Extraction Of Alumina And Silica From Ash Filed Fly Ash

With the development of coal-fired power in our country over the years, the problems caused by the emissions of fly ash have increased because of the increasing coal-consumption growth. A large number of fly ash accumulation caused serious social and environmental problems. Fly ash has high value-added use because of the high content of silica and alumina.In this paper, fly ash of Huainan power plant was used as the raw material for extracting alumina and silica. The main findings are as follows:(1) After mechanical grinding in ball mill for40min, the particle size of fly ash becomes smaller, solid protection film of vitreous surface was destroyed, and smoothness reduced, reactivity of fly ash increased significantly; The mullite and quartz structure of fly ash can be destroyed absolutely using Na2CO3as calcination additive, and convert to high activity nepheline phase. The best calcination process were got from experiments:ash to alkali ratio is1:0.9, the calcination temperature is875℃, calcination time is2h;(2) Sintering clinker was leached in sulfuric acid, the aluminum dissolution rate can reach95%. The single factor and orthogonal experiments were made to get the best leaching process:the concentration of sulfuric acid is3mol/L, leaching temperature is90℃, leaching time is2.5h, the liquid-to-solid ratio is5:1; After recrystallization twice, the filtrate gained by acid leaching becomes aluminum sulfate crystals which meet the industry standard. Aluminum sulfate crystals calcined at800℃for2.5h, γ-Al2O3products can be obtained.(3) After the alumina extraction from fly ash, the residue was leached in NaOH solution, where sodium silicate can be obtained. The best leaching process was got from single factor and orthogonal experiments: concentration of NaOH solution is30%, leaching temperature is90℃, the liquid-to-solid ratio is4:1, the alkali leaching time is80min, silica leaching rate can achieve82%;(4) High purity precipitated silica was prepared from the sodium silicate solution by two steps carbonation process. The optimum conditions were: carbonation reaction temperature is75℃, CO2flow rate is25mL·min-1, the concentration of the sodium silicate solution was50·L-1, select10.8as the first carbonation pH value, and selected9.3as the second carbonation pH value.