A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na_2CO_3 and was followed by leaching using Na OH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows： an Na_2CO_3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO_2 was 98.13%. The optimized carbonation conditions included a final solution p H value of 9.0, a temperature of 40°C, a CO_2 flow rate of 6 m L/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1：9. The precipitation rate and granularity of the SiO_2 particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.
Mono-disperse spherical silicon dioxide was synthesized in 2-propanol-H2O-NH3 system by the ultrasonic hydrothermal method.The catalyst ammonia acted as strong nucleophilic reagent.With orthogonal experiments,the effects of ultrasonic power,reaction temperature,stirring intensity and molar ratio on the size of silicon dioxide were studied.The results indicated that the diameter of silicon dioxide increased greatly with increasing ultrasonic power and molar ratio.The size of silicon dioxide also increased with increasing temperature and stirring intensity,but with a less extent.The process of forming mono-disperse spherical silicon dioxide could be divided into two steps: hydrolysis and condensation,with hydrolysis as the key step.Mono-disperse spherical silicon dioxide was characterized with XRD,TEM,DTA and IR,and the results showed that the sample was noncrystalline with regular shape and uniform granularity and there was a large amount of hydroxyl group in the SiO2 sample.
By means of energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscope (SEM) analysis, the phase structure characteristics of high titanium slag were analyzed. Through the single factor and the orthogonal experiment methods, the effects of material particle size, mass ratio of acid to ore, roasting temperature, and roasting time on the acidolysis ratio of TiO2 during the process of roasting high titanium slag with concentrated sulfuric acid were systematically investigated. The results show that the sequence of each factor affecting the acidolysis ratio of TiO2 is: mass ratio of acid to ore, roasting time, and roasting temperature. The optimum technological conditions are obtained as mass ratio of acid to ore of 2.1, roasting temperature of 310°C, roasting time of 75min, and material particle size of 45–53μm. The acidolysis ratio of TiO2 is over 96% under the optimum conditions. The roasting process is proved to be significant in the exploitation and utilization of high titanium slag. The advantages of the proposed roasting process are of high efficiency, low power consumption, and minimum pollution.
A novel method of roasting high-titanium slag with concentrated sulfuric acid was proposed to prepare titanium dioxide, and the roasting kinetics of titania was studied On the basis of roasting process. The effects of roasting temperature, particle size, and acid-to-ore mass ratio on the rate of roasting reaction were investigated. The results showed that the roasting reaction is fitted to a shrinking core model. The results of the kinetic experiment and SEM and EDAX analyses proved that the reaction rate of roasting high-titanium slag with concentrated sulfuric acid is controlled by the internal diffusion on the solid product layer. According to the Arrhenius expression, the apparent activation energy of the roasting reaction is 18.94 kJ/mol.
