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 (3Al2O3·2SiO2), 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 SiO3 and AlO2. The insoluble impurities including Fe2O3, FeO, CaO, and CaSO4 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 Fe2O3 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.