Method for preparing metallurgical-grade alumina by using fluidized bed fly ash

A method for preparing metallurgical-grade alumina by using fluidized-bed fly ash, comprising the following steps:

• a) crushing the fly ash to a size of 100 mesh or smaller, adding water into the crushed fly ash to prepare a slurry having a solid content of 20-40 wt %, removing iron from the slurry by wet magnetic separation, such that Fe content of the fly ash is reduced to 1.0 wt % or less, and filtering the slurry to obtain a filter cake;
• b) adding hydrochloric acid into the filter cake to react the fly ash with the hydrochloric acid, and then subjecting the reaction product to solid-liquid separation and rinse to yield a hydrochloric leachate having a pH value in the range of 1-3;
• c) passing the hydrochloric leachate through a column loaded with a cationic resin to further remove iron to obtain a refined aluminum chloride solution;
• d) subjecting the refined aluminum chloride solution to vacuum concentration, then cooling the concentrated solution for crystallization, and conducting solid-liquid separation to obtain crystalline aluminum chloride;
• and
• e) calcining the crystalline aluminum chloride with a one-stage process at a temperature in the range of 900-1200° C. for 1-4 hours to obtain the metallurgical-grade alumina;
• or calcining the crystalline aluminum chloride with a two-stage process at a temperature in the range of 300-500° C. for 1-2 hours, then at an elevated temperature in the range of 900-1100° C. for additional 1-3 hours to obtain the metallurgical-grade alumina,
• wherein the cationic resin comprises a strong-acid styrene-based cationic-exchange resin.