CC BY
16
Muftullaeva Marzia Begdullaevna, doctoral student of basic doctoral studies of the Karakalpak
branch of the Academy of Sciences of the Republic of Uzbekistan, Nukus Ibadullaev Ahmadjon, doctor of technical sciences, professor, the head of the Department "Chemical technology of oil and gas refining", Tashkent chemical-technological institute, Tashkent, Uzbekistan
E-mail: [email protected]
STUDY OF ADSORPTION PROPERTIES OF MONTMORILLONITE OF KARAKALPAKSTAN
Abstract. The physicochemical properties of montmorillonite in Karakalpakstan is studied in this article. The chemical composition, structure, adsorption properties, extra-geometric surfaces are established and the possibility of using composite elastomeric materials in production is determined.
Keywords: liquid rubber, composition, technology, montmorillonite, isotherms, adsorption, macromolecule, elastomer, physics, chemistry, diluted solutions, kinetics, mass, number, particle distribution, wettability, structuring.
Introduction. In recent years, natural montmo-rillonites abroad have been used in animal husbandry, agriculture, food production, pharmaceuticals, and petrochemical industries. Currently, it is directed to the study of the physicochemical properties of mineral resources for use in the production of composite elastomeric materials as a filler in the Republic. Up to now, a number of measures aimed at solving this common problem have already been implemented, which a large place belongs to the introduction of montmorillonite from Karakalpakstan (MMC) with different natures and structures.
As above-stated, the purpose of this article is to study the physicochemical properties and structural features of montmorillonite of Karakalpakstan and the possibility of their use in the production of composite elastomeric materials as a filler.
Objects and research methods. The objects of study are the montmorillonites of Karakalpakstan, Muinak, Turtkul, Khojakul, Kushkanatau, Beltauand Karateren deposits. Samples have been taken from seven deposits and the physicochemical properties
of each sample have been studied three times and the average values have been obtained. The study has been carried out by physical-chemical methods to study the properties of mineral fillers, such as electron microscopy, IR-spectra, DTA, and standard chemical analysis methods.
The gained results and their discussion. The results obtained by numerous studies have determined [1; 2] that MMC is confined to the upper gloss deposits of the pH of an aqueous suspension of 7-9. The chemical composition of MMC has several characteristic features, the molar ratio between SiO2 and Al2O3 ranges from 4 to 5. It has been established that there are oxides of iron, calcium, sodium, magnesium, titanium and othersin almost all MMC deposits (Table 1).
A study ofthe structure ofMMC clays by electron microscopic studies showed that they consist of scaly particles, mostly dense and having a loose outline: in places there are also fibrous folds, apparently formed as a result of twisting of plate-like particles. The sizes oflarge particles reach to 0.6 microns. The scaly shape
of the MMC particles is apparently explained by the specific crystal structure of montmorilloniteclay. The plane (0.001) of montmorillonite is covered with the-lattice ofhydroxyl ions (Fig. 1.), which exhibit a strong
polarizing effect with respect to polar molecules. It is known that these hydroxyls are involved in the formation of both intramolecular hydrogen bonds and intermolecular hydrogen bonds.
Table 1.- The chemical composition of montmorillonite of Karakalpakistan
№ Name of indicators Deposits of montmorillonite
Muinak (MM) Turtkul (TM) Khojakul (KhM) Kushkana-tau (KM) Beltau (BM) Kranteren (KM)
1. SiO2 52.50 67.96 54.84 55.0 58.2 60.5
2. Al2O3 17.20 12.80 16.76 13.5 15.7 16.8
3. CaO 1.20 2.0 2.08 1.8 2.02 1.5
4. Na2O 5.06 0.28 2.48 1.8 2 3.02
5. K,0 0.27 0.13 1.22 1.03 1.10 0.3
6. MgO 3.62 3.35 2.00 2.35 2.8 3.0
7. Fe2°3 3.56 1.26 6.04 2.00 2.04 3.0
8. FeO 0.13 0.10 0.07 0.12 0.11 0.9
9. TiO2 0.30 0.10 1.00 0.50 0.70 0.90
10. CO2 1.68 0.20 0.60 0.40 0.55 0.65
11. SO3 0.28 0.21 0.15 0.20 0.26 0.18
12. 9.15 4.30 4.32 4.8 6.00 8.05
13. H2O 5.05 7.31 8.44 6.01 6.80 7.55
nH2O
O (O) • o
O OH Si Al
Figure 1. Scheme of the structure of montmorillonite according to Edilman and Fevaye
Therefore, in the clay crystal lattice there are both free and interconnected hydroxyl groups; the state of these groups is usually detected using infrared absorption spectra. The results of studying the IR-spectra of bentonite show (Fig. 2) that absorp-
tion bands appear in the region of 3700-300 cm-1, which correspond to vibrations of free hydroxyl with a maximum at 3636 cm-1, and hydroxyl bound by an intramolecular hydrogen bond with a maximum at 3440 cm-1.
Figure 2. IR-i
In (Fig. 3) differential heating curves for MMC are given. It can be seen from this figure that the dehydration curves are characterized by two endo-
;ctra of MMC
thermic effects caused by the removal of interpackage (adsorbed) and constitutional (hydroxyl) water located in the absorbed base, respectively.
a <
1043
V 373 983 2
V 973
T 363
0 473 673 873 1073
Figure 3. Thermograms of MMC: 1 - natural; 2 - purified
Removal of adsorbed water proceeds in the temperature range 363-463 K and depends on the type of cation. The bleeding of hydroxyl water and the formation of anhydrous clays occurs in the temperature range 933-983 K, and a dehydration temperature is observed to decrease. The degree of this decrease
is due to the size of the cation atom. As a result of studies, it was found that MMC has a highly developed specific geometric surface due to this it has an increased oil absorption (Table 2). The latter indicator significantly decreases with increasing aromatic hydrocarbon content in the oil.
Table 2.- Specific adsorption surface and oil absorption of MMC various deposits before and after heat treatment at 673K
MM TM KhM KM BM KM
R* Ht* R. Ht. R. Ht. R*. Ht. R. Ht. R. Ht.
Specifically-geometrical surface. Ssp.. m2/g
29.1 36.2 29.1 35.4 28.3 | 4.1 27.1 34.0 28 31.0 33.5 33.8
Oil absorption. ml/100g
flaxseed oil
32.0 35.5 32.0 34.1 31.0 33.2 31.5 34.0 32.1 33.0 33.5 33.9
paraffinic oil
32.0 35.5 32.0 34.1 31.0 33.2 31.5 34.0 32.3 33.2 33.7 33.8
dibutylphtholate
38.2 46.1 38.2 44.2 35.6 39.6 33.2 40.2 32.2 33.1 33.6 33.7
dibutylsebacate
36.4 45.2 36.4 43.0 34.3 39.2 32.9 40.2 32.1 32.0 33.3 33.6
R*- raw montmorillonite, Ht* - Heat-treated montmorillonite
As can be seen from the table, after heat treatment, MMCs have a more developed specific surface area, which is due to their high dispersion. Detailed information on the dispersion of fillers can be obtained by comparing their histograms. Mass and numerical distributions of the initial and heat-treated MMCs by the equivalent particle diameter have been determined by the method of small-angle scattering of a laser beam of drug suspensions in n-heptane with constant dispersion on a Molvern-SI 11800 instrument with automatic processing of the results using a special computer program and with fifteen step-wise numerical output histograms.
The results of the mass and numerical distribution of MMC particles by equivalent diameter (D) are given in (table 3). The table shows that the numerical and mass distribution of particles of R and Ht over the equivalent diameter indicate a unimodal distribution pattern. A nonlinear semilogarithmic anamorphosis of the numerical distribution of particles of IS indicates an exponential dependence of ND on D. Moreover, Ht is accompanied by a fragmentation of their particles and an approximation to the exponential dependence of ND on D. Dispersion of bentonite particles at high temperature is probably due to the thermal explosion of some particles under the influence of evaporating constitutional moisture.
Table 3.- Equivalent diameter characteristics of the mass and numerical distribution of particles of the raw and heat-treatedMMCs
Name of fillers Dispersionmedium dn, mkn Y
R n-heptane 84.0 1.0
Ht n-heptane 94.0 1.0
Sedimentation analysis ofMMC particles revealed that their most probable radius is in the range of 5-10 ^m. A qualitative assessment of the wettability and structuring ofMMC has been carried out according to the methods of sedimentation volumes [3]. The study
showed that R and Ht particles precipitate in different ways and occupy different sedimentation volumes. At the same time, the sedimentation of R particles proceeds at a faster rate and an almost constant value of sedimentation volume is achieved in 210 minutes
and in Ht in 3600 minutes. This, apparently, is due to their structural feature and high dispersion. When determining the wettability of R and Ht in heptane by sedimentation volume, differences are observed in the behavior of these systems as compared to water-filler systems. In heptane, fillers precipitate and occupy an almost constant sedimentation volume for 10 minutes. However, in terms of the sedimentation volume of Is and Tob, the fillers differ significantly from each other. For example, the sedimentation volume for Is and Tob is 20% and 31%, respectively.
It is seen that Ht occupies a larger sedimentation volume in comparison with R, which is apparently
due to its high affinity for a nonpolar medium and a change in their structure after heat treatment.
It is known [1] that the main area of application of mineral resources is the production of composite elastomeric materials. One of the most important tasks in the field of physical chemistry of filled elastomers is the study ofprocesses occurring at the phase boundary of the elastomer-filler, which largely determine the behavior of the compositions under conditions of their processing. In connection with this method of statistical adsorption from dilute polymer solutions, the interaction features of elastomer mac-romolecules with R and Ht have been studied.
3,0
2,0
tg e u
1,0
1,0
c C---- c----*
- -
/ / // / / r---- p----Ci
¥ —'—" 1
a
0,6
0,2
_ A
> / —' — — "H r*** ---- \
/ ----1 r-1 » •
i' / f f ____ c ----- (----i t----X
w b
10
20
30
40
t, hour
Figure 4. Dependence of the kinetics of adsorption of rubber macromolecules: SKMS-30ARKM-15 (a) and SKI-3 (b) in dilute solutions Cl4. MMR (- x-), MMHt (- A-), (- • -), TMHt (- o -), concentration 4.75 mg/g
0
A study of the kinetics of adsorption of elastomer macromolecules on R and Ht showed that with an increase in time (t) the adsorption value (G) noticeably increases up to 20 hours (Fig. 4). The adsorption increment is determined mainly by the dispersion of the filler and their structural feature. So, for example, in the case of R and Ht, when their structure and dispersion change under the influence of temperature, the value of G noticeably changes. It has been found that the adsorption value also depends on the nature of the elastomers. In particular, in the studied system, the filler - SKI-3 solution, adsorption equilibrium is reached in about 48
hours, and the equilibrium adsorption value (Gy) is 0.8-1.4 m g/m2. At the same time, in the case of SKMS-ZOARKM-15 solutions, the influence on the adsorption parameters is very pronounced. As can be seen from the figures, the adsorption mechanism is more complex, at the initial moment of time (t < 4 hours), an intensive increase in the adsorption rate is observed up to the value G~ 0.7 mg/m2, however, in the further slow adsorption, and after 48 hours of saturation is not achieved. It should be borne in mind that the magnitude of G is influ-
c max
enced by the chemical nature and segmental mobility of elastomer macromolecules.
3,0
2,0
1,0 0
1,5
tg 1 A
e 1,0
u
^. ^^ ----* I---> u---
/ e- ^ r y
a
'A y
y
0,5
0
- -3 fc = = î|
A / A / / r'A — , _ £ ----1 )----c
b
/
4,5 3,0
1,5
1___J L___ I --> 1---+
/ y c^ZJ y • c
! ' A' p
/
0 1 2 3 4 C, mg/g
Figure 5. Dependence of the rubber adsorption isotherm SKMS-30ARKM-15(a)
SKI-3 (b) and SKN-18 (c) in dilute CCl4 solutions. KhMR (- A -), KhMHt (---),
KMR (- o -), KMt (- x -), concentration 4.75 mg/g 48-hour exposure
0
Figure 5 shows the adsorption isotherms of fractions. With a further increase in concentrations
macromolecules of elastomers on R and Hte, which (C> 0.5 mg/g), high molecular weight macromol-
are the dependence G = f (c). In the region of low ecules, adsorbing on the surface of the filler, displace
concentrations (C< 0.5 mg/g), a sharp rise is ob- low molecular weight fractions from it.
served on all isotherms, apparently associated with At the same time, isotherms are more individual in
the adsorption of low molecular weight elastomer nature, depending on the adsorbent-elastomer system.
References:
1. Kurbaniyazov K. K., Zokirov M. Z. Bentonites of Karakalpakstan // Publishing house "Fan", 1979.- 250 p.
2. Fillers for polymer composite materials // Ed. G. S. Katz and D. B. Milevsky.- M.: Chemistry, 1981.- 736 p.
3. Teshabaeva E. U., Ibadullaev A., Negmatov S. S., Tadjibaeva G. S. Investigation of the adsorption of rubber macromolecules from their diluted solutions with modified mineral fillers // Composite materials -Tashkent, 2006.- No. 2.- P. 11-13.
