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高铝粉煤灰协同活化制备莫来石工艺基础研究
张建波
学位类型博士
导师李会泉
2017-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工艺
关键词高铝粉煤灰 协同活化 深度脱硅 活化指数 莫来石
摘要

高铝粉煤灰产生于我国内蒙古中西部、山西北部和宁夏东部地区,年排放量达3000万吨,其中Al2O3和SiO2含量分别高达40%和35%以上,主要以莫来石-刚玉相和非晶相形式存在。针对其资源特点,制备以莫来石为代表的铝硅系耐火材料已成为高铝粉煤灰资源化利用的重要途径。本文针对粉煤灰原料铝硅比低、杂质含量高的问题,提出了机械-化学协同活-化深度脱硅除杂制备莫来石新工艺,重点开展了非晶相SiO2多场温和活化、酸活化过程硅溶胶凝胶化调控、晶相/非晶相高效剥离机理、深度脱硅动力学等研究;进一步开展了耦合调控活化酸液制备聚合氯化铝、脱硅粉煤灰物性调控制备莫来石、物质流分析与全流程工艺优化等研究,形成了高铝粉煤灰协同活化-深度脱硅制备莫来石耐火材料多联产技术体系。主要研究内容和结论如下:(1)开展了机械、化学、微波单独和协同活化方式对非晶态SiO2反应活性的影响规律研究,提出“活化指数”用于评价其反应活性,确定了机械-化学活化为最优活化方式,并完成工艺优化,活化指数可达12.4%,较粉煤灰原料反应活性提高8倍,同时Ca、Fe、Mg等杂质含量均可降低至1%以下。进一步开展了协同活化机理研究,采用电子探针、核磁等分析发现协同活化过程可有效降低其晶相/非晶相嵌粘夹裹程度,促进惰性玻璃相Q4(3Al)结构转化为活性较高的Q4(2Al)和Q2(1Al),增加Si-O-活性作用位点,实现杂质的深度脱除和非晶态SiO2反应活性的大幅提高。(2)基于DLVO理论和Zeta电位理论,建立了电位、粘度及pH实时监测一体化平台,结合TEM及in-situ FTIRS分析突变过程胶体粒子形貌及Si-O-Si配位变化,进一步考察了不同价态阳离子(K+、Na+、Ca2+、Mg2+、Fe3+、Al3+)和阴离子(Cl-、Br-、I-、NO3-、SO42-、PO43-)对硅溶胶凝胶化过程的影响,研究发现离子价态和浓度过高极易破坏双电层结构,促进凝胶化过程。因此,选择盐酸作为活化酸液,通过控制体系pH小于1.9,并调控溶液中阳离子含量,可有效缓解凝胶转化过程,提高液固分离效率。(3)针对脱硅正交实验结果,考察了不同因素对脱硅率及矿相变化的影响,在优工艺条件下,脱硅率可达60%,铝硅比可达2.8,钠含量可控制在0.5%以下;进一步开展了非晶相复杂配位Al-O-Si变化规律、元素赋存状态及转化规律、颗粒孔道结构、矿相及形貌变化规律等研究,发现脱硅反应主要是碱介质强化进攻非晶态SiO2,同时高效破坏非晶相中Al-O-Si配位结构,实现非晶态SiO2的高效剥离;基于脱硅工艺及机理分析,开展了脱硅动力学研究,明确了脱硅反应前期受表面反应控制,反应后期受固膜扩散控制,实现了非晶态SiO2高效脱除同时避免副反应发生,为脱硅过程的有效控制、工程设计与放大提供基础数据。(4)开发了耦合调控制备聚合氯化铝关键技术,考察了不同因素对聚合氯化铝制备过程的影响,在优化条件下,钙离子的架桥作用促进铝离子高效聚合,得到聚合氯化铝产品中Al2O3含量高达11%,盐基度为76%,密度为1.1g/mL,其性能指标均满足国标要求。开发了脱硅粉煤灰物性调控制备莫来石关键技术,考察了不同因素对莫来石关键指标体积密度和显气孔率的影响,在优化条件下,莫来石晶粒生长为棒状莫来石,得到的莫来石产品氧化铝含量高于70%,体积密度高于2.85g/cm3,显气孔率小于0.5%,其性能指标均满足国标要求。在此基础上进行了整体工艺物料衡算、物质流分析和初步经济性评价,为工程放大提供关键基础数据。 

其他摘要

High alumina fly ash (HAFA) is mainly generated in the midwestern Inner Mongolia / north of Shanxi and Ningxia region, whose emission amount is about 30 million tons annually. But the comprehensive utilization ratio is lower, and its accumulation leads to serious pollutions. Simultaneously, abundant alumina and silica resources are contained in HAFA, whose contents reach to 45% and 35% respectively, and the mullite / corundum / amorphous phase are the main mineral phases. In terms of the characteristics of elements and mineral phases, the preparation of mullite is the strategic demand for the comprehensive utilization of HAFA, and the elevation of Al/Si ratio by mild desilication is the key point. In this work, because of the low Al/Si ratio and high impurities contents in HAFA, some mild activation processes have been investigated, and the preparation of mullite by mechanical-chemical activation-deep desilication process has been promoted. The activated mechanism of different mild activation / mechanism of silica sol to gel during the acid activation / efficient separation between amorphous phases and crystal phases / preparation of polyaluminum chloride by activated acid solution and preparation of mullite by desilicated HAFA have been studied in detail. The main contents and conclusions are as follows:(1) In terms of the reactivity of amorphous silica in HAFA, the activation index (EDR) is promoted to estimate the reactivity of amorphous silica. Firstly, the effects of mechanical activation / chemical activation and microwave activation on EDR are researched respectively, and the chemical activation can elevate its EDR obviously; simultaneously, the mechanical-chemical activation / microwave-chemical activation and mechanical- microwave activation on EDR have also been studied, and the mechanical-chemical activation is the best method. Secondly, the mechanical-chemical activation process is optimized, and the EDR can reach to 12% under the condition of mechanical process (t=90min) and acid activation process (T=75-80°C, t=90min, C=6mol/L, L/S=4:1), at the same time, the contents of Fe/Ca/Mg impurities have also been decreased to below 1%. Lastly, the mechanism of synergistic activation has been analyzed, the analysis by EPMA/BET and NMR indicates that the bond Al-O-Si in amorphous phases is complicated, after the synergistic activation, the small particles are distributed, and the encapsulated amorphous and crystal phases are destructed. The inert Q4(3Al) structure in the amorphous phase is transferred to active Q4(2Al) and Q2(1Al), which promotes the decompose the Al-O-Si bonds by H+, and the specific surface area is elevated to 2 times, which increase the active sites of Si-O-. Therefore, the impurities are removed, and the reactivity of amorphous silica is improved obviously.(2) In terms of the difficult separation between solid and liquid caused by the transformation from silica sol to gel during the acid activation, based on the theories of DLVO and Zeta potential, a novel method to analyze the transformation from silica sol to gel by zeta potential/ viscosity and pH online continuously is established. The morphology of colloidal particles and changes of Si-O-Si bonds during the potential mutation period have also been analyzed and verified by the in-situ FT-IR and TEM, which presents that the silica sol is transferring to silica gel during the potential mutation period. Therefore, the effects of different valent cations (K+, Na+, Ca2+, Mg2+, Fe3+, Al3+) on the silica sol to gel are studied, which indicates that the higher concentrations and valences of cations accelerate the gelation process, and this process can be alleviated when the pH is controlled under 1.90 and the concentrations of cations is below a lower level; simultaneously, the effects of different anions (Cl-, Br-, I-, NO3-,SO42-, PO43-) on the silica sol to gel are studied, which presents that the aggregation of silica sol is accelerated when the ionic radius is decreased and the valence is increased, which can destroy the stable electric double layers.(3) In order to accomplish the deep desilication and avoid the side reaction, firstly, based on the results of orthogonal experiments, the effects of different factors on the desilicated ratio and mineral phase are investigated, and the optimal results indicate that the desilicated ratio can reach to 60% under the condition: T=95°C, t=90min, C=6mol/L, L/S=5:1, simultaneously, the contents of Na can be controlled below 0.5%. Secondly, the changes of complicated Al-O-Si bonds / occurrence state of elements and phases / changes of pores in HAFA are investigated, which indicates that the amorphous Si-O bonds are decomposed by alkali solution. Lastly, the kinetics of deep desilication are studied, and the results indicate that the earlier stage is mainly controlled by surface reaction, and the later stage is mainly controlled by solid film diffusion due to the zeolites formed on the surface of particles.(4) In terms of the waste acid solution generated by acid activation process, a novel method to prepare the polyaluminum chloride is promoted. The concentration of Al/Fe/Ca ions are elevated from 3.0g/L, 2.5g/L, 2.5g/L to 22.0g/L, 14.0g/L, 10.0g/L respectively when the recycling times of acid solutions is 8 under the optimal conditions: T=85°C, t=90min, ratio between calcium aluminate and H+=0.3-0.5, and the Al2O3 contents, basicity and density in polyaluminum chloride reach to 11%, 76% and 1.1g/mL respectively, which can meet the industrial demand well. In terms of the desilicated HAFA, the mullite grains grow to columnar mullite crystal under the conditions: moisture content=8%, no additives, forming pressure=168MPa, calcination temperature=1650°C, calcination time=2-3h, and the Al2O3 contents, bulk density and apparent porosity reach to 70%, 2.85g/cm3 and below 0.5%. Besides, the material balance, material flow analysis and preliminary economic evaluation have been finished to support the fundamental data for engineering application. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/24225
专题研究所(批量导入)
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张建波. 高铝粉煤灰协同活化制备莫来石工艺基础研究[D]. 北京. 中国科学院研究生院,2017.
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