2. PREPARATION OF PILLARED CLAYS
2.2. S ELECTION OF CLAYS
2.2.2. X-ray analysis
As the scheme of identification of clays to be presented here is based on X-ray diffraction recordings, some special problems connected with these must be described.
The only instrument used in clay mineral investigation by XRD is the diffractometer, primarily for the facility it offers in recording the indispensable low-angle reflections.
High-angle reflections, on the other hand, are not strong enough when recorded with the narrow slits necessary to resolve the low-angle ones they can be recorded with the
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further factor worthy of attention in preparing X-ray patterns, is the considerable preference of clay mineral samples for oriented aggregation. The conventional ways of making preparative invariably result in a preferred particle orientation, and this effect is enhanced even more when the sample in hand requires treatment with ethylene glycol.
The orientation effect requires close attention because of its controversial nature. In qualitative identification, by enhancing the 00l reflections, it lowers the sensitivity threshold of the method, whereas in quantitative analysis it increases its error.
Figure 2.9. X-ray pattern of the Istenmezeje montmorillonite (red) and the Na-Istenmezeje montmorillonite (black)
0 20 40 60
0 5000 10000 15000 20000 25000
Na-Istenmezeje Istenmezeje
Intensity (counts)
2Θ degree
0 20 40 60
In order to get rid of, or at least to reduce this effect, a special apparatus is used in which the preparative is made by shaking rather than by pressure. The basic step in clay mineral identification is preferably the observation of the basal reflection in the diffraction pattern. These reflections are usually so strong that their positions can be measured quite accurately.
One of the most conspicuous features of smectites exploited both in identification and in practical applications, is intra-crystalline swelling. This phenomenon, which can be readily traced by measuring changes in the basal reflection, enables smectites to absorb a remarkable variety of polar molecules including water or organic liquids into the inter-laminar spaces between their triple layer complexes, the mode and degree of intake depending on conditions. As a result, the layer complexes are forced apart; the c period of the lattice increases, and the mineral expands. The expansion of a smectite is a function of (1) charge density and degree of substitution, respectively; (2) the nature of the cation; (3) the nature of the absorbed liquid, and (4) the grain size of the mineral sample [26].
Table 2.1. X-ray powder-pattern lines of smectites: 001 lattice plane spacing of original clay and after saturation with glycerol
The smectites do exhibit by far the strongest tendency to form complexes with a remarkable variety of organic molecules. Of the several thousand known reactions, routine X-ray analysis prefers the complexes resulting from treatment with ethylene
Basal-spacing Basal-spacing after Difference
glycol or glycerol. The basal reflections at 17 Å and 17.7 Å of these complexes are among the important criteria of smectite identification. It is, however, essential to bear in mind that both the position and the width of the 001 reflection are also influenced by grain size, and may even vary with the localities from which the individual montmorillonite samples have been extracted [140]. The X-ray patterns of ethylene glycol treated clay samples are presented in Figure 2.12.-2.20. The basal spacings of original clay samples and also after saturation with ethylene glycol are reviewed in
Fig.2.12. XRD pattern of Istenmezeje. Fig.2.13. XRD pattern of Na-Istenmezeje montmorillonite and with ethylene- montmorillonite and with ethylene-
glycol glycol
Fig.2.14. XRD pattern of Koldu. Fig.2.15. XRD pattern of Na-Koldu montmorillonite and with ethylene- montmorillonite and with ethylene-
glycol glycol
Table 2.1. The values are between minimum 17 Å and maximum 17.5 Å, showing that smectites have not interstratified components. The swelling ability of sodium-clays is higher than the original or calcium form of smectites. Koldu clay samples have the
2 4 6 8 10 12 14
lowest-key d-spacing values with glycerol compared to the other bentonites, in all because of the lowest content of montmorillonite.
Fig.2.16. XRD pattern of Mád mont. Fig.2.17. XRD pattern of Na-Mád and with ethylene-glycol montmorillonite and with ethylene-glycol
Fig.2.18. XRD patterns of Texas Fig.2.19. XRD patterns of Wyoming montmorillonite and STx-1 with montmorillonite and with ethylene-glycol ethylene-glycol treatment
Fig.2.20. XRD patterns of Zenith montmorillonite and also after ethylene-glycol treatment
Wyoming and Istenmezeje clays have very similar behavior according 001 reflections;
original basal reflections are very broad and have two maximum values; the glycol saturated sample of Wyoming clay has higher basal spacing, indicates the larger swelling ability.
Figure 2.21. The difference between the basal-spacing values of the original bentonites and bentonites after glycol treatment
The Figure 2.21. shows that among Hungarian bentonites Na-Mád and Na-Koldu have the biggest difference between the basal-spacings of original and glycol treated clay samples, what is means the highest swelling ability. Na-Istenmezeje bentonite has a doublet XRD peak as Wyoming clay has it but the value of swelling ability is smaller.
Admixtures of alien minerals, present in almost all samples, mean that the accurate determination of the chemical composition of any smectite mineral is exceedingly difficult. The removal of contamination is often impracticable; in fact, if they occur in
Based on chemical and phase analyses we assumed the following composition for Mád clay:
♦ a% SiO2
♦ b% KMg3Si3AlO10(OH)2
♦ c% Na6Si30Al6O72.20H2O
♦ d% (Si4 - xAlx) O10(OH)2 (Al2-y-zMgyFez)Ca(x+y-t)/2Mg.
Table 2.2. Results of the phase analyses of the Hungarian clays
The balance can then be written for every element, and the mass of montmorillonite also can be calculated from the general chemical formula. From the X-ray diffractogram, we estimated the value of d (content of the montmorillonite) to be between 0.5 and 0.8.
The resolution of the system was achieved by successive iterations. Using data how the
Name of phase Name of clay
ICCD number
Istenmezeje Koldu Mád
Clinoptilolite
39-1383 5% no 4%
Cristobalite
39- 1425 7% no 4%
Dolomite
36- 0426 9% no no
Kaolinite
29-1488 no 3% no
Montmorillonite
13-259 71% 52% 73%
Muscovite
6-263 5% 3% 3%
Sanidine
25-618 no 5% no
Quartz
33-1161 3% 37% 16%
CEC measurement the like best set of values is. In computation of the formula from the chemical analysis the following arbitrary assumptions are made:
There are 20 oxygen atoms and 4 OH groups (sometimes substituted by F) per unit cell, or 10 and 2, respectively, in the chemical formula representing half a unit cell.
All the Si present is assigned to the tetrahedral sheet.
The remainder of the tetrahedral positions are filled exclusively by Al. Any additional Al is assigned to the octahedral sheet, together with Mg, Fe, and others, except, of course, those cations which are in exchange position.
The analytical values for the percentage of the oxides of the crystal elements and the exchangeable ions must be reduced to atomic proportions. The percentage of the oxides of the crystal elements is divided by the molecular weight of the oxides and multiplied by the number of atoms of the positive element in the oxide. The percentages of the oxides of the exchangeable ions are divided by the equivalent weight of the oxides. Alternatively, the cation exchange capacity of the clay, expressed in equivalents of exchangeable ions per 100 g of clay, may be chosen.
Thus the structural formula of the Mád montmorillonite:
(Si
3.989Al
0.011) (Al
1.404Mg
0.398Fe
0.198) Ca
0.199Mg
0.005O
10(OH)
2And the composition of the Mád bentonite is then:
20% cristobalite and quartz
3% muscovite
4% zeolite
73% montmorillonite.
The chemical formula of Istenmezeje and Koldu clay was calculated on the same way as Mád clay.
The chemical formula of the Koldu clay is the following:
(Si
3.82Al
0.18) (Al
1.69Mg
0.18Fe
0.13) Ca
0.12Mg
0.04K
0.12O
10(OH)
2 And the composition of the Koldu bentonite is then: 37% quartz
3% muscovite
5% sanidine
3% kaolinite
52% montmorillonite.
The chemical formula of the Istenmezeje clay is the following:
(Si
3.98Al
0.02) (Al
1.05Mg
0.38Fe
0.56Ti
0.01) Ca
0.18K
0.05O
10(OH)
2And the composition of the Istenmezeje bentonite is then:
10% cristobalite and quartz
5% muscovite
9% dolomite
5% clinoptilolite
71% montmorillonite.
The summarized results of the phase analyses of the Hungarian clays are reviewed in Table 2.2.
Wyoming (Swy-1) montmorillonite (Ward’s International; Catalogue No. 46W0439) was dispersed in distilled water and the <2µm clay fractionated was collected by sedimentation.
The chemical formula of the Wyoming montmorillonite is:
(Si
3.88Al
0.12) (Al
1.54Mg
0.23Fe
0.21) Na
0.35O
10(OH)
2Texas clay (STx-1) from Gonzales County, Texas, USA was bought as Ca-form montmorillonite powder. This clay was chosen because the iron content of this clay is especially low, and this is very important factor in the case of iron pillaring.
The chemical formula of the Texas montmorillonite is:
(Si
3.96Al
0.04) (Al
1.56Mg
0.38Fe
0.07) Na
0.12Ca
0.38K
0.05O
10(OH)
2 Zenith clay was taken from the Greek Island of Milos with code name Zenith-N (OCMA).The clay was fractionated to <2µm by gravity sedimentation and purified by standard methods.
Centrifuging four times with diluted solution of NaCl completed the procedure of cation exchange. The samples were finally washed with distilled-deionized water and transferred into dialysis tubes in order to obtain chloride free clays and then dried at room temperature. H+ - Zenith was prepared by passing a 1-% suspension of Na+ - montmorillonite through a column of hydrogen-saturated Amberlite IR-120 resin.
The structural formula for Zenith clay as determined from chemical analysis is: