Abstract: A method for the treatment of air pollution control (APC) residues comprising the steps of washing the residues at least one time in an alkaline solution maintained at a pH not lower than about 11.5, separating the alkaline washed residues from the alkaline solution. The present method further comprises an optional step of verifying whether the alkaline washed residues are substantially devoid of metal components. When the alkaline washed residues are not substantially devoid of metal components, the alkaline washed residues are washed at least one time in an acid solution maintained at a pH between about 2 and about 4.5 and the acid washed residues are separated from the acid solution so as to produce residues substantially devoid of metal components. The APC residues obtained in application of the methods according to the present invention constitute non-hazardous material/waste.