The Research On Preparation Of Nano Magnesium Oxide Via Dolomite

The storage of dolomite is rich,and it distributes widely in China,which provides plenty of raw materials for the production of calcium and magnesium products.Because of surface effect,volume effect,quantum size effect and macroscopic quantum tunneling effect of nano materials,nano magnesium oxide not only has the nature of the bulk material,but also exhibits light,heat,electricity,magnetic,mechanical and chemical properties.Therefore,nano magnesium oxide is widely used in antibacterial materials,catalysis,adsorption,inorganic flame and other fields,which has become the points and hot spots of inorganic materials.In this study,nano magnesium oxide was fabricated via combining ammonium sulfate leaching and direct precipitation method with dolomite as raw material.The calcined products were characterized by TG,XRD and FT-IR,and the effect of calcination temperature on chemical composition of the products was investigated.The results show that the calcined dolomite can be obtained by calcination at 800 ?,which is composed of CaCO₃,MgO and a small amount of CaO.With the calcined dolomite as magnesium source,and ammonium sulfate as the lixiviant,magnesium and calcium were separated and magnesium ion was leached from the calcined dolomite.The effects of?NH₄?₂SO₄/MgO mole ratio,volume of distillate,and dosage of calcined dolomite on leaching rate of magnesium were evaluated.These researches show that the optimum conditions are determined to be following:?NH₄?₂SO₄/MgO molar ratio is 1.8:1,the volume of distillate is 350 mL and the dosage of calcined dolomite is 20 g.Under the optimum experiment parameters,the content of magnesium is 15.76%,while that of calcium is only 1.15%.Meanwhile,the maximum leaching rate of magnesium is obtained to be 96.81%.These results show that calcium and magnesium are separated effectively,and magnesium leaching rate is very high.With the magnesium sulfate solution obtained from ammonium sulfate leaching process as raw material,and the distillate as precipitant,nano magnesium oxide was prepared by direct precipitation method.The sample was characterized by TG,XRD,FT-IR,SEM and TEM,and the effect of calcination temperature on grain size and crystal growth behavior of nano magnesium oxide was studied.Nano magnesium oxide was obtained by calcining the precursor at 800 ?,and it exhibits a micron hollow-tube-like structure with 600 nm in outer diameter and 180-250 nm in width of tube wall consisted of small nanoparticles.During heat treatment process,pure magnesium oxide could be obtained by calcination at above 650 ?.With the increase of calcination temperature,the grain size of magnesium oxide also increases.The crystal growth of magnesium oxide can be divided into two stages that the first stage is before 650 ? and the second stage is beyond 650 ?.The activation energy for crystal growth of magnesium oxide is 10.69±1.13 kJ/mol before 650 ?,while that of magnesium oxide is 27.03±0.85kJ/mol beyond 650?.The effects of different surfactants on grain size and crystal growth behavior of magnesium oxide were investigated.It is found that the addition of surfactants is beneficial to reduce grain size of nano magnesium oxide.With the increase of calcination temperature,the grain size of magnesium oxide prepared by adding PEG200 increases fastest,while after adding SDS it grows slower than that produced by adding CTAB.It indicates that surfactants have some influence on the growth rate of grain size.Therefore,these would directly affect crystal growth behavior of magnesium oxide.As shown in previous researches,the grain growth of nano magnesium oxide can be divided into two stages:the first stage is before 650 ? and the second stage is beyond 650 ?.Without surfactant,the activation energy for crystal growth of magnesium oxide is 10.69±1.13 kJ/mol in the first stage,and that in the second stage is 27.03±0.85 kJ/mol.By adding SDS,CTAB and PEG200 during preparing precursor,the activation energy increases to 11.76±1.94 kJ/mol,14.85±0.46 kJ/mol and 16.87±1.18 kJ/mol in the first stage respectively,while the activation energy is 28.38±0.77 kJ/mol,28.50±0.41 kJ/mol and 28.53±1.07 kJ/mol in the second stage respectively.Compared with that prepared without surfactant,the activation energy for crystal growth of magnesium oxide increases in the first stage and in the second stage during adding different surfactants in precursor.Meanwhile,the comparison for activation energy of nano magnesium oxide fabricated with different surfactants can be obtained as follows:EPEG200>ECTAB>ESDS.Relatively,the effect of surfactants on activation energy for crystal growth in the first stage is greater than that in the second stage.