A DRIFT Spectroscopic Study of Potassium Acetate Intercalated Mechanochemically Activated Kaolinite

Kaolinite has been mechanochemically activated by dry grinding for periods of time up to 10 h. The kaolinite was then intercalated with potassium acetate and the changes in the structure followed by DRIFT spectroscopy. Intercalation of the kaolinite with potassium acetate is difficult and only the layers, which remain hydrogen bonded, are intercalated. The mechanochemical activation of the kaolinite may be followed by the loss of intensity of the hydroxyl-stretching vibrations. The intensity of the 3695 and 3619 cm−1 bands reach a minimum after 10 h of grinding. The observation of a band at 3602 cm−1 is indicative of the intercalation of the kaolinite with potassium acetate. The degree of intercalation decreases with mechanochemical treatment. The effect of exposure of the intercalated mechanochemically activated kaolinite to moist air results in de-intercalation. The effect of the mechanochemical treatment is loss of layer stacking, which prevents the intercalation of the kaolinite

Modification of Low- and High-defect Kaolinite Surfaces: Implications for Kaolinite Mineral Processing

A comparison is made of the mechanochemical activation of three low and one high defect kaolinites using a combination of X-ray diffraction, thermal analysis and DRIFT spectroscopy. The effect of mechanochemical alteration of the kaolinites is greatest for the low defect kaolinites. The effectiveness of the mechanochemical treatment is represented by the slope of the d(001)peakwidth-grinding time line. High defect kaolinites are not significantly altered by the grinding treatment. The effect of mechanochemical treatment on peakwidth was independent of the presence of quartz; the quartz acts as an additional grinding medium. The effectiveness of the mechanochemical treatment depends on the crystallinity of the kaolinite. Two processes are identified in the mechanochemical activation of the kaolinite: first the delamination of kaolinite appears to take place in the first hour of grinding and secondly a recombination process results in the reaggregation of the ground crystals. During this process proton hopping occurs and reaction to form water takes place. This water is then adsorbed and coordinated to surface active-sites created during mechanochemical treatment

Slow Transformation of Mechanically Dehydroxylated Kaolinite to Kaolinite - An Aged Mechanochemically Activated Formamide-Intercalated Koalinite Study

Formamide-intercalated high defect kaolinite which was mechanochemically activated for periods of time up to 6 h has been aged for up to 1 year. These modified materials were studied using a combination of X-ray diffraction, thermal analysis and DRIFT spectroscopy. Ageing of the formamide-intercalated mechanochemically activated kaolinite results in de-intercalation of the formamide and the de-intercalated kaolinite returns to its original d-spacing. Thermal analysis shows that the temperature of dehydration and dehydroxylation increase by up to 30 °C. The temperature of the dehydroxylation of the aged samples was identical to that of the untreated kaolinite. The DRIFT spectroscopy showed that the spectrum of the aged samples approached that of the untreated kaolinite. The kaolinite showed partial de-intercalation and the 6 h sample had reformed to a mineral resembling the untreated kaolinite. The process of ageing the mechanochemically activated kaolinite enabled the reformation of the kaolinite

The Effect of Quartz Content on the Mechanochemical Activation of Kaolinite

The mechanochemical activation (dry grinding) causes destruction in the crystal structure of kaolinite by the rupture of the O–H, Al–OH, Al–O–Si, and Si–O bonds. The major mineral constituents of natural kaolins are kaolinite and quartz. In this study, the attention was mainly directed to the role of quartz content (4, 25, 50, and 75 wt%) in the mechanochemical amorphization of kaolinite. Grinding experiments were carried out for 1, 2, 3, and 4 h in a planetary mill. The rate of destruction of the kaolinite structure was followed by X-ray diffraction, thermal analysis, and Fourier transform infrared (DRIFT) spectrometry. The distortion and rupture of the kaolinite structure induced by grinding was reflected in line broadening, increases in mean lattice strain, and reduction of peak areas (intensities). The increased quartz content resulted in acceleration of the mechanically induced amorphization of the kaolinite structure. The crystalline order of kaolinite was completely destroyed after grinding the sample containing 75 wt% quartz for 4 h. On the other hand, 4 h of grinding was sufficient only to cause some increase in the defect density of kaolinite in the case of samples with lower quartz contents (25 and 4 wt%). The results indicate that quartz grains act as grinding bodies during the intensive dry grinding of kaolinite

The Effect of Mechanochemical Activation upon the Intercalation of a High-Defect Kaolinite with Formamide

The effect of mechanochemical activation upon the intercalation of formamide into a high-defect kaolinite has been studied using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. X-ray diffraction shows that the intensity of the d(001) spacing decreases with grinding time and that the intercalated high-defect kaolinite expands to 10.2 A. The intensity of the peak of the expanded phase of the formamide-intercalated kaolinite decreases with grinding time. Thermal analysis reveals that the evolution temperature of the adsorbed formamide and loss of the inserting molecule increases with increased grinding time. The temperature of the dehydroxylation of the formamide-intercalated high-defect kaolinite decreases from 495 to 470oC with mechanochemical activation. Changes in the surface structure of the mechanochemically activated formamide-intercalated high-defect kaolinite were followed by DRIFT spectroscopy. Fundamentally the intensity of the high-defect kaolinite hydroxyl stretching bands decreases exponentially with grinding time and simultaneously the intensity of the bands attributed to the OH stretching vibrations of water increased. It is proposed that the mechanochemical activation of the high-defect kaolinite caused the conversion of the hydroxyls to water which coordinates the kaolinite surface. Significant changes in the infrared bands assigned to the hydroxyl deformation and amide stretching and bending modes were observed. The intensity decrease of these bands was exponentially related to the grinding time. The position of the amide C&unknown;O vibrational mode was found to be sensitive to grinding time. The effect of mechanochemical activation of the high-defect kaolinite reduces the capacity of the kaolinite to be intercalated with formamide

Thermal Treatment of Mechanochemically Activated Kaolinite

The mechanochemical activation of a high defect kaolinite has been studied using a combination of high-resolution thermogravimetry and DRIFT spectroscopy. The effect of grinding causes a decrease in the dehydroxylation temperature and an increase in the amount of adsorbed/coordinated water. The temperature of dehydration also increases with grinding time. It is proposed that this dehydroxylation occurs through a homogenous process involving proton transfer through point heating. The amount of adsorbed water decreases with the increase in temperature of the thermal treatment

Modification of Kaolinite Surfaces by Mechanochemical Treatment

Kaolinite surfaces were modified by grinding kaolinite/quartz mixtures with mole fractions of 0.25 kaolinite and 0.75 quartz for periods of time up to 4 h. X-ray diffraction shows the loss of intensity of the d(001) spacing with mechanical treatment resulting in the delamination of the kaolinite. Thermogravimetric analyses show the kaolinite surface is significantly modified and surface hydroxyls are replaced with water molecules. Changes in the molecular structure of the surface hydroxyls of the kaolinite/quartz mixtures were followed by infrared spectroscopy. Kaolinite hydroxyls were lost after 2 h of grinding as evidenced by the decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm-1 and the deformation modes at 937 and 915 cm-1. Changes in the surface structure of the OSiO units were reflected in the SiO stretching and OSiO bending vibrations. The decrease in intensity of the 1056 and 1034 cm-1 bands attributed to kaolinite SiO stretching vibrations were concomitantly matched by the increase in intensity of additional bands at 1113 and 520 cm-1 ascribed to the new mechanically synthesized kaolinite surface. Mechanochemical treatment of the kaolinite results in a new surface structure

Mechanochemical Treatment of Kaolinite

Kaolinite surfaces were modified by mechanochemical treatment for periods of time up to 10 h. X-ray diffraction shows a steady decrease in intensity of the d(001) spacing with mechanochemical treatment, resulting in the delamination of the kaolinite and a subsequent decrease in crystallite size with grinding time. Thermogravimetric analyses show the dehydroxylation patterns of kaolinite are significantly modified. Changes in the molecular structure of the kaolinite surface hydroxyls were followed by infrared spectroscopy. Hydroxyls were lost after 10 h of grinding as evidenced by a decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm−1 and the deformation modes at 937 and 915 cm−1. Concomitantly an increase in the hydroxyl stretching vibrations of water is found. The water-bending mode was observed at 1650 cm−1, indicating that water is coordinating to the modified kaolinite surface. Changes in the surface structure of the OSiO units were reflected in the SiO stretching and OSiO bending vibrations. The decrease in intensity of the 1056 and 1034 cm−1 bands attributed to kaolinite SiO stretching vibrations were concomitantly matched by the increase in intensity of additional bands at 1113 and 520 cm−1 ascribed to the new mechanically synthesized kaolinite surface. Mechanochemical treatment of the kaolinite results in a new surface structure