Abstract: An improvement to methods for heat treating flue gas cleaning residues (1) and residues from the industrial process generating said flue gases. For this purpose, the method comprises a physicochemical treatment step (2, 7), a heat treatment step (13) and a step involving treating gases generated by said heat treatment (19, 22, 28). These three steps are closely overlapped and combined both to minimise the volatilisation of volatile compounds during heat treatment and to remove separately the elements that cannot effectively be immobilised in the treated residue matrix during said heat treatment. The physicochemical treatment step may advantageously be combined with the wet cleaning step that may be included in the industrial process flue gas cleaning step. The method is particularly suitable for melting/vitrifying fly ash, agglomerating the finest fly ash, and destroying organic compounds such as dioxins and furans.