 %) to eliminate the

246 N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253
Fig. 3. Mechanism proposed of the chemical treatment of date stones.
amount of sulfuric acid for 2 h at room temperature. Finally, the
CTDS ( Fig. 2 b) oven at 105 °C dried for 24 h and sieved to size 50–
100 μm again.
The mechanism proposed of the reaction of this treatment is
detailed in Fig. 3 .
The DS and CTDS were characterized by FTIR spectroscopy with
resolution 4 cm
−1 in a spectrometer Jasco 4100, coupled to ATR.
The morphology of DS and CTDS were examined by SEM and was
recorded on Supra 40 VP Colonne Gemini Zeiss instrument at 15 kV
tension. Thermal stability of raw and treated biomass was studied
with TGA in the range 25–600 °C with the heating rate 10 °C/min at
air atmosphere, recorded using thermogram Shimadzu D60.
2.3. Adsorption batch
Adsorption measurement was determined by batch experi-
ments, 0.05 g of CTDS at size 50–100 μm with 50 mL of aqueous
of MB or CV of 100 mg/L in a series of 100 mL conical flasks. The
mixture was shaken at 293 K using an external circulation thermo-
stat. The impudence of contact time (5–180 min), pH (3–10), tem-
perature (20–50 °C) and initial dye concentration (10 0–80 0 mg/L)
were evaluated during the present study. After the stirring time,
the liquid phase is separated from the residue (crushed) by a cen-
trifuge Sigma 1–6 at speed 40 0 0 rpm/min for 15 min. After cen-
trifugation, the equilibrium concentrations of the solutions were
analyzed using a spectrophotometer ultraviolet (UV–visible 2300-
Techcomp). The standard calibration curve was prepared by record-
ing the absorption of various concentrations values of MB and CV
dyes at a maximum absorption wavelength of 661 nm and 590 nm,
respectively. The percentage removal (%) and the quantity adsorbed
q
e
(mg/g) of dye on CTDS were calculated using the following
Eqs. (1) and (2) , respectively:
% Removal =
( C
0
−C
e
) ×100
C
0
(1)
q
e
=
( C
0
−C
e
) ×V
W
(2)
Where, C
0
(mg/L) and C
e (mg/L) are the initial and equilibrium
concentrations of MB or CV, respectively, V (L) is the volume of so-
lution and W (g) is the weight of adsorbent used.
2.4. Desorption
In order to consider the practical usefulness of the adsorbent,
desorption experiment as performed. After the adsorption test in
3870 3440 3010 2580 2150 1720 1290 860
1147
1262
1616
937
1022
869
1315
937
1147
1262
1517
1616
1747
2852
2921
1025
869
1064
1318
1519
1747
2852
2921
3449
3435
CTDS
DS
Wavenumber (1/cm
)
Fig. 4. FTIR spectra of DS and CTDS.
optimal conditions, the dye-sorbent dried in an oven for 24 h at
60 °C, and then was stirred in 20 mL of nitric acid solution HNO
3
.
The concentration desorbed of MB and CV was determined by
spectrophotometer UV–visible. Desorption behavior of MB and CV
was studied in batch experiment such as concentration of eluent
(0.01-2 N) at 25 °C and 60 min of the agitation time. Desorption (%)
was measured using Eq. (3) :
% Desorption =
C
d
C
a
×100 (3)
Where, C
a (mg/L) and C
d
(mg/L) are concentrations adsorbed and
desorbed of MB or CV, respectively.
3.1. FTIR spectroscopy
The FTIR spectra of DS and CTDS were shown in Fig. 4 . The two
infrared spectra reveal the presence of a broad band at 3435 cm
−1
for DS and 3449 cm
−1 for CTDS, which corresponds to the O–
H bond of elongation vibration [9] . The bands at 2921 cm
−1 and
2852 cm
−1 corresponds to the vibration of asymmetric and sym-
metric stretching, C–H bands of cellulose, respectively [10,11] . The
peak around 1747 cm
−1 is characteristic of the stretching vibration
of C = O of the carboxylic acids of xylan present in hemicelluloses
[12,13] . The vibration at 1616 cm
−1
and 1517 cm
−1
attributed to the
deformation (C = C) aromatic of lignin [14] The bands observed at
1315 cm
−1
and 1262 cm
−1
attributed to the vibration C–O méthoxy
groups of lignin [15] . The peaks between 1147 cm
−1 and 937 cm
−1
correspond to stretching vibrations of C–O and C–O–C bonds of
cellulose [16,17] . The peak at 106 4 cm
−1 corresponds to the S–O
elongation vibration [18] . The band at 869 cm
−1 attributed to the
C–H deformation in cellulose [15] . From this interpretation we can
confirm the presence of -O-SO
3
−groups on the structure of CTDS.
3.2. TGA analysis
Fig. 5 shows the TGA curves matching the weight losses of
DS and CTDS. For each curve, the initial weight loss was due
to release of water of the surface (105 °C), with percentages of
7.17 % for DS and 6.61 % for CTDS. Degradation of organic matter
(cellulose, hemicelluloses and lignin) starts from 210 to 540 °C for
raw DS and from 220 to 500 °C for CTDS [19] , with percentages
of 90.51% and 67.12%, respectively. The rest mass correspond to
the mineral matter, with percentages of 2.32 % ( > 540 °C) for DS
and 26.12 % ( > 500 °C) for CTDS, This difference in amount of the

N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253 247
0 100 200 300 400 500 600
0
20
40
60
80
100
Weight loss (%)
T (°C)
DS
CTDS
Fig. 5. TGA curves of DS and CTDS.
mineral matter between DS and CTDS indicates that the -O-SO
3
−
groups are grafted onto the surface of CTDS.
3.3. SEM images
The SEM images of DS and CTDS were shown in Fig. 6 . The ob-
servation of these images shows a significant change in the mor-
phology of treated support. Indeed, the examination of the mor-
phology of DS ( Fig. 6 a) and CTDS ( Fig. 6 b) shows that the structure
of treated support becomes microporous and irregular. This can be
explained by the introduction of the graft chains in the nuclei of
dates that are processed grains that donot cover the entire surface.
We also observe the presence of porosities can be interesting for
the removal of dyes. The porosity of the structure is essential be-
cause it can provide more binding sites and increase the contact
surface, which facilitates the distribution of the pores in the ad-
sorption process [20] .
3.4. Adsorption
3.4.1. Effect of contact time
The variation of the quantity adsorbed by MB and CV as
function of time at initial dye concentration varied from 10 0 to
300 mg/L, at constant temperature of 20 °C, CTDS dosage of 1 g/L,
pH (MB) = 5.57 and pH (CV) = 5.46 is illustrated in Fig. 7 . From
these results, the quantity adsorbed of MB ( Fig. 7 a) and CV ( Fig.
7 b) ions on the surface of CTDS with increases in time then
reached equilibrium, this equilibrium due the saturation of the ma-
jority of sites by dye ions [21] . The amount adsorbed increased
from 98.07 to 280.37 mg/g for MB and from 98.74 to 283.26 mg/g
for CV with increases in initial dye concentration from 100 to
300 mg/L, at time of 60 min.
3.4.2. Effects of temperature and initial dye concentration
The effects of temperature (20–50 °C) and initial dye concen-
tration (10 0–80 0 mg/L) on the adsorption of MB and CV, at con-
stant contact time of 60 min, CTDS dosage of 1 g/L, pH (MB) = 5.57
and pH (CV) = 5.46. The experimental results are presented in Fig.
8 . This figure shows that the adsorption capacity increased from
97.96 to 99.35 mg/g for MB ( Fig. 8 a) and from 99.18 to 99.77 mg/g
for CV ( Fig. 8 b) on CTDS with increase in the temperature of
the systems 20–50 °C, at 100 mg/L, this temperature increase also
causes the mobility of the dye molecules and decreasing retarding
Fig. 6. SEM images of DS (a) and CTDS (b).
forces acting on the molecules
[22] . Since the adsorption increased
with temperature, therefore, the stem is endothermic. Similar ob-
servations reported in the literature [23–26] . The amount adsorbed
increased at equilibrium from 99.35 to 495.41 mg/g for MB and
from 99.77 to 533.31 mg/g for CV with increases in dye concen-
tration from 100 to 800 mg/L, at 50 °C, when the removal of ad-
sorption decrease from 99.35 to 61.93 % for MB and from 99.77

248 N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253
a
b
Fig. 7. Effect of contact time on adsorption of MB (a) and CV (b) on CTDS: C
0
=
10 0–30 0 mg/L, T = 20 °C, CTDS dosage = 1 g/L, pH (MB) = 5.57, pH (CV) = 5.46.
to 66.67 % for CV .The increase of amount adsorbed with initial
dye concentration can be explained by the enhancement of mass
transfer rates due to a higher MB or CV gradient concentration at
a higher initial dye concentration, subsequently causing the uptake
of more MB or CV molecules and thereby increasing the mass ratio
of dye to CTDS [27] .
3.4.3. Effect of initial dye pH
Fig. 9 shows the effect of the initial solution pH (3–10) on the
adsorption of MB and CV on CTDS, at constant MB and CV concen-
tration of 100 mg/L, CTDS dose of 1 g/L, temperature of 20 °C and
contact time of 30 min. By analyzing these results, we find that
the adsorbed amount increase on CTDS from 88.86 to 99.53 mg/g
for MB and from 90.65 to 99.97 mg/g for CV when the pH of the
solution changes from acidic state to the basic state. The increase
in the adsorbed amount of MB and CV with the pH may be ex-
plained by the fact that the addition of cations H
+ to lower pH,
results in the neutralization of the positive adsorbent load, which
discriminates the adsorption of MB and CV in very acidic environ-
ment. For against, when the pH increases there is a decrease of
cations H
+
, so the adsorbent load is significantly negative which
favors adsorption of MB and CV [28] .
Fig. 8. Effects of temperature and initial concentration on adsorption of MB (a) and
CV (b): C
0
= 10 0-80 0 mg/L, t = 60 min, CTDS dosage = 1 g/L, pH (MB) = 5.57, pH
(CV) = 5.46.
2345678910
89,1
91,8
94,5
97,2
99,9
q
e
(mg/g)
pH
MB
CV
Fig. 9. Effect of initial pH on adsorption of MB and CV on CTDS: C
0
= 100 mg/L, T
= 20 °C, CTDS dose = 1 g/L, t = 30 min.

N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253 249
Fig. 10. Langmuir isotherm model for adsorption of MB (a) and CV (b) onto CTDS:
C
0
= 10 0–80 0 mg/L, t = 60 min, CTDS dosage = 1 g/L, pH (MB) = 5.57, pH (CV) =
5.46.
3.5. Adsorption isotherms
Then most commonly employed adsorption isotherms models
were applied in present study as Langmuir and Freundlich. The
Langmuir model can be described by the following linear form
( Eq. (4) ) [29] :
C
e
q
e
=
1
q
m
K
L
+
C
e
q
m
(4)
Where, K
l
is the Langmuir constant (L/mg) and q
m is the maxi-
mum amount of adsorbate retained on the medium used (mg/g).
The evaluation of the isotherm and their feasibility of the adsorp-
tion process were checked less separation factor R
l
( Eq. (5) ):
R
l
=
1
1 + K
l
C
0
(5)
The R
l
value indicates the mode sorption isotherm process, if
the process is unfavorable ( R
l
> 1) or linear ( R
l
= 1) or favorable
(0 < R
l
< 1) or irreversible ( R
l
= 0) [30] .
The linearized Freundlich model is represented by the following
Eq. (6) [31] :
Ln q
e
= Ln K
f
+
1
n
Ln C
e (6)
Where, K
f
((mg/g) (L/mg)
1/n
) is the Freundlich constant and 1/n is
the intensity of the adsorption.
Fig. 11. Freundlich isotherm model for adsorption of MB (a) and CV (b) onto CTDS:
C
0
= 10 0–80 0 mg/L, t = 60 min, CTDS dosage = 1 g/L, pH (MB) = 5.57, pH (CV) =
5.46.
The Langmuir and Freundlich parameters for adsorption of MB
and CV onto CTDS are determined from the corresponding plots
( Figs. 10 a, b, 11 a and b), which summarized in Table 1 .
Considering the results, the Langmuir isotherm model appears
most satisfactory for the modeling of sorption of MB and CV on
CTDS. The experimental points line up perfectly on a line with
very close correlation coefficient of 1. However, the Freundlich
isotherm appears not give meaningful results for both dyes. Note
that the maximum adsorption capacities 458.71, 473.93, 507.61and
515.46 mg/g for MB, 495.04, 507.82, 531.91and 543.47 mg/g for CV
at 20, 30,40 and 50 °C, respectively, calculated according to the
Langmuir model are very important .The lowest recorded values
of K
l
learn about the building’s stability formed between the ad-
sorbent and the substrates. The values of 1/n and R
l
are always
between 0 and 1, this shows that the adsorption of MB and CV
is favorable for concentrations considered. The data presented in
Table 2 compares the maximum capacities of some adsorbents re-
ported in the literature for the removal of MB and CV.
3.6. Adsorption kinetics
To study the sorption kinetics of MB and CV on CTDS, two ki-
netic models namely the pseudo- first-order and pseudo-second-
order ( Eqs. (7) and (8) ) [47,48] were used in this study at different

250 N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253
Tabl e 1
Isotherms parameters for adsorption of MB and CV onto CTDS.
Dye Langmuir Freundlich
T q
m K
l R
l r
2 K
f 1/n r ²
( °C) (mg/g) (L/mg) ((mg/g)(L/mg)
1/n
)
20 458 .71 0 .061 0 .019–0.139 0 .990 77 .909 0 .300 0 .957
30 473 .93 0 .060 0 .020–0.142 0 .993 82 .682 0 .301 0 .956
MB 40 507 .61 0 .058 0 .021–0.147 0 .993 89 .389 0 .304 0 .959
50 515 .46 0 .051 0 .023–0.163 0 .994 108 .361 0 .276 0
.971
20 495 .04 0 .241 0 .004–0.051 0 .997 124 .290 0 .267 0 .850
30 507 .82 0 .183 0 .006–0.052 0 .999 127 .497 0 .262 0 .861
CV 40 531 .91 0 .164 0 .007–0.057 0 .998 132 .356 0 .256 0 .882
50 543 .47 0 .159 0 .008–0.059 0 .999 135 .058 0 .288 0 .798
Tabl e 2
MB and CV adsorption maximum capacities of various adsorbents reported.
Dye Adsorbent q
m
(mg/g) Ref.
MB Sugar beet pulp 714 .29 [32]
Phosphoric acid treated parthenium hysterophorus 88 .89 [33]
NaOH-modified date stones 130 .54 [34]
Activated sludge biomass 256 .41 [35]
Pretreated spirogyra sp. 64 .61 [36]
Modified sugarcane bagasse by acid TiO
2
hydrosol 564 .00 [37]
Esterified wheat straw 312 .50 [38]
Modified corynebacterium glutamicum 337 .50 [39]
Chemically treated date stones 515 .46 This study
CV Bacillus amyloliquefaciens biofilm 582 .41 [40]
Grapefruit peel 254 .16 [41]
Saw dust 341 .00 [42]
Treated ginger waste 277 .70 [43]
Sugarcane bagasse modified with meldrum’s acid 692 .10 [44]
Formosa papaya seed powder 85 .99 [45]
Coffee grounds 36 .82 [46]
Chemically treated date stones 543 .47 This study
Tabl e 3
Kinetics parameters for adsorption of MB and CV onto CTDS.
Dye C
0
(mg/L) q
e, exp
(mg/g) Pseudo-first-order model Pseudo-second order model
q
e, cal K
1 r
2 q
e,cal K
2 r ²
(mg/g) (1/min) (mg/g) (g/mg/min)
MB 100 99 .35 4 .85 0 .042 0 .871 99 .50 0 .019 0 .999
200 194 .76 53 .94 0 .036 0 .837 198 .80 0 .016 0 .999
300 287 .45 145 .34 0 .032 0 .887 289 .11 0 .009 0 .998
CV 100 99 .53 3 .52 0 .021 0 .872 99 .70 0 .017 0 .999
200 195 .95 48 .90 0 .015 0 .878 199 .45 0 .011 0 .997
300 290 .10 131 .93 0 .013 0 .821 292 .23 0 .002 0 .995
concentrations. The results are shown in Figs. 12 a, b, 13 a and b,
and the characteristic parameters of each model are summarized
in Table 3 .
Log ( q
e
−q
t
) = Log ( q
e
) −K
1
2 . 303
t (7)
t
q
t
=
1
K
2
q
2
e
+
1
q
e
t (8)
Where, q
t (mg/g) and q
e (mg/g) are the amounts adsorbed at time
t and equilibrium, respectively, K
1
(1/min) and K
2
(g/mg/min) are
the pseudo-first-order and pseudo-second-order constants.
According to the results, we find that the adsorbed amounts
calculated ( q
e, cal
) by the model of the pseudo-first-order and
adsorbed amounts experimental ( q
e, exp
) vary widely, unlike the
pseudo-second-order model cases are very close, as the correlation
coefficients are very close to 1. Therefore, the adsorption kinetics
and of MB and CV on CTDS better described by the model of the
pseudo-second-order. We notice that the values of K
1
and K
2
de-
crease with increasing initial concentration of MB and CV, due may
be to competition for the adsorptions sites at higher concentration.
3.7. Desorption and regeneration studies
Regeneration of the CTDS is an important step in order to check
in economic the feasibility of adsorption process. Desorption of MB
and CV from CTDS using HNO
3
as an eluent at concentration from
0.01 to 2 N, as indicated in Fig. 14 . The results show that the maxi-
mums desorption of MB (95.38 %) and CV (97.86 %), were obtained
with 0.1 N of HNO
3
. We observe a decrease of desorption of MB
and CV at higher concentrations of HNO
3
. This may be due to the
fact that the reactions involved in desorption are exchange reac-
tions. These are governed by the law of chemical equilibrium, they
take place until the concentrations of various ions reach certain
specific proportions. Therefore, a 0.1 N HNO
3
solution is adopted
as the desorption agent. After each test of desorption using HNO
3
(0.1 N), the support washed with distilled water several times to
remove traces of HNO
3
, then dried in an oven for 24 h at 60 °C.

N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253 251
Fig. 12. Pseudo-first-order kinetic for adsorption of MB (a) and CV (b) onto CTDS:
C
0
= 10 0–30 0 mg/L, T = 20 °C, CTDS dosage = 1 g/L, pH (MB) = 5.57, pH (CV) =
5.46.
After drying the CTDS reuse for the adsorption of MB and CV in
optimal conditions. The results obtained are presented in Fig. 15 a
and b. The result that the CTDS are employed at least 4 cycles
desorption-adsorption without losing their desorption efficiency of
MB and CV.
3.8. Sorption mechanism of MB and CV
The retention of dyes onto the CTDS surface is attributed to the
functional groups of its surface and the role of electrostatic attrac-
tion. Indeed the CTDS surface has a large number of oxygen- con-
taining functional groups, as illustrated in Fig. 16 , which are bene-
ficial to the adsorption of CV and MB.
Fig. 16 shows the schematic diagram of DS treatment and ad-
sorption of MB and CV onto CTDS through interaction of different
parts.
4. Conclusion
The chemically treated date stones (CTDS) is an effective ad-
sorbent for removing cationic dyes, methylene blue and crystal
violet from aqueous solutions. Infrared spectroscopic FTIR study
allowed us to identify the grafted groups on CTDS. The TGA
analysis suggests that the chemical treatment of date stones has
Fig. 13. Pseudo-second-order kinetic for adsorption of MB (a) and CV (b) onto
CTDS: C
0
= 10 0–30 0 mg/L, T = 20 °C, CTDS dosage = 1 g/L, pH (MB) = 5.57, pH
(CV) = 5.46.
Fig. 14. Desorption of MB and CV from CTDS using HNO
3
.

252 N.E. Messaoudi et al. / Journal of the Taiwan Institute of Chemical Engineers 67 (2016) 244–253
Fig. 15. Regeneration of CTDS using HNO
3
(0.1 N): MB (a) and CV (b).
reduced the organic matter (cellulose, hemicelluloses, and lignin)
and the increase of the mineral matter. We have also focused on
the morphology of DS and CDTS with SEM. This technique shows
the increase in porosity of the support treated. Indeed, the study
of the influence of various parameters influencing adsorption,
concluded that MB and CV dyes are eliminated very quickly CTDS.
We conducted a MB adsorption equilibrium modeling and CV by
equations of Langmuir and Freundlich. The parameters for each
isotherm were determined. This study showed that the adsorption
of MB and CV on CTDS is best described by Langmuir isotherm,
with maximums amounts adsorbed very important. The kinetics
of the adsorption was modeled by two models of the pseudo first
and second orders, the result showed that it is the pseudo second
order. Finally, excellent regenerative efficacy of the CTDS con-
tributes a significant achievement toward sustainable development
in dye contaminated wastewater treatment.
Acknowledgments
The authors would like to acknowledge the Professor A. Khal-
laayoun, Department of Chemistry, Faculty of Science, Ibn Zohr
University for his support.
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