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本论文以高压碳化法处理碱解法硼泥回收其中的镁资源，解决传统碳化工艺中富镁液浓度低(以MgO计5～12g/L)的问题，获得杂质含量低的高浓镁浸出液，以提高后续热解工序中设备利用效率、降低能耗。另外，从动力学、热力学方面重点研究加压碳化体系中镁、钙(主要杂质)的溶解规律，为实际生产操作提供现实指导和理论依据。论文主要研究内容与成果如下：进行了硼泥加压碳化提镁工艺方面的研究。考察了二氧化碳压强、原料固液比、搅拌强度及温度对碱解法硼泥碳化提镁的影响。在二氧化碳压强5MPa、固液比0.18、搅拌强度500rpm、温度50°C的条件下，将碱解法硼泥碳化1.5h，获得了氧化镁浓度为26.63g/L的浸出液，其中杂质氧化钙、硼、铁、铝、硅的浓度分别为0.16g/L、0.11g/L、0.23g/L、0.01g/L和0.06g/L，氧化镁浸出率为38.80%。发现氧化镁浸出率受镁的硅酸盐矿物含量的限制。考察了加压碳化法对其他富镁原料的适用性，以菱镁矿轻烧粉、白云石轻烧粉、碳碱法硼泥轻烧粉为原料，经加压碳化获得了氧化镁浓度分别为32.96g/L、18.04g/L、28.76g/L的浸出液，氧化镁浸出率分别为82.21%、45.17%、35.99%，浸出液中杂质含量低。对氢氧化镁高压碳化溶解过程的动力学进行了研究。阐述了氢氧化镁在高压下碳化溶解过程的机理，推导了动力学模型，并利用所推模型和Arrhenius方程对氢氧化镁加压溶解过程进行了动力学分析，溶解过程受氢氧化镁颗粒周围渐进液膜扩散控制，200rpm、300rpm、400rpm下的表观活化能分别为17.10kJ/mol、25.11kJ/mol 和25.39kJ/mol。计算了氢离子在渐进液膜中的表观扩散系数，回归得到了氢离子表观扩散系数与搅拌强度、温度之间关系的经验方程。为得到高溶出率、高浓度的溶出液，优化了原料固液比、二氧化碳压强、搅拌强度、温度等溶解条件，在固液比0.10、二氧化碳压强5MPa、搅拌强度700rpm、温度30 °C的条件下溶解40min，得到了溶出率86.83%、氧化镁浓度59.88g/L的溶出液，并发现在本论文实验条件下，氢氧化镁碳化过程中的析出固体物相为三水碳酸镁。测定了20～70°C下二氧化碳压强为1～5MPa时三水碳酸镁在碳酸水中的溶解度，其随温度的升高而减小、随二氧化碳压强的增大而增大。对三水碳酸镁溶解度与温度、二氧化碳压强之间的关系进行了拟合，得到形式简洁的经验方程。研究了杂质钙的高压碳化溶解。考察了不同实验条件对氢氧化钙碳化溶解的影响，并发现在本论文实验条件下，氢氧化钙碳化过程中的析出固体物相为碳酸钙。测定了20～70°C下二氧化碳压强为1～5MPa时碳酸钙在碳酸水中的溶解度，其随温度的升高而减小、随二氧化碳压强的增大而增大。对碳酸钙溶解度与温度、二氧化碳压强之间的关系进行了拟合，得到经验方程。 研究了高压碳化体系中镁与钙之间的影响。考察了氢氧化镁与氢氧化钙在碳化溶解过程中的相互影响：氢氧化钙的存在对氢氧化镁溶解影响较小，原料中钙镁比越高氢氧化镁初始溶解速率越慢；氢氧化镁的存在对氢氧化钙溶解影响较大，原料中镁钙比越高溶液中能达到的氧化钙浓度越低。测定了20～70°C、二氧化碳压强为1～5MPa下于碳酸水中共存时三水碳酸镁、碳酸钙的溶解度，前者与溶质单独存在体系中相差不大，后者降低了1个数量级，两者都随温度的升高而减小、随二氧化碳压强的增大而增大。对两溶质共存体系中三水碳酸镁、碳酸钙溶解度与温度、二氧化碳压强之间的关系进行了拟合，得到经验方程。 ;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 (5g/L to 12g/L in MgO concentration) in magnesic leaching liquor and, therefore, could 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 was 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 rpm, leaching temperature 50°C, and leaching time 1.5h, meanwhile, the impurity concentrations of CaO, B, Fe, Al 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 400rpm 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 to acheive 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 700rpm, temperature 30°C and reaction time 40min. Nesquehonite was found to be the solid phase precipitated during the carbonization of magnesium hydroxide under this paper’s experimental conditions. 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 an empirical equation in concise form. The high pressure carbonization of impurity calcium was studied. The effect of different experimental conditions on the carbonization of calcium hydroxide was investigated. Calcite was found to be the solid phase precipitated during the carbonization of calcium hydroxide under this paper’s experimental conditions. 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 an empirical equation. 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’s existence had little effect on the dissolution of magnesium hydroxide and the higher the ratio of calcium to magnesium in the raw material, the slower the initial dissolution rate of magnesium hydroxide was found. The existence of magnesium hydroxide had 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 could 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.
|薄婧. 硼泥加压碳化提镁应用基础研究[D]. 中国科学院大学,2018.|
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