Aluminum and iron leaching from power plant coal fly ash for preparation of polymeric aluminum ferric chloride

In this work, aluminum and iron existing in coal fly ash were extracted by the method of hydrochloric acid leaching. Effects of solid-liquid ratio, reaction temperature, reaction time, acid concentration, and raw ash mesh on recovery efficiencies of Al₂O₃ and Fe₂O₃ were investigated. X-ray diffraction analysis indicated that anhydrite, hematite, mullite and quartz were the dominant minerals in the raw fly ash sample. X-ray fluorescence technique was applied to determine the mass fractions of chemical components in the raw ash and leached residues, while the concentrations of Al₂O₃ and Fe₂O₃ in leaching solutions were measured by titration method. The optimal recovery efficiencies of Al₂O₃ and Fe₂O₃, obtained under the reaction condition of 95°C, 5 h, acid concentration of 20 wt.%, a solid-liquid ratio of 1:3.5 and raw ash mesh of 400, were 42.75% and 35.10%, respectively. After removing the leached residues, the leaching solutions were employed to manufacture flocculants of polymeric aluminum ferric chloride for treating the oil recovery wastewater from polymer flooding, which possessed high contents of suspended solids (SS) and oils. Microfiltration membrane and ultraviolet spectrophotometer were utilized to determine the contents of SS and oils in water samples. Through adjusting Al/Fe molar ratio to 20:1 and basicity to 70%, the maximum removing efficiencies of SS and oils can be achieved, respectively 96.1% and 91.5%. Moreover, increasing the iron content and basicity of flocculants within certain ranges contributed to improving the settling characteristic of flocs.