Abstract: In order to obtain the suitable process parameters for preparing porous magnesium carbonate trihydrate by aqueous solution,the effects of magnesium source,reaction temperature,reaction time,additive type and dosage on the phase composition and microstructure of the product were studied by XRD and SEM. The results showed that porous magnesium carbonate trihydrate crystals with an average diameter of 10 μm and good sphericity could be obtained with magnesium chloride as magnesium source,ammonium carbonate as carbon source,and 1% glucan added at the reaction temperature of 58 ℃ and reaction time of 200 min. The type and amount of additives have no effect on the phase composition of the product,but have a great effect on the morphology. The type of magnesium source and reaction temperature have significant influence on the phase composition and morphology of the product. The growth mechanism analysis showed that dextran formed a network structure in solution,and the [MgO6] octahedral growth unit reacted with the hydroxyl group on the dextran chain to form sheet crystals. At the same time,the network structure formed by the long chain of dextran acts as a limited template for the formation of porous spheres. The network structure makes the growth units of magnesium carbonate trihydrate grow along the direction of dextran chain,and finally forms porous spherical magnesium carbonate trihydrate crystals.

Key words: magnesite,nesquehonite,glucan,porous,growth mechanism