Mineralogy of Clay Raw Materials from Cote d`ivoire: Case of the Deposit from Katiola

MATERIALS AND METHODS

Two samples of clays (K₁ and K₂) used in this study are from the deposit of Katiola, a city located in the centre of Cĉte d’Ivoire. The accurate geographic coordinates of the samples K₁ and K₂ obtained from a Global Positioning System are, respectively K₁(N: 08° 14.709’; W: 005°06.505’) and K₂ (N: 08°08.945’; W: 005°05.959 ’).

A quantometer Jobin-Yvon 70-P equipped with ICP (Inductively Coupled Plasma) plasma was used to make the chemical analysis in total rock.

The x-rays diffraction was done with a Brucker’s D8 diffractometer that use Co-Kα monochromatic radiation (λ = 1.7889 Å) at ambient temperature over the domain 3≤θ≤35.

The absorption spectra are carried out in the field of the mean infrared, that is to say for numbers of wave (v = 1/λ) ranging between 400 and 4000 cm^-1. Measurements were taken in diffuse reflection). In order to minimize the loss of energy, the samples are diluted in a KBr (70 mg of sample for 370 mg of KBr). The device used is a Fourier transform infrared spectrometer (Brucker YEWS 55). This device has a laser He-Ne and a high sensitive large bandwidth of wavelength (6000-600 cm^-1) detector of type MCT (Cadmium and Mercury Telluride).

The DTA-TGA was carried out with a device ATD Linseis, an entirely automated differential thermal analyser. The samples have been ground to a granulometry lower to 100 μm. The reference is a charred alumina and the trial mass is 70 mg for the sample and the reference. The powders are packed slightly and the measures were carried out in identical platinum crucibles according to a programme for heating, run at 10°C min^-1 under an air atmosphere.

RESULTS AND DISCUSSION

Chemical analysis: The chemical analysis results are presented in Table 1. From the analysis, one can see that the samples (K₁ and K₂) have similar composition. Silica, alumina and iron are the main constituents of those samples. However, the percentage of alumina and iron is higher in K₂ than in K₁. The results also reveal the presence of a relatively important amount of Mg in the samples. Nevertheless, the percentage of Mg is higher in K₁ than in K₂. For what concern the chemical elements Ca, Na and K, the percentage is not negligible for K₁ but quasi inexistent for K₂.

X-rays diffraction: Figure 1 shows the results of the analysis made with the X-rays diffraction. The diagrams were obtained from normal films and Ethylene Glycol (EG) saturated films. The patterns exhibit predominantly the presence of inflating minerals in K₁ and K₂ (Brindley and Brown, 1980; Caillère et al., 1982; Bouchet et al., 2000). The wavelength of the major ray is shifted from 14.36 Å to 17.132 Å on the EG test. The diagram also shows a peak for K₁ at the wavelength 12.243 Å confirming the presence of inter-stratified clay, probably illite-montmorillonite (Brindley and Brown, 1980; Caillère et al., 1982).

The results of the Hofmann and Klemen (1950) test on K₁ and K₂ are shown in Fig. 2. It can be seen that the samples exchanged with lithium and heated at 300°C does not inflate anymore after saturation with glycerol. This structural modification can be explained as an irreversible closing of intrafoliar due to the migration of the Li⁺ cations toward emptied octahedral cavities, characterizing the presence of montmorillonite clay.

Infrared spectroscopy: Inside the domain corresponding to the elongating vibration of the hydroxyl (3750-3500 cm^-1), the spectrogram shows a large massive complex that reflects the diversity of the hydroxyl groups environment (AlAlOH, AlMgOH, AlFeOH, FeFeOH etc.) (Fig. 3). The remarkable bands around 3696 and 3620 cm^-1 wavenumber confirm the presence of Kaolinite (Farmer, 1974). At low frequencies corresponding to the range 1000 to 600 cm^-1, it is observed bands around 915, 890 and 795 cm^-1. This can be attributed to the distorting vibrations of AlAlOH, AlFeOH and FeFeOH, respectively. This is characteristic of the presence of dioctahedral smectite. The other characteristic frequencies around the bands 1109 and 1017 cm^-1 correspond to the distortion vibrations of the SiO (Fripiat, 1970; Famer, 1974).

Thermal analysis: The plots of thermal analysis of K₁ and K₂ (Fig. 4, 5) are similar. Indeed, it can be observed:

Table 1:	Chemical composition in total rock of the studied samples

Fig. 1:	Comparison of X-rays patterns of K1 and K2 obtained by normal thin films and saturated EG

Fig. 2:	Study of Hoffmann-Klemen effect on K1 and K2 samples

At 800°C, we also observe a relatively marked endothermic accident due to the emergence of an amorphous, followed by an exothermic peak which characterized the recrystallization toward 900°C (Greene, 1957). The position of the experimental peaks as described above (dehydration around 130°C and deshydroxylation between 450 and 600°C) corresponds to the phenomenon reported by several authors during the heating of the phyllosilicates 2:1 dioctahedrals (Poinsignon, 1977; Emmerich et al., 1999). In the case of the samples studied, the experimental peaks are probably cis-vacant montmorillonite clay, agreeing with the x-rays diffraction analysis (Emmerich et al., 1999; Vantelon, 2001).

Fig. 3:	Infrared spectrograms of K1 and K2 obtained with diffuse reflection

Fig. 4:	Differential thermal analysis of K1

Fig. 5:	Differential thermal analysis of K2

Quantitative mineralogy: It is noted that the samples of the deposits of Katiola are primarily made of inflating clays contrary to various deposits formerly highlighted through Cĉte d’Ivoire (Dorthe, 1984; Andji et al., 2001; Konan et al., 2001).

Table 2:	Relative quantification of argillaceous minerals present in K1 and K2

Indeed, the results show:

These compositions could explain the difficulties experienced by Mangoro’s cooperative. The results of quantitative mineralogy are consigned in Table 2.

Due to their high capacity of water absorb to inflate; montmorillonite clays induces strong withdrawals during the drying of the potters manufactured products (Delineau, 1994).

Taking into account their composition, K₁ and K₂ clays lets predict large perspectives in the clayey materials valorisation in Cĉte d’Ivoire. These materials can be used in environment protection, for heavy metals immobilization (Nir et al., 1986; Carretero, 2002), in health science, cosmetic products and in all applications that use the properties of montmorillonites.

CONCLUSION

The experimental technique used for this study has shown that the studied sample K₁ is composed of montmorillonite (74.5%) associated with inter-stratified clay (13.5%), kaolinite (7%) and illite (5.4%). The sample K₂ is composed of 73.4% of montmorillonite 23.5% of kaolinite and 3.1% of illite.

The composition of the clay raw materiel explains the high rate of loss during the drying of potters products. Nevertheless, this raw materiel may be used in the cosmetic industry, in the environment protection and health science.

ACKNOWLEDGMENTS

This study was done in the Laboratoire Environnement et Minéralurgie (LEM) of Nancy. We are grateful to the staff members of the LEM for their appreciate contribution to this work. We take this opportunity to thank the French department of foreign affairs for the financial support to this work.