Study On Synthesis Of Alumina From Coal Fly Ash And The Thermal Conductive Property Of Its Filled Polymeric Composites

Guizhou thermal power as a big province, a large number of fly ash as a kind of solid waste piling up on the environment caused tremendous impact. Extraction of useful minerals from fly ash and fine utilization will play an important role in the development and utilization of fly ash in Guizhou.In this paper, the extraction of Al₂O₃ from fly ash is studied. PP/Al₂O₃ composites are synthesized by Al₂O₃ and polyprolene?PP?, and the properties of the composites were investigated.The fly ash and desiliconized fly ash from raw material analysis, Then the desiliconized fly ash of sulfuric acid leaching test. The results showed that the leaching rate of alumina was 37.9%.CaCl2 was used as activator to mix with desilica fume to increase the leaching rate of Al3+. The CaCl2 as an activator of the activation effect of desiliconized fly ash was studied. TG-DSC curves were used to determine the extent of the calcination temperature, and the effect of the calcination temperature,holding time and mixture ratio on the activation effect were also studied. The appropriate roasting conditions were determined: the roasting temperature was 900 ?,the roasting time was 120 min, and the mixture ratio was 1:1?mass ratio?. In the following, the selection of acid leaching was investigated. The results of sulfuric acid as a suitable acid leaching acid were obtained by the comparison of sulfuric acid, i.e.hydrochloric acid and nitric acid leaching. Then the leaching conditions of the experiment, the results showed that the best experimental conditions were: sulfuric acid concentration of 1 mol/L, leaching temperature of 90 ?, and leaching time of 40 min. The highest leaching rate of Al₂O₃ was 96.9%. Aluminum sulfate solution was used to adjust the pH value to remove iron. And the iron concentration of aluminum sulfate was 0.26% after removing of iron. The evaporation temperature of aluminum sulfate solution was 116 ?, and the sheet aluminum sulfate was calcined to Al₂O₃.According to the thermodynamic calculation, the calcination temperature was 800 ?,and the experiment results showed that the 150 min was suitable for the calcination time. The purity of alumina was 81.49%.Modified PP with different mass fraction of Al₂O₃ were used to analyze the performance of Al₂O₃/PP composites, and the maximum amount of Al₂O₃ in the composites was 7%. Scanning electron microscopy showed that the Al₂O₃ was dispersed evenly in the composites with low filler content, but when Al₂O₃ Al₂O₃ content up to 7%, the trend started a reunion. For the mechanical properties, the strength and toughness increased with the increasing filler content. The temperature of crystallization and melting temperature also increased with the increasing filler content. The thermal conductivity increased with the increasing filler content, and when the filler content up to 7%, thermal conductivity was increased by 21.1%compared with that of the base material.Cell size of PP/Al₂O₃ foams decreases with the increasing filler content. Cell density with filler increase showed the trend of first increased and then decreased.Cell density of foams with 5% Al₂O₃ reached maximum value. With further increasing filler content, bubbles collapsed, which compromised the foam performance.In this paper, the extraction of alumina from fly ash and its application in PP modification are studied, and a new kind of composite material with better performance is developed. The high added value of Guizhou fly ash is used for a new solution.