Abstract: A method and apparatus for wet flue gas desulfurization in a two-circuit washer having two washers for an absorption agent based on suspensions containing calcium compounds, a sump for supplying the absorption agent to the first washer, and a container for at least partial recovery of the absorption agent from the second washer. The absorption agent, while being returned to the container, is actively brought into contact with oxygen to oxidize calcium sulfite to calcium sulfate. The return line has apparatus for actively blowing in oxygen with only a relatively slight overpressure necessary to blow the air into the absorption agent. The absorption agent to be oxidized is already moving because the difference in elevation along the return line from the recovery apparatus to the container, whereby the absorption agent then arrives more or less completely oxidized.