| الملخص | Samples of Iraqi bentonite taken from Wadi Bashira deposite - western desert of Iraq , were heated at various temperatures between 100-1100C° for 1hr in ambient atmosph-ere .
X-ray diffraction (XRD),cation–exchange capacity(CEC)data, specific surface area (S) and the specific micropre- mesopore volume (V)by BET method were obtained. Also , FT-IR spectra were determined for each sample , besides bentonite was observed by Atomic Force Microscope (AFM).S and V values show a "Zig-Zag " variation with increasing temperature and they reach a maximum at 550-600C°.The XRD data and the FT-IR spectra clearly show that the 2:1 layer structure completely collapses above 900C°.
From that we can conclude that Iraqi bentonite from Wadi Bashira deposit can be used in industry after heating it for 1 hour at certain temperature , and can be used as drilling mud at high temperature up to 800C°.
Key words: Bentonite ,thermal activation , specific Pore volume , specific surface area ,FT-IR,AFM and XRD .
Introduction
The properties of bentonite clays had made them valuable in many important industrial applications .Application fields include edible oils , industrial oils , cosmetics ,pharmaceuticals, paints, …etc. Bentonites are also used as binders in foundries , and in ceramic production , since they produce muds of high plasticity with water , iron ore pelletizing and as drilling fluids .They may be subjected to high temperature when used in these applications . Bentonites ,which have high content of smectite , are strongly affected by thermal treatments . For example , physicochemical properties , like specific surface area , pore structure , particle size , cation-exchange capacity (CEC) , adsorptive properties , swelling and catalytic activity as well as the chemical composition of the particles and the mineralogy can change considerably depending on thermal effects(1) .
For these reasons it is important to investigate the change in the physicochemical properties of bentonites as a function of temperature.
In general , thermal activated bentonite , and other activations of bentonites, may be used as adsorbents in the bleaching of edible oils and other materials. Our group is actively involved in the research and development activities focused on the area of variation in the chemical composition and physicochemical properties after thermal treatment from 100 to 1100C˚ of Iraqi bentonites collected from Wadi Bashira deposite – Western desert of Iraq .
The treated samples are expected to have different properties compared to the precursor , and it is hoped that the properties of the resulting materials could be improved in relation to its precursor .
Materials and methods
All samples were dried at 105C˚ for 48 hours and then ground to 100% below 200 mesh using porcelain mill to avoid contamination of samples .These samples were used as starting materials for characterization and physicochemical tests.
Samples , each having a mass of 30 gm , were heated in an electric furnace at various temperatures , from 100 to 1100C°for one hour in ambient atmosphere .
Samples were then labeled as T200 ,T300 ,…..etc , and then kept in sample bottles and stored in a desiccators for further characterization : XRD, FT-IR,BET, Particle size,CEC and Atomic Force microscopy observations .
Results and Discussion
X-ray diffraction analysis
XRD analysis shows that the intensity of 001 peak of natural bentonite decreases during thermal treatment between 200 -800C° .At 800 C° the intensity becomes significantly smaller , and the XRD patterns at various temperatures show that this peak changes its position from d(001) =1.36nm for untreated sample to d(001)=0.97nm and remains constant in position between (200-800)C°. Also , we can see that montorollonite structure (2:1 layerstructure )completely collapses above 900C°giving rise to a new peek that was attributed to quartz . Previous workers have recorded similar results.
FT-IR analysis
FT-IR spectrum shows the bands at 3546 and 3419 cm-1 which were assigned to a bond between the basal hydroxy groups of one sheet and the puckered oxygen's of the next sheet , and the band at 3629 cm-1 was attributed to interlayer hydrogen bonding . Peaks at 541cm-1 and 472 cm-1 were assigned to Si-O-R , and at 916 ,972 and 1031cm-1 to Si-O stretching vibrations . On heating bentonite between 200C° and 925C°, the bands at 3500-3700 cm-1 , were seen to decrease rapidly in intensity above 550C°. Upon further heating the shape of many peaks were changed , However the structure of bentonite was collapsed completely above 900C°.This result is in a good accord with XRD analysis .
BET measurements
From BET measurement we can conclude that in untreated sample , the S and V values were 63.22m2g-1 and 0.136cm3g-1 respectively .
S reached maximum value of about 70 m2g-1 at 550 C˚, and V reached maximum value at 0.207 m3 g-1 at 600C˚ . After that S and V values start to decrease reaching their minima at 925C˚ .Figure (1) shows the specific surface area (BET)of original and thermal activated samples.
Figure (1) :Variation in Specific Surface area Vs. Temperature
CEC measurements
Upon thermal treatment from 100 to 1100 C° ,CEC reached its maxima at 550C° and decreases rapidly with increasing temperature at 700C° and approaches approximately zero at 900C° .
The explanation for this is that as the temperature increases above 550C° , the space between 2:1 bentonite layers is reduced and it becomes difficult for methylene blue to enter the interlayer of bentonite because the interlayer is partially collapsed(3).
Atomic force microscopy
Figure 2 shows 3D-image of bentonite colloid surface on mica .Particles diameters range from 45 to 400nm . Most of the particles have blocky shapes typical for their monoclinic crystal symmetry
However the major strength of AFM is to determine particle size and shapes simultaneously from the nanometer to micrometer range .
These results are in fair agreement with M.Plaschke (2001) findings . By considering these results and results of XRD and FT-IR ,one can conclude that Iraqi bentonites from Wadi Bashira deposite – western desert of Iraq is potentially useful in industry after heat treatment to certain temperature ,and useful as oil drilling fluid at high temperature up to 800C˚ .
Figure 2 3D -AFM image shows bentonite colloids surface
References
1. Reicle ,W.T., Catalysis reaction by thermally activated , synthetic , anion clay minerals ,Journal of Catalysis,94,547-557(1985).
2. Turgay Seckin ,Ahmet Guftek ,Yunus Onel ; Synthesis ,Characterization and thermal properties of bentonite-polyacnylate sol-gel materials ;J.Mater .Chem ., (1997),7(2),265-269.
3. Yoksel Sarikaya et.al ;The effect of thermal treatment on some of the physicochemical properties of the a bentonite clays;clay and clay minerals,vol.48,No.5,557-562(2000). | en_US |
