Phase Transformation of Hercynite During the Oxidative Roasting Process
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https://doi.org/10.1007/s11837-020-04215-3 2020 The Minerals, Metals & Materials Society
ALUMINUM: RECYCLING AND CARBON / ENVIRONMENTAL FOOTPRINT
Phase Transformation of Hercynite During the Oxidative Roasting Process XIAOBIN LI,1 HONGYANG WANG ,1,2,3 QIUSHENG ZHOU,1,4 TIANGUI QI,1 GUIHUA LIU,1 and ZHIHONG PENG1 1.—School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, China. 2.—School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China. 3.—e-mail: [email protected]. 4.—e-mail: [email protected]
Converting the aluminum in hercynite into a readily soluble state in alkali solution is significant for extracting alumina from hercynite. Thermodynamic analysis shows that the aluminum in hercynite is insoluble in alkali solution and that it can be chemically separated from iron through oxidative roasting. X-ray diffraction combined with x-ray photoelectron spectroscopy analysis indicates that, during oxidative roasting, hercynite first decomposes into cAl2O3 and Fe3O4 with lattice distortion. With increasing temperature, the former subsequently converts into a-Al2O3 while the latter into c-Fe2O3 followed by a-Fe2O3. Hercynite can be completely converted into alumina and iron oxides through treatment at > 1173 K for 20 min. Alumina in the oxidized hercynite obtained at 1173 K to 1373 K can be efficiently digested by the Bayer digestion at 513 K and 533 K, with an alumina digestion ratio of 96% and 98%, respectively. This work lays the foundation for alumina extraction from hercynite.
INTRODUCTION A large amount of coal-based solid waste, including coal gangue, circulating fluidized bed slag and coal fly ash, has to be stockpiled owing to low utilization.1–3 To improve the use the coal-based solid waste at a large scale, scholars should increasingly focus on the production of building materials, such as brick,4 cement5 and pottery.6 However, these approaches cannot absorb a great amount of such minerals, because the building materials have limited transportation distance owning to the low value. Moreover, some of the minerals are rich in alumina and may be potential candidates for producing alumina especially in China. In 2018, the alumina yield reached 72 million tons in China, but the bauxite reserve is about 1 billion tons and bauxite production is 70 million tons per year.7 According to statistics,8 100 billion tons of high alumina coal (HAC) has Al2O3 content in its ash of 38–51%, which is mainly distributed in Northern China, including Xinjiang Autonomous Region, Inner Mongolia and Shanxi Province. About 100– 125 million tons of solid HAC waste is generated
annually. Therefore, exploring a new method for alumina extraction from such solid waste is of great importance in China. In the last decade, several attempts were made to recover alumina from coal-based solid waste with high alumina content through acid leaching and sintering. In acid leaching, alumina is extracted with sulfuric acid or hydrochloric acid from minerals activat
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