Knowledge Management System Of Institute of process engineering,CAS
|Alternative Title||Fundamental research of extracting alumina from high-alumina coal fly ash using NH4HSO4/H2SO4 mixed solution|
高铝粉煤灰中氧化铝含量达40-50%，年排放及累积堆存量巨大，蕴藏着丰富的氧化铝资源，其综合利用已纳入国家战略规划。开发高铝粉煤灰提取氧化铝技术，不仅有着非常重要的社会、环境效益，而且可降低我国铝土矿对外依存度。本文围绕高铝粉煤灰中氧化铝低成本高效提取迫切需求，提出了一种NH4HSO4/H2SO4混合介质提取高铝粉煤灰中氧化铝新工艺，开展了浸出过程工艺条件、矿相转化、浸出动力学及介质循环研究，同时对中间体十二水硫酸铝铵在酸性介质中结晶与热分解制备氧化铝过程进行了系统研究，形成了NH4HSO4/H2SO4混合介质提取高铝粉煤灰中氧化铝原则流程。主要研究内容与结论如下：（1）基于Aspen plus物性系统及ELECNRTL模型，研究了NH4HSO4/H2SO4溶液的热力学性质，考察了浸出过程工艺条件，在较优条件下，对应氧化铝提取率可达88.9%，实现了高铝粉煤灰中氧化铝高效浸出。采用XRD、SEM-EDS、FTIR等对粉煤灰颗粒在浸出过程中变化情况进行系统研究，结果表明随着氧化铝浸出反应的进行，粉煤灰颗粒粒径呈减小的趋势，而比表面积明显增大；含铝矿相莫来石相、刚玉相逐渐分解，氧化铝浸出后残余的固相主要以非晶体的二氧化硅为主。（2）分别开展了高铝粉煤灰在NH4HSO4溶液、H2SO4溶液、NH4HSO4/H2SO4混合溶液介质体系中氧化铝的浸出动力学研究，基于缩芯模型进行了动力学分析。结果表明，在上述三种体系中，浸出过程均为固体产物层内扩散控制，相对应的活化能分别为：78.04±3.38kJ/mol、89.33±2.27kJ/mol、91.10±8.98kJ/mol。利用经验动力学方程成功关联了转化率与c[HSO4-]、c[H3O+]、温度、时间的关系，得出了经验动力学速率表达式。（3）采用动态法测定了不同温度、不同H2SO4浓度及不同NH4+/Al3+摩尔比条件下NH4Al(SO4)2·12H2O在NH4+-Al3+-H3O+-HSO4--SO42--H2O体系中的溶解度，并以electrolyte NRTL模型对实验数据进行回归分析，其中温度、(NH4)2SO4浓度、H2SO4浓度和Al2(SO4)3浓度计算值与实验值总平均相对偏差分别为：1.04%、0.32%、0.26%和0.45%，得到了新的电解质对参数，建立了NH4Al(SO4)2·12H2O在NH4+-Al3+-H3O+- HSO4--SO42--H2O体系中的溶解度模型。同时，采用Aspen plus模拟及实验相结合的方式研究了十二水硫酸铝铵的结晶过程。（4）采用TG-DSC、TG-MS技术开展了十二水硫酸铝铵热分解过程研究，分析表明其热分解过程包括三个失重阶段；研究了不同气氛对十二水硫酸铝铵热分解过程的影响，结果表明气氛中O2的存在会一定程度地抑制热分解反应过程。同时，对空气气氛中十二水硫酸铝铵进行了动力学分析，采用FWO法求解得到了第二、三阶段热分解活化能分别为246.3kJ/mol、286.3kJ/mol，动力学最概然机理函数分别为R3（收缩球状函数）、D3（Jander方程），对应的反应机理为三维相界面反应类型、三维扩散类型。（5）开展了介质循环浸出实验研究，氧化铝浸出率维持在86-90%。考察了循环液中杂质积累情况，其中，铁是主要杂质元素，随循环次数的增加而增加，其浓度在1.0-4.5g/L。在完成浸出过程介质循环实验研究的基础上，提出了高铝粉煤灰NH4HSO4/H2SO4法提取氧化铝工艺原则流程，利用大型通用流程模拟软件Aspen plus，以ELECNRTL模型为物性方法，对整体工艺进行初步流程模拟，对浸出、结晶、热分解、介质回收四个核心步骤分别进行了优化分析。基于全流程模拟结果，从理论上计算了原材料、燃料及动力直接消耗费用。;High-alumina coal fly ash (HAFA) is a typical industry solid waste and its emission and accumulation are very huge. The HAFA contains 40%–50% of alumina and is a potential resource for extracting alumina. The comprehensive utilization of HAFA is taken into account as China’s strategy. The developing of alumina extracting technology from HAFA not only has an important social and environmental benefits, but also can reduce the external dependency of bauxite in China. In view of alumina extraction at a low cost from HAFA, this dissertation proposes a new process of alumina extraction from HAFA using NH4HSO4/H2SO4 mixed solution. The leaching technological conditions, phase transformation, leaching kinetics and medium circulation were systematically investigated. Simultaneously, the crystallization of intermediate ammonium aluminum sulfate dodecahydrate in acidic medium and its thermal decomposition to prepare alumina were studied in detail. Based on the fundamental research, a conceptual process of extracting alumina from high-alumina coal fly ash using NH4HSO4/H2SO4 mixed solution was developed. The main contents and results are as follows:(1) Based on the physical properties system and ELECNRTL modeling in Aspen plus, the thermodynamic properties of NH4HSO4/H2SO4 mixed solution were studied. The leaching process was then investigated systematically and the alumina extraction efficiency can reach 88.9% in optimal conditions, realizing the efficient extraction of alumina. The changes of HAFA in the leaching process were systematically analyzed via X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), fourier transform infrared spectrometer (FTIR), etc. Results showed the HAFA particles gradually decreased and the specific surface markedly increased; the mullite and corundum, which were the main form taken by alumina in HAFA, gradually decomposed to release the alumina and the residue mainly contained amorphous silica phase.(2) The alumina leaching kinetics in NH4HSO4 solution, H2SO4 solution and NH4HSO4/H2SO4 mixed solution from HAFA were studied with the shrinking core models, respectively. Results showed that the leaching of alumina in above three systems were all controlled by diffusion through the product layer with an apparent activation energy of 78.04 ± 3.38 kJ/mol, 89.33±2.27kJ/mol and 91.10±8.98kJ/mol respectively. The alumina extraction efficiency was expressed successfully with c[HSO4-], c[H3O+], temperature and time by using an empirical kinetic relationship.(3) Solubilities of NH4Al(SO4)2·12H2O in the NH4+-Al3+-H3O+-HSO4--SO42--H2O system were measured at different temperatures, concentrations of sulfuric acid and NH4+/Al3+ molar ratios using a dynamic method. The electrolyte NRTL model embedded in Aspen plus was applied to model the solubilities and the new electrolyte pair parameters were obtained via regressing the experimental results. The total relative average deviations of temperatures, (NH4)2SO4 molalities, H2SO4 molalities and Al2(SO4)3 molalities were 1.04%, 0.32%, 0.26% and 0.45% respectively, indicating that the calculation values have good coherence with experiment data. With the newly obtained model parameters, the fundamental solubilities of NH4Al(SO4)2·12H2O in the NH4+-Al3+-H3O+-HSO4--SO42--H2O system can be calculated precisely for its crystallization process. Meanwhile, the crystallization process of NH4Al(SO4)2·12H2O was studied by way of experiment and Aspen plus simulation.(4) The thermal decomposition of ammonium aluminum sulfate dodecahydrate was studied systematically by TG-DSC and TG-MS technologies and the results indicated that its thermal decomposition contains three stages. The influence of different atmosphere on the thermal decomposition was also investigated and the results showed that O2 in atmosphere could restrain the thermal decomposition process. Meantime, the kinetic analysis in air was conducted and the activation energy of decomposition in the 2ed and 3rd decomposed stage were 246.3kJ/mol and 286.3kJ/mol calculated by Flynn-Wall-Ozawa (FWO) method. The most probable kinetic mechanism function are R3 (contraction spherical function) and D3 (Jander equation) with the reaction types of three-dimensional phase boundary reaction and three-dimensional diffusion, respectively.(5) The medium circulation experiment was conducted and the alumina extraction efficiency can maintain 86-90%. The accumulation of impurities in medium circulation experiment were investigated in detail and iron element was the main impurity (1.0-4.5g/L in circulation solution), which gradually accumulated with the increasing of circulation number. Based on the medium circulation experiment, the principle process of alumina extraction from HAFA using NH4HSO4/H2SO4 mixed solution was proposed. The Aspen plus software was applied to simulate the whole process with the ELECNRTL model, and the four key steps (leaching, crystallization, thermal decomposition and medium recovery) were discussed and optimized in detail. At last, the direct consumption costs (raw material, fuel and power) were calculated in theory on the basis of the simulated results.
|许德华. 高铝粉煤灰NH4HSO4/H2SO4法提取氧化铝基础研究[D]. 中国科学院大学,2017.|
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