Abstract: A process for converting a copper or nickel matte comprising at least 30% by weight of a copper or nickel based material and a substantial weight amount of an iron based material as one of the impurities to be removed from the matte by oxidation in a converter wherein during a first step of said process substantially all of the iron based material is oxidized with an oxygen comprising gas to make ferrous oxide which is thereafter transformed into slag by addition of a solid material to the molten metal and during a second step of said process, the copper based material is oxidized with said oxygen comprising gas to generate substantially pure copper and residues, said residues being essentially in gaseous form, the oxygen comprising gas being injected through an internal injector of a concentric shrouded tuyere comprising the internal injector and an external injector concentrically disposed around said internal injector with a gas passage therebetween, a shrouding substantially inert gas being injected throu