Research On The Preparation Of Magnesium Hydroxide In The Gas-liquid-solid Three Phase Hydration Reaction System

Magnesium hydroxide, as a green material, is widely used in environmental protection field because of its unique physical and chemical properties. Magnesium hydroxide can be obtained by several methods, i.e. precipitation of a magnesium salt with an alkaline, smashing natural mineral brucite, and hydration of magnesium oxide (MgO).The traditional magnesia hydration are both intermittent process. The efficiency is not high due to the long hydration time and low hydration rate. In addition, the volume of reaction vessel is larger. Therefore, this paper puts forward a kind of high efficient hydration method of preparing magnesium hydroxide called the gas-liquid-solid three-phase reaction system.Firstly this paper analyzed the hydration mechanism of magnesium oxide, summarizing the existing two kinds of magnesia hydration model. The relations between the initial concentration of magnesium oxide the hydration temperature the hydration time and the hydration rate the hydration efficiency were studied respectively in liquild-solid reaction system. The relations between the initial concentration of magnesium oxide the vapor pressure and the hydration rate the hydration efficiency were studied respectively in gas-liquild-solid reaction system. Meanwhile, the hydration model were used to fitting the experimental data. Secondly, the hydration products were analyzed by SEM and XRD to study the morphology and the composition change of hydration products and the hydration rate differences under different reaction conditions. On the basis of further analysis, there existed a new reaction mechanism in the gas-liquid-solid three phase system. It was called the peeling-off mechanism which the hydration reactions occurred in the surface and the pores of the MgO particles. Then the layer started cracking and peeling off from the mother magnesia particles by the impact of steam "microexplosion". The fresh oxide surface continued to be attacked by water. Due to the existence of the microexplosion, the hydration rate of the gas-liquid-solid three phase system was significantly higher than the liquid-solid system.Finally, a stable and efficient preparation of magnesium hydroxide slurry was obtained by comparing changing trends of the hydration rate under different conditions. When the initial concentration of magnesium oxide was10%and the vapor pressure was0.25Mpa, the hydration rate can be as high as above92%. Meanwhile, the hydration time also reduced to27min.