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山西北部/内蒙古中西部地区是我国重要的能源基地，当地特色高铝煤炭经煤电转化后产生大量高铝粉煤灰，综合利用率低，生态环境危害巨大。高铝粉煤灰中富含伴生金属锂，可作为锂资源的重要来源。目前高铝粉煤灰中锂的赋存状态、迁移规律等基础问题尚不明晰，难以有效支撑后续技术研发。本论文以4个电厂产生的高铝粉煤灰为研究对象，分析了锂在高铝粉煤灰不同矿相中的含量分布。进一步采用飞行时间-二次离子质谱仪研究了锂在高铝粉煤灰及其矿相中的面分布。结合29Si固体核磁和分子模拟手段分析了锂在高铝粉煤灰玻璃相中的赋存状态。基于上述研究结果，进一步开展了预脱硅过程锂的浸出规律研究。主要结论如下：（1）针对高铝粉煤灰矿相组成复杂、难以分离的特点，采用磁选和酸碱联合浸出法分离了高铝粉煤灰中的铁质微珠相、莫来石-刚玉-石英相和玻璃相，并对高铝粉煤灰及分离的矿相进行分析，结果表明磁选和酸碱联合法分别有效分离了高铝粉煤灰中的铁质微珠、玻璃相和莫来石-刚玉-石英相。基于矿相定量分析和元素组成，明确粉煤灰中79-94%的锂分布在玻璃相中，5-16%的锂分布在莫来石-刚玉-石英相中，<5%的锂分布在铁质微珠中。（2）锂原子质量小、含量低，常规的分析方法难以直接分析高铝粉煤灰中锂的赋存状态。采用飞行时间-二次离子质谱仪分析了锂在高铝粉煤灰及其矿相中的面分布。结果表明锂在高铝粉煤灰颗粒中相对均匀分布，锂与铝、硅的面分布具有显著的正相关性；锂在莫来石-刚玉-石英相中含量很低，在玻璃相中显著富集。为了进一步明晰锂在高铝粉煤灰玻璃相中的赋存状态，本研究结合了29Si固体核磁和分子模拟手段，分析了氧化锂与玻璃相中硅的配位结构的反应能力，发现高铝粉煤灰玻璃相中存在Q4(3Al)、Q4(2Al)、Q4(1Al)、Q4(0Al)共4种化学配位结构，氧化锂更易与Q4(0Al)和Q4(1Al)反应，锂更多地存在于玻璃相中的Q3(0Al)和Q3(1Al)结构中。（3）基于锂在高铝粉煤灰玻璃相中的赋存特点，研究了预脱硅过程锂的浸出规律。考察了预脱硅条件对锂浸出率的影响，在较优的预脱硅条件下锂的浸出率可超过80%。高铝粉煤灰预脱硅过程锂的浸出动力学研究结果表明，预脱硅过程锂的浸出受固体产物内层扩散控制，反应的表观活化能为103.31 kJ/mol，碱浓度反应级数为1.55。循环脱硅5次后脱硅液中锂的浓度逐渐接近240 mg/L。;High-alumina coal (HAC) has been found in the northern part of Shanxi Province and in the middle-western part of Inner Mongolia, China. High-alumina-coal fly ash (HAFA) is the by-product during the conversion from HAC into electricity. Currently, the huge amount of unutilized HAFA is treated by stockpiling, which causes serious eco-environmental concerns. HAFA with a high Li content is regarded as a potential resource for Li production. However, the mode of occurrence of Li in HAFA and its migration during leaching process are still not clear, which limit the development of the recovery of Li from HAFA. In this project, the distribution of Li in phases of HAFA were determined based on mineral separations, and chemical imaging of Li in HAFA were studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Mode of occurrence of Li in the glass phase of HAFA was analyzed using 29Si solid-state-magic angle-spinning nuclear magnetic resonance (MAS NMR) and molecular simulation. Based on the mode of occurrence of Li in HAFA, the leaching behaviors of Li during pre-desilication were studied. The main conclusions were presented below.(1) The magnetic particles, glass phase and mullite-corundum-quartz (MCQ) of HAFA were separated based on the magnetic separation and acid-alkali combination method, and the raw HAFA samples and the separated phases were analyzed. The results showed that the lithium contents in HAFA were 260-420 μg/g. Magnetic particles, glass phase and mullite-corundum-quartz (MCQ) were effectively separated by the separation methods. Based on the quantification and chemical composition of mineral phases in HAFA, 79-94% of the Li was found in glass, with the remaining 5-16% and<5% of Li in MCQ and magnetic particles, respectively.(2) Mode of occurrence of Li in HAFA is hard to be analyzed for its low content and light atom. Chemical state imaging of Li in HAFA and its phases was obtained using TOF-SIMS. Lithium was found relatively uniformly distributed in the HAFA particles and strongly correlated with Al and Si. Lithium was barely detected in MCQ by TOF-SIMS. It was deduced that Li occurred in glass phase of HAFA with high content. The 29Si MAS NMR analysis and molecular simulation results showed that the coordinate structures of Si in glass phase of HAFA were Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al). Lithium occurred in Q3(0Al) and Q3(1Al) structures by reacting with Q4(0Al) and Q4(1Al). (3) Leaching behaviors of Li during pre-desilication were studied. According to the condition optimization, it was found that the leaching efficiency of Li during pre-desilication reached >80% under the optimal conditions. After the studies of leaching kinetics of Li during pre-desilication, it were found that the leaching of Li was greatly affected by the reaction temperature and NaOH concentration, and was controlled by the solid product layer. The activation energy and reaction order were determined to be 103.31 kJ/mol and 1.55, respectively. The concentration of Li in desilication solution reached approximately 240 mg/L after being recycled for 5 times.
|胡朋朋. 高铝粉煤灰中锂的赋存状态及预脱硅过程浸出规律研究[D]. 中国科学院研究生院,2018.|
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