Physicochemical and Sorption Properties of Anionites Based on Aromatic Amines, Epichlorohydrin and Polyethylenimine with Regard to Strontium (II) Ions

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 4, Pages: 1568-1573

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

https://doi.org/10.47277/JETT/1573

Physicochemical and Sorption Properties of

Anionites Based on Aromatic Amines,

Epichlorohydrin and Polyethylenimine with Regard

to Strontium (II) Ions

Edil Ergozhin, Tulegen Chalov, Tatyana Kovrigina, Yevgeniy Melnikov*

A.B. Bekturov Institute of Chemical Sciences, 106 Sh. Ualikhanov Str., Almaty, 050010, Republic of Kazakhstan

Received: 27/06/2020

Accepted: 27/09/2020

Published: 20/12/2020

Abstract

Multifunctional anion exchangers based on aromatic amines, epichlorohydrin and polyethylenimine have been synthesized. Their

composition, structure, and thermal stability have been studied using IR spectroscopy, elemental and thermogravimetric analyses. Extraction

of strontium ions has been studied using classical polarography, and sorption of strontium (II) ions in static regime has been determined as a

function of solution acidity, metal ion concentration, and contact duration of ionites with SrCl solution. It has been established that the

obtained ion exchangers are characterized by high sorption properties with regard to strontium ions. The novelty of these studies is that the

sorption dependence of synthesized ionites with regard to Sr²⁺ions has been studied for the first time. The practical importance of this work

is the development of anion exchangers with higher extractability, which could successfully solve the issues of elimination of strontium (II)

ions from process wastes of nonferrous metallurgy.

Keywords: Sorption, Strontium, Sorption capacity, Anion exchanger, Extraction

and readily recovered sorbents [7]. A significant number of

Introduction

publications are devoted to studying the features of separation and

extraction of strontium and its purification from the impurities

using anionites of various structure [3, 8–10]. In [3], the authors

studied the sorption capacity of new adsorbent obtained from

almonds in relation to strontium ions, where the sorption capacity

Development of nuclear power engineering and

accompanying industries results in contamination of

environmental objects by radioactive metal ions, which poses a

health risk, since long-living radionuclides tend to accumulation,

can easily be transferred to high distances and quite often

participate in the biological cycle [1]. In this regard it is very

important to develop efficient sorbents produced by simple and

inexpensive process as well as characterized by high capacity and

selectivity with regard to extracted cations and reliably holding

radionuclides extracted from contaminated solutions in the form

suitable for long-term storage, processing, or disposal [2].

Strontium is one of the main contaminants of radioactive

waste waters widely occurring in nuclear fuel, medicinal and

industrial radioactive wastes [3, 4]. It is well known that strontium

is characterized by long half-life, high solubility, and high

bioaccessibility. After penetration with contaminated food into

organism strontium will accumulate in bones and marrow, which

can cause cancer of adjacent tissues and leukemia. Therefore,

systematic and efficient methods of elimination are especially

important to provide steady development of humans and

environmental protection [3–6].

-1

SC) reached 11.45 mg·g at pH = 10.8. At strontium

-1

(

concentration of 20 mg·l and pH = 7.0 ± 0.1 of the solution, the

SC values of the modified ion exchangers approached the value

-1

of 1.6 mg·g [4]. In [5], the authors analyzed the environmental

conditions impact on the sorption behavior of Sr (II) and

identified that the Sr (II) sorption was greatly affected by ionic

strength at pH <9.5, and no effect at pH> 9.5 was found. This fact

indicated that in the mechanism of Sr (II) sorption, outer-sphere

surface complexation or ion exchange at low pH prevailed; at pH

7.0 ± 0.1 and сSr = 15 mg·l , the SC value reached 20 mg·g .

In [6], the authors found that the SC of complexing polymeric

sorbents based on EDE-10P and chlorine-containing quinones

-1

was 358.2 - 420.4 mg·g at pH = 4.6, cSr = 1.926 mg·l . Thus, in

8] it was established that maximum SC of polymer complexing

sorbents of various structure with regard to strontium ions was 50

[

mg·g at pH of solution from 2.2 to 7.0. Thus, certain interest is

attracted to analysis of strontium ions sorption on specially

produced anionites characterized by high SC and containing

Sorption is one of the most efficient approaches to treatment

of wastes with heavy metals due to its low cost, high efficiency

Corresponding author: Yevgeniy Melnikov, A.B. Bekturov Institute of Chemical Sciences, 106 Sh. Ualikhanov Str., Almaty, 050010,

Republic of Kazakhstan. E-mail: sebas273@mail.ru

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2020, Volume 8, Issue 4, Pages: 1568-1573

active groups in their structure. This work is aimed at analysis of

physicochemical and sorption properties of multifunctional

anionites based on epoxy derivatives of aromatic amines and

polyethylenimine with regard to strontium (II) ions.

elemental analysis using a CHN628 instrument (LECO, USA). As

can be seen in Fig. 1, a, b , the IR spectra of A–ECH–PEI and

BA–ECH–PEI anionites are very similar, which probably could

be attributed to close chemical structure. These spectra do not

-1

contain characteristic bands (cm ) of epoxy groups (810–920;

,250; 3,000–3,010), there appear bands of N–H bending

vibrations (1,599–1,600) and C–N stretching vibrations (1,020–

,220) of amine group bonds, which evidences chemical

Methods

On the basis of aniline (A) or benzylamine (BA) and

epichlorohydrin (ECH) we synthesized epoxy amines, and then,

by condnesing them with polyethylenimine (PEI), multifuctional

anionites A–ECH–PEI and BA–ECH–PEI [11]. At first, using A

or BA and ECH in the presence of caustic soda at 50°C for 6 h,

glycidyl derivatives of amines (epoxy amines) were synthesized.

Then, their polycondensation with PEI was carried out in

dimethylformamide (DMFA) solution at various ratios, 60–65°C

for 5–6 h, then the reacted mass was solidified at 100°C for 16–

interaction of diglycidyl derivatives of A and BA with PEI. The

frequency at 3,500 characterizes occurrence of hydroxyl groups.

Absorption in the 1,502–1,504 area, stipulated by stretching

vibrations of benzene ring, confirms existence of aromatic

fragments in the anionite structure [12]. The elemental

composition of anionites (detected/predicted), % for A–ECH–

PEI: C – 73.32/73.86; H – 17.60/17.34; N – 5.89/5.60; O –

.19/3.20; and for BA–ECH–PEI: C – 70.72/70.92; H –

7.61/17.48; N – 7.81/8.09; O – 3.86/3.51. On the basis of

4 h. Composition and chemical structure of the anionites were

analyzed by IR spectroscopy using a Nicolet 5700 Fourier

spectrometer (Thermo Electron Corporation, USA) and by

chemical and spectral analyses, the structure of synthesized

polymers can be presented as follows (Figure 2):

Figure 1: IR spectra of BA–ECH–PEI (a) and A–ECH–PEI (b). I – intensity, ν – wave number (cm )

CH₂CH CH2

CH2 CH CH2

CH₂CH CH₂

CH₂

CH2

CH₂

CH2

CH₂

^C^H2

CH2

CH₂

^C^H2 CH CH2

CH2 CH CH2

CH CH₂

CH₂CH CH2

CH2

A–ECH–PEI

BA–ECH–PEI

Figure 2: Structures of synthesized polymers

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The morphology and chemical structure of polymer matrix,

as well as the structure of surface of the given anionites are similar

to that studied previously and described in [13]. Thermal

resistance of anionites in OH form was studied by

thermogravimetric analysis (TGA). Thermograms were obtained

using TGA/DSC1 thermogravimetric analyzer (Mettler Toledo,

Switzerland) in air in the range of 20–600°C at heating rate of

The contact duration of sorbents with solutions was from 0.5 h to

7 days. The model solutions were prepared using SrCl *6H O,

2 2

reagent grade. The SC was calculated by the difference between

initial and equilibrium concentration of solutions, determined by

classical polarography against 0.5 M LiCl by the reduction wave

Sr (E1/2 = −2.03 V). Polarograms were recorded using a PU-1

universal polarograph with the measurement error of ±0.5% in

thermostatic cell at 25±0.5°C using dropping mercury electrode.

Oxygen was removed from the analyzed solution by purging

argon for 5 min. Saturated calomel electrode was used as

reference. The modes of sorption experiments were selected

(sorbent-to-solution ratio, concentration and pH of strontium

containing model solutions, and contact duration) being close to

commercial conditions.

0°C/min. In order to determine static exchange capacity (SEC)

of anionites using 0.1N HCl solution, a sample of anionite in the

OH from in the amount of 1 g on dry basis measured with the

accuracy of 0.0002 g was poured with 100 ml of 0.1N titrated

solution of hydrochloric acid in 250 ml flat bottom flask and

sealed. Reaching equilibrium (24 h), 25 ml of filtrate was titrated

by 0.1N solution of sodium hydroxide in the presence of three

droplets of methyl red until pink color changed into yellow. The

concentration of functional groups in polymer phase

Results and discussion

Practical application of ionites requires for analysis of their

-1

corresponding to the ionite SEC (mg-eq·g ) was calculated as

follows: SEC = (100 – 4V)/10 P, where V was the exact volume

of 0.1N solution of sodium hydroxide consumed for titration (ml);

P was the ionite sample on dry basis (g). In order to determine the

volume occupied by mass unit of dry ionite after swelling in

water, a sample of about 10 g was placed into cylinder and poured

with 70 ml of water. The cylinder was tightly sealed and agitated

up to complete wetting of lower layers of ionite and held in

horizontal position for 12 h. Then the cylinder was positioned

vertically, water was refilled to 100 ml, and compacted to constant

volume by tapping cylinder bottom against wooden surface. After

the compaction, the volume occupied by ionite was measured.

physicochemical properties as well as of sorption of metal ions

depending on process conditions. Aiming at determination of

optimum sorption parameters, the influence of concertation and

pH of SrCl solutions as well as the contact duration on the

extraction of strontium (II) ions was studied. Table 1 summarizes

the main physicochemical properties of the synthesized anionites

determined according to the procedures in [14, 15].

Table 1: Main physicochemical properties of the synthesized

anionites

Chemical resistance in

-1

The specific volume of swelled ionite (Vsp, ml·g ) was

determined as follows: Vsp. = V/G, where V was the volume of

swelled ionite, ml; G was the sample of dry ionite, g.

Anionites

based on

SEC_H_C_l

V ,

ml·g

solutions, %

5N 5N

-1

mg eq·g

.83

8.95

10%

H O

2 2

NaOH

94.9

A–ECH–

PEI

BA–ECH–

PEI

In order to determine chemical resistance of the ionites with

regard to solutions of acids and alkalis, two ionite samples, 0.1 g

on dry basis each, were placed into 250 ml round bottom reflux

flask. One sample was poured with 100ml of 5N solution of

sulfuric acid, the other sample was poured with 100 ml of 5N

solution of sodium hydroxide. The content of the flasks was held

for 30 min on boiling water bath. Then the mixture was cooled in

air to ambient temperature and the ionite was separated by

filtration. The anionite was converted into hydroxyl form when

required. The ionites were washed in distilled water, their SEC

was determined. Chemical resistance (CR, %) of the ionites was

determined by the ratio of the obtained exchange capacity to the

4.5

5.7

92.5

97.9

70.1

72.0

98.7

Stringent requirements to thermal resistance are set to ion

exchangers intended for long-term operation at higher

temperatures [16]. The thermal resistance is an important property

of polymer materials allowing to detect destruction processes at

higher temperatures, leading to impairment of operational

properties and environmental pollutions. Destruction of ionites in

dry state allows better estimation of the thermal stability of matrix

and ionogenic groups and determination of initial temperatures of

destruction of these structural elements. Thermograms of A–

ECH–PEI and BA–ECH–PEI are illustrated in Figure 3. The use

of TGA allows to determine the weight loss of ionite during

thermal destruction. The results of TGA of anionites based on

epoxy derivatives of aromatic amines and polyethylenimine are

summarized in Table 2. The TGA curves (Fig. 1, a, b), the shapes

of which are identical, illustrate that the initial temperature of

their destruction, after which the weight loss is significant, is

0 0

initial one: CR = SEC/SEC * 100, where SEC and SEC were the

static exchange capacity of ionites before and after processing

with acid or alkali, respectively. In order to determine the ionite

CR with regard to oxidizing solutions, a sample of ionite (1 g) was

poured with 100 ml of 10% solution of hydrogen peroxide, held

at ambient temperature for 48 h with periodic stirring. The ionite

was separated by filtration, converted into hydroxyl form, washed

in distilled water, the SEC was determined. The ionite resistance

was determined using the previous equation.

260°C for A–ECH–PEI and 280°C for BA–ECH–PEI. These

Sorption of strontium (II) ions by A–ECH–PEI and BA–

ECH–PEI in OH form was analyzed under static conditions at

sorbent:solution ratio equaling to 1:400, 20±2°C, varying the

temperatures on the curves of differential scanning calorimetry

correspond to occurrence of exothermal maximums, which can be

probably attributed to heat evolution upon further structuring of

ionites, then the polymer matrix is destructed. Herewith, their

weight loss is 8%. The commercial sorbent EDE-10p upon

heating to 100–200°C loses more than 20% of its weight [17].

concentration of strontium ions in SrCl

solutions from 0.184 to

-1

.015 g·l and varying their acidity by addition of 5N HCl

solution in the pH range from 1.0 to 6.3. pH was measured using

pH-150 MI meter with the measurement error of ±0.05 pH units.

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2020, Volume 8, Issue 4, Pages: 1568-1573

a) – (On the left there is a TG curve from top to bottom, and on the right –

b) – (On the left there is a TG curve from top to bottom, and on the right –

DSC curve)

Figure 3: Thermogravimetric analysis of anionites based on A–ECH–PEI (a) and BA–ECH–PEI (b). T is the temperature (ºC), DSC is the thermal capacity

-1

dependence (J·10 ·mg ), TG is the weight loss (%)

Table 2: Weight loss of A–ECH–PEI and BA–ECH–PEI at

rate reaches 83%. The sorption capacity of BA–ECH–PEI upon

various temperatures

extration of Sr ions is higher in comparison with A–ECH–PEI,

-1 -1

Weight loss, %

their SC is 507.7 mg·g and 491.36 mg·g , respectively. One of

the main factors upon extraction of metal ions from solution is the

medium acidity, which influences both the form of the considered

ion in solution, and the state of ionogenic groups [11]. It can be

seen in Fig. 5 illustrating sorption capacity of anionites with

regard to lead ions as a function of acidity of SrCl solutions that

the optimum pH for their extraction is 1.0. Under such conditions,

the absorption of strontium (II) ions is maximum.

T, °C

A–ECH–PEI

BA–ECH–PEI

It has been established that these anion exchangers are

characterized by sufficiently high thermal resistance. The

structure of their polymer matrix exerts significant effect on

thermal stability of anionites, which at 300–350°C decreases as

follows: A–ECH–PEI > BA–ECH–PEI

Figure 5: Sorption of Sr²⁺ions by A–ECH–PEI (1) and BA–ECH–PEI (2)

-1

as a funciton of acidity of SrCl solution; c Sr = 2.015 g·l , duration of

contact: 7 days

It also follows from Figure 5 that the sorption capacity of

ionites is determined mainly by the ionic state of strontium in the

solution. The acidity range corresponding to maximum SC, is

stipulated, on the one hand, by the ratio of the interaction energy

of metal cations and hydrogen with active polymer centers, and

on the other hand, by pH values determining the started formation

of hydroxide deposits and main metal salts. Further decrease in

the solution acidity leads to deposition of strontium hydroxide.

The mentioned facts evidence the necessity to achieve certain pH

of acidity of purified water. Figure 6 illustrates the isotherms of

sorption of strontium (II) ions by BA–ECH–PEI and A–ECH–

PEI. Equilibrium state between the ionites and the solution

Figure 4: Sorption isotherms of Sr²⁺ions by A–ECH–PEI (1) and BA–

ECH–PEI (2). Duration of contact is 7 days; pH = 1.0; ceq is the

equilibrium concentration; SC is the sorption capacity (mg·g ), cSr eq is the

equilibrium concentration (g·l )

It can be seen in Figure 3 illustrating the sorption isotherms

_o_f_S_r₂+ ions that the anionite SC increases with the content of

strontium ions in solutions. The curve rising at low equilibrium

concentrations evidences that these anionites extract strontium

(

II) ions with sufficient completeness. Herewith, the extraction

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2020, Volume 8, Issue 4, Pages: 1568-1573

containing 2.015 g·l^-¹strontium and having pH 1.0 is reached for

BA–ECH–PEI in 1 h, and for A–ECH–PEI – in 3 h. Herewith, the

SC of BA–ECH–PEI is 507.7, and of A–ECH–PEI is 491.36

Authors’ contribution

All authors of this study have a complete contribution for data

collection, data analyses and manuscript writing.

mg·g .

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