Study On The Extraction Of Gallium From High-alumina Fly Ash And Preparation And Gas Sensing Properties Of CuO-Ga₂O₃

At first,the paper introduce the nature of coal fly ash and the harmful effects of CFA on the ecological environment.By the analysis of composition and properties of CFA,the paper describes the application of fly ash in agriculture,metallurgy and architecture.Due to the scavenging properties of gallium and its application in the fields of solar cells,semiconductor materials,computer chips and magnetic materials,the research progress of extracting gallium from fly ash was introduced.The paper also discusses the preparation method of metal composite oxide and the application of gas sensor in detail.In order to improve the comprehensive utilization of CFA,the calcined CFA was dissolved in hydrochloric acid by hydrothermal activation method.The influence factors of sintering process and acid leaching process on the leaching of gallium have been discussed,including calcination temperatures,calcination time,hydrochloric acid concentrations,the ratio of solid to liquid,leaching temperatures and leaching time.The results show that the best experimental parameters,including calcination temperatures,calcination time,hydrochloric acid concentration,the ratio of solid to liquid,leaching temperature and leaching time,was 800?,2 h,6 mol/L,15:1?mL:g?,140?and 2 h respectively.By optimizing the conditions of gallium,a leaching rate of 89.7 % of gallium in CFA can be achieved.The paper also reports,dissolution of CFA by alkaline hydrothermal method.Single-factor and multiple–factors experiments were performed to explore the effects of reaction temperatures,calcium-silicon ratio,the ratio of solid to liquid,alkaline concentrations and reaction time on extraction ratio of gallium from CFA.Considering the extraction ratio of gallium and reaction costs and other factors,we evaluated the best experimental conditions.The results show that the best experimental condition,including reaction temperatures,calcium-silicon ratio,the ratio of solid to liquid,alkaline concentrations reaction time,was 180 ?,1:1,20:1,200 g/L and 3.0 h respectively.By optimizing the leaching conditions of gallium,the results show that the extraction ratio of gallium from CFA could reach 87.84 %.The calcined fly ash was dissolved by microwave alkali dissolution.The singlefactor experiments were performed to explore the effect of calcination temperatures,calcination time,m?Na2CO3?:m?CFA?,microwave reaction temperatures,calcium-silicon ratio,the ratio of solid to liquid,alkaline concentrations and microwave reaction time on extraction ratio of gallium from CFA.The results show that the best experimental condition,including calcination temperatures,calcination time,m?Na2CO3?:m?CFA?,microwave reaction temperatures,calcium-silicon ratio,the ratio of solid to liquid,alkaline concentrations and microwave reaction time,were 850?,2 h,1:1,90 ?,1:1,14,200 g/L and 40 min respectively.By optimizing the leaching conditions of gallium,the results show that the extraction ratio of gallium from CFA could reach 82.28 %.The CuO-Ga₂O₃ composites were prepared by sol-gel method.The composites were characterized by XRD,SEM,IR,UV-vis and nitrogen adsorption.The effect of different heat treatment temperatures on the sensitivity and selectivity of composite materials with respect to common gases was studied.The experimental results show that the CuO-Ga₂O₃ complex prepared at the heat treatment temperature of 600? has high sensitivity and selectivity towards acetaldehyde.The corresponding gas sensor exhibits high selectivity and sensitivity towards acetaldehyde at room temperature.