Melting and Dissolving Fly Ash by NaOH for the Removal of Iron, Calcium, and Other Impurities

Abstract

A mixture of fly ash and sodium hydroxide was calcined, which converted mullite (3Al 2 O 3 •2SiO 2), the high-temperature stability phase containing silicon and aluminum oxides, and quartz into activated silica alumina phase, and they were dissolved by concentrated NaOH solution into soluble SiO 3 2− and AlO 2 −. The insoluble impurities including Fe 2 O 3 , FeO, CaO, and CaSO 4 were filtered out. Experiment results show the optimum experimental conditions for the dissolution: temperature is 60°C, 15% NaOH solution is used, liquid-solid mass ratio is 11:1, stirring time is 3 h, and about 78.9% of silicon and 78.1% of aluminum are dissolved. The obtained pure silicon aluminum solution provides the raw material for preparing high-purity molecular sieves, and Fe 2 O 3 content of the prepared P-type molecular sieve is only 0.25%, and the CaO content is only 0.066%. The paper provided a viable method to remove Fe, Ca, etc. in mineral thoroughly.