Abstract: A method of treating inorganic solid waste in a bath of molten metal contained in a vessel (3) which has a space above the bath and a waste gas outlet (11) is disclosed. The method comprises injecting waste into the bath to form a primary reaction zone (13) in which there are reactions between the waste and the bath or in which the waste undergoes a change of phase to convert the waste into more readily recoverable or disposable products. The method further comprises injecting oxygen-containing gas towards the surface of the bath to form a secondary reaction zone (17) in a section above the bath through which oxidisable products released from the primary reaction zone (13) flow to reach the waste gas outlet (11) in the vessel (3) and in which the oxidisable products are oxidised and the heat released by such oxidation is transferred into the bath.