DELAMINATION OF NATURAL VERMICULITE USING OXALIC ACID Petra Majorová a, Jana Seidlerová a, Gražyna Simha Martynková a, Eva Gryčová a, a Centrum nanotechnologií VŠB TU Ostrava, 17.listopadu 15, 708 33, Ostrava Poruba, Czech Republic, jana.seidlerova@vsb.cz Abstract There are several methods of the phyllosilicate delamination/exfoliation described in literature, that can be used for preparation of further modification of material. They use both physical and physico-chemical processes. The present paper deals with influence of oxalic acid on vermiculite structure. The particles size less than 0.2 mm of natural powdered vermiculite from Brazil was used. Powdered natural vermiculite sample were treated for 60 and 180 minutes in water solution with oxalic acid at define temperature. Using the same condition the vermiculite particles was treated in deionised water. The cations Ca, Mg, K, Si and Al concentrations in filtrate were determined by the spectroscopy methods. The changes of vermiculite structure using X-ray diffraction analysis, infra-red spectroscopy and scanning electron microscopy with EDS detector were studied. Sample particle size and specific surface area were detected using laser granulometry. It was found that the oxalic acid solution has an impact on vermiculite structure and size of particle. Significant influence has an experimental temperature. Keywords: vermiculite, delamination, hydrogen peroxide, oxalic acid 1. INTRODUCTION Clay minerals are very extended materials for applications in advanced materials. Their availability and financial modesty are positive facts to use their in different application. Nowadays phylosilicates are used in agriculture, building industry and ceramics 1. Recently, a modification of clay minerals structure allows their new applications such as cosmetics and medicine. Clay minerals are generally formed by octahedrons and tetrahedrons sheets, which are connected to the layered network structure. Their division into group is derived from centre atoms octahedral or tetrahedral, type of adjustment layers and interlayer cations. Generally, clay minerals are soft granular materials with large specific area. Into theirs structure can be captured water and others inorganic or organic substances due to expandability 2. Vermiculites as a significant group of clay minerals, are formed layer 2:1 (2 tetrahedral and 1 octahedral). Cation exchange capacity depends on the place and conditions of vermiculite formation. Generally, the value of layer charge is from 0.6 to 0.92 3. The structure modification and changes in the particles size can be done by mechanical process (e.g. grinding), chemical process which are based on interaction with organic compounds (e.g. intercalation) or combination of both. One of the popular methods is the use of ultrasound treatment or combination ultrasound treatments with effect of hydrogen peroxide. F. Franco et al reduced particles of dickitite and kaolinite by ultrasonic treatment during 10-20 hours. It has been observed, that reduction of particles size depends on treatment time. Depending on the change of particle size has been observed, that the specific surface area increased, but not as rapidly as was observed in kaolinite, which may be due to greater cohesion in the dicktite crystal structure 4. Jimenéz de Haro et al. studied the effects of ultrasound on the particle size of vermiculite 5. The changes of talc after 40 hours treatment observed Magueda Peréz et al 6. The results of all the cited authors show, that longer exposure of ultrasound on any clay, induce reducing of particles and thereby increasing the specific surface. Replacement ultrasonic treatment by affect the microwave radiation and hydrogen peroxide described Weiss et al. In his work treatment of Mg-vermiculite, using 30 % and 50 % hydrogen peroxide was performed. The vermiculite particles were treated for 1 or 5 hours at the temperature 25 C and 80 C without and with microwave field. The results showed to prepare
vermiculite nanoparticles the higher concentrations of hydrogen peroxide and longer treatment time is required. After exposure of vermiculite to hydrogen peroxide and microwave radiation the characteristic peak 001 from X-ray diffraction pattern complete disappeared, suggesting of decay crystal structure 7. The aim of this work is to study the structural changes of vermiculite using oxalic acid as a reagent which was not described in literature at different temperature so far. Oxalic acid is the white crystalline substance, which occurs in nature, it is soluble in water and reacts well with alkaline-earth metals. In industry it use as a reducing agent for metal cleaning and glycerine 8. 2. EXPERIMENTS 2. 1 Materials To test the impact of aqueous solution oxalic acid was chosen Brazilian vermiculite with crystallochemical formula (Si 6,32 Al 1,58 Ti 0,1 )(Mg 4,75 Ca 0,34 Fe 0,91 )O 20 (OH) 4 Ca 0,04 K 0,38. The natural material was grinded and followed by sieving fraction smaller than 200 µm was prepared. The saturated solution of oxalic acid, purity p.a. in deionised water with ph 1.96 was used for the experiments. 2.2 Experimental devices Morphology of particles was studied by scanning electron microscopy (SEM), PHILIPS XL-30 with spectrometer EDAX. Specific surface area of vermiculite particles and their size distribution were determined using laser granulometry Analysette C22. Changes in the structure of particles were observed using X-ray diffraction methods (XRD) BRUKER D8 ADVANCE. Concentration of elements in filtrate obtained after separation solid phase was determined by atomic emission spectroscopy with inductively coupled plazma (AES-ICP) SPECTRO VISION and atomic absorption spectroscopy (AAS - FA) UNICAM 969. 2.3 Procedures At first the suspension of vermiculite in oxalic acid saturated solution in ratio VER : OXA = 1 : 200 were prepared. The suspension was stirred for 2 hours at define temperature. After separation of the liquid part, the sample was vacuum filtered to the filtration cake. Amount of 200 ml of saturated solution oxalic acid was added again and the suspension was stirred for 2 hours. After that the procedure was repeated once more. Simultaneously with experiments the same experiments with deionized water were performed for comparison, as shown in tab.1. Table 1 Experimental details Exp. No. Oxalic acid Treatment H 2 O Treat. Temp. ( C) Exp. No. Oxalic acid Treatment H 2 O Treat. Temp. ( C) S1 no yes 25 S6 yes yes 60 S2 yes yes S7 no yes 80 S3 no yes 40 S8 yes yes S4 yes yes S9 no yes 95 S5 no yes 60 S10 yes yes After stabilization of the filtrate with concentrated nitric acid the concentration of elements Ca, K and Mg was determined. Solid phase was dried at 25 C to constant weight and study by XRD and other method was performed.
3. RESULTS AND DISCUSSION Vermiculite after treatment with a saturated oxalic acid solution at different temperatures changed the structure as showed at the diffraction patterns in Fig. 1a). The characteristic peak 001 reduced the most after treatment at the temperature of experiment 95 C. From the comparison the diffraction patterns of vermiculite after treatment in deionized water and saturated oxalic acid solution is evident, that after interaction with oxalic acid solution the changes in the structure are more pronounced than at the same temperature after exposure to water only. 1.42 nm 1.42 nm 1.24 nm 3 10 20 2 theta CoK alpha ( ) S9 S1 VER 1.24 nm S10 S2 VER 3 10 20 2 theta CoK alpha ( ) a) b) Fig. 1 The sections of the powder X-ray diffraction patterns original vermiculite (VER) and after treatment in deionized water (a) or saturated oxalic acid solution (b) at 25 o C and 95 o C. Dependence of particle size on treatment temperature 25 o C and 95 o C with and without oxalic acid of represented particle size shows fig. 2. Fig 2 Effect of thermal treatment on particle size, D(50) - represented the largest particle size in the sample, D(0.9) - 90% of the particles in the sample is below a given value. The particle size decreased the most after treatment of saturated oxalic acid solution at 95 C. Due to oxalic acid effect the specific surface area changed at the lower temperature, as shown in fig. 3 in comparison with original vermiculite sample.
Fig. 3 Effect of experiment temperature on specific surface area (SSA) in suspension of vermiculite with saturated oxalic acid solution. Results of the shape and particle size study of vermiculite using SEM shows fig. 4. It is visible, that the saturated oxalic acid solution had effect on shape and particle size compare to vermiculite treatment in deionized water samples at the same temperature. a) b) Fig. 4 Shape of the particle of original vermiculite (a), magnification 200x, vermiculite after treatment in saturated oxalic acid solution at 95 o C (b), magnification 2000x and vermiculite after treatment in deionized water at 95 o C (c), magnification 200x. c) The content Ca, Mg and K in filtrate after treatment with saturated oxalic acid solution proved that the leaching of Ca, Mg and K occurred. The concentration listed elements in filtrate were higher in comparison with concentration in filtrate after treatment with deionized water.
CONCLUSION In the paper the effect of saturated oxalic acid solution using different temperatures on structure and particle size of the Brazilian vermiculite were studied. According the intensity of 001 peak of X-ray diffraction pattern is visible that described method changed the structure and particle size of vermiculite. The resulting particles size and specific surface area is depended on temperature of treatment and enhanced with increasing temperature. Delamination of vermiculite structure occurred at higher temperatures of experiment. From the comparison of XRD patterns intensity of 001 vermiculite peak after treatment with water and saturate oxalic acid solution at the same temperature is evident the positive effect of oxalic acid to change the structure of vermiculite due to reaction of Ca and Mg ions with oxalic acid. ACKNOWLEDGEMENTS Authors thanks to prof. J. Zegzulka (Laboratory of Bulk Materials VŠB-TUO) and the financial support from the projects by the Ministry of Education of the Czech Republic (MSM 6198910016). LITERATURE 1. KLEIN, Cornelis; DUTROW, Barbara. Manual of mineral science. 23. Hardcover: Wiley, 2007. 716 pp. ISBN 978-0-471-72157-4. 2. ŠUCHA, V. Íly v geologických procesoch. Bratislava: Univerzita Komenského, 2001. 159 pp. (in Slovac) 3. WEISS, Zdeněk; KUŽVART, Miloš. Jílové minerály: jejich nanostruktura a využití. Univerzita Karlova v Praze: Karolinum, 2005. 281 pp. ISBN 80-246-0868-5. (in Czech) 4. FRANCO, F., et al. Particle-size reduction of dickite by ultrasound treatments: Effect on the structure, shape and particle-size distribution. Applied Clay Science. 2007, 35, 1-2, p. 119-127. 5. JIMÉNEZ DE HARO, M. C., et al. Effect of ultrasound on preparation of porous materials from vermiculite. Applied clay science. 2005, 30, 1, p. 11-20. 6. PÉREZ-MAGUEDA, L. A.; DURAN, A.; PÉREZ-RODRÍGUEZ, J. L. Preparation of submicron talc particles by sonication. Applied clay science. 2005, 28, 1-4, p. 245-255. 7. WEISS, Zdeněk, et al. Preparation of Vermiculite Nanoparticles Using Thermal Hydrogen Peroxide Treatment. Journal of Nanoscience and Nanotechnology. 2006, 6, 3, p. 726-730. 8. Science.jrang.org [online]. 2010 [cit. 2010-09-24]. Oxalic acid. WWW: http://science.jrank.org/pages/4958/oxalic-acid.