Resumo

COLLINS, A.C. et al. Production of sodium-based zeolites and a potassium-containing leach liquor by alkaline leaching of South African coal fines ash. J. S. Afr. Inst. Min. Metall. [online]. 2023, vol.123, n.3, pp.145-155. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/1167/2023.

South African coal discards derived from feed coal for thermoprocesses pose human health and environmental problems and incur high disposal costs. These issues need to be resolved. Coal fines and a coal fines/ K₂CO₃ blend were combusted at 700°C in a laboratory rotary kiln to produce ashes containing metakaolinite (Al₂O₃.2SiO₂) and illite/muscovite/orthoclase amorphous materials. The blend ash and coal fines ash, containing 18% K₂O and <1% K₂O respectively, were leached with water and with 1 M and 8 M NaOH at 80°C for 4 hours using a solid to liquid ratio of 1:5. The 8 M NaOH leach yielded 17% sodalite (Na8Si6Al6O24(OH)2) formation through SiO3^2-, Al(OH)4^_, and Na+ precipitation in the leached ashes. The 1 M NaOH leach yielded no sodalite. X-ray fluorescence analysis of the original ashes and leached ashes showed low Al and Si dissolution efficiencies due to the sodalite formation. Sequential NaOH leaching resulted in the highest potassium dissolution efficiency of 89% for the ashes of fines/K₂CO₃ blend and 59% for the fines. It may be possible to increase the ash-derived zeolite concentration by using even higher NaOH concentrations (12-20 M NaOH) during leaching. Sodalite derived from coal ash could possibly be utilized for water purification in industrial applications, or as molecule separators. The potassium-containing liquid could be used in fertilizer manufacture.

Palavras-chave : low-temperature combustion coal ash; alkaline leaching; sodalite; potassium leach liquor.

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