CC BY
33
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 544.72
ADSORPTION STUDY OF Fe(III) IONS BY MASC-2-AMINO-4-NITROPHENOL E.J.Eyyubova, Kh.J.Nagiyev, F.M.Chiragov
Baku State University
Received 14.05.2019 Accepted 10.09.2019
Adsorption of ferric(III) ions by a chelating synthetic sorbent based on the copolymer of styrene with ma-leic anhydride (MASC) and 2-amino-4-nitrophenolwas studied. Adsorption characteristics of the sorbent with respect to Fe(III) ions have been investigated. Various parameters influencing adsorption - optimal pH, the ionic strength, the time necessary for establishing complete sorption equilibrium, the initial concentration of metal ions were studied. It was shown that the maximum adsorption capacity of the sorbent with respect to ferric ions is 373.33 mg/g at pH=5. Several adsorption isotherm and kinetic models have been explored and the most relevant to our experimental data has been revealed .
Keywords: sorption, Fe(III), chelate-forming sorbent, preconcentration.
doi.org/10.32737/0005-2531-2020-2-26-33
Introduction
Iron is found in chemical wastewater, metallurgical, machine-building, metalworking, petrochemical, textile, chemical-pharmaceutical and other industries. When the iron content is more than 1 mg/l, the water becomes brown. In connection with the growth of industrial production, there is an increase in the consumption of natural water and, as a result, an increase ingen-erated wastewater. Insufficiently treated wastewater is the main source of pollution and clogging of natural reservoirs, lead to significant physicochemical changes in the properties and composition of water, making it unsuitable for household use. The most common toxic impurities of wastewater are heavy metals. Sources of these impurities are waters of textile, leather, electroplating, chemical and machine-building enterprises, as well as ore and mine enterprises production [1, 2].
The aim of this work is to study the sorption of Fe(III) ions from its aqueous solutions by a polymeric chelating-forming sorbent based on a copolymer of styrene with maleic anhydride and 2-amino-4-nitrophenol [3-6]. Various sorption characteristics, in particular the effect of pH, time, ionic strength, initial concentration of the metal ion, were studied. The process of desorption was also investigated and the optimum elu-ent was established. Several adsorption isotherm and kinetic models have been studied [7].
Experimental part
Preparation of solutions. The initial metal solution of Fe(III) ions with concentration
3 1
of 5-10 mol/L was prepared by using 10-1 M FeCl3 solution, prepared by dissolving reduced iron in HCl and HNO3. The equilibrium concentrations of Fe(III) ions in the solution were determined with the help of the corresponding reagent 2,2'-([1,1'-biphenyl]-4,4'-diilbis(diazen-2,1-diyl)è/s(benzene-1,3,5-triol) C18H18O6N4 (R) [8]. Optical densities of the solutions were measured on KFK-2 and optimal pH=5 and X=490 nm were established.
Buffer solutions from 1 to 5 were prepared on the basis of 0.1 N solutions of CH3COOH and NH3 H2O. To study the effect of ionic strength on the sorption capacity of the sorbent, 2 mol/L KCl solution was used, as well as 2 mol/L KOH solution to study the desorption process. For the synthesis of the sorbent, a styrene maleic anhydride copolymer (Scheme 1) and 2-amino-4-nitrophenol (Scheme 2) were used.
- CH— CH
Scheme 1. Molecular structure of a copolymer of styrene with maleic anhydride.
n
OH
NH,
My
O ^O
Scheme 2. Molecular structure of 2-amino-4-nitrophenol.
Synthesis of sorbent. Synthesis of the sorbent was carried out according to a known technique [1]. As the polymer matrix for the synthesis of the sorbent, styrene maleic anhydride copolymer and 2-amino-4-nitrophenol were used. For that purpose, 3 g of polymer were added to the round bottom flask. Subsequently, the appropriate amount of 2-amino-4-nitrophenolwas weighed, dissolved in water and added to the original contents of the flask. The synthesis was carried out in the presence of formalin, as a cross-linking agent. The reaction was carried out at a temperature of 60-700C, for 30-40 minutes. During the reaction, the following transformations were observed:
CH2— CH-
+ nH2O
n
CH?—CH
I ^O HO OH
n
Since the process is carried out in an aqueous medium, the anhydride groups of the polymer undergo hydrolysis.
H9C í
O
+ R—NH9
HO
NHR
O
HO
NHR
+
OH
NH
\ R
O
O
Scheme 3. The mechanism of the sorption process.
As a result of the mutual influence of formaldehyde and amine, an unstable carbonyl-amine is formed. The resulting carbonylamine interacts with the carboxyl groups of the mac-romolecule and thus the amine is introduced into the macromolecule.
At the end, the resulting synthesis product is passed through a filter paper, washed, dried, ground and used for further research.
Preconcentration. Sorption studies of Fe (III) ions were carried out at room temperature. For each experiment, 2 ml of a solution of a metal ion with a known concentration (5-10" mol/L) was added to 50 ml conical flasks. In each flask, 30 mg of sorbent and corresponding pH were added. The pH of the solutions was monitored using a pH meter Ionomer-130. The resulting mixture was kept for 24 hours. The contents of the flask were then passed through a filter paper and the liquid phase was separated from the solid phase.
Subsequently, 1 ml samples were taken from each flask, diluted with a buffer solution of pH 5, and final concentrations of Fe (III) ions were measured with the reagent 2,2 -([1,1-bi-phenyl]-4,4' -diilbis(diazen-2,1 -diyl)é/s(benzene-1,3,5-triol) C18H18O6N4 (R) on the photoelectro-colorimeter KFK-2 at X=490 nm. The degree of metal ion extraction was calculated by the following formulas:
= loo (co -c)v
q =
m
(1)
t
where C0 is the initial concentration of the metal ion (mol-L"1), Ce is the equilibrium concentration of the metal ion (mol-L"1), V is the volume of the solution (L), and m is the sorbent mass (mg).
The desorption process. Desorption studies were carried out using different inorganic acids of the same concentration, namely: 0.5 mol-L-1 solutions of HNO3, HCl, H2SO4 and CH3COOH acids. To carry out the experiment, 30 mg of sorbent were weighed into 4 flasks, 2 ml of a 540" mol/LFe (III) solution and 18 ml of pH 5.0 were added and left for 24 hours. Subsequently, the solid portion of the solution was separated from the liquid by filtration. To the filtered portion was added 20 ml of 0.5 mol/L solutions of HNO3, HCl, H2SO4 and CH3COOH acids.
Tightly closed and left for 24 hours. At the end of the day, the liquid portion of the solution was again separated from the solid. 1 ml was then taken from the homogeneous solution, 1-2 ml of a 2 mol/L solution of KOH was added, diluted with a buffer solution of pH 5.0, and final concentrations of Fe (III) ions were determined with (R) on KFK-2 [2].
Equipment. Absorbances of solutions were measured on photoelectrocalorimeter KFK-2 in a cuvette with a layer thickness l = 1. pH values measured on the pH meter IonomerI-130. The IR spectrum of the sorbent was taken on a Varian 3600 Fourier spectrometer in the region from 400 to 4000 cm-1.
Results and discussions
Sorbent structure. The result of stud-
ying the structure of the sorbent is shown in Figure 1.
As can be seen from Figure 1, the following functional groups are present in the structure of the sorbent. The vibrational frequencies are observed in IR spectra of sorbent: at 36003100 cm-1 [valence oscillations of the -OH group in the carboxyl group, the covalent vibrations of the group -NH (3400-3200 cm-1)], 1780-1750 cm-1 (valence oscillations of the -C=O group of the carboxyl group), 1570-1540 cm-1 (the valence oscillations of the C-N group and the deformation vibrations of the N-H group), 725-675 cm-1 (deformation vibrations of the C-C group in the benzene ring)
Effect of pH on the degree of Fe(III) extraction. One of the most important parameters that affect the degree of sorption is pH, so studying the effect of this parameter is an important task. For this purpose, 30 mg of sorbent was weighed and added to the flask. Further, 2 ml of a 5-10'3mol/L metal ion solution and 18 ml of an appropriate pH of 1 to 5 were added. The contents of the flask were stored for 24 hours.
After a day, the solid portion of the solution was separated from the liquid and the optical densities of the homogeneous solutions were measured on a KFK-2 photoelectrocalorimeter with a buffer solution pH 5.0 at a wavelength 490 nm. The results of the studies showed that the greatest metal recovery is observed at a pH value 5.0. Further sorption experiments were carried out at a given pH value 5.0. A graphic representation of the data is shown in Figure 2.
Fig.1. IR spectra of adsorbent.
s
CL S
^ 00
S "IP ■- S "S.
L.
o
rjï <
120 100 80 60 40 20 0
0 2 4 6
PH
Fig. 2. Effect of pH on adsorption capacity
msorb.=30 mg, Vgen=20 ml, CMe=5^10-3mohL-1.
The influence of time on the degree of the metal ion extraction. The effect of time on the sorption capacity of the Fe(III) metal ion is shown in Figure 3. In order to study this parameter, measurements were made in the range from 0 to 270 min. The equilibrium concentrations of metal ions in the sample were determined at the appropriate time intervals on KFK-2 and X = 490 nm.
Cl- ions has a negligible effect on the extraction of metal ion and practically does not affect the adsorption capacity of the adsorbent.
Effect of the initial concentration of Fe(III) ions on the adsorption capacity. In the course of the experiment, the effect of the initial -n metal ion concentration on the degree of adsorption by the synthesized sorbent was studied. For this purpose, the concentration range of Fe (III) ions was used from 0.1-10" mol/L to 6-10" 3mol/L. For this, 30 mg of sorbent were weighed, the corresponding volumes of the metal ion solution and pH 5.0 were added. After 150 minutes, the optical densities of the homogeneous solutions on KFK-2 were measured with a buffer solution pH 5.0 at X = 490 nm. The degree of extraction of the metal ion by the adsorbent was calculated using the well-known formula (1). The results are graphically depicted in Figure 4 and Table 1.
Fig.3. Effect of time on adsorption capacity
msorb=30 mg, Vgen=20 ml, CMe=5-10-3mol/L-1.
As can be seen from Figure 3, in the period from 0 to 120 min, the degree of sorption gradually increases, and from 150 min remains constant. This indicates to the attainment of complete sorption equilibrium.
Effect of ionic strength on the sorption capacity of the sorbent. In the course of this work, the influence of ionic strength on the degree of the Fe(III) ion extraction was investigated. For these purposes, 2 mol/L potassium chloride KCl solution was used.
Studies have shown that within the range of ^ = (0.2-1.4)mol/L, the presence of K+ and
Fig.4. Effect of initial metal ion concentration on the adsorption capacity. msorb.=30 mg, VKen=20 ml, CMe=5-10-3mol/L-1.
Table 1. Extraction degree of Fe(III) ions by a synthesized sorbent
CMe, x-10-3 mol/L 0.1 0.2 0.4 0.8 1 2 4 6
R, % 42 58 69 75 82 85 95 93
The results of the studies showed that the greatest sorption capacity is observed at a Fe(III) concentration of 4-10- mol/L.
The desorption process. This work also involves studying the reverse process-desor-ption. The presence of the necessary eluents for
desorbing the metal ion is an important task. In our article, this process is carried out by using different inorganic acids with the same concentration, in particular 0.5 mol/L solutions of HNO3, HCl, H2SO4 and CH3COOH acids. The results of the studies have shown that maximum desorption ability over Fe(III) ions shows 0.5 mol/L solution of HNO3.
Langmuir isotherm
Langmuir model can be described using the following equation [Langmuir 1918]
q =
qmKLCe
1 + KLCe
(3)
where Ce (mmol/L) is concentration of adsorbate in the aqueous phase at equilibrium, qe (mmol/g) is the equilibrium adsorption capacity, qm is equal to qe for the complete monolayer and KL (L/mmol- ) is the Langmuir isotherm constant.
Linear plot of dependence of 1/qe versus 1/Ce is shown in Figure 5. The values of the qmax and KL were calculated from the slope and the intercept of the plot, respectively.
Fig.5. Langmuir isotherm model.
The essential characteristic of the Lang-muir isotherm can be represented by a separation factor called equilibrium parameter (RL) and has the following form:
R = , (4)
1 + bC0
where b is the Langmuir constant (L/mmol), Co is the initial concentration of adsorbate (mmol/L). The value RL indicates the isotherm type. A value between 0 and 1 shows favorable adsorption process.
Results show that RL lies between 0 and 1 and is equal to 0.99, which shows that adsorption is favorable under the specified experimental conditions by Langmuir model. Also the value of the coefficient of regression R =0.9382 indicates that isotherm model fits good with experimental adsorption data. Freundlich isotherm The Freundlich model is described by the following equation [Freundlich 1906]
1
ln qe = ln Kf + - ln C
n
(5)
where Ce (mmol/L) is adsorbate concentration at equilibrium, qe (mmol/g) is the equilibrium adsorption capacity, KF is the Freundlich constant and 1/n the heterogeneity factor.
The plot of dependence of lnqe versus lnCe is shown in Figure 6. The values of KF and 1/n were calculated from the slope and intercept of the plot, respectively.
Fig.6. Freundlich isotherm model.
KF indicates capacity of adsorption process (mg/g), n provides an approximation of adsorption intensity. A favourable adsorption is estimated when the value of n is 1 -10. Results show that the value of n is equal to 1.66 for, which indicates favorable adsorption process. On the other hand 1/n is considered as a function of adsorption strength. If value of 1/n is lower than 1 it means a normal adsorption, if 1/n>1 it shows cooperative adsorption. In our case 1/n= 0.602, which indicates to normal adsorption process.
Dubinin-Raduskhevich isotherm
The Dubinin-Radushkevich (D-R) model is used to explain adsorbent's porosity. The iso-
e
therm is obtained on the basis of the following equation [Dubinin 1947]
ln qe = ln qs ~ kD-Rs2, (6)
where qsis the theoretical saturation capacity (mmol/g), kD_R is the D-R isotherm constant related to the free energy of adsorption, and s is Polanyi potential that is related to the equilibrium concentration as follows:
e = RT ln
k) •
(7)
where R (8.314 Jmol-1K-1) is the gas constant and T (300 K) is the absolute temperature.
Adsorption energy was calculated by the following equation:
e = -j=^ • (8)
\2kd- r
Linear plots of ln^e versus e2 are given in Figure 7. The values of q3and kD_R are calculated from the intercept and slope.
The value of R2 is equal to 0.8829. E is equal to 3.5 kJ/mol. If E lies between 8 and 16 kJ/mol then it shows chemisorptions process, while the value of E lower than 8 kJ mol-1 means physical adsorption process. So in our case 3.5 kJ/mol value of E means that physical adsorption process is observed between S and Fe(III).
Pseudo-first-order model The adsorption kinetic data in this model is rated using pseudo-first-order equation (Lagergren's equation). It helps to evaluate the adsorption degree by adsorption capacity. The equation is as follows:
(9)
ln (qe ~ qt ) =ln qe ~ k i,
where qeand qt are adsorption capacities at equilibrium and time t (min), respectively (mgg"1) and kt is the rate constant of pseudofirst-order adsorption (min"1).
The plot of dependence of — versus t is shown in Figure 8.
Fig.7. Dubinin-Raduskhevich isotherm model. Fig.8. Pseudo-first-order kinetic model.
Table 2. Langmuir, Freundlich and Dubinin-Raduskhevich isotherm parameters
Langmuir Freudlich Dubinin- Raduskhevich
Adsorbent 1? q J 1? j i (Rl) (R2) 'tg 1? i (1/n) (R2) '->0 I? dq (E, kJ-mol-1) <n (n* 1 (R2)
S 13.44 24.08 0.99 0.93 0.35 0.60 0.75 384.25 3.5 4 -10-8 0.88
Values of k± and qe were calculated from slope and intercept of the plot of — ?t) versus t. The large difference between the experiment qg value tf0(exP) and the calculated qB value £?0(Cai) shows that pseudo-first order kinetic model was poor fit for the adsorption process of sorbent S for Fe(III).
Pseudo-second-order model
Adsorption kinetics can also be explained by using pseudo-second-order model. For that purpose the following equation is used:
t
1
-1(10) qe
where fe2is the rate constant of pseudo-second-order adsorption (g/mg~' min"1) and kq^ is the initial adsorption rate (mg/g-1 min"1).
The plot of dependence of t/qt versus t is shown in Figure 9.
CT"
25 I 20 -15 10 5 0
j = 0.128.V-0.0057 R2 = 1
0
100
200
300
time, t
Fig.9. Pseudo-second-order kinetic model.
Values of k2 and qe were evaluated from the intercept and slope of the plot of t/qt versus t. For pseudo-second order kinetic model we can see that the experiment qe value qe(exp) and the calculated qe value qe(cal) are close to each other, so that adsorption process of synthesized sorbent S for Fe(III) can be well described by the pseudo-second order kinetic model.
Results of kinetic studies are shown in Table 3.
Table 3. Adsorption kinetic parameters
Adsorbent Pseudo-first-order Pseudo-second-order
qe, (exp), mg/g &i, (min-1) qe (cal), mg/g (R2) k2, (g/mgmin-1) qe (cal), mg/g (R2)
S 373.33 0.0106 20.16 0.8514 1.36 435 1
Conclusion
The results of the investigations are quite high, in particular, when studying the effect of the initial concentration of metal ions on the sorption capacity of the sorbent, the maximum sorption capacity of the sorbent is 373.33 mg/g. The foregoing allows us to assume the possibility of using the synthesized sorbent, based on a copolymer of styrene with maleic anhydride and m-aminophenol, for extracting Fe (III) ions from various natural and industrial objects.
Acknowledgement
This work has been performed with the support of Internal University Grant of Baku State University "50+50".
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Fe(III) MASS-2-AMÏNO-4-NÎTROFENOL ÏLO SORBSiYASININ ÖYRONiLMOSi
E.C.Eyyubova, X.C.Nagiyev, F.M.Çiraqov
Maqala damir(III) ionlarinin malein anhidridinin stirol ila birga sopolimeri va 2-amino-4-nitrofenol asasinda sintez edilmiç xelatamalagatirici sintetik sorbent tarafindan adsorbsiyasinin öyranilmasina hasr edilmiçdir. Sorbentin Fe(III) ionlarina qarçi sorbsion xüsusiyyatlari ôyranilmiçdir. Tadqiqat zamani sorbsiyaya tasir edan müxtalif parametrlar, xüsusila, optimal pH, ion qüvvasinin tasiri, zamandan asililiq, metal ionlarinin ilkin qatiliginin tasiri ôyranilmiçdir. Araçdirmalar göstarir ki, maksimum sorbsiya tutmu mühitin pH=5 qiymatinda 373.33 mq/q taçkil edir. Tadqiqat zamani bazi sorbsiya izotermlari va kinetikasi ôyranilmiçdir.
Açar sözlar: sorbsiya, Fe(III), xelat3m3hg3tirici sorbent, qatila§dmlma.
ИЗУЧЕНИЕ СОРБЦИИ ИОНОВ Fe(Ш)ССМА-2-АМИНО-4-НИТРОФЕНОЛОМ
Э.Дж.Эюбова, Х.Дж.Нагиев, Ф.М.Чырагов
Исследована адсорбция ионов железа(Ш) хелатобразующим синтетическим сорбентом на основе сополимера стирола с малеиновым ангидридом (МАСС) и 2-амино-4-нитрофенолом. Изучены адсорбционные характеристики сорбента по отношению к ионам Fe(Ш). Исследовано влияние различных параметров на адсорбцию -оптимального рН, ионной силы, времени необходимого для установления полного сорбционного равновесия, начальной концентрации ионов металлов. Показано, что максимальная адсорбционная емкость сорбента по отношению к ионам трехвалентного железа составляет 373.33 мг/г при рН=5. Изучено несколько изотермических и кинетических моделей адсорбции и выявлена наиболее соответствующая нашим экспериментальным данным.
Ключевые слова: сорбция, Fe(Ш), хелатообразующий сорбент, концентрирование.
