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AZ9RBAYCAN KIMYA JURNALI № 1 2017
UDC 543.54.54.72; 661.183
COLLOIDAL CHARACTERIZATION AND SORPTION OF COBALT(II) AND CADMIUM IONS FROM MODEL SOLUTIONS ON MODIFIED BENTONITE
Kh.N.Ilyasova, A.I.Yagubov, N.M.Muradova, T.A.Salimova, N.A.Imanova, A.N.Nuriyev
M.Nagiev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
chemistry-bsu@rambler. ru Received 14.12.2015
We studied sorption of cadmium and cobalt(II) ions from model solutions on natural and thermally processed Na-bentonite at the range 20-650C. In different temperatures on both natural and Na-bentonites equilibrium constants of sorption amount of Co2+ and Cd2+ ions were calculated. It was determined that when the temperature increases sorption efficiency of sorbents increases towards the ions. In all cases at high density and temperature sorption efficiency of Cd2+ was higher than Co2+ ions. By cation exchange method we have determined that modified form of bentonite has a higher sorption capacity, equilibrium coefficient of distribution and sorption selectivity of metal cations. It was found out that during ion exchange swelling ability and exchange capacity of bentonite samples have incredibly changed.
Keywords: bentonite, cobalt(II), cadmium, sorption, ion exchange, sedimentation.
Owing to a rapid increase of the global industry pollution of waste waters with heavy metal ions causes serious troubles. Toxic and biologically undecomposable properties of heavy metal ions, inclusion into water composition turned to be one of the important problems of environment and health. From this point, metal ions such as cadmium, zinc, cobalt, nickel, chromium and mercury are hazardous heavy metal ions and very toxic elements in the composition of waste waters. This fact proves the importance of extracting these metal ions from waste waters.
Due to being inhibited by heavy metal ions, some ferments are considered to be toxic in prohibited concentrations for most organisms. For example, Co, Cd, Pb featuring compounds are widely used in many industrial fields as mining, dye stuffs, pigment and electronics. Co can also be found in the composition of waste water of nuclear power plants. Acceptable limit of Co in irrigation water and cattle-breeding waste water is found to be 0.05 mg/l. Severe cobalt poisoning in human beings causes serious health problems such as allergy, asthma, heart disease, cardiac failure, thyreoadenitis, liver disorder and mutation of cells.
Ionizing radiation increases the risk of cancer.
Since the activated charcoal has a porous sorption structure with high surface, is widely used in adsorption process. The use of activated coal leads to the development of new adsor-
bents with similar properties.
From the other side, the extraction of metal ions from waste water by activated coal particles can be a complex problem.
Therefore there is a need to research alternative sorbents for studying high profitable and economically useful adsorbents.
Waste materials which have rich reserves in nature and were formed as wastes in industrial fields, can be cited as an example for cheaper adsorbents. Besides, there is a need for studying alternative adsorbents for elimination of pollutants by adsorption method.
The selection of adsorbents is one of the main criteria for elimination of pollutants by adsorption method. From this point it is more useful to conduct studies with productive, cheap and natural minerals. For this purpose clay minerals as montmorillonite and sepiolite can be used as an adsorbent for adsorption process and they are found in the form of minerals which are characterized with high cation-exchange and ion adsorption ability [1-4]. Bentonite is a clay mineral which contains more montmorillonite.
Experimental part
Bentonite of Dash-Salahli deposit has the
"3
following properties: p= 2.22 g/sm3, SiO2:Al2O3 ratio approximately is 5.7:2.1, the amount of exchange cations - mg/100 g - Na+ and K+(49.90), Ca2+ and Mg2+ (43.20), total exchange capacity for mg/100 g sorbent - 93.00 mg.
Adsorption experiments were conducted thermostatically in a controlled flask (thermostat IT-l) with 0.10C accuracy 0.5 g adsorbent and 10 ml solvent in glassware. Concentrations of cadmium and cobalt(II) ions were calculated by SF-26 spectrometer.
Kinetic researches were calculated basing to generalized Sakavich proportion of adsorption [3]. K - constancy degree of adsorption process, n - is non-stable and depends on the experiment and mutual mechanism of adsorbent with ions. (0<n<1). Dependence of metal ions adsorption in bentonite at temperature was clearly described by the following equation:
c.
V = ■
solid, i
(1)
where V - average rate of ion sorption, g/g; csolid,x - density of ion in sorbent, g/g; x -duration of sorption process, s;
lnK = , (2)
where T - absolute temperature (K), c and d are constants quantities and characterize relevant enthalpy and entropy of activation of adsorption processes.
For each dependence of equilibrium coefficients during equilibrium distribution (Kd) and adsorption of metal ions at different temperatures the following equation is obtained according to their concentrations:
\nKd = a + b + lnCY,
(3)
where Kd - equilibrium constant of metal ion distribution in the system (mg/g), a and b initial solvent constants in pH value at different tem peratures. By using Johnson-Mehl-Avrami-Ero-
feev-Kolmogorov equation and Sakovich formula were used to study the kinetics of adsorption of metal ions. Experimental data were given in Tables 1 and 2. In the Table 1 we gave the final state of Co(II) and Cd ions which were modified on sodium and natural bentonite.
Depending on surface charge density and balance of exchange cations Na-bentonite can fully, partially widen or it may not widen at all. These cations which are situated between layers of montmorillonite, are effective parameters for determination of bentonite properties. Therefore during the exchange of a surface with Na+ cation the diffusion coefficient of bentonite increases. Different structures of bentonite have water preserving potential.
At high temperature stratum water disappear and interporous character of bentonite remains. As a result of all these factors, at high temperature the loss percentage of bentonite mass also increases. This mass loss is more typical for Na-bentonite. Natural and Na-bentonite decompose at high temperature, and this limitation can be also eliminated by heat factor. It is known that
2+ 9+
Cd and Co ions have a higher adsorption on Na-bentonite. Adsorption capacity of Na-ben-tonite (comparing with literature materials)
2+ 2+
against Cd and Co ions is 1.3-1.4 times higher than natural bentonite [4]. This comparison can be clearly seen from Table 1. It must be stated that besides ion exchange adsorption the isomorpho-logical replacement of Al3+ and Si4+ in octatetra-gonal position of crystal cell occurs during transition of metal cations in adsorption process [4].
Table 2 shows the effect of Na-bentonite
2+ 2+
particles in adsorption of Cd and Co ions.
T
Table 1. Temperature dependence of cobalt(II) and cadmium ions adsorption from model solutions (adsorbent size 2.5-10~2sm) on thermally processed natural and Na-bentonite _
Adsorbent Metal cations, pH Properties of adsorbent Adsorption at different temperatures
Temperature, K
293.4 303.4 313.4 323.4
Na-bentonite Cd2+ pH~7.8 Kd Cd2+ sorb. g/g 2.7403 19.710-3 3.3103 23.610-3 1.1104 27.410-3 2.0104 29.3 10-3
Natural bentonite 4.2104 14.3 10-3 9.1104 18.710-3 1.3105 21.910-3 2.4105 24.610-3
Na-bentonite Co2+ pH~7.8 Kd Co2+ sorb. g/g 1.3103 17.81 • 10-3 4.2103 21.02 10-3 1.4104 23.62 10-3 3 104 25.07^10-3
Natural bentonite 1.1103 12.4210-3 2.6103 17.1610-3 1.7104 20.02 10-3 2.4104 23.04 10-3
36 Kh.N.ILYASOVA et al.
Table 2. Logarithmic change of distribution coefficient in adsorption of cobalt(II) and cadmium ions from model solutions on Na-bentonite
Table 4. The change of colloid fraction depending on exchange cations of Dash-Salahli bentonite and pH medium
Temperature, Size of Na-bentonite
K 1.5-2.0-10-2 3.5-4.010-3
lnKd
Co Cd2+ Co Cd2+
293.4 8.15 8.21 8.63 8.84
308.4 8.41 8.46 8.35 8.43
323.5 9.12 9.24 9.10 8.95
328.5 9.82 9.82 9.67 9.63
Adsorbents pH= 2 pH=5 pH=9
Natural bentonite Co2+ 11.3 68.6 99.8
Na-bentonite Co2+ 5.3 71.8 96.8
Natural bentonite Cd2+ 10.0 64.1 97.4
Na-bentonite Cd2+ 54.2 78.4 98.9
As it seen from the figure distribution coefficient of Cd2+ and Co2+ ions from model solutions is practically found to be 6.32-10-5 mol/l and concentration does not change in adsorption process. During the experiment we have studied the change of colloid fraction depending on thermal processing and pH in exchange process of Na-bentonite with Cd2+ and Co ions. Obtained results were given in Tables 3 and 4.
Table 3. The change of colloid fraction depending on
During thermal processing (200-6000C) at high temperature amount of colloid fraction considerably decreases. As it seen from tables
2+ 9+
though Cd and Co ions are different we did not observe serious differences between colloid fractions. This case is related to the fact that charges of these ions are similar by nature. Decrease of colloid fraction is sharply observed in the samples which were processed at 4000C and as a result of it the amount of hydrated deposit increases. During thermal processing crystalline structure was formed on bentonite samples and interlayer distances decrease.
The change of pH medium plays important role in the change of amount of colloid fraction. As seen from table 4 when the value of pH decreases from 9 to 2, amount of colloid fraction decreases in all cases. Shortly, when pH=9 the amount of colloid fraction is maximum, but at pH=2 it reaches minimum limit.
exchange cations of Dash Salahli bentonite
Adsorbents 1050C 2000C 4000C 6000C
Natural bentonite Co2+ 68.2 43.6 31.9 1.04
Na-bentonite Co2+ 78.8 74.7 46.6 1.8
Natural bentonite Cd2+ 64.2 44.9 46.3 2.74
Na-bentonite Cd2+ 73.4 48.4 69.7 8.5
-3.1 -3.2 -3,3 -3.4 -3,5 -3,6 -3.7 -3.8 -3.9
2
-1-1-1-1-1-1-1
0028 0,0029 0,0030 0,0031 0,0032 0,0033 0,0034 0,0035 1/T (1/K)
-3,6 _
-3,8 _
-4,0 _
-4,2
-4,4
-4,6
-1-1-1-1-1-1-1
0,0028 0,0029 0,0030 0.0031 0,0032 0,0033 0,0034 0,0035 1/T (1/K)
Dependence of temperature on CT in sorption of Cd2+ and Co2+ ions: 1 - natural bentonite, 2 - Na-bentonite.
References
1. Аннагиев М.Х., Сафаров Р.С., Адыгезалов Х.М., Ягубов А.И., Исследование адсорбции фенола на модифицированных формах бентонита // Журн. прикл. химии. 2010. Т. 83. № 1. С.172-174.
2. Ягубов А.И., Биннатова Л.А., Мурадова Н.М., Нуриев А.Н. Очистка сточных вод от катионных красителей с использованием монокатионных форм бентонита // Журн. прикл. химии. 2010. Т. 83. № 3. С. 421- 424.
3. Нассери Ш.А., Ягубов А.И., Нуриев А.Н., Ильясова Х.Н., Эфендиева Н.Г. Сорбция некоторых неорганических ионов из модельных растворов на Na-бентоните // 1st International Chemistry and Chemical Engineering Conference. Baku-2013, 17-21 Aprel. Р. 425- 431.
4. Nasseri S., Alemi A., Yagubov A.I., Nuriyev A.N. Adsorption of copper(II) and cobalt(II) from model sewage onto modified bentonite // Environ. Sci. An Indian Journal. 2014. V. 9. Issue 4. P.142-148.
MODÍFÍKASÍYA OLUNMU§ BENTONÍTDO Co2+ VO Cd2+ ÍONLARININ MODEL MOHLULLARDAN SORBSÍYASI VO KOLLOÍDAL XARAKTERÍSTÍKASI
X.N.Ílyasova, O.Í.Yaqubov, N.M.Muradova, T.O.Salimova, N.O.imanova, O.N.Nuriyev
Tabii va Na-formali termiki i§lanmi§ bentonitda Co2+ va Cd2+ ionlannin model mahlullardan 20-650C temperatur intervalinda sorbsiyasi tadqiq olunmu§dur. Müxtalif temperaturlarda ham tabii, ham da Na-forma bentonit nümunalarinda Co2+ va Cd2+ ionlannin sorbsiya miqdannin taraziliq sabitlari hesablanmi§dir. Müayyanla§dirilmi§dir ki, temperaturun artmasi ila sorbentlarin tadqiq olunan ionlara qar§i sorbsiya effektivliyi artir. Bütün hallarda qatiliq va temperaturun artmasi ila Cd2+ ionlannin sorbsiya effektivliyi Co2+ ionundan yüksak olmu§dur. Kation mübadila üsulu ila bentonitin modifikasiya olunmu§ formasinin daha yüksak sorbsiya tutumuna, paylanmanin taraziliq amsali va metal kationlannin sorbsiya segiciliyina malik olmasi müayyan olunmu§dur. Aydinla§dinlmi§dir ki, ion dayi§ma zamani bentonit nümunalarinin §i§ma qabiliyyati va mübadila tutumu nazara garpacaq daracada dayi§mi§ olur.
Agar sözlar: bentonit, kobalt(II), kadmium, sorbsiya, ion d3yi§m3, sedimentasiya.
СОРБЦИЯ ИОНОВ Co2^ Cd2+M МОДЕЛЪНЫХ РАСТВОРОВ НА МОДИФИЦИРОВАННОМ БЕНТОНИТЕ И ИХ КОЛЛОИДНАЯ ХАРАКТЕРИСТИКА
Х.Н.Илъясова, А.И.Ягубов, Н.М.Мурадова, Н.А.Иманова, А.Н.Нуриев
Исследована адсорбция ионов Co2+ и Cd2+ из модельных растворов в интервале температур 20-650С на термически обработанных природном и Na-форме бентонитах. Рассчитаны константы равновесия и количество адсорбционных Co2 - и Cd2+-ионов на природном и Na-форме бентонитах при различных температурах. Установлено, что с увеличением температуры эффективность сорбции ионов повышается. При всех концентрациях с повышением температуры сорбция ионов Cd2+ выше, чем сорбция ионов Со2+. Методом катионного обмена установлено, что сорбционная активность модифицированной формы и величина равновесного распределения катионов металлов более высокая, чем у природного образца. Выяснено, что при ионном обмене у бентонитных образцов значительно изменяется набухание и обменная емкость.
Ключевые слова: бентонит, кобальт(11), кадмий, сорбция, ионный обмен, седиментация.
