Fly ash decomposition method

The invention discloses a fly ash decomposition method. The method comprises the following steps: sending fly ash powder to an acidolysis process, adding sulfuric acid or hydrochloric acid or nitric acid to carry out a multistage acidolysis reaction with fluorite or industrial calcium fluoride as an activator in order to convert aluminum and iron elements in the fly ash powder into corresponding soluble salts entering a liquid phase, filtering, and separating to obtain an acid leachate containing aluminum salt and iron salt; washing acidolysis residues, mixing the acidolysis residues with water, adding sodium hydroxide to carry out an alkaline hydrolysis reaction, and filtering to prepare high modulus water glass; and washing alkaline hydrolysis residues, filtering, and sending the obtained acid leachate to a fore acidolysis process in order to be used for burdening. The decomposition rates of alumina and iron oxide in the fly ash reach above 90% and above 85% respectively; the modulus of the water glass is controlled between 3.2 and 3.8, the device investment is reduced, and the energy consumption and the raw material cost are reduced; and the method realizes recycling of decomposition residues, eliminates influences of secondary waste residues on environment, and lays a foundation for the preparation of aluminum, iron and silicon compounds.