Apophyllite alteration in aqueous solutions A nano-scale study of phyllosilicate reactions Dissertation zur Erlangung des Grades Doktor der Naturwissenschaften (Dr. rer. nat.) an der Fakultät für Geowissenschaften der Ruhr-Universität Bochum vorgelegt von Kirill Aldushin aus Moskau, Rußland Bochum 2004 ANKNOWLEDGEMENTS First of all I would like to thank my supervisor Priv.-Doz. Dr. Guntram Jordan for the opportunity to do my PhD thesis at the Ruhr-University of Bochum. I am grateful for his valuable advices and educational discussions. I also want to express my gratitude for his patience and continuous support during the last three and a half years. I would like to thank Prof. Dr. Wolfgang W. Schmahl for the constructive criticism and aiding of this work. I thank Prof. Dr. Werner Rammensee (Köln) for his help at the early stage of the work. I would also like to acknowledge the review by Prof. Dr. Michael Alber. Special thanks to Dr. Hans-Werner Becker (Institut für Physik mit Ionenstrahlung, RUB) for his friendly assistance in working with RBS and XPS. Priv.-Doz. Dr. Michael Fechtelkord for his kindly support in NMR is gratefully acknowledged. I am grateful to Dr. Heinz-Jürgen Bernhardt for his help with EPM analysis. The aid provided by Dr. Ralf Dohmen in handling RBS spectra is greatly appreciated. I am grateful to Dr. Thomas Lohkämper for his help with PSIM measurements and to Dr. Thomas Reinecke and Dr. Bernd Marler for the aid with XRD. Many thanks to Sandra Grabowski, Astrid Michelle, and Udo Trombach for their help in laboratory work; thanks to Achim Schlieper for the computer support. I also appreciate very much various kinds of help provided by all members of the Mineralogy department of Ruhr-University Bochum. Thanks a lot for your openness and friendly atmosphere. Funding for the construction of the HAFM and for conducting this project was provided by the Deutsche Forschungsgemeinschaft (DFG) and is gratefully acknowledged. Finally, I warmly thank my family, especially my wife Elena and my parents, who made an inestimable contribution into this thesis. Without their continuos encouragement and moral support it would have been not possible to accomplish this work. Thank you for everything! Bochum, October 2004 Kirill Aldushin 2 Contents 1. INTRODUCTION…....………………………………………………………….. 5 2. MINERAL DATA AND PREVIOUS STUDIES OF APOPHYLLITE…....…. 11 2.1 Definition of apophyllite, its properties, and occurrence…...……………... 11 2.2 Apophyllite structure and its relation to other minerals…………………... 13 2.3 Apophyllite alteration……………………..…………………………………. 16 3. EXPERIMENTAL…………………………………..………………………….… 19 3.1 Experimental methods………………..……………………………………… 19 3.1.1 Hydrothermal atomic force microscopy (HAFM)………………….…….. 19 3.1.2 Rutherford backscattering spectrometry (RBS)………………………...... 23 3.1.3 X-ray photoelectron spectroscopy (XPS)………………………….……... 24 3.1.4 Nuclear magnetic resonance (NMR)………….………………………….. 24 3.2 Sample preparation……………..………………………………………...…. 25 4. RESULTS AND DISCUSSION……….…………………………………………. 27 4.1 Introduction into apophyllite alteration at acidic conditions……………... 27 4.1.1 HAFM…………………............…………………………………………. 27 4.1.2 RBS………………………………....……………………………………. 37 4.1.3 XPS………………………………………………………………………. 39 4.1.4 Discussion…………………………………………....…………………... 41 4.2 Protonation stages……….…………………………………………………... 45 4.2.1 AFM……………………………………………………………………… 45 4.2.2 NMR……………………………..……….……………………………… 51 1H MAS NMR………………………………..………………………….….... 51 3 29Si MAS NMR and {1H} 29Si CPMAS NMR………………………………… 52 4.2.3 Discussion……………………………........……………………………... 54 Transformation P → T……………………………………………….…….. 55 Transformation T → A……………………………………………….…….. 56 Transformation T → H and A → H, amorphous structures……….……….. 58 4.3 Alteration at pH 4 - 5.6………….……………..…………………………….. 59 4.3.1 Results……………………………………………………………………. 59 4.3.2 Discussion………………………………………………………………... 64 4.4 Hillock rotation……………..………………………………………………... 69 4.4.1 Results……………………………………………………………………. 69 4.4.2 Discussion………………………………………………………………... 71 5. CONCLUSION….......…………………………………………………………… 81 REFERENCES…..………………………………………………………………….. 85 Erklärung ……………………………….................................……...........……….... 92 Curriculum Vitae…………………………………………............…………………. 93 4 1. INTRODUCTION Detailed studies of reactions of silicates with acidic solutions provide insight into fundamental natural processes, such as weathering, formation of minerals, or global cycling of chemical elements (see e.g. Nagy et al., 1991; Wieland and Stumm, 1992; Walther, 1996). Among the diversity of silicate minerals, sheet silicates can be distinguished as one of the most important subclass. Phyllosilicates are known as important rock-forming minerals present in all types of rocks (magmatic, metamorphic, and sedimentary) and they play a key-role in soils as nutrient components. Furthermore, phyllosilicate minerals are widely used in many industrial fields. These facts may explain the huge interest of researchers in these minerals. Many investigations have been conducted to study the alteration of phyllosilicates (generally clays and micas) in aqueous solutions (e.g. Newman, 1970; Sposito, 1984; Kalinowski and Schweda, 1996; Zysset and Schindler, 1996; Malmström and Banwart, 1997; Huertas et al., 1999). Aside from the significance for environmental science, these studies are also important for technical applications e. g., production of sorbents, catalyst carriers, decontaminants (Corma and Perez-Pariente, 1987; Ravichandran and Sivasankar, 1997; Saito et al., 1997; Temuujin et al. 2001). Most sheet silicates can be composed by two modular units: a sheet of corner- linked tetrahedra and a sheet of edge-linked octahedra (e.g. Moore and Reynolds, 1997). In the tetrahedral sheet (Fig. 1a), the dominant cation T is Si4+, but Al3+ substitutes it 3+ frequently and Fe occasionally; the cation/oxygen ratio is T2O5. The octahedral sheet can be thought of as two planes of closest-packed oxygen and hydroxyl ions with cations occupying the resulting octahedral sites between the two planes (Fig. 1b). The cations are basically Al3+, Mg2+, Fe2+, or Fe3+. Phyllosilicates in which the cations occupy all available octahedral positions are called trioctahedral; dioctahedral phyllosilicates are those in which only two-thirds of octahedral positions are occupied by cations. The assemblage of one tetrahedral sheet and one octahedral sheet is called a 1:1 layer silicate structure. The structures with one octahedral sheet sandwiched between two tetrahedral sheets are called 2:1 layer silicate. The structure of chlorites consists of alternating 2:1 layers and octahedral layers, thus making a 2:1:1 structure. In some 5 a c b Al3+, Mg2+, Fe2+, Fe3+ O2- or OH- Figure 1. Structure of sheet silicates: (a) sketch of sheet structure of silica tetrahedra arranged in a hexagonal network; (b) sketch showing the sheet structure of the octahedral units; (c) an example of phyllosilicate structure: TOT-layers alternate with the layers of interlayer cations. minerals, e.g. talk, pyrophyllite, or kaolinite the layers are connected together by Van der Vaals bonds. In other phyllosilicates, such as most clays and micas, a cation substitution within the layers (basically Si4+ → Al3+) causes a positive charge deficiency. This deficiency is compensated by interlayer cations (usually K+, Mg2+, Na+, or Fe2+) which couple the silicate layers together. An example of such structure is shown in Figure 1c. Phyllosilicates show a variety of reactions while being in contact with aqueous solutions. The type of the reaction may depend on inherent mineral properties (e.g. mineral structure, composition, grain size and texture) and conditions, such as temperature, pressure, or solution composition. One of the reactions is ion-exchange: 6 the uptake of ions by the surface and interlayers coupled with a release of ions from the surface and interlayers. In acidic solutions phyllosilicates usually undergo selective leaching of interlayer cations and cations located in the octahedral sheet. In some cases this leaching leads to the formation of an amorphous phase or at least to a significant loss of crystallinity of the product (Frondel, 1979; Kaviratna and Pinnavaia, 1994; Aznar et al., 1996). In other cases, cation depletion does not cause decomposition of the structure and the product retains the structural features of the parental mineral (Lagaly et al., 1975; Frondel, 1979; Pabst, 1958; Rodriguez et al., 1994; Kosuge et al., 1995). Another interesting property of phyllosilicates is their ability to swell while being exposed to aqueous solutions. This property is basically attributed to the minerals of the smectite group (saponite, hectorite, montmorillonite, beidellite, and nontronite) and vermiculite. The swelling effect together with the ion exchange reactions are probably the most extensively studied processes of phyllosilicates (e.g. Norrish, 1954; Walker, 1960; van Olphen, 1965; Barshad and Kishk, 1968; Newman, 1970; Sposito and Prost, 1982; Laird, 1996). Such a great interest is caused by the importance of these processes in environmental and engineering science, as well as in industrial applications. Generally, mineral reactions in aqueous solutions have been studied e.g., by X- ray diffraction (XRD), nuclear magnetic resonance (NMR), infra-red spectroscopy (IR), or high resolution transmission electron microscopy (HRTEM). Mineral reactions can be also studied by using surface-sensitive techniques. Since any reaction of a mineral starts from its surface, investigation