Preparation Of Analcime Crystals Using Solid Geopolymer-Gels-Conversation Method

Geopolymer, is a class of amorphous or semi-crystalline inorganic polymer gelling material, which is composed of amorphous aluminosilicate minerals (containing aluminum oxide and silicon dioxide) and sodium silicate, phosphate and phosphoric acid. Zeolite molecular sieves are not only in its traditional areas of application:toxic and harmful substances, petrochemical catalysis, ion exchange adsorption has been rapid development; Application in high-tech field of advanced materials, such as molecular reactor, microelectronics, optical excitation device, also is developing rapidly, the industrial prospect, become one of the important direction of inorganic porous materials.In this paper, on the basis of predecessors’research, through the Na2O-4SiO2-Al2O3geopolymer gel conversion can be controlled in the preparation of the size of50-1200μm analcime zeolite crystals, is investigated detailily in hydrothermal time, hydrothermal temperature, alkalinity, aging temperature on the influence of zeolite size and morphology, and preliminary discussion on the large size conversion process and the growth mechanism of the zeolite crystals.Metakaolin reacting with sodium silicate is the classic of preparation and research of geological polymer system, in order to reduce the influence of impurities in raw material, and guarantee the reactivity. Our group synthesized Al2O3-2SiO2gel dry powders which were similar to metakaolin composition and structure by the sol-gel method. In this paper, using synthetic Al2O3-2SiO2powders, with industrial grade sodium silicate as alkali excitation agent, according to the theory of analcime ratio (Na:Al:Si=1:1:2) was prepared by Na2O-4SiO2-Al2O3geopolymer dry gel, and then was prepared by hydrothermal synthesis method with zeolite crystals with different dimensions. Experiments by XRD, SEM, FT-IR and BET test means such as product of analcime phase composition, microstructure and aperture are studied, determining the preparation of large size analcime geopolymer using optimum technological parameters. The main conclusions:(1) According to the analcime zeolite composition to prepared geopolymer, to study the curing time, curing temperature, different modulus sodium silicate on preparation of analcime zeolite through geopolymer. Determines the optimum conditions for preparation of geopolymer base:sodium silicate modulus is1.0, the modulus of1.0silica in sodium silicate and the molar ratio of Al2O3-2SiO2powders in silicon is1.0, curing temperature is70℃, curing time is72h.(2)The effects of the concentration of NaOH in hydrothermal mother liquid, the volume of hydrothermal liquid, hydrothermal time, hydrothermal temperature, and different modulus of water glass and different molar ratios of Si source on the structure analcime zeolites converted from geopolymers. The optimum process conditions of the preparation of analcime zeolites derived from geopolymers are as flollows:the volume of hydrothermal mother liquid was100ml, the hydrothermal time was6h, the hydrothermal temperature was240℃, the modulus of water glass was1.0.(3)The relationship between Na2O-Al2O3-4SiO2geopolymers and analcime zeolites crystals was mass transfer and genetic structure. The reaction mechanism of analcime zeolites derived from geopolymers can be divided into depolymerization, condensation polymerization and hydrothermal crystallization processes. In addition, the formation of large size analcime zeolite crystal need to strictly control the crystallization process of various factors. In the growth process of zeolite crystal, the activity of the reactants to the large size of zeolite crystal formation and growth plays a most important role, different silicon sources (sodium silicate and A12O3-SiO2powders) due to the different form and the structure of the material, its solubility in the alkaline solution, dissolved silicon ions after the state of aggregation and sialic acid radical combining degree are different, which controlled the crystal growth kinetics, had an impact on zeolite crystal nucleation and growth that affects product crystal particle size and distribution.