Chemico-mineralogical study of a Moroccan clay Ann. Chim. Sci. Mat, 1998, 23, pp. 173-176

CHEMICO-MINERALOGICAL STUDY OF A MOROCCAN CLAY

A. ALAMI, M. BOULMANE, M. HAJJAJI, S. KACIM*

Laboratoire de Chimie Physique, Facult6 des Sciences Semlalia, B. P. S15, Marrakech, Maroc. *Laboratoire de Chimie de Coordination Facult6 des sciences Semlalia, B. P. S15, Marrakech, Maroc.

R&urn&: Etude chimico - min&alogique d’unc argile marocaine: Un tchantillon argileux, utilist traditionnellement comme mat&e premiere en poterie, a fait I’objet d’une itude minbralogique. Plusieurs techniques d’analyse (diffraction des rayons x, analyses thermiques, spectroscopic infrarouge, microscopic Clectronique en transmission,...) ont Ctt employ&es. Cette etude montre que cet Cchantillon contient du quartz et de la dolomite associbs d une fraction argileuse constituge de palygorskite et de glauconite.

Abstract: A moroccan clay sample, traditionally used in the pottery, have been the subject of a chemico-mineralogical study. For this purpose, the following techniques: x-ray diffraction, infrared spectroscopy, differential thermal analysis, thermogravimetry and transmission electron microscopy, were used. Some chemical analysis were also done. It was found that the clayey fraction consisted of a mixture of palygorskite and glauconite. Quartz and dolomite arc the main associated minerals.

1 - INTRODUCTION

Clays are used as raw materials in many industrial fields (ceramics, paper, paint, petroleum industry, clarification of various effluents, catalysis,...)( l-6). Their applications are tightly dependent upon their structure, composition, and physical attributes (7). The knowledge of these characteristics can help for a best exploitation and eventually may open-up new areas of application.

The purpose of this work is to carry out a detailed chemico-mineralogical study on a moroccan clay sample picked-up from the area of the haut-Atlas (district of marrakech).

2- EXPERIMENTAL PROCEDURES

The crude clayey sample was roughly crushed, and the fraction < 100 km was attacked successively by HCl (N/10) and H202 (30 wt %) solutions. These operations were experienced in

&p&&: A. ALAMI, L. C. P. B.P. S15, Marrakech, 40000, Morocco.

174 A. Alami et al.

order to eliminate carbonates and organic matter respectively. Then, the clayey fraction ($2 pm) was extracted using standard sedimentation procedures (8). The identification of the cristalline minerals was performed by x-ray diffraction, using either a Philips diffractometer with CoKol radiation (h= 1.78897 A) or a Diano x-ray diffractometer with CuKo radiation (A= 1.54 18 A). Thermal analyses (DTA-TGA) were done by a seteram apparatus operating at a heating rate of lO”C/min, under nitrogen atmosphere. The calcined alumina was used as reference. IR spectra were recorded thinks to a Perkin Elmer 580 IR spectrometer. The explored range of frequencies was 4000-400 cm-‘. The microscopic examinations were carried out with a Philips EM 300 transmission electron microscope operating at 100 kV. The elemental composition determination was done by x- ray fluorescence spectrometry employing a Philips PW 1404 spectrometer with a Rh tube.

3- RESULTS and DISCUSSION

The x-ray powder diffractogram of the crude sample (figure la) exhibited, apart from characteristic reflections of quartz and dolomite, the presence of weak peaks which may be attributed to clays and/or other associated minerals. The chemical analysis performed on the raw material (RM) as well as on the clayey fraction (CF) (table 1) allowed to deduce that calcium resulted essentially from carbonate in dolomite form since the x-ray diffraction did not evidence the presence of calcite. The dolomite content is estimated to be 33.5 wt %. The percentage (PC) of the clay fraction was determined to be 39.4 wt % and that of quartz (Po)was calculated on the basis of the following formula: Pe = P -P’ XP, where, P and P’ were the percentage of SiOZ in RM and

CF respectively. On the other hand, the appreciable amount of potassium may serve as an indication of the presence of mica or feldspar minerals.

The infrared spectrum of the raw material (figure 2a) displays several bands at 2525.9, 1816.7, 1455.6, 879.6 and 728.4 cm-’ related to the vibrations of COj2- groups of dolomite (9). Furthermore, it confirms the presence of quartz which is particularly characterized by the doublet at 797.7 and 778.2 cm-’ (10). However, it did not show bands assignable to feldspar. Hence potassium arise likely from a mica mineral. It is worth mentioning that a trace of organic matter, in the form of a long chain paraff’nic waxy component, evidenced by two weak bands at 2919.9 and 2843.4 cm-‘, is also present ( 11).

In order to identify the nature of argillaceous minerals, the clayey fraction was analyzed by x-ray diffraction. Owing to the following observations:(l) the presence of the reflexions at 10.37, 6.32, 5.37,4.45,3.69, 3.5 and 3.17 fi on the x-ray powder pattern (figure lb), (2) the position of the reflexion at the Bragg angle 4.9’ (d= 10.5 A) was neither affected by the ethylene glycol saturation nor by a heat treatment at 5OO”C, (3) the intensity of the later reflexion expecienced a marked decrease upon the heating operation, it may be stated that palygorskite is a constituent of the clayey fraction. This statement is supported by the transmission electron microscopy examinations (figure 4-J. The presence of palygorskite manifests on the DTA-TGA curves (figure 3) three weight losses of 7.1,3.7 and 4.1 % at about 100, 250 and 400°C respectively. The first loss is due to the adsorbed and zeolitic water. The second corresponds to the loss of a part of bound water; while the last one is associated to the remainder of the bound water of palygorskite as well as to the dehyroxylation (12, 13). At high temperature (around 8OO”C), an endothermic effect, followed by an exothermic one, occurred. These phenomena which are less pronounced are associated to the dehydroxylation of

Chemico-mineralogical study of a Moroccan clay 175

a I

FIG. 1 - X-ray powder diffiactograms : a) raw material, b) clayey fraction.

FIG. 2 - Infrared spectra. a) raw-material ; b) untreated clayey fraction ; c) heated clayey fraction (4S0°C)

FIG. 3 - DTA and TGA thermograms of the clayey fraction

FIG. 4 - Transmission electron micrograph o the clayey fraction

Table 1 - Chemical analysis of the raw sample and of its clayey Fraction

1 SiO2 1 A1203 Fe203 1 My0 CaO 1 Ti02 CuO ZnO K20 1 ignition loss RM* 145.61 1 10.43 3.76 1 14.43 10.18 ) -- -- -- 1.84 1 16.75 CF* 149.02 1 16.06 II.85 [ 6.51 -- 1 1.43 1.26 0.59 5.3 1 801 *RMraw material; *CF: clayey fraction

176 A. Alami et al.

(060) plane and the persistence of hydroxyl stretching band at 3622.2 cm-’ after thermal treatment at 450°C (figure 2c), this mineral has a dioctahedral character (11). Its thermal behaviour is similar to that of muscovite. Nevertheless, the endothermic effect due to the dehydroxylation occurred at a lower temperature. This temperature shifting may be ascribed to a partial substitution of iron for aluminium in the octahedral layer (15). Indeed, an important amount of iron is present in the specimen (table 1). Referring to the previous observations, this dioctahedtal layered silicate is considered as glauconite.

4- CONCLUSION

It was shown from the present study that the investigated clay sample includes quartz and dolomite as associated minerals. Their respective proportions ate 26.3 and 33.5 %. In addition, the clayey fraction consists of a mixture of glauconite and palygorskite.

5- REFERENCES

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