Method and apparatus for treating a gas mixture

A method (100) for treating a starting gas mixture comprising carbon dioxide, sulphur dioxide and water, wherein the method comprises forming a fraction predominantly or exclusively containing carbon dioxide. The starting gas mixture is enriched in carbon dioxide and depleted in sulfur dioxide and water in a first group (10) of method steps forming an intermediate gas mixture, and the method steps including compressing (11), cooling (12, 13), condensing and drying (13). The intermediate gas mixture is at least partially submitted to a second group of method steps (20), the second group (20) of method steps including an absorbing (21) step in which liquid carbon dioxide is used to absorb sulphur dioxide from the intermediate gas mixture, and the method steps (20) further including liquefying (22) and rectifying (23) at least a part of a gaseous overhead product being produced in the absorbing step (21 ).