Preparation of Lithium Aluminum Layered Double Hydroxide from Ammonium Dawsonite and Lithium Carbonate
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Preparation of Lithium Aluminum Layered Double Hydroxide from Ammonium Dawsonite and Lithium Carbonate C. A. Contreras Soto, E. Ramos-Ramírez, V. Reyes Zamudio and J. I. Macías. Universidad de Guanajuato, Campus Guanajuato, División de Ciencias Naturales y Exactas, Departamento de Química, Noria alta s/n, Col. Noria alta, Guanajuato, Gto., México. Tel.: (+05) 473-73 20006 Ext. 6022. E-mail: [email protected]
ABSTRACT Aluminum lithium hydroxide carbonate hydrate, also known as Al/Li layered double hydroxide or Al-Li hydrotalcite-like compound [Al2Li(OH)6]2CO3•nH2O, was prepared by reaction of lithium carbonate with ammonium dawsonite [NH4Al(OH)2CO3]. The reaction of ammonium dawsonite with a lithium carbonate satured solution at different temperatures and lithium carbonate concentrations was studied. The obtained solids were characterized by differential thermal analysis (DTA), thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). By this method, crystalline Li/Al LDH [Al2Li(OH)6]2CO3·3H2O can be obtained at 60 °C and 4 h reaction time.
Keywords. Al, Li, chemical synthesis, thermogravimetric analysis (TGA), transmission electron microscopy (TEM).
INTRODUCTION The terms layered double hydroxides (LDHs) or hydrotalcite-like compounds (HTLc) are used to designate synthetic or natural lamellar hydroxides with two or more kinds of metallic cations in the main layers and hydrated interlayer domains containing anionic species. LDHs may be synthesized with a wide range of compositions and a large number of materials with a wide variety of M(II)/M(III) cation combinations as well as M(I)/M(III) cation pairs (e.g. Li/Al) with different anions in the interlayer can be obtained [1]. Li/Al hydroxycarbonate hydrate [Al2Li(OH)6]2CO3 • nH20, with laminar structure, belongs to the LDHs family, and is obtained by hydrolysis of Al3 + in the presence of lithium carbonate solutions [2]. LDHs possess very interesting properties with applications in catalysis, adsorption, pharmaceutics, and other areas [3-5]. Owing to its technical importance, several synthesis methods have been developed as for example coprecipitation, reconstruction, sol-gel technique, hydrothermal, microwave, and ultrasound treatments, anion-exchange reactions, among others [6].
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In a previous work, Li/Al HLC was prepared by reaction of basic aluminum sulfate with lithium carbonate [7]. However, the sulfate anion present in the final aqueous solution must be eliminated from solution in order to the lithium carbonate solution can be used again in the process. In this work, ammonium dawsonite [NH4Al(OH)2CO3] is proposed as a precursor of Li/Al LDH. The use of ammonium dawsonite as a precursor permits the mother liquid to be reused because of elimination of the ammonium ion from solution owing to the high solution pH attained at the end of the process. EXPERIMENTAL The ammonium dawsonite precursor (NH4-Dw) was prepared by reacting basic aluminum sulfate with ammonium carbonate at 6
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