Preparation Of Mg-Al Layered Double Hydroxides By Mechanochemical Method

Hydrotalcite is a kind of important inorganic function materials with layered structure, and the divalent and trivalent metal ions and hydroxyl groups constitute the laminates. Metal ions form Laminates take place isomorphous substitution when they have similar radius, and hydrotalcite has exchangeable anions among laminates. Hydrotalcite presents weakly alkaline, and it has thermal stability, absorption, memory structure, low surface energy, geometry effects and so on. It has been widely used in the ion exchange, catalyst supports, pharmaceuticals, water treatment and other fields because of its unique spatial structure adjustable variability and excellent catalytic properties. Traditional preparation methods of hydrotalcite including co-precipitation,hydrothermal method,ion exchange,reduction roasting, etc. In this paper, a new method which we callled mechanochemical method was used in the preparation of hydroxides, it is a method to utilite mechanical force, which causes elastic strain and stress on surface of the powder to enhance chemical activity of the system. Hydrotalcite is widely used, so it is significant apply mechanochemical method to the preparation of Mg-Al hydrotalcite.In this paper, Mg(OH)2 and Al(OH)3 as magnesium source and aluminum source. Carbonate, nitrate radical, sulfate radical, chloridion, dodecylbenzene sulfonic acid radical, benzoic acid radical, Kwai acid radical and other anions intercalated hydrotalcite precursors are prepared by mechanochemical method. We get the desired uniformity and regular hexagonal lamellar hydrotalcites with different anions intercalated through washing and aging treatment of the precursor.The influence of high energy ball milling time, Mg-Al molar ratio, ratio of the ball, washing temperature and washing time on the Mg-Al hydrotalcite's grain size and morphology are investigated in the experiment. X-ray diffraction, scanning electron microscopy, infrared spectroscopy, TG-DTA, EDS and other testing methods are used to observe and analyze the performance of the product.The results show that the laminate structure of hydrotalcite develop and improve gradually as the rise of milling time and washing temperature, in the same time the diffusion activation energy of mixtures significantly reduced. In the reaction system produces a large amount of elastic stress field by ball milling and the elastic stress field accelerates the diffusion of ions. When the water temperature reach to 90℃,and water treatment time reach to 8h, various ions of the reaction system diffuse into the laminate and interlamellar space in aqueous solution and forme well-developed and crystalline Mg-Al hydrotalcite.