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AZ9RBAYCAN KIMYA JURNALI № 3 2016
UDC 661.183.123.54.678.072
ADSORPTIVE AND COLLOIDAL-CHEMICAL CHARACTERISTICS OF BENTONITE AND ITS MODIFIED FORMS
A.I.Yagubov, N.M.Muradova, S.A.Mammadova, U.H.Osmanova, G.M.Heyderzade
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan [email protected] Received 04.04.2016
On the basis of experimental and theoretical researches we determined the impact of kinetic and diffusion coefficients on the change of concentration of cation active dye stuffs during their extraction by modified bentonites. Using mathematical model the values of all parameters calculated on laboratorial and industrial level were given. Samples of Na-form of nanobentonite were obtained. Na-form of nano-bentonite shows very high results with regard to Zn2+ ions. Kinetic laws of the process were studied. The values of entropy and enthalpy of adsorption of zinc ions, as well as equilibrium coefficients depending on temperature were calculated. Negative values of Gibbs' free energy AG0 show that on ben-tonite samples the process of thermodynamic adsorption is possible. As well high value of AG0 with the increase in temperature shows that at high temperatures adsorption is possible.
Keywords: sorption, nanobentonite, cation active dye stuffs, kinetics, entropy, enthalpy, free energy, zinc ions.
Introduction
Development of chemical, lacquer dye, petrochemical, textile and other branches of national economy in our republic requires effective, cheap sorbents and catalysts. From this point of view one of the promising materials is natural alumino silicates, in particular, natural and clay minerals. One of the features of natural zeolites and clay minerals is that their structure enables to perform purposeful modification for controlling surface properties and adsorption characteristics. From practical point of view clinoptilolite, mordenite, caolinite and bentonite are of great importance among natural zeolites and clay minerals having huge deposits of industrial importance in our republic [1-5].
Creation of scientific bases for producing and application of effective adsorbents based on natural zeolites and clay minerals makes it necessary to study nature of active centers, nature of exchange cations and free porosity of structure of their adsorptive space, to detect these factors in adsorption processes (in particular, treatment of waste waters from different chemical pollutants), as well as to establish interrelation between their physico-chemical properties. The task of separate researches is to prepare adsorbents on the basis of natural zeolites and clay minerals for certain sorption processes.
Analysis of carried out studies shows that the most promising ones are above-mentioned aluminium silicates which have large deposits.
The methods of modification of these adsorbents are multiple and enable to control quantitatively and qualitatively surface properties with the purpose of increasing their activity and selectivity in treatment processes of waste waters from chemical contaminates. In this connection, study of new sorbents has not only scientific, but also practical importance.
For the first time the scientific direction which is the basis for controlling surface properties of some aluminium silicate sorbents has been developed. According to the researches of physico-chemical characteristics under the impact of the nature, charge of exchange cations, as well as pH medium, thermo stability, porosity structural properties of natural aluminium silicates we have developed scientifically based recommendations on application of sorbents for treatment of waste waters from organic pollution of different nature. The power and concentrations of acidic, basic centers of cation exchange forms of clinoptilolite, mordenite, cao-linite and bentonite were determined.
Production technique of effective sor-bents on the basis of natural aluminium silicates (Azerbaijani patent №2005031) for treatment of waste waters from cation dye stuffs has been developed.
We determined general laws and optimum conditions for treatment of waste waters from inorganic and organic pollutants with ad-
sorbents obtained on the basis of natural aluminium silicates depending on concentration, nature, charge of exchange cations, as well as power of electron-accepting centers.
According to formulated scientific bases for purposeful control of sorbents properties for the first time we have developed and purposed new promising sorbents which allow controlling selectivity regarding to separate inorganic and organic pollution of waste waters. The results allow recommending modified sorbents instead of a number of unavailable and expensive synthetic ion exchange materials for removal of inorganic and organic compounds from waste waters.
Experiment part
Nature, radius and charges of exchange cations, as well as pH medium essentially impact on such practically important properties of poly- and monocation forms of adsorbents like selectivity and porosity [3-6].
Recommended effective sorbents based on natural aluminium silicates for application in relevant industrial branches of Azerbaijan are promising sorbents which enable to produce economical effect due to simplifying sorption method of waste waters treatment.
The researches related to surface properties of natural zeolites, clay minerals and their modified forms were performed. Some untouched issues relating to this field were solved. Comprehensive experiments were carried out and optimum conditions were defined for sorption of surface active substances (SAS), chlo-roorganic compounds, dye stuffs, phenols, oil and oil products, cations of heavy metals from waste waters by above-mentioned natural sor-bents and their modified forms. We also used modern techniques (IR-spectroscopy, X-ray analysis, EMA, DTA and others).
According to the results of experimental researches it was determined that bentonite hy-drophobizated with octadecylamine in benzol has the highest adsorption capacity both as ion-ogenic, and non-ionogenic organic dye-stuffs (Table 1).
Capacity of hydrophobizated bentonite is
3+
approximately two times bigger than its Al3+,
3+
Fe monocation substituted forms regarding to these dye-stuffs. Use of SAS causesthe formation of organophilic layers between bentonite particles which reduce surface energy on phase boundary, increase distance between silicate sheet and facilitates penetration of dye-stuff molecules into interplanar spacing of bentonite mineral (Table 1).
Table 1. Adsorption of dye-stuffs from solutions on modified bentonite
Concentration of dye-stuffs Methyl orange Rhodamine-G Brilliant green Thionine Methylene blue
Co, mg/l S, mg/g
100 10 12.5 9 9 11.5
250 18.5 25 15.2 15,0 20.2
500 25 37.5 22.3 23.0 35.5
700 37.8 50.0 35.7 35.0 50.2
1000 52.85 75.5 49.8 49 73.3
1500 75 102.0 70.3 70.3 100.0
2000 1000 120 92.0 90.0 115.0
On the basis of found optimum conditions of adsorption on case of methylene blue (MB) (diameter of column dcolumn=0.0005 cm, size of sorbent granule Gsorb=0.2-0.4 mm, linear transmission rate of solution through sorbent layer V=0.00085 m/s, solution with initial concentration MB C0=500 mg/l, in which the most adsorption is observed), kinetic and output data of the process were obtained at high layer of Fe(III)-bentonite L=0.10, 0.25 and 0.30 m it was found out that adsorption equilibrium reaches within 3 hours.
Combination of experimental and theoretical researches permits to determine which stage of sorption process is limiting the transition of MB from solution to solid phase or replacement of it in pores of solid phase. Therefore for expanding the data on sorption of MB from solutions on Fe(III)-bentonite we performed mathematical modeling of this process by using experimental data.
Thus, as a result of experimental and theoretical investigations adsorption of MB on Fe(III)-bentonite it has been established that kinetic coefficient and diffusion coefficient of
axial mixing vary by the change of concentration of dye-stuff in solution, but a value of general and internal coefficients of kinetics are constant. It was defined that as far as mass transfer resistance in solution is about two orders of magnitude less than in solid phase, the process is limited by internal mass transfer. Good agreement between estimated and experimental concentrations of sorbate and solute gives reason to conclude that during modeling of analogue processes we can use the technique developed in the work [4]. By obtained model we calculated all parameters of considered processes from laboratory to industrial scale [4, 5].
The model and method of calculation were recommended for application in the planning organizations during projecting this process into implementation. According to these results it is necessary to repeat obtained calculations, the result of which can be used without changes during projecting industrial adsorption process of MB, as well as other cation dye-stuffs not only on Fe(III)-bentonite, but also on oktadesylamino-bentonite (ODAB).
Polymer nanocomposites have unique properties and are widely used in many fields of science and technology [7].
Being hydrophilic, natural clay is unsuitable with polymer matrix. For using clay as filler in production of polymer composites it is necessary to give it organophilic character. It is reached by modifying the clay with organic substances (organo-modifiers). At present organically modified layered silicates which improve mechanical properties of a number of polymers, are promising fillers.
Polymer nanocomposites are multicompo-nent material consisting of plastic polymer basis (matrix) and filler - organo modified nanoclay. Modified organo clay is well dispersed in polymer matrix and interacts with polymer chain.
At present nanosized laminated silicate fillers (organoclays), which with minor amounts (up to 5% mass) in polymer matrix lead to increase in elasticity of modulus, density, increase of thermo-, heat resistance and stability to burning, decrease of gas transmission of material, are of great importance among polymer materials.
Due to their effective physical and chemi-
cal properties nanocomposites can be successfully used in different fields of industry, electronics and even medicine.
We conducted researches on kinetics and thermodynamics of adsorption of modified na-nobentonites of zinc ions and achieved important results. As is known heavy metals are very dangerous as a living source and harmful for health. Natural and purified waters were polluted with some heavy metals. They do not decompose, are very stable and cause great problems. For extraction of toxic metal ions from aqueous solutions different methods have been used. For purification of industrial waste waters there are many methods and they include: precipitation, coagulation-flotation, adsorption, membrane processes, electrochemical methods, ion-exchange, biological processes and chemical reactions.
Adsorption process is one of the best methods for extracting residual concentrations of metal ions from waste waters. For adsorption of metal ions many mechanisms were studied, for example, cation exchange, surface complexation, surface precipitation, surface codeposition, surface colloiding and distribution of micro pores with particles [12-14]. During adsorption process a layer with thickness conforming to one or several diameters of metal ions is formed. Adsorbed molecules are either local or active. This means that they stand in certain areas of a cell and easily move to the location. Particles of dissolved substances spread to the pore on sorbent surface and cover the area of pores in it. For example, when amount of transition metal ions is high, copper, zinc, cadmium, lead, mercury, iron, nickel ions have negative impact [15].
Zinc is widely used in different fields of industry, for example, in the production of dry batteries, galvanization, desinsection preparations, foundry, metallurgy, pigments and explosive materials. High amount of zinc may cause depression, lethargy, aridity, neurological symptoms, apoplexy and ataxy. For purification of waste waters from zinc an application of adsorption method is effective and can be economically useful with the use of cheap adsorbent bentonite [16].
Bentonite is a natural, polysilicate mineral, has high cation exchange, ion adsorption ability and due to it is a relevant sorbent for adsorption of metal ion. Its structure is decomposed with atoms and can be shown in tetrahedral form [SiO4]4- and [MO4]5-. We may achieve more negative electric charge and cation exchange by substitution of Si in tetrahedal field.
Bentonite is a mineral containing one silicon and two silicon band with 2:1 ratiowhich forms a layer.The layer stands with van der Waals' force, that's why water molecule easily penetrates into the layers and balances cation deficiency. Bentonite has an intermediate character for zinc adsorption.
Though many research were performed on extraction of zinc ion by bentonite, natural ben-tonite has weaker adsorption ability. Investigation of extraction of zinc ion by modified bentonite can be useful for studying the adsorption. For this aim Na-bentonite and Ca-ben-tonite were used. Na-bentonite can adsorb large amount of water, and form adhesive, thixotropic suspension. But Ca-bentonite can weakly adsorb water, is less swellable and cannot stay as a suspension in water. Due to weak adsorption of water saturated damp composition of Ca-bentonite is lower than Na-bentonite [17, 18].
The aim of research work is the study of adsorption potentials in extraction of zinc ions of Ca-bentonite and Na-bentonite forms of thermally treated nano-bentonite.
Total rate constants, thermodynamic parameters AH, AS and ag of adsorption of zinc ions were calculated. As well as, equilibrium and kinetics of adsorption of zinc ions on modified nano-bentonite were studied. In the work we used zinc chloride (ZnCl2) for obtaining of Zn-form from bentonite of Dash-Salahli deposit of Azerbaijan Republic (Figure 1). Technique was performed with preparation of nano-particles by purifying HCl solution and calcination at 6000C for 2-10 hours to obtain nanometer bentonite on ball mill (MM400 Retcsh).
Na- and Ca-bentonite forms of thermally treated bentonite were characterized by Scanning Electron Microscopy (SEM) TESCAN MIRA 3).
Fig. 1. Electron Scanning Microscopic analysis of Zn bentonite
It was shown that for adsorption of zinc ions on bentonite the most relevant pH value is 8. That's why kinetics and thermodynamics of adsorption of zinc ions in Na- and Ca-bentonite forms of thermally treated nanobentonite were studied in the 20-600C temperature range, pH= 7.80±0.05, model solutions (2.58-10-5-8.37-10-4 mol/l) in different initial densities of zinc ions.
Experiments were performed on modified forms of bentonite samples at constant condition. Certain amount of sorbent was poured into thermostat flask containing 100 ml zinc chloride. To measure all particles of sorbent solution containing sorbent we mixed it in a glass mixer.
Adsorption process was performed at different temperatures 293.2, 303.1, 323.2, 333.1 K and standard temperature 298.1 K and at pH value 7.80±0.05. Initial and equilibrium densities of zinc ions in solution were determined in UB spec-trophotometry (SF-26) and atomic-absorption method on Perkin-Elmer 180.
Theoretical calculations. We used John-son-Mehl-Avrami-Erofeev-Kolmoqorov equation to describe kinetics of adsorption of metal ions by Sakovich ratio [19]. Though this equation was created by Avrami at the end of 1930s, other employees also created the same relation and the model was now named Johnson-Mehl-Avrami-Erofeev-Kolmoqorov or JMAEK. JMAEK equation [20]:
a=1-exp[-(m (1)
here a - obtained fraction, n - Avrami coefficient, Kt - temperaure dependence of rate constant.
Generalized rate constant of adsorption K was calculated by Sakovich ratio [21]:
1
k =n■k" , (2)
here k - rate constant of adsorption process and n - constant which depends on interaction mechanism of ion adsorption with (0<n<1) sorbent and experiment condition.
Temperature dependence of adsorption of bentonite containing sorbents with metal ions are described by the following equation:
lnK = ^, (3)
C - concentration of Cu and Zn ions, d - constant.
Adsorption of heavy metals was investigated by calculating distribution coefficient (Kd) and this was accepted as a standard parameter in evaluation of physical and chemical character of metal ion between solid and liquid phases. This was calculated by the following equation [22]:
Kd =
Co - Cлв V
Cc
m
(4)
here V- capacity of solution, m - bentonite mass.
Separation factor describes selectivity of adsorption of two metals. Here K - generalized rate constant of adsorption (s-1), T - total temperature (K), C and d constants which characterize entropy and enthalpy of activity of adsorption. Equation (4) was obtained at different temperatures Cp,J from their equilibrium densities for each dependences of equilibrium distribution coefficients of Kd of metal ions:
lnKd = a + b • ln C,
■p,a
(5)
here Kd - equilibrium coefficient of distribution of metal ions in system (ml/g); a and b - constants of initial pH and temperature values of the solution.
Thermodynamic parameters were calculated by the following equation:
ln Kd =
AS0 AH0
R
RT
(6)
here AH0, AS0 and T - enthalpy, entropy and temperature, R - gas constant.
Values of enthalpy (AH0)2 and entropy
0 3
(AS0)3 were obtained from sections and slopes of lnK diagrams calculated by the program forbuilding curves.
Gibbs' free energy (AG0)4 of special adsorption was calculated by equation [23, 24]:
AG = -RT lnKd , AG0 = AH0 -T AS .
(7)
(8)
Na- and Ca-forms of thermally treated nano-bentonite were characterized by Scanning Electron Microscopy. Figure 2 shows Scanning Electron Microscopy of Na- and Ca-bentonite. As is seen in the Figure, nano-bentonite sample consists of different phases and particles with 200 nm less distribution size. Aluminium silicate mineral contains large amount of aluminium (Al) and silicon (Si). This was confirmed by X-ray Energy Dispers analysis and it was determined that energy spectrum is sodium (Na), aluminium (Al), silicon (Si) and others.
Fig. 2. Scanning Electron Microscopy analysis of thermally treated Na- and Ca-bentonite.
Temperature dependences of rate constants of adsorption process which conforms to entropy and enthalpy were calculated by using equation 3 at different initial densities and temperatures. For each condition Gibbs' free energy value was determined.
1 - equilibrium concentration at different temperatures;
- enthalpy,
- entropy,
- free energy respectively at standard conditions.
2
3
4
Fig. 3. Analysis of Na-bentonite of thermally treated nanobentonite by X-ray Energy Dispers analysis.
For determining the general laws in adsorption of zinc ions by sorbent initial solution and temperature constants a and b parameters were studied by equation (4) at a = /(1/7) and b = /(1/7) temperatures and general equation which describes adsorption of zinc ions in system with Na- and Ca-forms of bentonite was determined:
13.49-0.25lnC -13361-98lnC m lnK =-p-j,-^, (9)
By using the same method we obtained another equation for sorbents on equilibrium coefficient of distribution of zinc ions by temperature and initial densities in solution:
^ 4.71-1.80 lnC0-(1229-3 03 lnC0) (1Q)
These parameters were calculated by small square analysis method. They are presented in the Table 2.
Table 2. Values of equation (3) and free energy of adsorption activation of zinc ions
Sorbent Co, mol/l Constants AG*, kJ/mol
d c
Na-bentonite 2.58-10° 7.54-10-5 1.77-10-5 8.37-10-5 -4.01 -7.56 -10.25 -6.86 1287.03 173.97 716.85 392.01 20.04 20.25 19.53 20.31
2.58-10-5 -7.19 414.20 21.31
Ca-bentonite 7.54-10-5 -7.22 239.78 19.95
1.77-10-4 -10.02 588.61 19.96
8.37-10-4 -7.84 174.86 20.87
It is possible to calculate a and b value from parameters presented in Table 3.
Table 3. Initial solution and temperature constants at four different temperatures
Sorbents T, K a b
293.2 -0.59=0.10 2.26=0.92
Na-bentonite 303.1 -0.60=0.10 2.46=0.93
323.2 -0.55=0.06 3.20=0.66
333.1 -0.54=0.05 3.70=0.47
293.2 -0.58=0,09 2.24=0.92
Ca-bentonite 303.1 -0.56=0.07 2.42=0.92
323.2 -0.54=0.07 3.30=0.67
333.1 -0.55=0.51 2.26=0.51
Na-bentonite
*Co - initial concentration of zinc ion in solution
lnC
Fig. 4. Precipitation of zinc ions with different concentrations on Na-bentonite: 2.58-10-5 (1), 7.54-10-5(2), L77-10-4(3) and 8.37-10-4 (4) (m ol/l).
Entropy and enthalpy values of adsorption of zinc ions were calculated by using temperature dependence of distribution coefficients. As to indicate thermodynamic parameters for standard condition of 298 K temperature and 1 atm or 101/3kPa pressure or standardized parameters is very simple, the most experiments were conducted at 298/16 K temperature and the results are presented in Table 3. Thermo-dynamic parameters of adsorption process were determined by van't Hoff 's equation and by constructing lnK-1/T (equations 6 and 7) diagram. Enthalpy is a thermodynamic potential. It is a thermodynamic state function and increasing quantity. Full enthalpy H of a system cannot be calculated directly. Change of enthalpy value AH0 is more useful quantity than its full
10.0
.5
.0
7.5
7.0
6.5
6.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
value wareas is positive in endothermal reactions. Howere it is negative in exothermic reactions.
In Table 3 show as enthalpy values adsorption can be considered as an endo-thermal reaction. Entropy is an increasing thermodyna-mic propertiy that it is measurement of thermal energy of a system for the temperature of each unit and this does not allow to carry out a useful work. Entropy is important for predicting the size, direction of complex chemical reactions.
Table 4. Entropy, enthalpy and free energy of activation of adsorption of zinc ions_
Sorbent Co, mol/l AH0, kJ/mol AS0, Jmol-1 grad-1 AG0, kJ/mol
2.58-10-5 23.72 147.69 -20.30
Na-bentonite 7.54-10-5 23.29 143.37 -19.41
1.77-10-4 25.03 144.70 -18.26
8.37-10-4 25.67 104.20 -15.42
2.58-10-5 39.31 197.41 -19.51
Ca-bentonite 7.54-10-5 39.43 193.89 -18.42
1.77-10-4 31.57 166.01 -17.81
8.37-10-4 21.86 125.72 -15.58
As is seen in Table 4, entropy values decrease when initial concentration increases by showing energy or low dispersion of a substance or improvement of an order. Combination of entropy, temperature and enthalpy explains if the reaction is mechanical or not.
Calculation of AG0value shows that adsorption of zinc ions on Na- and Ca-bentonites is exothermal. As to adsorption the value of each thermodynamic parameter may be fully discussed.
Negative values of Gibbs energy for free energy AG0 show that in bentonite samples ther-modynamic adsorption is possible and mechanical. But the increase in AG0 values due to high temperature shows that adsorption is possible at high temperatures. aH positive values display endothermic behavior of adsorption reaction of Zn ions and it is supposed that the large amount of heat is required to transfer zinc ions from liquid phase to solid phase. Before transition metal ions enter the smallest spaces it must throw large amount of water. Obtained results show that these metal ions are captured at high temperature and the latter activates metal ions to increase adsorption in coordination fields of minerals.
It should be stated that when the temperature is high the cations move faster. Extraction of double-charged cations from water by this way results in obtaining of pozitive values of AS0. Positive values of AS0 are also impact on adsorption mechanism of Zn ions and Zn ions are less hydrated on bentonite layers unlike aqueous solutions. Besides, the positive value of AS0 which shows the changes in hydratation of absorbed Zn ion and disorder in other system, shows that positive AS0 value occurs due to distribution of energy between and adsorbate and adsorbent. Before adsorption the heavy metals ions around adsorbent surface will be more regulated and higher in adsorption state unlike free heavy metal ions which react with adsorption state and adsorbent.
According to obtained results when distribution of periodical and transition energy between molecules obtains positive AS0 value, disorder will increase on solid-solution surface during adsorption and adsorption process.
In Figure 5 ln Kd change of adsorption of zinc ions with temperature on Na- and Ca-bentonites at different concentrations of zinc ions was presented. Obtained results confirm that for all samples ln Kd value decreases whcn the temperature is reduced. But for Ca-bentonite this reduction is more higher.
We studied adsorption of zinc ions by using model solutions at constant-packet mode in thermally treated Na- and Ca-bentonite forms of nanobentonites. For constant-packet mode effective adsorption, thermodynamics and different concentrations (Co) were studied. At different temperatures 20-600C, nature of adsorption of ions were investigated. Total rate constants, thermodynamic parameters, entropy, enthalpy and free energies of adsorption of zinc ions were calculated. It was determined that adsorption process is endothermal and mechanical. When the temperature increases, due to high values of AG0 adsorption process occurs at high temperatures. We may consider that for both sorbents adsorption process is endothermic reaction due to possibility of adsorption process at high temperatures.
Fig. 5. Temperature dependence of distribution equilibrium of adsorption of zinc ions on two adsorbents. Concentrations of zinc ions, mol/l: 2.5810-5 (1), 7.5410-5 (2), 1.7710-4 (3) and 8.3710-4 (4) .
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BENTONiT УЭ ONUN MODiFiKASiYA OLUNMU§ FORMALARININ ADSORBSiON УЭ KOLLOiD-KlMYOVi XÜSUSiYYOTLORl
O.LYaqubov, N.M.Muradova, S.A.Mamm3dova, Ü.H.Osmanova, G.M.Heydarzada
Kationaktiv boyalann bentonit va onun modifikasiya olunmu§ bentonitda tacrübi va nazari tadqiqi naticalari asasinda mahlulda boyalarin qatiliqlannin dayi§masinin kinetik va diffuziya amsalina tasiri müayyanla§dirilmi;jdir. Burada hamginin riyazi modelin kömayila baxilan laborator va sanaye miqyasinda bütün parametrlarin hesablanmi§ qiymatlari göstarilir. Na-formali nanobentonit nümunalari hazirlanmi§dir. Na-formali nanobentonitin Zn2+ ionlarina qar§i sorbsiya qabiliyyatinin cox yüksak olmasi müayyanla§dirilmi§dir. Prosesin kinetik qanuna uygunluqlari oyranilmi§dir. Sine ionlarinin adsorbsiyasinin entropiya va entalpiya qiymatlari paylanmanin tarazliq amsalinin temperatur asililigindan istifada etmakla hesablanmi§dir. Sarbast enerji AG0 ücün Hibbsin manfi qiymatlari göstarir ki, bentonit nümunalarinda termodinamiki adsorbsiya prosesi mümkündur va qeyri-ixtiyaridir. Hamginin temperaturun artmasi ila AG0-nin qiymatinin artmasi göstarir ki adsorbsiya yüksak temperaturda mümkündür.
Acar sözlar: sorbsiya, nanobentonit, kation aktiv boyalar, kinetika, entalpiya, entropiya, sarbast enerji, sink ionlari.
АДСОРБЦИОННАЯ И КОЛЛОИДНО-ХИМИЧЕСКАЯ ХАРАКТЕРИСТИКА БЕНТОНИТА И ЕГО МОДИФИЦИРОВАННЫХ ФОРМ
А.И.Ягубов, Н.М.Мурадова, С.А.Мамедова, У.Х.Османова, Г.М.Гейдар-заде
На основе экспериментальных и теоретических исследований определено влияние кинетических и диффузионных коэффициентов от изменения концентрации катионоактивных красителей при их извлечении модифицированными бентонитами. C помощью математической модели даны значения всех параметров, рассчитанные на лабораторном и промышленном уровнях. Получены образцы Na-формы нанобентонитов. Na-форма нанобенто-нита показывает очень высокие результаты в отношении ионов Zn2+. Изучены кинетические закономерности процесса. Рассчитаны значения энтропии и энтальпии адсорбции ионов цинка, а также коэффициенты равновесия в зависимости от температуры. Отрицательные значения свободной энергии Гиббса AG0 указывают на возможность процесса термодинамической адсорбции на бентонитовых образцах. Кроме того, показано, что повышение значения AG0 с повышением температуры позволяет проводить адсорбцию при высоких температурах.
Ключевые слова: сорбция, нанобентонит, катионоактивные красители, кинетика, энтропия, энтальпия, свободная энергия, ионы цинка.
