Method for secondary acid leaching of alumina in coal ash residues

The invention provides a method for secondary acid leaching of alumina in coal ash residues. The method comprises the following steps of carrying out direct acid leaching on coal ash residues to obtain an aluminum ion-containing primary acid leaching liquid and aluminum crystal-containing primary acid leaching residues, carrying out calcination on the aluminum crystal-containing primary acid leaching residues added with sodium carbonate so that aluminum-containing crystals in the aluminum crystal-containing primary acid leaching residues are destroyed, carrying out water leaching on the calcined clinker to obtain a sodium silicate solution and aluminum-containing water leaching residues, carrying out secondary acid leaching treatment on the aluminum-containing water leaching residues and feeding the residual aluminum into the secondary acid leaching liquid. The total leaching efficiency of the two aluminum acid-leaching processes is more than 98%. The method has the advantages of good operation conditions, wide coal ash residue application range, no waste residue, high resource utilization rate, low comprehensive cost, good benefits and less pollution.