Experiment On Preparation Of Nano-silica From Acid Leaching Residue Of Coal Ash

Coal as the most abundant primary energy accounts for over 70% of the total energy production and consumption in China. With the rapid growth of large-scale industrial construction drives the development of the domestic power industry, coming with a sharp increase of coal ash emission. The bulk deposition of coal ash not only occupies the land, but also brings many environmental problems. If take effective technological methods to extract the main elements of silicon and aluminum, both solve environmental problems and improve economic value. Combined with coal gradient utilization technology proposed by Thermal Power Engineering Institute of Zhejiang University, fully explore the characteristics of coal energy and resource properties, and realize high added value utilization of resources. The paper proposes the technology on preparation of nano-silica from acid leaching residue of coal ash and carries out related experimental researches:Extraction of aluminum from coal ash under suitable reaction conditions utilizing sulfuric acid at first, leaving acid leaching residue rich in silicon. Calcinate the acid leaching residue with Na2CO3, and take thermodynamic analysis and calculation based on the sintering process of acid leaching residue-Na2CO3 system, through designing orthogonal experiment to determine the calcination condition. Afterwards discuss the effects of calcination temperature, Na2CO3 ratio, calcination time and temperature rise methods on silicon dioxide leaching rate respectively. Experiments results indicate that the leaching rate of silicon dioxide in the acid leaching residue attains to 86.14% at the optimal reaction conditions with calcination temperature 1153K, calcination time 1.5h, mi(the acid residue):m2(Na2CO3)=2:3.05.Whereafter the results of kinetic study on acid leaching residue-Na2CO3 system’s thermal dissociation process indicate the process accords with Crank-Ginstling-Braunshtein equation, and the apparent activation energy of the reaction is 156.46kJ/mol calculated by experimental datas. The product after calcination can dissolving out over 85% silicon by water leaching in the form of Na2SiO3 solution. The water leaching residue rich in amorphous forms of silicon and aluminum which can be considered extracting aluminum and silicon again to ultimately achieve the comprehensive utilization.Preparation of precipitated nano-silica from Na2SiO3 solution by carbonation method, explore the preparation factors affecting the product properties through single factor method to get the optimal reaction conditions:2wt% of SiO2, v=0.5min-1, reaction temperature 65-75℃, reaction end PH=8, aging time 2h. After filtration、 lavatio、azeotropic distillation and 120℃ drying, loose nano-silica production with 250m2/g specific area was prepared.The addition of surfactant and dispersant can change the particle surface condition remarkably, reduce the reunion of particle, improve the dispersion and stability of the system. At the reasonable preparation conditions, adding 1wt% surfactant of polyethylene glycol 10000 and 1wt% dispersant of NaCl obtains the optimal result, and the preparation of SiO2 with 20nm grain size, the primary particle with homogeneous distribution and smaller aggregate. The nano-silica product conforms to standard A of HG/T 3061-2009, the content of SiO2 is up to 92.34% with 3.10 ml/g oil absorption of DBP.However the technology on preparation of nano-silica from acid leaching residue of coal ash not only basically realizes the totally separation of aluminum and silicon resources, but also realizes the efficient classification utilization of the two resources. The leaching water residue secondary acid leaching can extract aluminum and silicon resources,and there is no strong acid during the carbonation process reducing the environmental pollution. After the carbonate reaction, Na2CO3 in the solution can realize cyclic utilization by recycled returning to calcination process. Therefore, the sustainable development and environment friendly technology has high economic value, extremely high resources comprehensive utilization rate.