A New Preparation Method of Sodium Aluminum Hydroxy Carbonate and Potassium Aluminum Hydroxy Carbonate from Basic Alumin
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A New Preparation Method of Sodium Aluminum Hydroxy Carbonate and Potassium Aluminum Hydroxy Carbonate from Basic Aluminum Sulfate C. A. Contreras, J. I. Macías and E. Ramos Universidad de Guanajuato, Departamento de Química, Noria alta s/n, Col. Noria alta, Guanajuato, Gto., México. Tel.: (+05) 473-73 20006 ext. 6022. Fax: (+05) 473-73 20006 Ext. 6002. E-mail: [email protected]
ABSTRACT Sodium aluminum hydroxy carbonate and potassium aluminum hydroxy carbonate, commonly named sodium dawsonite and potassium dawsonite respectively, with formula MAl(OH)2CO3 (M=Na,K), were prepared by slow evaporation of a solution obtained by dissolution of basic aluminum sulfate in 1M sodium carbonate or 1M potassium carbonate, respectively. The basic aluminum sulfate was prepared by precipitation in homogeneous solution of an aluminum bisulfite solution. The basic aluminum sulfate was dissolved in 1M sodium carbonate or 1M potassium carbonate at 80 °C. Then, the solution was heated at 60 °C in order to the crystallization of sodium or potassium dawsonite takes place. The crystallized solid was separated from the liquid by vacuum filtration and oven dried at 90 °C before to be analyzed. The synthesized powders were characterized by differential thermal analysis (DTA), thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), Xray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By this method crystalline sodium dawsonite and potassium dawsonite were obtained. The morphology of the particles was acicular in shape with high aspect ratio (≈267). Keywords: Crystalline, Al, Na, compound, chemical synthesis. INTRODUCTION Dawsonite is a naturally occurring mineral having the formula NaAl(OH)2 CO3 and which crystallizes orthorhombically with an acicular habit. Because of its chemical and thermal properties, dawsonite has been used as a flame retardant material, for example, in plastics [1], as a fire control agent in aircrafts [2] and as a precursor of sodium aluminate [3]. This later compound has been used as a metal adsorbent in water treatment [4], as catalyst [5,6], as adsorbent for acid gases [7] and as a precursor for zeolites [8]. Because of dawsonite mineral occurs in nature in very limited quantities, several synthetic methods have been developed. Dawsonite-type compounds of formula MAl(OH)2CO3 (M=Na,K,NH4) have been synthesized by hydrothermal method [9,10]. Sodium and potassium dawsonites have also been prepared at lower temperatures such as 60°C or 100 °C [11]. However, in this case amorphous dawsonite type materials are usually obtained. Sodium dawsonite have been successfully synthesized by a variety or reactions. It has been prepared by reacting sodium aluminate with sodium carbonate and/or sodium bicarbonate [12]; sodium aluminate with carbon dioxide [11]; aluminum hydroxide with citric acid and sodium bicarbonate [13]. By hydrolysis of aluminum tri-sec-butoxide in the presence of stoichiometric amounts of sodium bicarbonate crystalline sodium dawsonite was
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