氟硅酸氨化制备高比表面积纳米二氧化硅

发布时间：2018-03-12 11:23

本文选题：氟硅酸　切入点：氨化沉淀法　出处：《北京化工大学》2015年硕士论文　论文类型：学位论文

【摘要】：本课题致力于解决工业冶炼稀土过程中产生的氟硅酸废水处理问题,并充分回收利用氟和硅资源,在低成本的条件下制备经济效益较高的产品。课题中主要研究以氟硅酸为原料,氨化沉淀法制备纳米级高比表面积二氧化硅的工艺技术。即以氨水为氨解剂,通过单因素试验、正交试验、定-转子反应器实验,制备出产率高、分散性好、高比表面积纳米级二氧化硅。课题中考察了各工艺参数对产品二氧化硅产率及比表面积的影响,研究了制备过程中不同的工艺条件；通过BET、XRD、SEM等测试手段对产品进行表征,并结合理论对氟硅酸氨化沉淀法生成二氧化硅的反应进行探究。研究结果表明：氟硅酸氨化沉淀法的正加方式(底液：氟硅酸,添加液：氨水)和反加方式(底液：氨水,添加液：氟硅酸)对产品二氧化硅的团聚方式、比表面积及分散度影响并不相同。正加方式制备二氧化硅以小颗粒团聚成无规则的空间网状结构,孔率高、比表面积较大。反加方式制备的二氧化硅以小颗粒聚集为球状,分散度较好,比表面比正加方式所制备二氧化硅小。通过实验研究获得氟硅酸氨化沉淀法制备二氧化硅的最佳工艺条件如下：①正加最优条件为：氨水滴加速率10mL/min、氨水质量分数5%,氨水用量与理论比值1：0.8、氟硅酸质量分数35%、打浆水洗两次,制备出比表面积高达768.3m2/g的纳米二氧化硅。②反加最优条件为：氟硅酸滴加速率23 mL/min、氟硅酸质量分数35%,氟硅酸用量与理论比值1：1.2、氨水质量分数10%,制备出比表面积高达548 m2/g的纳米二氧化硅。在使用定-转子反应器进行氟硅酸氨化沉淀制备二氧化硅的实验中,研究表明定-转子反应器可强化液-液相间微观混合,使二氧化硅粒径更均匀,分散性更好,比表面积更高。通过实验获得了适宜的定-转子反应器操作条件,即定-转子反应器转速为2800r/min,循环量为600 mL/min,加料速度35 mL/min,在此条件下可以制备出分散性好,比表面积达到573m2/g的纳米二氧化硅。本课题创新点在于：首次使用定-转子反应器进行氟硅酸氨化沉淀反应,利用其强化传质及微观混合特点,在生产氟化铵产品的同时,制备出高比表面积二氧化硅。
[Abstract]:This project is devoted to solve the problem of wastewater treatment of fluorosilicic acid produced in the process of industrial smelting rare earth, and fully recover and utilize fluorine and silicon resources. The technology of preparing nanometer silica with high specific surface area by ammoniation precipitation method with fluorosilicic acid as raw material was studied in this paper, that is, ammonia water was used as ammonolytic agent, and single factor test was carried out. Orthogonal experiments and stator rotor reactor experiments were conducted to prepare nano-sized silica with high yield, good dispersion and high specific surface area. The effects of various process parameters on the yield and specific surface area of silica were investigated. The different process conditions in the preparation process were studied, and the products were characterized by means of BET-XRDX SEM. The results show that the positive adding method (substrate: fluorosilicic acid, additive solution: ammonia water) and reverse adding method (bottom liquid: ammonia water) of fluorosilicic acid ammoniation precipitation method are used to study the reaction of producing silica by ammoniation precipitation method of fluorosilicic acid. The additive solution: fluorosilicic acid) has different effects on the agglomeration mode, specific surface area and dispersion of silica. The specific surface area is large. The silica prepared by reverse addition method is spherical with small particles, and the dispersion is better. The optimum technological conditions for the preparation of silica by ammoniation and precipitation of fluorosilicic acid were obtained as follows: the optimum conditions of positive addition of ammonia water were as follows: the adding rate of ammonia water was 10ml / min, the mass fraction of ammonia water was 10mL / min, and the optimum conditions were as follows: the addition rate of ammonia water was 10ml / min. The ratio of ammonia to theory is 1: 0.8, the mass fraction of fluorosilicic acid is 35 and the water is washed twice. The optimum conditions for preparation of nano-silica with a specific surface area of 768.3 m2 / g are as follows: dropping rate of fluorosilicic acid 23 mL / min, mass fraction of fluorosilicic acid 35, ratio of fluorosilicic acid to theoretical value 1: 1.2, mass fraction of ammonia water 10, and the specific surface area as high as 10. 548 m2 / g nanocrystalline silica. In the experiment of preparing silica by ammoniation of fluorosilicic acid in a stator rotor reactor, The results show that the liquid-liquid phase micromixing can be enhanced in the stator rotor reactor, and the particle size of silica is more uniform, the dispersion is better and the specific surface area is higher. That is, the speed of the stator / rotor reactor is 2800r / min, the circulation is 600 mL / min, and the feed rate is 35 mL / min, and under these conditions the dispersion can be very good. Nano-silica with a specific surface area of 573m2 / g. The innovation of this project lies in the first use of a stator rotor reactor for the ammoniation of fluorosilicic acid, and the use of its enhanced mass transfer and microcosmic mixing characteristics to produce ammonium fluoride at the same time. Silica with high specific surface area was prepared.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.2;TB383.1

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