Preparation Of High Specific Surface Area Nano Silicon Dioxide By Fluosilic Ammonification Reaction

The issue to address problems of industrial wastewater treatment fluorosilicic acid produced during the smelting of rare earth, and full recycling of fluorine and silicon resources, and preparation of high cost-effective products at low cost conditions.The main research topics fluorosilicic acid as raw materials, ammoniated precipitation method with high surface area silica nano technology. Namely ammonia as ammonia solution agent, through a single factor experiment, orthogonal experiment, Rotor-Stator reactor experiments, prepared high productivity, good dispersion, high specific surface area nanoscale silica.The subject examined in the various process parameters and product yields silica surface area of influence, studied the preparation process different process conditions; By BET, XRD, SEM and other testing methods to characterize the product, and the combination of theory formation reaction of silica precipitation on fluoride acid amide to explore.The results showed that:fluorosilicic acid amide precipitated positive plus mode (base solution:fluorosilicic acid, add fluid:aqueous ammonia) and anti-plus method (base solution:ammonia, add liquid: fluorine acid) silica products reunion way, is not the same surface area and dispersion effect. A positive addition to small particles of silica prepared agglomerate into irregular spatial network structure, high porosity, large surface area. And the silica prepared in a manner of reverse adding will be a spherical shape by small particle aggregation, and the dispersion is much more better, and the specific surface is smaller than the positive adding.Fluorosilicic acid amide obtained by experimental study precipitated silica prepared by the optimum process conditions are as follows:①the positive addition optimum conditions are:the aqueous ammonia was added drop wise rate lOmL/min, the mass fraction of 5 percent ammonia water, ammonia and theoretical amount ratio 1:0.8, the mass fraction of 35 percent fluorosilicic acid, washed twice with beating to prepare a specific surface area of up to 768.3 m2/g of nano-silica.② the reverse adding optimum conditions are:the fluorosilicic acid was added dropwise rate 23 mL/min, the mass fraction of 35 percent fluorosilicic acid, fluosilicic acid and theoretical amount ratio 1:1.2, the mass fraction of 10% ammonia water to prepare a specific surface area of up to 548 m2/g of nano-silica.Using Rotor-Stator reactor, fluorosilicic acid amide precipitated silica prepared experiments, the researchers showed that Rotor-Stator reactor may strengthen liquid-liquid mixing between microscopic, making more uniform particle size of the silica, better dispersion and higher specific surface area. Suitable Rotor-Stator reactor operating conditions were obtained by experiments, that is the speed is 2800 r/min, the amount of circulating is 600 mL/min, the feeding rate is 35 mL/min, under these conditions we can prepared better dispersion, and the specific surface area is 573 m2/g of nano-silica.The innovation of this subject is:the first use of Rotor-Stator reactor, fluorosilicic acid amide precipitation reaction, using its mass transfer enhancement and micromixing characteristics in the production of ammonium fluoride products, prepared a high surface area silica.