| Magnesite consisting of magnesium carbonate, is a main source of magnesium, ranking first across the world. Its Products have been widely used in the field of metallurgy, chemistry and construction and so on. Although our country is rich in magnesite reserves, the resource of high grade magnesite is more and more absent. Low grade magnesium contains Ca, Si, Al, Fe impurities. Contaminated environment and huge waste of resources are caused by lots of magnesite. Improving the rate of resource sutilization has become an urgent problem in magnesite products field.Magnesium hydroxide is an important inorganic functional material with good properties, used widely in various aspects. Magnesium hydroxide has lots of special properties, such as it can be used as acid neutralizing agent with weakly alkaline, can be used as flame retardants because of its highly the decomposition temperature,may also be used in the environmental industry as a desulfurization agent.The process of actived magnesium oxide was discussed by magnesite calcined in the paper. The results show that the calcining temperature and the calcining time influence significantly the activity of MgO. It is also reveals the optimum calcining temperature and the calcining time are about 750℃ and 2h respectively.According to the composition and characteristics of magnesite’s impurities,The new methods was adopted by directly removing imputies from magnesium to prepare of excellent performance of the magnesium hydroxide, two different preparation process of magnesium hydroxide have been stdutied. Firstly using hydrothermal method, at 180℃ hydrothermal temperature, sodium hydroxide concentration 6.25mol/L, time 4h, after filtering and washing, the final acid insoluble content of magnesium hydroxide reaches to 0.1%. Specific surface area and morphology of the product were characterized by scanning electron microscope (SEM), X-ray diffraction(XRD), and cryogenic nitrogen adsorption BET analyzer. The results show that magnesium hydroxide particles with hexagonal flake, and specific surface area of 10 m2·g-1 is obtained. The hydrothermal process not only resolved the acid insoluble material removal processes, and magnesium hydroxide particles have also been a good growth. Then adding magnesium chloride in Magnesium Hydroxide synthesized by hydrothermal, which is equal of the calcium oxide molar. The content of calcium oxide in the magnesium Hydroxide product reduced to 0.2%. Finally content of magnesium hydroxide is more than 98%.The magnesia was directly calcined with sodium hydroxide, the sodium silicate and sodium aluminate, which was formed by silica and aluminum oxide reacting with sodium hydroxide, are removed by washing. Then the magnesia was hydrated further. Magnesium chloride was added at the same time to remove calcium oxide impurities.At a calcination temperature of 750℃, the calcination time 2h, sodium hydroxide was added in an amount of 10% of the raw material. And the acid insoluble content is reduced to 0.07%. In the removal process of calcium oxide, the molar ratio of magnesium chloride and calcium oxide is 2:1, the time is 3 to 4 hours, the temperature is 90℃. Calcium oxide content is reduced to 0.1%. The final product content of magnesium hydroxide is 98.98%. The small amount of alkali, low energy was consumed in the method compared with the hydrothermal method.The chloride calcination, oxidation-reduction and high intensity magnetic separation method were used respectively to remove iron. The result is not too ideal, further experiment was required. |
