A Systematic Investigation into the Extraction of Aluminum from Coal Spoil through Kaolinite

This research has applied kaolin and active carbon (AC) to the investigation of the recovery of aluminum from coal spol (CS). The kaolin, AC-containing kaolin mixture, and CS have been calcined at 500, 600, 700, 800, and 900 °C for 15, 30, 60, and 120 min. The transformation of kaolinite and aluminum extraction that occurred in each calcined sample have been characterized using XRD, TG, IR, and hydrochloric acid leaching methods. The dehydroxylation of kaolinite and the decomposition of metakaolin were influenced by thermal treatment temperature and time. The metakaolin had kept a portion of OH− in its structure until it was calcined at a temperature of 800 °C. Under 60 min treatment, new SiO2 phase was able to be formed at 500 °C, kaolinite was totally converted to metakaolin at 600 °C, and the SiO2 rejoined the reaction at 800 °C. The decompositions of CS were similar to those of kaolin mixture containing 20 wt % AC (MKC). The combustion of combustible matter accelerated the decomposition of kaolinite in the CS and MKC. Higher AC content led to lower aluminum extraction. The treatment at 600 °C was optimal for both CS and MKC.