高铝粉煤灰非晶态氧化硅高值化利用基础研究

发布时间：2018-08-09 13:49

【摘要】：高铝粉煤灰年排放量超过2500万吨,综合利用率低,大量堆存造成严重的环境污染。高铝粉煤灰中氧化铝含量可达50%左右,同时富含大量的非晶态氧化硅组分。当前,研发经济可行的氧化铝提取技术是高铝粉煤灰综合利用的战略需求,而通过碱法脱除非晶态氧化硅、提高高铝粉煤灰铝硅比是其中的关键环节。本文主要针对高铝粉煤灰脱硅过程中产生的高碱性脱硅液高值化利用问题,开展了高碱体系中硅基材料可控制备与介质循环的基础研究,提出了硅酸钙晶须及保温材料制备、高比表面二氧化硅联产超细碳酸钙两种工艺路线,将为高铝粉煤灰中伴生非晶态氧化硅高值化利用提供技术支撑。主要研究内容和结论如下：(1)针对高碱体系中硅酸钙晶须的水热制备过程,考察了钙硅比(CA/SI)、碱浓度、反应温度等条件对硅酸钙晶型和形貌的影响,建立了反应条件与不同形貌及晶型的硅酸钙晶须对应关系,并可合成长径比大于100且分散性良好的变针硅钙石型晶须；研究发现硅灰石族硅酸钙均具有晶须形貌,通过晶面表面能计算得到变针硅钙石晶须的轴向和径向晶面晶面能分别为0.057 eV/A3和0.027 eV/A3,确定晶体轴向的优先生长是晶须形貌的成因。(2)提出低温苛化制备低碱含量无定型水合硅酸钙(C-S-H),并进一步水热制备硬硅钙石的新工艺路线；分析表明C-S-H为硅氧四面体链状结构,C-S-H中残留的Na+包括吸附钠和层间结合钠；基于此,开发了离子交换三级逆流洗涤工艺,5倍洗水下C-S-H中Na+可降低至0.35%,以此C-S-H为原料可水热制备得到硬硅钙石型保温材料；进一步研究发现过量铝会促使晶型转变为托贝莫来石,但配入硅或加入螯合剂EDTA可以抑制晶型转变。(3)开展了高碱低模数脱硅液碳化法制备低密度高比表面二氧化硅研究,提出了两段碳化法制备白炭黑路线,开展了工艺优化,白炭黑比表面积最高420.82 m2/g；针对碳化法制备气凝胶过程,开展了工艺条件影响考察,优化条件下制备气凝胶密度最低为0.34g/mL,比表面积最高为700.72 m2/g；系统考察了反应过程中体系pH值、表面基团的变化规律,发现溶剂分层导致气凝胶无法有效表面改性；基于此,采用溶剂预置换二氧化硅气凝胶表面形成疏水结构,密度可降至0.25 g/mL。(4)针对碳化残液循环利用问题,开发了苛化过程碱回收和碳酸钙形貌的协同控制技术；考察了工艺条件对转化率和碳酸钙形貌的影响,优化条件下碳酸根转化率为95.70%,并得到形貌均一、粒径约100nm超细碳酸钙产品；深入研究了反应过程中碳酸钙形貌变化规律,结果表明反应初始阶段碳酸钙是晶体和无定型的复合结构,反应时间延长,碳酸钙形貌主要为规整的正方体颗粒,然后出现其他形状的碳酸钙颗粒,碱性条件下,大部分立方体形颗粒开始溶解形成团状物质。(5)针对超细碳酸钙晶体颗粒分散性差、易团聚的特点,利用混合悬浮混合产品排料技术(MSMPR)开展了高碱体系中碳酸钙结晶动力学研究；结果表明该体系中,碳酸钙晶体生长是表面反应控制,而成核速率则是受粒径控制,体系中过量的OH-会与Ca2+结合导致生长速率常数和成核速率常数均较低；团聚因子与平均停留时间呈正比例关系,氢氧化钙浓度升高后,悬浮密度的增加则会导致颗粒间碰撞概率增加从而破坏碳酸钙颗粒的团聚。
[Abstract]:The annual discharge of high alumina fly ash is more than 25 million tons, and the comprehensive utilization rate is low. A large number of storage can cause serious environmental pollution. The alumina content in high alumina fly ash can reach about 50%. At the same time, it is rich in a large number of amorphous silicon oxide components. The key link is to remove the amorphous silicon oxide and improve the ratio of aluminum and silicon to high alumina fly ash. This paper mainly aims at the high value utilization of high alkaline desilication liquid produced in the process of high alumina fly ash deilication. The basic research on the controllable preparation and medium circulation of silicon based materials in the high alkali system is carried out, and the calcium silicate whisker and the heat preservation are put forward. Two process routes of material preparation, high ratio surface silica and superfine calcium carbonate will provide technical support for the high value utilization of associated amorphous silica in high alumina fly ash. The main contents and conclusions are as follows: (1) in the hydrothermal preparation process of calcium silicate whiskers in high alkali system, the calcium silicon ratio (CA/SI), alkali concentration and reaction are investigated. The effects of temperature and other conditions on the crystal form and morphology of calcium silicate have been established. The relationship between the reaction conditions and the crystalline form of calcium silicate whiskers with different morphologies and crystal forms is established. The change of the length to diameter ratio is more than 100 and the dispersibility of the calcium silicate whisker can be synthesized. The study found that the calcium silicate of the wollastonite has the morphology of the crystal whisker and can be calculated by the surface of the crystal. The axial and radial crystal facets of the needle silicon carbide whiskers can be 0.057 eV/A3 and 0.027 eV/A3 respectively. It is determined that the preferential growth of the crystal axis is the cause of the morphology of the whisker. (2) a new process for preparing low alkali content of calcium silicate (C-S-H) with low alkali content and further hydrothermal preparation of hard silicon calcium stone is proposed. The analysis shows that C-S-H is silicon oxygen. The tetrahedral chain structure, the residual Na+ in C-S-H includes sodium adsorbed and interlayer sodium. Based on this, the ion exchange three stage countercurrent washing process is developed. The Na+ can be reduced to 0.35% in the 5 times washing water, and the C-S-H is used as the raw material for the preparation of the hard silicalite type thermal insulation material. Further research has found that the excess aluminum will promote the crystal transformation. For Tobey mullite, silicon or chelating agent EDTA can inhibit crystalline transformation. (3) a low density and low modulus silica solution was developed to prepare low density and high specific surface silica. The process of preparation of white carbon black by two stages of carbonization was put forward, and the surface area of silica was up to 420.82 m2/g. The aerogel process has carried out the influence of the process conditions. Under the optimized conditions, the aerogel density is lowest 0.34g/mL and the specific surface area is 700.72 m2/g. The system pH value and the change law of the surface group are investigated, and the solvent stratification leads to the aerogel without the effective surface modification; based on this, the solvent preposition is used. A hydrophobic structure was formed on the surface of the silica aerogel, and the density could be reduced to 0.25 g/mL. (4) for the recycling of carbonated residue. The synergistic control technology of alkali recovery and calcium carbonate morphology was developed, and the effect of process conditions on the conversion rate and the morphology of calcium carbonate was investigated. The conversion rate of carbonates under optimum conditions was 95.70%, and the results were obtained. The morphology is uniform, the particle size is about 100nm superfine calcium carbonate, and the change regularity of calcium carbonate in the reaction process is deeply studied. The results show that calcium carbonate is a crystal and amorphous composite structure at the initial stage of the reaction, the reaction time is prolonged, the morphology of calcium carbonate is mainly regular cube particles, and then other shapes of Calcium Carbonate Granules and alkali appear. Under the sexual condition, most of the cubic body particles began to dissolve to form a mass of mass. (5) the crystallization kinetics of calcium carbonate in the high alkali system was studied with the characteristics of the poor dispersion of superfine calcium carbonate particles and easy reunion. The results showed that the crystal growth of calcium carbonate was the table in the system. The surface reaction control, while the nucleation rate is controlled by the particle size, the excess OH- in the system will combine with the Ca2+ leading to the low growth rate constant and the nucleation rate constant; the aggregation factor is proportional to the average residence time, and the increase of the concentration of the suspension will lead to the increase of the collision probability between the particles. The reunion of Calcium Carbonate Granules.
【学位授予单位】：中国科学院研究生院(过程工程研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ127.2

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