Knowledge Management System Of Institute of process engineering,CAS
|关键词||高铝粉煤灰 氧化铝 提取 脱钠 水热法|
我国高铝粉煤灰年排放量约2500万吨，累积堆存超过1亿吨。高铝粉煤灰大量堆存导致严重的大气、水体和土壤污染。与此同时，我国缺乏高品位铝土矿，对外依存度高。开发高铝粉煤灰提取氧化铝技术，不仅能够有效缓解高铝粉煤灰堆存产生的环境污染问题，而且能够降低我国对高品位铝土矿的对外依存度。高铝粉煤灰的铝硅比较低，传统拜耳法提取氧化铝工艺难以适用。水热法在添加CaO条件下，使用NaOH溶液提取氧化铝，其反应条件温和，但提铝液一般存在苛性比高、氧化铝分离回收困难等问题。基于此，本论文针对高铝粉煤灰碱法提取氧化铝过程，系统开展了高铝粉煤灰一步水热法提取氧化铝过程工艺条件优化、矿相转化机理研究，并在此基础上进一步提出了两步水热法提取氧化铝新工艺，可显著降低提铝液苛性比。之后，进行了高铝粉煤灰分解动力学和提铝尾渣脱钠等研究工作，本论文取得的进展如下：（1）系统开展了高铝粉煤灰一步水热法提取氧化铝过程工艺条件优化研究，考察了反应温度、NaOH浓度以及钙硅比等工艺条件对氧化铝提取率及提铝浸出液苛性比的影响规律，并进一步研究了高铝粉煤灰在水热体系中的矿相转化规律。结果表明，在水热体系中高铝粉煤灰中主要矿相变化过程为莫来石-羟基方钠石-沸石和硅酸钠钙。研究发现，提铝残渣中沸石物相的形成是造成高铝粉煤灰提铝过程中氧化铝损失的主要原因，提高反应温度和液固比可有效降低沸石含量，从而提高氧化铝的提取率。在260℃，40% NaOH，钙硅比1.0，液固比12和反应时间45min 条件下，高铝粉煤灰中氧化铝的提取率达到91.3%。（2）针对高铝粉煤灰直接水热法提取液苛性比偏高的问题，提出形成羟基方钠石过程和羟基方钠石转化过程相结合的两步水热新工艺，提铝溶液的苛性比从一步水热法的11.5降低到7.2。与一步水热法从高铝粉煤灰提取氧化铝相比，氧化铝溶出过程和铝酸钠晶种分解过程的NaOH循环量均显著降低。（3）基于高铝粉煤灰提取氧化铝过程的矿相转变规律，开展了高铝粉煤灰水热体系溶出氧化铝过程的莫来石及羟基方钠石分解动力学研究。结果表明，莫来石在NaOH体系下分解过程的速控步骤为表面化学反应为主的混合控制，得到反应的活化能为29.70 kJ/mol；使用Avrami-Erofeev 方程对羟基方钠石在Ca(OH)2存在下的分解过程进行研究，确定速控步骤为硅酸钠钙晶核形成和晶体生长，得到反应的活化能为148.90 kJ/mol。（4）为回收提铝残渣中的Na2O和实现提铝残渣的综合利用，开展了低碱水热体系下提铝残渣Na2O脱除的研究。结果表明，经过低碱水热处理，提铝残渣中硅酸钠钙主要变为链长较短的托贝莫来石，其Na2O含量为2.2%。通过红外光谱和核磁共振等分析手段，确定了Na2O在产物中主要以未分解的硅酸钠钙、平衡铝取代硅产生电荷和硅羟基吸附三部分的形式存在。进一步使用温水洗涤处理，其Na2O含量最终降低到0.6%。;
Fundamental research on the extraction of alumina from high alumina coal fly ash by hydrothermal processIn China, 25 million tons of high-alumina coal fly ash (HACFA) is emitted every year and above 100 million tons is piled up over the years. The HACFA causes seroius air, water and earth pollution. Meanwhile, due to the lack of high-grade bauxite, the degree of dependence on foreign bauxite is very high. Therefore, efficient extraction of alumina from HACFA not only resolves the the pollution caused by HACFA, but also decreases degree of dependence on foreign bauxite. The alumina-silica ratio of HACFA is low. Thus, tranditional Bayer Process is not fit for the treatment of HACFA. The hydrothermal Process could extract alumina from alumina-containing minerals in NaOH solution with CaO. The reaction parameters of hydrothermal process is mild, but the caustic ratio of alumia-extraction solution was usually high, and the alumina in solution was difficult to recover.The extraction of alumina from HACFA is considered as research object. Mechanism of alumina extraction by one-step hydrothermal process were studied, and optimized conditions were obtained. On the base of one-step process, two-step hydrothermal method was proposed, to decrease the caustic ratio of alumina-extraction solution. Then, the kinetics of alumina extraction and Na2O removal from alumina-extraction slag was studied. In this thesis, the following results and progresses were achieved.(1) The regulation of decomposition and transformation of HACFA in hydrothermal system was studied systematically. The effect of conditions, such as temperature, concentration of NaOH and calcium-silicon ratio on the extraction rate of alumina and caustic ratio was studied systemly. The result shows the conversion process of HACFA was followed by mullite, hydrosodalite, zeolite and sodium calcium silicate (NaCaHSiO4) successively. The formation of zeolite accounts for the main leaching loss of alumina. Elevating reaction temperature and liquid-solid ratio lower the content of zeolite, thus increasing the extraction ratio of alumina. Under the condition of 260 °C, 40% NaOH, liquid-solid ratio 12, calcium-silica ratio 1.0 and 45 minutes, 91.3% of alumina was extracted from HACFA. (2) To lower the high caustic ratio of alumina extraction solution in one-step hydrothermal process, two-step hydrothermal method was put forward, which is composed of one-step hydrothermal process and the process of lowering the caustic ratio. After treated by two-step alkaline hydrothermal process, the caustic ratio of solution was decreased from 11.5 to 7.2. Compared with one-step hydrothermal process, the decrease of caustic ratio improved the efficiency of NaOH solution. (3) On the basis of decomposition mechanism of HACFA, the kinetic analysis of extracting alumina from HACFA by hydrothermal process was studied. The alumina-extraction process was divided by decomposition of mullite and decomposition of hydrosodalite. Decomposition kinetics of mullite was fitted by shrinking core model, and the surface reaction is determined as the main rate-limiting step. The resulting activation energy was determined as 29.70 kJ/mol. Nucleation& crystallization of NaCaHSiO4 was determined as the rate-controlling step of decomposition process of hydrosodalite. The kenitics was fitted by Avrami–Erofeev equation and the activation energy was 148.90 kJ/mol. (4) Removal of Na2O in alumina-extraction slag was explored by low-alkaline hydrothermal process to recycle the soda and utilize alumina-extraction slag. After the treatment by low-alkaline hydrothermal process, the slag was converted to short-chained tobermorite, and the residual Na2O content of 2.2%. The XRD, FTIR and NMR analysis showed that Na2O occurred in alumina-extraction slag in three forms: as unreacted NaCaHSiO4, adsorption due to the substitute of aluminum and adsorption by silicon hydroxyl. The residue was further washed with warm water, and the content of Na2O was decreased to 0.6%.
|回俊博. 高铝粉煤灰水热法提取氧化铝工艺的基础研究[D]. 北京. 中国科学院研究生院,2015.|
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