Basic Research On Application Of Boron Mud For Pressurized Carbonization Of Magnesium Extraction

In this study,magnesium in boron mud by alkaline leaching was recovered using pressurized carbonation processe and concentrated magnesic leaching liquor of low impurity content was obtained,which resolved the problem of low concentration(5 g/L to 12 g/L in MgO concentration)in magnesic leaching liquor and,therefore,can enhance the equipment capacity and decrease the energy consumption in the decomposition of the magnesic solution.Moreover,the dissolution rules of magnesium and calcium,the main impurity,were researched from the dynamics and thermodynamics aspects,providing practical guidance and theoretical basis for actual production operation.The main contents and results were as follows.The process of magnesium extraction by pressurized carbonization of boron mud is studied.The influence of the parameters,such as pressure of CO2,ratio of solid to liquid,stirring speed and leaching temperature,on leaching magnesium oxide in boron mud was investigated.And the concentration of MgO in the solution was achieved as high as 26.63g/L with MgO leaching efficiency of 38.80%under the condition of CO2 pressure 5MPa,solid/liquid ratio 0.18,stirring speed 500 r/min,leaching temperature 50?,and leaching time 1.5h,meanwhile,the impurity concentrations of CaO,B,Fe,A1 and Si were 0.16,0.11,0.23,0.01 and 0.06g/L,respectively.The applicability of pressurized process for treating with calcined magnesite,dolomite and boron mud by CO2-soda process was investigated and leaching liquor with MgO concentration of 32.96,18.04 and 28.76g/L and leaching efficiency of 82.21%,45.17%and 35.99%was obtained correspondingly.The concentrations of impurities were finite in the leaching liquor.The kinetics of the high pressure carbonization process of magnesium hydroxide was studied.The reaction mechanism was proposed and the kinetic model for the dissolution was derived.The pressurized magnesium hydroxide dissolution was found to be rate-controlled by the diffusion in the progressive liquid film around the solid Mg(OH)2.Based on the Arrhenius expression,the apparent activation energy at stirring speed of 200,300 and 400r/min was obtained as 17.10,25.11 and 25.39kJ/mol,respectively,which also indicated that the dissolution inclined to be diffusion rate controlled.Moreover,the apparent diffusion coefficients of H+ in the liquid film were calculated and an empirical expression was obtained for the first time as well.Parameters,such as solid/liquid ratio,CO2 pressure,stirring speed and temperature,were optimized for concentrated solution and high Mg(OH)2 dissolution ratio.Solution with MgO concentration of 59.88g/L and Mg(OH)2 dissolution ratio of 86.83%was obtained under the condition of solid/liquid ratio 0.10,CO2 pressure 5MPa,stirring speed 700r/min,temperature 30? and reaction time 40min.The solubility of nesquehonite in carbonated water with CO2 pressure between 1 and 5MPa was measured at 293.15 to 343.15K.The results showed that the solubility increased with CO2 pressure but decreased with temperature.The solubility was correlated with both temperature and CO2 pressure by empirical equations in a concise form.The high pressure carbonization of impurity calcium is studied.The effect of different experimental conditions on the carbonization of calcium hydroxide was investigated.The solubility of calcite in carbonated water with CO2 pressure between 1 and 5MPa was measured at 293.15 to 343.15K.The results showed that the solubility increased with CO2 pressure but decreased with temperature.The solubility was correlated with both temperature and CO2 pressure by empirical equations in a concise form.The influence of magnesium and calcium in the high pressure carbonization system was studied.The interrelationship of magnesium hydroxide and calcium hydroxide in the carbonation dissolution process was investigated.Calcium hydroxide existence had little effect on the dissolution of magnesium hydroxide and the higher the ratio of calcium and magnesium in the raw material,the slower the initial dissolution rate of magnesium hydroxide.The existence of magnesium hydroxide has great influence on the dissolution of calcium hydroxide.The higher the ratio of magnesium to calcium in the raw material,the lower the concentration of calcium oxide can be achieved in the solution.The solubility of nesquehonite and calcite in carbonated water for the solutes coexisting cases was measured within the temperature range 293.15 to 343.15K and the CO2 pressure range 1 to 5MPa.The nesquehonite's solubility changed little from the solute solo existing cases while the calcite's decreased one order of magnitude.The solubility of the two solutes increased with CO2 pressure but decreased with temperature.The solubility was correlated with both temperature and CO2 pressure by empirical equations in a concise form.