Patents

The invention is related to a process for the production of alumina from high silica bearing fly ash. The process of recovering alumina from fly ash comprises partial desilication through sodium hydroxide leaching followed by precipitation of calcium silicate, sulphation roasting of the partially desilicated residue and then solubilisation of aluminium through water leaching of the roasted residue, separation of iron from the sulphate liquor through precipitation of iron hydroxide, precipitation of aluminium hydroxide from iron free sodium aluminate liquor, and production of alumina by calcination of the precipitated aluminium hydroxide. According to the invention, alumina of 99.5% purity can be produced from fly ash with an overall recovery of about 85%.