| Magnesium is one of the elements that are high levels in the crust and wide distribution.Magnesium only exists as compound form in nature. Now there are large-scale industrial exploitation of magnesite, dolomite and carnallite and so on, but a lot of magnesium mainly dissolved in seawater, salt water and brine wells in the form of chloride and sulfate. China's coastal brine resources are abundant.There are salt lakes and bittern that contain high concentrations of magnesium.They provide rich raw materials base for the development of China's magnesium industry. There is a little impurity in the brine of saline. The production process is simple, so it is more easy to achieve high purity. Moreover it is a renewable resource. So the method of using brine in saline to make magnesium products have been widely adopted around the world.Lightweight magnesium oxide is also called industrial magnesium oxide.It's more extensive use in ceramics,refractory products,various adhesives,paint packing,rubber accelerator and activator, medicine, architecture and food industries and so on. Light magnesium carbonate is also called magnesium hydrogen carbonate. It is of small relative density, and it's light,loose, non-toxic odorless, and stable in air. Light magnesium carbonate is used as fine filler and reinforcing agent to rubber in order to improve the quality of rubber products. And Because it is of noncombustible and loose texture, it is widely used in the construction industry as insulation and high temperature-resistance material. Light magnesium carbonate can be used as additives in the food industry and magnesium supplements, and also is used desiccant, color agents, carriers, anti-caking agent.There are brine-soda method,brine-ammonium bicarbonate method and so on with brine as raw material to produce lightweight magnesium oxide and lightweight magnesium carbonate.They are widely used because of the less required of the equipment and simple technology.But the production cost is influenced by the market price of soda and ammonium bicarbonate.There are many abandoned industrial alkali, treated for the preparation of light magnesium oxide, you can turn waste into treasure,reduce environmental pollution and produce economic benefits, which is of great significance in energy conservation and emission reduction.Nano-MgO is a new high-performance fine inorganic material, the particle size is between 1-100nm. Its properties in heat, light, electricity, magnetism and chemistry is different from the MgO.Its application is more broader. So the nano-MgO become the the preferred products.Our country is rich in magnesium, which make magnesium hydroxide cheap and easy to get. The alkaline of magnesium hydroxide is more moderate. by controlling the conditions It can react with industrial oxalic acid to produce nano-MgO.This process is less demanding on the equipment, the MgO products is of high purity, fine crystal, and easy to apply in industrial production.In this thesis, lightweight magnesium oxide and lightweight magnesium carbonate were prepared with industrial waste alkali and brine as raw materials.At the same time,nano-MgO was prepared with magnesium hydroxide and industrial oxalic acid as raw material.We have explored optimal conditions that provide a reference value for the realization of large-scale production. The main contents are:1.Preparation of lightweight magnesia by using industrial waste alkali and brineWith industrial waste alkali and brine as raw materials, lightweight magnesia have been prepared in 50℃. The calcining temperature were 850℃and the holding time were 1h. With the constant total alkalinity, influences of sodium carbonate and sodium hydroxide concentration ratio on chloride ion washing and filtration of intermediate products were studied. We also explored the influences of it on precursors weightlessness rate, MgO content, bulk density, CAA value and tablets diameter distribution.The research showed that, in the case of constant total alkalinity,when the ratio of the concentration of sodium carbonate and sodium hydroxide is 1.5:1, filtration of the intermediate was the best and chloride ions were more easily washed. At the same time, the product of magnesium oxide obtained a smaller particle size and the uniform distribution with the lowest precursors weightlessness rate. MgO content was more than 98% with the smaller bulk density and the better activity of the product, and moreover, the chlorine content was less than 0.03%.2.Preparation of lightweight magnesium carbonate with industrial waste alkali and brine as raw materialsLightweight magnesium carbonate have been prepared in 50℃with industrial waste alkali and brine as raw materials. The intermediate slurry was dubbed for a certain concentration.The slurry was pyrolysed and filtrated after accessing certain time of carbon dioxide,drying the product at 110℃. In this paper, through controlling CO2 flow for the certain value,we studied the Mg2+ concentration changes in serum trends, the trend of stacking density and loss on ignition of magnesium carbonate, the particle size change using grain size analysis tester. Experiments showed that controling CO2 for 25-30L/h,access to CO2 for 1 hour, with certain heating rate rose to 60℃to stay for 10min then warmed up again to 90-95℃for pyrolysis, the product is short rod-like with rough surface. Pyrolysis at 60℃accessing to air, the product is rod-like with smooth surface.This method has simple production process, no pollution, and gains high purity.3.Preparation of Nano-MgO with industrial oxalic acid and magnesium hydroxideWith industrial oxalic acid and magnesium hydroxide as raw materials, influences of the calcination temperature, calcination time, reaction temperature, reaction time, acid concentration and surfactant concentration on particle size of magnesia products were studied. The products were characterized by means of X-ray diffraction(XRD), thermogravimetric differential thermal analysis (TG-DTA), scanning electron microscopy (SEM). The results showed that when oxalic acid concentration was 0.8mol/L and the concentration of surfactant was 1.0mmol/L, reaction at 40℃for 20min, calcination at 600℃for 2h, magnesium oxide nanoparticles can be obtained and the particle size was about 50nm. The product of high purity has been obtained by the method with simple process, convenient operation, less demanding on the equipment and technology, easy-to-industrial production.
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