Dissolution Kinetics Of Alumina By Leaching Coal Fly Ash With Ammonium Hydrogen Sulfate

Coal fly ash is an industrial waste slag produced during high temperature combustion of fossil fired power plant.At present,about 80 tons of coal fly ash is produced every year,and the amount of coal fly ash in China will reach to 5.8 tons by 2015.The mass accumulation of coal fly ash results in land and environmental pollution,which has caused tremendous pressure to the sustainable development of economy and ecology.Although the comprehensive utilization and resource of industrial waste,including coal fly ash,have become important parts of the sustainable development strategy in our country,which has been paid more and more attention,the utilization,especially the high added value,of coal fly ash is not sufficient.As an important aluminum resources,the main chemical components of coal fly ash are alumina(10-55 wt.%)and silica.The development and use of high alumina coal fly ash to produce alumina for realizing green resource production of the solid waste,has great significance.In this study,a new technology of extracting alumina by leaching hydrometallurgically of coal fly ash with ammonium hydrogen sulfate solution was proposed,which was used as the main raw material for ammonium hydrogen sulfate and coal fly ash from circulating fluidized bed boiler.The thermodynamic properties of the main mineral of coal fly ash in the leaching process are calculated.The effect of the leaching temperature,the ratio of liquid to solid,the leaching time and the speed of stirring on the leaching process was investigated.The technological conditions are optimized by using response surface method.Using the method of reduced time and the least square principle,the kinetic mechanism function in the leaching process is obtained.The results show that: in the range of 298.15K-573.15 K,alumina,sillimanite and metakaolin can be dissolved by ammonium hydrogen sulfate.Increasing the leaching temperature,the liquid / solid ratio and leaching time can effectively improve the extraction rate of alumina,and in the experimental range,the effect of stirring speed on the extraction rate of alumina is little.Response surface analysis results show that the main factors which affect the extraction rate of alumina are the leaching time,followed by the leaching temperature and liquid / solid ratio,and the optimum technological conditions are as follows: the leaching temperature is 240 min,the leaching time is 170 ? and the ratio of liquid to solid is 7:1.The extraction rate of alumina can be up to 83.48% by those technological conditions.The integral mechanism of the kinetic equation can be expressed by G(?)=(1-?)-1-1.The expression of reaction rate constant is km= 1562.28 ×(L?)0.38exp(-40950?).The apparent activation energy is 40.95 kJ/mol,and the leaching process belongs to the chemical reaction control process.The main component of the leaching residue is amorphous silica,which is due to deconstruction of the complex aluminum silicate network structure of coal fly ash.