Study Of Separation Magnesium And Boron From Szaibelyite Mineral And Boron Mud By Vacuum Thermal Reduction Process

At present, the szaibelyite mineral in China is employed to produce borax by carbon dioxide-soda process. The yielding of the process is less than75%, and boron mud is produced with borax. The boron mud contains all MgO and the rest boron of the szaibelyite mineral. Therefor, using szaibelyite mineral to produce borax by carbon dioxide-soda process not noly wastes the resource but also pollutes the environment. At the same time, the components of szaibelyite mineral are basically meeting the requirements of non-alkali glass fiber, and the boron in szaibelyite mineral is especially indispensable. But then there is an obstacle that the MgO in szaibelyite mineral is much more than non-alkali glass fiber needing. Similarly, the components of boron mud removing MgO are suitable to produce flat glass. In this dissertation, magnesium is extracted from boron mud and szaibelyite mineral by vacuum thermal reduction process, and other components of raw material are left in reduction residue. So the residue can be used to producing non-alkali glass fiber or other content boron productions. The szaibelyite resource is all utilized by this process. Consequently the main contents of this dissertation are extracting Mg with vacuum thermal reduction process from raw material and saving boron in residue.Firstly, the thermodynamics are employed to analyse the MgO in reduction process with Si, CaC2and Al as reductant. The starting reaction temperature can be reduced by adding CaO and reducing the system pressure. With the contrast of vapor pressure of chief impurities, magnesium will be condensated in varied position which is separated from Na.In the research of calcining boron mud and reducting the calcined boron mud with CaC2as reductant, the optimal condition of calcining boron mud is fixed at650～700℃for0.5～1.0h. In the calcination process, boron mud will decompose into MgO and react with SiO2. Therefor, the main component of calcined boron mud is2MgO·SiO2.In vacuum thermal reduction process, when the temperature is up to1150℃for2.0h with the CaC2mass coefficient (the molar ratio of CaC2to MgO) of2.58, the reduction rate can reach99%.In the experiment of extracting Mg from szaibelyite mineral with the Si powder as reductant, the influences of the calcination conditions and the CaO mass on reduction rate are researched, and the decomposition kinetics of the szaibelyite mineral are also investigated. The results show that3MgO·B2O3will be produced in calcining szaibelyite mineral process, and the optimal calcination condition is fixed at1000℃for0.5h. By analysis of the decomposition process during950～1100℃, the kinetic equitation can be expressed as with an apparent activation energy E=471.49kJ/mol. In the reduction process, the CaO will firstly produce to3CaO·B2O3, and then produce2CaO·SiO2.In the research on reduction of szaibelyite mineral with the CaC2powder as reductant, the influences of the CaC2addition and briquetting pressure on reduction rate have been discussed. When the CaC2mass coefficient (the molar ratio of CaC2to MgO) is1.34, the reduction rate is72.69%. The suitable briquetting pressure for reduction material is10MPa.In the research on reduction of szaibelyite mineral with the Al powder as reductant, szaibelyite mineral powder is mixed with CaCO3powder to be compacted into briquettes which will be calcined and reduced by Al, due to that3CaO-B2O3can be made and MgO will be replaced from3MgO-B2O3if CaO is added in calcination process. The influences of calcination and reduction conditions as well as the additions of each reagent on reduction rate have been systematically investigated. The results show that when the mixture of szaibelyite mineral and CaCO3powder is compacted under45～60MPa and then calcined at1000℃for0.5h, the calcined material can get a higher reduction rate. Al is added and at13.68%above the stoichiometric requirements. CaCO3must be adequate for yielding12CaO·7Al2O3and3CaO·B2O3, with an addtion of CaF2that3%of total charge mass, and the briquetting pressure for reduction material is30MPa. The main phases in residue are3CaO·B2O3and HCaO·CaF2·7Al2O3. By analysis during1100～1200℃, the process of aluminothermic reduction follows the liquid-solid reaction kinetic model, the relation equitation between apparent rate constants and temperature is lnk=-27489.79/T+13.5631, the apparent activation energy is E=228.55kJ/mol.There are much Al2O3in the residue of aluminothermy, and the Al2O3can be leached in the alkali liquor containing sodium carbonate and sodium hydroxide. The results show that the alumina leaching rate can reach to63.60%with the sodium carbonate concentration of173.33g/L, sodium hydroxide concentration of0g/L, L/S of5, leaching temperature of98℃, leaching time of120min, and stir speed of600r/min.