Conversion of coal gangue into alumina, tobermorite and TiO₂-rich material

Abstract

A large amount of coal gangue from coal mining and processing is regarded as waste and usually stockpiled directly. In order to recycle the valuable elements from the coal gangue, an integrated process is proposed. The process consists of three steps: 1) concentrating alumina from the coal gangue via activation roasting followed by alkali leaching of SiO₂ which produces alumina concentrate for alumina extraction by the Bayer process; 2) synthesizing tobermorite whiskers from the filtrated alkali liquor containing silicate via a hydrothermal method and reusing excess caustic liquor; and 3) enriching titanium component from the Bayer process residue by sulfuric acid leaching. Alumina concentrate with 69.5% Al₂O₃ and mass ratio of alumina to silica (A/S) of 5.9, pure 1.1 nm tobermorite whisker and TiO₂-rich material containing 33% TiO₂ are produced, respectively, with the optimal parameters. Besides, the actual alumina digestion ratio of alumina concentrate reaches 80.4% at 270 ºC for 40 min in the Bayer process.

Keywords

coal gangue / recycle / alumina / titanium dioxide / tobermorite

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