Characterization of modified kaolin from the Ranong deposit Thailand by XRD, XRF, SEM, FTIR and EPR techniques

Abstract

Various physical and analytical techniques (XRD, XRF, SEM, FTIR and EPR) have been used to investigate the effects of chemical and/or physical modification of Ranong kaolin, which has been proposed as a potential bleaching clay for vegetable oils. Acid treatment after grinding resulted in major changes compared with acid treatment of the original mineral sample or mechanical treatment alone. Previous work has shown that the combined treatments produce increases in surface area and new porous structures, and the present measurements show reductions in Al:Si ratios. These are accompanied by a major reduction in O–H stretching vibrations as a result of grinding, although acid treatment produced little subsequent effect on the O–H bands in the FTIR spectra. However, acid treatment resulted in a reduction in the Al–OH–Al bending vibrations and the appearance of Si–O bands associated with newly synthesized material; these effects were much greater with samples that had been ground prior to the acid treatment. There were appreciable qualitative differences in the way in which the EPR spectra of Fe and Mn were affected; the Fe signal was sensitive to mechanical treatment, but little subsequent change was induced by acid extraction, whereas the Mn peaks were sensitive to the both the pH and the chemical nature of the acid used. These results therefore indicate that the Fe and Mn are in different types of site in the kaolin structure. Little change was observed in the main oxygen-based free radical centre associated with Si atoms, but that associated with Al was lost as a result of the treatments. Such mineral characterization is of fundamental importance to understanding the modification of kaolins and their uses as adsorbents in the food and environmental sciences.

Organic template free synthesis of ZSM11 from kaolinite clay

“…The Kankara kaolinite clay (Figure 2a) was found to contain anatase, potassium iron oxide and for sterite, while Onibode (Figure 2b) was observed to be purer though having some inherent impure phases, namely ilmenite and halloysite and less crystalline in nature. The SEM in Figure 3(a) shows the card-like or platy morphology of kaolinite material [35] and presence of rod or tubular material attributed to halloysite and clinochlore and micelles-to mica and muscovites, which corroborates the XRD findings. The average particle size was estimated as 2.0 μm for both the raw and beneficiated kaolin.…”

Effect of Alumina Content and Surface Area of Acid‐Activated Kaolin on Bleaching of Rice Bran Oil

“…This peak is due to the formation of free amorphous silica. Quartz showed a peak at 790 cm −1 [24,25] that was present in the initial and acidtreated samples. The band at 753 cm −1 was assigned to Si-O-Al stretching vibration of the clay sheet; the band at 693 cm −1 corresponded to Si-O stretching of kaolinite, the band at ~537 cm −1 corresponded to Si-O-Al (octahedral) stretching, and those at 469 and 430 cm −1 corresponded to Si-O bending vibrations [26], which also decreased in the GRH 2 sample.…”

“…The acid activation enhances the sorption properties of clays by manipulating its structural, mineral and physico-chemical properties with a limited decomposition of its crystal structure [29][30][31]. Acid treatments partially or totally destroy the kaolin's crystal structure, disintegrate the clay particles, and decompose the minerals, thereby forming an amorphous silica phase [6,13,25]. Results from SEM/EDX analysis of the Ranong kaolin in previous studies indicated that hot sulfuric or oxalic acid treatments of the ground sample resulted in the formation of products with globular morphology [25].…”

“…Acid treatments partially or totally destroy the kaolin's crystal structure, disintegrate the clay particles, and decompose the minerals, thereby forming an amorphous silica phase [6,13,25]. Results from SEM/EDX analysis of the Ranong kaolin in previous studies indicated that hot sulfuric or oxalic acid treatments of the ground sample resulted in the formation of products with globular morphology [25]. Upon acid activation, specific surface area, porosity and number of acid centers are also changed in the activated clay due to the leaching of alumina and other mineral impurities [28,[32][33][34][35][36][37][38][39][40].…”

Stability of kaolin sand from the Vyšný Petrovec deposit (south Slovakia) in an acid environment

“…Sillitoe 2010; Kadir et al 2011;Premović et al 2012) and weathering pathways controlling processes of clay-mineral formation in acidic soils (Uzarowicz et al 2011). Many studies were devoted to acid treatment of bentonites or smectites (Fijał et al 1975;Číčel & Novák 1976;Stoch et al 1977;Novák & Číčel 1978;Komadel et al 1993Komadel et al , 1996Tkáč et al 1994;Breen et al 1997;Madejová et al 1998;Rožić et al 2010Rožić et al , 2011Sciascia et al 2011), illites, micas or kaolinites (Bahranowski et al 1993;Ganor et al 1995;Kalinowski & Schweda 1996;Dubíková et al 2002;Hradil et al 2002;Jozefaciuk & Bowanko 2002;Pentrák et al 2009Pentrák et al , 2010Nguetnkam et al 2011;Valášková et al 2011;Worasith et al 2011 Al) in octahedral sheets leads to enhancement of the clay mineral dissolution due to higher negative layer charge density (Pentrák et al 2012). The tetrahedra are rearranged from layered into three-dimensional adjustment.…”