The invention relates to a method for treating a hydrocarbon feed gas stream containing CO2 and H2S to recover a purified CO2 gas stream (vii), comprising: a. Separating said feed gas stream into a sweetened gas stream (i), and an acid gas stream (ii); b. Introducing stream (ii) into a Claus unit wherein an oxygen-rich stream is used as a combustive agent in the Claus furnace, thereby recovering a liquid stream of elemental sulfur (iii) and a tail gas stream (iv); c. Introducing the stream (iv) into a Tail Gas Treatment Unit (TGTU) thereby separating said tail gas stream into a CO2 enriched gas stream (v), and a stream enriched in sulfur compounds (vi); d. Compressing stream (v) exiting the TGTU; e. Passing the compressed CO2 enriched gas through a CO2 purification unit thereby recovering a purified CO2 gas stream (vii), and the device for carrying out said method.